CA1177539A

CA1177539A - Apparatus for monitoring and utilizing a data processor

Info

Publication number: CA1177539A
Application number: CA000442116A
Authority: CA
Inventors: Paul Citron; Dennis G. Hepp; Thomas L. Jirak
Original assignee: Medtronic Inc
Current assignee: Medtronic Inc
Priority date: 1980-01-23
Filing date: 1983-11-28
Publication date: 1984-11-06

Abstract

ABSTRACT
Apparatus for monitoring and storing heart activity signals is disclosed as including a data processor illustra-tively in the form of a digital microprocessor. The monitoring and storing apparatus comprises a memory comprising first and second pluralities of storage locations, a circuit operating in a real time frame for sampling at a regular rate the patient's heart activity and for storing such sample signals in corres-ponding locations of said first plurality, and the data pro-cessor for processing the signals stored in the first plurality and for storing the processed signals in selected locations of said second plurality. The storage of the signals in the second plurality is performed in a second computer time frame and at a rate faster than the real time sampling rate. A sampling clock provides a sampling clock signal to the sampling circuit whereby the samples of the patient's heart activity are taken. A second computer clock provides computer clock signals to at least a portion of the data processor whereby the processing of the heart activity is effected in the relatively fast computer time frame. The data processor comprises a first portion or means that operates in response to the sample clock signal for evaluating the heart activity signals to determine the existence of a valid heartbeat and a second portion operating in the computer time frame for processing the detected heartbeat and in particular for determining the interval therebetween, which is evaluated to determine whether the heartbeat is occurring with a regular rhythm or not.

Description

~ 377~39 This applicat~on is à divisional of our Canadian patent application Serial No. 369,045 filed January 22, 1981.
I. DESCRIPTION
Technical Fiel~
This invention relates to apparatus for compacting and storing data indicative of a patien~'s heart activity.

The prior art has recognized, as described in the article entitled "The Use of R-R Interval and Different Histo-grams in Classifying Disorders of Sinus Rhythm" by P.M.M. Cash-man appearing in the January 1977 issue of Journal of Medical Engineering_Technology, the need to provide heart activity and in particular ECG recordings over a relatively long period of time from ambulatory patients. The primary objective of such recordings is to permit identification o infrequent and tran-sient disturbances of cardiac rhythm, which may be important in diagnosing patients with vague or intermittent symptoms such as dizzy spells, blackouts, and fainting attacks. While recording for a longer period of time, the physician's interest is to de-tect short, specific dysrhythmic ev~nts which occupy only asmall percentage of the total recording time. Such dysrhythmic events are considered as singularities in a background rhythm.
Typically, the physician is interested not only in the back-ground rhythm but also the specific dysrhythmic events which may comprise slower responses of ~he heart to influences such as .

_ . , . ., . . .. _ . . . .. , .... . ,, . . , .. . ,, ..... . . .. .. . , . _ .. -2-drug treatment or psychological stress over long periods of time. In this regard, it may be desirable to compare the long recordings from either different patients or from the same patient at different times.
- 5 At present, the use of amhulatory heart monitors typified by the Holter recorder, is well known in the art.
The ~olter technique typically records the patient's ECG
activity for at least 24 hours. The difficulty with the use of a Holter recorder is that it provides a large volume of inform~tion which requires processing and analysis. Such analysis is usually time consuming and expensive. Typically, the review and processing time may be reduced by reading out and displaying the data at increased speeds, typically multi-ples of 25, 32, 60, and 120 of the normal playback rate. In order to display the heart data, and in particular the QRS
complex, with sufficient clarity, it may be necessary to use recording apparati with frequency responses in excess of 12 kHz. This is possible with ultraviolet recorders~ fiber optical recording oscilloscopes, or inklet records, all of which are expensive.
The prior art has suggested a variety of apparati for the processing and display of a patient's heart activity data. Such apparatus may include a detector for automatically sensing a dysrhythmia and in response thereto, stores and dis- .
plays a sample of the patient's ECG either directly onto paper or onto a screen. Further, a contourogram may be provided by a storage oscilloscopeoroscilloscope camera whereby subsequent lengths of a patient's ECG are displayed one beneath the other.
Each such segment or tracelength is proportional to the ~eat-to-beat interval and the right-hand edge of the trace gives a continuous r~cord of the R-R interval trend. One of the most common methods of presenting ECG data is to provide a heart rate trend wherein the R-R interval is continuously measured and the R-R interval data is segmented into continous time periods. In particular, the rate or interval of the heartbeat -3- ~ 7 7 5 3 ~

is averaged to provide a display of average heart rates or intervals for a series of adjacent kime periods. For resolv-ing individual beats on a trend plot, it may be preferable to plot the instantaneous rate in a form of a trend plot.
In add~ition to the methods of display as discussed above, there is the need to identify and to highlight the iso-lated occurrence of an abnormal or ectopic beat. Typically, the ectopic bea~ is detected and is counted during the course of the heart monitoring period. Apparatus has been provided to detect premature heartbeat. The degree of prematurity can often be preset by the operator to provide selection of the beats to be detected. The output of such detectors is applied to a counting circuit, a trend recorder, or some form of alarm depending upon the desired application. Several techni~ues have been used to detect the abnormal shape of the patient's ECG signal including simple integrators, filters, and digital pattern recognition systems. It is contemplated that normal ECG signals are analyzed to determine the limits of occurrence of the peaks of the QRS complexes, and to compare such limits with the incoming signal to determine whether the present ECG
signal fits within these predetermined, normal limits.
In more sophisticated systems, the patient's normal ECG signal is detected and stored. In subsequent monitoring, the patient's normal signal is used as a template against which to compare the current heart data. U. S. Patent 4,115,864 discloses such a cardiac monitor, utilizing a computer to con-trol the storage of the patient's normal signal, to process the inputted ECG signal into digital segments, and to compare those segments with corresponding segments of the previously stored normal ECG of the patient. When the stored normal signal does not fit the current signal, an alarm or detector circuit is actuated and the number of occurrences of that ectopic signal is stored within the memory of the computer.
The described system is capable of providing a trend history of such ectoplc beats in the form of a histogram or trend plot.

.

. _ ~ 1 7753~
In any processing of ECG data, it is necessary to use dis-crimination techniques to extract a trigger pulse for each cardiac cycle.
In most instances, the detection circuit triggers on the R-wave, and it i8 thus necessary to distinguish the R-wave of the QRS complex from the rest of the signal. It is contemplated that it may be necessary, in the presence of heavy background noise, to terminate the monitoring for the duration of the high level background noise. In other instances, the detection circuitry may provide an alarm so that the operator can intervene.
Noting the desire to provide monitoring for long periods of time of a patient's heart activity, the continuous monitoring by the Holter monitor provides a complete record at relatively inexpensive cost. On the other hand, the methods of processing and compacting the data for simpler, limited display oftentimes requires a more complex system of increased cost.
To avoid either pitfall, it has been suggested that the data be presented in the form of an R-R interval histogram. A histogram presents heart activity data taken over a period of time in a compact manner, wherein the successive intervals between R-waves are computed and are classified as to their dura-tion. As shown in Figure 1, the X axis is in seconds corresponding to the R-R interval, whereas the Y axis provides the number of beats that occur within each interval. Such a presentation provides a large data reduction in a v1sual way which allows easy comparison between the histograms of the same patient taken at different times and between different patients. The R-R interval hlstogram (IH) is formed by generating an array of columns or bins, each corresponding to a range of values of beat-to-beat (or R-R) interval. As each ECC complex is detected, the time interval between it and its predecessor is measured and the total in the appropriate bin incre-mented. A typical histogram might contain a hundred bins, each having a wid~h of 20 milliseconds, giving a total range of R-R intervals from O to 2 seconds. A bin capacity of 4,095 beats (a 12-bit binary word) will permit about 4 hours of normal heart monitoring.
A variation of the R-R interval hlstogram is the R-R interval "7S3~

difference histogram (IDH). l'he rDH is formed simllarly except that the quantity as displayed along the X axis is the amount by which the R-R
interval changes between successive beats. ~he central bin is designated 0, i.e., 0 difference between successive beats, and a hundred columns provide a range between -1 second through 0 to +1 second, with a bin width of 20 milliseconds. The mean of the ir.terval differences is always very close to 0. The IDH provides an indication of the manner of change of the heartbeat, where the width of the I~ is the measure of the spread of heart rates about the mean value. It is apparent that the use of both ~he IH
and the ID~ provide the physician with a powerful tool for diagnosis of the patient's heart.
Further, U.S. Patent 4,146,029 describes a system lmplanted within the body of the patient for dispensing medication into the patient's body. The sys~em is implemented by a ~icroprocessor for the control of the process whereby each QRS complex of the patient's heart is detected as to the length of the QRS complex and to the interval therebetween. A program of comparing the length of the QRS complex to an acceptable length is provided to determine the validity of each QRS complex and further to first calculate the interval between QRS complexes and to compare the measured length to a known or standard length for a partlcular paeient. ~ore specifically, the process compares the length to determine how much shorter the measured ongoing intervals are with regard to the normal length and dependent upon the decrease of length, i.e., the increase of heart rate, the microprocessor controls dispensing apparatus to vary the dosage given to the patient.

-6~ 3~

Included in the apparatus is a process for measuring the R-R
interval and for accumulating the average of the R-R interval over a given period of time, for example, an hour. The averaged R-R intervals are compared with known standards to variably control the dispensation of medication to the patient.
Brief Summary of the Invention It is an object of this invention to provide ne~ and improved apparatus for monitoring and storing heart activity signals utilizing a data processor illustratively in the form of a digital microprocessor.
It is a further object of this invention to operate the aata processor in a most efficient manner to evaluate and store signals indicative of the patient's heart signals.
It is a more specific object of this invention to pro-vide new and improved apparatus for monitoring and storing sig-nals i~dicative of a patient's heart activity, wherein the apparatus is embodied by a data processing apparatus that operatles in a first, relatively slow real time frame to sample the signals of the patient's heart and in a second, relatively `
fast computer time frame for processing and evaluating the sam-pled heart signals.
In accordance with these and other objects of the invention, there is provided apparatus for monitoring and s-toring electrical signals indicative of a patient's heart activity including a memory comprising first and second pluralities of storage locations, a circuit operating in a real time frame for sampling at a regular rate the patient's heart activity and for storing such sample signals in corresponding locations of said first plurality, and a data processor for processing the signals stored in the first plurality and for storing the processed signals in the selected locations of said second plurality. The storag~ of the signals in the second plurality is performed in a second computer time frame and at a rate faster than the real time sampling rate.
In an illustrative embodiment of this invention, there is provided a sampling clock for providing a sampling clock -7~

signal to the sampling circuit whereby the samples of the patient's heart activity are taken. A second computer clock provides computer clock signals to at least a portion of the data processor whereby the processing of the heart activity is effected in the relatively fast computer time Erame.
- In a further aspect of this invention, the data processor comprises a first portion or means that operates in response to the sample clock signal for evalua-ting the heart activity signals to determine the existence of a valid heart-beat. In an illustrative embodiment, the heart activity sig-nals are evaluated to determine segments thereof and thereafter to examine a series of such segments to determine whether a valid heartbeat has been monitored.
In a still further aspect of this invention, the data processor includes a further portion operating in the com-puter time frame for processing the detected heartbeat and in particular for determining the interval therebetween, and subsequently the heartbeat rate. The manifestations of the in~rvals between successive heartbeats and the rate of the heartbeat are stored i~ a further location of the memory.
Such stored data is evaluated to determine whe~her the heartbeat is occurring with a regular rhythm or, if not, is an anomaly.
If such an anomaly is detected or the patient has, through a manually operable switch, provided indication of an anomaly or a heart discomfort, the data processor transfers a series of ~he sampled heart signals to a still further storage loca-tion to be stored therein for subsequent read out and display.

' 7~

Thus, in accordance with a broad aspect of the inven-tion, there is provided apparatus for comparing electrical sig-nals indicative of a patient's heart activity, with a set of criteria of regular heart ac-t.ivity comprising a defined relation-ship between one and a subsequent R-R interval, and for storing the electrical signals indicative of regular heart activi-ty, said apparatus comprisingo a) memory means including first, second and third pluralities of storage locations; b) a real time sam-pling clock and a computer clock; c) means coupled to receive a patient's heart activity and responsive to said sampling clock for sampling at periodic intervals in real time the patient's heart activity signal, and for storing the sampled signals in respective locations of said first plurality, and d) data pro-cessing means comprising means responsive to the output of the said computer clock and for providing and storing a series of R-R interval signals in corresponding storage locations of said second plurality, each indicative of the time interval between the successive peaks of the patient's heart activity, and means for examining selected of said series oE R R interval signals as stored in said second plurality of storage locations with each other in accordance with said defined rela-tionship to provide a mani:Eestation indicative that the patient's heart sig-nals are regular or irregular, and means responsive to said man-ifestation for storing regular heart signals in corresponding storage locations of said third plurality.
In accordance with another broad aspect of the inven tion there is provided apparatus for evaluating electrical sig-nals indicative of a patient's heart activity, with a set of criteria of regular heart activity comprising a defined relation-ship between one and a subsequent R~R interval, said apparatus .... ~ 7a ~

RJ~ e~

comprising: a) a real time sampling clock; b) a computer time clock; c) means coupled to receive a patient's hea~t activity signal and responsive to the outpu-t of said sampling clock for sampling at periodic intervals the patient's heart activity signal, and d) data processing means comprising means responsive to said output of said sampling clock and to said sampled heart activity signals to provide a series of R-R interval signals, each indicative of the time interval between successive peaks of the patient's heart activity, and means responsive to the out.put of said computer clock for examining selected of said series of R-R interval signais with each other in accordance with said defined relationship to provide a manifestation indicative that the patient's heart signals are regular.
In accordance with another broad aspect of the invent-ion there is provided apparatus for monitoring over a prolonged monitoring period and evaluating electrical signals indicative of a patient's heart activit~ with a set of criteria indicative of the waveform of a QRS complex, said apparatus comprising:
a) a real time sampling cloek; b) a computer time cloek; c) - 20 sampling means responsive to the output of said sampling elock for sampling the patient's heart activit~ signal to provide a sequenee of sampled heart signals of a single QRS complex; and d) data processing means eompxising means responsive to said output of said sampling clock for comparing one sampled heart signal with a subsequent sampled heart signal of the same QRS
complex to determine whether the relationship therebetween meets said criteria of a valid QRS complex waveform, and means res-ponsive to the output of said computer time clock Eor further processing valid sampled heart signals.
Tn accordance with another broad aspect of the inven-- 7b -~ t7~

tion there is provided apparatus for mon-toring and comparing elec-trical signals indicative of a patlent's heart activity, with a set of criteria of regular heart ackivity comprising a defined relationship between one and a subsequent R-R inter-val, said apparatus comprising: a) means responsive to a pat-ient's heart activity for providing a series of R-R interval signals, each indicative of the time interval between the successive peaks of the patient's heart activity; and b) eval-uating means for examining selected of said series of R-R inter-val signals wi.th each other in accordance with said definedrelationship to provide a first manifestation indicative that the patient's heart signals are regular or irreyular, said evaluating means comprises means for comparing the current R--R
interval signal with respect to a maximum value thereof and if exceeded, to provide a second manifestation that the patient's heart signals are irregular.
In accordance with another broad aspect of the inven-tion there is provided apparatus for monitoring and comparing electrical signals indicative of a patient's heart activity, with a set of criteria of regular heart activity comprising a defined relationship between one and a subsequen-t R-R interval, said apparatus comprising: a) means responsive to a patient's heart activity for providing a series of R.-~ interval signals, each indicative of the time interval between -the successive peaks of the patient's heart activity; and b) evaluating means for examining selected of said series of R-R interval signals with each other in accordance with said defined relationship to provide a manifestation indicative that the patientls heart signals are regular or irregular, said evaluating means comp-rises means for determining whether the value of a first occur-:~ -- 7c -~^f ~t"~

ring interval is less than that of a subsequent interval by a predetermined amount and, if so, to provide the manifestation indicating the existence of a premature heartbea-t.
In accordance with another broad aspect of the inven-tion there is provided apparatus for monitoring and compariny electrical signals indicative of a patientls heart activity, with a set of criteria of regular heart activi-ty comprising a defined relationship between one and a subsequent R-R interval, said apparatus comprising: aj means responsive to a patient's heart activity for providing a series of R-R interval signals, each indicative of the -time interval between the successive peaks of the patient's heart activity; and b) evaluating means for examining selected of said series of R-R interval signals with each other in accordance with said defined relationship to provide a manifestation indicative that the patient's heart signals are regular or irregular, said evaluating means comp-rises means for comparing the values of successive R-R interval signals to provide the manifestation indicative oE a premature beat.
In accordance with another broad aspect o:E the inven-tion there is provided apparatus :Eor monitoring and comparing electrical signals indicative of a patien-t's heart activity, with criteria indicative of regular heart activity comprising a defined relationship between one and a subsequent R-R inter-val, said apparatus comprising: a) means for measuring in real time a patient's heart activity and for providing a sequence of discrete R-R interval signals, each signal indicative of the time interval between successive peaks of the patient's heart activity; b) means coupled to said monitoring means for receiving the R-R interval signals and for storing a continuously .
- 7d -7~7~3~

updated set of the R-R interval signals; and c) evaluating means or examining selected of said updated set of R-R inter-vals with each other in accordance with said defined relation-ship to provide a manifestation indicative that the patient's heart activity is regular or irregular.

- 7e -3~
Brief Description of the Drawings These and oth0r objects and advantages of the present invention will become more apparent by referring to the following detailed description and accompanying drawings, in which:
FIGURES 1 and 2 show, respectively, histograms of the R-R in-terval and of the interval differences, over an extended period of time;
FIGURES 3A and B show, respectively, a high-level functional block diagram of the basic elements of the heart monitoring system in accordance with the teachings of this invention, and a perspective view of the portable data acquisition unit incorporated into the system of FIGURE 3A;
FIGURES ~A, B, C, D and E are detailed circuit diagrams show-ing the elements of the system generally shown in FIGURE 3A;
FIGURE 5~ on the second sheet of drawings, is a diagram of the storage structure areas of the RAM comprising a memory within the portable data acquisition system as shown in FIGURE 3A;
FIGURE 6 is a high-level diagram of the non-rea] time program as stored within the ROM and as executed by the CPU o:E the system shown in FIGURE 3A;
FIGURE 7 shows the various service routines and the manner in which they are related to coordinate the real time tasks for the system o:E
FIGURE 3A;
FIGURES 8, 9, 10, and 11 illustrate the monitoring routine as generally shown in FIGURE 6;
FIGURES 12 to 17 show the details of the MONITOR~SERVICE rout-ine as generally shown in FIGURE 7, with FIGURES 13 to 17 being on the same sheet;
FIGURES 18A) B, C, and D illustrate, in graphical form, the wave shapes of various anomalies that may occur within the patient's ECG
signal and their timing; and FIGURES 19A, B, and C illustrate the segments making up valid R-wave forms as detected by the MONITOR$SERVICE routine as shown in FIGIJRES
12 to 17.

~.~L7~7535~
Description of the Preferred Embodiment . ~
Referring now to the drawings and in particular to FIGURE 3A, there is shown a heart monitoring system 10 adapted to be coupled by leads 22a, b, and c to a patient 20 to receive - 5 signals to be processed and in particular compacted, before storage in a random access memory (R~M) 26 of a portable acqui-sition unit 12. The heart monitoring sys-tem 10 is capable of monitoring a pa-tient's heart for an extended period of time, e.g., 3 hours and 20 minutes, while continuously processing and 10 in particular compacting data as received in real time for storage in a manner that facilitates the later playback and display by a display unit 30 of the data in a dense form -that is readily discernible to the physician. In particular, the patient's ECG signals are continuously monitored to pro~ide 15 heart data in the nature of trends of the average, maximum~
and minimum heart rates for consecutive intervals, e.g., 5 minutes, throughout the data acquisition. In addition, the system furiher stores data in a form, whereby histograms of the R-R interval difference and heart rate may be displayed.
20 In addition, the heart monitoring system is designed to detect certain arrhythmias of interest and upon detection, automa~i-cally stores for a limited period of time a segment of the ECG
signal indicative of the detected arrhythmia. Ater the acqui-sition period is over, the heart monitoring system 10 is o 25 assembled so that the portable acquisition unit 12 is coupled to its playback unit 30 to initiate a readout and display upon its analog chart recorder 36. The playback unit is divided into a first portion known as an adaptor 32 and a second por-tion including the recorder 36 and a chart edge printer 3B.
30 As will be explained in detail later, the edge printer 38 com-prises an array of elements for printing a series of marks along the edge of the chart of the recorder 36 to provide an indication of the occurrence of certain events during the monitoring operation; for example, the occurrence of a heart 35 anomaly as detected by the acquisition unit 12 would be noted -lo~ 7t7~39 by a mark that would be placed upon an outputted trend chart to designate that interval in which anomaly occurred. Further, the patient 20, upon sensing heart pain, presses a mark button 84, as shown in FIGURES 3B and ~A, to cause the heart signals occurring during that i~terval to be identified by a mark pro-vided by the chart edge printer 38. In addition, the printer 3 8 may provide marks to separate the various charts as are printed out by the recorder 3 6 .
The heart monitoring system is generally shown in 10 FIGURE 3A wherein the ECG signals are applied by the leads 22a, b, and c from electrodes attached to the patient 20, via a dif-ferential preamplifier 18 to the portable acquisition unit 12 and in particular to an A/D converter 16. The signals now in digital form are applied to the central processor unit (CPU) 14. The input of the A/D converter 16 is coupled via the dif-ferential amplifier 18 to the connectors 22a and 22b. The dif-ferential amplifier 18 includes an ECG preamplifier that buf-fers the ECG snap connectors 22a and 22b to reduce cable generated artifacts. The ECG preamplifier drives,~ differen-tial amplifier 18 with a passive ground system. The snap con-nector 22b is attached to a pre-gelled ECG electrode approxi-mately located at site V5 of the patient's side, whereas the connector 22a is attached to a pre-gelled ECG electrode approx-imately located at the sternum. These preampli~ier connections will produce a positive-going R-wave for most patients. The ground connector 22c is attached to a pre-gelled ECG electrode located on the left pectoral region. Though the illustrative embodiment shown in FIGURE 3A externally monitors the patient's heart, it is contemplated within the teachings o~ this inven-tion to connect the sensing electrodes directly to the patient'sheart and transmit the detected heart signals from an internally implanted transmitter to an external receiver coupled suitably to the data acquisition unit; the contemplated transmitter and receiver may illustratively take the form of that disclosed in U. S. Patent-4,166,470 assigned to the assignee of thisinvention.
A clock signal, as derived from a sample clock 24, is applied to the CPU 14 to control the rate at which sample signals .

are derived from the patient 20. It is understood that the CPU ~ has its own internal clock, as is well known in the art, for controlling its internal operations as well as its interfacing with the other elements of the unit 12. The CPU 1~ is coupled by a data/instruction (I/D) bus 27 to each of a read only memory ~ROM) 28 and to the RAM 26. The ROM 28 is adapted to store the instructions which the CPU 1~ executes to detect or recognize the input ECG signals, to process these signals including compaction and to appropriately store the processed signal in designated areas of the RAM 26; the programs or routines as stored in the ROM 28 will be explained generally with respect to FIGURES 6 and 7, and in detail with respect to FIGURES 8 to 17. The data as processed and compacted by the CPU 14 is stored in designa~ed areas of the R~M 26 dependent upon the nature of the data, the areas of the RAM 26 in which data is stored are shown in FIGURE 5.
The playback unit 30 is optically coupled to an isolating latch or playback adaptor 32 which acts as an isolating digital buffer to receive from the acquisition unit 12 information to be transmitted to and displayed upon the analog chart recorder 36 and the chart edge printer 38.
Because of the optical isolation, the patient 20 may be connected to the zo acquisition unit 12 when the acquisition unit 12 is connected to the line powered playback unit 30 without fear that the patient's ECG signal will be affected by noise or that an electrical shock hazard will be affected by noise or that an electrical shock hazard will be presented to the patient 20. As shown in FIGURE 3A, data is applied via a D/A converter 34 to the analog chart recorder 36 which may illustratively take the form of a pen recorder as manufactured by Astromed under their designation Model 102. The latch 32 is also coupled to an edge printer 38 as manufactured by Texas Instruments under their designation EPN 3300.
FIGURE 5 discloses a data structure or memory map illustrating the manner in which the various types of data are ~ 7S~9 stored in corresponding regions of the RAM 26. As shown in FIGURE 5, the RAM 26 includes a first area 26a for receiving ECG data as continously monitored by the system 1~ when dis-posed in its monitoring mode. In the monitoring mode, as will - 5 be explained in detail later, each QRS complex of the patient's ECG signal is detected and analyzed to determine whether it is valid, i.e. r that it is not noise, and upon occurrence of a valid QRS complex signal, the signal is processed and stored within the first area 26a. It is desired to retain a strip of the ECG signal if there is detected an arrhythmia which may occur after a desired portion of the signal has already been detected. To this end, the first area 26a of the RAM is operated as a pseudo-tape loop by storing each sample piece of data in successively lower RAM addresses until the lower limit of a $ection of the area 26a is reached. At that point, the storage point of address P is returned to the topmost storage location of that section and the next data is over-written upon the old data. The cycle is repeated continuously until an arrhythmia is detected at which time a pointer to the first/last data boundary is stored and further data storage is inhibited. After the storage is complete, the first/last data pointer-or boundary is saved, in a location noted as STARTING POINT, for directing output of data therefrom. The area 26a of the RAM 26 is divided into a plurality, e.g., nine .
of buffer sections 26a-0 to 26a-8, each buffer section includ-ing a given number (e.g., 360) of consecutive locations, wherein data indicating samples of every fourth ECG signal are placed in gequence as indicated above. When one buffer section has been filled, the address or pointer P to the area 26a is moved to designate the topmost location available within the next buffer section. In this manner, nine strips of the ECG signal may be recorded and stored within the RAM 26 to play out and reproduce, as will be explaîned, a visual display of the ECG signal at that time. Though only nine buffer sections are shown within the area 26a of the RA~I 26, it is contemplated -13- ~ ~77539 that 40 or even more such sections could be lnc~rp~rated within the area 26a limited only by the size of the desired memory and its cost, and considerations of battery drain.
In a further contemp~ated embodiment of this invention, a single circular buffer section could be used with the data stored therein replicated into permanent storage locations of the RAM 26 upon the detection of a heart anomaly.
The second area 26b is dedicated for storing data to be displayed in a histogram format. In particular, the area 26b is confi~ured illustratively as two arrays of 50 16-bit cells. A ~irst of the 50-cell arrays is intended for storing an interval difference histogram (IDH), wherein each cell is 4 sample clocks, i.e., 16-2/3 ms. wide. As will be explained later, after the R-R interval has been calculated and the difference between successive intervals obtained, that internal difference is divided by 4, the fractional part being disregarded. The result of the division process is used to point to the appropriate IDH array cell within the first array of the area 26b and that cell is incremented to indicate the occurrence of a difference of that particular order. In an illustrative embodiment of this invention, each of 25 IDH cells is provided on the negative and positive sides of the center to handle differences ranging from 0 to 100 sample clocks, i.e., 0 to 416-2/3 ms. with all differences laryer than 416-2/3 ignored. The second 50-cell array of the area 26b is intended for storing the rate histogram, wherein each cell is 5 beats per minute wide. As will be ex-plained later, after the R-R interval has been measured and the equivalent heart rate calculated, that rate is divided by 5, the fractional part being disregarded. The result of the division process is used to point to the appropriate rate his-togram cell, and that cell is incremented to indicate the occurrence of that particular interval. The interval differ-ence histogram is primarily used to indicate rhythm instabili-ties, such as might be produced by atrial flutter, sick-sinus-1~'7~ii3~
syndrone, and premature contraction, while the rate his~ogram indicates the distribution o~ intervals. By contrast, a trend plot indicates gross changes in intervals as will now be dis~
cussed.
Area 26c of the RAM 26 provides a storage area for re-ceiving trend data including three sets of 40 8-bit cells, each cell for storing one of the minimum and maximum of the patient's heart rate and the average of the heart rate as detected during that interval, e.g., 5 minutes. Each set of cells corresponds to a trend interval.
In addition, area 26c provides storage for data indi-cating whether the mark button 84 was pressed or ECG was stored during a trend sample interval. Typically, if the patient no-tices some symptom, e.g., dizziness, fainting, or some other discomfort indicative of a heart condition, he may push the mark pushbutton 84 as disposed upon his portable acquisition unit 12 and as shown more specifically in FIGURES 3B a~d 4B. Upon the actuation of the pushbutton 84, a specific bit pattern is stored in the cell corresponding to the trend sample interval wherein pushbutton 84 was pressed. If an ECG strip was saved in area 26c during a given trend sample interval, the bit pattern in the corresponding cell will be modified to indicate that fact. Upon playbackJ~an indication is made upon the analog chart recorder 36 as to that interval in which the pushbutton 84 was depressed in the form of a mark identifying the time interval, whereby the reviewing physician may identify the time of button depre~sion or ECG sample storage with the corresponding values o~ minimum, maximum, and average heartbeat rate.
Area 26d provides data storage to receive various variables including state indications and flags that are set during execution of the process.
Referring now to FIGURES 4A, B, C, and D, there is shown detailed circuit diagrams of the heart monitoring appara-tus 10 as generally shown in FI5URE 3A. The data acquisition unit 12 is found principally in FIGURES 4A and 4B, wherein there is shown the CPU 14 which may illustratively :~ ~77~3~

take the form of a central processing unit manufactured by Intel under their designation 8085A. The CPU 14, in conjunction with address latch 44, receives and transmits data via its address bus 46, control bus 50, the data bus 48, and the connectors Jl and J2. Data is received from the A/D converter 16, as shown in FIGURE 4C, and is transferred to and from the RAM 26 via the data bus 48, as shown in FIGURE. 4A. The RAM 26 is comprised of a plurality of memory elements as manufactured by Harris under their designation No. HM 6514. The data bus 48 is connected ~o the data transport ports DQl-4 of each of these elements. The ROM 28 is comprised of two memory elements as manufactured by Intel under their designation 2716 and upon being addressed, instructions of the programs to be described are read out via their output ports 00-07 to be transmitted via the data bus 48 to the CPU 14. As shown in FIGURES 4A and B,addresses are applied via an address bus 46 to the elements of the RAM
26 and of the ROM 28 to address one of the elements and a selected location therein. The CPU 14 generates an initial set of addresses from its outputs A10, 11, and 12 to be applied to a pair of chip or element decoders 40 and 42, illustratively taking the form of a decoder manufactured by RCA under their designation 4028. The outputs of the chip decoders 40 and 42 develop address signals whereby one of the chips or elements of the RAM 26 or ROM 28 is addressed at a time. The particular location within one of the elements of the RAM 26 or the ROM 28 to be addressed is selected by an address latch 44 whose inputs are taken from the ports ADE and AD 0-7 of the CPU 14 to provide output signals applied by the address bus 46 to each of the aforementioned elements to address a selected location therein.
Further command signals are developed from the I0/M to control whether data is to be transferred between the RAM 26 or whether data is to be transferred to the input/output~I/O) and in particular to be transferred via ~he data bus 48 from the A/D converter 16 (as shown in FIGURF. 4C) or to ~'7~3~
transfer data to the addressing latch 140 (as shown in FIGURE
4D), which comprises a part of the latch 32 ~as shown in FIGURE
3).. The ports designated RD and WR control whether data is to be written onto or read out from the RAM 26. As shown in 5 FIGURE 4A, the CPU 14 includes a set of interrupt inputs that - are used in a manner, as will be more fully explained, to sim-plify the programs that are required to imple~ent the various processes and functions of recognition and storage of ECG data.
For example, the sample clock 24, as shown in detail in FIGURE
4C, applies its sample signal via conductor 80, connectors Pl and Jl to the RST 7.5 interrupt of the CPU 14. The sample clock calls a SAMPLE$ECG$AND$DO$TIMING routine, whereby sam-ples of the ECG signal are taken and the R-wave of the QRS
complex is examined to determine whether a valid R-wave is detected to set thereby an R$FLAG, as will be explained with respect to FIGURES 12 to 17.
A further interrupt is made when a voltage detection circuit in the form of a Schmitt trigger 54, a part of the power supply 52, as shown in FIGURE 4A, senses that the battery voltage has fallen below a predetermined level. A battery 82, as shown in FIGURE 4C, is coupled via connectors Pl and Jl to the power supply 52 and illustratively comprise an 18-volt battery, when the Schmitt trigger 54 senses that the voltage of the battery 82 has fallen below 10 volts, an output is developed and applied to the TRAP interrupt of the CPU 14 to initiate a controlled transfer to a shutdown mode of opera-`tion, as will be explained with respect to FIGURE 7, wherein only the logic addressing and processing circuitry and the chips of the RAM 26 remain energized, thereby to preserve the energy level of the battery 82. ~n particular, the Schmitt trigger 54 comprises an operational amplifier Ul9 that compares the voltage output of the battery 82, normally 18 volts, with the regulated voltage 5SD as provided from the output 55 of the power supply 52, and if the battery voltage falls below a minimum, illustratively lO volts, the operational amplifier ~.~'7~3~3 Ul9 provides a high-going output signal via the NOR gate U8 to the TRAP
interrupt of the CPU 14 to thereby initiate the LOW~VOLTAGE.~ETECTOR~SERVICE
604, as will be explained with respect to PIGURE 7.
The circuitry, as shown in FIGURE 4A, of the acquisition unit 12 responds to such a low voltage condition in the following manner. First the A15, IO/M, and RD output terminals of the CPU 1~ all go high, causing the NAND gate U5 to apply a low-going output signal to a pulse-shaping circuit comprised of capacitor C16, diode CR5, and Tesistor R40. The shaped output is in turn applied to set a flip-flop circuit 57 comprised of two NOR gates, each designated by the notation U8. ~s seen in FIGURE 4A, the delayed output 56 of this flip-flop circuit 57 is applied to the power supply 52 via transistor Ql and also to an array of NAND gates U4 and U5. When transistor Ql is turned on, a current is applied to a switching regulator U20 that causes power supply 52 to deenergize most elements of the system 10, as will be explained later. In this manner, generally the power supply 52 removes energization from most of the elements of the system 10 while maintaining energization to the various elements of the RAM 26 and further, the array of NAND gates U4 and U5 are disabled to prevent the further application of address signals from the chip decoders 40 and 42 to the RAM 26. In this way, the data previously stored in the elements of the RAM 26 will continue to be stored, and further, addresses and/or spurious signals that may be generated by the CPU 14 and/or the chip decoders 40 and 42 cannot be applied after voltage shutdown to the RAhl 26. Further~ the output of the flip-flop 57 is applied to drive conductive the transistor Q2 of the power supply 52 whereby a positive-going signal is applied to the SD input of the switching regulator circuit U20, which may illustratively take the form of that regulator manufactured by Silicon General under their designation SG1524. In the normal mode of operation, the regulator U20 periodically energizes the base of the transistor Q3 via `: .

-18- ~'7~39 its outputs CA and CB at a rate to charge capacitor C14 to a desired voltage in the order of +5 volts; the capacitor C14 is repeatedly recharged while tending to be discharged by the load via inductor ~1 whereby a substantially constant, regu-lated +5 volts is applied to its output terminal 55, alsodesignated +5SD. In addition, the periodic voltages are also applied by the primary winding of the transformer T2 to its output secondaries whereb~ +8 volts are applied to energize elements of the circuit shown in FIGURE 4C. Linear regulator U20 provides at its output VR a +5 regulated voltage. As can be seen from an examination of FIGURES 4A, B, C, and D, most of the elements of the system 10 are energized by the regulated +5SD voltage as derived from the output 55 of the power supply 52 while it is being operated in its normal, regulating mode.
However, when the transistor Q2 is driven conductive upon the occurrence of a low voltage condition, an input signal is applied to the SD input thereby disposing the regulator U20 to the second, non-operative mode whereby the regulated +5SD volt-age is removed from most of the elements of the system 10 thereby reducing significantly the drain as applied upon the battery 82. During its shutdown mode of operation, a voltage of +5 volts is only applied by the output terminal VR of the power supply 52 to the various elements of the RAM 26, the chip decoders 40 and 42, the NAND gates U4, U5, and U6, and the flip-flop 57. In particular, the normally applied output from the terminals CA and CB of the regulator U20 goes high to render the transistor Q3 non-conductive, thereby disconnecting the voltage from the primary winding of the trans~ormer T2 and the inductor Ll,and turning off the output voltage of +8 derived from the secondary of the transformer T2 and the output derived from the terminal 55. However, as noted above, the regulator U20 continues to apply the +5 voltage from its output VR to the above-noted elements.
The RST 6.5 interrupt of the CPU 14 is used to detect whether the preamplifier 18 is connected via connector J4 to I ` -19- 11'7'7S39 the portable acquisition unit 12, as shown in FIGURE 3. AS
illustrated in FIGURE 4C, the pins 1 ~nd 2 of the connector J4 are connected to the preamplifier connector P4 which has a short across pins 1 and 2 whereby a low ox "0" signal is applied via the conductor 94 and connectors Pl and Jl to the RST 5.5 ¦ interrupt of the CPU 14. As will be explained with respect to FIGURE 7, in the absence of a connection to the ECG pre-amplifier 18, the system 10 is prevented from entering its monitor or calibration mode of operation.
In the course of either the calibration or monitor modes of operation, a switch 84, as shown in FIGURE 4C, may be depressed to apply a signal via conductor 86 and connectors Pl and Jl to the SID input of the CPU 14. In the monitoring mode, the depression of the switch 84 effects a storage of a flag identifying a relatively small interval durlng the entire monitoring period in which the patient sensed some symptom or felt some discomfort. In the calibration mode, depression of switch 84 causes the refractory period associated with sensing of the QRS to be increased. The SOD terminal of the CPU 14 drives via conductor 87 and connectors Jl and J2 the transistor Ql, as shown in FIGURE 4C, whereby the ECG LED 88 is energized. As will be explained, during the calibration modes a potentiometer R9 within the ECG amplifier 19, as shown in FIGURE 4C, is adjusted to set the gain oE the ampli-fier 19 to an appropriate level dependent upon the amplitudeof the patient's ECG signal. The LED 88 is energized in a manner to indicate when the potentiometer R9 has been appro-priately adjusted. A start button 96, as shown in FIGURE 4C, is depressed to initiate the operation of the system 10 whereby a low signal is applied to the RESET IN input of the CPU 14. In particular, the start button 96 is depressed to apply a low-going signal via the terminals Pl and Jl to a NAND gate U5, whose output is in turn applied to reset the flip-flop 57. Upon being reset, the flip-flop 57 applies a low signal ts deenergize the transistor Q2, whereby the high -3~

level applied to the SD input of the switching regulator U20 is removed, permitting regulator U20 to return to the normally energi~ed mode. In addition, the CPU 14 develops an output reset signal that is applied to reset and clear the addressing latch 140, as shown in FIGURE 4D.
As shown in FIGURE 4A, a computer clock 15 provides a 1.843 M~lz clock signal that times the e~ecution of ~heprogram by the CPU 14 as well as the various other data transfer functions controlled thereby. As will be explalned later, the functions of the CPU 14 including various data transfer functions and calculations are carried out under the control and within the time frame of the computer clock 15, whereas many of the data gathering functions, including the sampling of the patient's ECG signals are carried out in real time under the control of the sample clock 24.
As shown in FIGURE 4C, the input ECG signals are applied to the differential ECG preamplifier 18 of a design familiar to those skilled in the art. The output of preamplifier 18 is fed to the ECG amplifier 19 which comprises operation~l amplifiers 90 and 92 that are connected in series with each other. As mentioned above, the variable potentiometer R9 controls the gain of the ECG amplifier 19. The output of ECG amplifier 19 is applied to the input Iin of the A/D converter 16. The converted digital signal is applied from the outputs BO-7 of the A/D converter 16 via the data bus 48 to be selectively stored under the control of the CPU unit 14 within the elements of the RAM 26, as shown in FIGURES 4A and 4B.
FIGURES 4D and 4E show the isolating latch 32 and the D/A
converter 34, generally shown in FIGURE 3, as coupled to the analog chart recorder 36 and the chart edge printer 38. The isolating latch 32 is comprised of the addressing latch 140, a 16-channel optical isolator 141, and a DC-DC converter 139. The data to be printed or displayed is applied via the data bus ~8 to the inputs DO to D7 of the addressing latch 140.
The latch 140 develops a first set of digital outputs PBO to PB7 that are applied via the 16-channel optical isolator 141 as `' ~: '' `
-21- ~ 39 shown in FIGURE 4D; an~ the D/A converter 34, as shown in FIGURE 4E, whereby ~he analog recorder 36 is driven. The latch 140 develops a second set of outputs PA~ to P~7 that are applied to the 7-dot chart printer 38. In particular, the outputs of the latch 140 are applied to an array of dual channel, optical isolators U4 to Ull, as shown in FIGURE 4D.
Isolators U4 to Ull are provided to isolate the analog chart recorder 36 and the chart edge printer 38, which may be powered by a conventional AC outlet, from the data acquisition unit 12 to insure that signals, including the energizing voltage as would be picked up by the recorder 36 and printer 38, will not be applied to either distort the ECG signals as derived from the patient 20 or present a shock hazard to the patient 20.
The isolated output signals from the optical isolators corre-sponding to the outputs PAl to PA7 and PB0 to PB7 are appliedvia connector~ P4 to the D/A converter 34, and to a set of drive transistors Ql to Q8, respectively. As shown in more detail in FIGURE 4E, the collectors of each of the drive tran-sistors Ql to Q8 are connected to the inputs of the chart print-er connector 35. FIGURE 4E does not explicitly show thechart edge printer 38, but it is understood that an array of printing elements in the form of heater resistors are incor-porated into the analog chart recorder 36 and are energized to selectively print out a mark or marks to hicJhlight the ~S various graphs or presentations of data made thereby. In par-ticular, the analog chart recorder 36 is capable of making a presentation indicative of a R-R interval histo~ram in a manner similar to that shown in FIG~RE 1, an interval differ ence histogram similar to that shown in FIGURE 2, and a trend sample showing for a series of consecutive trend sample inter-vals, e.g., 5 minutes, the minimum/maximum heartbeat rates.
In the course of the presentation by the analog chart recorder 36, the chart printer 38 will provide a series of marks on the same paper to separate these various graphs and, with respect to the trend sample graph, will provide a series of different marks to indicate the occurrence of various events in a trend sample. For example, a triple mark above a trend sample ~:~'7~;.3~

indicates tha-t the system has detected an anomaly, as will be described in detail later. If the patient 20 senses distress possibly related to his heart activity and in response thereto depresses the mark button 84, the chart edge printer 38 is energi~ed to place a double mark adjacent that trend sample. If excessive noise is imposed upon the ECG signal as derived from the patient 20, the occurrence of that noise will be indicated by the chart edge printer 38 forming a single mark above the corresponding trend sample. The connector 35 applies via leads to energize the heat resisting elements ~not shown) to form the noted marks.
As indicated above, the addressing latch 140 applies a series of outputs PBO to PB7 via the optical isolators U8 to Ull to the D/A converter 34, which provides an output signal to its Io output to an operational amplifier U2. In turn, the operational amplifier U2 output is applied to the signal input of the chart recorder 36, whereby its pen is moved to reflect the input analog signal. The circuit as shown in FIGURE 4E provides means in the form of the potentiometer R36 whereby an offset may be provided to the signal to be applied to the analog chart recorder 36.
As will be explained later in detail, the partic~lar mode of operation in which the system lO is disposed i5 dependent upon which of the elements of the system are connected to the data acquisition ~mit 12, as shown in FIGURE 3A. For example, the system is operative in either a playback mode or a calibration mode if the playback unit 30 is coupled to the portable acquisition unit 12. As shown in FIGURE 4D, the addressing latch 140 inclu-des outputs PCl and PCO that are set, respectively, high and low by the signals imposed upon the outputs PC5 and PC4. If the connector P3 is in fact coupled to the connector J3, as shown in FIGURE 4C, the addressing latch 140 may be accessed to determine the signals imposed upon terminals PCl and PC0 to thereby set the system lO to enter either its calibration or playback mode of operation.

~ ~77~3~
In addition, inputs are provided from the All and A12 out-puts of the CPU 14, as shown in FIGURE 4A, to the Al and A0 inputs of the addressing latch 140 to control whether the particular signal as applied via the data bus 48 is to be applied to the chart recorder 36 from its outputs PB0 to PB7 or to the chart edge printer 38 from the outputs PAl to PA7.
Referring now to FIGURE 6, there is shown a high-level flow diagram of the method in which the heart data moni-tor of this invention operates to record and compact heart data and to playback the stored data in a form that intelligi-bly informs the physician of the patient's heart condition.
Initially, in step 200, the operator depresses the start/reset button 96 upon the control panel of the acquisition unit 12 as shown in FIGURE 3B. Thereafter, in step 202, the interrupts to the CPU 14 are disabled. As explained above, the CPU 14 has a variety of interrupt inputs which permit the CPU 14 to take data from different areas of the ROM 28. As will be explained with respect to FIGURE 7, the interrupt permits a hardware mechanization of various processes to simplify the software and to effect a saving in time of execution.
Initially, these CPU interrupts are disabled. The interrupts are enabled by a series of flags that are disposed within an interrupt array or register within the CPU 14 that permit selected of the CPU's interrupts to be used while disabling the remainder. Initially, each of the CPU's interrupts are disabled and thereafter an initialization process enables selected of the CPU's interrupts by applying flags to the corresponding areas of the interrupt array. As a further - part of the initialization, signals are applied by the CPU 14 to set the isolating latch 32, permitting data flow to and from the analog chart recorder 36 and the chart edge printer 38, and to sense whether the playback unit 30 is coupled to the acquisition unit 12. Thereafter, the select step 204 is executed whereby one of the following operating modes is selected: playback (PB~M), calibration (CALIBM), and monitoring

-2~ J7S39 (~NTRM). Basically, step 204 looks at the system configura-tion in terms of which elements are connected to the acquisi-tion unit 12 to determine in which mode the system 10 may be operated. For example, if only the playback unit 30 i5 coupled to the acquisition unit 12, then step 204 transfers . the pro~ram to the playback mode by step 300. However, if the playback unit 30 is disconnected from the acquisition unit 12 and the preamplifier 18, and in particular its connector J4, as shown in FIGURE 4C, is coupled to the portable acqui-sition unit 12, the system 10 transfers to the monitoring mode 500 via the initializing step 400. In particular, the connector J4 interconnecting the preamplifier 18 and the acquisition unit 12 has two pins connected together, wnereby the RST 6.5 input to the CPU is shorted or rendered to its lowest state, so that an input state is stored in a register of the CPU 14, to be accessed during the select step 204.
Similarly, the coupling of the acquisition unit 12 to the playback unit 30 and in particular to the isolating latch 32 is made via the input/output port of the CPU 14 which responds if the isolating latch 32 is coupled to the CPU 14.
Before entering into the monitoring mode 500, it is necessary to check PERMIT$FLAG indicating that the system had been calibrated by the ralibration mode 206. Otherwise, if the PERMIT$FLAG is not sensed, the system cannot enter -the monitoring mode 500. The MCLEAR routine 400 rese-ts PERMIT$FLAG
after directing the process to monitoring mode 500 to prevent reentry into the monitoring mode 500 unless the calibration mode 206 has been rerun to set PERMIT$FLAG. In order to enter the calibration mode 206, it is necessary to detect that the data acquisition unit 12 is connected to both the preamplifier 18 by detecting the shorted pins of its connector J4, as well as to the isolating latch 32. On the other hand, if the data acquisition unit 12 is not coupled to any other device, the system exits immediately to the standby mode 208.
In.the calibration mode 206, the CALI~M (calibration mode controller) program is executed to help the operator 7~53~

adjust the system to accept different amplitudes of heart sig-nals and set different refractory periods as are needed to pro-perly detect the QRS complexes of a patient. In connection with the amplitude of the patient's R-wave, these amplitudes may vary as much as 20:1 within a normal patient population. Thus, to prevent saturation of the A/D converter 16 and to permit it to operate within a range of 30 to 50% of its total capability, it is necessary to set the gain of the operational amplifier 90 tsee FIGURE 4C) of the EGC amplifier 19 until the normal ampli-tude of the R-wave is of a height to permit a 2:1 increase of the ECG signal amplitude without reaching the upper or lower count limits of the A/D converter 16. In this mode, the output of the preamplifier 18 is continuously monitored via A/D conver-ter 16, to determine whether the deviation from baseline peak, whether negative or positive, exceeds 40 A/D converter units or counts. If the peaX input is below this limit, the CALIBM pro-gram causes the ECG LED 88, as shown in FIGURE 4C, to be left unenergized. If the peak amplitudes result in peak deviations from baseline that exceed a second limit corresponding to 60 units of the A/D converter 16, then the LED 88 is continuously lit. If the peak deviation from baseline measured by the A/D
converter 16 is between 40 and 60 units, the LED 88 will flash each time a QRS complex is detected. ~ormally, it is desired to set the gain of amplifier 90 such that the output of the A/D
converter 16 around the baseline deviates about ~ 50 counts throughout the cardiac cycle. To this end, the variable gain of the input amplifier 90 within the A/D converter 16 is adjusted, via R9, so that the LED 88 flashes on each QRS. In addition, the calibration mode 206 adjusts the refractory period, i.e., the expected period between the R and ~ waves of the patient's heart signal, during which ECG signals applied to the data ac-quisition unit 12 will be inputted but not processed to detect QRS complexes. To se-t the refractory period, the mark button 84 is depressed, whereby a buzz or ~.'7'~;3~ .
high frequency signal is imparted to the ECG chart -~or a period as long as the mark button 84 is depressed. Such a signal is developed by the analog chart recorder 36 and increases in duration every 4 seconds while the operator holds mark button 84 down. The operator holds mark button 84 down until the refractory period indicated by the buzz signal extends to the end of the T wave. As will be explained later, the refractory period is computed in accordance with a SET$REFRACTORY$TIME subroutine dependent upon the length of the last occurring R-R interval and a constant that is changed only during adjustment of the refractory period, i.e.,the correspond-ing count of the refractory period counter in turn sets the refractorycalibration constant which is used in the calculation of the refractory period upon successive occurrences of the R-R interval.
After calibration, as indicated by the setting o~ the RERMIT$FLAG, and the detection -that the data acquisition unit 12 is coupled to the preamplifier 18, the select step 204 branches to the clear/initializing routine 400, executing the MCLEAR program wherein the storage areas as shown in FIGURE 5 are cleared for receiving the refractory constants in preparation to entering the monitoring mode 500. The monitoring mode 500 will be explained later with respect to FIGURES 8, 9, 10, and 11, and is controlled by the MNTRM program to detect successive QRS complexes, to determine whether such complexes are valid or not, to characterize valid QRS complexes, to measure R-R intervals, and to control the processing of such data and the subsequent storage of the processed data within the RAM 26. The R-R interval is computed and the corresponding rate is obtained before storage within area 26c of the RAM 26, as shown in FIGURE 5. Next, the differences between the successively calculated R-R intervals are calculated to increment one of the bins within area 26b of the RAM 26. Further, there is included a classification subroutine to sense abnormal or arrhythmic heart 753~
signals; in particular it is determined whether the rate is above 120 or below 40 beats per minute (BPM) or whether there has bee~ a skipped or early beat. If so, the SAVE$FLAG is set ana ~ trigger signal is generated to store the current set or strip of ECG rhythm signals within one of the nine buffers within area 26a of the RAM 26. Shortly after the SAVE$FLAG is set, the data in the current buffer is frozen and the pointer to the address of the storage buffer moves to the next buffer if available within the area 26a.
The monitoring routine 500 controls monitor mode operations; it does not include routines for performing real time tasks such as timing intervals, R-wave detections, and calculating the R-R interval. The real time routines are separate, as shown generally in FIGURE 6, in order to simplify the total software requirement of ~his system. Briefly, real time tasks, including the R-wave detection routine, are entered once for each cycle of the sample clock 24. The moni toring routine 500 is executed as long as a RUN$FLAG remains true. Any of the following events can set RUN$FLAG false, thus terminating the monitor mode: first, the battery for energizing the system 10 may fall below a predetermined level;
second, area 26c for receiving the trend data may be filled, i.e., no more data may be stored therein; and third, the con-nector J4 of the preamplifier 18 may be disconnected. After RUN$FLAG is set false, MNTRM completes Einal housekeeping tasks in block 500 and transfers control to step 208 wherein the standby mode controller deenergizes all system components except the RAM 26. In particular, upon the completion of each of the steps in routines 300, 206, or 500, the process transfers to the standby mode 208 wherein the interrupts of the CPU 14 are disabled and the data as stored within the RAM 26 is protected from being read out or written upon. Further, the power supply 52 is shut down to all parts of the system 10 with the exception of the power that is supplied to the RAM 26, thereby insuring the data as stored therein is safely continued -28~ ~ 3~3 to be stored. In this fashion, the drain as placed upon the system's battery 82 is minimized to insure maximum battery life.
Further, the select step 204 may directly transfer the process into the standby mode 208 if the terminal of the preamplifier 18 as well as the playback unit 30 are discon-nected from the acquisition unit 12.
Further, as shown generally in FlGURE 6, a real time interface program 600 is provided that organizes the various tasks required to be performed in real time, for example, the detection of the R-wave, as a service to the mode controller programs that may be executed in computer time. These real time service routines may detect certain conditions which place the system 10 directly into the standby mode 208.
Referring now to FIGURE 7, the real time interface program 600 is shown in greater detail. Step 602 detects whether the output of the system battery 82 is low and, if so, actuates the CPU 14 to enter a LOW$VOLTAGE$DETECTOR$SERVICE or routine 604, whereby the process is transferred to the standby mode 208. As shown in FIGURE 4A, there is included a Schmitt trigger circuit 54 that is coupled to sense the output of the battery 82. In response to detection of its voltage below a predetermined level, e.g., 10 volts, the circuit 54 applies a high or ~5 signal to the TRAP input of the CPU 14 causing the CPU 14 to enter the LOW$VOLTAGE$DETECTOR$SERVICE 604. In this service 604, a determination is first made of whether the process is in the monitoring mode 500 and, if so, sets the RUN$FLAG false. As will be explained in detail later with respect to FIGURE 8, the monitoring mode 500 responds to the setting of the RUN$FLAG false to insure that the ECG data is completely recorded, that the calculations of the current R-R interval is completed, and that the average of the then obtained R-R interval~ is calculated and stored in an appro-priate location within the RA*I 26. Thereafter, the RAM 26 is shut down in a manner so as not to lose any stored data and -29- ~ S39 to maintain its energization, as will be explained later. The Schmitt circuit 54 actuates the TRAP interrupts o~ the CPU 14 in this manner to effect an interrupt of the proyram to its standby mode 208 in order to reduce the progxamming that ~ould otherwise be required. Step 606 senses the absence of the ECG preamplifier 18 and in particular that terminal J4 associated with the preamplifier 18 is disconnected, i.e., the shorted pins are removed from the RST 6.5 interrupt of the CPU 14, and the RST 6.5 interrupt goes to +5 volts, whereby the CPU 14 initiates a PRE-AMP$STATUS$SERVICE 608 wherein the process may be transferred to the standby mode 208. In par-ticular, if the system is in the monitoring mode 500, the ser-vice 608 will force the system to loop until the preamplifier 18 is reconnected to the acquisition unit 12 or the mark button 84 is pushed. When the mark button 84 is pushed, the RUN$FLAG
is set false, causing MNTRM to put the system into its standby mode 208. While the system is looping, no further data is stored within the RAM 26 or processed to detect QRS complexes.
Further, when the mark button 84 is pushed, the average of the 20 R-R signals received to that point in time is calculated and the pointers stored in various other locations of RAM 26 are reset. If the process is in its calibrate mode 206 of opera-tion, the system transEers directly to the standby mode of operation 208 upon the sensing that the preamplifier of the ECG 18 is disconnected.
Though but a single mark button 84 is shown in the described specific embodiment of this invention, it is con-templated that a series of such buttons could be incorporated into this system, whereby the patient could more specifically designate the type of sensation that is being felt as to a particular symptom, body function, or activity. In adaition, it is contemplated that an accelerometer type device as ~ould be attached to the patient's body could be substituted for the mark button 84 and upon rapid motion of the patient's body, indicative of a high rate of body activity, that switch . . .

~ ~30~ S39 would be closed whereby the patient's ECG sign~1 would be recorded for a given period of time.
As shown in FIGURES ~A and C, the sample clock 24 provides a 240 Hz sample clock signal to the RST 7.5 interrupt input of the CPU 14. The sample clock causes the CPU 14 to effect a CRYSTAL$CLOCK SERVICE 612 whereby the appropriate mode service routine is set, as shown in FIGURE 7~ In par-ticular, the service 612 checks the current mode of operation, i.e., determines which of the modes 300, 205, or 500 is i~
operation and,dependent upon the current mode, selects one of the service routines 614, 616, 618, 620, or 622 to execute.
In particular, the service 612 examines XCMODE, a mode status variable assigned to a specified location within ~he RAM 26, to determine whether its value is 0, 1, 2, 3, or ~, corre-sponding to the service 614, 616, 618, 620, or 622 that mustbe selected. The services 614, 616, 618, 620, and 622 are carried out in real time and act as an interface between the input signals which are received in real time and the further operations and calculations that are carried out by the corre-sponding mode controllers i~ computer time under the controlof the clock 15 coupled to the CPU 14.
A CALIBRATION$SERVICE 614 performs in real time the basic system timing necessary to the calibration mode controller (CALIBM) 206. In particular, the service 614 responds to the sample clock to repetitively call the R-wave detecting sub-routine whereby the QRS complex of the ECG siqnal is detected and its amplitude provided. The obtained ECG peak signals are saved and passed ~o the calibration mode controller (CALIBM) 206 that operates in response to the computer clock 15 to determine whether the QRS complex amplitudes are accept-able. Further, the CALIBRATION$SERVICE 614 also applies the ECG signal and the "buzz" signal as needed to the analog chart recorder 36 to facilitate refractory adjustment as explained above.
The MONITORSSERVICE 616 acts as a real time interface for the monitoring mode 500, performing basic timing functions, -31- ~t~53~

calling the R-wave detecting routine, and effecting the storage of every fourth ECG byte, i.e., its corr~sponding amplitude, into one of the nine rotating buf~ers formed within the area 26a of the RAM 26. If during the course of the monitoring mode 500, a flag is set by MNTRM indicating the detection of an arr~ythmic signal, the current buf~er of the area 26a is saved and the MONITOR$SERVICE 616 develops a pointer to the next buffer, if available, within the area 26a.
Basically, the DATA$CHART$SERVICE 618 provides timing for the various data charts whereby data is output from the RAM 26 at a rate that corresponds to the incremental advance of the paper chart as driven by the recorder 36. For example, each cell of the trend data indicative of the average minimum and maximum R-R intervals is applied to the chart recorder 35 at a rate that one cell will be displayed per milllmeter advance of the paper chart. In this regard, it is noted that the paper chart is advanced one millimeter per 40 ms. To produce such timing, the service 618 is responsive to the outpu-t of the sample clock 24 to produce a drive clock to the recorder 36. It is noted that the sample clock may not be simply divided to obtain the desired 40 ms. drive signal but rather a timing subroutine is provided to respond to 10, 10, 9, 10, 9 clock signals to produce corresponding drive advance signals to the recorder 36. The corresponding 48 clock signals occur- .
ring over a timing of 200 ms. are precisely equivalent to the occurrence of five 40 ms. intervals. The fact that each drive advance signal is slightly in error does not affect the overall accuracy of the chart provided by the recorder 36.
The DATA$CI~RT$SERVICE 618 operates in real time to effect a playback of the trend and histogram data stored in the R~M 26 upon the analog chart recorder 36 and the chart edge printer 38. In addition, the service 618 provides a 60 Hz square wave to the analog chart recorder 34 to provide marks between the graphs displayed upon the recorder 34. For exam-ple, there is a marked interval between the trend chart and J~S3~

the histogram chart to indicate clearly to the physician a divi-sion theretween.
The positive and negative SLOPE$PLAYBACK SERVICES 620 and 622 respond, respectively, to positive-going and negative-going slopes of the inputted ECG signal to interpolate between ECG points to provide a series of straight lines between two ad-jacen~ points to produce a smooth-looking curve on the chart recorder 36. A series of straight line segments each 16.67 ms.
long are used to reproduce an essentially smooth appearing curve between the two points. Realizing that the data acquisition unit 12 is a portable unit and comprises a RAM 26 that has a limited storage capacity, it is desirable to store less than each sample of the patient's ECG signals in order to increase the length of time for which the monitoring system 10 may be used. However, upon playbac~ wherein the stored data within the RAM 26 is read out, it is necessary to provide a smooth appear-ing curve.
The monitoring mode 500, as generally shown and des-cribed with respect to FIGURE 6, is more fully shown in FIGURE 8. The select step 204 transfers control to MNTRM 502, the entry point label for the monitor mode controller 500 via the MC~EAR program 400. Control then passes to ~tep 504 to implement a delay for warm-up and to store selected variables within the area 26d of the RAM 26~ For example, it is neces-sary to set the pointer to designate an initial bufer loca-tion in the area 26a, in the trend sample area 26c, and in the histogram area 26b. Further, all storage locations in the minimum rate location o the trend data area 26c are set to a maximum value to simplify the steps of the programming required to determine the subsequent minimum heartbeat rate. Further, a count is stored to be counted down by the subsequent occurrences of the sample clock and upon counting down to zero, that corresponding ECG

_33~ 7S3~

sample is stored within the desiynated lo a~ion of area 26a.
A variable named XCMODE, located in RAM ~ , is set to "1" to indicate to block 612 that the system is in monitor mode.
Thus the MONITOR$SERVICE routine 616 will be called to pro-vide the monitor mode controller with appropriate real timeservices, such as timing and QRS detection, on each-positive-going transition of the sample clock. A count to determine the length of the trend interval in terms of a selected num-ber of sample clock signals is provided to be counted down upon the occurrence of each clock sample to determine at the "0~ c~unt a five-minute interval, for example. In addition, a lock out time is stored to provide a delay before a flag can be set by MNTRM to effect the permanent storage of data within a buffer of the area 26a.
After storage of these and other variables, the process moves through loop entry label 506 to the decision step 508, which determines whether the RUN$FLAG has been set true or false. As indicated above, the RUN$FLAG is set false if the battery voltage is determined to be low, the connector J4 of the ECG amplifier 18 is disconnected, the trend storage area 26c, or the histogram storage section 26b is filled, or the pointer to designate the buffer within area 26a indicates that all buffers are already full. If the RUN$FLAG is set false, the program moves through step 520 wherein the data in the current trend sample or interval is calculated to pro-vide an average based upon the previously received R-R inter-vals. Thereafter the process is transferred to the standby mode controller 208 where commands are given to the power supply to deenergize all elements of the system except the RAM 26 and associated chip select logic to continue the stor-age of the previously recorded data at reduced battery drain.
If on the other hand in step 508, the RUN~FLAG is set true, i.e., the system is in a functional condition to receive, process, and store ECG signals, thc process moves to step 510 to check whether the mark button 84 has been _3~ '77~39 pressed, and if pressed, step 512 stores an event marker in an auxiliary history array wit~in the RAM 26 indicative of which sample or interval in which the mark button 84 was pressed. Thereafter, after step 512 or if the decision block 510 indicates that the mark button was not pressed, ~he process moves to step 514 to determine whether the R$FLAG was set true by the execution of the R-wave sensing portion of the MOI~ITOR$-SE~VICE routine, as will be described with respect to FIGURE 16. If yes, the process moves to routine 700 as will be described below in detail with respect to FIGURE 10. In rou~ 700, the data secured by the execution of the MONIT~R$-SERVICE routine 616, as shown in FIGURE 7 and in particular the R-wave sensing routine called thereby, is used to reset the R$FLAG, to process the R$WAVE$TYPE data indicative of the presence of contaminating noise as stored withln a designated area of the RAM 26 and to operate on the R-R interval stored within one of the buffers of RAM 26. Af-ter either the routine 700 has been executed or decision step 714 has indicated the R$FLAG to be set false, the process moves to step 518, wherein the ELAPSED$TIME within a trend sample interval is compared with respect to that value END$0F$TSI as stored within area 26d to determine whether the trend sample interval is over, e.g., whether 5 minutes has expired. ELAPSED$TIME is stored within a counter formed within area 26d of the RAM 26 and is incremented upon the occurrence of the sample clock. ~f the interval is over, i.e., yes is indicatcd by step 518, a routine 8D0, as will be explained with respect to FIGURE 9, summarizes the data stored in the completed trend sample inter-val to determine the average R~R interval and therefore the average heartbeat rate and thereafter directs the storage of the R-R interval data to the next location or cell within area 2~b. After the decision step 518 has indicated that the trend sample interval has not expired or the completion of the routine 800, the process moves to step 516 wherein the process is halted until the next sample cloc~ occurs and i39 causes execution of the MONITOR~SERVICE routine which inputs and processes the next piece of the ECG data as derived from the patient.
Thereafter, the process completes its loop, reentering at label 506 to examine and process the next piece of ECG data.
The summarizing routine 800, as generally shown in PIGURE 8, is more fully shown with respect to FIGURE 9 wherein the routine 800 is entered via the label 804 to initiate the summarizing process. More specifically, in step 806, the sum of R-R intervals within a single trend sample interval as stored within a storage location of the area 26d is divided by a count indicative of the number of R-R intervals sensed during a single trend sample interval. Thereafter, the average interval is inverted to provide the average rate of the patient's heartbeat during the trend sample interval. Next, in step 808, the pointer TSI$PTR is incremented by "1" to cause the R-R interval data for the next trend sample interval to be stored in the next cell or bin of the area 26c. Thereafter, in step 810, the current pointer TSI$PTR is compared with an indication of the maximum capacity of the area 26c and if in excess of the maximum capacity, the RUN$FLAG is set false in step 812 whereby, as explained above with respect to PIGURE 8, step 508 transfers the process via step 520 to the standby mode controller 208.
If, as determined by step 810, there is further storage available in area 26c or the RUN$FLAG has been set false by step 812, step 81~ clears the counters as formed within area 26d of the RAM 26 and used to count the number of intervals and to sum the intervals occurring during the new current trend sample interval. Thereafter in step 816, the end time indicator of the current trend sample interval, END$0F$TSI, is reset to indicate the next end of trend sample interval by adding 300 seconds to the present value of the ELAPSED$TIME counter. Thereafter, step 818 returns the process to the monitoring routine MNTRM as shown in FIGURE 8.
The processing and storing of the R-R data, as generally shown in routine 700 of FIGURE 8, is shown in greater ~.~'7~S39 detail in FIGURE 10. The routine en~ers via label 704, as shown in FIGURE 10, to process and store data pertaining to the R-R interval associated with the QRS complex recently detected by the MON~TOR$SERVICE routine 616. In block 706, R$FLAG is set false to acknowledge detection of a QRS com-plex by MONITOR$SERVICE 616~ In addition, block 706 obtains the variable R$WAVE$TYPE, indicative of whether the detected QRS complex is contaminated with noise, and a RR$INTERVAL, indicative of the measured R-R interval. Next, the value of RR$INTERVAL is placed into that ocation of the area 26d known as NEW$RR. rhereafter, the value of the CoMBo$RR is set equal to the sum of CURRENT$RR plus NEW$RR, thereby sum~
ming the two most recently recorded values of the R-R intervals.
As will be explained later in detail, the values of NEW$RR corresponding to the most recently calculated R-R inter-val and of COMBO$RR are used to determine whether to save a strip or set of the patient's ECG signal corresponding to detection of an anomaly, as will be explained with respect to FIGURE 11. It is necessary to classify R-wave data so the inte~-vals associated with valid R-wave signals are processed while noise contaminated signals are ignored. In addition, intervals following a premature beat should be treated in a different manner than intervals occurring in a regular rhythm.
As shown in FIGURE 10, there is provided step 708 that evalu- , ates a variable R$WAVE$TYPE. The strategy for changing the value of R$WAVE$TYPE, in conjunction with block 708, provides the means for classifying each detected QRS complex. For purposes of illustration, assume that the QRS complexes are not contaminated by noise and that the system }-as just been turned on, i.e., R$WAVE$TYPE is setto "4". Consequently, when the very first QRS is detected, block 708 passes control to step 728, which does not use any R-R intervals information because that information ismeaningless when no prior interval has been detected. Since the interval associated with the next QRS
complex will have meaning, step 728 sets RSWAvE$TYPE to "3".

Consequently, the next uncontaminated complex will be processed by step 724, wherein the detection of the first uncontaminated QRS complex is used to initialize the system to store the subsequent uncontaminated signals. In step 724~ the serial locations wherein the most recent values of the R-R
interval, namely NEW$RR, CURRENT$RR, PRIOR$RR, and PRE$PRIOR$RR are shifted to place the most recent value of the R-R interval in the NEW$RR RAM loca~cion Thereafter, the SET$REFRACTORY$TIME program is called to set the refractory period as a function of the most recently detected interval between QRS
complexes. Thereafter, the R$WAVE$TYPE is set to "2" in order to process the next QRS complex which will be considered to be a normal, uncontaminated QRS signal. After execution of step 724, the program 700 returns via step 726 to step 518 of the monitoring program 500.
Upon the occurrence of detection of the next QRS complex, as indicated by the setting of the R$FLAG signal, the process returns to the subroutine 700 wherein, since R$WAVE$TYPE has been set equal to "2", step 708 directs the program to step 722 wherein an acceptable QRS complex is stored as a regular rhythm or premature signal. The SET$R~FRACT0RY$TIME
subroutine is executed for setting the refractory time as a function of the R-R interval, and thereafter the UPD~TE$DELTA subroutine is called to calculate and store the difference between successive R-R intervals in the delta or difference histogram in area 26b of the RAM 26. Thereafter, a CLASSIFY$AND$STORE subroutine, as shown in FIGURE 11, is executed to determine whether the detected, uncontaminated QRS is part of a regular rhythm or is a premature beat. If part of a regular rhythm, the R$WAVE$TYPE
is left at "2", whereas if the QRS complex occurs early or prematurely, the R$WAVE$TYPE is set equal to "1". The regular rhythm and premature beats will be appropriately processed and stored, as will be explained in conjunction with FIGURE 11. Thereafter, the various locations for receiving and storing the R-R intervals 38~ '7~S3~

are updated with the most recent value of the R-R interval being stored in the NEW$RR location. After completion of step 722, the subroutine 700 exits Vih step 726 ta step 518 of the monitoring program 5~)0.
Upon the detection of the next QRS complex after - 5 the setting of the R$WAVE$-TYPE equal tc "l", step 708,upon sensing the "l" state,-transfers control to step 720 wherein the QRS complex that has been preceded by a premature beat is processed. Such a beat is typically known as a compensatory beat and such a beat is not stored within the trend area 26c of the RAM 26. However, the difference between successive R~R intervals is calculated and the UPDATE$~ELTA routine is called to store the calculated difference within the IDH
array of RAM area 26b. In addition, the refractory period is set by the SET$REFRACTORY$TIME subroutine as a function of the last calculated QRS interval. Thereafter, the R$WAVE$TYPE
is set equal to "2" to condition the ~CCEPTABLE routine to receive the subsequent, normal QRS complex. In addition, the areas of the RAM 26 for receiving the previously calculated and stored values`of the R-R interval are updated with tlle most recent value of the R-R interval being stored in the NEW$RR location.
In the instance that the MONITOR$SERVICE routine 616 determines that the signal is noise contaminated, MONITOR$- ~.
SERVICE sets R$WAVE$TYPE to "0", whereby step 708 passes con-trol to step 718 wherein the newly measured R-R interval is not stored because it is contaminated. However, R$~AVE$TYPE
is set to "2" to permit initialization of the next uncontami-nated QRS complex.
The ACCEPTABLE routine 722~ as shown generally in FIGURE 10, is described in detail with respect to FIG[JRE 11, for processing the patient's ECG signal and or storing data that has been found to be a valld and acceptable R-wave. The ACCEPTABLE routine 722 begins with step 730, wherein the SET$-REFRACTORY$TIME subroutine is called to set the refractory period, wherein the system 10 is disabled from sensing further heart activity or signals placed upon the input leads for th~t period ater the occurrence of the R-wave. Typically, the refractory period for a patient having a heart rate of 75 BPM is in the order of 300 to ~00 ms.
The refractory period is variably set by the SET$REFRACTORY$TIME subroutine as a function of the previously determined R-R interval as stored within the NEW$RR location within a rotating buffer of area 26d of the RAM 26.
As generally described above, this rotating buffer includes four locations wherein four consecutive values of the most recently determined values of the R-R interval are stored, in order, in the locations NEW$RR, CURRENT$RR, PRIOR$RR, and PRE$PRIOR$RR. As a new value of the R-R interval is calculated or selected, as will be explained with respect to FIGURE 16, it is first stored in the NEW$RR location of the noted rotating buffer, and the old values of the R-R intervals are transferred to the next locations.
The SET$REFRACTORY$TIME subroutine selects that value of the R-R interval located in the NEW$RR location and, using the following expression, REFRACTORY = KQT ~NEW$RR ~ 27)/60, determines the length of the refractory period in terms of sample clock counts as generated by the clock 2~.
Thereafter in step 730, the subroutine UPDATE$DELTA is called for determining the difference between adjacent R-R intervals by subtracting the value stored in the PRIOR$RR location from that stored in the CURRENT$RR location. The calculated value of the difference between adjacent R-R intervals is used to define a pointer to a bin or cell within the interval difference histogram array of area 26b of the RAM 26 and that bin is thereafter incremented by "1" to count the occurrence of that difference between the CURRENT$RR and PRIOR$RR intervals.
Decision block 732 is executed to determine whether a premature beat has occurred, based upon the most recent data indicative of the R-R
intervals as stored within the NEW$RR, CURRENT$RR, PRIOR$RR, and PRE$PRIOR$RR locations of the noted rotating buffer. In particular, there are two types of premature . ~
_40- ~-~ 6~ 3 ~

beats that are detected, a premature beat with compensatory pause and an interpolated beat; these types of beats are detected in that they are attributable to malfunctions of the ventricles and are considered to be more serious than premature beats arising due to malfunctions of the atria.
- The occurrence of a premature beat wi-th compensatory pause is illustrated in FIGURE 18A wherein there is shown a series of R-waves R0, Rl, R2, R3, and R~ with the R-~ave R0 occur-ring first in time and the R-wave R4 occurring last in time.
As illustrated, the R-wave R3 has occurred early in time, being shifted to the right as seen in FIGURE 18A toward R-wave R2; further, the space between R-waves R3 and R4 is greater than normal providing a compensatory pause so that the R-wave R4 occurs at approximately its normally expected time. An interdigitated premature beat is illustrated in FIGURE 18C wherein a beat having R-wave R3 is inserted approx-imately midway between the beats corresponding to waves R4 and R2, noting that the interval between the R-waves R4 and R2 is approximately equal to the normally occurring R-R inter-val. As will be explained, the subroutine 732 detects whethera premature beat with compensatory pause or interdigitated premature beat has occurred. Premature beat data is processed and stored in a first manner by steps 736 through 742 whereas if no premature beat has occurred, the R-R interval is processed in a second manner by steps 748 through 764.
The determination of whether the beat is premature or not is made by examining the values as stored within the locations NE~1$RR, CURRENTSRR, RRIOR$RR, and PRE$PRIOR$RR of the noted rotating bufer in the following manner. Sub-routine 732 dctermincs whethcr a first condition is met, i.e.,whether the R-R interval as stored within the CURRENT$RR inter-val location is less than 75% of that value as stored in the PRIORS~R location; this comparison can be visualized by examining FIGURE 18~, wherein the interval between the R2 and R3 waves is lcss than 75 percent of the interval between the Rl and R2 waves. Next, to determine the existence of a com-pensatory pause, the value CO`~BOSRR, indicative of the sum of il1'7~

the R-R intervals as stored within the NEW$RR and CURRENT~P~R locations, is compared with a value indicative of 175~ of the R-R interval as stored within the PRIOR~RR location. As shown in FIGURE 18B, the length between the R4 and R2 waves is compared to the length between the Rl and R2 waves, and if greater than 1.75 times the length between the Rl and R2 waves, and if the first condition is met, the decision block 732 provides an indication that the beat is a premature beat with compensatory pause by transferring control to step 736.
Second and third tests are made to determine whether an inter-digitated premature beat R3, as shown in FIGURE 18C, exists. In particular, the value COh~0$RR indicative of the sum of the values within the NEW$RR
and the CURRENT$RR locations is determined to be less than 1.25 times the value of the R-R interval as stored within the PRIOR$RR location. As seen in FIGURE l~D, this indication compares the total length in time between the R2 wave and the R4 wave to the length between the Rl and R2 waves.
Further, a third test is made of whether the values stored in the COh~O$RR
location is less than 1,25 of the value of the R-R interval stored within the PRE$PRIOR$RR location. In other words, the length between the R2 and R4 waves is compared with the length between the RO and Rl waves to provide an indication of the stabi:Lity of the heartbeat pattern; if the heartbeat pattern is very irregular, the detected beat may not be a premature beat but an indication of some other, more dangerous anomaly. If the first condition and second and third test results are positive, there is provided an indication by the decision step 732 that an interdigitated premature beat has been detected and the process moves to step 736.
Step 736, shown in FIGURE 11, is the start of a premature beat processing routine. Step 736 sets the R$WAVE$TYPE flag equal to ~
whereby the processed R-wave is noted as an anomaly; as a result~ when the STORE$RR$INTERVAL$DATA routine 700 of FIGURE 10 is again run, a branch to the PROCESS$ANOhlALY

-42- J ~7753~

subroutine 720 will be executed whereby only the R-R inter~al data is stored and the system is prepared to receive the next R-wave as an acceptable R-wave. Next, step 738 looks to the location Ps$HIsToRY within area 26d of the RAM 26 where the number of premature beats for the current trend sample inter-val is counted and recorded, to determine whether there is space left there for further incrementation. If space is left, the PB$HISTORY ~ocation is incremented by one in step 740. In either event, the process moves to step 742, wherein the routine WAVEFORM$SToRAGE$MANAGER is called to initiate processes executed by the MONITOR$S~RVICE routine that save a waveform sample containing the premature beat within one of the circulating buffers of area 26a of the RAM 26. In addition to initiating waveform storage, WAVEFoRM$STORAGE$MANAGER, step 742, implements a storage lockout system that prevents the waveform storage area 26a of the RAM ~rom being filled up in a few minutes by a "run" of premature beats or other arrhythmias.
In particular, when WAVEFORM$STORAGE$MANAGER is called to store a waveform, it compares the current value of EI,APSED$TIME with the type of arrhythmias being savedO If the lockout period has not expired, WAVEFoRM$SToRAGE$MANAGER simply returns with-out initiating a sample save. If the lockout has expired, a sample save will be initiated and the lockout period will be initiated to prevent storage of other similar arrhythmias for 10 minutes by adding 600 seconds to the current time as taken from ELAPSED$TIME to determine that time when the storage of a sample of that particular arrhythmia waveform will be permitted. ~hereafter, in step 744, the locations of the rotating buffer are advanced, whereby the R-R intcrvals as stored in the various indicated locations are set to the next later location and the latest calculated value of the R-R
interval is set in the NEWSRR location.
If the decision step 732 decides that the beat or R-wave under investigation is not premature, the process advances to step 748, which is the start of a routine that ~43~ ~75~

processes non-premature beats. Step 748 computes the curren~
heartbeat rate by inverting the value of the R-R interval stored within the CURRENT$RR location and, further, the cells within the current bin of the trend sample area 26c are updated for the maximum/minimum rate trends. In particular, the cell locations where the maximum/minimum rate trends are stored, are compared with the current computed value of the heartbeat rate and, if greater or less, respectively, the corresponding bin location is updated with the new maximum or minimum rate.
The determination of the maximum and minimum rates of heart-beat provides a statistical indication of the regularity of the heartbeat and, as will be e~plained, will be displayed for the benefit of the physician. It is also contemplated within the teachings of this invention that the differences between suc-cessive intervals of the peak heart activity signal or heart-beat,as are calculated to obtain the interval difference histo-gram, could also be used in calculations to determine the standard deviations of the interval differences and that such standard deviation could be determined for each trend sample interval and stored in an appropriate location in memory corre-sponding to that interval. ~ext in step 750, a portion of the recently selected or calculated value of the R-R interval stored in the CURRENT$RR location is added to that location known as RR$SUM within area 26d of the RAM 26. A portion of 25 the R-R interval, as opposed to using the whole amount, is used to reduce the amount of storage space required for the RR$SUM location. As indicated above, at the end of a particular trend sample interval, the subroutine TSI$SU~MATION is called to calculate the average R-R interval by dividing the sum value of the R-R intervals as stored within the RR$SUM loca-tion by the number of samples taken.
Next, as shown in FIGURE 11, a determination is made of whether an anomaly other than a premature beat is occurring and in particular whether a tachycardia, a bradycardia, or a skipped beat is present, to set a series of flags whereby that particular sample of the ECG signal corres~onding to the anomaly is stored within one of the circulating buffers of the area 26a of the RAM 26.
First, in step 752, the most recently calculated value of the heartbeat rate is compared with that maximum rate above which there is an indication that an anomaly known as a tachycardia is occurring within the patient's heart. Further, the step 752 determines whether the rate is increasing by comparing the values of the R-R intervals as stored within the CURRENT$RR
and NEW$RR locations and if the values stored in the NEW$RR location is equal to or greater than that stored within the CURRENT$RR location indicating that the rate has begun to decrease, then the process moves to step 754, wherein the subroutine WAVEFoRM$SToRAGE$MANAGER is called to set those flags whereby a strip of ECG samples indicating the tachycardia is placed within a rotating buffer of area 26a of RAM 26. Illustratively, the selected maximum rate is set at 120 beats per minute. If the most recent value of the heartbeat rate is not above that maximum level, the subroutine moves to step 758, wherein the most recently calculated rate is compared with respect to a minimum rate indicative of the occurrence o a bradycardia and if below the minimum, e,g., 40 BPM, step 760 calls the WAVEFoRM$SToRAGE$MANAGER subroutine to set those flags whereby a strip of the ECG data illustrating the bradycardia, is stored within a rotating buffer of the RAM area 26a. If not below the noted minimum value, the process moves to step 762, wherein it is determined whether a beat has been skipped. In particular, that value of the R-R interval as stored within the CURRENT$RR location is compared with 1.75 times that value of the R-R
interval as stored within the location PRIOR$RR and if greater, there is an indication of a skipped beat whereby the process moves to step 764 to call the WAVEFoRM$SToRAGE$MANAGER to set flags that cause that strip of the patient's ECG samples to be stored within one of the circulating buffers of area 26a of the RAM 26. After each of the steps 754, 760, 762, and 764, step 756 increments the appropriate rate histogram cell and step 744 updates

3~

the values of the R-R intervals within the locations of the rotating buffer, before returning to the MNTRM program and in particular -to step 518, as shown in FIGURE 8.
Referring now to FIGURE 12, the MONITOR$SERVICE routine 616, as generally shown in FIGURE 7, will now be described in greater detail.
First the SAMPLE$ECG$AND$DO$TIMING routine 800 is called in response to the detection of the sample clock signals as input to the CPU 14; as will be explained in detail later with respect to FIGURF. 13, a sample of the ECG
signal is taken and processed before being stored. Four such samples are stored and then averaged before being placed in a location ECG$BYTE.
Further, the routine 800 determines whether an R-wave is present and, if so, sets the R$FLAG true, and further determines if the R-wave is noise contaminated or not; if the R-wave is noise contaminated, the R$WAVE$TYPE is set equal to "O". The SAMPLE$ECG$AND$DO$TIMING routine 800, as generally shown in FIGURE 12, is more fully explained with regard to FIGURES 13 to 17.
In step 802, it is determined whether the fourth ECG sample has been taken by examining the CLOCK$COUNT and if "O", the corresponding ECG sample is the fourth. In addition~ step 802 determines whether there is space available to store the nextECG sample in one of the nine rotating buffers within area 26a of the RAM 26. I:E it is the fourth sample and there is space available, the process moves to step 804; if not, the process returns via exit point 820 to the main program. In step 804, the average indication of the last four samples is stored within a location of one of the circulating buffers as identified by the pointer LOOP$PTR:thereafter, the LOOP$PTR is incremented to select the next location in the rotating buffer. Thereafter, in step 806, the process looks to see if the SAVE$ECG$FLAG has been set true by WAVEFoRM$SToRAGE$MANAGER as called from one of the steps 742, 754, 760, or 764 to indicate, respectively, an anomaly such as a tachycardia, bradycardia, or a skipped beat. If SAVE$ECG$FLAG

~..

-46- 3~7~

is set true, the process moves to step 808 wherein ~he counter LOOP$REMAINING is counted down ~o permit a given number, e.g., 60, of additional samples of the ECG signal to be stored within the rotating buffer after khe anomaly has been detected.
In this regard, it is noted that a total of 360 ECG samples are disposed within one of the rotating buffers o~ the area 26a of the RAM 26. If a no decision is made in step 806, the subroutine 616 returns to the main program.
Step 810 determines whether the rotating buffer has been filled by the ECG data, delaying the execution of the further steps until the 60 samples of the patient's ECG sig-nals occurring after the SAVE$ECG flag is set true have been filled as decided by step 810. If filled, the process moves to step 812 wherein the starting/end pointer within the filled - 15 rotating buffer is stored to permit access when it is desired to read out the data stored in that buffer. Further, step 812 sets the storage pointer to the first location of the next available circular buffer within the area 26a of the RAM 26.
In step 814, a decision is made as to whether there is a fur-ther rotating buffer available within the area 26a, and if no,the RUN$FLAG is set false whereby the MNTRM routine 500 is directed to transfer control to the standby routine 208. If there is a further rotating buffer available, as decided in step 814, step 816 loads the location LOOP$REMAINING with the predetermined count of the additional ECG samples, e.g., 60, to be stored after the detection of the anomaly, and there-after, the SAVE$ECG flag is set false to terminate thc saving of the ECG samples in one of the rotating buffers. Thereafter, - the process returns through exit 820 to execute that step of the monitor mode controller program 500 which was interrupted by the sample clock.
As indicated above with respect to FIGURE 7, the MONITOR$5~RVICE routine is called in response to the occurrence of each of the sample clocks if the system 10, as shown in FIGURE 3, is disposed in its mode for monitoring, i.e., the , t~ âJ5,;3~3 preamplifier 18 is coupled to the data acquisition uni~ 12. The SAMPLE$ECG$AND$DO$TIMING routine 80Q *akes samples of the ECG signal in response to the sample clock occurring at the rate of 2~0 ll~ and determines whether there is present a valid R-wave, as will now be explained in greater detail with respect to FIGURES 1~ to 17. R~ferring now to FIGURE 13, the subroutine 800 begins with a ti~ing step 822, wherein the ECG LED 88, as shown in FIGURE 4C, is energized for a fixed period, e.g., 40 ms.
corresponding to 24 counts of the sample clock, in response to the detection of each R-wave; in particular, 24 counts are loaded into a RAM location LED$TI~ER and isdecremented until it is set equal to "O", when a command is issued to deenergize the LED 88. In addition, step 822 steps two counters within area 26d of the RAM 26 that serve to time two separate functions.
First, the ELAPSED$TIME location is incremented each second and is used as a system timer that is initiated at the beginning of the monitor or calibration mode;the ELAPSED$TIME variable is used to control the timing of the trend sample and, in addition, the timing of the lockout period in which further strips of the ECG signals may not be stored, as explained above with respect to the WAVEPoRM$SToRAGE$MANAGER routine 7~2 o FIGURE 11.
The second clock is formed by the RR$TIMER location and is used to time the R-R interval, i.e., that interval between successive, val:id R-waves; the initiation and termination of the RR$TIMER location will be explained below. Next in step 824, an INPUT$AND$FILTER$ECG routine is called whereby a sample ECG signal is taken and stored in a four location rotating buffer that is incremented each time a new ECG sample is obtained. The ECG data is filtered af~er a sample is taken by averaging the contents of the four location buffer and storing the result in the location ECG$BYTE. Upon the occurrence of the next sample, the average ECG data stored in the ECG$BYTE
location is transferred to the PRIOR$ECG$BYTE location, the rotating buffer is updated, and a new average is stored in ECG$BYTE. ECG$BY'I'E and PRIOR$-ECG$BYTE will be used, in a ma~mer to be explained, to determine whether a valid R-wave has been detected. Next, -48- ~'7~S3~

in step 826, the process examines the current count of the RR$TIMER to determine whether the refractory period is over and in particular compares the current count o~ the RR$TIMER
to the refractory period determined by the SET$REFRACTORY$TIME
routine, as explained above. If the refractory period is over as determined by step 826, the SEGMENT$~UN~rER routine 900, as will be described more fully with respect to FIGURE 14, is called to determine the existence of an R-wave segment. ~f-ter the execution of the SEGMENT$HUNTER routine 900 or there has been indication that the refractory period is not yet o~er as determined by step 826, step 828 makes a decision as to whether a possible R-wave segment has been found; as will be explained in detail below with respect to FIGURE 14, the SEGMENT$HUNTER routine sets the SEGMENT$STATUS location equal to "1" or l'2" if a valid segment has been found, or to "3" if a "runt" or short segment has been found; thus, if step 830 finds a "1", "2", or "3" within the SEGMENT$STATUS location, the process moves to the SEGMENT$ANALYST routine 1000 wherein the detected segments are compared to determine if a valid R-wave has been detected. After the routine 1000 has been executed.or if the SEGMENT$STATUS has been found equal to "0", the process moves to step 830 wherein the SEGMENT$STATUS
location is set equal to "0" to prepare the process for the next ECG sample. Thereafter, the process exits via step 832 to complete either the MONITOR$SERVICE routine 616 or the CALIBRATION$SERVICE routine 614. In particular, if the system - is in monitor mode, the process returns via step 832 to step 802, as shown in FIGURE 12.
The SEGMENT$~UNTER routine 900, as generally shown in FIGURE 13, is more fully explained with respect to FIGURE 14, wherein initially step 902 evaluates the HUNTER$MODE location of R~ 26 to determine the state of the SEGMENT$HUNTER routine 900;
initially, the HUNTER$MODE location is set to "0" by the ini-tialization step 504 of the monitoring routine 500. When HUNTER$MODE is set to "0", the process proceeds to step 906 to 7~7~;39 begin the process of detecting the start o~ a potential R-wave segment.
As shown in FIGURES 19, the QRS complex, of which the R-wave is shown to form a positive-going peak, can be approximated by a series of segments.
FIGURES l9A and B show examples of valid R-waves wherein such ECG signals have been represented as a series of three segments. As will be explained below, the existence of a valid R-wave is detected by measuring the time interval between segments, the length, slope, and magnitude of segments, and the number of segments. Initially, in step 906, the time of interval or space between two consecutive segments .is measured and, if greater than 62.5 ms., a decision is made that any previously detec~ed segments are part of a deformed QRS complex or noise signal because the maximum interval between two related signal segments has been exceeded. Consequently, the process moves to step 916 wherein the SEGP~NT$STATUS location is set equal to "3"
to indicate tha~ the maximum interval between two valid segments has been exceeded. If the maximum allowable space between two segments has not timed out as decided by step 906! step 908 stores the current data in a segment start location of the RAM area 26d and initializes the timing of a period corresponding to the maximum length of a valid segment, e.g., 95.8 ms. The current data includes the previous value of the average F:CG signal as stored in the PRIOR$ECG$BYTE location, and the current value of time from the RR$TIMER location. Next step 910 determines whether there is a change of slope and if the change of slope is positive by comparing the value stored in ECG$BYTE location and the PRIOR$ECG$BYTE location. If the first value is greater than the second value by a predetermined amount indicating a positive slope greater than a threshold value, then step 912 sets the HUNTER$MoDE location equal to "1" to direct the SEGMENT$1~UNTER routine 1000, as shown in FIGURE 16, to look for the end of that segment. If step 910 makes a "no" decision, step 91~ determines whether a segment with a negative slope is present by examining the ECG$BYTE and the PRIOR$ECG$BYTE

_ ~9 _ locations, and i~ the PRIO~ECG$BYT value is greater than that value stored in the ECG~BYTE location by a predetermined amount, there is an indication that a beginning of segment has been found, and the process moves to step 918 wherein the HUNTER$MoDE flag is set e~ual to "2" to direct the SEGMENT$HUNTER routine 1000 to look for an end of that segment.
After any of the steps 916, 912, or 918, the process returns to step 828 of the SAMPLE$ECG$AND$DO$TIMING routine 800.
Upon the further calling of the SEGMENT$HUNTER routine 900 and either step 912 or 918 has set the HUNTER$MODE flag equal to "1" or "2", step 902 will sense the particular flag state and direct the process to either of steps 922 or 928 to locate the end of a segment. As an illustrative example, assume that the start of a segment with positive slope was detected on a prior pass through SEGMENT$HUNTFR 900 so that HUNTER$MoDE flag has been set to "1". Consequently, the evaluation step 902 transfers control to step 922 to locate the end of the segment with the positive slope. First, step 922 ch-ecks to see whether there has been a slope reversal or whether the segment duration limit, which was set in step 908, has timed out. If either there has been a slope reversal or the duration of a segment has timed out, the process moves to step 92~ wherein the amplitude or magnitude of the segment is calculated in terms of its absolute value and thereafter the SEGMENT$END$HOUSEKEEPING subroutine, as will be further explained with respect to FIGURE 15, is executed, whereby the various counters or timers are reinitialized to prepare for recalling the SEGMENT$HUNTER routine 900 to find a new segment. In particular, the step 924 recalls the value of the PRIOR$ECG$BYTE that was initially stored by step 908 at the commencement of detection of the segment and subtracts that value from the PRIOR$ECG$BYTE stored at the detection of the end of the segment to obtain in absolute terms the amplitude ~rom the beginning to the end point of the ECG sample. After step 92~ has been completed or step 922 has responded "no" to both ~ ~7t7S3~
` -51-inquiries, the SEG~ENT$HUNTER routine 900 returns to process-ing the service procedure step 828.
Upon a subsequent execution of the SEGMENT$HUNTER
routine 900 wherein the HUNTER$MoDE is set equal to "2", step 902 directs the routine to step 928 wherein the end o a nega-tive slope is determined in a manner similar to that described above. Briefly, step 928 determines whether there has been a slope reversal by examining the PRIOR$ECG$BYTE and ECG$BYTE
locations of the rotating buffer and/or whether the segment duration limit has timed out. If either of these conditions is met, the process moves to step 930 wherein the absolute value of the m~gnitude or amplitude of the segment is deter-mined before calliny the SEGMENT$END$HOUSEKEEPING, as will be explained with respect to FIGURE 15. Thus, in the SEGMENT$-HUNTER routine 900, as explained above with respect to FIGURE14, the beginning and end of a segment as well as its amplitude are detected in preparation for executing the SEGMENT$ANALYST
routine lO00 wherein a plurality of such segments will be examined to determine whether the particular combination of segments are so detected makes up a valid R-waveO
Referring now to FIGURE 15, there is shown the SEGMENT$END$HOUSEKEEPING subroutine 930 wherein after the cal-culation of the amplitude of the segment by either step 924 or 930, the various counters and storage locations are initialized.
in preparation to identify and measure the parameters of the next segment. In particular, step 932 compares the measured values of the duration and magnitude of the detected segment with predetermined minimum values, for example, 15 units or counts of the D/A converter 34, and 16.7 ms. corresponding to four counts of the sample clock 24. If these minimum require-ments are exceeded, the process moves to step 934 wherein the value of HUNTER~MODE is transferred to SEGMENT$STATUS to be used, as will be explained, in the execution of the SEGMENT$-ANALYST routine lO00. If the minimum requirements are not met as decided by step 932, a further determination is made whether 7~3~

the maximum interval between segments, e.g., 62.5 ms. has elapsed since the end of the last segment; in particular, step 938 compares the current value o~ the RR$TIMER with the SEGMENT$START$DEADLINE and, if greater, the process moves to step 940 wherein the SEGMENT$STATUS is set to "3" indicating a time out with no valid segment detected. After steps 934 and 940, and if step 938 answers in the negative, the sub-routine moves to step 936 wherein the HU~TER$MODE flag is set equal to "0" to prepare for the recalling of the SEGMENT$HUNTER
routine 900 to detect the next segment and in particular to detect the beginning of the next segment.
As shown in FIGURES l9A and B, a series of segments can represent valid R-waves. In particular, the QRS complex is defined, in accordance with this invention, by three seg-ments having a particular slope, amplitude, duration, andsequence. As shown generally in FIGURE 13, the SEGMENT$HUNTER
routine 900 identifies an individual valid segment by obtain-ing values of its duration, slope, and magnitude, and passes those values to the SEGMENT$ANALYST routine 1000, which stores these values in specific locations, examines the sequence of segments, classifies them as QRS signal or as noise, computes the R-R interval, and resets RR$TIMER. The execution of the SEGMENT$ANALYST routine 1000 will now be explained in more detail with respect to FIGURE 16. Initially, in step 1002, ANALYSIS$MODE is accessed to determine which of the "0", "1", or "2" values that is currently set in that location. In the initializing step 504, as shown in FIGURE 8, ANALYSIS$MODE
is set equal to "0" so that initially the process will branch to step 1006 wherein the first segment will be obtain~d and analyzed, as will now be discussed. Upon obtaining the data corresponding to the first segment, step 1006 examines the SEGMENT$STATUS location to determine whether it is less than "3n. As was described with respect to step 934 of FIGU~E 15, SEGMENT$STATUS is set equal to "1" or "2" corresponding to detection of valid segments with positive or nesative slopes, I ` _53_ ~7~3~
respectively; if the space between seyments has timed out, .~he SEGMENT$STATUS flag was set equal to "3" by steps 916 or 940.
Thus, if the segment was found by the SEGMENT$HUNTER to be valid, step 1006 stores the segment data in the first segment location within the RAM 26. In particular, the first segment data includes its magnitude, the time the segment began as recorded by the RR$TIMER, the amplitude at its peak as stored in the PRIOR$ECG$BYTE location, and the time at the end of the segment as recorded in the RR$TIMER. In addition, step 1008 changes the ANALYSIS$MODE value from "0" to "l" so that upon the subsequent execution of the step 1002, the SEGMENT$ANALYST
routine 1000 moves to step 1012 to evaluate the second segment.
First, step 1012 determines whether SEGMENT$STATUS is equal to "3", i.e., a time period in excess of that maximum period corresponding to 62.5 ms. has timed out since the end of the first segment and, if so, step 1014 calls the TREAT$AS$NOISE
subroutine 1034 whereby, as will ke explained later with regard to FIGURE 17, the various storage locations, timers, and counters are reset to erase data corresponding to the first segment to prepare the SEGMENT$ANALYST to receive and analyze the next segment data as a first segment. When step 1012 detects a SEGMENT$STATUS of "3", it indicates tha-t a single segment, as shown in FIGURE l9C, has been detected but a second segment has not occurred within the acceptable time limit; therefore, no valid R-wave has been detected.
However, if step 1012 indicates that the status of the second segment is either a "l" or a "2", i.e., not a "3", the process moves to step 1016 wherein a determination is made of whether the first and second segments have the same slope;
in particular, step 1016 compares the SEGMENT$STATUS locations of the first and second segments, and if the same, i.e., both segments have the same slope, the process moves to step 101S
wherein the data corresponding to the first and second seyments are merged with each other, thus assuming that a larqe single segment was interrupted by noise or cardiac conduction S3~

abnormality and that only a single segment has been detected.
In particular, the starting point of the first segment portion is retained, whereas the termination point of the second seg-ment portion is used as the terminating point of the combined first segment. The magnitude of the combined first segment is taken as the sum of the previously determined magnitudes of the first and second segment portions. Further, the A~ALYSIS$MODE
flag is left as "1" 50 that upon the reexecution o~ the SEG-ME~T$A~ALYST routine 1000, the second segment will be obtained and analyzed. On the other hand, if step 1016 determines that the slopes of the first and second segments are different, the identifying data of the second segment in terms of starting and stopping points and magnitude are stored in that location of the RAM 26d ~or the second ssgment data; thereafter, the ANALYSIS$-MODE flag is set equal to "2" to prepare the SEGME~T$ANALYST
routine 1000 to receive and analyze data corresponding to the third segment.
Upon the third reexecution of the SEGME~T&ANA~YS~ rou-tine 1000 with A~ALYSIS$MODE set equal to "2", step 1002 trans-fers the routine 1000 to step 1022, so that the data correspond-ing to the third segment can be received and analy~ed. Step 1022 compares the slope of the current segment with the slope of the previous segment. If the slopes of the successive seg-ments are determined to be the same, step 1024 assumes that the second segment was interrupted and the data corresponding to the current segment is merged into that data of the second segment, i.e., the starting point is taken as that of the second seg-ment, the terminating point is taken as that of the ~ubsequent or current segment, and the amplitude is obtained by summing the amplitudes of the prior and current segment portions. Step 1024 does not change ANALYSIS$MODE from its current value of "2", and thereafter the process returns to continue the service routine at step 830. If the slopes differ, step 1026 stores the current data including starting and stopping points and magnitude in the area 26d of the RA~I 26 corresponding to data for the third seg-ment.

~7~75;3~

Thereafter, the ANALYSIS$MODE is set equal to "O" to prepare the SEGMENT$ANALYST routine 1000 to receive and analy7e the next sequence of segments.
Thereafter, step 1028 initiates an evaluation of the stored data of the three segments to determine whether a valid or invalid R-wave has been detected. First, step 1028 determines whether the magnitude o the first segment is larger than that of the third segment by comparing the values of magnitude as stored within the assigned locations to the first and third segments. If the first request is greater, the case shown in FIGURE l9a, the first two segments, i.e., from point 1 to point 2 and from point 3 to point 4, are recognized as forming the outline of the R-wave, whereby the R-R interval is computed, the RR$TIMER is reset, and the QS duration is computed. In this regard, it is understood that the data for identifying all three segments is obtained at a point in time after the detection and analysis of the segments; therefore, the process of analysis is made by determining when the peak of the R-wave occurred, and in case one, as shown in FIGURE 19A, the peak occurs at the end of the first segment and the R-R interval is determined by examining the value of the RR$TIMER at the end of the first segment. In slmilar fashion, the QS duration is taken as the difference between the beginning of the first segment and the end of the second segment. Further, it is now necessary to reset the RR$TIMER to begin the timing of the next R-R
interval. To this end, the RR$TIMER is reset not to zero but to a time corresponding to the interval between the end of the first segment and the end of the third segment. On the other hand, if the first segment is not larger than the third segment corresponding to a second case, as shown in FIGURE l9B, the last two segments, i.e., that second segment beginning at point 3 and ending at point 4 and that third segment beginning at point 5 and ending at point 6, are selected as the outline of the R-wave, the R-R
interval and QS duration are set accordingly, and the ~7~3~ .
RR$TIMER is reset accordingly. In particular, the peak of the R-wave is selected as the end of the second segment to thereby define the R-R interval as the value of the RR$TIMER
at the end of the second segment. Further, the QS duration is thereby defined as the difference between the values of the RR$TIMER taken at the end of the third segment and the begin-ning of the second segment. The RR$TIMER is set to be~in its timing at the beginning of the thira segment; more particularly, the RR$TIMER is reset at the end of the third segment to a time corresponding to the length o~ the third segment to reflect the actual time at the resetting of -the RR$TIMER whereby the subsequent R-R interval may be measured. After each of steps 1030 and 1032, a further check is made by step 1033 ~o determine whether the measured R-wave passes further validity tests; in particular, it is determined that the QS duration is less than 221 ms. and that the determined R-R interval is greater than 242 ms. or 58 counts of the sample clock. It is also contemplated within the teachings of this invention that the average R-R interval, as determined for the corresponding trend sample interval, may be compared with a given limit period to identify the existence of a heart anomaly. If within these limits as determined by step 1033, step 1036 sets the R$FLAG true to indicate detection of the occurrence of a valid R-wave. Thereafter, the ECG LED is turned on for an interval of 83.3 ms. by setting the LED$TIl~ER for a co~re-sponding period. Then the process continues with the block 830 of the service routine. If the parameters of the detected R-wave do not fall within the noted limits step 1032 calls, in step 1034, the TREAT$AS$NOISE subroutine, as will be explained with respect to FIGURE 17.
If the three segments do not occur within a given interval of each other as determined by step 1012 or the QS
duration and the R-R interval are not within the predetermined limits as determined by step 1032, the TREAT$AS$NOISE routine 1034 is called, as will be explained with regard to FIG~RE 17.

35~
First, in step 1038, the RR$TIMER is reset to "0" and the ANALYSIS$MODE is set to "0" to prepare the SEGMENT$ANALYST
routine 1000 to receive and analyze data corresponding to I the first segment of a new complex. Thereafter, step 1040 determines whether R$WAVE$TYPE is greater than "2", and if yes, the routine resets the R$WAVE$TYPE to "4" insuring initialization during the STORE$RR$INTERVAL$DATA subroutine 700, as generally shown in FIGURE 8 and in more detail in FIGURE 10. If the R-wave is less than or equal to "2", indicative of complete initialization, the R$WAVE$TYPE is set equal to "0" to insure that the next R-R interval is ignored because it is noise contaminated. After either of steps 1048 or 1042, step 1044 determines whether the system is in its monitor mode by checking the XCMODE and, if yes, the LED 88 is flashed for a period of 41.6 ms. to provide an indication to the operator that noise is being detected; in this regard, this len~th or duration for flashing the LED 88 is about half the period as would be displayed for energizing the LED 88 in response to detection of a valid R-wave. If the system is not in the monitor mode as determined by step 1044, the system is immediately returned to continue ~he execution of the SEGMENT$ANALYST routine without flashing the LED 88.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus for comparing electrical signals indicative of a patient's heart activity, with a set of criteria of regular heart activity comprising a defined relationship between one and a subsequent R-R interval, and for storing the electrical signals indicative of regular heart activity, said apparatus comprising:
a) memory means including first, second and third pluralities of storage locations;
b) a real time sampling clock and a computer clock;
c) means coupled to receive a patient's heart activity and res-ponsive to said sampling clock for sampling at periodic intervals in real time the patient's heart activity signal, and for storing the sampled signals in respective locations of said first plurality, and d) data processing means comprising means responsive to the output of the said computer clock and for providing and storing a series of R-R interval signals in corresponding storage locations of said second plurality, each indicative of the time interval between the successive peaks of the patient's heart activity, and means for examining selected of said series of R-R interval signals as stored in said second plurality of storage locations with each other in accordance with said defined relation-ship to provide a manifestation indicative that the patient's heart signals are regular or irregular, and means responsive to said manifestation for storing regular heart signals in corresponding storage locations of said third plurality.

2. Apparatus for evaluating electrical signals indicative of a patient's heart activity, with a set of criteria of regular heart activity comprising a defined relationship between one and a subsequent R-R interval, said apparatus comprising:
a) a real time sampling clock;

b) a computer time clock;
c) means coupled to receive a patient's heart activity signal and responsive to the output of said sampling clock for sampling at periodic intervals the patient's heart activity signal, and d) data processing means comprising means responsive to said output of said sampling clock and to said sampled heart activity signals to provide a series of R-R interval signals, each indicative of the time interval between successive peaks of the patient's heart activity, and means responsive to the output of said computer clock for examining selected of said series of R-R interval signals with each other in accordance with said defined relationship to provide a manifestation indicative that the patient's heart signals are regular.

3. Apparatus for monitoring over a prolonged monitoring period and evaluating electrical signals indicative of a patient's heart activity with a set of criteria indicative of the waveform of a QRS complex, said apparatus comprising:
a) a real time sampling clock;
b) a computer time clock;
c) sampling means responsive to the output of said sampling clock for sampling the patient's heart activity signal to provide a sequence of sampled heart signals of a single QRS complex; and d) data processing means comprising means responsive to said out-put of said sampling clock for comparing one sampled heart signal with a subsequent sampled heart signal of the same QRS complex to determine whether the relationship therebetween meets said criteria of a valid QRS complex waveform, and means responsive to the output of said computer time clock for further processing valid sampled heart signals.

4. Monitoring and evaluating apparatus as claimed in claim 3, wherein there is included memory means comprising a first plurality of storage locations for receiving and storing respectively said sequence of sampled heart signals, and a second plurality of storage locations, said comparing means comprises means for identifying a sequence of the valid, sampled heart signals as a segment of a plurality of segments comprising a single QRS complex, and for storing data indicative of an identified segment in a corresponding location of said second plurality.

5. Apparatus for monitoring and comparing electrical signals in-dicative of a patient's heart activity, with a set of criteria of regular heart activity comprising a defined relationship between one and a subse-quent R-R interval, said apparatus comprising:
a) means responsive to a patient's heart activity for providing a series of R-R interval signals, each indicative of the time interval between the successive peaks of the patient's heart activity; and b) evaluating means for examining selected of said series of R-R interval signals with each other in accordance with said defined relationship to provide a first manifestation indicative that the patient's heart signals are regular or irregular, said evaluating means comprises means for comparing the current R-R interval signal with respect to a maximum value thereof and if exceeded, to provide a second manifestation that the patient's heart signals are irregular.

6. Monitoring and comparing apparatus as claimed in claim 5, wherein said evaluating means comprises means for comparing the current R-R inter-val signal with a predetermined minimum value thereof and if less, for providing a third manifestation indicative that the patient's heart signals are irregular.

7. Monitoring and comparing apparatus as claimed in claim 6, wherein there is included means for providing an average value of said series of R-R interval signals, and said evaluating means comprises means for comparing said average value with a predetermined value and if less, for providing a fourth manifestation indicative that the patient's heart signals are irregular.

8. Monitoring and comparing apparatus as claimed in claim 7, wherein said evaluating means comprises means for comparing said average value with a predetermined maximum value and if greater, for providing a fifth manifestation indicative that the patient's heart signals are irregular.

9. Monitoring and comparing apparatus as claimed in claim 8, wherein there is included a first plurality of storage locations and a second plurality of storage locations, means for sampling the patient's heart activity and for storing the samples thereof in corresponding locations of said first plurality, and means responsive to one of said third, fourth or fifth manifestations for effecting the permanent storage of the heart activity sample signals in said storage locations of said first plurality.

10. Monitoring and comparing apparatus as claimed in claim 9, wherein there is included means responsive to a manifestation indicative that the patient's heart signals are regular for storing the heart activity signals in corresponding storage locations of said first plurality in a compressed format that facilitates readout and display.

11. Monitoring and comparing apparatus as claimed in claim 9, and as adapted to monitor the patient's heart activity for a prolonged period comprising a plurality of consecutive trend sample intervals wherein each location of said second plurality stores heart activity signals corresponding to one of a plurality of consecutive trend sample intervals, and there is further included address means for disposing the heart activity signals into a current storage location of said second plurality.

12. Monitoring and comparing apparatus as claimed in claim 9, wherein each location of said second plurality corresponds to a range of a parti-cular characteristic of the heart activity signals and there is urther included address means for addressing a particular location of said second plurality in accordance with the particular detected range of the heart activity signal.

13. Monitoring and comparing apparatus as claimed in claim 12> wherein said characteristic is said time interval between successive peaks of the patient's heart activity.

14. Monitoring and comparing apparatus as claimed in claim 13, wherein said characteristic includes the difference between successive R-R interval signals.

15. Monitoring and comparing apparatus as claimed in claim 14, where-in said addressed, current storage location of said second plurality receives the currently determined R-R interval signal, while the earliest determined R-R interval signal is being cleared.

16. Apparatus for monitoring and comparing electrical signals in-dicative of a patient's heart activity, with a set of criteria of regular heart activity comprising a defined relationship between one and a subse-quent R-R interval, said apparatus comprising:
a) means responsive to a patient's heart activity for providing a series of R-R interval signals, each indicative of the time interval between the successive peaks of the patient's heart activity; and b) evaluating means for examining selected of said series of R-R
interval signals with each other in accordance with said defined relation-ship to provide a manifestation indicative that the patient's heart signals are regular or irregular, said evaluating means comprises means for deter-mining whether the value of a first occurring interval is less than that of a subsequent interval by a predetermined amount and, if so, to provide the manifestation indicating the existence of a premature heartbeat.

17. Monitoring and comparing apparatus as claimed in claim 16, where-in there is included means for adding the values of first and second occurring intervals to provide a summed interval manifestation, and said evaluating means comprises means for comparing said summed interval mani-festation with a value of a third interval occurring after the second inter-val and if greater than a predetermined portion thereof, for providing a second manifestation indicating the existence of a premature beat with compensatory pause.

18. Monitoring and comparing apparatus as claimed in claim 17, where-in said comparing means compares said summed interval manifestation with the value of a third later occurring interval, and if less than a predeter-mined factor times the value of the third interval and said summed interval manifestation is less than a predetermined factor times the value of a fourth occurring interval for providing a third manifestation of an inter-digitated premature beat.

19. Apparatus for monitoring and comparing electrical signals indica-tive of a patient's heart activity, with a set of criteria of regular heart activity comprising a defined relationship between one and a subsequent R-R interval, said apparatus comprising:
a) means responsive to a patient's heart activity for providing a series of R-R interval signals, each indicative of the time interval be-tween the successive peaks of the patient's heart activity; and b) evaluating means for examining selected of said series of R-R interval signals with each other in accordance with said defined relationship to provide a manifestation indicative that the patient's heart signals are regular or irregular, said evaluating means comprises means for comparing the values of successive R-R interval signals to provide the manifestation indicative of a premature beat.

20. Apparatus for monitoring and comparing electrical signals indica-tive of a patient's heart activity, with criteria indicative of regular heart activity comprising a defined relationship between one and a subse-quent R-R interval, said apparatus comprising:
a) means for measuring in real time a patient's heart activity and for providing a sequence of discrete R-R interval signals, each signal indicative of the time interval between successive peaks of the patient's heart activity;
b) means coupled to said monitoring means for receiving the R-R
interval signals and for storing a continuously updated set of the R-R
interval signals; and c) evaluating means for examining selected of said updated set of R-R intervals with each other in accordance with said defined relation-ship to provide a manifestation indicative that the patient's heart activity is regular or irregular.

21. Monitoring and comparing apparatus as claimed in claim 20, where-in said evaluating means examines one R-R interval signal with another R-R
interval signal displaced in time from said one R-R interval signal, as stored in said storing means.

22. Comparing and storing apparatus as claimed in claim 1, wherein said storing means stores the processed R-R interval signals in said storage locations of said second plurality in a manner to be readily read out.

23. Comparing and storing apparatus as claimed in claim 22, wherein there is included display means, and said data processing means includes means for reading data from the locations of said second plurality in a manner to be readily displayed upon said display means.

24. Monitoring and evaluating apparatus as claimed in claim 4, where-in said data processing means comprises means for evaluating the segment identifying data stored in the locations o-f said second plurality to deter-mine whether a detected and processed combination of the segments forms a valid QRS complex of the patient, and if so, for providing a second manifestation thereof.

25. Monitoring and evaluating apparatus as claimed in claim 24, wherein said data processing means includes means for accessing the segment identifying data as stored in the locations of said second plurality and for determining the intervals between the valid heartbeats.

26. Monitoring and evaluating apparatus as claimed in claim 25, where-in said memory means comprises a third plurality of storage locations, each location of said third plurality for receiving and storing data indicative of the interval between successive heartbeats, and said data processing means comprises means responsive to the output of said computer clock for examining adjacent locations of said third plurality to determine whether a valid QRS complex occurs at a regular rhythm and, if not, to provide a third manifestation of a heart anomaly.

27. Monitoring and evaluating apparatus as claimed in claim 26, where-in said examining means determines whether the valid heartbeat signal occurs prematurely to provide the third manifestation indicative of a premature heartbeat.

28. Monitoring and evaluating apparatus as claimed in claim 26, where-in said examining means determines whether the valid heartbeat signal occurs outside of an expected interval to provide the third manifestation indica-tive of a delayed or skipped heartbeat.

29. Monitoring and evaluating apparatus as claimed in claim 26, where-in said examining means compares the determined interval with respect to a maximum value thereof and, if exceeded, to provide a fourth manifestation of a heart anomaly.

30. Monitoring and evaluating apparatus as claimed in claim 16, wherein said examining means compares the interval with a predetermined minimum value thereof and if less, provides a fifth manifestation of a heart anomaly.

31. Monitoring and evaluating apparatus as claimed in claim 30, wherein there is further included sensor means responsive to a body func-tion of the patient for providing a sixth manifestation thereof.

32. Monitoring and evaluating apparatus as claimed in claim 31, where-in said data processing apparatus comprises means responsive to each of said third, fourth, fifth, or sixth manifestations for effecting the per-manent storage of the heart activity sample signals in the storage locations of said first plurality.

33. Monitoring and evaluating apparatus as claimed in claim 26, where-in said memory means comprises a fourth plurality of storage locations, each location of said fourth plurality for receiving data indicative of the patient's heart activity and said data processing means comprises means responsive to the output of said computer clock for storing the heart acti-vity data in a compressed format that facilitates readout and display.

34. Monitoring and evaluating apparatus as claimed in claim 33, where-in said monitoring period comprises a plurality of consecutive trend sample intervals, each location of said fourth plurality stores heart activity data corresponding to one of a plurality of consecutive trend sample inter-vals, and said data processing means comprises address means for selecting and storing the heart activity data into the current location of said fourth plurality.

35. Monitoring and evaluating apparatus as claimed in claim 33, where-in each location of said fourth plurality corresponds to a range of a particular characteristic of the heart activity data, and said data pro-cessing means comprises means for addressing a particular location of said fourth plurality in accordance with the particular detected range of the heart activity data.

36. Monitoring and evaluating apparatus as claimed in claim 35, wherein said characteristic includes an indication of the patient's heart-beat rate.

37. Monitoring and evaluating apparatus as claimed in claim 35, where-in said characteristic includes the difference between the intervals associated with successive heartbeats.

38. Monitoring and evaluating apparatus as claimed in claim 33, where-in the addressed, current location of said fourth plurality receives the currently determined interval between successive heartbeats as it is being calculated while the earliest determined interval signal is being cleared.

39. Comparing and storing apparatus as claimed in claim 1, wherein the earliest sampled signal is being cleared from its location of said first plurality as the most recently sampled signal is being stored in the current, addressed location of said first plurality, and said data processing means comprises means responsive to an irregular manifestation for permanently storing a series of the sampled heart activity signals in the locations of said first plurality.