GB2156124A

GB2156124A - Cardiac monitors

Info

Publication number: GB2156124A
Application number: GB08407155A
Authority: GB
Inventors: Maria Spencer
Original assignee: Cardiac Recorders Ltd
Current assignee: Cardiac Recorders Ltd
Priority date: 1984-03-20
Filing date: 1984-03-20
Publication date: 1985-10-02
Also published as: GB2156124B; JPS61501493A; DK531485A; DK531485D0; GB8407155D0; WO1985004087A1; EP0175734A1

Abstract

A cardiac monitor includes a heartbeat rate meter (4), an alarm such as a loudspeaker (11), and a comparator (8) which operates the alarm when the heart rate is abnormal, in particular on cardiac arrest. To enable the staff to know how long the cardiac arrest has lasted, the alarm comparator also triggers a timer (10). The timer can be reset manually, or automatically after normal heart rhythm has been re-established. A delay device (12) is provided so that the timer can be reset only after a delay following resuscitation of the patient. Consequently, if the patient relapses soon after resuscitation the timer will measure the total time spent in cardiac arrest.

Description

SPECIFICATION Cardiac monitors This invention relates to cardiac monitors, in particular for long-term monitoring of patients, for example in intensive care or coronary care units. operating theatres, and pace maker clinics.

In conventional cardiac monitors, an alarm is generated if the patient goes into rate alarm, usually an audible alarm. For example, the bleep commonly produced by a monitor in step with the heart beats is replaced by a continuous tone when the monitor detects cardiac arrest.

A serious disadvantage of known monitors is that the attending staff have no way of knowing how long the patient has been in a state of rate alarm, and therefore do not know how much time they have left to resuscitate the patient before brain damage occurs.

According to the present invention, a cardiac monitor is fitted with timing means arranged to provide an indication of the time that has elapsed from the beginning of a rate alarm.

The time indication can for example be presented on a CRT screen of the monitor, instead of or in addition to the conventional display of heart beat and numerical pulse rate, or alternatively a separate time display can be provided.

The timing means is preferably arranged so that it can be reset to zero either manually, or automatically when the patient is in normal heart rhythm, for example after a certain length of time in normal rhythm or after a certain number of beats in normal rhythm.

Preferably, the timing means is so arranged that if the patient is resuscitated but relapses into rate alarm soon after resuscitation, the timing means will measure and display the total time spent in the successive episodes of rate alarm. Accordingly, re-setting of the timing means may be rendered ineffective for a predetermined delay after normal heart rhythm has been restored.

Cardiac monitors commonly include a rate meter for determining the heart beat rate, controls for setting beat rates at which alarms are given, and a comparator which triggers the alarm when the measured rate reaches a predetermined value. Conveniently, this comparator also triggers the operation of the timing means, both to initiate timing and for automatic resetting when normal heart rhythm has been restored.

By way of example only, the accompanying drawing is a block diagram of a cardiac monitor incorporating timing means, according to the present invention.

The monitor has an ECG amplifier 2 connected to suitable ECG electrodes 1 and providing an output to a QRS detector 3 which detects successive beats of the patient's heart.

The ORS detector provides outputs to a heart rate meter 4, and also to display control circuitry 5.

The rate meter 4 provides an output voltage proportional to the mean heart rate, which is also supplied to the display control circuitry.

The monitor also includes control logic 6, providing timing signals and other controlling signals for the display control circuitry, such that the latter controls the display on a built-in CRT display unit 7.

The display may for example comprise upper and lower traces showing the heart beat wave form as a cascaded rolling display. The lower trace can be frozen or the upper trace can be transferred to the lower trace and held frozen, to permit close examination of an event appearing on either trace. A three-digit display of the heart rate determined by the rate meter appears above the upper trace, together with symbols indicating that a QRS has been detected, or a lead or electrode fault, or the presence of heart pacemaker pulses.

The monitor may also include means for sychronous defibrillation in conjunction with a defibrillator.

The features described above are known, for example in the "Cardiorater CR7" monitor made by Cardiac Recorders Ltd.

The monitor also includes a loudspeaker or other sound source 11, connected to the ORS detector so as to produce a bleep each time a QRS (heartbeat) is detected.

To provide an alarm, the rate meter 4 is connected to an alarm comparator 8 in which the signal representing the heart rate is compared with upper and lower alarm levels manually set by controls indicated generally by the reference numeral 9, for example slide potentiometer controls provided with scales calibrated in beats per minute on the front panel of the monitor. If the measured heart rate falls outside the range between the upper and lower set levels, the comparator 8 provides an output signal to the sound source 11 so that the latter produces a continuous alarm tone.

The alarm is delayed from the onset of the alarm condition, for example by seven seconds, and if the alarm state ceases within this delay no alarm is given. The alarm ceases when the alarm state ceases. The alarm can be turned off, by moving the "low" alarm control to its lowest position.

The signal from the alarm comparator is also applied to a timer 10 of any convenient type, so that the latter starts timing from the onset of an alarm condition. The timer provides an output signal which is used to generate a display of elapsed time, either on the CRT display unit 7, or on a separate timer display. This provides a direct indication of the length of time for which the patient has been in a state of rate alarm. Since the patient must be resuscitated within about four minutes to avoid brain damage, knowledge of the duration of the rate alarm is extremely important to those attempting resuscitation.

When the state of rate alarm has ended, the timer will stop and its display may remain on the screen for a limited time. The recorded time is held in the timer long enough to ensure that if the patient's heart stops again after a short time, the timer will resume counting from the previously recorded time so that it will display the total time for which the heart has been stopped in two or more successive episodes.

The timer is reset to zero manually or automatically when the heartbeat has been restored to a normal rhythm for a predetermined time or a predetermined number of beats. Thus, the monitor may be provided with a reset button providing a reset input to the timer, this input also being connected to the comparator 8 to reset the timer when the comparator no longer provides an alarm signal. To prevent the timer from being reset too soon, in case the heart stops again, a reset delay 12 may be included in the reset signal path.

The circuitry of the block diagram is not illustrated in detail, since circuit elements capable of performing the required functions will readily suggest themselves to the skilled reader.

As mentioned above, the alarm can be turned off manually. Staff may well forget to turn it on again when the patient has been resuscitated. The monitor may be provided with means for restoring the alarm circuitry to its previous operating condition automatically when the heartbeat has returned to a normal rhythm, either after a predetermined time or after a predetermined number, for example ten to twenty, of R waves.

Claims

1. A cardiac monitor incorporating an alarm arranged to operate on detection of abnormal heart action, and further incorporating timing means arranged to provide an indication of the time elapsed from initial operation of the alarm.

2. A cardiac monitor incorporating an alarm arranged to operate if a patient being monitored suffers cardiac arrest, and timing means arranged to provide an indication of the time that has elapsed from the beginning of cardiac arrest.

3. A cardiac monitor as claimed in claim 2 in which the timing means is so arranged that if the patient is resuscitated but relapses into cardiac arrest soon after resuscitation, the timing means will measure and display the total time spent in the successive episodes of cardiac arrest.

4. A cardiac monitor as claimed in claim 3 including means for resetting the timing means, the resetting means being ineffective for a predetermined delay after restoration of normal heart rhythm.

5. A cardiac monitor as claimed in claim 1, 2 or 3 including means for manually or automatically resetting the timing means to zero.

6. A cardiac monitor as claimed in any preceding claim including a comparator which triggers the alarm when the measured heartbeat rate reaches a predetermined value and also triggers operation of the timing means.

7. A cardiac monitor, substantially as herein described with reference to the accompanying drawings.