DE102014207730A1 - A method, apparatus and computer program product for determining an isoelectric point - Google Patents

Abstract

The present invention relates to a method, a device and a computer program product for determining an isoelectric point in an electrocardiogram (1). In this case, a wavelet transformation of the electrocardiogram (1) is performed and two mutually overlapping wavelet coefficients are checked for a simultaneous undershooting of threshold values (SWA, SWB). If a simultaneous undershooting in a data point is determined as isoelectric point.

Description

The present invention relates to a method for determining an isoelectric point, a device for carrying out the method and a computer program product for carrying out the method and / or for driving the device.

An electrocardiogram (ECG) reflects the condition and function of a heart and, as an established technique, is an important tool for medical diagnostics. The electrocardiogram directly relates to the condition and function of the heart, is non-invasive, and provides a quantitative assessment , It is also possible to use long-term ECG monitoring to assess performance during sports and in extreme situations, to detect stress or to monitor vigilance while driving a car. For this purpose, an ECG module is mounted close to the body, for example, integrated into clothing. However, these devices have to be adapted in size and weight and constantly improved in terms of quality and functionality and optimized for low costs and low energy consumption. As the goal is to constantly increase the efficiency, safety and autonomy of the device function, new powerful ECG real-time detection algorithms are needed.

Because of their ability to accurately capture high-frequency signal components at the same time and low-frequency signal components, the wavelet-based time-frequency analysis for biosignals such as electrocardiograms is particularly well suited. Thus, in the frequency-typical scales, QRS complexes of the ECG can be identified efficiently and with high reliability via so-called "modulus maximum pairs" and serve as the basis for further signal analysis steps. For example, the publication also discloses US 2012/123232 A1 a method of reliable R-wave detection.

Biosignal analysis in the image area of the time-frequency transformation supports subsequent steps of the signal processing such as filtering or correlating. The disadvantage of this, however, is working in the unimaginable image area. A detection of further ECG sections - such as P-waves and T-waves - can not be realized with the same degree of safety as the R-wave detection. In addition, a measurement of an amplitude of the observed biosignal (which corresponds to a voltage value) is not possible in the image area. Thus, also the course of the isoelectric line and the direct comparison to the level of the ST route can not be detected. However, these quantities are important for a physiological assessment of the biosignal and must be determined indirectly when using the time-frequency analysis.

The present invention is therefore based on the object of proposing a method and a device for determining an isoelectric point in an electrocardiogram, which avoids the disadvantages mentioned, with which therefore the isoelectric point can be detected in an electrocardiogram with high reliability and fast.

This object is achieved by a method according to claim 1, an apparatus according to claim 8 and a computer program product according to claim 10. Advantageous embodiments and further developments are described in the dependent claims.

A method for determining an isoelectric point or an isoelectric line (i.e., multiple consecutive isoelectric points) in an electrocardiogram comprises several steps. First, the electrocardiogram is recorded and a wavelet transformation of the electrocardiogram is performed. A first wavelet coefficient and a second wavelet coefficient are partially overlapped. In the obtained wavelet transform of the electrocardiogram, the R-wave is determined and a data region lying ahead of the R-wave, which is to be checked for the presence of the isoelectric point, is selected. The selected data area is subsequently examined for falling below a first predetermined threshold value of a first parameter, the first parameter being dependent on the first wavelet coefficient. In addition, the selected data area of the wavelet transform is checked for a falling below a predetermined second threshold value of a second characteristic. The second parameter depends on the second wavelet coefficient. If both the first threshold value and the second threshold value are undershot in a data point of the selected data area, this data point is defined as the isoelectric point.

By investigating the wavelet transform, which is to be understood as a linear transformation while preserving the signal energy at which frequency components of a signal can be analyzed and localized in time and place, the isoelectric point or the isoelectric line can be reliably detected without shape recognition , The use of parameters that depend on the wavelet coefficients obtained anyway in the context of the wavelet transformation, allows a rapid and resource-saving implementation of the method. Finally, the R-wave detection, which can be performed with high security using modern methods, also defines the data area to be examined in a simple manner. An atrial ventricular conduction can thus be performed on the electrocardiogram Found image area and measured for each heartbeat directly in a carried digital signal, ie in the electrocardiogram. This also makes it possible to conclude the presence of a sinus rhythm of the heartbeat in the case of a reliably detected R wave and equally reliably recognized isoelectric point.

It can be provided that the first parameter and / or the second parameter is a sum of two wavelet coefficients. This allows an increase in the detection security.

Typically, at the same time, the checking for falling below the first threshold and the second threshold is performed. Due to the parallel testing, the method can be carried out quickly, especially even if the two threshold values are undershot, the determined data point is determined as an isoelectric point. Preferably, the two wavelet coefficients are already determined during the execution of the wavelet transformation in order to be able to carry out the method very quickly, typically in real time.

The first characteristic may be equal to an absolute value of the first specific wavelet coefficient and the second characteristic equal to the sum of the absolute values of the first wavelet coefficient and the second wavelet coefficient. The formation of absolute amounts facilitates the further processing, whereby the summation of absolute amounts in turn results in an easily verifiable quantity.

Preferably, the first wavelet coefficient is the wavelet coefficient of the scale 3 and the second wavelet coefficient is the wavelet coefficient of the scale 4, since these coefficients cover a frequency range typically of interest in the analysis of the electrocardiogram. Of course, it may also be provided that other wavelet coefficients are used, with their scales typically differing by one.

Alternatively or additionally, the first threshold value can amount to at most one tenth of a total energy of the electrocardiogram and / or the second threshold value to at most one fifth of the total energy of the electrocardiogram. The maximum values mentioned are favorable with regard to a simple and reliable determination of the isoelectric point. The two thresholds can be set both before taking the electrocardiogram and after taking the electrocardiogram.

If the isoelectric point has been detected, a corresponding amplitude of the electrocardiogram for the determined isoelectric point can be determined from the electrocardiogram. Preferably, both this amplitude and the determined isoelectric point are displayed on an output unit to make the information recognizable to a user of the method.

The described method can be repeated with the described steps, typically with an uninterrupted repetition. As a result, an isoelectric point can be determined continuously and the presence of the sinus rhythm can be monitored very easily. In this case, the first threshold value and / or the second threshold value are preferably determined as a function of preceding amplitude values or preceding values of the first wavelet coefficient and of the second wavelet coefficient.

An apparatus for carrying out the method described above according to one of the preceding claims has a receiving unit, a computing unit and an output unit. The acquisition unit is designed to record the electrocardiogram, while the arithmetic unit is used to perform the wavelet transformation and to determine the isoelectric point.

It can also be provided that the first wavelet coefficient and the second wavelet coefficient are stored in a memory of the device, preferably in a ring memory, and the arithmetic unit is adapted to load the coefficients therefrom or in a new determination the two coefficients to overwrite the stored values of the coefficients.

The device is typically a device for performing a long-term ECG or pacemaker.

A computer program product contains a command sequence stored on a machine-readable carrier for carrying out the described method and / or for driving the described device when the computer program product runs on a computing unit.

Embodiments of the invention are illustrated in the drawings and are described below with reference to the 1 to 4 explained.

Show it:

1 an idealized electrocardiogram;

2 a real voltage curve of the electrocardiogram and derived wavelet coefficients;

3 a flowchart of a method for determining an isoelectric point and

4 a schematic representation of a mounted on a body device for performing the in 3 illustrated method.

In 1 is an example of an electrocardiogram 1 , that is, a time series of electrical signals from cardiac muscle fibers. Different voltages are registered over a time axis, with excursions usually being designated by the letters P, Q, R, S and T for easier discrimination. Periodically, such a complex of rashes in the electrocardiogram is repeated 1 ,

QRS complexes, often referred to simply as R-waves or major chamber fluctuations, follow one another, with intervals between two consecutive major chamber fluctuations being RR intervals 2 be designated. If the heart beats with a sinus rhythm, deviates one temporal length of each of the RR interval 2 by no more than 15 percent of a duration of an immediately preceding RR interval 2 from.

Between a P-wave and the QRS complex appears in the electrocardiogram 1 an isoelectric course 4 due to a transmission of arousal, ie atria of the heart are fully excited, while chambers of the heart are still completely unexcited. The isoelectric course 4 is composed of several isoelectric points and is often used as the baseline or zero line of a biosignal such as the electrocardiogram 1 designated.

A length of this isoelectric curve 4 or this isoelectric path and their distance to the following QRS complex as part of a PQ distance 3 vary only slightly, inter alia, depending on a heart rate. Ultimately, both are set by law by a physiological course of a heart activity. The signal sections 4 represent a feature of physiological cardiac excitation, which the physician calls sinus beat or sinus rhythm. This feature is to be automatically detected by the method described in more detail below

This is done directly in the image area of the wavelet transformation without shape recognition by scanning two selected wavelet coefficients in a fixed time range before each detected R wave to a simultaneous undershooting of a threshold. As soon as the two selected wavelet coefficients have fallen below this threshold for the first time, there is a time of the atrial-ventricular conduction.

This allows the location of the baseline of the electrocardiogram 1 read directly on the entrained voltage timing and used as a reference point for later analysis steps such as an ST line measurement.

Such a voltage curve of the electrocardiogram 1 is exemplary of a single heartbeat in 2 shown. Recurring features are provided with identical reference numerals in this as well as in the following figures. The actual voltage curve deviates from that in 1 Ideally illustrated course slightly off. Below the electrocardiogram 1 two wavelet coefficients are shown. In the middle is the wavelet coefficient of the scale 3 and in the lower part of the scale 2 the wavelet coefficient of scale 4 is shown.

These wavelet coefficients are within an automatic analysis of the electrocardiogram 1 very resource-efficient feasible. The detection of the R-wave is in any case necessary and very safe feasible, which in any case often a detection algorithm with a wavelet transformation of the biosignal, so the electrocardiogram 1 , is carried out.

3 shows a flowchart of a method for computational analysis of the electrocardiogram 1 , which is carried out under time-critical conditions, ie in real-time or signal-rich signal processing. The aim of the method is to find the isoelectric point in the electrocardiogram in real-time operation 1 , whereby it can be decided whether the measured current heartbeat is associated with a normal heart activity, ie a sinus rhythm.

After starting the procedure will be in one step 5 a first detection threshold SWA and a second detection threshold SWB set. These threshold values can be set variably, for example as a function of previous amplitude or coefficient values, but can also be statically predetermined. The setting of the threshold values can also take place within the framework of a learning phase and the determination is intended to guarantee a sufficiently smooth signal course in the considered time windows. In further embodiments, the setting of the detection threshold values can also take place at a later time.

In one step 6 there is a signal recording, ie the measurement of the electrocardiogram 1 at a sampling rate of 250 sps (samples per second) in the illustrated embodiment. The electrocardiogram 1 is discretized and the loaded digital values are held ready for wavelet transformation. Subsequently, the measured electrocardiogram 1 in a further step 7 subjected to wavelet transformation. In this case, relevant wavelet coefficients, which were determined in advance, are stored in ring memories, which are constantly updated in correlation to the detected voltage-time profile of the biosignal.

The detection of the R-wave takes place in one step 8th , for example via "modulus maximum pairs" at the scales 2 and 3 of the wavelet transform. The individual identified major fluctuations in the electrocardiogram 1 , which are referred to as R-Triggers, are stored and fed consecutively to further processing. The detection trigger for the R wave lies within the QRS complex, with one step 9 It is checked whether this recognition trigger exists. If so, the procedure goes to step 10 and sets a counter n to a clock of the chronologically oldest determined R-trigger, ie the time of occurrence, ie a clock number in the discrete time signal is set to the counter n.

If no detection trigger is found, the procedure checks in step 16 if there is more data and, if yes, the procedure starts with step 6 again through. If there is no more data, the procedure is ended.

In step 11 a data area or window boundaries is selected which is to be examined for the presence of the isoelectric point. In the illustrated embodiment, this data area is at an initial data point n-10, so 10 clocks before the corresponding R-trigger, and an end data point n-25, ie equal to 25 clocks before the corresponding R-trigger. Depending on an instantaneous heart rate, the search interval can also be made variable in further embodiments. However, the search range may not exceed one end of the T wave of the previous beat.

In this defined range, the wavelet coefficients of the scales 3 and 4 present in a ring memory or determined during the wavelet transformation are to be tested. These wavelet coefficients capture energy components of the electrocardiogram 1 between 9 Hz and 27 Hz or between 4 Hz and 13 Hz. It has the advantageous effect that the corresponding filter lengths of 13 interpolation points or 29 interpolation points (corresponding to 52 ms and 116 ms, respectively) have a smoothing effect and mutually centered (centered) overlap. The electrocardiogram 1 is thus examined in two different resolutions.

The search starts at the starting point 40 ms before the R trigger and progresses to the end point 100 ms ahead of the R trigger. In step 12 From the absolute values of the two wavelet coefficients, a sum is first formed and in step 13 examines whether at one of the data points the absolute value of the wavelet coefficient of the scale 3 is smaller than the first threshold SWA and the sum formed is smaller than the second threshold SWB. If the wavelet coefficient of the scale 3 falls below the power threshold SWA and at the same time the sum of the two coefficients of the scales 3 and 4 is below the threshold SWB, then the isoelectric line is valid 4 or the isoelectric point in step 17 as recognized. The search is then terminated and an amplitude associated with the determined data point, ie the associated voltage value directly from the entrained biosignal, ie the electrocardiogram 1 , in step 18 accepted. Finally, in step 19 the detected clock and the amplitude of the isoelectric point output. Subsequently, in step 16 the presence of further data for checking for the presence of the isoelectric point is checked. The SWA threshold is one-tenth of the total energy and for the SWB threshold one-fifth of the total energy of the electrocardiogram 1 proved favorable.

Are in step 13 If the given conditions are not met, the counter n in step 14 decremented, ie reduced by 1. If the counter is now at the specified endpoint of the search in the interval before the R trigger, the step goes to 16 continued. Otherwise, the edit loop will start with step 12 with reduced counter n - 1 and correspondingly recharged wavelet coefficients again.

Were finally all sections of the electrocardiogram 1 finished, the process ends.

The method can be stored as a computer program on a machine-readable carrier and run on the computer or computer. Likewise, the computer program can control a device, which will be shown in greater detail below, for carrying out the method.

The method can be performed on a computer or microcontroller and serves a stepwise processing of the externally or intracardially derived, digitized electrocardiogram 1 in the image area with the aim of recognizing certain invariant form sections that are associated with the excitation conduction from the atria to the chambers and indicate the time of their occurrence. For this purpose, an uninterrupted pattern search is carried out in a physiologically defined interval before detection of a chamber excitation by testing two overlapping wavelet coefficients to a threshold value undershooting and thus the temporal position and the amplitude an isoelectric section 4 are determined, which is typical for a heartbeat with physiological excitation, ie a sinus beat.

This will be the baseline of the electrocardiogram 1 Determined beat by beat and is available for real time measurement of other ECG components, such as an ST segment. In addition, the determined baseline can be used in a further method step for baseline correction or used, in the rhythm analysis section of the electrocardiogram 1 with sinus rhythm separate from other sections with other rhythm forms.

Alternatively or additionally, isolated ventricular extrasystoles can be diagnostically further evaluated in further procedural steps, for example in order to calculate parameters of a so-called "heart rate turbulence" or sections with undisturbed sinus rhythm can be used for the determination of a so-called "heart rate variability" without falsifying signal manipulation such as filtering, beat set or interpolation.

An unnecessary storage or telemetric transmission or evaluation of undisturbed sinus rhythm can thus be suppressed and a charge-free functional time of an implanted device with Holterfunktion or other wearable devices can be extended.

In other embodiments, an implanted pacemaker may be controlled based on the described method, in particular to avoid unnecessary stimulation stimuli. An effectiveness of an antiarrhythmic therapy, in particular a cardioversion can be controlled by the real-time detection of ECG sections with undisturbed sinus rhythm. This allows a cardiac situation to be determined correctly, beat by beat, thus controlling therapeutic interventions of implanted devices with therapeutic function, particularly with regard to cardiac function or unnecessary defibrillation surges.

In further embodiments, the isoelectric point may also be searched for after the R wave with the method described, for example at another physiologically defined point of a cardiac revolution such as the ST segment or after a recognized end of the T wave.

In 4 is a schematic view of a Holter ECG device 20 shown by a user 21 worn on the body and is supplied by a battery with electrical energy, but can also be implanted in other embodiments. The Holter ECG device 20 enables ECG analysis under time-critical conditions, which saves space, mass and energy with simple hardware. The illustrated Holter ECG device 20 is in a user's clothing 21 integrated and can work autonomously for a long time without external energy supply. The safety of the biosignal analysis determines whether the signal is permanently stored and the frequency and length of necessary radio transmissions to a base station. In the Holter ECG device 20 are a recording unit 22 , a computing unit 23 and an output unit 24 arranged and electrically connected to each other.

The recording unit 22 has several on the user's body 21 attached electrodes and serves to record the electrocardiogram 1 , The recorded data are processed by the arithmetic unit 23 , Evaluated in the present case, a microcontroller by the method described, ie the isoelectric point is determined and on the output unit 24 , In the illustrated embodiment, a display, together with the from the electrocardiogram 1 determined amplitude at the isoelectric point output graphically or in text form. The display can also be set up to record the entire recorded electrocardiogram 1 display. In other exemplary embodiments, a data transmission device can also be used for wireless or wired transmission of the data to the long-term ECG device 20 be provided. This data transmission device may also be a connection for a memory card. The determined wavelet coefficients are stored in a ring memory 25 stored and held and can be loaded from this if necessary.

In further embodiments, the output unit 24 also only have individual diodes instead of the display or in addition to the display.

Only features disclosed in the embodiments of the various embodiments can be combined and claimed individually.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2012/123232 A1 [0003]

Claims (10)

Method for determining an isoelectric point in an electrocardiogram ( 1 ) with the steps: a) recording ( 6 ) of an electrocardiogram ( 1 ); b) performing a wavelet transformation ( 7 ) of the electrocardiogram ( 1 ); c) determining a first wavelet coefficient and a second wavelet coefficient that partially overlap each other; d) determining an R wave (R) in the wavelet transform of the electrocardiogram ( 1 ) and Select ( 11 ) of a data area ahead of the R wave (R); e) Check ( 13 ) of the selected data region of the wavelet transform falls below a predetermined first threshold value (SWA) of a first characteristic which depends on the first wavelet coefficient; f) Check ( 13 ) of the selected data region of the wavelet transform to a falling below a predetermined second threshold value (SWB) of a second characteristic, which depends on the second wavelet coefficient; g) where, when the two threshold values (SWA, SWB) are undershot, the determined data point is defined as an isoelectric point in a data point of the selected data area ( 17 ). A method according to claim 1, characterized in that the first characteristic and / or the second characteristic is a sum of two wavelet coefficients. A method according to claim 1 or claim 2, characterized in that the first characteristic is equal to an absolute value of the first specific wavelet coefficient and the second characteristic is equal to the sum of absolute values of the first wavelet coefficient and the second wavelet coefficient. Method according to one of the preceding claims, characterized in that the first wavelet coefficient is the wavelet coefficient of the scale 3 and the second wavelet coefficient is the wavelet coefficient of the scale 4. Method according to one of the preceding claims, characterized in that the first threshold (SWA) at most one tenth of a total energy of the electrocardiogram and / or the second threshold (SWB) at most one fifth of the total energy of the electrocardiogram ( 1 ) is. Method according to one of the preceding claims, characterized in that a corresponding amplitude for the determined isoelectric point from the electrocardiogram ( 1 ) and preferably the amplitude and the isoelectric point on an output unit ( 24 ) are displayed. Method according to one of the preceding claims, characterized in that the method with steps a) to g) is carried out repeatedly and preferably the first threshold value (SWA) and the second threshold value (SWB) in dependence on preceding amplitude values or preceding values of the wavelet Coefficients are determined. Contraption ( 20 ) for performing the method according to any one of claims 1-7 with a receiving unit ( 22 ) for recording the electrocardiogram ( 1 ), a computing unit ( 23 ) for performing the wavelet transformation and determining the isoelectric point and an output unit ( 24 ) for outputting the data point of the isoelectric point. Contraption ( 20 ) according to claim 8, characterized in that the arithmetic unit ( 23 ), the determined first wavelet coefficient and the second wavelet coefficient in a ring memory ( 25 ) or from the ring buffer ( 25 ) to load. Computer program product comprising a sequence of instructions stored on a machine-readable carrier for carrying out the method according to any one of claims 1-7 and / or for driving the device ( 20 ) according to claim 8 or claim 9, when the computer program product runs on a computing unit.

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