Cardiac monitoring system with normally conducted QRS complex identification
In one example, a cardiac monitoring system, comprises a processor to receive a segment of an electrocardiogram (ECG) signal of a patient, and a memory to store the segment of the ECG. The processor is configured to identify QRS complexes in the segment of the ECG signal, compare the QRS complexes in the segment to the other QRS complexes in the segment to identify a main template QRS complex, identify the QRS complexes in the segment that are similar to the main template, determine RR intervals between consecutive similar QRS complexes to calculate RR variability in the RR intervals, and detect atrial fibrillation (AF) in the segment when RR variability is greater than a threshold value. Other examples and related methods are also disclosed herein.
1 . A cardioverter defibrillator system, comprising:
a support structure;
a plurality of electrocardiogram (ECG) electrodes coupled to the support structure and configured to couple to a body of a patient;
a processor to receive multiple segments of multiple ECG signals of the patient, wherein the multiple ECG signals are received from multiple ECG channels from the plurality of ECG electrodes;
a memory to store the segments of the ECG signals,
wherein the processor is configured to:
detect QRS complexes in the multiple segments of the multiple ECG signals;
compare the detected QRS complexes in the multiple segments with one or more templates to identify a main template;
compute a correlation value between each of the detected QRS complexes and the main template;
identify one or more QRS complexes, among the detected QRS complexes, having a correlation value exceeding a correlation threshold value as supraventricular (SV) complexes:
determine RR intervals between consecutive SV complexes to calculate RR variability in the RR interval; and
detect atrial fibrillation (AF) in the segments when the RR variability is greater than a threshold value;
a plurality of defibrillation electrodes configured to couple to the body of the patient; and
a high voltage subsystem to:
apply a defibrillation voltage across the plurality of defibrillation electrodes to provide therapeutic shocks to the patient when a shockable rhythm is detected, and
inhibit provision of the therapeutic shocks to the patient in response to a determination that the AF is detected as non-shockable.
2 . The cardioverter defibrillator system of claim 1 , wherein the main template is a template similar to a highest number of other QRS complexes in the one or more templates.
3 . The cardioverter defibrillator system of claim 1 , wherein the processor is configured to identify the main template by:
for an initial QRS complex of the multiple segments,
comparing the initial QRS complex with the one or more templates, the one or more templates including existing templates and/or templates generated from other QRS complexes;
incrementing a template count by one when the initial QRS complex is sufficiently correlated with any of the one or more templates;
adding another template when the initial QRS complex is not correlated with the any of the one or more templates; and
selecting a template having the highest template count as the main template.
4 . The cardioverter defibrillator system of claim 1 , wherein the correlation value comprises a sample correlation coefficient value between the detected QRS complex and the main template, and the correlation threshold value is 0.9.
5 . The cardioverter defibrillator system of claim 1 , wherein the processor is configured to calculate the RR variability as an average absolute difference of RR intervals between the consecutive SV complexes.
6 . The cardioverter defibrillator system of claim 5 , wherein the processor is configured to detect the AF when the average absolute difference of RR intervals is greater than the threshold value.
7 . The cardioverter defibrillator system of claim 1 , wherein:
the support structure is configured to be worn by the patient.
8 . The cardioverter defibrillator system of claim 1 , wherein:
the support structure is part of an automated external defibrillator.
9 . The cardioverter defibrillator system of claim 1 , wherein the processor is configured to identify the main template by comparing each QRS complex with fiducial points.
10 . A wearable cardiac monitor (WCM), comprising:
a support structure configured to be worn by a patient;
a plurality of electrocardiogram (ECG) electrodes coupled to the support structure and configured to couple to a body of the patient;
a processor to receive multiple segments of multiple ECG signals of the patient, wherein the multiple ECG signals are received from multiple ECG channels from the plurality of ECG electrodes;
a memory to store the segments of the ECG signals,
wherein the processor is configured to:
detect QRS complexes in the multiple segments of the multiple ECG signals;
compare the detected QRS complexes in the multiple segments with one or more templates to identify a main template;
compute a correlation value between each of the detected QRS complexes and the main template;
identify one or more QRS complexes, among the detected QRS complexes, having a correlation value exceeding a correlation threshold value as supraventricular (SV) complexes;
determine RR intervals between consecutive SV complexes to calculate RR variability in the RR intervals;
detect an arrhythmia in the segments when the RR variability is greater than a threshold value; and
distinguish between atrial fibrillation (AF) or supraventricular tachycardia (SVT) and ventricular tachycardia (VT) or ventricular fibrillation (VF) for the detected arrhythmia, wherein the detected arrythmia is determined to be shockable when VT or VF is detected in the segments;
a plurality of defibrillation electrodes configured to couple to the body of the patient; and
a high voltage subsystem to:
apply a defibrillation voltage across the plurality of defibrillation electrodes to provide therapeutic shocks to the patient when the detected arrythmia is determined to be shockable, and
inhibit provision of the therapeutic shocks to the patient in response to a determination that the AF is detected as a non-shockable arrhythmia.
11 . The WCM of claim 10 , wherein the processor is further configured to:
determine heart rate (HR) variability of the patient based on the RR variability.
12 . The WCM of claim 10 , wherein the main template is a template similar to a highest number of other QRS complexes in the one or more templates.
13 . The WCM of claim 10 , wherein the correlation value comprises a sample correlation coefficient value between the detected QRS complex and the main template, and the correlation threshold is 0.9.
14 . The WCM of claim 10 , wherein the processor is configured to calculate the RR variability as an average absolute difference of RR intervals between the consecutive SV complexes.
15 . The WCM of claim 14 , wherein the processor is configured to classify the arrythmia as AF or SVT when the average absolute difference of RR intervals is greater than the threshold value.
16 . The WCM of claim 10 , wherein:
the detected arrythmia is determined to be non-shockable when SVT is detected in the segments.
17 . The WCM of claim 10 , wherein the processor is configured to identify the main template by comparing each QRS complex with fiducial points.