Heart rate calculator with reduced overcounting
A heart rate (HR) monitor for use in a medical device configurable to measure a patient's ECG such as, for example, a WCD system. Embodiments can include an ECG sensor and a processor configured with classification criteria to classify a received ECG signal into one of a plurality of ECG rhythm types each with a corresponding algorithm to determine the patient's heart rate. The processor uses the classification criteria to identify the ECG signal's type and determine a heart rate of the patient using the corresponding algorithm. The HR monitor is configurable to avoid overcounting of erroneous measurements of R-R intervals that can result from large T-waves and/or bigeminy by comparing the mean of even R-R intervals with the mean of odd R-R intervals. If the means are significantly different double counting or bigeminy is indicated and the HR calculation is adjusted accordingly.
1. A wearable cardioverter defibrillator (WCD) system, comprising:
a support structure configured to be worn by an ambulatory patient;
an energy storage module configured to store an electrical charge;
a discharge circuit coupled to the energy storage module;
sensors configured to sense an Electrocardiogram (ECG) signal of the ambulatory patient while the ambulatory patient is wearing the support structure; and
a processor configured to:
receive the ECG signal,
perform a segment-based rhythm analysis of the received ECG signal, wherein a segment used by the segment-based rhythm analysis is between substantially 2.5 seconds and substantially 15 seconds of the ECG signal,
detect peaks in the received ECG signal that exceed a peak threshold,
determine a plurality of measured intervals wherein each measured interval is substantially equivalent to a time between successive detected peaks,
determine a mean of odd measured intervals of the received ECG signal,
determine a mean of even measured intervals of the received ECG signal,
determine an ECG rhythm pattern of measured intervals based on determination of whether the mean of the even measured intervals is substantially different from the mean of the odd measured intervals using pattern criteria, wherein determining the ECG rhythm pattern is further configured to:
determine whether the mean of a selected one of the even and odd measured intervals (selected mean) plus a first margin is less than the mean of the other of the even and odd measured intervals (other mean) minus a second margin,
responsive to a determination that the selected mean plus the first margin is less than the other mean minus the second margin, determine whether the selected mean is less than a threshold,
responsive to a determination that the selected mean is less than the threshold, provide an indication that double counting of intervals has been detected,
responsive to a determination that the selected mean plus the first margin is not less than the other mean minus the second margin, determine whether the other mean plus the second margin is less than the selected mean minus the first margin,
responsive to a determination that the other mean plus the second margin is less than the selected mean minus the first margin, determine whether the other mean is less than another threshold,
responsive to a determination that the other mean is less than the another threshold, provide an indication that double counting of intervals has been detected,
responsive to a determination that the other mean is less than the another threshold, to determine the ambulatory patient's heart rate as equivalent to an inverse of the sum of the selected mean and the other mean, and
responsive to a determination that the other mean is not less than the another threshold, to provide an indication that bigeminy has been detected.
2. The WCD system of claim 1 , wherein the first margin is derived from a standard deviation of the selected mean and the second margin is derived from a standard deviation of the other mean.
3. The WCD system of claim 1 , wherein the processor is further configured, responsive to a determination that the selected mean plus the first margin is not less than the other mean minus the second margin, to determine the ambulatory patient's heart rate as substantially equivalent to an inverse of a mean of the plurality of measured intervals.
4. The WCD system of claim 1 , wherein the threshold is equivalent to a refractory period.
5. The WCD system of claim 1 , wherein the mean of the even measured intervals is substantially different from the mean of the odd measured intervals is based on standard deviations of the even measured intervals and the odd measured intervals.
6. The WCD system of claim 5 , wherein each of the standard deviations of the even measured intervals and the odd measured intervals comprises a scaled standard deviation.
7. The WCD system of claim 1 , wherein the processor is further configured, responsive to a determination that the other mean plus the second margin is not less than the selected mean minus the first margin, to determine the ambulatory patient's heart rate as substantially equivalent to an inverse of a mean of the plurality of measured intervals.
8. The WCD system of claim 1 , wherein the processor is further configured, responsive to bigeminy being detected, to determine the ambulatory patient's heart rate as equivalent to twice an inverse of the sum of the selected mean and the other mean.
9. A heart rate monitor system, comprising:
one or more sensors configured to sense an Electrocardiogram (ECG) signal of a patient; and
a processor configured to:
receive the ECG signal,
perform a segment-based rhythm analysis algorithm, wherein the segment used by the segment-based rhythm analysis is between substantially 2.5 seconds and substantially 15 seconds of the ECG signal,
detect peaks in the received ECG signal that exceed a peak threshold,
determine a plurality of measured intervals wherein each measured interval is substantially equivalent to a time between successive detected peaks,
determine a mean of odd measured intervals of the received ECG signal,
determine a mean of even measured intervals of the received ECG signal,
determine an ECG rhythm pattern of measured intervals based on determination of whether the mean of the even measured intervals is substantially different from the mean of the odd measured intervals using pattern criteria, wherein determining the ECG rhythm pattern is further configured to:
determine whether the mean of a selected one of the even and odd measured intervals (selected mean) plus a first margin is less than the mean of the other of the even and odd measured intervals (other mean) minus a second margin,
responsive to a determination that the selected mean plus the first margin is less than the other mean minus the second margin, determine whether the selected mean is less than a threshold,
responsive to a determination that the selected mean is less than the threshold, provide an indication that double counting of intervals has been detected,
responsive to a determination that the selected mean plus the first margin is not less than the other mean minus the second margin, determine whether the other mean plus the second margin is less than the selected mean minus the first margin,
responsive to a determination that the other mean plus the second margin is less than the selected mean minus the first margin, determine whether the other mean is less than another threshold,
responsive to a determination that the other mean is less than the another threshold, provide an indication that double counting of intervals has been detected,
responsive to a determination that the other mean is less than the another threshold, to determine the ambulatory patient's heart rate as equivalent to an inverse of the sum of the selected mean and the other mean, and
responsive to a determination that the other mean is not less than the another threshold, to provide an indication that bigeminy has been detected.
10. The heart rate monitor system of claim 9 , wherein the first margin is derived from a standard deviation of the selected mean and the second margin is derived from a standard deviation of the other mean.
11. The heart rate monitor system of claim 9 , wherein the processor is further configured, responsive to a determination that the selected mean plus the first margin is not less than the other mean minus the second margin, to determine the ambulatory patient's heart rate as substantially equivalent to an inverse of a mean of the plurality of measured intervals.
12. The heart rate monitor system of claim 9 , wherein the threshold is equivalent to a refractory period.
13. The heart rate monitor system of claim 9 , wherein the mean of the even measured intervals is substantially different from the mean of the odd measured intervals is based on standard deviations of the even measured intervals and the odd measured intervals.
14. The heart rate monitor system of claim 13 , wherein each of the standard deviations of the even and odd interval margins comprises a scaled standard deviation.
15. The heart rate monitor system of claim 9 , wherein the processor is further configured, responsive to a determination that the other mean plus the second margin is not less than the selected mean minus the first margin, to determine the ambulatory patient's heart rate as substantially equivalent to an inverse of a mean of the plurality of measured intervals.
16. The heart rate monitor system of claim 9 , wherein the processor is further configured, responsive to bigeminy being detected, to determine the ambulatory patient's heart rate as equivalent to twice the inverse of the sum of the selected mean and the other mean.