Arrhythmia detection in a wearable medical system

1 . A wearable medical system, comprising:

a support structure;

a plurality of electrocardiogram (ECG) electrodes to sense an ECG signal of a patient;

an energy output device to store an electrical charge;

an output circuit coupled to the energy output device;

a plurality of therapy electrodes, coupled to the support structure and the output circuit, wherein the plurality of therapy electrodes deliver therapy to the patient; and

a processor, coupled to the plurality of ECG electrodes and the output circuit, comprising:

a QRS detector module, wherein the QRS detector module has a first threshold and a second threshold, and configured to:

detect a sensed event responsive to the ECG signal exceeding at least one of the first threshold or the second threshold;

observe a refractory period after the sensed event is detected;

inhibit identification or detection of a new sensed event during the refractory period;

measure a maximum absolute ECG signal amplitude during the refractory period;

recalculate the first threshold and/or the second threshold based on the maximum absolute ECG signal amplitude during the refractory period;

detect a subsequent ECG signal after the refractory period using the plurality of ECG electrodes in contact with the patient; and

determine whether the subsequent ECG signal exceeds the recalculated first threshold or the recalculated second threshold.

2 . The wearable medical system of claim 1 , wherein the QRS detector module further comprises:

a first QRS detector, wherein the first QRS detector analyzes ECG signals for the first threshold; and

a second QRS detector, wherein the second QRS detector analyzes ECG signals for the second threshold.

3 . The wearable medical system of claim 1 , further comprising a user interface, wherein the user interface comprises audio and/or visual alarms.

4 . The wearable medical system of claim 1 , wherein the first threshold is configured to detect tachyarrhythmia and the second threshold is configured to detect bradyarrhythmia.

5 . The wearable medical system of claim 1 , wherein when the recalculated first or second threshold is exceeded, a heart rate is calculated; wherein the heart rate is used to determine the presence of tachyarrhythmia or bradyarrhythmia; and wherein a defibrillation shock is delivered to the patient by the plurality of therapy electrodes when the presence of tachyarrhythmia is determined, or a pacing pulse is delivered to the patient by the plurality of therapy electrodes when the presence of bradyarrhythmia is determined.

6 . The wearable medical system of claim 1 , further comprising a band pass filter for filtering ECG signals.

7 . A method for identifying a cardiac condition using a wearable medical system having a processor and a memory, the method comprising:

detecting an electrocardiogram (ECG) signal of a patient using a plurality of electrodes in contact with the patient;

determining whether the ECG signal exceeds a first threshold of a QRS detector module;

determining whether the ECG signal exceeds a second threshold of the QRS detector module;

identifying or detecting a sensed event responsive to the ECG signal exceeding at least one of the first threshold or the second threshold;

observing a refractory period after the sensed event is detected;

inhibiting identification or detection of a new sensed event during the refractory period;

measuring a maximum absolute ECG signal amplitude during the refractory period;

recalculating the first threshold and/or the second threshold based on the maximum absolute ECG signal amplitude during the refractory period;

detecting a subsequent ECG signal after the refractory period using the plurality of electrodes in contact with the patient;

determining whether the subsequent ECG signal exceeds the recalculated first threshold or the recalculated second threshold;

calculating, based on determination that the subsequent ECG signal exceeds the recalculated first threshold or the recalculated second threshold of the QRS detector module, a heart rate to determine the presence of tachyarrhythmia or bradyarrhythmia;

delivering a defibrillation shock to the patient when the presence of tachyarrhythmia is determined; and

delivering a pacing pulse to the patient when the presence of bradyarrhythmia is determined.

8 . The method of claim 7 , wherein the first threshold and/or the second threshold are recalculated by multiplying a start drop coefficient by the maximum absolute ECG signal amplitude.

9 . The method of claim 7 , further comprising decreasing at least one of the recalculated first threshold or the recalculated second threshold with time in an exponential manner.

10 . The method of claim 7 , wherein the recalculated first threshold and the recalculated second threshold stop decreasing when the recalculated first threshold and the recalculated second threshold reach a minimum threshold level.

11 . The method of claim 7 , wherein the heart rate is calculated using an inverse of an R-R interval of the ECG signals exceeding the first threshold and the recalculated first threshold or exceeding the second threshold and the recalculated second threshold.

12 . The method of claim 7 , wherein the first threshold is configured to identify tachyarrhythmia and the second threshold is configured to identify bradyarrhythmia.

13 . The method of claim 7 , wherein the QRS detector module comprises:

a first QRS detector, wherein the first QRS detector analyzes ECG signals for the first threshold; and

a second QRS detector, wherein the second QRS detector analyzes ECG signals for the second threshold.

14 . A non-transitory computer-readable medium encoded with QRS detection instructions stored thereon that, when executed by a computing device, cause the computing device to perform operations for identifying a cardiac condition in a patient, the operations comprising:

detecting an electrocardiogram (ECG) signal using one or more ECG electrodes;

activating a QRS detector module to:

analyze the ECG signal, wherein the QRS detector module has a first threshold and a second threshold;

determine whether the ECG signal exceeds the first threshold or the second threshold;

identify or detect a sensed event responsive to the ECG signal exceeding the first threshold or the second threshold;

observe a refractory period after the sensed event is detected;

inhibit identification or detection of a new sensed event during the refractory period;

measure a maximum absolute ECG signal amplitude during the refractory period;

recalculate the first threshold and/or the second threshold based on the maximum absolute ECG signal amplitude during the refractory period;

detecting a subsequent ECG signal after the refractory period using the one or more ECG electrodes;

reactivating the QRS detector module to determine whether the subsequent ECG signal exceeds the recalculated first threshold or the recalculated second threshold;

calculate, based on a determination that the subsequent ECG signal exceeds the recalculated first threshold or the recalculated second threshold, a heart rate to determine the presence of tachyarrhythmia or bradyarrhythmia; and

controlling an output circuit and an energy output device to:

deliver a defibrillation shock to the patient through a plurality of therapy electrodes when the presence of tachyarrhythmia is determined; and

deliver a pacing pulse to the patient through a plurality of therapy electrodes when the presence of bradyarrhythmia is determined.

15 . The non-transitory computer-readable medium of claim 14 , wherein the first threshold and/or the second threshold are recalculated by multiplying a start drop coefficient by the maximum absolute ECG signal amplitude.

16 . The non-transitory computer-readable medium of claim 14 , wherein the operations further include decreasing at least one of the recalculated first threshold or the recalculated second threshold with time in an exponential manner until the recalculated first threshold and/or the recalculated second threshold reach a minimum threshold level.

17 . The non-transitory computer-readable medium of claim 14 , wherein the heart rate is calculated using an inverse of an R-R interval of the ECG signals exceeding the first threshold and the recalculated first threshold or exceeding the second threshold and the recalculated second threshold.

18 . The non-transitory computer-readable medium of claim 14 , wherein the first threshold is configured to further detect tachyarrhythmia and the second threshold is configured to further detect bradyarrhythmia.