Arrhythmia detection in a wearable medical system

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.

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.