Methods and systems for distinguishing VT from VF
Embodiments of a wearable cardioverter defibrillator (WCD) system include a support structure for wearing by an ambulatory patient and at least one processor. When worn, the support structure maintains electrodes on the patient's body, and using the patient's ECG received via the electrodes, the processor determines widths of the QRS complexes, consistency of the QRS complexes, and/or heart rate and uses these determinations to make no-shock, delay-shock, and shock decisions. Shock decisions can be made for heart rates lower than a VF threshold.
1 . A method for a defibrillator system to selectively deliver a shock to a patient, the defibrillator system including an energy storage module configured to store an electrical charge, a plurality of electrodes, and one or more processors, the method comprising:
receiving at least one electrocardiogram (ECG) signal of the patient via one or more of the plurality of electrodes;
identifying QRS complexes of the received ECG signal;
measuring width values of the QRS complexes and a heart rate from the QRS complexes;
determining a consistency metric of the QRS complexes, wherein determining the consistency metric further comprises:
detecting a goodness point in each of the QRS complexes of the received ECG signal, and
determining an average of the goodness points of the QRS complexes;
responsive, at least in part, to the width values, the heart rate, and the consistency metric, classifying the received ECG signal into one of a plurality of rhythm types, the plurality of rhythm types including at least a non-shockable rhythm type, a ventricular fibrillation (VF) rhythm type, and a ventricular tachycardia (VT) rhythm type; and
discharging, responsive to an ECG signal being classified into the VF rhythm type, at least some of the stored electrical charge through at least one of the plurality of electrodes to deliver the shock to the patient.
2 . The method of claim 1 , wherein classifying the received ECG signal into one of the plurality of rhythm types comprises classifying the received ECG signal into the VF rhythm type in response to the heart rate being greater than a VF heart rate threshold and/or the heart rate being above a VT heart rate threshold and the consistency metric meeting a disorganized criterion.
3 . The method of claim 2 , further comprising classifying the received ECG signal into the VF rhythm type in response to the heart rate being greater than the VF heart rate threshold and an average of the width values being above a width threshold and/or the heart rate being above a VT heart rate threshold and the consistency metric meeting a disorganized criterion and the average of the width values being above the width threshold.
4 . The method of claim 3 , wherein the VF heart rate threshold ranges from 150 beats per minute (BPM) to 250 BPM, the VT heart rate threshold ranges from 130 BPM to 200 BPM, and the width threshold ranges from 80 milliseconds (ms) to 160 ms.
5 . The method of claim 2 , further comprising:
prompting a user or a bystander to initiate manual delivery of the shock to the patient responsive to the heart rate being below the VT heart rate threshold and the width values of the QRS complexes being below and an average of the width values being below a width threshold.
6 . The method of claim 1 , further comprising:
responsive to the ECG signal of the patient classified in the VT rhythm type for an entirety of a predetermined time period, discharging at least some of the stored electrical charge through at least one of the plurality of electrodes to deliver the shock to the patient; and
responsive to the ECG signal of the patient being reclassified into the non-shockable rhythm type during the predetermined time period, not discharging any of the stored electrical charge during the predetermined time period.
7 . The method of claim 6 , further comprising:
responsive to the ECG signal of the patient being reclassified into the VF rhythm type during the predetermined time period, discharging at least some of the stored electrical charge through at least one of the plurality of electrodes to deliver the shock to the patient during the predetermined time period.
8 . The method of claim 1 , further comprising:
determining whether one or more delay shock criteria is met based on the heart rate, the width values, and the consistency metric; and
in response to a determination that one or more delay shock criteria is met, monitoring the ECG signal of the patient for a predetermined time period after the received ECG signal was classified into the VT rhythm type.
9 . The method of claim 8 , wherein determining whether the one or more delay shock criteria is met comprises determining whether an index value, derived from the heart rate and the width values, is greater than a predetermined index threshold or is less than the predetermined index threshold.
10 . The method of claim 9 , wherein determining whether the one or more delay shock criteria is met further comprises determining whether the consistency metric is greater than a predetermined disorganized threshold or the consistency metric is less than the predetermined disorganized threshold.
11 . The method of claim 10 , further comprising:
responsive to the index value being less than the predetermined index threshold, determining that one of the one or more delay shock criteria is met.
12 . The method of claim 10 , further comprising:
responsive to the index value being greater than the predetermined index threshold and the consistency metric being less than the predetermined disorganized threshold, discharging at least some of the stored electrical charge through at least one of the plurality of electrodes to deliver the shock to the patient.
13 . The method of claim 1 , further comprising:
determining the heart rate of the patient from at least one heart rate sensor,
wherein classifying the received ECG signal into one of the plurality of rhythm types is further responsive at least in part to the determined heart rate.
14 . A method for a wearable cardioverter defibrillator (WCD) system to deliver a shock to a patient, the WCD system including a support structure, an energy storage module configured to store an electrical charge, a plurality of electrodes coupled with the support structure, and one or more processors, the method comprising:
receiving at least one electrocardiogram (ECG) signal of the patient wearing the support structure, wherein the at least one ECG signal is received via one or more of the plurality of electrodes;
identifying QRS complexes of the received ECG signal;
measuring width values of the QRS complexes and a heart rate from the QRS complexes;
determining a consistency metric of the QRS complexes, wherein determining the consistency metric further comprises:
detecting a goodness point in each of the QRS complexes of the received ECG signal, and
determining an average of the goodness points of the QRS complexes;
responsive, at least in part, to the width values, the heart rate, and the consistency metric, classifying the received ECG signal into one of a plurality of rhythm types, the plurality of rhythm types including at least a non-shockable rhythm type, a ventricular fibrillation (VF) rhythm type, and a ventricular tachycardia (VT) rhythm type; and
discharging, responsive to an ECG signal being classified into the VF rhythm type, at least some of the stored electrical charge through at least one of the plurality of electrodes to deliver the shock to the patient.
15 . The method of claim 14 , wherein classifying the received ECG signal into one of the plurality of rhythm types comprises classifying the received ECG signal into the VF rhythm type in response to the heart rate being greater than a VF heart rate threshold and/or the heart rate being above a VT heart rate threshold and the consistency metric meeting a disorganized criterion.
16 . The method of claim 15 , further comprising classifying the received ECG signal into the VF rhythm type in response to the heart rate being greater than the VF heart rate threshold and an average of the width values being above a width threshold and/or the heart rate being above a VT heart rate threshold and the consistency metric meeting a disorganized criterion and the average of the width values being above the width threshold.
17 . The method of claim 16 , wherein the VF heart rate threshold ranges from 150 beats per minute (BPM) to 250 BPM, the VT heart rate threshold ranges from 130 BPM to 200 BPM, and the width threshold ranges from 80 milliseconds (ms) to 160 ms.
18 . The method of claim 15 , further comprising:
prompting a user or a bystander to initiate manual delivery of the shock to the patient responsive to the heart rate being below the VT heart rate threshold and the width values of the QRS complexes being below and an average of the width values being below a width threshold.
19 . The method of claim 14 , further comprising:
determining whether one or more delay shock criteria is met based on the heart rate, the width values, and the consistency metric; and
in response to a determination that one or more delay shock criteria is met, monitoring the ECG signal of the patient for a predetermined time period after the received ECG signal was classified into the VT rhythm type.
20 . The method of claim 19 , wherein determining whether the one or more delay shock criteria is met comprises determining whether an index value, derived from the heart rate and the width values, is greater than a predetermined index threshold or is less than the predetermined index threshold.
21 . The method of claim 20 , wherein determining whether the one or more delay shock criteria is met further comprises determining whether the consistency metric is greater than a predetermined disorganized threshold or the consistency metric is less than the predetermined disorganized threshold.
22 . The method of claim 21 , further comprising:
responsive to the index value being less than the predetermined index threshold, determining that one of the one or more delay shock criteria is met.
23 . The method of claim 21 , further comprising:
responsive to the index value being greater than the predetermined index threshold and the consistency metric being less than the predetermined disorganized threshold, discharging at least some of the stored electrical charge through at least one of the plurality of electrodes to deliver the shock to the patient.
24 . The method of claim 14 , further comprising:
responsive to the ECG signal of the patient classified in the VT rhythm type for an entirety of a predetermined time period, discharging at least some of the stored electrical charge through at least one of the plurality of electrodes to deliver the shock to the patient; and
responsive to the ECG signal of the patient being reclassified into the non-shockable rhythm type during the predetermined time period, not discharging any of the stored electrical charge during the predetermined time period.
25 . The method of claim 24 , further comprising:
responsive to the ECG signal of the patient being reclassified into the VF rhythm type during the predetermined time period, discharging at least some of the stored electrical charge through at least one of the plurality of electrodes to deliver the shock to the patient during the predetermined time period.
26 . The method of claim 14 , further comprising:
determining the heart rate of the patient from at least one heart rate sensor,
wherein classifying the received ECG signal into one of the plurality of rhythm types is further responsive at least in part to the determined heart rate.