Wearable cardioverter defibrillator (WCD) system selecting previously identified preferred channel for attempting to detect pacing artifacts
A wearable cardioverter defibrillator (WCD) system is adapted for use by an ambulatory patient who already has an implanted pacemaker. If implanted, such a pacemaker may occasionally be emitting, without the knowledge of the WCD system, pacing signals that may be adding pacing artifacts to the ECG signal. The WCD system may use multiple electrodes to sense ECG signals along multiple vectors that have channels. In embodiments, the WCD system identifies a preferred one of its available channels according to how easily the pacing artifacts are detected within its ECG signal. When the patient's parameters indicate that an alert criterion is met, the WCD system may attempt to read the ECG signal from the preferred channel first. This way the WCD system may be able to identify faster the pacing artifacts, and therefore analyze the ECG signal faster, with an opportunity to react faster to the alert criterion being met.
1. A wearable cardioverter defibrillator (WCD) system configured for use by a patient with an implanted heart pacing device that is configured to occasionally emit pacing signals, the WCD system comprising:
an energy storage module configured to store an electrical charge;
an electrode;
a support structure configured to be worn by the patient to maintain the electrode on a body of the patient;
a plurality of sensors that pairwise define a plurality of distinct vectors, each vector of the plurality of distinct vectors having a respective channel, wherein each pair of the plurality of sensors is configured to sense a respective electrocardiogram (ECG) signal portion of the patient along the respective channel;
a measurement circuit configured to render sets of ECG values, wherein the sets of ECG values include one set corresponding to each of the respective ECG signal portions;
a pacing signal detection functionality configured to:
detect sets of pacing artifacts comprising one set of pacing artifacts corresponding to each of the respective ECG signal portions, arising from the occasionally emitted pacing signals that are present in each of the respective ECG signal portions; and
render sets of pacing values comprising one set of pacing values corresponding to each of the sets of the pacing artifacts; and
a processor configured to:
compute a heart rate (HR) value from at least one of the sets of the ECG values;
determine, from the HR value, whether an alert criterion is met;
responsive to the alert criterion being met, determine if a preferential channel of the channels has been identified previously;
attempt inputting at least one of:
preferential pacing values from the pacing signal detection functionality corresponding to the preferential channel, in response to a successful identification of the preferential channel; and
generic pacing values from the pacing signal detection functionality corresponding to at least one of the channels, in response to an unsuccessful identification of the preferential channel;
determine, in view of the attempt to input the preferential pacing values or the generic pacing values, whether a shock criterion is met; and
responsive to the shock criterion being met, cause at least some of the stored electrical charge to be discharged via the electrode through the patient to deliver a shock to the patient.
2. The WCD system of claim 1 , wherein:
the pacing signal detection functionality is implemented at least in part by the measurement circuit.
3. The WCD system of claim 1 , wherein:
the pacing signal detection functionality is implemented at least in part by the processor.
4. The WCD system of claim 1 , wherein:
the pacing signal detection functionality is implemented at least in part by a pacing detector module distinct from the processor and from the measurement circuit.
5. The WCD system of claim 1 , wherein:
the pacing signal detection functionality is configured to detect sets of pacing artifacts included in the respective ECG signal portions by:
filtering the ECG signal portions for detecting possible pacing artifacts;
determining whether or not selected ones of the detected possible pacing artifacts meet a validation criterion; and
confirming, responsive to the validation criterion being met, the selected possible pacing artifacts as the pacing artifacts.
6. The WCD system of claim 5 , wherein:
the validation criterion includes that the possible pacing artifacts occur at regular time intervals.
7. The WCD system of claim 1 , wherein the processor is further configured to:
compute a value for a status parameter from the HR value, and the alert criterion is met if the computed value for the status parameter exceeds an alert threshold.
8. The WCD system of claim 7 , wherein the processor is further configured to:
identify a QRS complex in the respective ECG signal portions or in the respective sets of ECG values, and
measure a pulse width of the identified QRS complex, wherein the value for the status parameter is computed from the measured pulse width.
9. The WCD system of claim 1 , further comprising:
a pacer implanted flag configured to have a value of at least true or false, and wherein the processor is further configured to:
responsive to the pacer implanted flag having a true value, attempt inputting of respective pacing values within the sets of pacing values rendered by the pacing signal detection functionality; and
responsive to the pacer implanted flag having a false value, determine whether a default shock criterion is met, and wherein:
responsive to the default shock criterion being met, cause at least some of the stored electrical charge to be discharged via the electrode through the patient to deliver the shock to the patient, and
responsive to the default shock criterion not being met, prevent discharge of any electrical charge to the patient.
10. The WCD system of claim 1 , wherein:
responsive to the alert criterion being met, the preferential channel not being previously identified, and the attempt to input the generic pacing values corresponding to two of the channels being successful, the processor is further configured to:
identify one of the two channels as the preferential channel; and
in response to the identifying, establish the preferential channel.
11. The WCD system of claim 10 , wherein the one of the two channels is identified as the preferential channel when a first set of pacing values corresponding to the one of the two channels meet a preference criterion better than a second set of pacing values corresponding to another one of the two channels.
12. The WCD system of claim 11 , wherein the preference criterion comprises that pacing artifacts in a first set of pacing artifacts corresponding to the one of the two channels occur within a threshold time difference from pacing artifacts in a second set of pacing artifacts corresponding to the another one of the two channels.
13. The WCD system of claim 1 , wherein the processor is further configured to:
responsive to the alert criterion not being met:
attempt inputting two sets of generic pacing values rendered by the pacing signal detection functionality corresponding to two candidate channels of the channels; and
responsive to a successful attempt of inputting the two sets of the generic pacing values:
determine that a set of the generic pacing values that corresponds to a first one of the two candidate channels meets a preference criterion better than a set of the generic pacing values that corresponds to a second one of the two candidate channels;
in response to the determining, identifying the first one of the two candidate channels as the preferential channel of the channels; and
in response to the identifying, establish the preferential channel.
14. The WCD system of claim 13 , wherein the attempt to input the two sets of generic pacing values is performed responsive to the preferential channel not being previously identified.
15. The WCD system of claim 13 , further comprising:
a memory, wherein the processor is further configured to establish the preferential channel by storing, in the memory, an indication of the identified first one of the two candidate channels as the preferential channel.
16. The WCD system of claim 13 , further comprising:
an input multiplexer configured to receive the sets of ECG values, wherein the processor is further configured to establish the preferential channel by adjusting the input multiplexer to advance to a next stage a set of the ECG values corresponding to the preferential channel.
17. The WCD system of claim 13 , wherein the preference criterion comprises that pacing artifacts corresponding to the first one of the two candidate channels occur within a threshold time difference from pacing artifacts corresponding to the second one of the two candidate channels.
18. The WCD system of claim 1 , wherein the processor is further configured to:
responsive to the successful identification of the preferential channel,
determine whether the attempt to input the preferential pacing values is successful.
19. The WCD system of claim 18 , wherein the processor is further configured to:
responsive to a determination that the attempt to input the preferential pacing values is successful, determine whether a first shock criterion is met in view of the preferential pacing values; and
perform at least one of:
responsive to the first shock criterion being met, cause discharge of at least some of the stored electrical charge via the electrode through the patient to deliver a shock to the patient; and
responsive to the first shock criterion not being met, prevent discharge of any electrical charge to the patient.
20. The WCD system of claim 18 , wherein the processor is further configured to:
responsive to a determination that the attempt to input the preferential pacing values is unsuccessful, determine whether a second shock criterion is met; and
perform at least one of:
responsive to the second shock criterion being met, cause discharge of at least some of the stored electrical charge via the electrode through the patient to deliver a shock to the patient; and
responsive to the second shock criterion not being met, prevent discharge of any electrical charge to the patient.
21. The WCD system of claim 1 , wherein the processor is further configured to:
responsive to the unsuccessful identification of the preferential channel,
determine whether the attempt to input the generic pacing values is successful.
22. The WCD system of claim 21 , wherein the processor is further configured to:
responsive to a determination that the attempt to input the generic pacing values is successful, determine whether a third shock criterion is met in view of the generic pacing values; and
perform at least one of:
responsive to the third shock criterion being met, cause discharge of at least some of the stored electrical charge via the electrode through the patient to deliver a shock to the patient; and
responsive to the third shock criterion not being met, prevent discharge of any electrical charge to the patient.
23. The WCD system of claim 21 , wherein the processor is further configured to:
responsive to a determination that the attempt to input the generic pacing values is unsuccessful, determine whether a fourth shock criterion is met; and
perform at least one of:
responsive to the fourth shock criterion being met, cause discharge of at least some of the stored electrical charge via the electrode through the patient to deliver a shock to the patient; and
responsive to the fourth shock criterion not being met, prevent discharge of any electrical charge to the patient.