Method to detect noise in a wearable cardioverter defibrillator
In one embodiment, a method to detect noise levels in electrocardiogram (ECG) signals is described. The method includes connecting to at least three sensing electrodes and obtaining a signal from each of the at least three sensing electrodes. The method also includes defining at least three channels between the at least three electrodes. The method includes calculating a morphological similarity value of at least one combination of the at least three channels based at least in part on the obtained signal from each of the at least three sensing electrodes and determining a noise level based at least in part on the calculated morphological similarity value.
1 . A wearable cardioverter defibrillator (WCD) system, comprising:
a support structure wearable by a patient;
a processor; and
a discharge circuit configured to discharge stored electrical charge through a body of the patient, the discharge circuit in communication with the processor, wherein the processor is configured to:
receive signals from at least three sensing electrodes that include a first sensing electrode located at a first location on the patient, a second sensing electrode located on a second location of the patient, and a third sensing electrode located on a third location of the patient, the at least three sensing electrodes configured to monitor electrical activity of a heart of the patient;
obtain, during the monitoring, a first signal from the first sensing electrode, wherein the first signal is based on a cardiac rhythm measured by the first sensing electrode at the first location during a first time period;
obtain, during the monitoring, a second signal from the second sensing electrode, wherein the second signal is based on the cardiac rhythm measured by the second sensing electrode at the second location during the first time period;
obtain, during the monitoring, a third signal from the third sensing electrode, wherein the third signal is based on the cardiac rhythm measured by the third sensing electrode at the third location during the first time period;
define, during the monitoring, at least three channels between the at least three sensing electrodes;
calculate, during the monitoring, a morphological similarity value of at least one combination of the at least three channels by comparing the first signal with at least one of the second signal or the third signal; and
determine, during the monitoring, a noise level based, at least in part, on the morphological similarity value calculated for the at least one combination of the at least three channels, wherein the noise level is used, at least in part, in determining that the patient has experienced an event of arrhythmia.
2 . The WCD system of claim 1 , wherein the processor is further configured to:
establish correlating channels based, at least in part, on the at least three channels, wherein the correlating channels have a similar morphological similarity value when no noise is present in electrocardiogram (ECG) signals; and
calculate a morphological similarity value of each of the correlating channels.
3 . The WCD system of claim 2 , wherein the processor is further configured to:
determine when the morphological similarity value of each of the correlating channels meets or exceeds a predetermined threshold.
4 . The WCD system of claim 3 , wherein the predetermined threshold is equal to or above 0.2.
5 . The WCD system of claim 3 , wherein the processor is further configured to:
analyze at least one of the first signal, the second signal, or the third signal for a shockable heart rhythm when the morphological similarity value is above the predetermined threshold.
6 . The WCD system of claim 1 , wherein the processor is further configured to:
suspend an electrocardiogram (ECG) shockable analysis of the first signal, the second signal, and the third signal when feature coefficient correlation (FCC) values are below a predetermined analysis threshold.
7 . The WCD system of claim 6 , where the processor is further configured to:
obtain an additional signal from each of the at least three sensing electrodes after the first time period has elapsed; and
calculate a second morphological similarity value of at least one combination of the at least three channels based, at least in part, on the additional signal obtained from each of the at least three sensing electrodes.
8 . The WCD system of claim 7 , wherein the processor is further configured to:
issue a noise alert to a person when the second morphological similarity value does not meet or exceed a predetermined threshold.
9 . The WCD system of claim 1 , wherein calculating the morphological similarity values includes calculating feature correlation coefficient (FCC) values.
10 . The WCD system of claim 1 , wherein the first time period is a fixed duration of between 3 and 15 seconds.
11 . The WCD system of claim 10 , wherein the fixed duration is 5 seconds.
12 . The WCD system of claim 1 , wherein the processor is further configured to assign individual predetermined noise thresholds for each pair of the at least three channels, based on a correlation level associated with positions of the at least three sensing electrodes.
13 . The WCD system of claim 1 , wherein the processor is further configured to suspend the calculation for a predetermined time period when the morphological similarity value falls below a noise threshold, and wherein the predetermined time period is between 5 seconds and 5 minutes.
14 . The WCD system of claim 1 , wherein the processor is further configured to determine a correlation between available electrode channels to define the at least three channels.