Pace pulse detection in cardiac signals

1 . An apparatus comprising:

an electrocardiogram (ECG) circuit having an input and an output, the input of the ECG circuit adapted for attachment to a user, the ECG circuit configured to receive an ECG signal on the input of the ECG circuit, and transmit data related to validated pulses on the output of the ECG circuit;

memory configured to include computer readable instructions; and

programmable circuitry configured to execute the computer readable instructions to:

identify a leading edge of a pulse in the ECG signal responsive to an amplitude change in the ECG signal;

identify a transition time of the leading edge of the pulse;

validate the leading edge of the pulse based on the amplitude change and the transition time;

identify a trailing edge of the pulse;

determine a width of the pulse between the leading edge and the trailing edge;

validate the pulse based on the width of the pulse;

transmit data related to the pulse after the pulse has been validated; and

suspend identification of leading edges of subsequent pulses in the ECG signal during a time window after validating the pulse.

2 . The apparatus of claim 1 , wherein to validate the leading edge of the pulse, the programmable circuitry is configured to:

determine a metric based on the amplitude change and the transition time;

compare the metric to a metric threshold; and

validate the leading edge of the pulse when the metric satisfies the metric threshold.

3 . The apparatus of claim 2 , wherein the programmable circuitry is configured to observe a ringing window after a validation of the pulse, during the ringing window the metric threshold is scaled down.

4 . The apparatus of claim 3 , wherein the ringing window includes a first ringing sub-window and a second ringing sub-window subsequent to the first ringing sub-window, and wherein the metric threshold is scaled down by a first factor in the first ringing sub-window and scaled down by a second factor in the second ringing sub-window, the second factor greater than the first factor.

5 . The apparatus of claim 1 , wherein the programmable circuitry is configured to identify N number of amplitude changes and N number of transition times for a respective N number of clock cycles in the ECG signals, and to validate the leading edge of the pulse, the programmable circuitry is configured to:

determine N number of metrics based on a respective amplitude change and a respective transition time;

compare respective ones of the metrics to respective metric thresholds; and

validate the leading edge of the pulse when a first metric of the metrics satisfies a respective first metric threshold and a second metric for a subsequent clock cycle is less than the first metric.

6 . The apparatus of claim 5 , wherein the programmable circuitry is configured to identify an end of the leading edge of the pulse based on a comparison of the first metric threshold and a second metric threshold for the second metric.

7 . The apparatus of claim 5 , wherein the programmable circuitry is configured to identify an end of the leading edge of the pulse when a second metric threshold for the second metric is less than a scaled value of the first metric threshold.

8 . The apparatus of claim 5 , wherein the programmable circuitry is configured to identify the trailing edge of the pulse.

9 . The apparatus of claim 1 ,

wherein a duration of the time window is programmable.

10 . A method comprising:

receiving a cardiac signal on an input of electrocardiogram (ECG) analog front end (AFE) circuitry;

identifying a leading edge of a first pulse in the cardiac signal by comparing an amplitude change in the first pulse and a first threshold;

identifying a trailing edge of the first pulse;

determining a width of the first pulse between the leading edge and the trailing edge;

validating the first pulse based on the width;

transmitting data related to the validating of the first pulse on an output of the ECG AFE circuitry; and

identifying a leading edge of a second pulse in the cardiac signal by comparing an amplitude change for the second pulse to a second threshold during a ringing window after the validation of the first pulse, wherein the second threshold leading edge is scaled relative to the first threshold.

11 . The method of claim 10 , further comprising:

categorizing the amplitude change for the second pulse as a ringing artifact based on the second threshold.

12 . The method of claim 10 , wherein the ringing window includes a first ringing sub-window and a second ringing sub-window subsequent to the first ringing sub-window, wherein the method comprises using the second threshold during the first ringing sub-window and a third threshold during the second ringing sub-window, the second threshold scaled relative to the first threshold by a first factor, and the third threshold scaled relative to the first threshold by a second factor, the second factor greater than the first factor.

13 . The method of claim 10 , wherein the second threshold is scaled down relative to the first threshold.

14 . The method of claim 10 , further comprising:

observing a block window after validating the first pulse; and

suspending identification of leading edges during the block window.

15 . The method of claim 14 further comprising observing the block window before observing the ringing window.

16 . The method of claim 10 , wherein the second threshold is scaled relative to the first threshold based on a peak amplitude change in the cardiac signal.

17 . An apparatus comprising:

electrocardiogram (ECG) analog front end (AFE) circuitry having an input and an output;

memory configured to store computer readable instructions; and

processing circuitry coupled to the memory and configured to execute the computer readable instructions to:

receive a cardiac signal on the input of the ECG AFE circuitry;

identify a leading edge of a first pulse in the cardiac signal based on an amplitude change of the first pulse and a first threshold;

identify a transition time of the leading edge of the first pulse;

validate the leading edge of the first pulse based on the amplitude change of the first pulse and the transition time;

identify a trailing edge of the first pulse;

determine a width of the first pulse between the leading edge and the trailing edge;

validate the first pulse based on the width;

transmit data related to the first pulse on the output of the ECG AFE after validating the first pulse; and

identifying a leading edge of a second pulse in the cardiac signal based on an amplitude change of the second pulse and a second threshold during a ringing window after validating the first pulse, wherein the second threshold is scaled relative to the first threshold.

18 . The apparatus of claim 17 , wherein the first threshold for identifying the leading edge of the first pulse is a metric threshold based on the amplitude change of the first pulse and the transition time, and the processing circuitry is further configured execute the computer readable instructions to:

identify N number of amplitude changes and N number of transition times for a respective N number of clock cycles in the cardiac signal; and

validate the leading edge of the first pulse by:

determining N number of metrics based on respective amplitude changes and transition times of the N number of amplitude changes and N number of transition times;

comparing each of the metrics in the N number of metrics to a respective metric threshold; and

validating the leading edge of the pulse when a first metric of the metrics satisfies a respective first metric threshold and a second metric for a subsequent clock cycle is less than the first metric.

19 . The apparatus of claim 17 , wherein the ringing window includes a plurality of sub-windows, and the processing circuitry is further configured to execute the instructions to scale the first threshold for identifying the leading edge differently among the sub-windows.

20 . The apparatus of claim 17 , wherein the ringing window includes a plurality of sub-windows, and the processing circuitry is further configured to execute the instructions to increasingly scale the first threshold for identifying the leading edge as the plurality of sub-windows progress in time.