Multi-channel cardiac measurements

• US 8,788,024 B1
• Filed: 03/15/2013
• Issued: 07/22/2014
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: APN Health, LLC
• Original Assignee: APN Health, LLC
• Inventors: Brodnick, Donald, Sra, Jasbir
• Primary Examiner(s): Wieland, Robert N
• Application Number:
  US13/842,994
• Time in Patent Office: 494 Days
• Field of Search: 600/509, 600/374
• US Class Current: 600/509
• CPC Class Codes: A61B 2505/05 Surgical care
• CPC Class Codes: A61B 2562/04 Arrangements of multiple sensors of the same type
• CPC Class Codes: A61B 5/282 Holders for multiple electrodes for introduction into the body A61B5/287
• CPC Class Codes: A61B 5/283 Invasive
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/364 Detecting abnormal ECG interval, e.g. extrasystoles, ectopic heartbeats
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7285 for synchronising or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal A61B6/5205, A61B6/541, A61B8/5207, A61B8/543 take precedence

Abstract

An automatic method of measuring parameters of multi-channel cardiac electrogram signals including at least one ventricular channel and at least two other cardiac channels, the method comprising: (a) digitizing and filtering a ventricular-channel signal and a first other cardiac signal over a first preset time window to generate corresponding absolute-value velocity signals; (b) estimating a pulse interval in the ventricular absolute-value velocity signal; (c) autocorrelating the first other cardiac absolute-value velocity signal; (d) selecting a peak value of the autocorrelation based on ventricular pulse-interval estimates; and (e) setting the cycle length of the first other cardiac signal to the lag value of the selected peak in the autocorrelation. Local activation times are measured, and several multiple-channel configurations decrease measurement time, decrease the impact of signal degradation, and increase the amount of data generated during a procedure.

Claims

1. An automatic method of measuring parameters of multi-channel cardiac electrogram signals including at least one ventricular channel and at least two other cardiac channels, the method comprising:

digitizing a first other cardiac signal and a ventricular-channel signal over a first preset time window;

filtering the ventricular-channel signal to generate a ventricular absolute-value velocity signal and filtering the digitized first other cardiac signal to generate a first other cardiac absolute-value velocity signal;

estimating a pulse interval in the ventricular absolute-value velocity signal;

autocorrelating the first other cardiac absolute-value velocity signal;

selecting a peak value of the autocorrelation based on ventricular pulse-interval estimates; and

setting the cycle length of the first other cardiac signal to the lag value of the selected peak in the autocorrelation.

2. The automatic measuring method of claim 1 wherein the absolute-value velocity signals are each generated by applying a low-pass filter followed by a first-difference filter and an absolute-value filter.

3. The automatic measuring method of claim 2 wherein each combination of low-pass filter and first-difference filter is two differenced sequential boxcar filters.

4. The automatic measuring method of claim 1 wherein the first signal autocorrelation is calculated by magnitude-coincidence autocorrelation.

5. The automatic measuring method of claim 1 wherein the first signal autocorrelation is calculated by dot-product autocorrelation.

6. The automatic measuring method of claim 1 wherein estimating the pulse interval includes determining ventricular-channel activations by measuring signal threshold-crossings.

7. The automatic measuring method of claim 6 wherein determining the ventricular-channel activations includes the steps of:

subdividing the first preset time window into three equal-length periods of time;

determining the signal maximum in each of the three periods of time;

setting the threshold to a fixed threshold-percentage of the minimum of the three signal maxima; and

identifying ventricular-channel activation times at threshold-crossing times at which a threshold-crossing is preceded by at least a fixed below-threshold period.

8. The automatic measuring method of claim 7 wherein the fixed threshold-percentage is about 50%.

9. The automatic measuring method of claim 7 wherein the below-threshold period is about 120 msec.

10. The automatic measuring method of claim 7 wherein estimating the pulse interval includes the steps of:

computing all activation double-intervals;

determining the median of all of the activation double-intervals; and

setting the pulse interval to one-half of the median.

11. The automatic measuring method of claim 7 further including determining a confidence interval for the pulse interval estimate, comprising the steps of:

computing a set of activation intervals;

identifying maximum and minimum activation intervals in the set; and

setting the confidence interval equal to the difference between the maximum and minimum activation intervals.

12. The automatic measuring method of claim 1 wherein selecting a peak value of the autocorrelation includes the steps of:

determining the lag W of the minimum of the autocorrelation for lag less than a preset lag threshold;

determining the maximum peak P₁ of the autocorrelation for lag CL₁ greater than W and setting an interim cycle length CL to CL₁ and an interim peak P_CL to P₁;

determining whether CL₁ is within a first lag interval of twice the pulse interval;

finding maximum P₂ in the autocorrelation at lag CL₂ within a second lag interval of the pulse interval, determining (a) whether the maximum P₂ is greater than P_CL/2 and (b) whether CL₂ is within a third lag interval of CL₁/2, and if (a) and (b) are true, setting CL to CL₂ and P_CL to P₂;

determining whether CL is within a fourth lag interval of the pulse interval;

finding maximum P₃ in the autocorrelation at lag CL₃ between a lag of CL/6 and a lag of 2CL/3, determining (a) whether the maximum P₃ is greater than P_CL/2 and (b) whether either 2CL₃ or 3CL₃ is within a fifth lag interval of CL, and if both (a) and (b) are true, setting CL to CL₃; and

setting the cycle length of the first other cardiac signal to interim cycle length CL.

13. The automatic measuring method of claim 7 wherein the first other cardiac signal is a reference signal and a second other cardiac signal is a mapping signal, and the method further includes:

computing a reference velocity signal;

selecting the mapping signal over a second preset time window, the second preset time window being a percentage of and overlapping the end of the first preset time window;

digitizing the mapping signal;

filtering the digitized mapping signal to generate a mapping velocity signal and an absolute-value mapping velocity signal;

determining mapping-signal activations by measuring signal threshold-crossings;

selecting a mapping-signal activation based on its time relative to the ventricular channel activation times;

finding time t_M of the maximum negative velocity in the selected mapping-signal activation;

finding the time t_R of the maximum negative velocity in the reference velocity signal within one half of the cycle length of the reference signal; and

computing local activation time as t_M minus t_R.

14. The automatic measuring method of claim 13 further including storing and displaying the local activation time in a map.

15. The automatic measuring method of claim 14 further including repeating the steps to store and display plural local activation times in a map.

16. The automatic measuring method of claim 13 further including finding a plurality of times t_R, computing a plurality of interim local activation times t_LAT based on the times t_R, and determining the local activation time based on a subset of the plurality of times t_LAT.

17. The automatic measuring method of claim 16 wherein the single local activation time is the median of the plurality of interim times t_LAT.

18. The automatic measuring method of claim 17 wherein the plurality of times t_R includes all of the times of local negative velocity maxima in the reference signal, and the subset includes times t_LAT based on each time t_R.

19. The automatic measuring method of claim 16 wherein the plurality of times t_R includes all of the times of local negative velocity maxima in the reference signal, and the subset includes times t_LAT based on an interquartile set of times t_LAT.

20. The automatic measuring method of claim 1 wherein the at least one ventricular channel includes two or more ventricular channels and the method further includes automatically selecting the ventricular-channel signal from among the two or more ventricular channels.

21. The automatic measuring method of claim 20 wherein the step of selecting the ventricular-channel signal comprises:

digitizing a plurality of candidate ventricular-channel signals over a first preset selection time window;

filtering each of the plurality of candidate signals to generate corresponding candidate absolute-value velocity signals;

dividing each candidate absolute-value velocity signal into a set of sequential, equal-length sub-signals;

estimating signal quality and pulse interval for each sub-signal of each candidate signal;

combining the sub-signal quality estimates of each candidate signal to generate a signal quality estimate SQ_VC for each candidate signal;

determining the maximum and minimum pulse intervals for each sub-signal and generating a pulse interval variability estimate VAR_VC for each candidate signal by selecting the maximum difference between sub-signal pulse-interval maxima and minima;

excluding candidate ventricular-channel signals with values VAR_VC above a variability threshold; and

selecting the ventricular channel as the non-excluded candidate channel with the highest signal quality estimate SQ_VC.

22. The automatic measuring method of claim 21 wherein estimating signal quality for each sub-signal comprises the steps of:

dividing each sub-signal into three equal-length chunks;

determining the maximum of each chunk;

determining the maximum MAX and minimum MIN of the three chunk maxima;

computing the median of the sub-signal to generate a noise estimate N_S equal to twice the median; and

calculating the signal-quality estimate as 2×

MIN−

MAX−

2×

N_S.

23. The automatic measuring method of claim 20 further including automatically selecting the first other cardiac channel from among the at least two other cardiac channels.

24. The automatic measuring method of claim 23 wherein the step of selecting the first other cardiac channel comprises:

digitizing a plurality of candidate other cardiac signals over a first preset selection time window;

filtering each of the plurality of candidate signals to generate corresponding candidate absolute-value velocity signals;

dividing each candidate velocity signal into a set of sequential, equal-length sub-signals;

estimating signal quality, cycle length and variability for each sub-signal of each candidate signal;

combining the sub-signal quality estimates of each candidate signal to generate a signal quality estimate SQ_RC for each candidate signal;

determining the maximum MAX_CL and minimum MIN_CL of the sub-signal cycle lengths and a cycle length variability VAR_RC for each candidate signal;

calculating a figure of merit value for each candidate signal based on signal quality SQ_Rc, MAX_CL, MIN_CL, and VAR_RC; and

selecting the other cardiac channel as the candidate channel with the highest figure of merit value.

25. The automatic measuring method of claim 24 wherein estimating signal quality for each sub-signal comprises the steps of:

dividing each sub-signal into three equal-length chunks;

determining the maximum of each chunk;

determining the maximum MAX and minimum MIN of the three chunk maxima;

computing the median of the sub-signal to generate a noise estimate N_S equal to twice the median; and

calculating the signal-quality estimate as 2×

MIN−

MAX−

2×

N_S.

26. The automatic measuring method of claim 1 wherein the at least two other cardiac channels includes three or more other cardiac channels and the method further includes:

selecting a reference channel and a mapping channel from among the other cardiac channels;

monitoring the signal quality of each of the reference channel and at least one of the other cardiac channel; and

if the signal quality of the reference channel falls below a signal quality threshold, replacing the reference channel with the other cardiac channel with a higher signal quality and calculating local activation time values based on the higher-signal-quality other cardiac channel.

27. An automatic method of measuring parameters of multi-channel cardiac electrogram signals including a plurality of cardiac channels and at least one ventricular channel wherein a reference channel is automatically selected from the plurality of cardiac channels based on signal quality, cycle length, and cycle-length variability measurements of a subset of the plurality of cardiac channels.

28. The automatic method of claim 27 wherein the at least one ventricular channel is two or more ventricular channels and the method further includes automatically selecting a ventricular channel based on signal quality and variability of the ventricular channels.