# US 8,788,024 B1 · Multi-channel cardiac measurements

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- Number: US 8,788,024 B1
- Document ID: US8788024B1
- Status: Granted
- Kind: B1
- Application number: 13/842,994
- Filed: 2013-03-15
- Granted: 2014-07-22
- Earliest claimed: 2013-03-15
- Assignees: APN Health, LLC
- Applicants: APN Health, LLC
- Inventors: Donald Brodnick; Jasbir Sra
- Web page: https://patentgrep.com/patent/US8788024B1

## CPC

- A61B 5/349: Detecting specific parameters of the electrocardiograph cycle
- A61B 5/282: Holders for multiple electrodes (for introduction into the body A61B5/287)
- A61B 5/283: Invasive
- A61B 5/7203: {for noise prevention, reduction or removal}
- A61B 5/7285: {for synchronizing or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal}
- A61B 5/363: Detecting tachycardia or bradycardia
- A61B 5/364: Detecting abnormal ECG interval, e.g. extrasystoles, ectopic heartbeats
- A61B 2505/05: Surgical care
- A61B 2562/04: Arrangements of multiple sensors of the same type
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)

## 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

### Claim 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.

### Claim 2 (depends on 1)

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.

### Claim 3 (depends on 2)

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

### Claim 4 (depends on 1)

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

### Claim 5 (depends on 1)

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

### Claim 6 (depends on 1)

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

### Claim 7 (depends on 6)

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.

### Claim 8 (depends on 7)

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

### Claim 9 (depends on 7)

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

### Claim 10 (depends on 7)

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.

### Claim 11 (depends on 7)

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.

### Claim 12 (depends on 1)

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 PCL 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 PCL/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 PCL 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 PCL/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.

### Claim 13 (depends on 7)

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 tM of the maximum negative velocity in the selected mapping-signal activation;
finding the time tR 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 tM minus tR.

### Claim 14 (depends on 13)

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

### Claim 15 (depends on 14)

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

### Claim 16 (depends on 13)

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

### Claim 17 (depends on 16)

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

### Claim 18 (depends on 17)

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

### Claim 19 (depends on 16)

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

### Claim 20 (depends on 1)

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.

### Claim 21 (depends on 20)

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 SQVC for each candidate signal;
determining the maximum and minimum pulse intervals for each sub-signal and generating a pulse interval variability estimate VARVC for each candidate signal by selecting the maximum difference between sub-signal pulse-interval maxima and minima;
excluding candidate ventricular-channel signals with values VARVC above a variability threshold; and
selecting the ventricular channel as the non-excluded candidate channel with the highest signal quality estimate SQVC.

### Claim 22 (depends on 21)

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 NS equal to twice the median; and
calculating the signal-quality estimate as 2×MIN−MAX−2×NS.

### Claim 23 (depends on 20)

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.

### Claim 24 (depends on 23)

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 SQRC for each candidate signal;
determining the maximum MAXCL and minimum MINCL of the sub-signal cycle lengths and a cycle length variability VARRC for each candidate signal;
calculating a figure of merit value for each candidate signal based on signal quality SQRc, MAXCL, MINCL, and VARRC; and
selecting the other cardiac channel as the candidate channel with the highest figure of merit value.

### Claim 25 (depends on 24)

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 NS equal to twice the median; and
calculating the signal-quality estimate as 2×MIN−MAX−2×NS.

### Claim 26 (depends on 1)

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.

### Claim 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.

### Claim 28 (depends on 27)

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.