Multi-channel cardiac measurements
An automatic method of determining local activation time (LAT) in multi-channel cardiac electrogram signals including at least two cardiac channels, one of the cardiac channels being a mapping channel and another cardiac channel being a reference channel, the method comprising: (a) estimating a cycle length CL in the reference channel; (b) determining a mapping-channel fiducial time t M in the mapping channel signal; (c) determining a plurality of reference-channel fiducial times t R ; (d) computing adjusted reference-channel fiducial times t RA by adding or subtracting multiples of cycle length CL to each time t R such that each time t RA is within a time window of length CL surrounding mapping-channel fiducial time t M ; (e) computing a single final reference-channel fiducial time t RF from the plurality of adjusted reference-channel fiducial times t RA ; and (f) computing the LAT as t M minus t RF .
1. An automatic method of determining local activation time (LAT) in multi-channel cardiac electrogram signals including at least two cardiac channels, one of the cardiac channels being a mapping channel and another cardiac channel being a reference channel, the method comprising:
(a) estimating a cycle length CL in the reference channel;
(b) determining a mapping-channel fiducial time t M in the mapping channel signal;
(c) determining a plurality of reference-channel fiducial times t R ;
(d) computing adjusted reference-channel fiducial times t RA by adding or subtracting multiples of cycle length CL to each time t R such that each time t RA is within a time window of length CL surrounding mapping-channel fiducial time t M ;
(e) computing a single final reference-channel fiducial time t from the plurality of adjusted reference-channel fiducial times t RA ; and
(f) computing the LAT as t M minus t RF .
2. The automatic LAT-determination method of claim 1 wherein the time window of length CL surrounding t M spans ±CL/2 of t M .
3. The automatic LAT-determination method of claim 1 wherein the adjusted reference-channel fiducial times t RA used to compute final reference-channel fiducial time t are a subset of the plurality of adjusted reference-channel fiducial times t RA .
4. The automatic LAT-determination method of claim 3 wherein computing a single final reference-channel fiducial time t RF comprises the steps of:
computing an average av RA of the subset;
including av RA in the subset; and
setting the final reference-channel fiducial time t to the median of the subset.
5. The automatic LAT-determination method of claim 4 wherein the median of the subset is the set-member median.
6. The automatic LAT-determination method of claim 1 wherein the adjusted fiducial times t RA are a set of adjusted fiducial times and computing a single final reference-channel fiducial time t RF comprises the steps of:
computing an average av RA of the set;
including av RA in the set; and
setting the final reference-channel fiducial time t to the median of the set.
7. The automatic LAT-determination method of claim 6 wherein the median of the set is the set-member median.
8. The automatic LAT-determination method of claim 1 wherein the mapping-channel fiducial time t M is at a time of maximum negative velocity of the mapping-channel signal.
9. The automatic LAT-determination method of claim 1 wherein the reference-channel fiducial times t R are at times of maximum negative velocity of the reference-channel signal.
10. The automatic LAT-determination method of claim 1 further including repeating steps (a) through (f) to generate a plurality of LAT values and displaying the plurality of LAT values as an LAT map.
11. The automatic LAT-determination method of claim 1 wherein computing a single final reference-channel fiducial time t RF from the plurality of adjusted reference-channel fiducial times t RA includes ordering the plurality of adjusted reference-channel fiducial times t RA and using a subset of times t RA to compute final reference-channel fiducial time t RF .
12. The automatic LAT-determination method of claim 11 wherein the subset of times t RA is the interquartile set of times t RA .
13. The automatic LAT-determination method of claim 12 wherein the final reference-channel fiducial time t RF is the median of the set.
14. The automatic LAT-determination method of claim 13 wherein the median of the interquartile set is the set-member median.
15. The automatic LAT-determination method of claim 1 further including computing a confidence interval for the determined LAT.
16. The automatic LAT-determination method of claim 15 wherein computing an LAT confidence interval comprises:
computing an intermediate LAT value as LAT=t M −t RA for each of the plurality of adjusted reference-channel fiducial times t RA , the intermediate LAT values comprising a set of values;
selecting the highest and lowest intermediate LAT values in the set; and
computing the confidence interval as ±a fraction of the difference between the highest and lowest intermediate LAT values.
17. The automatic LAT-determination method of claim 16 wherein the fraction of the difference is one-half.
18. The automatic LAT-determination method of claim 16 wherein the set is a subset of the intermediate LAT values.
19. The automatic LAT-determination method of claim 18 wherein the fraction of the difference is one-half.
20. The automatic LAT-determination method of claim 1 wherein estimating a cycle length CL in the reference channel comprises:
digitizing the reference-channel signal over a first preset time window;
filtering the reference-channel signal to generate a reference-channel absolute-value velocity signal;
autocorrelating the reference-channel absolute-value velocity signal; and
selecting a peak value of the autocorrelation and setting the cycle length CL as the lag at the peak.
21. The automatic LAT-determination method of claim 20 further including determining a CL confidence interval by setting a lag value L2 as the lag at a second autocorrelation peak near twice CL and setting the CL confidence interval at ±(L2−2CL).