Methods and systems for mapping cardiac repolarization
View Patent ↗Cardiac repolarization activity can be mapped using action potential duration (“APD”) and/or activation recovery interval (“ARI”). APD can be measured using a bipolar electrogram signal measured, for example, using a monophasic action potential (“MAP”) catheter. ARI can be measured using unipolar electrogram signals. The electrogram signal is used to identify a depolarization tick time. A repolarization tick time can be identified using either a point in time when the electrogram signal passes below a threshold or via local maxima and minima of a first derivative of the electrogram signal. Diastolic intervals can also be computed using depolarization and repolarization tick times.
1. A method of mapping cardiac repolarization activity, comprising:
receiving a unipolar electrogram signal S(t) at a signal processor; and
using the signal processor:
identifying a local activation time (“LAT”) tick time within a preset window about a reference time T ref ;
defining the LAT tick time as a depolarization tick time T D for the preset window;
computing a first derivative S′(t) of the electrogram signal S(t) for the preset window;
identifying a repolarization tick time T R using local maxima and local minima of S′(t); and
computing an activation recovery interval for the preset window using the depolarization tick time T D and the repolarization tick time T R ,
wherein identifying a repolarization tick time T R using local maxima and local minima of S′(t) comprises:
identifying a maximum tick time T max and a minimum tick time T min within a preset refractory window ΔRW surrounding the depolarization tick time T D using S(t);
computing a LAT amplitude L 1 using S(T max ) and S(T min );
identifying a next cycle tick T next occurring after T max using S(t);
determining a search period following the depolarization tick time T D for the repolarization tick time T R ;
identifying a time T SLM during the search period at which S′(t) reaches a local maximum;
identifying a time T slm during the search period at which S′(t) reaches a local minimum; and
defining the repolarization tick time T R using one or more of T SLM and T slm .
2. The method according to claim 1 , wherein computing a first derivative S′(t) of the electrogram signal S(t) for the preset window comprises computing the first derivative S′(t) according to a formula
S
′
(
t
)
=
S
(
t
+
Δ
t
)
-
S
(
t
)
Δ
t
,
wherein Δt comprises a preset time interval.
3. The method according to claim 1 , wherein identifying a next cycle tick T next occurring after T max using S(t) comprises:
defining a local minimum threshold higher than S(T min );
defining a local maximum threshold higher than S(T max );
analyzing S(t) after T max ; and
identifying T next as a first to occur of:
a time at which S(t) drops below the local minimum threshold;
a time at which S(t) exceeds the local maximum threshold; and
a time at which S(t) ends.
4. The method according to claim 3 , wherein:
the local minimum threshold is computed as S(T min )+0.3*L 1 ; and
the local maximum threshold is computed as S(T max )+0.3*L 1 .
5. The method according to claim 1 , wherein determining a search period following the depolarization tick time T D for the repolarization tick time T R comprises:
computing a search interval L 2 as T next T D 2(ΔRW);
defining a start of the search period at T D +ΔRW; and
defining an end of the search period at T D ΔRW+0.75*L 2 .
6. The method according to claim 1 , wherein defining the repolarization tick time T R using one or more of T SLM and T slm comprises:
defining T R as
min
(
T
SLM
,
T
slm
)
+
T
SLM
+
T
slm
2
for a biphasic T-wave;
defining T R as T SLM for a negative T-wave; and
defining T R as T slm for a positive T-wave.
7. The method according to claim 1 , further comprising computing a diastolic interval for the preset window using the depolarization tick time T D for the preset window and an immediately previous repolarization tick time T R-1 .
8. A system for mapping cardiac repolarization activity, comprising:
a cardiac repolarization detection processor configured:
to receive a unipolar electrogram S(t);
to identify a local activation time (“LAT”) tick time within a preset window about a reference time Tier and define the LAT tick time as a depolarization tick time T D for the preset window;
to compute a first derivative S′(t) of the electrogram S(t) for the preset window;
to identify a repolarization tick time T R using local maxima and local minima of the first derivative S′(t) of the electrogram S(t) by executing a process comprising:
identifying a maximum tick time T max and a minimum tick time T min within a preset refractory window ΔRW surrounding the depolarization tick time T D using S(t);
computing a LAT amplitude L 1 using S(T max ) and S(T min );
identifying a next cycle tick Text occurring after T max using S(t);
determining a search period following the depolarization tick time T D for the repolarization tick time T R ;
identifying a time T SLM during the search period at which S′(t) reaches a local maximum;
identifying a time T slm during the search period at which S′(t) reaches a local minimum; and
defining the repolarization tick time T R using one or more of T SLM and T slm ; and
to compute an activation recovery interval using the depolarization tick time T D and the repolarization tick time T R .
9. The system according to claim 8 , wherein the cardiac repolarization detection processor is further configured to compute a diastolic interval using the depolarization tick time T D and a an immediately previous repolarization tick time T R-1 .