The Transmural Activation Interval in Dilated Cardiomyopathy: A New Mapping Tool for Intramural VT Substrates

In dilated cardiomyopathy (DCM), the substrate for ventricular tachycardia (VT) is frequently located deep intramurally, and it may be identified by delay or block of transmural activation during sinus rhythm.

The aim of this study was to analyze whether transmural activation during sinus rhythm can identify the substrate for VT in nonischemic DCM.

In patients with DCM and a narrow QRS complex who underwent endocardial and epicardial VT ablation, electroanatomical maps were analyzed to calculate the transmural activation interval (TAI). The interventricular septum was excluded. Transmural activation delay (TAD) was defined as the 99th percentile of TAI in control subjects with idiopathic ventricular arrhythmias. The spatial relation was assessed of epicardial critical isthmus sites (CIS) and VT-related sites (VRS) to areas with TAD, late gadolinium enhancement on cardiac magnetic resonance imaging, and low unipolar voltage (<8.27 mV).

In 27 patients with DCM (mean age 49 ± 16 years; left ventricular ejection fraction 38% ± 11%; QRS duration 96 ± 10 milliseconds), the median TAI was 21 milliseconds (Q1-Q3: 9-35 milliseconds). The median epicardial surface area with TAD (>39.9 milliseconds, based on the 99th percentile in 3 control subjects) covered only 7.7% of the total epicardial surface and contained 95% of the CIS and 82% of the VRS. The median late gadolinium enhancement-derived scar area (29% of the epicardial surface) contained 85% of the CIS and 84% of the VRS. The area with low unipolar voltage (8.6% of epicardial surface) contained 72% of the CIS and 58% of the VRS.

In patients with DCM and VTs, the transmural activation interval is a novel, voltage-independent mapping tool that may improve intramural substrate identification and VT ablation.