Background: In non-ischemic cardiomyopathy (NICM), intramural fibrosis may impact transmural activation facilitating VT reentry circuits within protected subepicardial areas. These areas may be identified by a prolonged transmural activation interval (TAI)
Objective: To determine whether prolonged TAI can localize critical VT isthmus sites.
Methods: NICM patients who underwent combined endo-epicardial electroanatomical mapping (EAM) and ablation with real-time image integration of LGE-CMR were included. Local activation time (LAT) of endo and epicardial EAM points were annotated. Subsequently, EAM points were exported and projected on the CMR derived epicardial shell. The endocardial LAT was interpolated across the endocardial surface based on acquired EAM data using a Gaussian weighted average and validated with leave-one-out cross validation. At each epicardial site, the corresponding endocardial LAT was determined. TAI was defined as difference between endo-and epicardial LAT. Epicardial areas with prolonged TAI, areas with any scar (SI>35% of SI_max) and areas with >75% scar transmurality on LGE-CMR were measured. Only sites with concealed entrainment and VT termination by ablation were considered critical isthmus sites (CIS).
Results: Twenty-seven patients (56±16 yrs, 23 male (74%)) and 4 controls (69±5 yrs years, all male) were included. TAI in controls was 7.7ms (0.8-15.9) . Based on the 99^th percentile TAI>40ms was defined as prolonged. In NICM patients, 40 CIS could be determined. In these patients, the area of prolonged TAI was 7.7% of the total epicardial surface and contained 90% of all CIS. In contrast, the LGE derived scar area comprised 35% of the epicardial surface including 80% of CIS and the area ≥75% scar transmurality was 3.7% of the surface but with only 45% of CIS.
Conclusion: A prolonged transmural activation interval (TAI>40ms) was more accurate to localize the critical VT substrate than LGE-CMR derived scar characteristics. While areas with prolonged TAI concerned only 7.7% of the epicardial surface, they contained 90% of all CIS. TAI is a voltage and imaging independent promising mapping tool allowing for substrate based ablation in NICM.