Identification of reentry vulnerable targets during substrate mapping for ablation in scar related VT: the "visual" reentry vulnerability index
Authors: Tonko J B , Lambiase P I E R 
Published: May 2024

Abstract

Introduction
Conduction abnormalities including zones of deceleration (DZ) & late activation are functionally important targets for ablation in scar-related ventricular tachycardias (VT). Repolarisation heterogeneities are equally important but are not routinely assessed. Visualisation of a combination of both conduction & repolarisation metrics whilst in sinus in the form of a re-entry vulnerability index (RVI) may enable more precise identification of critical ablation targets.
Rationale: To test accuracy of a novel functional substrate mapping strategy combining conduction & repolarisation metrics to "visually" estimate reentry vulnerability sites (RVIv) during scar related VT ablation without the need for offline processing required for "computational" RVI.

Methods
VT cases using a multipolar grid-catheter for contact mapping were reviewed. DZ &areas of late activation were tagged on omnipolar LAT substrate maps. The corresponding unipolar repolarisation maps depicting local repolarisation time (LRT) based on the Wyatt method (WOI over T-Wave annotating to +dV/dt, UEGM-Filter 0.05-100Hz) were then displayed side-by-side with the LAT map. Timing reference was set to onset of surface QRS. Colour scale of LRT maps was set to start at or ahead of the timing of latest LAT. "Visual RVI" zones were identified if the tagged zone of late activation was overlapping and/or directly adjacent to an area of "early" repolarisation (defined as before or within 100ms of latest LAT point) based on colour. In visually identified RVI areas, temporal (timing difference in ms) & spatial relationship (distance in mm) of EGMs with earliest RT (RTe) to EGM with latest AT (ATL) separated by max. 20mm were measured & RVI calculated (RTe subtracted by ATL). Number of RVIv zones per map, RVI metrics & distance from closest RVI to VT Exit site (defined per activation±entrainment or pace mapping) were assessed. The lower/negative the numeric RVI, the higher the vulnerability for reentry.

Results
20 patients with scar-related reentry VT were included (90% male, 63.8±11.6 years, LVEF 36±16%, 60% ischemic/40% non-ischemic). LAT & LRT map point counts were 4835±2625 and 3596±2805. In 17 (85%) patients at least 1 RVIv zone was identified, with on avg. 3.3±1.7 RVIv zones/patient. Manual RVIs were calculated to 10.4±78.9ms ( "most vulnerable" RVI was -227ms) with on avg. 9.5±5.3mm distance between RTe & ATL. All maps with no RVIv zone on the mapped surface were of non-ischemic etiology. The shortest distance of RVIs to functionally critical sites during VT was 8.9±7.4mm (range 0-33mm).

Conclusion
Visual reentry vulnerability estimation based on a combination of established conduction and novel repolarisation maps is feasible & may help to identify functionally critical zones during substrate mapping. Future efforts should include dedicated automated repolarisation mapping tools to facilitate integration of repolarisation dynamics in functional VT substrate mapping workflows.Figure 1Example Visual RVI Mapping