MRI-guided multipolar functional substrate mapping identifies intramural conduction corridors: The TRAMPOLINE VT study.

BACKGROUND: Characterising mid-myocardial substrate during ventricular tachycardia (VT) ablation is challenging. OBJECTIVE: We evaluated how electrode spacing, multipolar signal annotation, and functional mapping affect the identification of conduction delay over endocardial and mid-myocardial substrate. METHODS: 18 patients with ischaemic cardiomyopathy underwent VT ablation with co-registered MRI scar models. Substrate was mapped in sinus rhythm (SR) and after a single sensed extra-stimulus (SE) from the right ventricle. Twelve patients (bipolar [BP] group) were mapped with both short-spline (Oct-S) and long-spline (Oct-L) Octaray catheters. Six patients (multipolar [MP] group) were mapped with both Oct-S and the OPTRELL catheter (OPT). Points within 1cm geodesic distance of MRI conduction corridors were analysed for late potentials (LPs), conduction velocity (CV), and anisotropic ratio (AR). RESULTS: Over endocardial substrate, SE mapping increased LP density versus SR for all catheters (Oct-L 6→14%, Oct-S 1→32%, OPT 21→45%; p<0.001). MP annotation identified more LPs than BP over endocardial (27% vs 9%, p<0.001) and mid-myocardial (41% vs 12%, p<0.001) corridors. With BP annotation, median LAT and CV were similar when stratified by corridor depth (p>0.1). With MP annotation, LAT delayed 12 ms per 10% increase in depth in SR and by 7 ms with SE (p<0.001), and CV slowed over mid-myocardial corridors (18cm/s vs 39cm/s, p<0.001). Substrate-adjacent conduction vector heterogeneity was greatest with functional MP mapping (AR: 0.59) and smallest with SR BP mapping (AR: 0.76, p<0.001). CONCLUSION: Functional mapping improved identification of delayed conduction for all catheters, and MP annotation enhanced the delineation of intramural conduction corridors via the endocardial surface.