Substrate Mapping for Ventricular Tachycardia Ablation Through High-Density Whole-Chamber Double Extra Stimuli

– A partial delineation of targets for ablation of ventricular tachycardia (VT) during a stable rhythm is likely responsible for a suboptimal success rate. The abnormal low-voltage near-field functional components may be hidden within the high-amplitude far-field signal. We aim to evaluate the benefit and feasibility of functional substrate mapping using a full ventricle S3 protocol and to assess its colocalization with conducting channels (CCs) in the late gadolinium enhancement cardiac magnetic resonance (LGE-CMR). – An S3 mapping protocol with a drive train of S1 followed by S2 (effective refractory period (ERP) +30ms) and S3 (ERP+50ms) from the RV apex was performed in 40 consecutive patients undergoing scar-related VT ablation. Deceleration zones (DZs) and areas of late potentials (LPs) were identified for all maps. A pre-procedural non-invasive substrate assessment was done with LGE-CMR and post-processing with automated CCs identification. – The S3 protocol was completed in 34 of the 40 procedures (85.0%). The S3 protocol enhanced the identification of VT isthmus based on DZs (89% vs. 62%, p<0.01) and LPs assessment (93% vs. 78%, p=0.04). The percentage of CCs unmasked by DZs and LPs using S3 maps was significantly higher than the ones using S2 and S1 maps (78%, 65%, and 48%; p<0.001, and 88%, 81%, and 68%; p<0.01, repectively). The functional substrate identified during the S3 activation mapping was significantly more extensive than the one identified using S2 and S1, including a higher number of DZs (2.94, 2.47, and 1.82, respectively; p<0.001), and a wider area of LPs (44.1, 38.2, and 29.4cm2, respectively; p<0.001). After VT ablation, 77.9% of patients have been VT free during a median follow-up of 13.6 months. – The S3 protocol is feasible in 85% of patients, allows for a better identification of targets for ablation, and may potentially improve VT ablation results.