Relationship between areas of delayed trans-septal conduction time and critical sites for septal ventricular...

Delayed trans-septal conduction time (DCT) accurately identifies intramural septal substrate (ISS) in non-ischemic cardiomyopathy (NICM). The relationship between DCT areas and critical ISS-ventricular tachycardia (VT) sites is unknown.

To assess the relationship between DCT areas and critical ISS-VT sites in NICM.

We included consecutive patients with NICM and ISS defined by (1) confluent septal areas of low unipolar voltage (<8.3 mV) with normal or minimal bipolar abnormalities and (2) DCT (>40 ms by pacing the basal right ventricular (RV) septum). Critical ISS-VT sites were identified by activation, entrainment, and/or pace mapping and corroborated by VT termination during ablation (for stable VT) and/or lack of VT reinducibility following ablation (for unstable VT).

56 distinct ISS-VTs in 28 patients (69 ± 11 years; ejection fraction, 35% ± 11%) were analyzed. Of these, 17 ISS-VTs were stable and terminated with ablation. Targeted ISS areas leading to VT non-inducibility or VT termination had a median DCT of 106 ms (interquartile range, 89-142) and 146 ms (interquartile range, 130-192), respectively. Of 17 (94%) termination sites, 16 had a DCT of >50% of the RV-paced QRS, with 35% showing only systolic local potentials during VT, confirming primarily intramural circuits. Elimination of the targeted ISS-VT was achieved in 96% of cases, with non-inducibility of any VTs in 79%.

Critical ISS-VT sites colocalize with areas of significant (>100 ms) DCT. Areas of septal DCT of >50% of the RV-paced QRS duration subtend the majority of the ISS-VT termination sites and can represent a novel and more specific target for septal substrate modification in this challenging population.