Relationship Between Areas of Delayed Trans-Septal Conduction Time and Critical Sites for Septal Ventricular Tachycardia in Non-Ischemic Cardiomyopathy.

BACKGROUND: 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. OBJECTIVE: To assess the relationship between DCT areas and critical ISS-VT sites in NICM. METHODS: We included consecutive patients with NICM and ISS defined by: 1) confluent septal areas of low unipolar voltage (<8.3 mV) with normal/minimal bipolar abnormalities; 2) trans-septal DCT (>40 ms by pacing the basal RV septum). Critical ISS-VT sites were identified with activation, entrainment and/or pace mapping and corroborated by VT termination during ablation (stable VT) and/or lack of VT reinducibility following ablation (unstable VT). RESULTS: Fifty-six distinct ISS-VTs in 28 patients (69±11 years, EF 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 [IQR: 89-142] and 146 ms [130-192], respectively. Sixteen out of 17 (94%) termination sites had DCT >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%. CONCLUSIONS: Critical ISS-VT sites colocalize with areas of significant (>100 ms) DCT. Areas of septal DCT >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.