Exit Sites on the Epicardium Rarely Subtend Critical Diastolic Path of Ischemic VT on the Endocardium: Implications for Non-Invasive Ablation.

BACKGROUND: Non-invasive electrocardiographic mapping of ventricular tachycardia (VT) and ablation using stereotactic radiotherapy was recently reported. This strategy does not directly evaluate the critical diastolic components and assumes that the epicardial exit site of VT subtends closely over the endocardial mid-diastolic isthmus.

OBJECTIVE: To determine if the epicardial exit site of VT spatially corresponds to the critical diastolic components of ischemic scar related VT.

METHODS: Intraoperative simultaneous endocardial and epicardial mapping was performed during VT using a 112-bipole endocardial balloon and 112-bipole epicardial sock array. In 8 patients, 9 VTs having entire diastolic circuit mapped were included in the study. The diastolic path and VT-exit sites (epicardial and endocardial) were determined.

RESULTS: The diastolic path was mapped in the endocardium for all 9 VTs (median length 50, IQR 28mm). The TCL (Tachycardia Cycle Length) ranged from 210- 500ms. The VT-exit site was early in the endocardium for 6 VTs and on the epicardium for 3 VTs. The mid-diastolic isthmus and endocardial exit site of the 6 endocardial VTs were spatially distant from their epicardial exit site by a median distance of 32mm and 27mm, respectively. For the 3 VTs with an early epicardial exit, the isthmus and endocardial exit sites were distant from the epicardial exit site by a median distance of 34 mm and 38 mm, respectively.

CONCLUSION: The epicardial exit site and the mid-diastolic isthmus sites were spatially distant and discrepant. Surface ECG derived strategy in identifying epicardial exit site to select non-invasive ablation targets is prone to identify epicardial exit sites and may not identify critical targets in ischemic scar VT. This article is protected by copyright. All rights reserved.