Background: The VT substrate in left ventricular non-ischemic cardiomyopathy (LV NICM) may be confined to the epicardium (EPI)/sub-epicardium.
Objective: To characterize the prevalence, distribution, endocardial (ENDO) electrogram diagnostic clues, and outcome of VT ablation in patients with NICM and VT, with isolated epicardial substrate.
Methods: Forty-seven of 531 (9 %) consecutive patients with LV NICM and VT demonstrated normal ENDO (>1.5mV)/ abnormal EPI bipolar (BI)low voltage area(LVA - <1.0mV and signal abnormality). We assessed: 1) the location of EPI BI LVA, 2) the presence and extent of ENDO unipolar (UNI) LVA (≤8.3 mV); 3) the presence/location of ENDO BI split electrograms with normal amplitude initial deflections followed by low amplitude 2^nd component coinciding with EPI late electrograms; 3) outcome and predictors of catheter ablation success targeting the LVA.
Results: EPI BI LVA (27.3 cm², IQR15.8-50.0) was localized to basal (39), mid (5) and apical (3) LV with inferolateral basal LV segment the most commonly involved in 25/47(53%). Of 44 patients with ENDO maps available for review, 40 (91%) had ENDO UNI LVA (24.5 cm², IQR 9.4-68.5) and 29 (66%) had characteristic ENDO split electrograms underlying the EPI LVA. The VT-free survival post ablation was 78% at mean 34 months. Greater area of ENDO UNI LVA than the EPI BI LVA (HR: 3.851; CI: 1.39-10.68, p=0.001) and greater number of inducible VTs (HR: 1.36; CI: 1.02-1.81, p=0.002) were independently associated with VT recurrence after single procedure.
Conclusion: In patients with LV NICM and VT, the substrate may be confined to the EPI/sub EPI LV in ~10% of patients. Although with important variability, the most common substrate location is the basal and specifically inferolateral LV. ENDO UNI LVA and characteristic BI split electrograms help identify EPI LVA in most patients. Catheter ablation targeting EPI substrate achieves long-term freedom from VT in 78%. Greater area of ENDO UNI LVA than the EPI BI LVA and greater number of inducible VT are independent predictors of VT recurrence.