Idenitification of an epicardial origin for right and left ventricular tachycardias

Resumen

Patients with arrhythmogenic right ventricular cardiomyopathy/dysplasia presenting with right ventricular tachycardia are usually suitable to endocardial successful ablation, which may sometimes include the use of irrigated-tip catheters. In those cases in which endocardial ablative therapy does not result in VT elimination, an epicardial VT origin should be suspected. A more extensive epicardial than endocardial area of electrogram abnormalities (a surrogate for scar tissue as the substrate for slow conduction and reentry) and occasional RV wall thickening is the common substrate of epicardial RV-VTs in the setting of ARVC/D. This observation is corroborated by histological patterns of epicardial scar, RV wall thickening and subendocardial fibrosis. These patterns are usually more pronounced in the proximity of the tricuspid annulus toward the acute angle of the RV, frequently leading to RV-VTs not amenable to endocardial successful elimination. The long-term outcome after epicardial ablation appears to confirm this principle. Morphological site-specific ECG criteria are useful to identify right ventricular tachycardias of an epicardial origin. The ECG criteria to identify an epicardial origin for right and left ventricular tachycardia are site and substrate dependent. Previously described interval criteria, including the pseudodelta wave, the intrinsicoid deflection time and the shortest RS complex do not apply to the RV and do not uniformly apply to all LV regions. Identification of a Q wave in lead I and absence of a Q wave in inferior leads are the strongest predictors of an epicardial origin for VTs arising from the basal superior and basal lateral LV in the setting of NICM. These LV regions are a very frequent site of VT origin in NICM patients. These two criteria, along with 2 additional revised interval criteria (PsD of ¿ 75 ms and MDI of ¿ 0.59) reach the best combined sensitivity/specificity for a precise identification of an epicardial VT origin in this LV region.