Characterization of Endocardial Electrophysiological Substrate in Patients With Nonischemic Cardiomyopathy and Monomorphic Ventricular Tachycardia

BACKGROUND: Although catheter mapping has been used to define the endocardial electrogram characteristics in patients with ventricular tachycardia (VT) and coronary disease, characterization of the electrophysiological substrate in patients with VT and nonischemic cardiomyopathy is limited. METHODS AND RESULTS: Left ventricular endocardial electroanatomical mapping was performed in 19 patients with nonischemic cardiomyopathy and monomorphic VT with an average of 178+/-83 sites per chamber mapped. Abnormal bipolar electrogram was defined as endocardial voltage signal amplitude of <1.8 mV. The extent and location of abnormal endocardium was estimated by measuring areas of abnormal electrogram recordings from 3D voltage maps. The origin of VT was approximated by identifying sites of entrainment with concealed fusion or early presystolic activity and/or by pace mapping. Abnormal electrograms were recorded over a 41+/-28 cm2 area that represented 20+/-12% of total endocardial surface. The majority of patients (14/19 patients) had only a modest area (<25%) of endocardial abnormality. All patients had abnormal low-voltage endocardial areas located near the ventricular base in the perivalvular region. There were 3+/-1 VT morphologies per patient. The majority (88%) of the 57 mapped VTs originated from the ventricular base, corresponding to regions with abnormal endocardial electrograms. CONCLUSIONS: Electroanatomical mapping in patients with monomorphic VT and nonischemic cardiomyopathy typically demonstrates a modest-sized basal area of endocardial electrogram abnormalities. The VT site of origin corresponds to these basal electrogram abnormalities. These findings have important implications regarding strategies for VT ablation in this setting.