Background: ECG criteria identifying epicardial (EPI) origin for ventricular tachycardia (VT) in nonischemic cardiomyopathy have not been determined. Endocardial (ENDO) and EPI basal left ventricle fibrosis characterizes the VT substrate.
Methods and results: We assessed the QRS from 102 basal-superior/lateral EPI and 67 comparable ENDO pace maps in 14 patients with nonischemic cardiomyopathy. Pace mapping focused on low bipolar voltage areas. Published morphology criteria: q wave in lead I (QWLI) and no q waves in inferior leads and interval criteria: pseudo-delta wave > or =34 ms, intrinsicoid deflection time > or =85 ms, shortest RS complex > or =121 ms, and maximum deflection index > or =0.55 were assessed for ability to identify EPI origin. Sixteen EPI and 8 ENDO of the 34 mapped VTs (71%) in the study population and 14 EPI and 7 ENDO VTs from an 11-patient validation cohort were localized to basal-superior/lateral left ventricle and corroborated pacing data. A QWL1 was seen in EPI but not ENDO pace maps (91% versus 4%; P<0.001), identified 14 of 16 EPI VTs (sensitivity, 88%), and was seen in 1 of 8 ENDO VTs (specificity, 88%). None of the remaining criteria achieved similar sensitivity without specificity <50%. We identified 4 criteria (q waves in inferior leads, pseudo-delta wave > or =75 ms, maximum deflection index > or =0.59, and QWL1) having > or =95% specificity and > or =20% sensitivity in identifying EPI/ENDO origin for pace maps. This 4-step algorithm identified the origin in 109 of 115 pace maps (95%), 21 of 24 VTs (88%) in the study population, and 19 of 21 VTs (90%) in validation cohort.
Conclusions: Morphological ECG features that describe the initial QRS vector can help identify basal-superior/lateral EPI VTs in nonischemic cardiomyopathy.