Novel ECG Predictor of Difficult Cases of Outflow Tract Ventricular Tachycardia: Peak Deflection Index on an Inferior Lead

Background: An ECG predictor of ablation success has not been determined for difficult cases of outflow tract ventricular tachycardia/ventricular premature contractions (OT-VT/VPC). Methods and Results: ECG analysis and radiofrequency catheter ablation (RFCA) were performed in 70 patients with OT-VT/VPC. The peak deflection index (PDI) was determined in the inferior lead presenting the tallest R wave by dividing the time from QRS onset to peak QRS deflection by total QRS duration. In 10 (14%) of the 70 patients, RFCA performed at a septal or epicardial site was unsuccessful (group 1), but was successful in the remaining 60 patients (group 2). Neither activation time (35±15 ms vs 40±12 ms, P=0.3) nor QRS duration (141±19 ms vs 137±19 ms, P=0.6) were significantly different between groups 1 and 2. However, PDI was significantly higher in group 1 than in group 2 (0.62±0.06 vs 0.55±0.06, P=0.002). A PDI >0.6 identified unsuccessful OT-VT/VPC with 80% sensitivity and 90% specificity, and may indicate that the origin of the OT-VT/VPC is deep within the ventricular septum or at an epicardial site. Conclusions: A PDI >0.6 is more likely to be associated with a higher rate of RFCA failure. (Circ J 2010; 74: 256-261)