Ventricular tachycardias mimicking those arising from the right ventricular outflow tract

Introduction: Ablation of ventricular tachycardia (VT) arising from the rig ht ventricular outflow tract (RVOT) has proven highly successful, yet VTs w ith similar ECG features may originate outside the RVOT. Methods and Results: We reviewed the clinical, echocardiographic, and ECG f indings of 29 consecutive patients referred for ablation of monomorphic VT having a left bundle branch block pattern in lead V-1 and tall monophasic R waves inferiorly, Nineteen patients (group A) had VTs ablated from the RVO T, and 10 patients (group B) had VTs that could not be ablated from the RVO T, The QRS morphology during VT or frequent ventricular premature complexes was the only variable that distinguished the two groups. During the target arrhythmia, ECGs of group B patients displayed earlier precordial transiti on zones (median V-3 vs V-5; P < 0.001), more rightward axes (90 +/- 4 vs 8 3 +/- 5; P = 0.002), taller R waves inferiorly (aVF: 1.9 +/- 1.0 vs 2.4 +/- 0.5; P = 0.020) and small R waves in lead V-1 (10/10 vs 9/19; P = 0.011). Radiofrequency catheter ablation from the RVOT failed to eliminate VT in an y group B patient, but ablation from the left ventricular outflow tract (LV OT) eliminated VT in 2 of 6 patients in whom left ventricular ablation was attempted. Conclusion: The absence of an R wave in lead V-1 and a late precordial tran sition zone suggest an RVOT origin of VT, whereas an early precordial trans ition zone characterizes VTs that mimic an RVOT origin. The latter VTs occa sionally can be ablated from the LVOT, Recognition of these ECG features ma y help the physician advise patients and direct one's approach to ablation.