Adenosine-Sensitive Ventricular Tachycardi From the Anterobasal Left Ventricle

Objectives. This study demonstrates that exercise-provocable tachycardi resembling right ventricular outflow tract tachycardi may originate from the anterobasal left ventricle. Background. Reentry is the operative mechanism of idiopathic left ventricular tachycardia, with QRS complex of right bundle branch block and superior axis that is responsive to verapamil but not adenosine. Whether some mechanism other than reentry is operative in some idiopathic left ventricular tachycardias is unclear. Methods. In 4 of 53 consecutive patients with idiopathic left ventricular tachycardia, the tachycardi was sensitive to adenosine. These four patients were women 63, 61, 61 and 31 years old and were the subjects of the present study. Results. In all four patients, spontaneous tachycardi was related to exercise or emotional stress. The tachycardi displayed atypical left (one patient) or right (three patients) bundle branch block with an inferior axis and marked variation in cycle length. An intravenous bolus of adenosine triphosphate (10 to 20 mg) terminated tachycardi in all four patients. Tachycardi was terminated or prevented in three patients given intravenous or oral verapamil. Atrial or ventricular incremental or extrastimulus testing induced tachycardi in all four patients (three with, one without isoproterenol infusion). Electrically induced tachycardi also demonstrated marked variation in cycle length, which ranged from 230 to 390 ms. Entrainment was not demonstrable with overdrive pacing from multiple sites. Endocardial mapping during tachycardi revealed that the earliest activations were registered 25, 40, 35 and 50 ms before onset of the QRS complex, respectively, from the anterior aspect of the left ventricle just below the mitral annulus, adjacent to the left ventricular outflow tract. High frequency Purkinje spikes were not recorded at this site. Radiofrequency current delivered to this site successfully ablated the tachycardi in three of the four patients. Conclusions. Exercise-provocable, catecholamine-mediated, verapamil-responsive, adenosine-sensitive ventricular tachycardi may arise from the anterobasal left ventricle adjacent to the outflow tract.