Autonomic and Pharmacological Responses of Idiopathic Ventricular Tachycardia Arising from the Left Ventricular Outflow Tract

Abstract

It is well recognized that the mechanism of idiopathic ventricular tachycardia (VT) arising from the right ventricular outflow tract (RVOT) is mostly due to cyclic AMP-mediated triggered activity. The mechanism of VT arising from the left ventricular outflow tract (LVOT) has not been well clarified whether it is the same as VT of RVOT. We studied autonomic modulations and pharmacological interventions on VT/premature ventricular contractions (PVCs) from LVOT to explore its possible mechanism in six patients (age: 49 +/- 14, three males). None of them had structural heart diseases. Isoproterenol application easily induced VT and/or PVCs from LVOT. Valsalva maneuvers suppressed isoproterenol-induced VT in two and PVCs in two, and carotid sinus massage (CSM) suppressed PVCs in one patient. Adenosine triphosphate inhibited both VT and PVCs in all six patients. Propranolol, lidocaine, and procainamide eliminated VT/PVCs in four, three, and four patients, respectively. Verapamil terminated VT in one and PVCs in another one patient, but aggravated PVCs to VT in one patient. The results suggest that the mechanism of VT from LVOT is mostly due to cAMP-mediated triggered activity as similar to that in VT from RVOT.