926-24 Clinical and Electrophysiological Characteristics in Patients with Exercise Induced Idiopathic Multiform Ventricular Tachycardia. Differential Effects of Atrial Pacing and Isoproterenol Infusion on QTc Interval and Induction of Ventricular Arrhythmia

Abstract

Idiopathic multiform ventricular tachycardia (VT) is characterized by normal QT interval at rest and 3 or more distinct QRS configuration during VT, which has been distinguished from torsade de pointes in long QT syndrome. Facilitation by exercise and suppression by β-antagonist of this VT suggest that it may depend on rapid heart rate (HR) or increased sympathetic tone. To determine which factors is responsible, we performed atrial pacing (120/min) and isoproterenol (ISP) infusion (0.5 or 1.0 μg to attain HR 120/min) in 6 patients (2 males/4 females, mean 15.8 years) and 10 control (4 males/6 females, mean 22.8 years). Inducibility of premature ventricular contraction (PVC) or VT, and response of QTc interval (QT/√RR) were evaluated during the procedures. control multiform VT p value PVCNT induction Atrial pacing 0/7 1/6 n.s. Isoproterenol 0/8 6/6 0.001 OTc (secl/2) Rest 0.40 ± 0.02 (n = 10) 0.40 ± 0.03 n.s. Atrial pacing 0.43 ± 0.02 (n = 7) 0.47 ± 003 <0.01 Isoproterenol 0.44 ± 0.01 (n = 8) 0.50 ± 0.05 <0.001 Although both rapid HR and increased sympathetic tone may be responsible for this VT, contribution of the latter is predominant. Differential response of QT interval to atrial pacing and isoproterenol infusion may have a possible role for the occurrence of this VT.