Sympathovagal Balance Prior to Onset of Repetitive Monomorphic Idiopathic Ventricular Tachycardia

Repetitive monomorphic idiopathic (RMI) ventricular tachycardia (VT) occurs typically in patients without structural heart disease, originates in most cases from the right ventricular outflow tract, and can often be induced by exercise or isoproterenol. This study analyzed the dynamic changes in autonomic tone immediately before the spontaneous onset of RMIVT using frequency-domain heart rate variability (HRV) indices. We analyzed the ambulatory electrocardiographic recordings from 6 men and 8 women (mean age: 43 +/- 18 years; mean number of VT runs per day: 134 +/- 213; mean VT rate: 194 +/- 40 bpm; median VT run length: 4 cycles) with RMIVT. A total of 36 clusters of nonsustained episodes of RMIVT preceded by >/=1 hour of sinus rhythm without VT were analyzed (25 minutes before the onset of RMIVT divided into five 5-minute periods; 8 minutes before onset of RIMVT divided into eight 1-minute periods). During 25 minutes preceding the onset of VT, the mean RR interval decreased from 767 +/- 118 to 723 +/- 105 ms (P = 0.015) and the low-frequency (LF)/high-frequency (HF) ratio increased from 2.24 +/- 0.79 to 2.49 +/- 1.0 (P = 0.03). During the 8 minutes before VT onset, the mean RR interval decreased from 745 +/- 118 to 718 +/- 102 ms (P = 0.001) and the LF components increased from 205 +/- 72 to 253 +/- 113 ms (P = 0.014). No change in HF components was observed during the 25 or 8 minutes periods preceding the RMIVT onset. The changes in HRV indices suggest a strong time-dependent primary activation of sympathetic tone prior to the occurrence of RMIVT. Withdrawal of vagal tone does not appear essential to the initiation of RMIVT clusters.