The Role of Parasympathetic Modulation of the Reentrant Arrhythmic Substrate in the Genesis of Sustained Ventricular Tachycardia

The influence of parasympathetic activity on the reentrant arrhythmic substrate in the genesis of sustained ventricular tachycardia remains unclear. To assess this influence, we studied the heart rate variability in 59 patients referred for invasive electrophysiological testing. In addition, the presence of late potentials and high grade ventricular ectopy, and the left ventricular ejection fraction was determined. The 28 patients with inducible sustained ventricular tachycardia were found to have lower heart rate variability by time- and frequency-domain measurements over 24 hours when compared to the 31 subjects who were noninducible. PNN50 was 4% in the inducible patients, whereas it was 9% in the subjects who were noninducible (P = 0.03). Similarly, HFP24H was 9 and 14 msec, respectively (P = 0.02). MAXHFP1H also differed (20 vs 27 msec [P = 0.04]) but not MINHFP1H (5 vs 6 msec). There was no association between heart rate variability and late potentials, degree of ventricular ectopy, or left ventricular ejection fraction. Thus, vagal tone does not appear to correlate with the presence of late potentials, ventricular ectopy, or left ventricular dysfunction. Low mean as well as maximal vagal tone, in contrast to minimal vagal tone, predicts inducibility of sustained ventricular tachycardia. Our data suggest that the inability to modulate parasympathetic tone appears to be an important determinant in the genesis of reentrant sustained ventricular tachycardia.