Increased sympathetic nervous system activity as cause of exercise-induced ventricular tachycardia in patients with normal coronary arteries.

In this prospective study, we set out to determine whether analysis of heart rate variability (HRV) in patients with exercise-induced ventricular tachycardia (EIVT) and normal coronary arteries would reveal increased sympathetic nervous system activity. From January 1996 to December 2001, we compared 16 patients with EIVT and normal coronary arteries with an age- and sex-matched control group. Analysis of HRV showed that parameters indicative of parasympathetic activity were lower in our study group than in our control group: standard deviation of the mean of qualified NN intervals (SDNN), 81.6 +/- 14.5 vs 139.3 +/- 11.0, P <0.001; root mean square of successive differences (RMSSD), 22.3 +/- 4.8 vs 36.3 +/- 6.6, P <0.001; number of NN intervals that differed by more than 5 ms from the adjacent interval, divided by the total number of NN intervals (PNN50), 4.8 +/- 1.5 vs 10.2 +/- 3. 1, P <0.001; and high-frequency component (HF), 28.7 +/- 2.5 vs 32.4 +/- 3.9, P <0.05. Conversely, parameters indicative of sympathetic activity were higher in patients with EIVT: low-frequency component (LF), 71.2 +/- 5.0 vs 52.0 +/- 5.8, P <0.001; and absolute low/high frequency component ratio (LF/HF), 2.7 +/- 0.2 vs 1.6 +/- 0.2, P <0.001. There was a positive correlation between EIVT and LF (r=0.79, P <0.001) and between EIVT and LF/HF (r=0.81, P <0.001). Our results suggest the presence of increased sympathetic and decreased parasympathetic tone in patients with EIVT. We conclude that EIVT is associated with an imbalance in the autonomic nervous system.