High-Intensity Interval Exercise Improves Vagal Tone and Decreases Arrhythmias in Chronic Heart Failure

Purpose: Autonomic dysfunction including sympathetic activation and vagal withdrawal has been reported in patients with chronic heart failure (CHF). We tested the hypotheses that high-intensity interval exercise (HIIE) in CHF patients would enhance vagal modulation and thus decrease arrhythmic events. Methods: Eighteen CHF patients underwent a baseline assessment (CON) and were then randomized to a single session of HIIE and to an isocaloric moderate-intensity continuous exercise (MICE). We evaluated the HR, HR variability parameters, and arrhythmic events by 24-h Holter ECG recordings after HIIE, MICE, and CON sessions. Results: We found that HR was significantly decreased after HIIE (68 +/- 3 bpm, P < 0.01) when compared with CON and MICE values (71.1 +/- 2 and 69 +/- 3 bpm, respectively). HIIE led to a significant increase in normalized high-frequency power (35.95% +/- 2.83% vs 31.56% +/- 1.93% and 24.61% +/- 2.62% for CON and MICE, respectively, P < 0.01). Both exercise conditions were associated with an increase in very low frequency power comparative to CON. After HIIE, premature ventricular contractions were significantly decreased (531 +/- 338 vs 1007 +/- 693 and 1671 +/- 1604 for CON and MICE, respectively, P < 0.01). An association was found between the changes in premature ventricular contraction and the changes in low-frequency/high-frequency ratio (r = 0.66, P < 0.01) in patients exposed to HIIE. Conclusion: We demonstrate that a single session of HIIE improves autonomic profile of CHF patients, leading to significant reductions of HR and arrhythmic events in a 24-h posttraining period. Cardioprotective effects of HIIE in CHF patients need to be confirmed in a larger study population and on a long-term basis.