Background: Low time domain measures of heart rate variability (HRV) have been shown to predict outcome after myocardial infarction (MI). The predictive value of HRV, when measured in patients with coronary artery disease (CAD) without MI is less clear. Further, little is known about the mechanisms of how autonomic imbalance affects outcome.
Methods and design: Forty patients following percutaneous coronary intervention (PCI) with stent implantation for angina pectoris were prospectively randomized to a six month supervised high-intensity interval training program (n=20) or to a control group (n=20). All patients underwent a 24-hour Holter monitoring to assess measures of HRV at baseline and at six months.
Results: At baseline there were no significant differences between groups. In the training group all time domain indices and the frequency domain indices, total power and ultralow frequency of HRV, increased significantly during the training period. Mean heart rate decreased significantly. In the control group only the root mean square of differences between successive NN intervals (ln RMSSD) increased significantly. Changes in standard deviations of the average NN intervals (SDANN) and ln RMSSD were significantly correlated to changes in peak VO(2) (R=0.47 and 0.39; p<0.01 and p=0.03 respectively). HRV measures were not significantly correlated to endothelial function.
Conclusions: High-intensity exercise training over 6 months significantly improved time and frequency domain measures of HRV in patients following PCI with stent implantation. The effect on HRV was correlated to changes in peak VO(2), but not to changes in endothelial function.
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