Effects of exercise training on the heart rate variability and QT dispersion of patients with acute myocardial infarction

Heart rate variability (HRV) reflects the autonomic tone of the heart, and QT dispersion reflects the regional inhomogeneity of ventricular repolariza tion. The purpose of the present study was to determine the effects of earl y exercise training on HRV and QT dispersion in patients with acute myocard ial infarction (AMI). Forty patients (mean age: 59 years) with AMI were ran domized to training rehabilitation (group Tr, n=20) or conventional rehabil itation (group C, n=20). Two weeks after AMI, group Tr underwent 10 min of exercise using a bicycle ergometer (80% of anaerobic threshold) twice a day . At the end of the second and fourth weeks, 12-lead and 24-h Holter ECGs w ere recorded. QT intervals were measured and corrected using Bazett's formu la (QTc), and QTc dispersion (QTcd) was defined as the difference between m aximum and minimum QTc. HRV was accessed by the high-frequency component (H F: 0.15-0.40 Hz) of the HRV power spectrum (parasympathetic activity) and t he ratio of low frequency (0.04-0.15 Hz) to HF (L/H ratio: sympathetic acti vity). In group Tr, HF increased (82.5 to 131.1 ms(2)), the L/H ratio decre ased (3.9 to 2.6), and QTcd decreased (77.2 to 57.2 ms). In group C, none o f the indices changed. It was concluded that early exercise training improv es sympathovagal balance and decreases QTcd, and may reduce the arrhythmoge nic substrate following AMI.