Effects of aerobic exercise training on indices of ventricular repolarization in patients with chronic heart failure

Background: Patients with chronic heart failure (CIIF) have a markedly incr eased incidence of malignant ventricular arrhythmias. QT dispersion (QTd), defined as the difference between maximal and minimal QT intervals, reflect s the regional inhomogeneity of ventricular repolarization dispersion and m ay mark the presence of malignant ventricular arrhythmias. Purpose: To determine the effects of exercise training on QTd in patients w ith CHF. Patients: Fifteen patients with CHF and ejection fractions < 40% (mean, 28 +/- 9%) who were on a stable medical regimen. Design and intervention: Standardized 12-lead surface ECGs were obtained at the beginning and end of the exercise training program, and QT and JT inte rvals were measured manually and corrected for heart rate by using Bazett's formula. QTd, heart rate-corrected QTd (QTc-d), JT dispersion (JTd), and h eart rate-corrected JTd (JTc-d) were measured in at least eight ECG leads i n each patient. Results: Following the cardiac rehabilitation and exercise training programs, patients with CHF had only slight improvements in exerci se capacity (results were not significant). However, these patients had mar ked improvements in QTd (71 +/- 11 to 59 +/- 17 ms; p < 0.02), QTc-d (82 +/ - 28 to 63 +/- 17 ms: p < 0.01), JTd (76 +/- 19 to 57 +/- 18 ms; p < 0.002) , and JTc-d (84 +/- 23 to 61 +/- 18 ms; p < 0.001) following the exercise t raining programs. Conclusion: These data indicate that aerobic exercise training significantl y reduces the indices of ventricular repolarization dispersion in patients with CHF. Further studies are needed to evaluate how effectively this reduc tion in ventricular repolarization dispersion decreases the risk of maligna nt ventricular arrhythmias and sudden death in patients with CHF.