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 increased incidence of malignant ventricular arrhythmias. QT dispersion (QTd), defined as the difference between maximal and minimal QT intervals, reflects the regional inhomogeneity of ventricular repolarization dispersion and may mark the presence of malignant ventricular arrhythmias. Purpose: To determine the effects of exercise training on QTd in patients with 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 intervals were measured manually and corrected for heart rate by using Bazett's formula. QTd, heart rate-corrected QTd (QTc-d), JT dispersion (JTd), and heart rate-corrected JTd (JTc-d) were measured in at least eight ECG leads in each patient. Results: Following the cardiac rehabilitation and exercise training programs, patients with CHF had only slight improvements in exercise capacity (results were not significant). However, these patients had marked 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 training programs. Conclusion: These data indicate that aerobic exercise training significantly reduces the indices of ventricular repolarization dispersion in patients with CHF. Further studies are needed to evaluate how effectively this reduction in ventricular repolarization dispersion decreases the risk of malignant ventricular arrhythmias and sudden death in patients with CHF.