Evaluation of exercise-induced T wave changes in patients with idiopathic dilated cardiomyopathy before and after...

Ventricular repolarization abnormalities are thought to contribute to lethal ventricular arrhythmias in patients with idiopathic dilated cardiomyopathy (DCM). The purpose of this study was to evaluate exercise-induced T wave changes in DCM patients before and after beta-blocker therapy to investigate repolarization abnormalities.

Treadmill exercise testing was performed in 20 DCM patients and 50 normal subjects. T wave amplitude (TA: baseline to T wave apex; mV) and recovery time (RT: QRS onset to the maximum dV/dt point of the T wave; msec) were measured before and 1 minute after peak exercise. TA was averaged in the right and left precordial leads (TA(V1-3), TA(V4-6)). RT was normalized to the maximum QT interval in the 12-lead ECG and expressed as the %RT (%RT). %RT was also averaged in the precordial leads (%RT(V1-3), %RT(V4-6)). After exercise, TA increased and %RT decreased in both groups. In DCM patients, TA(V1-3) was greater and TA(V4-6) was less than in normal subjects before and after exercise. There was no difference in %RT(V1-3) between the groups, but %RT(V4-6) was greater in DCM patients both before and after exercise. DCM patients repeated the same evaluation after 6 months of oral beta-blocker therapy. Compared with measurements before beta-blocker therapy, TA(V1-3) and %RT(V1-3) did not change. However, TA(V4-6) increased and %RT(V4-6) decreased significantly both before and after exercise.

DCM patients showed small TA and large %RT in the left precordial leads at rest as well as after exercise. Chronic beta-blocker therapy in DCM patients normalized these ventricular repolarization abnormalities.