Evaluation of Exercise-Induced T Wave Changes in Patients with Idiopathic Dilated Cardiomyopathy Before and After Beta-Blocker Therapy

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Abstract

Introduction

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.

Methods and Results

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 (TAV1–3, TAV4–6). 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 (%RTV1–3, %RTV4–6). After exercise, TA increased and %RT decreased in both groups. In DCM patients, TAV1–3 was greater and TAV4–6 was less than in normal subjects before and after exercise. There was no difference in %RTV1–3 between the groups, but %RTV4–6 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, TAV1–3 and %RTV1–3 did not change. However, TAV4–6 increased and %RTV4–6 decreased significantly both before and after exercise.

Conclusion

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.

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