Evaluation of exercise-induced T wave changes in patients with idiopathic dilated cardiomyopathy before and after beta-blocker therapy.
ABSTRACT 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.
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ABSTRACT: To map global epicardial repolarization patterns and test the "SI" model of T wave generation, the patterns of epicardial activation and repolarization in patients with chronic pulmonary thromboembolism and right ventricular hypertrophy were studied by computerized mapping techniques and monophasic action potential (MAP) recording. The ventricular activation patterns were characterized by delayed right ventricular activation and the absence of normal early epicardial ventricular breakthrough in some cases. The repolarization patterns were characterized by nonuniform distribution of T wave morphologies. The T waves were predominantly positive over the left ventricular epicardium and negative or biphasic over the right ventricular epicardium. The activation-recovery (A-R) intervals were measured from the local activation to the maximal dV/dt of the upstroke of the T waves (Wyatt method). The difference between the A-R intervals and the MAP from onset of activation to 90% repolarization (MAP90) varies according to T wave morphology and could be as high as 96 msec with positive T waves, despite significant correlations (r = 0.56-0.90) between MAP90 and A-R intervals for each morphology. Better overall correlations were found if the minimal dV/dt on the downslope of the positive T waves was chosen to estimate the time of local repolarization (alternative method). Using this method, the mean A-R intervals were the same over the right and left ventricles. Cardiopulmonary bypass significantly prolonged the action potential duration equally at all parts of the epicardium. We conclude that in patients with right ventricular hypertrophy, the time of local repolarization can be estimated by our alternative method; the right ventricle completes activation and repolarization later than the left ventricle, and the distribution of T wave morphologies is nonuniform, with predominantly positive T waves observed over the left ventricle and negative or biphasic T waves observed over the right ventricle. These findings are compatible with the SI model of the generation of T waves.Circulation 02/1991; 83(1):104-18. · 15.20 Impact Factor
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ABSTRACT: QT dispersion was measured in the 12-lead standard electrocardiogram in 107 patients with idiopathic dilated cardiomyopathy (IDC) and 100 age- and sex- matched controls without structural heart disease. All 107 study patients with IDC were prospectively followed in order to determine possible associations between QT dispersion and arrhythmic events, i.e., sustained ventricular tachycardia, ventricular fibrillation, or sudden death. QT dispersion, rate-corrected QT dispersion, and adjusted QTc dispersion, which takes account of the number of leads measured, were significantly greater in patients with IDC than in controls. During 13 +/- 7 months follow-up, arrhythmic events occurred in 12 of 107 study patients with IDC (11%). QT dispersion was increased in patients with versus without arrhythmic events during follow-up (76 +/- 17 vs 60 +/- 26 ms; p=0.03). QTc dispersion and adjusted QTc dispersion were not significantly different between patients with and without arrhythmic events (80 +/- 21 vs 75 +/- 35 ms, and 27 +/- 6 vs 24 +/- 10 ms, respectively). Thus, although QT dispersion was increased in patients with IDC and arrhythmic events during follow-up, its usefulness for arrhythmia risk prediction was limited by the large overlap of QT dispersion between patients with and without arrhythmic events.The American Journal of Cardiology 09/1996; 78(4):458-61. · 3.21 Impact Factor
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ABSTRACT: Twenty-five healthy black men between 17 and 21 years of age were evaluated. Their resting and exercise electrocardiograms were recorded at simulated sea level and at a simulated altitude of 4,000 m. Sea level exercise caused a reduction in the amplitudes of R waves and a lowering of J points. Exercise at a simulated altitude of 4,000 m caused a lowering of the J point in several leads and a reduction of the R wave amplitude in lead aVF. Hypoxia caused a reduction in the amplitudes of the T waves and a lowering of the J points in several leads. These effects of exercise and altitude, to a great extent, eliminated the appearance of "early repolarization," which is very common among young black men.Journal of Electrocardiology 08/1992; 25(3):197-201. · 1.09 Impact Factor