Medium-term effectiveness of L-thyroxine treatment in idiopathic dilated cardiomyopathy

Background In dilated cardiomyopathy, short-term administration of L-thyroxine (100 μg/ day) improves cardiac and exercise performance without changing the heartʹs adrenergic sensitivity. The aim of this study was to test the medium-term (3 months) efficacy of L-thyroxine (10 patients) compared with placebo (10 patients) and to find out whether later effects are obtainable. Methods Echocardiographic parameters in the control state and during acute changes of left ventricular after load, cardiopulmonary exercise test, and hemodynamic parameters, including cardiac β1 responses to dobutamine, were obtained before and at the end of treatment. Results Significant (P<0.05) changes were observed only with the active drug. After L-thyroxine, patients did not show evidence of chemical hyperthyroidism, despite the increase in thyroxine and the reduction in thyroid-stimulating hormone plasma levels. Cardiac performance improved, as shown by the increase in the left ventricular ejection fraction and rightward shift of the slope of the relation left ventricular ejection fraction/end-systolic stress. Resting cardiac output increased, and the left ventricular diastolic dimensions and systemic vascular resistances decreased. The responses of cardiac output and heart rate to dobutamine infusion were also enhanced. Functional capacity markedly improved, together with an increase in peak exercise cardiac output. Conclusion L-thyroxine does not lose its beneficial effects on cardiac and exercise performance on medium-term administration and does not induce adverse effects. In addition to the short-term study, the left ventricular diastolic dimensions were decreased. An up-regulation of β1 receptors might explain the cardiac response to dobutamine.