USEFULNESS OF L-THYROXINE TO IMPROVE CARDIAC AND EXERCISE PERFORMANCEIN IDIOPATHIC DILATED CARDIOMYOPATHY

The short-term effects of L-thyroxine (100 mu g/day, 10 patients) and placebo (ib patients) on idiopathic dilated cardiomyopathy were compar ed. Before and at the end of the treatment, a hemodynamic study was pe rformed in the control state and during dobutamine infusion. A cardiop ulmonary exercise test was also performed with hemodynamic monitoring. An echocardiogram was recorded in the control state and during acute changes of left ventricular afterload. Plasma revels of triiodothyroni ne, thyroxine, thyroid-stimulating hormone and norepinephrine were mea sured. Placebo was ineffective. After administration of L-thyroxine al l patients had normal thyroid function. The increase in left ventricul ar ejection fraction and the rightward shift of the slope of left vent ricular ejection fraction/end-systolic stress relation (p < 0.05) indi cated an improvement in the cardiac inotropic state. This proved to be independent of adrenergic influences by the unchanged beta(1) respons e to dobutamine. A decrease in resting systemic vascular resistances a nd an increase in cardiac output (p < 0.05) were also observed. Cardio pulmonary effort parameters improved (p < 0.05) without hemodynamic ch anges at peak exercise. It is concluded that L-thyroxine short-term ad ministration improves cardiac and exercise performance in patients wit h chronic heart failure, without modifying the adrenergic support to t he heart and the circulatory parameters at peak exercise.