[The improvement in physical exercise capacity in dilated cardiomyopathy during short-term treatment with L-thyroxine].

: Reduced left ventricular function and other factors, such as vascular resistances, redistribution of cardiac output and impaired muscular metabolism, limit exercise performance in chronic heart failure. Thyroid hormones have a positive cardiac inotropic effect, stimulate protein synthesis (particularly at muscular level) and reduce peripheral vascular resistances with consequent increase of cardiac output. Therefore, it is possible that thyroid hormones can improve exercise performance in chronic heart failure. We have administered L-thyroxin (100 mcg/die) for 1 week to 9 patients affected by primary dilated cardiomyopathy. All the patients were euthyroid (T3 = 1.06 +/- 0.1 mcg/ml, T4 = 8.5 +/- 1.9 mcg/dl, TSH = 1.32 +/- 0.7 mU/ml) and in II-III NYHA functional class. Before starting the treatment and at the end of it, we performed the cardiopulmonary exercise test and the echocardiogram. We also evaluated the resting hemodynamic parameters through catheterization and the plasmatic values of thyroid hormones and noradrenaline. At the end of the treatment all patients were euthyroid, despite a significant (p less than 0.05) increase of T4 (10.5 +/- 3.2 mcg/dl) and a decrease of TSH (1.1 +/- 0.1 mU/ml). Mean values of effort parameters changed as follows: peak oxygen consumption from 19.6 +/- 1.6 to 20.6 +/- 1.3 ml/min/kg, tolerance time from 460 +/- 61 to 481 +/- 60 s. These variations were not associated with changes in resting hemodynamic parameters and noradrenaline. Left ventricular ejection fraction, calculated by echocardiography, increased from 26 +/- 6 to 28.9 +/- 8% (p less than 0.05). We conclude that in dilated cardiomyopathy short term treatment with L-thyroxin significantly improves patient's response to cardiopulmonary exercise test.(ABSTRACT TRUNCATED AT 250 WORDS)