STUDIES ON THE USE OF THYROID-HORMONE AND A THYROID-HORMONE ANALOG INTHE TREATMENT OF CONGESTIVE-HEART-FAILURE

In heart failure, cardiac output is insufficient to meet the needs of the body for oxygen delivery. Available data suggest that alterations in thyroid hormone metabolism may contribute to defective myocardial p erformance. Accordingly, thyroid hormone or a thyroid hormone analogue that improves cardiac performance might be useful in the treatment of heart failure and has been studied. Experimental and theoretical resu lts of these studies are reviewed and indicate that thyroid hormone in creases cardiac output by a combination of effects on the heart and pe ripheral circulation, specifically by increasing myocardial contractil e performance and decreasing venous compliance. In the rat postinfarct ion model of heart failure, treatment with low doses of thyroxine (1.5 mug/100 g) for 3 days produced a positive inotropic response, includi ng an increase in rate of change of left ventricular pressure and a de crease in left ventricular end-diastolic pressure. These changes could be attributed to conversion to triiodothyronine, the active intracell ular form of thyroid hormone. When treatment with thyroxine was contin ued at the same or higher doses (3 to 15 mug/100 g) for 10 to 12 days, heart rate increased and improvement in left ventricular end-diastoli c pressure was not sustained. More favorable results were obtained wit h 3,5-diiodothyropropionic acid, a cardiotonic thyroid hormone analogu e administered at doses of 375 mug/100 g, given in combination with ca ptopril. Thus, triiodothyronine or a thyroid hormone analogue may be a useful adjunct to other measures in the treatment of heart failure.