The nature and prognosis of thyrotoxic heart disease.

Thirty-two patients with uncomplicated hyperthyroidism were compared to 17 patients deemed to be suffering from pure thyrotoxic cardiac failure, other heart disease having been excluded. The thyrotoxic failure group were older and had clinically and biochemically milder endocrinal abnormalities for a longer time. Haemodynamic studies at rest and exercise showed that the thyrotoxic failure patients had no functional cardiac reserve. Their response to propranolol indicated that myocardial function was dependent on beta-adrenergic activity. Following specific anti-thyroid medication cardiac function returned to normal in the majority of cases with cardiac failure. This study shows that hyperthyroidism by itself can cause a reversible cardiomyopathy.