Hyperthyroidism as a high cardiac output state.

Abstract Hyperthyroidism is the most common cause of hyperkinetic circulatory disease. Thyroid hormone probably produces this high output state by inducing vasodilatation of the circulatory beds supplying muscle and skin. This hormone induced effect lowers the total peripheral resistance which increases cardiac output. The heart responds to the low peripheral resistance by accelerating the heart rate and augmenting stroke volume. In addition, the thyroid hormone enhances ventricular contractility. These cardiac responses are generated by a direct effect of thyroid hormone on the cardiovascular system and are essentially independent of autonomic influence. Thyrotoxicosis can induce congestive heart failure without complicating influences. Present information does not allow a full explanation of this phenomenon, but improper utilization of energy by an oversized heart may be a contributing factor. Adequate treatment of this high cardiac output state, whether or not it is accompanied by congestive heart failure, cannot be properly accomplished without vigorous treatment of the underlying endocrine disorder. Most adjunctive therapeutic measures presently recommended are of only slight and temporary benefit. Digitalis and diuretics can help control the manifestations of heart failure and should be used when these symptoms are present. Bed rest in a quiet environment is certainly more important in reducing the circulatory load of an already overstressed heart. Reserpine and other autonomic-blocking drugs cannot be recommended on a rational scientific basis. There is little evidence that these agents have any salutory effect on the circulatory disease of hyperthyroidism.