Influence of beta sympathetic blockade (propranolol) on the hemodynamics of hyperthyroidism

Abstract

The circulatory effects of propranolol (0.15 to 0.38 mg. per kg. given intravenously) were studied in seven hyperthyroid patients during periods of rest and exercise before and after the administration of propranolol and the results compared with propranolol effects in euthyroid subjects. Indices of left ventricular work (LVWI); stroke work (SWI); left ventricular tension time (TTI); mean systolic ejection rate (MSER); and cardiac output (CI) were derived in the usual manner. The mean rate of left ventricular isovolumetric pressure development (MRIPD) was employed as an index of contractility. Propranolol altered the thyrotoxic hyperkinetic circulatory state toward euthyroid levels. The mean changes after administration of propranolol in exercising hyperthyroid patients were heart rate decreased 19 per cent (P < 0.01), TTI decreased 18 per cent (P < 0.01), MRIPD decreased 14 per cent (P < 0.01). Comparison of the data in hyperthyroid patients with those in normal subjects showed an exercise increment in CI (35 per cent) and TTI (38 per cent) and LVWI (95 per cent) (P < 0.05) in excess of that seen in euthyroid subjects. Since TTI is generally considered a major determinent of myocardial oxygen consumption, the ratio of LVWI:TTI was considered an estimate of myocardial efficiency. Following propranolol administration LVWI:TTI increased 14 per cent (P < 0.05), indicating enhanced efficiency. It is concluded that beta adrenergic blockade attenuates the positive inotropic and chronotropic effects of thyroid hormone and presumably reduces the exaggerated myocardial oxygen requirement of thyrotoxicosis. Myocardial efficiency is thereby improved. The study supports the concept that the cardiac effects of thyroid hormone are mediated at least in part via the sympathetic nervous system.