The Effect of Beta Adrenergic Blocking Drugs on Left Ventricular Function in Thyrotoxicosis

Summary

Propranolol is a beta adrenergic blocking drug used to diminish the tremor, palpitations and tachycardia of thyrotoxic patients. It reduces cardiac output and myocardial contractility. We have examined the effect of propranolol on the left ventricular function of 20 patients with hyperthyroidism. Serial changes in left ventricular volume, ejection fraction and systolic ejection rate were monitored, allowing the construction of time-activity curves before and after 40 mg of oral propranolol hydrochloride (Inderal). Using an equilibrium multiple gated technique with in vivo ^99mTc red blood cell labelling, left ventricular performance was observed for as long as 3 h. In 20 patients treated with propranolol, the LVEF decreased by 20%, the maximum systolic ejection rate by 30% and the time of electromechanical systole increased by 25% over a 2-h period.