Effect of timolol on clinical features and echocardiographic assessment of left ventricular function in hyperthyroidism.

The effect of timolol, a beta-adrenoceptor blocking drug on the clinical status, thyroid status and left ventricular function as measured by serial M-mode echocardiographic recordings was assessed in a double-blind randomised study in 18 hyperthyroid patients. A significant clinical improvement was documented after 2 weeks of timolol treatment compared with placebo. There was no evidence that timolol impaired peripheral monodeiodination of thyroxine (T4). There were significant increases in left ventricular fractional shortening (Fr. Sh.) and velocity of circumferential shortening (Vcf) as well as a significant decrease in the left ventricular systolic internal dimension (LVIDs) (all P less than 0.01) in the untreated thyrotoxic patients compared with a normal euthyroid control group. After timolol treatment (2/52) there were significant increases in LVIDs and LVIDd and a significant decrease in Vcf (all P less than 0.05). No further changes occurred after a further 2/52 treatment with carbimazole. The cardiac data suggest that both an augmented sympathetic drive and a direct effect of thyroid hormone on myocardial contractility are mediators of the haemodynamic changes in hyperthyroidism.