An echocardiographic and electrocardiographic study of cardiovascular function in hypothyroid dogs

Echocardiograms and ECG were obtained for 11 hypothyroid dogs before and after levothyroxine supplementation (0.022 mg/kg of body weight, q 12 h for 64 +/- 12 days). Evidence of impaired left ventricular function was found in the dogs before treatment. A significant decrease in shortening fraction and velocity of circumferential fiber shortening, increase in left ventricular end-systolic diameter, and prolongation of preejection period was noted when comparing measurements before and after levothyroxine supplementation. Amplitude of the P and R waves was significantly higher after treatment than before. It was concluded that changes in cardiac function can be reversed in hypothyroid dogs.