AN ECHOCARDIOGRAPHIC AND ELECTROCARDIOGRAPHIC STUDY OF CARDIOVASCULARFUNCTION IN HYPOTHYROID DOGS

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