Echocardiographic LV function in thyrotoxicosis.

Serial echocardiographic studies were made in 11 patients with thyrotoxicosis. In the untreated thyrotoxic state heart rate was increased (96 ± 14 (SD) beats/minute) as were measurements of left ventricular (LV) contractility. LV shortening fraction was 40 ± 6 per cent (mean ± SD), mean velocity of circumferential fiber shortening was 1.60 ± 0.32 circumferences/sec., and velocity of posterior wall motion 71 ± 13 mm./sec. Stroke index and cardiac index were increased: 52 ± 18 (SD) ml./beat per M.² and 5.0 ± 1.8 (SD) liter/minute per M.², respectively. Cardiac chamber size was normal in all but one very ill patient and did not change during the study. Treatment with propranolol, 60 mg./day, produced a dramatic and immediate improvement in the clinical state of the patient. Heart rate decreased to 84 ± 11 beats/minute (p < 0.01), stroke index increased marginally (p > 0.05), and cardiac index was unaltered (p > 0.05). There was no change in parameters of LV contractility (p > 0.05). Treatment with a specific antithyroid drug (methimazole or propylthiouracil) brought about further improvement in the clinical state and a further decrease in heart rate (p < 0.01). LV contractility decreased and after two to three months, when the patients were euthyroid, these measurements were in the range of normal (per cent shortening of the LV diameter 37 ± 4, p < 0.01; mean velocity of circumferential fiber shortening 1.31 ± 0.23 circumferences/sec., p < 0.05; maximum velocity of posterior wall motion, 46 ± 14 mm./sec., p < 0.01). Systolic time interval measurements were in keeping with these data. They showed enhanced LV performance in the control state, no change with propranolol, and they returned toward the range of normal after definitive antithyroid treatment.