Effect of thyroid hormones excess on left ventricular function in thyrotoxic patients: Effects of metoprolol versus carbimazole

ABSTRACT

To determine the role of beta adrenoreceptors in the pathophysiology of thyroid hormones excess on left ventricular [LV] function, 12 patients with thyrotoxicosis were studied before and after using beta adrenoreceptor blocker metoprolol [M] versus antithyroid drug carbimazole [C]. LV functions were assessed by Doppler echocardiography. M and C were equally effective in slowing the heart rate. Both drugs equally prolonged preejection/ejection time ratio, while C, but not M, significantly slowed the velocity of LV circumferential fiber shortening suggesting direct effect of thyroid hormones on myocardial contractility. However, both drugs showed similar effect on LV diastolic function by prolonging time to peak LV filling and increasing early to peak mitral flow velocity ratio [E/A]. However, the increase in E/A was due to decrease in A velocity with atrial contraction suggesting increased atrial contractility in thyrotoxicosis. In conclusion, thyroid hormones excess increased myocardial contractility by direct effect, and increased heart rate, atrial contraction and LV relaxation by increasing cardiac beta adrenoreceptor activity