Acute myocardial infarction and Graves thyrotoxicosis
RA Chudleigh, PJD Owen, S Bhattachrya & JS Davies
The link between thyrotoxicosis and coronary artery disease is complex with associations between therapy and vasculitis, as well as thyroid hormone excess and coronary artery spasm described. We present a 37-year-old female with a one-year history of Graves thyrotoxicosis treated with Propylthiouracil, who presented acutely with chest pain and a left hemiparesis. Typical electrocardiography changes and elevation of Troponin T confirmed a recent myocardial infarction, and CT scanning demonstrated a right cerebral infarction. Echocardiography demonstrated severely impaired left ventricular function with a suspected left ventricular thrombus. Persistent thyrotoxicosis was also demonstrated with a T4=120 pmol/l and TSH<0.02 mU/l. Beta-blockers and Propylthiouracil, together with Aspirin, Enoxaparin and Simvastatin were commenced. Warfarin was started 10 days later. At that stage coronary angiography demonstrated severe left main stem stenosis.
Following the restoration of euthyroidism, repeat angiography demonstrated complete resolution of the left main stem stenosis. Normal left ventricular function was noted on repeat echocardiography. These findings suggest coronary artery spasm in association with thyrotoxicosis.
Coronary artery spasm can account for myocardial infarction in the absence of atherosclerosis. Abrupt decrease in the diameter of epicardial coronary arteries leads to myocardial ischemia, which if prolonged leads to myocardial infarction. Thyrotoxicosis is a recognised cause of coronary artery spasm and enhanced sympathoadrenal activity is a postulated mechanism. Increased numbers of myocardial beta-adrenergic receptors, increased sensitivity of these receptors and increased myocardial tissue levels of catecholamines are thought to mediate this. This provides a rationale for the successful use of sympatholytic agents here. Our patient responded well to rapid restoration of euthyroidism with beta blockade and Propylthiouracil together with conventional cardiac therapy. Once euthyroid a block and replace regime was employed pending radioactive iodine therapy.