Abnormalities in cardiac function, eg, arrhythmias and congestive heart failure, often accompany thyrotoxicosis. A relationship between thyroid hormone excess and the cardiac complications of angina pectoris and myocardial infarction (MI) remains largely speculative.
The results of thyroid function studies on blood samples drawn from a total of 1049 patients (aged 40 years or older) immediately on emergency medical admission were related to frequencies of angina pectoris and myocardial infarction as determined according to current diagnostic algorithms. After 3 years, those patients who had initially presented with angina pectoris or acute MI were observed for subsequent coronary events; of these (n=185), 98% of the subjects (n=181) could be reevaluated.
On hospital admission, the relative rate of angina pectoris and MI was markedly high (odds ratio, 2.6; 95% confidence interval, 1.3-5.2; P=.007) in patients with elevated serum free and total triiodothyronine (T3) levels. An initially elevated free T3 level was a risk factor for subsequent coronary events during the 3-year follow-up (adjusted odds ratio, 4.8; 95% confidence interval, 1.3-17.4; P=.02).
An elevation of serum free T3 levels at hospital admission is associated with a 2.6-fold greater likelihood of the presence of a coronary event. Moreover, an initially elevated T3 level is associated with a 3-fold higher risk of developing a subsequent coronary event during the next 3 years. Excess T3 seemed to be a factor associated with the development and progression of acute myocardial ischemia.