Thyroid Dysfunction in Patients With Myocardial Infarction With Normal Coronary Arteries

Abstract

Recently, in a pilot study, we 1 compared risk factors in patients with myocardial infarction (MI) with normal coronary arteries (MINCAs) with data from patients with MI with coronary artery stenosis. In a letter to the journal, Gunebakmaz and coworkers 2 comment on the role of hyperthyroidism in patients with MINCA.Both hypothyroidism and hyperthyroidism have been associated with increased risk of coronary heart disease (CHD) events in previous reports. Subclinical hyperthyroidism is defined as a patient having normal free thyroxine and total triiodothyronine levels in conjunction with a thyrotropin (TSH) level persistently below the normal range in the absence of factors known to suppress TSH. In the HUNT study, which included 26 707 people without previously known thyroid or cardiovascular disease or diabetes at baseline, a high TSH within the reference range was associated with increased risk of coronary death in women, but not in men after 12 years of follow-up. The risk of coronary death was also increased among women with subclinical hypothyroidism or subclinical hyperthyroidism, compared to women with TSH of 0.50 to 1.4 mU/L. However, thyroid function was not associated with the risk of being hospitalized with MI. 3In a meta-analysis, 55 287 participants with 542 494 personyears from 11 prospective cohorts, the authors reported that subclinical hypothyroidism was associated with an increased risk of CHD events and CHD mortality. 4 Another metaanalysis consisting of 52 674 participants pooled from 10 cohorts reported that endogenous subclinical hyperthyroidism was associated with increased risks of total CHD mortality and incident atrial fibrillation.5 In a population-based cohort study, in patients treated for thyroid dysfunction, event rates among patients with thyroid dysfunction were compared to rates in the general population. There were 15 889 patients with primary hypothyroidism and 3888 patients with hyperthyroidism. There was no increase in all-cause mortality in participants with treated thyroid disease. However, there was increased risk of cardiovascular morbidity in patients with treated primary hypothyroidism and dysrhythmias in treated hyperthyroidism. 6 Also, the risk of heart failure may be increased with both higher and lower TSH levels.7 Individual data on 25 390 participants with 216 248 person-years of follow-up were supplied from 6 prospective cohorts in the United States and Europe. In age-and sex-adjusted analyses, risks of heart failure events were increased with both higher and lower TSH levels.Since there are a few case reports reporting MI in patients with subclinical hyperthyroidism with angiographically normal coronary arteries, [8][9][10] Gunebakmaz and coworkers 2 ask for data on thyroid status in our pilot study.1 The problem is that the incidence of subclinical hyperthyroidism may be as low as approximately 1% in the general population.11 Therefore, our study is far too small to answer this important issue. We need larger studies on patients with MINCA to evaluate this int...