Coexistence of hypothyroidism and myocardial infarction.

OBJECTIVE: To assess the coexistence of overt hypothyroidism and acute myocardial infarction (MI) in respect of clinical and biological manifestations and outcome. DESIGN: Retrospective study of patients with coincident untreated or uncontrolled hypothyroidism presenting to Notre-Dame Hospital with acute MI. Each patient's MI was matched with two controls for date of admission (within three years) of MI, age, sex, diabetes mellitus and number of previous MIs. SETTING: All patients were admitted to Notre-Dame Hospital, which is a secondary and tertiary care institution. PATIENTS: From 1975 to 1990, 5691 patients were seen at the authors' institution with acute MI, of whom 17 had simultaneously an untreated or uncontrolled hypothyroidism. Hypothyroidism was defined as thyroid-stimulating hormone levels greater than 40 mU/L associated with low or normal levels of serum thyroxine. RESULTS: Chest pain was documented in each case. Electrocardiogram location of the MI was inferior in 10 (59%) patients and in 14 (41%) controls, anterior in seven (41%) patients and in 20 (59%) controls. There was a trend towards higher creatine kinase peak levels in patients with hypothyroidism (1409 +/- 1145 U/L versus 943 +/- 788 U/L). The Killip index was similar in the two groups (1.8 +/- 1 versus 1.8 +/- 1), as was the incidence of arrhythmias (seven of 17 versus 11 of 32). There was no significant difference in mortality between the two groups (18% [three of 17] versus 12% [four of 34]). However, the incidence of residual ischemia was greater in patients with hypothyroidism (12 of 17 versus 10 of 34, P < 0.008). CONCLUSIONS: Hypothyroidism is not associated with an unfavourable effect on the clinical course of acute MI. However, patients with hypothyroidism seem to have an increased incidence of residual ischemia.