Hypothyroid Status Predicts Poor Outcomes Following Acute Myocardial Infarction

Hypothyroidism was found to be an independent predictor of adverse cardiovascular events in patients who experienced acute myocardial infarction (AMI), according to the results of a study published in Endocrine.

In recent years, the role of thyroid dysfunction in AMI has been of interest to the medical community, with animal models identifying that “hypothyroidism aggravates multiple pathological alterations” following MI, the study authors stated.

Previously published research has found that in patients with AMI, rapid fluctuations in thyroid hormone levels are common during the 24 to 36 hours prior to symptom onset; these levels also correlate closely with the extent of myocardial damage and recovery of cardiac function, noted the study authors.

In the current study, the researchers evaluated the prognostic role of thyroid dysfunction in AMI. The large, prospective cohort included patients from the China Patient-centered Evaluative Assessment of Cardiac Events (China PEACE) study. The investigators sought to present “more persuasive data” on the role of thyroid status in AMI prognosis independent of other risk factors.

The China PEACE study (ClinicalTrials.gov Identifier: NCT01624909) included patients from 53 hospitals in 21 provinces in China who were hospitalized for AMI and were enrolled beginning December 2012; follow-up was terminated in June 2015. The researchers collected baseline data and data from months 1, 6, and 12 after hospital discharge.

A diagnosis of AMI was made based on cardiac biomarker levels with at least 1 value above the 99th percentile of the upper reference limit. The reference range for free T3 was 2.76 to 6.30 pmol/L, for free T4 was 10.3 to 24.2 pmol/L, and for thyroid stimulating hormone was 0.3 to 5.0 mIU/L.

The total cohort included 2569 patients (mean age, 61.1±11.9 years; 76.6% men) who experienced AMI. The cohort was divided into 3 groups based on thyroid function: euthyroid (n=2036), hypothyroid (n=431), and hyperthyroid (n=102).

Patients with hypothyroidism were older (aged 63±12.4 years; P =.001); more likely to be women (32.7%; P <.001); and more likely to have a history of diabetes, hypertension, dyslipidemia, coronary artery disease, angina, heart failure, and/or renal failure. Patients in the hyperthyroid group were more likely to be smokers and had higher heart rates on hospital admission.

Incidence of in-hospital heart failure was higher among the patients with hypothyroidism than in the other 2 groups; however, this difference was not statistically significant. Rates of in-hospital cardiac arrest and cardiac shock were generally low (0.2% and 1.9%, respectively), although the hyperthyroid group also had an increased risk of in-hospital cardiac shock (5.9%).

A total of 1857 patients had ST-segment elevation: 74.5% in the euthyroid group, 30.9% in the hypothyroid group, and 89.1% in the hyperthyroid group. Killip class (≥2) was higher among patients in the hypothyroid group, as well. Patients with hyperthyroidism were more likely to undergo primary percutaneous coronary intervention (29.4%).

At 1 year, composite cardiovascular endpoints (CCVEs) occurred in the euthyroid group (21.3%), in the hypothyroid group (30.9%), and among 27.5% of the patients in the hyperthyroid group. Total all-cause death incidence was 6.6% and higher in the hypothyroid and hyperthyroid groups (9.7% vs 5.7% and 10.8% vs 5.7%). The hypothyroid group also significantly differed in terms of heart failure incidence (18.1% vs 12.7% and 11.9% in the hyperthyroid and euthyroid groups, respectively).

Using Kaplan-Meier and Cox regression analyses, the researchers found that the rates of survival free from CCVE, composite cardio-cerebral vascular endpoint (CCCVE), and heart failure were lower in the hypothyroid group, and the frequency of all-cause death during the follow-up period was higher in both the hypothyroid and hyperthyroid groups. Rates of survival free from MI, revascularization, or stroke did not significantly differ between these 2 groups.

The investigators also found that compared with the euthyroid group, the hypothyroid group had an increased risk of CCVE (hazard ratio [HR], 1.540), CCCVE (HR, 1.531), revascularization (HR, 1.587), and heart failure (HR, 1.605). Hypothyroid and hyperthyroid status were both correlated with a higher risk of all-cause death (HR, 1.736 and 1.960, respectively).

After adjusting for covariates, the researchers found that hypothyroid status was associated with an increased CCVE risk vs euthyroid status (HR, 1.337); similarly, hypothyroid status was a significant independent predictor of CCCVE among people who had AMI and a higher risk of revascularization and heart failure.

Study limitations included the observational nature of the study, the use of information abstracted from medical records and a single thyroid function test, as well as exclusion of patients taking thyroid-alerting medications.

“The presence of hypothyroid status [is] clearly associated with an increased risk of cardiovascular events in [patients with AMI],” the researchers concluded. “Given the high prevalence of abnormalities in thyroid function, identifying hypothyroidism as a critical factor in affecting the prognosis of [patients with AMI] is of great clinical value.”

Further investigation, they added, is necessary to illustrate if and how thyroid treatment could improve clinical outcomes in this patient population.

Reference

Wang W, Wang S, Zhang K, et al. Hypothyroidism is associated with clinical outcomes in patients with acute myocardial infarction: subgroup analysis of China PEACE study. Endocrine. Published online June 3, 2021. doi:10.1007/s12020-021-02742-w