Examining Hypothyroidism and Heart Failure

The link between hypothyroidism and increased risk of cardiovascular events, including coronary heart disease (CHD) and heart failure (HF), has been well-established. For example, myocyte contractility, oxygen consumption, and systemic vascular resistance are all affected by thyroid hormone.¹

In a study published in 2010, Mario Rondoni, MD, PhD and fellow investigators conducted a meta-analysis for prospective cohort studies with baseline thyroid function and subsequent heart disease events and mortality, as well as total mortality. They reviewed data on 55,287 participants encompassing 542,494 person-years of follow-up collected from 1972 to 2007 in 11 prospective cohorts in the United States, Europe, Australia, Brazil, and Japan.²

Normal thyroid stimulating hormone (TSH) level was defined as 0.50 mIU/L to 4.49 mIU/L. Subclinical hypothyroidism was defined as a TSH level of 4.5 to 19.9 mIU/L with normal thyroxine concentrations. Roughly 6% of patients had hypothyroidism.

In age- and sex-adjusted analyses, the researchers found that subclinical hypothyroidism was associated with an increased risk for CHD events and CHD mortality, especially in patients whose TSH levels were 10 mIU/L or greater (see tables).

CHD Events*

TSH Level (mIU/L)	Hazard Ratio	95% Confidence Interval
4.5 to 6.9	1.00	0.86-1.18
7.0 to 9.9	1.17	0.96-1.43
10 to 19.9	1.89	1.28-2.80

CHD Mortality*

TSH Level (mIU/L)	Hazard Ratio	95% Confidence Interval
4.5 to 6.9	1.09	0.91-1.30
7.0 to 9.9	1.42	1.03-1.95
10 to 19.9	1.58	1.10-2.27

*(per 1000 person-years)

Findings were similar after researchers adjusted for traditional cardiovascular risk factors, and risks did not significantly differ by age, sex, or pre-existing cardiovascular disease. However, controversy remains over best practices between cardiologists and endocrinologists treating these patients.

Results from a large, long-term study of heart and other chronic disease among the middle-aged and elderly Dutch adults showed that those with elevated, but normal, free thyroxine hormone levels were 2.5 times more likely to die of sudden cardiac death compared with patients with lower levels. Furthermore, the 10-year risk for sudden cardiac death was 4 times greater among patients with higher free thyroxine levels compared with those with lower levels.⁴

Layal Chaker, MD, the study’s lead author and a research fellow in endocrinology and epidemiology at Erasmus University Medical Center Rotterdam, was quoted as cautioning against the overuse of hormone therapy.⁴

“We know that a considerable proportion of patients on thyroid hormone replacement therapy are overtreated and so have high blood levels of thyroid hormone,” Dr Chaker said. “Our study suggests more caution is warranted in the treatment of thyroid hormone replacement. Replacement therapy is often aimed at the high normal range, which carries a risk of overtreatment.”

In 2015, the US Preventive Services Task Force concluded “the current evidence is insufficient to assess the balance of benefits and harms of screening for thyroid dysfunction in nonpregnant, asymptomatic adults.”⁵ In an editorial published in Annals of Internal Medicine, Anne R. Cappola, MD, ScM and David S. Cooper, MD, called the recommendations “disheartening” because there had been so little change since the previous recommendations issued in 2004.⁶

They further criticized the USPSTF for not taking results from 3 meta-analyses—Rodondi 2010, Collet 2012, and Gencer 2012—into account^2,7,8

This article originally appeared on The Cardiology Advisor