The Endocrine Society's 97th Annual Meeting & Expo:

Untreated Hypothyroidism, Thyroid Hormone, and Cardiac Effects

The effects of thyroid hormone on myocardial function, lipoprotein metabolism, and atherosclerotic cardiovascular disease (CVD) were the topics addressed by Paul W. Ladenson, MD, Professor and Director of the Division of Endocrinology, Diabetes and Metabolism at John Hopkins University School of Medicine in Baltimore. Dr. Ladenson spoke in the E. Chester Ridgway Memorial Symposium on March 6, 2015, at the Endocrine Society Annual Meeting in San Diego, California.

Untreated Hypothyroidism
“Untreated hypothyroidism can exert effects on myocardial performance and atherosclerotic heart disease risk,” said Dr. Ladenson, who emphasized the seminal contributions of Dr. E. Chester (Chip) Ridgway to these aspects of thyroidology.

Effects of thyroid hormone deficiency can lead to heart failure—usually due to exacerbation of intrinsic cardiac disease, but occasionally due to hypothyroidism alone. Mechanisms include bradycardia, reduced left ventricular contractility, diastolic dysfunction, and increased systemic resistance. This is a reversible form of cardiomyopathy with recovery over a period of weeks after initiation of levothyroxine therapy.

Secondary Hypercholesterolemia
Hypothyroidism is also a common cause of secondary hypercholesterolemia with its associated ischemic heart disease risk. This effect occurs not only in overt hypothyroidism, but also in mild or subclinical hypothyroidism.

In the Rotterdam population-based study of 1149 women aged 69 ± 8 years, the 11% of women with subclinical hypothyroidism were found to be twice as likely to have ECG evidence of a preceding myocardial infarction. (Hak et al, Ann Int Med, 2000). Similarly, prospective studies have shown that subclinical hypothyroidism raises risk of coronary heart disease (CHD) events and mortality.

In the 2010 meta-analysis by Rodondi et al (JAMA), 55,287 participants from 11 cohorts were assessed for mortality due to CHD and 25,977 participants from seven cohorts were assessed for CHD events. A total of 3450 participants (6.2%) were found to have had subclinical hypothyroidism. In follow-up, 2168 participants had died of CHD events and 4470 had experienced CHD events. Risk of CHD events and mortality were higher among those with higher thyroid stimulating hormone concentrations, even after adjusting for traditional cardiovascular risk factors.

Conclusion
Hypothyroidism reversibly impairs left ventricular function and can even cause heart failure. Even mild hypothyroidism can impair left ventricular performance and cause hypercholesterolemia, raising the risk of CHD events and death.  Levothyroxine therapy can reverse impaired myocardial performance as well as dyslipidemia due to thyroid hormone deficiency. “The final step,” said Dr. Ladenson, “will be a prospective randomized trial to confirm that thyroid hormone treatment of subclinical hypothyroidism really does reduce risks of ischemic heart disease events and mortality.”

March 13, 2015

 

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