September 13, 2016
1 min read

Higher free thyroxine levels increase risk for sudden cardiac death

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New data published in Circulation show that adults with higher free thyroxine levels are at a significantly greater risk for sudden cardiac death compared with those with normal levels.

“Currently, we do not have a good way to predict sudden cardiac death in the general population,” said Layal Chaker, MD, MSc, doctoral candidate and research fellow in endocrinology and epidemiology at Erasmus University Medical Center, Rotterdam, Netherlands. “Thus, identifying additional risk factors is crucial. Our results indicate that thyroid hormone levels may be useful for assessing risk to prevent sudden cardiac death.”

Researchers analyzed 10,318 participants from the Rotterdam Study aged 45 years or older (mean age, 65 years; 57% women; nearly all participants were white).

Chaker and colleagues assessed a possible link between thyroid-stimulation hormone and free thyroxine with the risk for sudden cardiac death in all participants and in euthyroid participants, defined as thyroid-stimulating hormone levels of 0.4 mIU/L to 4 mIU/L.

The results were adjusted for age, sex and CV risk factors, including hypertension, serum cholesterol and smoking. In a sensitivity analysis, the researchers excluded participants with abnormal free thyroxine values.

The outcome of interest was witnessed sudden cardiac death. Median follow-up was 9.1 years.

According to the results, there were 261 incident sudden cardiac deaths during the study period.

Elevated free thyroxine levels, even in those with normal thyroid function, were associated with increased risk for sudden cardiac death (HR = 2.28 per 1 ng/dL of free thyroxine; 95% CI, 1.31-3.97), according to the researchers. Similar results were observed across age and sex strata and in the sensitivity analysis.

In the sensitivity analysis population, the absolute risk for sudden cardiac death over 10 years was four times higher among those with high free thyroxine levels vs. those with normal levels (4% vs. 1%), the researchers wrote.

“We know that a considerable proportion of patients on thyroid hormone replacement therapy are overtreated and so have high blood levels of thyroid hormone,” Chaker said in the release. “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.” – by Dave Quaile

Disclosure: The researchers report no relevant financial disclosures.