Circulation

ORIGINAL RESEARCH ARTICLE

Thyroid Function and Sudden Cardiac Death

A Prospective Population-Based Cohort Study

Layal Chaker, Marten E. van den Berg, Maartje N. Niemeijer, Oscar H. Franco, Abbas Dehghan, Albert Hofman, Peter R. Rijnbeek, Jaap W. Deckers, Mark Eijgelsheim, Bruno H.C. Stricker and Robin P. Peeters

 http://dx.doi.org/10.1161/CIRCULATIONAHA.115.020789 

Circulation. 2016;134:713-722

Originally published September 6, 2016

Abstract

BACKGROUND: The association between thyroid function and cardiovascular disease is well established, but no study to date has assessed whether it is a risk factor for sudden cardiac death (SCD). Therefore, we studied the association of thyroid function with SCD in a prospective population-based cohort.

METHODS: Participants from the Rotterdam Study ≥45 years with thyroid-stimulating hormone or free thyroxine (FT4) measurements and clinical follow-up were eligible. We assessed the association of thyroid-stimulating hormone and FT4 with the risk of SCD by using an age- and sex-adjusted Cox proportional-hazards model, in all participants and also after restricting the analysis to euthyroid participants (defined by thyroid-stimulating hormone 0.4–4.0 mIU/L). Additional adjustment included cardiovascular risk factors, notably hypertension, serum cholesterol, and smoking. We stratified by age and sex and performed sensitivity analyses by excluding participants with abnormal FT4 values (reference range of 0.85–1.95 ng/dL) and including only witnessed SCDs as outcome. Absolute risks were calculated in a competing risk model by taking death by other causes into account.

RESULTS: We included 10 318 participants with 261 incident SCDs (median follow-up, 9.1 years). Higher levels of FT4 were associated with an increased SCD risk, even in the normal range of thyroid function (hazard ratio, 2.28 per 1 ng/dL FT4; 95% confidence interval, 1.31–3.97). Stratification by age or sex and sensitivity analyses did not change the risk estimates substantially. The absolute 10-year risk of SCD increased in euthyroid participants from 1% to 4% with increasing FT4 levels.

Conclusions: Higher FT4 levels are associated with an increased risk of SCD, even in euthyroid participants.

This is an interesting new information, the mechanism of which is unknown,

although clinicians have been aware of for a long time the association between 

hyperthyroidism (and hypothyroidism as well) and heart attack.

This study indicates the level of free T4 in the presence of normal TSH is associated

with sudden cardiac death.

Most practicing general internists have been checking TSH only without T4 in their

usual screening for their patients for many years.