In Euthyroid Individuals, Higher Free Thyroid Levels Linked To Greater Risk of Atrial Fibrillation Interview with:
Christine Baumgartner MD
Universitätsspital Bern
Bern, Switzerland
Research Fellow, Division of Hospital Medicine
UCSF What is the background for this study? What are the main findings?

Response: Overt and subclinical hyperthyroidism increase the risk of atrial fibrillation, but it is unclear whether subclinical hypothyroidism, which is known to increase cardiovascular events, or thyroid function in the normal range are also associated with incident atrial fibrillation. Given the high prevalence of atrial fibrillation and its associated morbidity and mortality, identifying potentially modifiable risk factors is important. Therefore, we aimed to assess the risk of atrial fibrillation in individuals with subclinical hypothyroidism or variations of thyroid function within the normal range.

Our main findings are that higher free thyroxine levels are associated with an increased risk of atrial fibrillation in euthyroid individuals, but thyroid-stimulating hormone levels within the euthyroid or subclinical hypothyroid range was not related to atrial fibrillation risk. What should readers take away from your report?

Response: Free thyroxine levels, but not thyroid-stimulating hormone levels, are associated with atrial fibrillation in euthyroid individuals and might add to further assessment of atrial fibrillation risk in these persons. However, before we can recommend to measure free thyroxine levels as a marker of atrial fibrillation risk in routine clinical practice, further studies are needed to investigate whether free thyroxine screening can relate to benefits such as decreasing atrial fibrillation risk. What recommendations do you have for future research as a result of this study?

Response: Future research should investigate whether our results also apply to persons that are treated with thyroxine, because these individuals generally have higher circulating free thyroxine levels compared to naturally euthyroid persons, in order to assess whether target thyroid hormone levels in thyroxine treatment should be adapted. This would be of high public health importance, because thyroxine is among the top most prescribed medications in the United States. Is there anything else you would like to add?

Response: The Study was funded by the Swiss National Science Foundation and Swiss Heart Foundation.

Disclosures: Dr Heckbert received research grant support from NIH grants U01HL130114 and HL080295; Drs Stott and Rodondi received research funding from the European Union FP7 for the TRUST trial (Thyroid Hormone Replacement for Subclinical Hypothyroidism). Thank you for your contribution to the community.


Thyroid Function Within the Normal Range, Subclinical Hypothyroidism and the Risk of Atrial Fibrillation

Christine Baumgartner, Bruno R. da Costa, Tinh-Hai Collet, Martin Feller, Carmen Floriani, Douglas C. Bauer, Anne R. Cappola, Susan R. Heckbert, Graziano Ceresini, Jacobijn Gussekloo, Wendy P. J. den Elzen, Robin P. Peeters, Robert Luben, Henry Völzke, Marcus Dörr, John P. Walsh, Alexandra Bremner, Massimo Iacoviello, Peter Macfarlane, Jan Heeringa, David J. Stott, Rudi G. J. Westendorp, Kay-Tee Khaw, Jared W. Magnani, Drahomir Aujesky, Nicolas Rodondi and for the Thyroid Studies Collaboration
Circulation. 2017;CIRCULATIONAHA.117.028753Originally published October 23, 2017

Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.


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