Your Thyroid and the Risk of Atrial Fibrillation

Patient Expert
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If you have high-normal levels of thyroid hormone within the reference range, research now confirms that you face an increased risk of atrial fibrillation. Atrial fibrillation — also known as AFib — is an irregular heartbeat where your heart quivers, beats out of rhythm, and can cause dangerous blood clots.

A research study published in October 2017 in the journal Circulation, evaluated more than 30,000 participants, and concluded that free thyroxine (free T4, or FT4) levels in the highest quartile of the reference range are associated with a 45 percent increased risk of AFib, compared to the lowest FT4 levels within the reference range. The second-highest quartile was associated with a 17percent greater risk, and the third-highest quartile had a 25 percent greater risk.

Thyroid stimulating hormone (TSH) levels were, however, not associated with the increased risk of AFib.

In a press release, the study’s author Christine Baumgartner, M.D., from the University Hospital of Bern, Switzerland, said:

“Our findings suggest that levels of the thyroid hormone, free thyroxine, circulating in the blood might be an additional risk factor for atrial fibrillation. Free thyroxine hormone levels might help to identify individuals at higher risk.”

In the past, research has shown that elevated FT4 levels above the reference range are a risk factor for AFib. This is the first time that elevated FT4 within the normal reference range — evidence of subclinical hyperthyroidism — is also linked to a higher risk of AFib.

About atrial fibrillation

It’s estimated that AFib affects between around 3 to 6 million people in the United States.

Symptoms of atrial fibrillation include:

  • heart palpitations
  • a racing heartbeat
  • irregular heart rhythm
  • a pounding sensation in the chest
  • weakness
  • fatigue
  • dizziness
  • shortness of breath
  • chest pain

If untreated, atrial fibrillation can lead to dangerous blood clots, stroke, heart failure, or death.

Your next steps?

The researchers called for further investigation of this important connection, and whether the thyroid hormone replacement drug levothyroxine, used to increase thyroid hormone levels and treat hypothyroidism, could prompt an AFib risk if they cause higher FT4 levels.

According to Dr. Baumgartner:

“Patients who are treated with thyroxine, one of the most frequently prescribed drugs in the United States, generally have higher circulating free thyroxine levels compared to untreated individuals. So, an important next step is to see whether our results also apply to these patients, in order to assess whether target free thyroxine thyroid hormone concentrations for thyroid-replacement therapy need to be modified.”

If you are a thyroid patient with symptoms of AFib or a diagnosis of AFib, especially if you are taking thyroid hormone replacement medication for hypothyroidism, see your healthcare provider for further evaluation.

See more helpful articles:

Understanding Your Thyroid Blood Tests

Your Heart and Your Thyroid: The Connection

How are Hyperthyroidism and Graves' Disease Treated?