Overtreating hypothyroidism: link to atrial fibrillation
For patients who take medication to treat hypothyroidism, being treated with too much medication can lead to an increased risk of atrial fibrillation, a common heart rhythm disorder associated with stroke, a new study of more than 174,000 patients has found.

The findings were presented at the American Heart Association Scientific Session conference.

"We know patients with hypothyroidism have a higher risk of atrial fibrillation, but we didn't consider increased risk within what's considered the normal range of thyroid hormones," said lead researcher author of the study. "These findings show we might want to re-consider what we call normal."

In the new study, researchers surveyed the electronic medical records of 174,914 patients treated at Intermountain Healthcare facilities whose free thyroxine (fT4) levels were recorded and who were not on thyroid replacement medication. Researchers then took what's considered a normal range of fT4 levels, divided it into four quartiles, then looked at those patients' records for a current or future diagnosis of atrial fibrillation.

They found a 40% increase in existing atrial fibrillation for patients in the highest quartile of fT4 levels compared to patients in the lowest, and a 16% increase in newly developing atrial fibrillation during 3-years of follow up.

These findings, suggest that the optimal healthy range of fT4 should be reconsidered and redefined.

The study also found that fT4 should be measured, along with thyroid-stimulating hormone (TSH), which is more commonly tested for in patients with irregular thyroid hormone levels but was not helpful within the normal range in refining risk.

Read more here: https://pxmd.co/G06U5
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