Overtreating patients with hypothyroidism could increase their risk of atrial fibrillation (AF), reveals this study from Intermountain Medical Center (UTAH) presented at the American Heart Association (AHA) Scientific Sessions 2018. If the link between FT4 and AF has recently and already been documented, this new study clarifies the link between FT4 levels and AF in treated patients.
Indeed, too many drugs to treat hypothyroidism can lead to an increased risk of AF, a common heart rhythm disorder associated with the risk of stroke, reveals this study of nearly 175,000 patients. "We know that patients with hypothyroidism are at higher risk for atrial fibrillation, but we hadn't considered this increased risk within the normal range of thyroid hormones," says lead author Dr. Jeffrey L. Anderson , researcher at the Heart Institute of the Intermountain Medical Center: "These results show that we should reconsider what we call 'normal'".
Increased AF risk in patients with high AF: The team reviewed electronic medical records of 174,914 patients including data on free thyroxine (FT4) levels. These patients were not on thyroid replacement medication and their FAT levels were within a normal range of FT4 levels. These participants were divided into 4 quartiles, and then the researchers reviewed the records of these patients for a current or future diagnosis of atrial fibrillation. The analysis leads to:
- a 40% increase in pre-existing AF in patients in the upper quartile for the FT4 rate vs the lowest quartile,
- a 16% increase in the risk of developing AF at 3 years.
Results, which, according to the authors, suggest that the optimal optimal range of FT4 should be reconsidered and redefined.
Thyroid hormones are associated with sometimes severe symptoms , including weight loss and increased energy, which may lead patients to seek treatment if levels are elevated but still within the normal range. In these patients, these possible adverse effects of atrial fibrillation, and therefore stroke, should be reconsidered.
The next step will be a randomized trial to investigate whether targeting a reduced range of FT4 in patients receiving thyroid hormone replacement therapy reduces the risk of atrial fibrillation and stroke, as well as other possible heart disorders like atherosclerosis.
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