Diabetes is linked to a 40 percent greater risk of developing atrial fibrillation- the most common kind of chronically irregular heartbeat, found a new study.

Led by Dr. Sascha Dublin of Group Health Research Institute, the researchers also found that this risk rises even higher the longer people have diabetes and the less controlled their blood sugar is. For three years, the researchers tracked more than 1,400 Group Health patients who had newly recognized atrial fibrillation. They compared these “cases” with more than 2,200 “controls.” The controls were matched to the cases by age, sex, year, and whether they were treated for high blood pressure; but unlike the cases, they had no atrial fibrillation.

Dublin’s study was the first to examine the relationship between atrial fibrillation and the duration of patients’ diabetes and their blood sugar levels. Unlike most prior studies, this one also adjusted for patients’ weight, which is important because both diabetes and atrial fibrillation are more common in heavier people. The researchers found that patients with diabetes were 40 per cent more likely to be diagnosed with atrial fibrillation than were people without diabetes.

The risk of atrial fibrillation rose by 3 percent for each additional year that patients had diabetes. For patients with high blood sugar (glycosylated hemoglobin, also known as HBA1c more than 9 per cent), the risk of atrial fibrillation was twice that for people without diabetes. But patients with well-controlled diabetes (HBA1c 7 per cent or less) were about equally likely to have atrial fibrillation as people without diabetes. “When a patient with diabetes has symptoms like heart palpitations, clinicians should have a higher level of suspicion that the reason could be atrial fibrillation. This heart rhythm disturbance is important to diagnose, because it can be treated with medications like warfarin that can prevent many of the strokes that the atrial fibrillation would otherwise cause,” said Dublin. It is hard to establish which comes first, diabetes or atrial fibrillation, with this kind of case-control study, unlike a randomized trial, said Dublin. “But our finding that the risk of atrial fibrillation is higher with longer time since patients started medications for diabetes, and with higher blood glucose levels, is strongly suggestive that diabetes can cause atrial fibrillation,” she said.

The study was published in the Journal of General Internal Medicine.

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