Larger women almost three times more likely to have atrial fibrillation

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New research suggests that women with a larger body surface area may have an increased risk of atrial fibrillation – a type of arrhythmia that can have serious cardiovascular consequences if left untreated.

The muscles of a healthy heart contract and relax regularly, pumping blood into the heart’s ventricles. In A-fib, however, the atria of the heart (or the upper chambers) beat irregularly, which prevents them from effectively moving blood into the ventricles.

If left untreated, the condition can cause blood clots, stroke, and a variety of cardiovascular complications, including heart failure. Approximately 15 to 20 percent of the people who have strokes also have A-fib.

Annika Rosengren, professor of internal medicine at the Sahlgrenska Academy of the University of Gothenburg in Sweden and co-author of the study, explains that the new research builds on a previous study that she also co-authored.

The researchers accessed clinical data on these women’s height, age, pregnancy, history of diabetes, high blood pressure, and smoking status from the Swedish Medical Birth Registry. The participants were followed clinically for more than 30 years, and data on A-fib-related hospital admissions were accessed from the Swedish Inpatient Registry.

During the follow-up period, more than 7,000 women were hospitalised with A-fib. The average age at the time of hospitalisation was 49 years.

The team calculated the women’s BSA in square meters (m2) using a standard formula that considers weight and height. The researchers divided the women into four groups based on their BSA: those with a BSA of between 0.97 and 1.61 m2, those with a BSA between 1.61 and 1.71 m2, a third group with a BSA of 1.71 to 1.82 m2, and finally, those with a BSA of 1.82 to 3.02 m2.

In ascending order of BSA, women in the second, third, and fourth groups had a 1.16, 1.55, and 2.61 times higher risk of A-fib compared with the women in the first and lowest BSA group.

“Atrial fibrillation is the result of obesity-related metabolic changes, but there is also a second cause,” Prof Rosengren says. “People with a bigger atrium have a higher risk of atrial fibrillation.”

“Generally, it is better to be tall because you have less risk of stroke and heart attack, and better survival,” Prof Rosengren continues. “Taller people are often better educated, have higher socioeconomic status, and may have received better nutrition at a young age and in the womb. But in this case being tall is less desirable because it alters the structure of the heart in a way that may be conducive to atrial fibrillation.”

However, Prof Rosengren points out that tall people could also reduce the risk of A-fib by avoiding a build-up of excessive weight.

Prof Rosengren also notes that age plays a significant role. The absolute risk of A-fib in younger women was revealed to be quite low – namely, lower than 0.5 percent – and this was independent of their weight or BSA. “In general young women need not worry about their risk of atrial fibrillation, whatever their body size,” she says, but older men and women might be at a higher risk of A-fib if their BSA is also high.