Atrial fibrillation (AFib) heightens stroke risk—but new research shows that this is true only in people with certain aortic shapes. Those with aortic arches that are less curved are more prone to stroke, according to a study published online Aug. 1 in Nature.

“Lower curvature angles (i.e., less than 90 degrees) or relatively less tortuous configuration of aorta lead to significant increase in stroke propensity by AFib while stroke propensity alteration by AFib was shown to be negligible at higher curvature angles,” wrote lead author Hyo Won Choi, with the California Medical Innovations Institute in San Diego, and colleagues.

The research team cited “elevated pressure gradient level in highly folded aorta configurations” that may influence clot trajectory and stroke propensity.

“The present study suggests that the elevated risk of left carotid artery embolization induced by AFib is critically dependent on the patient-specific geometry of aortic arch,” the authors stated. They found that, for patients with less tortuously configured aortic arches, risk was elevated 2.5 to 3.8 times.

The researchers conducted computational fluid dynamics simulations based on patient data extracted from CT scans. The study was small, based on data from only five patients. Acknowledging that limitation, the authors called for future investigation to confirm their findings with a larger sample of patient-specific data.

As the U.S. population is aging, stroke rates are rising sharply and are expected to more than double over the next 40 years, the researchers wrote. Their simulations suggest that the aortic arch’s curvature represents a significant risk factor, one worthy of further testing in future clinical trials.