Millions of older Americans have an elevated risk of suffering an ischemic stroke — a dangerous blood clot in the brain — as a result of having an irregular heart rhythm called atrial fibrillation.

A new University of Pennsylvania study finds that such strokes may occur even before the patient is aware of having the heart-rhythm problem, nicknamed a-fib, and that this risk is higher for black patients.

The study did not identify the reason for that higher risk, but the difference was marked enough to warrant an extra layer of preventive action for black patients, said senior author Rajat Deo, a Penn Medicine cardiologist. Blood-thinning medicines called anticoagulants are proved to reduce the chance of a stroke, so a targeted campaign to increase usage would make sense, he said.

"I strongly believe that we have enough information from our study and others to implement community-based programs for the detection of cardiac arrhythmia such as atrial fibrillation and the subsequent initiation of anticoagulation therapy," Deo said.

Penn Medicine cardiologist Rajat Deo found that black patients with atrial fibrillation are at a higher risk of stroke than white patients.
Penn Medicine
Penn Medicine cardiologist Rajat Deo found that black patients with atrial fibrillation are at a higher risk of stroke than white patients.

The study, published Tuesday in the journal HeartRhythm, illustrates yet another way in which black patients are at greater risk of heart problems for reasons that physicians cannot fully explain.

Heart disease tends to occur earlier in African American patients than in white counterparts, and the death rate from heart-related causes is higher, too. In recent years, life expectancy for African Americans has been more than three years less than that for white people, largely due to a higher rate of heart attacks, sudden cardiac arrest, heart failure, and stroke, according to the American Heart Association. Some of these differences can be attributed to socioeconomic status and diet, but researchers have found that even middle- and upper-class black people experience poorer heart health, on average, suggesting that genetics and environmental factors such as stress may play a role.

In the Penn study, the authors identified 3,507 patients who developed a-fib, then looked back to see if any had suffered a stroke in the previous six months. The authors also monitored the patients for strokes going forward — for a median of 3.6 years after their diagnosis with a-fib.

Out of 538 strokes, nearly half — 254 — occurred before diagnosis with atrial fibrillation. Though the authors could not say for sure, they suspect that in many of those 254 cases, the patients already had a-fib but were unaware.

Symptoms of a-fib may include palpitations, a racing heart, and shortness of breath, but some patients feel fine and are nevertheless at a higher risk of stroke, Deo said.

"In many cases, you are asymptomatic," he said, though the condition may be detected by a cardiologist.

For the strokes that occurred in the six months before a-fib diagnosis, the rate in black patients was about one-third higher than the rate in white patients.

For the strokes that occurred in the years following an a-fib diagnosis, the rate in black patients was two-thirds higher than in white patients — a 2.5 percent chance of stroke per year in black patients compared with a 1.5 percent chance for whites.

The increased stroke risk for black patients was especially high among those who did not have prescriptions for blood-thinning medicines, which include warfarin as well as "novel" anticoagulants such as Xarelto.

But even the black patients with prescriptions had a somewhat higher risk of stroke than their white counterparts. The study authors did not examine whether patients took the medicines, only if they had been given a prescription. The authors also did not collect data on income and education, but Deo said people of lower socioeconomic status may have more trouble filling prescriptions.

"It's enough of a clue now that we need community-based efforts to ensure they are getting adequate care," he said.