They further found that the odds of blacks being treated with warfarin, which reduces stroke risk by 60 percent, were one-fourth those of whites.

In other words, blacks in this study with atrial fibrillation were two-thirds less likely to know they had the disorder and three-fourths less likely to be treated with warfarin, the standard of care.

Reasons for the racial disparity are not known from this study, but researchers suggest several explanations. Many study participants might have been undiagnosed because atrial fibrillation is often not symptomatic, Dr. Meschia says. Or, participants may have been diagnosed but did not remember or fully appreciate the significance of the condition, he says. Dr. Meschia says other possible reasons could include utilization or delivery of health care, reluctance by physicians to use warfarin in patients with multiple health conditions, or disinclination by patients to use the drug.

Insurance status was not a factor, the researchers add, because the majority of study participants were over age 65 and were covered by Medicare.

"Whatever the reasons behind these observations, it appears that there is a missed opportunity to prevent stroke and other thromboembolic complications from atrial fibrillation because many individuals may fail to have the condition diagnosed and/or fail to receive treatment with warfarin," Dr. Meschia says. "It would benefit public health if future research could tease out the reasons behind this disparity."