Harvard Heart Letter

Hidden atrial fibrillation is a possible culprit in mystery strokes

Atrial fibrillation—the rapid and ineffectual quivering of the heart's upper chambers—dramatically increases a person's risk of having a stroke. In fact, doctors estimate that about 15% of all strokes arise from atrial fibrillation. But a even greater proportion of strokes—25%—have no known cause. A new study suggests that hidden atrial fibrillation could account for many of these strokes as well.

Doctors use the term "subclinical" to describe a disease that's hidden. People don't feel any symptoms of it, and nothing abnormal shows up in routine medical tests. But it's there.

Researchers looked at more than 2,500 people ages 65 and older who had recently received an implanted pacemaker or defibrillator. These people had no prior history of atrial fibrillation, having received the implant to treat another heart problem.

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