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.

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