Assertion: atrial fibrillation's heart rhythm | /r/CapableOf | develop within the six months
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Source sentences:
text: Although doctors have studied AF for over 100 years, the risk of stroke was not fully appreciated until the 1980s, when the Framingham Heart Study reported that 24% of its stroke patients were also in AF, and that the abnormal heart rhythm developed within the six months preceding the stroke in about a third of these participants.