Assertion: atrial fibrillation | /r/CapableOf | begin in pulmonary veins
Facets:
value: usually
type: TEMPORAL
Source sentences:
text: Because atrial fibrillation usually begins in the pulmonary veins or at their attachment to the left atrium, energy is applied around the connections of the pulmonary veins to the left atrium during the pulmonary vein ablation procedure .