A commonly used algorithm to determine the stroke risk after onset of atrial fibrillation is calculation of the CHADS 2 score. The higher the CHADS 2 score, the higher the risk of cerebral thromboembolism or stroke. One point is assigned if any of the following four conditions are present:
Congestive heart failure
Age > 75
In addition, 2 points are assigned if the patient has symptoms of a TIA or stroke previously. A low CHADS 2 score (0-1) usually does not require anticoagulation.