Assessment of three schemes for stratifying stroke risk in patients with nonvalvular atrial fibrillation

PURPOSE: The risk of ischemic stroke varies widely among patients with nonv alvular atrial fibrillation, influencing the choice of prophylactic antithr ombotic therapy. We assessed three schemes for stroke risk stratification i n these patients who were treated with aspirin and who did not have prior c erebral ischemia. SUBJECTS AND METHODS: Criteria from three schemes of risk stratification we re applied to a longitudinally observed cohort of patients with atrial fibr illation who did not have prior cerebral ischemia and who were treated with aspirin alone or aspirin combined with low, ineffective doses of warfarin in a multicenter clinical trial. The ability of the schemes to identify pat ients at high (greater than or equal to 6%), low (less than or equal to 2%) , and intermediate annual risks of ischemic stroke was assessed. RESULTS: During a mean follow-up of 1.8 years. 48 ischemic strokes occurred among 1,073 patients with atrial fibrillation who were taking aspirin (rat e = 2.5 per 100 person-years). Each of the three schemes predicted stroke a nd disabling stroke, and successfully identified patients at low risk (obse rved stroke rates of 0.3 to 1.1 per 100 person-years), although the fractio ns of the cohort that were categorized as low risk varied from 14% to 45%. The observed rates of ischemic stroke among patients categorized as high ri sk ranged from 3.5 to 7.2 per 100 person-years among the stratification sch emes. Two schemes considered all patients >75 years old as high risk (obser ved stroke rate 4.2 per 100 person-years), while the remaining scheme class ified one third of patients in this age group as low risk (observed stroke rate 0.6 per 100 person-years). CONCLUSIONS: When tested in a large cohort of patients with atrial fibrilla tion who were treated with aspirin, available risk-stratification schemes s uccessfully identified patients with low rates of ischemic stroke, but less consistently identified high-risk patients. Am J Med. 2000;109:45-51. (C) 2000 by Excerpta Medica, Inc.