Validation of clinical classification schemes for predicting stroke: results from the National Registry of Atrial Fibrillation.
CONTEXT: Patients who have atrial fibrillation (AF) have an increased risk of stroke, but their absolute rate of stroke depends on age and comorbid conditions. OBJECTIVE: To assess the predictive value of classification schemes that estimate stroke risk in patients with AF. DESIGN, SETTING, AND PATIENTS: Two existing classification schemes were combined into a new stroke-risk scheme, the CHADS( 2) index, and all 3 classification schemes were validated. The CHADS( 2) was formed by assigning 1 point each for the presence of congestive heart failure, hypertension, age 75 years or older, and diabetes mellitus and by assigning 2 points for history of stroke or transient ischemic attack. Data from peer review organizations representing 7 states were used to assemble a National Registry of AF (NRAF) consisting of 1733 Medicare beneficiaries aged 65 to 95 years who had nonrheumatic AF and were not prescribed warfarin at hospital discharge. MAIN OUTCOME MEASURE: Hospitalization for ischemic stroke, determined by Medicare claims data. RESULTS: During 2121 patient-years of follow-up, 94 patients were readmitted to the hospital for ischemic stroke (stroke rate, 4.4 per 100 patient-years). As indicated by a c statistic greater than 0.5, the 2 existing classification schemes predicted stroke better than chance: c of 0.68 (95% confidence interval [CI], 0.65-0.71) for the scheme developed by the Atrial Fibrillation Investigators (AFI) and c of 0.74 (95% CI, 0.71-0.76) for the Stroke Prevention in Atrial Fibrillation (SPAF) III scheme. However, with a c statistic of 0.82 (95% CI, 0.80-0.84), the CHADS( 2) index was the most accurate predictor of stroke. The stroke rate per 100 patient-years without antithrombotic therapy increased by a factor of 1.5 (95% CI, 1.3-1.7) for each 1-point increase in the CHADS( 2) score: 1.9 (95% CI, 1.2-3.0) for a score of 0; 2.8 (95% CI, 2.0-3.8) for 1; 4.0 (95% CI, 3.1-5.1) for 2; 5.9 (95% CI, 4.6-7.3) for 3; 8.5 (95% CI, 6.3-11.1) for 4; 12.5 (95% CI, 8.2-17.5) for 5; and 18.2 (95% CI, 10.5-27.4) for 6. CONCLUSION: The 2 existing classification schemes and especially a new stroke risk index, CHADS( 2), can quantify risk of stroke for patients who have AF and may aid in selection of antithrombotic therapy.[1]References
- Validation of clinical classification schemes for predicting stroke: results from the National Registry of Atrial Fibrillation. Gage, B.F., Waterman, A.D., Shannon, W., Boechler, M., Rich, M.W., Radford, M.J. JAMA (2001) [Pubmed]
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