Validation of risk stratification schemes for predicting stroke and thromboembolism in patients with atrial fibrillation: nationwide cohort study

Abstract

Objectives To evaluate the individual risk factors composing the CHADS₂ (Congestive heart failure, Hypertension, Age≥75 years, Diabetes, previous Stroke) score and the CHA₂DS₂-VASc (CHA₂DS₂-Vascular disease, Age 65-74 years, Sex category) score and to calculate the capability of the schemes to predict thromboembolism. Design Registry based cohort study. Setting Nationwide data on patients admitted to hospital with atrial fibrillation. Population All patients with atrial fibrillation not treated with vitamin K antagonists in Denmark in the period 1997-2006. Main outcome measures Stroke and thromboembolism. Results Of 121 280 patients with non-valvular atrial fibrillation, 73 538 (60.6%) fulfilled the study inclusion criteria. In patients at “low risk” (score=0), the rate of thromboembolism per 100 person years was 1.67 (95% confidence interval 1.47 to 1.89) with CHADS₂ and 0.78 (0.58 to 1.04) with CHA₂DS₂-VASc at one year’s follow-up. In patients at “intermediate risk” (score=1), this rate was 4.75 (4.45 to 5.07) with CHADS₂ and 2.01 (1.70 to 2.36) with CHA₂DS₂-VASc. The rate of thromboembolism depended on the individual risk factors composing the scores, and both schemes underestimated the risk associated with previous thromboembolic events. When patients were categorised into low, intermediate, and high risk groups, C statistics at 10 years’ follow-up were 0.812 (0.796 to 0.827) with CHADS₂ and 0.888 (0.875 to 0.900) with CHA₂DS₂-VASc. Conclusions The risk associated with a specific risk stratification score depended on the risk factors composing the score. CHA₂DS₂-VASc performed better than CHADS₂ in predicting patients at high risk, and those categorised as low risk by CHA₂DS₂-VASc were truly at low risk for thromboembolism.