In a large, independent, community-based cohort of patients with atrial fibrillation, the Anticoagulation and Risk Factors in Atrial Fibrillation (ATRIA) risk score more accurately identified patients at low risk of stroke compared to the CHADS2 and CHA2DS2-VASc ischemic stroke risk scores.
Currently, both the U.S. and European guidelines recommend the use of the CHA2DS2-VASc score for risk stratification. The CHA2DS2-VASc score better identifies patients who are truly at low risk by incorporating vascular disease, age between 65 and 74 years, and sex. The ATRIA risk score incorporates factors from the CHADS2, but also includes renal function, and takes into consideration a broader range of age, as well as interaction of age and prior stroke.
A total of 60,594 patients with atrial fibrillation who were not using warfarin were included from the U.K.’s Clinical Practice Research Datalink database. Patients (mean follow-up= 2.1 years; mean age= 74.4 years) were followed from diagnosis of atrial fibrillation through occurrence of ischemic stroke, prescription of warfarin, death, or the study’s end. Comorbidities included hypertension (54.6%), vascular disease (30.8%), and renal dysfunction (28%). Annualized stroke rate was 2.99%, with 3,751 ischemic strokes occurring during follow-up of 125,296 person-years.
Among patients with no prior history of stroke, increasing age was a strong risk factor compared to younger participants (HR 2.87; 95% CI: 2.40 to 3.42), but was muted in patients who had a prior stroke or TIA. Those with prior history were at high risk of subsequent stroke, regardless of age (P < 0.001). Multivariate analysis revealed associations including female sex (HR: 1.23; 95% CI: 1.14 to 1.32), hypertension (HR: 1.14; 95% CI: 1.06 to 1.22), and diabetes mellitus (HR: 1.24; 95% CI: 1.12 to 1.37). Vascular disease, major bleed, renal dysfunction, and congestive heart failure were associated with a higher risk in the univariate but not multivariate analysis.
The ATRIA risk score classified 49% of patients as high-risk and 40% as low-risk, while the CHA2DS2-VASc risk score classified 82.6% as high-risk and 6.6% as low-risk. C statistics for full point scores were 0.70 (95% CI: 0.69 to 0.71) for Atria, 0.68 (95% CI: 0.67 to 0.69) for CHADS2, and 0.68 (95% CI: 0.67 to 0.69) for CHA2DS2-VASc risk scores. Event rates for moderate- and high-risk categories for CHA2DS2-VASc were lower than those for ATRIA and CHADS2. Net reclassification improvement was 0.23 (95% CI: 0.22 to 0.25) for ATRIA compared with CHA2DS2-VASc.
Overall, the ATRIA score performed better than the CHADS2 and CHA2DS2-VASc risk scores. The results persisted even after restricting analysis to more recent follow-up, excluding unspecified strokes, and excluding renal dysfunction as a predictor. Most improvements with ATRIA were the result of down classification, suggesting that using the CHA2DS2-VASc risk score could lead to overtreatment of patients at very low risk of stroke.