Comparative performance of stroke risk scores in patients with atrial fibrillation with low stroke risk

Background Australian guidelines recommend the CHA 2 DS 2 -VA (congestive heart failure, hypertension, age ≥75 years (double weight), diabetes mellitus, previous stroke (double weight), vascular disease, age 65–74 years) score to identify patients with atrial fibrillation (AF) at low stroke risk who should avoid oral anticoagulation. Treatment thresholds were derived from heterogeneous international data, and alternate scores require validation in an Australian population. We evaluated whether existing stroke scores (CHADS 2 (congestive heart failure, hypertension, age ≥75 years, diabetes mellitus, previous stroke (double weight)), CHA 2 DS 2 -VA, ATRIA (anticoagulation and risk factors in atrial fibrillation) and Modified-CHADS 2 ) accurately identify truly low-risk patients in Australia. Methods We conducted a population-based cohort study using linked data from the New South Wales Admitted Patient Data Collection, the National Death Index and the Pharmaceutical Benefits Scheme databases. Oral anticoagulant-naïve patients with a first hospital admission for AF between July 2003 and January 2021 were included. Patients were followed for ≥12 months and classified into low-risk, intermediate-risk or high-risk categories for each score. ‘Truly low-risk’ was defined as annual ischaemic stroke incidence <0.9%. Predictive accuracy was assessed using the concordance-statistic. Results Among 224 451 eligible patients, 3552 (1.6%) were hospitalised for ischaemic stroke within 12 months. The proportion labelled low-risk ranged from 2.0% (Modified-CHADS 2 ) to 50.9% (ATRIA). Patients assigned low-risk using each score, and intermediate-risk with the CHA 2 DS 2 -VA score, met the definition of truly low-risk. Concordance-statistics were modest, with the weakest performing score being the CHA 2 DS 2 -VA score (0.61, 95% CI 0.60 to 0.61) and the best performing model being the ATRIA score (0.66, 95% CI 0.66 to 0.67). Conclusions The guideline-endorsed CHA 2 DS 2 -VA score showed the lowest discrimination, and patients classified as intermediate-risk using this score had stroke incidence below the treatment threshold. Strong consideration should be given to the development and validation of locally applicable risk tools.