Objectives To determine the accuracy of CHADS₂ and CHA₂DS₂-VASc tools for predicting ischaemic stroke or transient ischaemic attack (TIA) and death in patients without a history of atrial fibrillation or flutter (AF).

Methods The study included 20 970 patients without known AF enrolled in the Alberta Provincial Project for Outcomes Assessment in Coronary Heart disease (APPROACH) prospective registry who were discharged after an acute coronary syndrome (ACS) between 2005 and 2011. The outcome measures were incident ischaemic stroke, TIA or death from any cause.

Results Over a median follow-up of 4.1 years, 453 patients (2.2%) had a stroke (n=297) or TIA (n=156) and 1903 (9.0%) died. The incidence of stroke or TIA increased with increases in each risk score (p<0.001), with an absolute annual incidence ≥1% with CHADS₂ ≥3 or CHA₂DS₂-VASc ≥4. Both CHADS₂ and CHA₂DS₂-VASc scores had acceptable discrimination performance (C-statistic=0.68 and 0.71, respectively). The mortality rate was also greater in patients with higher CHADS₂ and CHA₂DS₂-VASc scores (p<0.0001).

Conclusions In patients with ACS but no AF, the CHADS₂ and CHA₂DS₂-VASc scores predict ischaemic stroke/TIA events with similar accuracy to that observed in historical populations with non-valvular AF, but with lower absolute event rates. Further study of the utility of the CHADS₂ and CHA₂DS₂-VASc scores for the assessment of thromboembolic risk and selection of antithrombotic therapy in patients without AF is warranted.