Atrial fibrillation patients categorized as "not for anticoagulation" according to the 2014 Canadian Cardiovascular Society algorithm are not "low risk".

BACKGROUND: Oral anticoagulation (OAC) is highly effective for stroke prevention in nonvalvular atrial fibrillation. We explored rates of stroke/thromboembolism/transient ischemic attack among the "OAC not recommended" patient group defined according to the 2014 Canadian Cardiovascular Society (CCS) algorithm (based on the Congestive Heart Failure, Hypertension, Age, Diabetes, Stroke/Transient Ischemic Attack [CHADS2] score) who would have been offered OAC using the European Society of Cardiology (ESC) guidelines approach (based on the Congestive Heart Failure, Hypertension, Age [≥75 years], Diabetes, Stroke/Transient Ischemic Attack, Vascular Disease, Age [65-74 years], Sex [Female]; CHA2DS2-VASc score).

METHODS: We identified 22,582 nonanticoagulated patients age < 65 years with a CHADS2 score of 0 who were stratified according to the CHA2DS2-VASc score, except female sex, which would be an indication for OAC according to the ESC guidelines. Event rates for each risk strata were compared using Cox proportional hazard ratios.

RESULTS: The overall rate of the combined end point of ischemic stroke/systemic embolism/transient ischemic attack was 4.32 per 100 person-years (95% confidence interval [CI], 3.26-5.74) at 1 year, among the patients who would have had an indication for OAC therapy according to ESC guidelines and "OAC not recommended" according to CCS algorithm. This corresponded to an adjusted hazard ratio of 3.08 (95% CI, 2.21-4.29) relative to the subgroup with no indication for OAC according to the ESC guidelines. A subgroup of patients with previous vascular disease and CHADS2 score of 0 (ie, recommended only aspirin treatment according to the CCS algorithm) had an event rate of 4.84 (95% CI, 3.53-6.62) per 100 person-years at 1-year follow-up.

CONCLUSIONS: Based on the 2014 CCS algorithm, the "OAC not recommended" subgroup can have a high 1-year stroke rate overall, showing that such patients are not "low risk." Use of the ESC guideline approach (based on the CHA2DS2-VASc) offers refinement of stroke risk stratification in such patients.