Our objective was to determine stroke and thromboembolism event rates in patients with atrial fibrillation (AF) classified as “low risk” using the Anticoagulation and Risk Factors in Atrial Fibrillation (ATRIA) score and to ascertain event rates in this group in relation to the stroke risk assessment advocated in the 2012 European Society of Cardiology (ESC) guidelines (based on the CHA2DS2-VASc [congestive heart failure, hypertension, age ≥ 75 years, diabetes, previous stroke/transient ischemic attack, vascular disease, age 65 to 74 years, sex category] score). We tested the hypothesis that the stroke risk assessment scheme advocated in the ESC guidelines would be able to further refine stroke risk stratification in the low-risk category defined by the ATRIA score.
In our cohort of 207,543 incident patients with AF from 1999 to 2012, we identified 72,452 subjects who had an ATRIA score of 0 to 5 (low risk).
Even among these patients categorized as low risk using the ATRIA score, the 1-year stroke/thromboembolic event rate ranged from 1.13 to 36.94 per 100 person-years, when subdivided by CHA2DS2-VASc scores. In patients with an ATRIA score 0 to 5, C statistics at 1 year follow-up in the Cox regression model were significantly improved from 0.626 (95% CI, 0.612-0.640) to 0.665 (95% CI, 0.651-0.679) when the CHA2DS2-VASc score was used for categorizing stroke risk instead of the ATRIA score (P < .001).
Patients categorized as low risk using an ATRIA score 0 to 5 are not necessarily low risk, with 1-year event rates as high as 36.94 per 100 person-years. Thus, the stroke risk stratification scheme recommended in the ESC guidelines (based on the CHA2DS2-VASc score) would be best at identifying the “truly low risk” subjects with AF who do not need any antithrombotic therapy.