Clinical and Laboratory Predictors Associated With Stroke or Systemic Embolism in Low Risk Atrial Fibrillation Patients (CLASS-AF)

Both European and American guidelines recommend the use of the CHA2DS2-VASc risk score which has been validated as useful risk stratification for stroke prediction in AF from several independent cohorts. The guidelines have suggested that, in non-valvular AF, OAC could be omitted for males with a CHA2DS2-VASc score of 0 and for females with a score of 1 given the true low risk of ischemic stroke in that population. The American guideline has still suggested anti-platelets therapy could be recommended in patients who only have one additional risk factor for stroke. The risk of ischemic stroke in Asian people, however, has been known to be quite different from that in Western people, especially in low risk (CHA2DS2-VASc score of 0 or 1) patients based on the CHA2DS2-VASc score. In a nationwide study from Taiwan, the annual risk of ischemic stroke was 1.21% in AF patients with a CHA2DS2-VASc score of 0 and 2.16% in AF patients with a CHA2DS2-VASc score of 1, which were much higher than that reported from Western countries. Another study which enrolled 9727 Hong Kong AF patients from a hospitalized cohort, the annual stroke rate was as high as 2.41% among 395 patients with a CHA2DS2-VASc score of 0. Furthermore, a population-based study in an East Asian cohort of 22 million people found an increased risk of stroke in younger patients (i.e., 30-55 years) with AF who are not recommended for prevention of thromboembolism by current guidelines.Thus, stroke risk among Asian patients with AF and a CHA2DS2-VASc score of 0 or 1 might be higher than that seen among Caucasians, and OAC should be recommended in such patients for effective stroke prevention.

In addition, literature review suggests that female sex as an independent risk factor of stroke is still controversial, because some studies demonstrated that the odds ratio or hazard ratio of female to male sex for thromboembolism is not significant. Indeed, the analysis of a J-RHYTHM registry revealed that female sex was not a risk for thromboembolism in the Japanese cohort. Therefore, the novel risk stratification for stroke prevention in AF patients who have CHA2DS2-VASc score of 0 or 1 in men or CHA2DS2-VASc score of 1 or 2 in female should be needed in Asian population in order to define true low risk patients in the low risk population based on the CHA2DS2-VASc scoring system.