Gurmeen Kaur, MBBS
@kaurgurmeen
Non-valvular atrial fibrillation (AF) is a cause of at least 15-20% of strokes in the U.S., with a 5-times increased risk when compared to patients with no atrial fibrillation. The safety, efficacy and availability of oral anticoagulants, in addition to Vitamin K antagonists like warfarin, have made strokes secondary to atrial fibrillation virtually preventable. This has created a need for accurate Stroke Risk Assessment and Stratification.
Various stroke risk schemas over the years have included AFI/ SPAF (1994), CHADS2 (2001), Framingham (2003), NICE (2006) and the relatively recent CHA2DS2-VASc Score, also referred to as Birmingham 2009, that accounts for congestive heart failure, hypertension, 75 years of age and older (2 points), diabetes mellitus, previous stroke or transient ischemic attack (2 points), vascular disease, 65 to 74 years of age, female sex.
Kim et al study a total of 5855 oral anticoagulant (OAC) naïve patients with AF to determine whether the CHA2DS2-VASc score could be reliably used for the Asian population, because the validation studies were performed in an all-Caucasian cohort and various Asian studies have previously reported ethnic differences in the conventional stroke risk factors.
Among the 5855 OAC naïve patients with AF, identified from the Korean NHIS sample cohort database, 14% experienced ischemic stroke in the 50-month follow-up period. Primary end point was incident ischemic stroke, and secondary end point was systemic embolism.
Literature suggests that the use of warfarin lowers stroke risk to 1.7%, and OACs may further reduce it to 0.9% or less (smoother therapeutic anticoagulation whereas warfarin approaches efficacy only 70% of the time). As expected, the group with low CHA2DS2-VASc scores (0 in men or 1 in females) had an incident stroke rate of less than 1% per year. As aspirin has about 19% efficacy in reducing thromboembolic events, adjustments were made in those exposed to aspirin.
Interestingly, the low risk category of the CHA2DS2-VASc score was predictive of an absence of new stroke in the 5-year follow up (p<0.001). Additionally, all the stroke risk factors showed significant association with incident strokes and composite thromboembolic events other than female sex. This is consistent with prior Asian studies (Japan, China and Taiwan) — female sex is not a risk factor in the Asian population, and stroke rates are actually lower than those in males.
In conclusion, CHA2DS2-Vasc is an excellent tool for stroke risk stratification in an Asian cohort, especially for identifying low-risk patients not needing anti-coagulation. Further studies are needed to establish if the lower risk in females is a true association.
