BACKGROUND Antithrombotic recommendations for relatively low risk patients with atrial fibrillation (AF) are not well established. Some patients with CHADS(2) score = 0 have a CHA(2) DS(2) -VASc score of 2, which indicated warfarin therapy in the latter system. We evaluated the thromboembolic risk in AF patients with a CHADS(2) score of 0 or 1.

METHODS A total of 695 patients with AF that were followed for ≥ 12 months (median 65.6 months, range 12-138 months), were analyzed retrospectively. The modified CHADS(2) score (MCS) was applied as follows. Each CHADS(2) score group was divided into 2 groups, A and B (i.e., MCS 0A vs 0B, and MCS 1A vs 1B) according to the number of nonmajor risk factors (female gender, chronic kidney disease, coronary artery disease, age 65-74 years). Group A had 0 or 1, and group B had 2 or more nonmajor risk factors.

RESULTS In patients with CHADS(2) score = 1, there were 13 thromboembolic events (0.65%/year) in 343 MCS 1A patients, and 12 thromboembolic events (1.90%/year) in 108 MCS 1B patients. Thromboembolic risk was significantly higher in the MCS 1B compared to the MCS 1A patients (P = 0.006). In 244 patients with CHADS(2) score = 0, the thromboembolic risk of MCS 0B was similar to that of MCS 0A (P = 0.095), and 26 patients had a CHA(2) DS(2) -VASc score of 2.

CONCLUSION Patients with MCS 1B had a higher thromboembolic risk than patients with MCS 1A. Antithrombotic strategies for patients with a CHA(2) DS(2) -VASc score of 2 but a CHADS(2) score of 0 need further investigation.