Residual stroke risk despite oral anticoagulation in patients with atrial fibrillation.

BACKGROUND

Oral anticoagulation (OAC) reduces the risk of thromboembolic events in patients with atrial fibrillation (AF); however, thromboembolism (TE) still can occur despite OAC. Factors associated with residual risk for stroke, systemic embolism, or transient ischemic attack events despite OAC have not been well described.

OBJECTIVE

The purpose of this study was to evaluate the residual risk of thromboembolic events in patients with AF despite OAC.

METHODS

A total of 18,955 patients were analyzed in the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF I and II) using multivariable Cox proportional hazard modeling. Mean age was 72 ± 10.7, and 42% were women. There were 451 outcome events.

RESULTS

The risk of TE despite OAC increased with CHADS-VASc score: 0.76 (95% confidence interval [CI] 0.63-0.92) events per 100 patient-years for CHADS-VASc score <4 vs 2.01 (95% CI 1.81-2.24) events per 100-patient years for CHADS-VASc score >4. Factors associated with increased risk were previous stroke or transient ischemic attack (hazard ratio [HR] 2.87; 95% CI 2.30-3.59; <.001), female sex (HR 1.52; 95% CI 1.24-1.86; <.001), hypertension (HR 1.50; 95% CI 1.09-2.06; = .01), and permanent AF (HR 1.47; 95% CI 1.12-1.94; = .001). When transient ischemic attack was excluded, the results were similar, but permanent AF was no longer significantly associated with thromboembolic events.

CONCLUSION

Patients with AF have a residual risk of TE with increasing CHADS-VASc score despite OAC. Key risk markers include previous stroke/transient ischemic attack, female sex, hypertension, and permanent AF.