Background: Female sex, old age, and time to cardioversion increase the risk of thromboembolic complications (TEC) after cardioversion of atrial fibrillation (AF) < 48 h. The interaction of these variables is not known. We investigated the interaction of sex, age, and time to electrical cardioversion (ECV) on TEC in anticoagulant-naive patients with acute AF.

Methods and results: The primary outcome was a TEC within 30 days following ECV. Patients were divided into three age groups and time to cardioversion into <12 h and ≥12 h in 4715 ECVs. TEC occurred in 40 (0.8%) patients. In multivariate analysis, female sex, time to ECV, and vascular disease were independent predictors of TEC. For patients ≤75 cardioverted within 12 h, the incidence of TEC was low. In patients >75 TEC increased in both sexes and particularly in women (1.4% vs. 0.9%, p = 0.03). When ECVs exceeded 12 h, the risk of TEC was two- to four-fold higher in women in all age groups.

Conclusions: The risk of TEC increases substantially in patients >75 and ECVs ≥12 h, particularly in women. Time to cardioversion should be added to risk-stratification of ECVs of acute AF.