How much does elective cardioversion increase the risk of ischaemic stroke compared to the baseline risk in atrial fibrillation? A nationwide study.

AIMS: Patients with atrial fibrillation (AF) undergoing cardioversion (CV) are exposed to increased risk of ischaemic stroke (IS), but the exact magnitude is unknown. We compared IS rates during the post-CV period with the long-term risk in AF patients using guideline-recommended anticoagulation therapy. METHODS AND RESULTS: This nationwide register-based study included all AF patients undergoing first-ever elective CV between 2012 and 2018 in Finland. Breakpoint analysis identified a cut-off point in the IS rate at 2 weeks after CV. Follow-up was split into two intervals: the immediate 2-week post-CV period and the subsequent period up to 360 days. Stroke rates were calculated, and incidence rate ratios were estimated with Poisson regression. Interactions between the two follow-up periods and conventional IS risk factors as well as anticoagulation treatment were assessed. A total of 9625 patients were identified (mean age 67.7 ± 9.9 years, 61.2% men, mean CHA2DS2-VA score 2.2 ± 1.4). Warfarin was used in 6245 (64.9%) and non-vitamin K oral anticoagulants in 3380 (35.1%) patients. Overall, 92 (1.0%) patients experienced IS during the year after CV. Breakpoint analysis and survival plot displayed a higher incidence of IS within the first 2 weeks after CV, stabilizing thereafter to a consistent level. The adjusted IS rate during the first 2 weeks was 7.5-fold (95% confidence interval: 4.8-11.8) compared to the subsequent IS rate. This excess risk was independent of the anticoagulation type or conventional stroke risk factors. CONCLUSION: The rate of IS was roughly seven times higher during the first 2 weeks after elective CV compared to the subsequent 360 days.