Aims: Rhythm control using electrical cardioversion (CV) is a common treatment strategy for patients with symptomatic atrial fibrillation (AF). To guide clinical decision making, we sought to assess if electrocardiographic interatrial blocks could predict CV failure or AF recurrence as the phenomenon is strongly associated with atrial arrhythmias. Methods: This study included 715 patients who underwent a CV for persistent AF lasting >48 h. P-wave duration and morphology were analyzed in post-procedure or the most recent sinus rhythm electrocardiograms and compared with rates of CV failure and AF recurrence within 30 days after CV as well as their combination (ineffective CV). Results: CV was unsuccessful in 63 out of 715 patients (8.8%) and AF recurred in 209 out of 652 (29.2%) patients within 30 days after CV. Overall, 272 (38.0%) CVs turned out ineffective. Advanced interatrial block (AIAB) defined as P-wave duration !120 ms and biphasic morphology in inferior leads (II, III and aVF) was diagnosed in 72 (10.1%) cases. AIAB was an independent predictor for CV failure (OR 4.51, 95%CI 1.76-11.56, p ¼ .002), AF recurrence (OR 2.93, 95%CI 1.43-5.99, p ¼ .003) and ineffective CV (OR 3.87, 95%CI 2.04-7.36, p < .001). Conclusion: AIAB predicted CV failure, AF recurrence as well as their composite. This study presents an easy electrocardiographic tool for the identification of patients with persistent AF who might not benefit from an elective CV in the future. KEY MESSAGESInteratrial blocks are very common in patients with atrial fibrillation. Advanced interatrial block predicts ineffective cardioversion.

at successful induction in the 0.3 and 0.4 mg kg À1 groups than that in the 0.2 mg kg À1 group.

Background Rhythm control using electrical cardioversion (CV) is a common treatment strategy for patients with symptomatic atrial fibrillation (AF). However, little is known about electrocardiographic (ECG) markers predicting CV failure and AF recurrence. Methods This study included 726 patients who underwent a CV for AF lasting &gt;48h in a referral hospital. We analysed markers of atrial cardiomyopathy in post-CV sinus rhythm ECGs and compared them with CV failure and AF recurrence rates within 30 days after CV as well as their combination (ineffective CV). Of those with failed CV the most recent sinus rhythm ECG was used. Results CV was unsuccessful in 66 out of 726 patients (9.09%). Advanced interatrial block (IAB) defined as P-wave duration ≥120ms and biphasic morphology in inferior (II, III and aVF) leads (OR 3.96, 95%-CI 2.09–7.52, p&lt;0.001) was an independent predictor for CV failure. Within 30 days after CV, AF recurred in 214 (32.4%) patients. Advanced IAB (OR 2.10, 95%-CI 1.19–3.72, p=0.011) was an independent predictor for AF recurrence. In total CV was ineffective (CV failure or AF recurrence) 280 of 726 times (38.6%). Advanced IAB (OR 2.72, 95%-CI 1.64–4.51, p&lt;0.001) was an independent predictor for ineffective CV. Partial IAB categorized as P-wave duration ≥120ms with no biphasic morphology did not predict any end points. Conclusions Advanced IAB predicts CV inefficacy. This study identified ECG markers of atrial cardiomyopathy for clinical use in CV patient selection. Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): This study research was funded by grants from the Finnish Medical Foundation, the Finnish Foundation for Cardiovascular Research, State Clinical Research Fund of Turku University Hospital, Turku, Finland, Finnish Cardiac Society, the Emil Aaltonen Foundation, and the Maud Kuistila Foundation.