Impact of serum potassium levels on success of electrical cardioversion in atrial fibrillation

Background Electrical cardioversion (ECV) is an effective treatment for restoring sinus rhythm in supraventricular tachycardias such as atrial fibrillation (AFib) and atrial flutter (AFlu). In clinical practice, serum potassium is often adjusted towards the upper normal range prior to ECV, although evidence supporting a beneficial effect on acute cardioversion success is limited. This study investigated whether serum potassium levels within the normal range influence immediate ECV outcomes. Methods We conducted a retrospective single-center cohort study including adult patients who underwent ECV for AFib, AFlu, or focal atrial tachycardia between 2019 and 2024. Patients with hypokalemia, hyperkalemia, recent potassium-altering interventions or missing potassium values were excluded. Serum potassium was categorized as low normal (3.5–4.4 mmol/l) or high normal (4.5–5.5 mmol/l). Immediate ECV success was defined as restoration of a stable sinus rhythm documented by a 12-lead ECG. Secondary outcomes included restoration and maintenance of sinus rhythm at discharge. Results A total of 647 patients were analyzed (48.5% low-normal vs. 51.5% high-normal potassium). Immediate ECV success rates were similar between groups (88.2% vs. 87.1%, p = 0.66), and potassium levels did not differ between successful and unsuccessful cardioversions ( p = 0.55). Potassium was not predictive of immediate ECV success and not associated with the shock number or maximum energy applied ( p = 0.563 and p = 0.836).). At discharge, sinus rhythm rates were comparable between groups (80.3% vs. 80.8%, p = 0.87). Again, potassium was not different between patients with successful and unsuccessful cardioversion ( p = 0.62). Subgroup analyses across predefined normokalemic ranges showed no significant associations regarding immediate ECV success as well as ECV success at discharge (each p > 0.05). Conclusion Serum potassium levels within the normal range do not influence immediate or short-term success of electrical cardioversion in patients with atrial fibrillation or atrial flutter. These findings suggest that routine potassium optimization beyond correction of abnormal values is unlikely to improve acute ECV outcomes.