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

Clinical Research in Cardiology https://doi.org/10.1007/s00392-026-02944-0 ORIGINAL PAPER Impact of serum potassium levels on success of electrical cardioversion in atrial fibrillation Manuel J. Vogel1 · Kilian Hacker1 · Jonas Herting1 · Moritz T. Huttelmaier1 · Stefan Frantz1 · Thomas H. Fischer1 Received: 20 February 2026 / Accepted: 9 May 2026 © The Author(s) 2026 Abstract 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. * Manuel J. Vogel 1 Department of Internal Medicine I, University Clinic Würzburg, Oberdürrbacherstraße 6, 97080 Würzburg, Germany Vol.:(0123456789) Clinical Research in Cardiology Graphical Abstract Keywords Atrial fibrillation · Potassium · Electrical cardioversion Introduction Electrical cardioversion (ECV) is a highly effective and routinely performed procedure for the immediate restoration of sinus rhythm in patients with supraventricular tachycardias like atrial fibrillation (AFib) and atrial flutter (AFlu). While the overall acute success rate is high, a subset of patients fails to convert to sinus rhythm or experience very early recurrence of arrhythmia. The identification of factors that influence the success of cardioversion is therefore of practical relevance, as they may help to optimize procedural conditions and improve acute outcomes. Serum potassium has been identified as a significant factor of myocardial excitability and electrical conduction [1]. It is well established that deviations from normal potassium levels have the capacity to alter action potential characteristics and thereby facilitate the occurrence of arrhythmias [1]. Consequently, the precise correction of electrolyte abnormalities is customary in patients with cardiac arrhythmia. In routine clinical practice, potassium levels are frequently adjusted towards the upper normal range prior to cardioversion, on the assumption that this may increase the likelihood of immediate rhythm conversion and electrical stability of the atrial myocardium. Nevertheless, there is a paucity of evidence to support the hypothesis that elevated levels of potassium have a beneficial effect on the acute success of ECV. Even though a number of studies have examined the relationship between potassium levels and the risk of arrhythmia in different clinical situations, data specifically addressing the immediate success of cardioversion in atrial fibrillation and atrial flutter are limited and inconsistent. Furthermore, the majority of extant studies do not differentiate between potassium values within the normal range, thereby leaving uncertainty as to whether higher normal potassium levels confer any procedural advantage. The present study therefore sought to evaluate the impact of serum potassium levels within the normal range on immediate ECV success in patients undergoing cardioversion for atrial fibrillation, atrial flutter, and focal atrial Clinical Research in Cardiology tachycardia. The objective of this study was to make a comparison between low-normal and high-normal potassium levels in a retrospective single-center cohort. Methods Study design This study was conducted as a retrospective observational single-center cohort study. Patients who underwent electrical cardioversion for supraventricular tachycardia (atrial fibrillation, atrial flutter, and focal atrial tachycardia) at the Department of Internal Medicine I at the University Hospital Würzburg between 2019 and 2024 were included. The study was approved by the local ethics committee and was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. Predefined exclusion criteria were as follows: – – – – – Age < 18 years Serum potassium missing or acquired > 24 h before ECV Hemolytic laboratory sample Patients with potassium < 3.5 mmol/l or > 5.5 mmol/l Potassium supplementation, intravenous diuretics, or dialysis between potassium measurement and ECV If one patient received multiple ECV in the analyzed period, we included the first case that was eligible. Data acquisition and definition Demographic and ECV data, baseline medication, preexisting diseases, and laboratory results were documented for each patient. Primary arrhythmia diagnosis was defined according to the discharge diagnosis; in uncertain cases, the electrocardiogram was re-analyzed by a member of the electrophysiology team. “Immediate ECV-success” was considered when the patient exhibited a sinus rhythm directly after the procedure documented by a 12-lead ECG. Further we evaluated short-term ECV success defined as immediate ECV success and maintenance of sinus rhythm until the time of discharge. Potassium levels were defined according to the 50th percentile/median as “low normal” (low normal potassium, lnp) ranging from 3.5 to 4.4 mmol/l, while values ≥ 4. (...truncated)