MAX-SHOCK: A Pragmatic Randomized Controlled Trial Comparing Biphasic Defibrillators Used in Routine Cardioversion of Atrial Fibrillation.

UNLABELLED: Atrial fibrillation (AF) frequently requires rhythm control with electrical cardioversion, with approximately 10%-20% of patients undergoing electrical cardioversion annually. Despite its widespread use, cardioversion failure remains common, and clinical practice varies considerably with respect to shock energy, pad positioning, and defibrillator technology. Commonly used biphasic defibrillators differ in not only maximum energy output but also proprietary waveform characteristics and impedance-compensation algorithms, factors that may independently influence cardioversion success. To date, these devices have not been compared directly in a randomized clinical trial.The maximum energy shocks trial is a single-centre, prospective, randomized, single-blinded controlled study comparing 2 widely used external defibrillators: the Physio-Control LIFEPAK 20 (Physio Control, location), capable of delivering up to 360 J, and the ZOLL Medical R-Series (ZOLL Medical, Chelmsford, MA), with a maximum programmable energy of 200 J. Rather than isolating shock energy alone, the trial evaluates real-world device performance, recognizing that waveform design and adaptive algorithms differ among manufacturers. We hypothesize that the 360-J-capable defibrillator will be associated with a higher rate of successful cardioversion when used within a standardized stepwise protocol.Adults (aged ≥ 18 years) with persistent AF scheduled for elective cardioversion are randomized in a single-blinded fashion. The primary outcome is successful cardioversion, defined as restoration of sinus rhythm with at least 2 consecutive sinus or atrial-paced beats. A total of 356 patients will be enrolled to assess superiority.This trial represents the first randomized comparison of real-world defibrillator system performance in AF cardioversion and will help inform future cardioversion protocols and defibrillator selection.

CLINICAL TRIAL REGISTRATION: NCT06556667.