Effect of the ligament of Marshall excision during minimally invasive cardiac surgery-coronary artery bypass grafting (MICS-CABG) on the prevention of postoperative new-onset atrial fibrillation (LOMEX-AF): study protocol for a randomised controlled trial.

introductionPostoperative atrial fibrillation (POAF) remains one of the most common complications following coronary artery bypass grafting (CABG), including minimally invasive cardiac surgery-CABG (MICS-CABG). The ligament of Marshall (LOM), containing myocardial fibres and rich autonomic innervation, has been implicated in atrial arrhythmogenesis. Despite evidence that catheter ablation targeting the LOM or surgical interruption during conventional CABG can be effective, prophylactic surgical excision of the LOM during MICS-CABG has not been evaluated in randomised controlled trials (RCTs). METHODS AND ANALYSIS: The Ligament of Marshall Excision for the Prevention of Postoperative New-Onset Atrial Fibrillation (LOMEX-AF) trial is a single-centre, prospective, triple-blind (participants, outcome assessors, statisticians) RCT. Adults 30-80 years scheduled for elective MICS-CABG who meet inclusion/exclusion criteria will be randomised to Standard MICS-CABG with posterior left pericardiotomy (control) or the same procedure plus excision of a segment of the LOM (intervention). Resected tissue will be fixed for histopathology. PRIMARY OUTCOME: new-onset POAF during index hospitalisation defined as atrial fibrillation or atrial flutter lasting ≥30 s detected by ECG/telemetry. Secondary outcomes include frequency and duration of episodes, need for Class I/III antiarrhythmics or electrical cardioversion, intensive care unit and hospital length of stay, mechanical ventilation time and reoperation for bleeding. SAMPLE SIZE: 340 per arm (n=680 total) to detect a 50% relative reduction from an estimated 17% control event rate with 90% power, two-sided α=0.05, allowing 5% attrition. Primary analysis: intention-to-treat; categorical comparisons by χ² or Fisher exact test; continuous variables by t-test or Mann-Whitney U as appropriate; analyses performed in R. ETHICS AND DISSEMINATION: The study has been approved by the institutional ethics committee of Peking University Third Hospital, Beijing, China (IRB00006761-M20250847. 11 October 2025). Written informed consent will be obtained from all participants before enrolment. The trial will be conducted in accordance with the Declaration of Helsinki, Good Clinical Practice principles and applicable national regulations. The findings will be disseminated through publication in peer-reviewed journals and presentation at academic conferences. TRIAL REGISTRATION NUMBER: ChiCTR2500110913.