Case Report: Transient Complete Atrioventricular Block During Coronary Sinus Reducer Implantation: An Unexpected Complication

Background and Clinical Significance: The Coronary Sinus Reducer (CSR) is a percutaneous therapeutic option for patients with refractory angina who are unsuitable for further myocardial revascularization. The procedure has a generally favorable safety profile, with a low rate of reported procedural complications. To our knowledge, major atrioventricular (AV) conduction disturbances during CSR implantation have not been previously described. This case highlights a rare but clinically relevant intraprocedural complication; Case Presentation: A 71-year-old man with multivessel coronary artery disease and previous coronary artery bypass grafting was referred for CSR implantation because of refractory angina despite optimal medical therapy and lack of further revascularization options. The procedure was performed via a right jugular venous approach. Baseline electrocardiography showed right bundle branch block and findings consistent with previous inferior myocardial infarction, without definite criteria for left anterior fascicular block. During coronary sinus cannulation, the patient developed transient complete AV block, resulting in an approximately 8–10-second ventricular pause without a stable ventricular escape rhythm. The conduction disturbance resolved after catheter withdrawal and repositioning. Given the severity of the event, a temporary transvenous pacemaker was inserted via the right femoral vein, allowing safe completion of CSR implantation. At three-month follow-up, angina had improved from Canadian Cardiovascular Society class III to class I, and no recurrent advanced AV block was documented; Conclusions: Transient complete AV block may occur during CSR implantation, particularly during coronary sinus manipulation and possibly in patients with pre-existing conduction disease. Careful catheter handling, prompt recognition of conduction disturbances, and immediate availability of temporary pacing support should be considered in selected high-risk patients undergoing CSR implantation.