Right bundle-branch block (RBBB) and acute coronary syndrome (ACS) a narrative review

Right bundle-branch block (RBBB) is a common electrocardiographic finding that may be benign or may signify acute myocardial ischemia, particularly in patients presenting with chest pain. This narrative review examines the pathophysiology, diagnostic challenges, and clinical implications of new-onset RBBB in acute coronary syndrome (ACS). Acute RBBB often indicates proximal left anterior descending artery occlusion, leading to larger infarcts, higher rates of cardiogenic shock, ventricular arrhythmias, and mortality. We discuss mechanisms involving septal perforator ischemia, differentiate benign RBBB from pathological causes through clinical history, ECG features (e.g., rsR' pattern, appropriate discordant T-wave changes), and advanced testing. Key ECG red flags for occlusion myocardial infarction include concordant ST elevation, excessive discordant ST elevation (>25 % of QRS amplitude), reciprocal changes, and new bifascicular block. Evidence from meta-analyses, cohorts, and guidelines (e.g., 2017 ESC STEMI, 2022 ACC Chest Pain) supports treating new RBBB with ischemic symptoms as a STEMI equivalent, warranting urgent reperfusion. Limitations include observational data and lack of RBBB-specific validated criteria. Clinicians should use serial ECGs, troponins, and low-threshold angiography. This review underscores the need for vigilant ECG interpretation in emergency settings to improve outcomes. (198 words).