Impact of quantitative ST-T analysis in patients with suspected myocardial infarction presenting with right bundle branch block

Background While left bundle branch block (LBBB) is a well-known risk feature in patients with acute myocardial infarction and a rapid invasive management is recommended, data supporting this strategy for patients with right bundle branch block (RBBB) is less robust. Methods In total, 2,139 patients with suspected ST-elevation myocardial infarction (STEMI) were triaged to acute coronary angiography based on a prehospital 12-lead ECG. Sensitivity and specificity for STEMI-ECG-criteria were compared in RBBB and non-BBB patients. Adjusted hazard ratios for 1-year overall mortality were computed. Results STEMI was adjudicated in 1,832/2,139 (85.6%) of all patients and in 102/117 (87.2%) of RBBB patients. ST-segment deviation followed typical ST-T patterns in most RBBB patients. Out of 17 RBBB patients without significant ST-changes STEMI was adjudicated in 14 (82%).Diagnostic accuracy of STEMI-criteria was comparable in RBBB and non-RBBB patients for inferior (sensitivity: 51.1% vs 59.1%, p=0.14; specificity: 66.7% vs 52.1%, p=0.33) and anterior STEMI (sensitivity: 35.2% vs 36.6%, p=0.80; specificity: 58.3% vs 49.5%, p=0.55). Diagnostic performance was lower for lateral STEMI in RBBB patients (sensitivity: 14.8% vs 4.4%, p=0.001; specificity: 75.0% vs 98.4%, p<0.001). Patients with RBBB had higher 1-year mortality compared to non-BBB patients (hazard ratio 2.3% (95% CI 1.25-4.21). Conclusion ECG-criteria used for detection of STEMI showed comparable diagnostic accuracy in RBBB and non-BBB patients. However, STEMI was frequently present in RBBB patients not fulfilling diagnostic ECG-criteria. RBBB-patients showed poorer outcome after 1 year. Consequently, the presence of RBBB in suspected STEMI cases signifies a high-risk feature, aligning with established guidelines.