Prognostic differences between different types of bundle branch block during the early phase of acute myocardial infarction: insights from the Hirulog and Early Reperfusion or Occlusion (HERO)-2 trial

Aims Bundle branch block (BBB) early during acute myocardial infarction (AMI) is often considered high risk for mortality. Little is known about how different BBB types influence prognosis. Methods and results The HERO-2 trial recruited 17 073 patients with ischaemic symptoms lasting >30 min and either ST elevation with or without right bundle branch block (RBBB) or presumed-new left bundle branch block (LBBB). Electrocardiograms were performed before and 60 min after the start of fibrinolytic therapy. Using patients with normal intraventricular conduction as a reference, odds ratios (ORs) for 30-day mortality were calculated for different BBB types (LBBB, RBBB with anterior AMI, and RBBB with inferior AMI) present at randomization and/or 60 min, with adjustment for recruitment region, pre-infarction characteristics, time to randomization, hemodynamics, and Killip class. At randomization, the 873 patients (5.11%) with BBB had worse baseline characteristics than patients without BBB. In patients presenting with LBBB (n=300), the ORs for 30-day mortality were 1.90 (95% CI 1.39–2.59) before and 0.68 (0.48–0.99) after adjustment for other prognosticators. In patients presenting with RBBB (n=415) and anterior AMI, the ORs were 3.52 (2.82–4.38) before and 2.48 (1.93–3.19) after adjustment. In patients presenting with RBBB and inferior AMI (n=158), the ORs were 1.74 (1.06–2.86) before and 1.22 (0.71–2.08) after adjustment. Within 60 min, 143 patients (0.92%) developed new BBB. The adjusted ORs for 30-day mortality were 2.97 (1.16–7.57) in the 25 patients with new LBBB, 3.84 (2.38–6.22) in the 100 with new RBBB and anterior AMI, and 2.23 (0.54–9.21) in the 18 with new RBBB and inferior AMI. Conclusion RBBB accompanying anterior AMI at presentation and new BBB (including LBBB) early after fibrinolytic therapy are independent predictors of high 30-day mortality. These electrocardiographic features should be considered in risk stratification to identify high-risk patients.