12-lead electrocardiogram (ECG) showing bifascicular block with right bundle branch block and left anterior fascicular block

The 12-lead ECG from a patient with a history of an anteroseptal myocardial infarction (Q waves seen in lead V1-V3) shows bifascicular block with RBBB and LAFB. A typical RBBB is seen with a QRS duration of 0.16 seconds and an rSR' configuration in lead V1 and a deep S wave in V6. The QRS complexes in leads II, III, and avF are negative, with a rS morphology, diagnostic of a pathologic left axis deviation, known as LAFB.