A 75-year-old man, followed in the cardiac clinic. He had triple aorto-coronary bypass surgery 15 year ago. He has remained stable and symptom-free during moderate exercise. His family doctor has referred him because his ECG has recently changed. He has continued to feel well:

• Sinus rhythm
• Right bundle branch block (RBBB)
• Left anterior fascicular block (LAFB)
• Bifascicular block (RBBB and LAFB)

Notice that the first 60-80 msec of the QRS show the pattern of LAFB: left axis deviation, qR in I and aVL, rS in the inferior leads. 

Please, compare this tracing with the ECG recorded two months earlier (ECG 2), that showed only left anterior fascicular block:

• Sinus rhythm
• Left anterior fascicular block