A 73-year-old woman suffered from a myocardial infarct 6 years ago, but recovered and is free of angina. Routine ECG recorded in the cardiac clinic is as follow: 

• Sinus bradycardia, 50/min
• Left anterior fascicular block (LAFB) and Right bundle branch block (RBBB) (RBBB plus LAFB: Bifascicular block)

In RBBB the first 60 msec portion of the QRS reflects left ventricular activation.
The presence of a left fascicular block can therefore be diagnosed.

7 months later a follow-up ECG is recorded: 

Notice the change in the QRS pattern. Right bundle branch block is no longer present. The ECG shows only the pattern of left anterior fascicular block.