- QRS Complex Duration of 120ms or More in Adults and Greater than 100ms in Children Ages 4-16.
- Broad, Notched or Slurred R Wave in Leads I, aVL, V5, and V6
- Absent Q waves in Leads 1, V5 and V6
- Time to (second) Peak of the R Wave in Leads with Notched QRS Complex (usually leads V5 and V6) Greater than 60ms
- ST and T Waves Usually Opposite in Direction to QRS Complex
The criteria for the ECG diagnosis of typical left bundle branch block recommended by the World Halth Organization (WHO) and the International Society and Federation for Cardiology (IFSC) in 1985 and recently endorsed by Ameican Heart Association and the American Colleege of Cardiology are listed here. In addition, the development of LBBB is frequently associated with a change in the mean frontal plane QRS axis, usually to the left, but less often to the right or superiorly.