- Prolonged QRS duration ≥120 ms in adults, >100 ms in children ages 4-16 years of age, and >90 ms in children <8 years of age
- rsR’, rsr’, or rSR’ complexes in V1 or V2, with the secondary R wave (r’ or R’) usually wider than the initial R wave (r); some have a wide and often notched R wave pattern in V1 and/or V2
- S wave duration greater than R wave duration, or S wave duration >40 ms in I and V6 in adults
- Normal R wave peak time in V5 and V6, but >50 ms in V1
*The first 3 criteria should be present to make the diagnosis. When a pure dominant R wave with or without a notch is present in V1, the last criteria should be satisfied.
Note: RBBB results in secondary ST-T segment changes (ST depression or T wave inversion) unrelated to ischemia in V1-V2. This can be seen in normal adults without structural heart disease; however, in the setting of known coronary artery disease, RBBB carries a 2-fold increase in mortality.