Diagnostic Criteria for Incomplete Right Bundle Branch Block

Essential Diagnostic Criteria

• The American College of Cardiology recommends that Incomplete RBBB is diagnosed when the QRS morphology matches complete RBBB criteria but with a QRS duration between 110-119 ms in adults, maintaining the characteristic rsr', rsR', or rSR' pattern in leads V1 or V2 1
• The American College of Cardiology states that in adults, QRS duration between 110 and 120 ms is required for diagnosis of Incomplete RBBB 2, 3
• The American College of Cardiology recommends that in children ages 4-16 years, QRS duration between 90 and 100 ms is required for diagnosis of Incomplete RBBB 2, 3
• The American College of Cardiology states that in children less than 8 years, QRS duration between 86 and 90 ms is required for diagnosis of Incomplete RBBB 2, 3
• The morphologic criteria for Incomplete RBBB are identical to complete RBBB and must include an rsr', rsR', or rSR' pattern in leads V1 or V2, where the R' or r' deflection is usually wider than the initial R wave, according to the American College of Cardiology 1, 2
• The American College of Cardiology recommends that an S wave of greater duration than R wave or >40 ms in leads I and V6 is required for diagnosis of Incomplete RBBB in adults 1, 2
• The American College of Cardiology states that a normal R peak time in leads V5 and V6 but >50 ms in lead V1 is required for diagnosis of Incomplete RBBB 1, 2

Special Pediatric Consideration

• The American College of Cardiology recommends that in children, incomplete RBBB may be diagnosed when the terminal rightward deflection is less than 40 ms but ≥20 ms, even with the other criteria present 2, 3

Critical Clinical Pitfalls to Avoid

Normal Variants That Mimic Incomplete RBBB

• The American College of Cardiology states that an rsr' pattern in V1 and V2 with normal QRS duration is a normal variant in children and should not be labeled as incomplete RBBB 2, 3
• The American College of Cardiology recommends that the pattern may appear when lead V1 is recorded higher than or to the right of normal position, particularly when the r' is <20 ms 2, 3
• The American College of Cardiology states that the terms "rsr'" and "normal rsr'" are not recommended to describe these patterns because their meaning can be variously interpreted 2, 3

Important Exclusion Criteria

• The American College of Cardiology recommends that these criteria do not apply to patients with congenital heart disease in whom left-axis deviation is present in infancy 2, 3, 4