Incomplete Right Bundle Branch Block Diagnosis

Age-Specific QRS Duration Criteria

• The American Heart Association recommends a QRS duration of 110-120 ms for incomplete right bundle branch block (RBBB) in adults, with the same morphologic features as complete RBBB 1, 2, 3, 4, 5
• In children ages 4-16 years, the American Heart Association recommends a QRS duration of 90-100 ms for incomplete RBBB, with alternative criteria including terminal rightward deflection between 20-40 ms 1, 2, 3, 4, 5
• In children under 8 years, the American Heart Association recommends a QRS duration of 86-90 ms for incomplete RBBB, with terminal rightward deflection ≥20 ms but <40 ms also establishing the diagnosis 1, 2, 3, 4, 5

Critical Morphologic Requirements

• The American College of Cardiology guidelines state that incomplete RBBB requires the same morphologic features as complete RBBB, including rsr', rsR', or rSR' pattern in leads V1 or V2 1, 3
• The American College of Cardiology guidelines also state that incomplete RBBB requires an S wave duration > R wave duration or >40 ms in leads I and V6 in adults 2
• The American College of Cardiology guidelines recommend a normal R peak time in V5/V6 but >50 ms in V1 for incomplete RBBB 2

Important Clinical Caveats

• The American Heart Association states that an rsr' pattern in V1/V2 with normal QRS duration (<110 ms in adults) is a normal variant, particularly in children and young adults 1
• The American College of Cardiology guidelines state that incomplete RBBB can appear artifactually with high placement of V1/V2 electrodes or in pectus excavatum 1
• The American Heart Association guidelines exclude congenital heart disease with left-axis deviation in infancy from the criteria for incomplete RBBB 1, 4
• The American College of Cardiology guidelines recommend against using the terms "rsr'" and "normal rsr'" due to variable interpretation 1