Diagnosing Right Bundle Branch Block on ECG: Must All Criteria Be Met?
Yes, all traditional diagnostic criteria must be fulfilled to diagnose complete right bundle branch block (RBBB) on ECG. The ACC/AHA/HRS guidelines explicitly require meeting all three morphologic criteria plus the QRS duration threshold—this is not a "pick and choose" situation. 1, 2, 3
Complete RBBB: All Four Criteria Are Mandatory
To diagnose complete RBBB in adults, you must document all of the following 1, 3:
QRS duration ≥120 ms (≥100 ms in children 4-16 years; ≥90 ms in children <4 years) 1, 3
Characteristic morphology in V1/V2: rsr', rsR', or rSR' pattern where the R' or r' deflection is typically wider than the initial R wave 1, 3
Prolonged S wave in leads I and V6: S wave duration greater than R wave duration OR >40 ms 1, 3
If any single criterion is missing, you cannot diagnose complete RBBB. This is a firm diagnostic standard, not a suggestion. 1
Incomplete RBBB: Same Morphology, Shorter Duration
Incomplete RBBB requires identical morphologic criteria as complete RBBB but with a QRS duration of 110-119 ms in adults. 2, 3 The morphology must still include:
- The rsr', rsR', or rSR' pattern in V1/V2 2
- S wave >40 ms or longer than R wave in leads I and V6 2
- Normal R peak time in V5/V6 but >50 ms in V1 2
You cannot diagnose incomplete RBBB based solely on QRS duration—the morphologic features must all be present. 2
Critical Pitfalls to Avoid
Normal Variant Mimicking RBBB in Children
An rsr' pattern in V1/V2 with normal QRS duration is a normal variant in children and should NOT be labeled as incomplete RBBB. 2, 3 This is one of the most common misdiagnoses in pediatric ECGs. The pattern may also appear when lead V1 is placed higher than normal or to the right of its standard position, particularly when the r' is <20 ms. 2
Nonspecific Intraventricular Conduction Delay
If the QRS is >110 ms but the morphology criteria for RBBB are not met, diagnose this as nonspecific intraventricular conduction delay, not RBBB. 1 Don't force a RBBB diagnosis when the characteristic patterns are absent.
Congenital Heart Disease Exception
These diagnostic criteria do not apply to patients with congenital heart disease who have left-axis deviation present in infancy. 2, 3 Use caution in this population.
Clinical Reliability of These Criteria
The diagnostic criteria demonstrate excellent interobserver reliability when applied by physicians trained in ECG interpretation. Complete RBBB diagnosis shows a Fleiss' kappa of 0.93-0.96, indicating very good agreement. 4 Incomplete RBBB has slightly more variability (kappa 0.71-0.85) but still demonstrates substantial agreement. 4
The ECG features of complete RBBB remain stable over time, making serial measurements reliable for longitudinal follow-up. 5 This stability supports the use of these strict criteria in both clinical practice and research settings.
Special Diagnostic Consideration: Bilateral Bundle Branch Block
When you see RBBB morphology in V1 with absent S waves in leads I and aVL, this indicates concomitant left bundle branch delay (bilateral bundle branch block). 6 This pattern is 100% specific for pre-existing left bundle branch block and occurs in approximately 1.5% of hospitalized patients with RBBB. 6 Pure RBBB and bifascicular blocks are associated with S waves present in leads I and aVL. 6