ECG Criteria for Right Bundle Branch Block
To diagnose complete right bundle branch block (RBBB) on a 12-lead ECG, you must identify a QRS duration ≥120 ms in adults along with an rsr', rsR', or rSR' pattern in leads V1 or V2, a prolonged S wave (>40 ms or longer than the R wave) in leads I and V6, and an R peak time >50 ms in V1 while remaining normal in V5-V6. 1
Complete RBBB Diagnostic Criteria
The AHA/ACCF/HRS 2009 guidelines establish the gold standard for RBBB diagnosis. All of the first three criteria below must be present to make the diagnosis 1, 2:
1. QRS Duration (Age-Dependent)
- Adults: ≥120 ms
- Children 4-16 years: >100 ms
- **Children <4 years:** >90 ms
2. Right Precordial Lead Morphology (V1 or V2)
- Classic patterns: rsr', rsR', or rSR' configuration
- The terminal R' or r' deflection is typically wider than the initial R wave
- Variant pattern: In a minority of patients, a wide notched R wave may appear in V1/V2 without the classic triphasic pattern
3. Lateral Lead Findings (Leads I and V6)
- S wave duration greater than R wave duration OR S wave >40 ms in adults
4. R Peak Time
- V1: >50 ms (delayed)
- V5-V6: Normal timing
- This criterion becomes essential when a dominant R wave (with or without notching) appears in V1 without the classic rsr' pattern
Incomplete RBBB
Incomplete RBBB shares the same morphologic features as complete RBBB but with shorter QRS duration 2:
QRS Duration Thresholds:
- Adults: 110-119 ms
- Children 4-16 years: 90-99 ms
- Children <8 years: 86-89 ms
Important Pediatric Consideration:
In children, incomplete RBBB may be diagnosed when the terminal rightward deflection is 20-39 ms. An rsr' pattern in V1-V2 with normal QRS duration is a normal variant in children and should not be labeled as RBBB 2.
Critical Diagnostic Pitfalls
1. Lead Placement Errors
The ECG pattern of incomplete RBBB may appear in healthy individuals when lead V1 is recorded higher or more rightward than the standard position, particularly if the terminal r' wave is <20 ms 2.
2. Brugada Syndrome Mimicry
RBBB must be differentiated from Brugada syndrome types 2 and 3, which can appear similar. Key distinguishing features include 3:
- Measure the β angle (between upslope of S-wave and downslope of r'-wave in V1/V2)
- β angle <58° suggests true incomplete RBBB (87% negative predictive value for Brugada)
- β angle ≥58° raises concern for Brugada pattern (73% positive predictive value)
3. Avoid Ambiguous Terminology
Do not use terms like "rsr'" or "normal rsr'" to describe patterns, as these can be variously interpreted and lead to diagnostic confusion 2.
Clinical Context Matters
While the guidelines focus on ECG parameters, recent evidence highlights that RBBB is not always benign 4, 5:
- In asymptomatic general population, RBBB associates with increased cardiovascular mortality (HR 1.87) and MI risk (HR 1.67) 4
- Incomplete RBBB, however, shows no adverse prognostic association in population studies 4
- In specific contexts (post-TAVI, pulmonary embolism, structural heart disease), RBBB carries amplified clinical significance 6, 7
Algorithmic Approach to Diagnosis
Step 1: Measure QRS duration
- If <110 ms in adults → Not RBBB (may be normal variant in children)
- If 110-119 ms → Proceed to evaluate for incomplete RBBB
- If ≥120 ms → Proceed to evaluate for complete RBBB
Step 2: Examine V1/V2 morphology
- Look for rsr', rsR', rSR', or wide notched R wave
- If absent → Not RBBB
Step 3: Check lateral leads (I, V6)
- Confirm S wave >40 ms or S wave duration > R wave duration
- If absent → Diagnosis uncertain
Step 4: Verify R peak timing
- V1 should show delayed R peak (>50 ms)
- V5-V6 should show normal R peak timing
- Essential when dominant R wave present in V1
Step 5: Apply age-appropriate criteria for pediatric patients
Step 6: If diagnostic uncertainty exists, consider Brugada syndrome and measure β angle in V1/V2