Diagnostic Criteria for Incomplete Right Bundle Branch Block
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
Essential Diagnostic Criteria
QRS Duration Requirements (Age-Specific)
- Adults: QRS duration between 110 and 120 ms 1
- Children ages 4-16 years: QRS duration between 90 and 100 ms 1
- Children less than 8 years: QRS duration between 86 and 90 ms 1
Required Morphologic Features
The morphologic criteria are identical to complete RBBB and must include: 1
rsr', rsR', or rSR' pattern in leads V1 or V2, where the R' or r' deflection is usually wider than the initial R wave 1
- In a minority of patients, a wide and often notched R wave pattern may be seen in lead V1 and/or V2 1
S wave of greater duration than R wave or >40 ms in leads I and V6 (in adults) 1
Normal R peak time in leads V5 and V6 but >50 ms in lead V1 1
Special Pediatric Consideration
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 1
Critical Clinical Pitfalls to Avoid
Normal Variants That Mimic Incomplete RBBB
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 1
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 1
The terms "rsr'" and "normal rsr'" are not recommended to describe these patterns because their meaning can be variously interpreted 1
Pathologic Conditions to Exclude
When encountering an rsr' pattern with QRS <120 ms, you must differentiate incomplete RBBB from: 2
- Type 2 Brugada ECG pattern (requires specific angle measurements and drug challenge testing) 3
- Right ventricular enlargement 2
- Arrhythmogenic right ventricular cardiomyopathy 2
- Atrial septal defect (particularly ostium secundum type—listen for fixed splitting of S2) 2
- Ventricular preexcitation (WPW syndrome) 2
- Hyperkalemia 2
Important Exclusion Criteria
These criteria do not apply to patients with congenital heart disease in whom left-axis deviation is present in infancy 1
Clinical Context and Significance
When Incomplete RBBB is Benign
- Usually does not require further evaluation if the clinical examination is normal 2
- Common finding in athletes and young patients, considered benign unless accompanied by family history, symptoms, or left ventricular hypertrophy 2
- May be seen with pectus excavatum (P wave may be negative) or flat chest 4, 2
When Further Evaluation is Warranted
If abnormalities are found on clinical examination, heart disease should be excluded 2. Pay particular attention to: