What are the criteria for diagnosing Right Bundle Branch Block (RBBB)?

Diagnostic Criteria for Right Bundle Branch Block (RBBB)

The diagnosis of complete Right Bundle Branch Block (RBBB) requires a QRS duration ≥120 ms in adults (>100 ms in children 4-16 years, >90 ms in children <4 years) along with specific morphological features including an rsr', rsR', or rSR' pattern in leads V1/V2, S waves of greater duration than R waves in leads I and V6, and normal R peak time in V5/V6 but >50 ms in V1. 1, 2

Complete RBBB Criteria

QRS Duration Requirements:

• Adults: ≥120 ms
• Children 4-16 years: >100 ms
• Children <4 years: >90 ms 1, 2

Morphological Features (all should be present):

1. rsr', rsR', or rSR' pattern in leads V1 or V2

   • The R' (second R wave) is usually wider than the initial r wave
   • In some cases, a wide and often notched R wave pattern may be seen in V1/V2 1

2. S wave characteristics in lateral leads

   • S wave of greater duration than R wave OR
   • S wave >40 ms in leads I and V6 in adults 1

3. R peak time

   • Normal R peak time in leads V5 and V6
   • R peak time >50 ms in lead V1 1

Incomplete RBBB Criteria

QRS Duration Requirements:

• Adults: 110-119 ms
• Children 4-16 years: 90-100 ms
• Children <4 years: 86-90 ms 1, 2

Morphological Features:

• Same morphological criteria as complete RBBB
• In children: terminal rightward deflection <40 ms but ≥20 ms 1

Special Considerations

Age-Related Variations:

• In children, an rsr' pattern in V1 and V2 with normal QRS duration is a normal variant 1
• ECG pattern of incomplete RBBB may be present without heart disease, particularly when lead V1 is recorded higher than normal position 1

Diagnostic Challenges:

• When a pure dominant R wave with/without notch is present in V1, the R peak time criterion becomes particularly important 1
• RBBB can sometimes present with atypical features, especially with abnormal QRS axis 3

Clinical Significance

• Complete RBBB is associated with increased risk of atrial fibrillation development (OR 3.329) 4
• Bifascicular block (RBBB plus fascicular block) shows statistically significant association with cardiovascular events 5
• Approximately 1.5% of patients with RBBB have bilateral bundle-branch delay pattern 6

Differentiating RBBB from Other Conditions

• In RBBB pattern with reversed R/S ratio in lead V6, an RS/QRS ratio >0.41 in lead V6 can help distinguish ventricular tachycardia from supraventricular tachycardia 7
• True bilateral bundle branch block can be identified by RBBB pattern with absent S waves in leads I and aVL 6

Common Pitfalls in RBBB Diagnosis

• QRS axis changes can alter the expected RBBB pattern, particularly in the left precordial leads 3
• Incomplete RBBB in asymptomatic young individuals or athletes is often benign and may represent normal physiological cardiac remodeling 2
• Progression from incomplete to complete RBBB may indicate development of heart failure or chronic kidney disease 5