What are the electrocardiogram (ECG) criteria to diagnose a right bundle branch block (RBBB)?

How to Identify Right Bundle Branch Block on ECG

To diagnose complete right bundle branch block (RBBB), you must identify a QRS duration ≥120 ms in adults combined with the characteristic rsr', rsR', or rSR' pattern in leads V1 or V2, along with a prolonged S wave (>40 ms or longer than the R wave) in leads I and V6. 1

Essential Diagnostic Criteria for Complete RBBB

The American Heart Association/American College of Cardiology Foundation/Heart Rhythm Society guidelines establish that all three of the following criteria must be present to diagnose complete RBBB: 1

1. QRS Duration Thresholds

• Adults: QRS duration ≥120 ms 1
• Children ages 4-16 years: QRS duration >100 ms 1
• **Children <4 years:** QRS duration >90 ms 1

2. Characteristic Morphology in Right Precordial Leads

The hallmark finding is an rsr', rsR', or rSR' pattern in leads V1 or V2, where the R' or r' deflection is typically wider than the initial R wave. 1 In a minority of patients, you may instead see a wide, often notched R wave pattern in V1 and/or V2. 1

3. Prolonged S Wave in Lateral Leads

In adults, the S wave duration must be greater than the R wave duration OR exceed 40 ms in leads I and V6. 1

4. R Peak Time Criteria

The R peak time should be normal in leads V5 and V6 but >50 ms in lead V1. 1 When a pure dominant R wave (with or without a notch) is present in V1, this criterion becomes particularly important for diagnosis. 1

Incomplete RBBB Criteria

Incomplete RBBB shares the same morphologic features as complete RBBB but with a shorter QRS duration. 2

QRS Duration for Incomplete RBBB:

• Adults: 110-120 ms 1, 2
• Children ages 4-16 years: 90-100 ms 1, 2
• Children <8 years: 86-90 ms 1, 2

The morphologic criteria remain identical to complete RBBB, including the rsr', rsR', or rSR' pattern in V1/V2 and prolonged S waves in leads I and V6. 2

Special Pediatric Consideration:

In children, incomplete RBBB may be diagnosed when the terminal rightward deflection is <40 ms but ≥20 ms, even with other criteria present. 2

Critical Pitfalls to Avoid

Normal Variants That Mimic RBBB:

• In children, an rsr' pattern in V1 and V2 with normal QRS duration is a normal variant and should NOT be labeled as incomplete RBBB. 1, 2
• This pattern may appear when lead V1 is recorded higher than or to the right of the normal position, particularly when the r' is <20 ms. 1, 2
• The terms "rsr'" and "normal rsr'" should not be used to describe these patterns due to variable interpretation. 1, 2

Important Exclusions:

• These diagnostic criteria do not apply to patients with congenital heart disease who have left-axis deviation present in infancy. 1, 2

Differential Diagnosis - Brugada Syndrome:

When evaluating RBBB patterns, consider Brugada syndrome if the patient has a personal or family history of sudden death, as this familial arrhythmogenic condition can mimic RBBB morphology. 3

Additional ECG Features

Associated Findings:

• ST depression and negative T waves may be seen in V1 and sometimes V2. 3
• Left axis deviation >-45° suggests associated left anterior fascicular block. 3
• Right axis deviation beyond +120° is equivocal and requires further evaluation. 3

Special Pattern - QR in V1:

A QR pattern in V1 with RBBB has high positive predictive value for high-risk pulmonary embolism in patients presenting with sudden cardiac arrest or hemodynamic collapse. 4 This finding should prompt urgent consideration of PE and potential thrombolytic therapy. 4

Clinical Context

RBBB in the absence of underlying cardiac disease generally has a good prognosis, but prognosis may be poor in the setting of coronary artery disease or other structural heart disease. 3 The progression to complete atrioventricular block is rare without associated cardiac disease. 3