Can you show me an example of a right bundle branch block on a standard 12‑lead electrocardiogram (ECG)?

Understanding Right Bundle Branch Block on ECG

I cannot provide you with an actual electrocardiogram image, but I can describe the characteristic ECG features you should look for when identifying right bundle branch block.

Complete RBBB ECG Diagnostic Criteria

To diagnose complete right bundle branch block on a 12-lead ECG, look for QRS duration ≥120 ms combined with specific morphologic patterns in the precordial and limb leads. 1

Key ECG Features in Right Precordial Leads (V1-V2)

• The hallmark finding is an rsr', rsR', or rSR' pattern in leads V1 and V2, where the R' or r' deflection is typically wider than the initial R wave 1
• The R peak time in V1 exceeds 50 ms, while remaining normal in leads V5-V6 1
• In some cases, a rare qR pattern may appear in V1 or V2 1

Key ECG Features in Lateral Leads (I, V6)

• Prolonged S waves appear in leads I and V6, measuring >40 ms or longer than the R wave in those leads 1
• These slurred S waves represent the delayed right ventricular activation 1

QRS Duration

• Complete RBBB requires QRS duration ≥120 milliseconds 2, 1
• QRS duration may be categorized as 121-150 ms or >150 ms for prognostic purposes 2

Incomplete RBBB Pattern

• Incomplete RBBB shows similar morphologic features but with QRS duration between 110-119 ms 3
• An rsr' pattern in V1-V2 with normal QRS duration (<120 ms) in children and athletes is often a benign physiologic variant 3

Clinical Context and Pitfalls

• RBBB reduces S wave amplitude in right precordial leads, which decreases ECG sensitivity for detecting left ventricular hypertrophy 1
• When RBBB appears with ST-elevation in V1-V3, this represents Brugada pattern and requires immediate specialized evaluation due to sudden cardiac death risk 3, 4
• The Minnesota criteria are the standardized diagnostic criteria referenced in ACC/AHA guidelines for RBBB diagnosis 2

Masquerading RBBB

• In rare cases with severe left anterior fascicular block and left ventricular enlargement, the characteristic slurred S wave in lead I may diminish or disappear, potentially mimicking left bundle branch block even though RBBB is present 5
• This "masquerading" pattern carries poor prognosis as it implies severe underlying heart disease 5