Right Bundle Branch Block (RBBB): Comprehensive Overview
Definition and ECG Characteristics
Complete RBBB is diagnosed when the QRS duration is ≥120 ms with characteristic morphologic features including an rsr', rsR', or rSR' pattern in leads V1-V2, prolonged S waves in leads I and V6 (>40 ms or longer than the R wave), and an R peak time >50 ms in V1 but normal in V5-V6. 1, 2
Key ECG Features:
- QRS duration: ≥120 ms for complete RBBB; 110-119 ms for incomplete RBBB 1, 3
- V1-V2 morphology: rsr', rsR', rSR', or rarely qR pattern where the R' or r' deflection is typically wider than the initial R wave 2
- Lateral leads (I, V6): Prolonged S waves (>40 ms or longer than R wave) 1
- R peak time: >50 ms in V1 but preserved in V5-V6 1
Underlying Causes and Pathophysiology
RBBB represents delayed or interrupted conduction through the right bundle branch, causing the right ventricle to depolarize after the left ventricle, producing characteristic asynchronous ventricular activation. 2, 4
Clinical Spectrum:
- Benign variant: RBBB may represent an idiopathic, isolated, clinically benign conduction delay, particularly in young athletes (1-2.5% prevalence) 1, 2
- Structural heart disease associations: Ischemic heart disease, cardiomyopathies, congenital heart disease (especially atrial septal defect), arrhythmogenic right ventricular cardiomyopathy, hypertensive heart disease 2, 5
- Ischemic etiology: RBBB is strongly associated with large anteroseptal scar from proximal LAD occlusion affecting septal perforators that perfuse the right bundle branch 6
Important anatomic consideration: A proximal septal perforating branch of the LAD most commonly perfuses the right bundle branch and left anterior fascicle, explaining why proximal LAD occlusions cause RBBB rather than LBBB. 6
Clinical Significance and Risk Stratification
Asymptomatic Patients Without Structural Disease:
For asymptomatic patients with isolated RBBB and no structural heart disease, observation without specific therapy is recommended, with annual follow-up ECG to monitor for progression of conduction disease. 1
- Athletes with RBBB, no symptoms, no structural heart disease, and no family history can participate in all competitive sports without restriction 1, 3
- RBBB itself is usually asymptomatic; any chest pain, dyspnea, or syncope typically reflects underlying cardiac disease rather than the conduction abnormality 2
High-Risk Clinical Contexts:
Acute Myocardial Infarction:
New RBBB in the setting of acute MI increases in-hospital mortality by approximately 64% compared with AMI patients without bundle branch block. 2
- Evidence-based AMI therapies (fibrinolysis, aspirin, heparin, β-blockers) are frequently under-utilized in RBBB patients despite worse outcomes 2
- RBBB can obscure ST-segment analysis and delay reperfusion decisions 2
Transcatheter Aortic Valve Replacement (TAVR):
Pre-existing RBBB is a strong independent predictor of permanent pacemaker implantation after TAVR, occurring in 40.1% versus 13.5% in patients without pre-existing RBBB. 7, 2
- Pre-existing RBBB independently associates with higher all-cause mortality (HR: 1.31) and cardiovascular mortality (HR: 1.45) at 18-month follow-up 7
- Patients with pre-existing RBBB without PPM at discharge had the highest 2-year cardiovascular death risk (27.8%) 7
- New RBBB following TAVR links to higher likelihood of permanent pacemaker implantation and increased late mortality 2
Bifascicular Block Considerations:
Bifascicular blocks (RBBB with left anterior or posterior fascicular block) reflect extensive conduction system involvement and carry increased risk of clinically significant AV block. 2
- Alternating bundle branch block (switching between left and right) is a Class I indication for permanent pacemaker implantation 2
- When first-degree AV block accompanies bifascicular block, this suggests trifascicular involvement with higher mortality risk 2
Diagnostic Evaluation Algorithm
Initial Assessment:
- Document symptoms: Assess for syncope, presyncope, dizziness, fatigue, or exercise intolerance 1
- Physical examination: Listen carefully for fixed splitting of S2, which suggests atrial septal defect (common with RBBB) 3, 5
- 12-lead ECG: Confirm RBBB criteria and assess for additional conduction abnormalities 1
Cardiac Imaging:
Transthoracic echocardiography is recommended to evaluate for right ventricular enlargement or dysfunction, structural heart disease, left ventricular hypertrophy, atrial septal defects, and other congenital abnormalities. 1, 2, 3
Additional Testing Based on Clinical Context:
- Exercise stress testing: To assess for exercise-induced arrhythmias or conduction worsening 2, 3
- 24-hour Holter monitoring: To detect intermittent conduction abnormalities, particularly if symptoms suggest higher-degree blocks 2, 3
- Electrophysiologic studies: Rarely necessary but considered for symptomatic patients with syncope; permanent pacing indicated if HV interval ≥70 ms or frank infranodal block demonstrated 3
Special Population Considerations:
- Athletes: May have larger right ventricular dimensions and lower RV ejection fraction but preserved fractional area change; isolated RBBB without family history or symptoms may not require extensive evaluation 1
- Young patients with bifascicular block: Obtain ECG in siblings to exclude genetically determined progressive cardiac conduction disease (Lenegre disease) 2
Management Approach
Asymptomatic Patients:
No specific treatment is required for asymptomatic patients with isolated RBBB and no structural heart disease; annual follow-up with ECG monitoring is recommended to detect progression. 1, 3
Symptomatic Patients:
Permanent pacemaker implantation should be considered for symptomatic patients with bradycardia and RBBB, and any underlying cardiac condition identified during evaluation should be treated. 1
Specific Indications for Permanent Pacing:
- Alternating bundle branch block (Class I indication) 2
- Syncope with HV interval ≥70 ms or evidence of infranodal block at electrophysiology study (Class I indication) 2, 3
- Progression to complete (third-degree) heart block 2
Impact on Other ECG Diagnoses
Left Ventricular Hypertrophy Detection:
RBBB reduces S wave amplitude in right precordial leads, which decreases sensitivity for detecting left ventricular hypertrophy. 2
- Ancillary ECG features improve LVH detection in RBBB: left atrial abnormality, left axis deviation, and specific voltage thresholds (SV1 >2 mm, RV5-6 >15 mm) 2
When RBBB Coexists with Left Anterior Fascicular Block:
- R wave amplitude in leads I and aVL becomes unreliable for LVH diagnosis 2
- S wave depth in left precordial leads improves detection 2
Critical Clinical Pitfalls
Incomplete RBBB Differential Diagnosis:
Clinicians must differentiate incomplete RBBB from pathological patterns including type-2 Brugada ECG pattern, right ventricular enlargement, arrhythmogenic right ventricular cardiomyopathy, ventricular preexcitation (WPW syndrome), and hyperkalemia. 5
Acute Coronary Syndrome Context:
In patients presenting with chest pain and RBBB, do not rely solely on traditional ST-elevation criteria; consider the clinical presentation strongly when making reperfusion decisions, as RBBB can obscure ST-segment analysis. 3
Post-TAVR Monitoring:
Among patients who develop new left bundle branch block after TAVR, 29% experience their first episode of high-degree AV block after hospital discharge, often accompanied by syncope, necessitating close outpatient monitoring. 2
Prognosis and Monitoring
General Population:
- In the general population without cardiovascular disease, approximately 8% have RBBB, with higher prevalence among men and elderly patients 8
- Complete RBBB tends to increase all-cause mortality and cardiovascular events, though only bifascicular block shows statistically significant association after adjusting for confounders 8
- Incomplete RBBB is not associated with adverse outcomes 8
Progression Risk:
Patients with incomplete RBBB who progress to complete RBBB show higher incidence of heart failure and chronic kidney disease. 8