Right Bundle Branch Block (RBBB)
Definition
RBBB is an intraventricular conduction disturbance in which impulses fail to traverse the right bundle branch, causing the right ventricle to be depolarized via slow trans-myocardial spread from the left ventricle. The initial 30–40 ms of ventricular activation are normal (LV septal activation preserved), distinguishing RBBB from LBBB. RBBB is generally benign in structurally normal hearts but is an independent predictor of all-cause mortality when combined with underlying cardiovascular disease.
Key Concepts
Anatomy
- Right bundle branch: thin, long, discrete Purkinje fiber structure
- Travels down the RV septum (upper 1/3 near endocardium → middle 1/3 deep in muscular septum → lower 1/3 near endocardium again)
- Ramifies near base of right anterior papillary muscle
- Blood supply: primarily septal branches of LAD; collateral from RCA or LCx depending on dominance
- (sources/rbbb-ccr-2021, medium)
Epidemiology
- General population prevalence: 2–3% (vs LBBB which rarely occurs in a normal heart)
- Strongly age- and sex-dependent: 1% at age 50 → 18% at age 80 in men (Swedish study, Eriksson 1998)
- Copenhagen City Heart Study: 1.4% men, 0.5% women; range 0.6% (women <40 yr) to 14.3% (men >80 yr)
- Incomplete RBBB: ~3× more prevalent than complete RBBB; less age-associated
- (sources/rbbb-ccr-2021, medium)
Causes
- Normal variant / idiopathic — most common
- Hypertension — associated with high systolic BP, but not consistently with other CV risk factors
- Structural disease: ischemic heart disease, cardiomyopathy, myocarditis, valvular disease, CHD
- Pulmonary: PE (acute new RBBB → consider PE), pulmonary hypertension
- Brugada syndrome — causes pseudo-RBBB pattern (see Differential Diagnosis section)
- Iatrogenic: right heart catheterization of basal ventricular septum
- (sources/rbbb-ccr-2021, medium)
ECG Diagnosis
Complete RBBB (AHA/ACCF/HRS 2009):
- QRS ≥120 ms (adults); >100 ms (4–16 yr); >90 ms (<4 yr)
- rsr', rsR', or rSR' in V1–V2 — rSR' is most common; rsR' ("bunny ear") is rare; R'/r' usually wider than initial R
- S wave duration > R wave, or S >40 ms, in leads I and V6
- R peak time >50 ms in V1; normal in V5–V6
- ST-T: discordant to terminal QRS — inverted T in V1–V2; upright T in I and V6
- Concordant T wave = abnormal → suggests ischemia or MI
Incomplete RBBB:
- QRS 100–119 ms with same morphological criteria
- Can be normal variant (especially if V1 lead placed high/right and R' <20 ms)
Rate-Dependent RBBB:
- Intermittent RBBB pattern at fast heart rates
- Resolves with slowing
- Can mimic VT or accelerated idioventricular rhythm
Combined RBBB Patterns:
- RBBB + LAFB = bifascicular block (most common combination)
- RBBB + LPFB or LSFB = also bifascicular
- Bifascicular block + 1st-degree AV block = trifascicular block
- Alternating RBBB/LBBB = high-risk bilateral infranodal disease → PPM (Class I)
- (sources/ecg-bbb-aha-2009, high) (sources/rbbb-ccr-2021, medium)
RBBB and MI Co-diagnosis
- RBBB does NOT interfere with MI diagnosis based on Q and R wave criteria — the initial 30–40 ms vectors are essentially normal
- QSR' pattern in V1–V2 in complete RBBB = acute anteroseptal MI coexistent with RBBB
- Contrast with LBBB, which significantly alters MI diagnosis criteria (Sgarbossa) — see concepts/Sgarbossa-Criteria
- (sources/rbbb-ccr-2021, medium)
Differential Diagnosis for RBBB-Morphology QRS
Ventricular Arrhythmias:
- VT (>100 bpm) and accelerated idioventricular rhythm (<100 bpm): AV dissociation distinguishes from RBBB (which always has P waves driving QRS)
Ventricular Pacing:
- RV apical pacing → LBBB pattern (not RBBB)
- Biventricular pacing → can occasionally mimic RBBB; pacemaker spikes visible
Brugada Syndrome (Pseudo-RBBB):
- Brugada ECG = pseudo-RBBB (NOT true RBBB)
- Pseudo-RBBB features: coved ST elevation + inverted T in V1–V2; wide S in I and V6 absent (key distinguishing feature); spontaneous ECG changes are common
- True RBBB in Brugada patients: Brugada ECG can be concealed when a patient has true RBBB
- Chiale maneuver: Right apical ventricular pacing with appropriately timed AV intervals unmasks concealed Brugada ECG pattern in patients with true RBBB
- (sources/rbbb-ccr-2021, medium); see entities/Brugada-Syndrome
Treatment
- Chronic RBBB: No treatment required
- New RBBB: Treat underlying cause (revascularization for ischemic HD; anticoagulation for PE)
- RBBB + syncope + advanced 2nd-degree AV block: Pacemaker implantation
- CRT: Generally no benefit in RBBB + heart failure (unlike LBBB)
- Exceptions: RBBB + LAFB, or RBBB + prolonged PR interval — may have electromechanical substrate for CRT response (Atwater 2017, Houston 2018) sources/rbbb-ccr-2021 (medium)
- (sources/rbbb-ccr-2021, medium); see concepts/Cardiac-Resynchronization-Therapy and concepts/Permanent-Pacing-Indications
Masquerading RBBB (LAH Concealing RBBB)
- Definition: LAFB superimposed on RBBB causes the terminal S waves of RBBB to disappear from leads I and aVL ("standard masquerading") and/or from V5–V6 ("precordial masquerading")
- The resulting QRS is so atypical that RBBB may resemble LBBB or be entirely missed — including in the right precordial leads
- Conditions required: high-degree LAFB + RBBB, and/or co-existing LVH or focal LV block from fibrosis/necrosis
- Clinical importance: unrecognized bifascicular block (RBBB + LAFB) means the risk of AV block progression is overlooked
- Detection: Precordial mapping 1 interspace above standard (V1H, V3RH) can unmask RBBB; intermittent LAFB allows comparison of QRS with and without masquerading
- (sources/hemiblock-circ-2007, high); see concepts/Fascicular-Blocks
Prognosis
- Isolated RBBB, no structural disease: Generally favorable; no increased risk in healthy individuals
- RBBB + cardiovascular disease: Independent predictor of all-cause mortality (multiple cohort studies and meta-analysis, Xiong 2015)
- Complete RBBB = independent predictor of mortality in patients with CAD or heart failure (Hesse 2001; Freedman 1987; Barsheshet 2011; Rasmussen 2019)
- Progression to 3rd-degree AV block: less common with RBBB than LBBB but can cause SCD
- Prognosis dominated by underlying structural disease and presence of other conduction disturbances (bifascicular block, AV block)
- (sources/rbbb-ccr-2021, medium)
Contradictions / Open Questions
- CRT in RBBB: There is no robust RCT evidence that CRT benefits RBBB patients; the "exceptions" (RBBB + LAFB, prolonged PR) are supported only by small observational studies — this remains controversial and is not incorporated into major guideline Class I/IIa recommendations
- Isolated RBBB prognosis in general population: While multiple large studies confirm RBBB is an independent mortality predictor in those with CVD, the absolute risk increase for isolated RBBB in truly healthy individuals (no structural disease) remains debated; some Danish data suggest a modest increase in cardiovascular events even in "healthy" RBBB subjects
- Brugada concealment: The Chiale maneuver for unmasking concealed Brugada in RBBB patients is described but lacks large prospective validation; not routinely used in clinical practice
- Rate-dependent RBBB vs VT: Rate-dependent RBBB (Ashman phenomenon) can be very difficult to distinguish from sustained VT on a surface ECG without careful analysis of P-QRS relationships; clinical context is essential
Connections
- Related to concepts/ECG-Conduction-Disturbances — AHA 2009 RBBB criteria; bifascicular/trifascicular terminology
- Related to entities/Brugada-Syndrome — pseudo-RBBB pattern; Chiale maneuver to unmask concealed Brugada
- Related to concepts/Atrioventricular-Block — bifascicular block + syncope/HV ≥70 ms → EPS/PPM
- Related to concepts/Permanent-Pacing-Indications — RBBB + syncope + advanced AV block → PPM; alternating BBB → PPM Class I
- Related to concepts/Cardiac-Resynchronization-Therapy — RBBB generally not a CRT indication; exceptions for RBBB + LAFB or long PR
- Related to concepts/LBBB-Criteria — comparison with LBBB: RBBB does not interfere with MI diagnosis unlike LBBB; LBBB rarely occurs in normal heart; different CRT implications
- Related to concepts/Sgarbossa-Criteria — Sgarbossa applies to LBBB, not RBBB (different ECG substrate for MI diagnosis)
- Related to concepts/Fascicular-Blocks — masquerading RBBB (LAH concealing RBBB); RBBB + LPFB near-trifascicular block and prognosis
Sources
- sources/rbbb-ccr-2021 — primary RBBB clinical review; epidemiology, anatomy, ECG criteria, causes, prognosis, Brugada differential
- sources/ecg-bbb-aha-2009 — AHA/ACCF/HRS 2009 formal RBBB criteria
- sources/hemiblock-circ-2007 — masquerading RBBB phenomenon; RBBB + LPFB prognosis (80-87% MI mortality; 42% complete AV block)