Right Bundle Branch Block

Right bundle branch block (RBBB) is delayed activation of the right ventricle through the right bundle, with normal left ventricular activation.

ECG criteria for complete RBBB are a QRS of 120 ms or more, rsr', rsR' or rSR' in V1 or V2 (R' usually wider than the initial R), an S wave wider than the R wave or longer than 40 ms in I and V6, and R-peak time over 50 ms in V1 with normal R-peak time in V5 and V6.

Incomplete RBBB has a QRS of 110 to 119 ms with the same morphology and is a common normal variant. Complete RBBB is found in about 0.2 to 1.3% of adults and increases with age. It is common after repair of tetralogy of Fallot and in atrial septal defect.

Causes are normal variant, congenital heart disease, pulmonary embolism, right ventricular pressure or volume overload, pulmonary hypertension and cardiomyopathy (arrhythmogenic right ventricular, sarcoid, Chagas).

Others are myocarditis, coronary disease (proximal left anterior descending occlusion), cardiac surgery, right heart catheterisation or biopsy, degenerative conduction disease, hyperkalaemia and antiarrhythmic drugs.

In sub-Saharan Africa, schistosomal and rheumatic pulmonary hypertension and endomyocardial fibrosis are important causes.

Pathophysiology. The long, thin right bundle is vulnerable to pressure, stretch and fibrosis. Delayed right ventricular activation produces the terminal right sided forces (R' in V1, S in I and V6) and secondary ST-T changes in V1 to V3. Isolated RBBB with a normal heart carries little risk.

In patients with heart disease, or when combined with left fascicular block, it marks conduction disease and higher mortality.

• Usually asymptomatic and found on ECG.
• Symptoms of the cause: dyspnoea and chest pain in pulmonary embolism or pulmonary hypertension, syncope with advanced conduction disease, palpitations.
• Examination: wide splitting of the second heart sound with preserved respiratory variation (it is fixed in atrial septal defect).
• Ebstein anomaly, atrial septal defect and repaired tetralogy of Fallot have typical murmurs.

Red flags.

• Syncope or presyncope
• New RBBB with chest pain (anterior infarction, particularly with left anterior fascicular block)
• New RBBB with hypoxaemia, tachycardia or dyspnoea (pulmonary embolism)
• RBBB with coved ST elevation in V1 and V2 (Brugada pattern)
• RBBB with epsilon waves
• RBBB with left fascicular block and PR prolongation, or alternating bundle branch block
• RBBB in a young patient with a family history of sudden death

• 12-lead ECG: complete RBBB shows QRS of 120 ms or more, an rSR' pattern in V1 or V2, and a wide terminal S wave in I and V6 (incomplete RBBB has QRS of 110 to 119 ms). Compare with old ECGs. In V1 and V2, the Brugada type 1 pattern is a coved ST elevation of 2 mm or more followed by a negative T wave, without the broad terminal S wave in I and V6 that defines RBBB. High precordial leads are recorded when suspected.
• Echocardiography: right ventricular size and function, pulmonary pressure, atrial septal defect, valve disease and left ventricular function.
• Troponin and D-dimer when infarction or embolism is suspected, with CT pulmonary angiography for pulmonary embolism.
• Ambulatory ECG or loop recorder for syncope.
• Cardiac MRI for suspected arrhythmogenic right ventricular cardiomyopathy or sarcoidosis. Chagas serology in patients from endemic regions of Latin America.
• Sodium channel blocker challenge in a specialist centre when a Brugada pattern is suspected.
• Electrophysiology study for syncope with bifascicular block: HV interval of 70 ms or more, or infra-Hisian block, indicates pacing.

Differential diagnosis.

• Incomplete RBBB as a normal variant, including the crista terminalis pattern
• Brugada syndrome
• Arrhythmogenic right ventricular cardiomyopathy (epsilon waves)
• Pre-excitation with a posteroseptal accessory connection
• Ventricular pacing from the left ventricle (RBBB morphology with a pacing spike)
• Ventricular tachycardia with RBBB morphology, including fascicular tachycardia
• Right ventricular hypertrophy and posterior myocardial infarction (tall R in V1)
• Atrial septal defect with rSr' and inferior notching
• Pectus excavatum
• Hyperkalaemia

• Isolated asymptomatic RBBB: no treatment. Echocardiography once for new RBBB, RBBB at a young age, with symptoms or with a family history. Manage cardiovascular risk. No pacemaker.
• Syncope: electrophysiology study or implantable loop recorder. Pacemaker for HV interval of 70 ms or more or induced infra-Hisian block.
• Pulmonary embolism with new RBBB (right ventricular strain): anticoagulation with apixaban 10 mg orally twice daily for 7 days, then 5 mg twice daily, for at least 3 months. Maximum 20 mg daily in the first 7 days. Avoid at creatinine clearance under 15 mL/min and use with caution at 15 to 29 mL/min. Avoid with strong dual CYP3A4 and P-glycoprotein inhibitors or inducers (ketoconazole, ritonavir, rifampicin, carbamazepine, phenytoin). Contraindicated in triple positive antiphospholipid syndrome. Reperfusion is considered for haemodynamic instability.
• Anterior myocardial infarction with new RBBB: reperfusion, with monitoring for atrioventricular block. Pacing for second degree type II or complete block. Atropine is not reliable for infra-nodal block.
• Brugada pattern: refer for risk assessment, avoid provocative drugs and treat fever promptly.
• Arrhythmogenic right ventricular cardiomyopathy, sarcoidosis and Chagas disease: specialist treatment, with defibrillator assessment.
• Repaired tetralogy of Fallot: QRS of 180 ms or more is a risk marker for ventricular tachycardia and sudden death. Surveillance and electrophysiology assessment.
• Pulmonary hypertension and endomyocardial fibrosis: treat the cause.

Special groups.

• Athletes: incomplete RBBB is common and benign when asymptomatic with no family history and normal echocardiography.
• Pregnancy: isolated RBBB needs no change in care.

Monitoring. ECG yearly for new complete RBBB, with echocardiography at 1 to 2 years if the initial study was normal and symptoms or ECG change appear. Ambulatory ECG for syncope.

Referral and escalation. Refer to cardiology for new complete RBBB with symptoms or structural disease. Urgent for syncope, ischaemic symptoms, haemodynamic instability, Brugada pattern or progression to bifascicular block.