What are the implications of Right Bundle Branch Block (RBBB)?

From the Guidelines

Patients with Right Bundle Branch Block (RBBB) should undergo evaluation for underlying cardiac conditions, especially if RBBB is newly diagnosed, as it may indicate underlying heart disease and affect pacemaker function and cardiac resynchronization therapy in patients requiring these interventions. RBBB is an electrical conduction abnormality in the heart where the right bundle branch fails to conduct electrical impulses properly, causing delayed activation of the right ventricle. It is diagnosed on an electrocardiogram (ECG) by a QRS complex duration of ≥120 milliseconds, with a characteristic RSR' pattern (rabbit ear appearance) in the right precordial leads (V1-V3) and wide S waves in leads I and V6 [ 1 ].

According to the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay, patients with RBBB or intraventricular conduction delay on ECG also have increased risk of left ventricular systolic dysfunction compared with those with completely normal ECGs [ 1 ]. The guideline recommends that an echocardiogram may be used to uncover treatable disease, or impact management decisions such as cardiac resynchronization device placement [ 1 ].

Some key points to consider in the evaluation and management of RBBB include:

• The presence of RBBB on ECG may indicate underlying heart disease, such as coronary artery disease, cardiomyopathy, or congenital heart defects [ 1 ].
• Electrocardiography is the primary method of diagnosing potential conduction disorders, and recording duration may vary from a 10-second ECG to continuous ambulatory recordings [ 1 ].
• An electrophysiological study (EPS) may provide acute diagnostic information, but has variable sensitivity depending on the presentation and does impart a small procedural risk [ 1 ].
• Cardiac MRI may be considered in selected patients with LBBB and normal left ventricular function by echocardiography where sarcoidosis, connective tissue disease, myocarditis, or other dilated cardiomyopathies are suspected on clinical grounds [ 1 ].

In terms of treatment, no specific treatment is typically required for isolated RBBB without other cardiac abnormalities. However, patients should undergo evaluation for underlying cardiac conditions, especially if RBBB is newly diagnosed [ 1 ]. The 2012 ACCF/AHA/HRS focused update incorporated into the ACCF/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities recommends that patients with bifascicular block, including RBBB, should be considered for permanent pacing if they have symptomatic advanced AV block or if the cause of syncope cannot be determined with certainty [ 1 ].

From the Research

Definition and Prevalence of RBBB

• Right Bundle Branch Block (RBBB) is a condition where there is a blockage in the right bundle branch of the heart's electrical conduction system 2.
• RBBB occurs in 0.2% to 1.3% of people and is considered a benign finding, but some studies have suggested increased risk of cardiovascular morbidity and mortality 2.

Association with Cardiovascular Disease

• A study found that RBBB was predictive of all-cause and cardiovascular-related mortality after adjusting for age, sex, diabetes mellitus, hypertension, obesity, current and past history of smoking, and use of a heart rate-lowering drug 2.
• Patients with RBBB exhibited more hypertension, decreased functional aerobic capacity, slower heart rate recovery, and more dyspnea on exercise testing 2.

Diagnostic Utility

• There is limited data on the diagnostic utility of exercise stress echocardiography (ESE) in patients with RBBB, but studies on left bundle branch block (LBBB) suggest that ESE may not be useful in diagnosing obstructive coronary artery disease in patients with LBBB 3, 4.
• A study found that stress echocardiography has a poor positive predictive value to identify significant angiographic coronary artery disease in higher-risk patients with LBBB, but the negative predictive value for hard ischemic events is similar to patients without LBBB 4.

Prediction of Sudden Cardiac Arrest

• RBBB with a QR pattern in V1 on ECG has a high positive predictive value for diagnosing cardiac arrest caused by high-risk pulmonary embolism 5.
• The presence of a QR pattern in V1 performs as an independent predictor for high-risk pulmonary embolism patients who may require advanced treatments, including systemic thrombolysis or invasive embolectomy 5.

Clinical and Coronary Angiographic Data

• A study found that complete right bundle branch block appearing during exercise stress testing was constantly associated with atherosclerotic coronary artery disease, while complete left bundle branch block occurring at heart rates of less than 120/mn was frequently associated with a proximal stenosis of the left anterior descending artery 6.