What is the management for Left Bundle Branch Block (LBBB) and Right Bundle Branch Block (RBBB)?

From the Guidelines

Management of bundle branch blocks (BBB) depends on whether they are symptomatic and if there are underlying cardiac conditions, with a focus on treating the underlying condition and improving morbidity, mortality, and quality of life. For asymptomatic left bundle branch block (LBBB) or right bundle branch block (RBBB) without structural heart disease, no specific treatment is typically required beyond regular cardiac monitoring 1. However, for symptomatic patients or those with underlying heart disease, management focuses on treating the underlying condition. In patients with LBBB and heart failure with reduced ejection fraction, cardiac resynchronization therapy (CRT) with a biventricular pacemaker is recommended, particularly when QRS duration exceeds 150ms 1. For patients with LBBB or RBBB who develop high-degree AV block or symptomatic bradycardia, permanent pacemaker implantation is indicated 1. Medications are not typically prescribed specifically for bundle branch blocks, but rather for associated conditions like heart failure (beta-blockers, ACE inhibitors, ARBs) or arrhythmias. Regular follow-up with electrocardiograms is important to monitor for progression to more advanced conduction disorders. The management approach differs because LBBB more significantly affects cardiac synchrony and is more commonly associated with underlying structural heart disease, while RBBB may be benign in many cases 1. Some key considerations in the management of BBB include:

• The presence of LBBB on ECG markedly increases the likelihood of underlying structural heart disease and of diagnosing left ventricular systolic dysfunction 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 or event monitors 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.
• The use of noninvasive imaging techniques to evaluate either the electrical or mechanical substrate of LV dyssynchrony may help to identify the patients with narrow QRS complex or RBBB who will benefit from CRT 1.

From the Research

Management for LBBB and RBBB

• The management of Left Bundle Branch Block (LBBB) and Right Bundle Branch Block (RBBB) involves various approaches, including cardiac resynchronization therapy (CRT) and conduction system pacing 2, 3, 4, 5, 6.
• CRT is a treatment option for patients with LBBB, and the response to CRT can be predicted by electrocardiographic (ECG) and echocardiographic (echo) criteria 2, 4.
• The ECG criteria for LBBB include QRS duration ≥140 ms (men) or 130 ms (women), QS or rS in leads V1 and V2, and mid-QRS notching or slurring in ≥2 of leads V1, V2, V5, V6, I, and aVL 2.
• Echo criteria for LBBB include early termination of contraction in one wall and prestretch and late contraction in opposing wall(s) 2.
• Conduction system pacing, including left bundle branch area pacing (LBBAP), is a treatment option for patients with LBBB and RBBB, and can result in paced QRS narrowing and improved ventricular synchrony 3.
• The success of LBBAP depends on the complex interaction between anatomy, site of pathophysiology, and delivery tools 3, 5, 6.

Predicting Response to CRT

• The response to CRT can be predicted by the presence of strict LBBB ECG criteria and typical LBBB echo contraction pattern 4.
• Patients with typical LBBB contraction pattern show more pronounced global longitudinal strain and larger longitudinal dissynchrony compared with other patients, and are more likely to respond to CRT 4.
• The combination of ECG and echo criteria can help identify patients who are likely to respond to CRT 2, 4.

Recent Insights into Conduction System Physiology

• Recent studies have provided new insights into the pathophysiology of human LBBB, highlighting the complex interaction between anatomy, site of pathophysiology, and delivery tools 5, 6.
• LBBB is not just a simple electrocardiogram alteration, but a complex entity that affects patient diagnosis, treatment, and prognosis 5, 6.