What is the pathophysiology and management of bundle branch block (BBB) in older adults with a history of hypertension (HTN) and coronary artery disease (CAD)?

Bundle Branch Block Pathophysiology

Mechanism of Conduction Disruption

Bundle branch block occurs when electrical impulses are interrupted or delayed in the specialized conduction pathways of the ventricles, forcing activation to proceed through slower myocardial tissue rather than the rapid His-Purkinje system. 1

Right Bundle Branch Block (RBBB)

• RBBB results from interruption of conduction through the right bundle branch, causing delayed right ventricular activation that manifests as QRS duration >120 ms on ECG 2
• Right ventricular endocardial activation begins before left ventricular activation in RBBB, but is delayed compared to normal conduction 3
• The prevalence is approximately 1% in the general population, with 0.6% in males under 40 years 2

Left Bundle Branch Block (LBBB)

• In LBBB, right ventricular endocardial activation begins before and is often completed before initiation of left ventricular endocardial activation 3
• Right-to-left septal activation follows, resulting in delayed left ventricular endocardial activation 3
• LBBB represents more than simple conduction block—it involves complex interactions between anatomy, site of pathophysiology, and underlying cardiac structure 1

Etiologies in Older Adults with HTN and CAD

Degenerative and Ischemic Causes

• Primary degenerative lesions of the specialized conducting tissue are the most common cause in older adults, particularly as an isolated phenomenon 2
• Ischemic heart disease, especially anterior myocardial infarction with persistent intraventricular conduction disturbances, carries an unfavorable prognosis 4, 2
• Hypertensive heart disease is a recognized structural cause of both RBBB and LBBB 2
• Coronary artery disease is strongly associated with LBBB development and progression 5

Structural Heart Disease

• Cardiomyopathies of various types can produce bundle branch block 2
• Left ventricular systolic dysfunction is markedly more likely when LBBB is present on ECG 4
• Cohort studies demonstrate an association between LBBB (but not RBBB) and the development of coronary disease and heart failure 4

Progressive Conduction System Disease

• Bifascicular block (RBBB with left anterior or posterior hemiblock) carries increased risk of progression to complete AV block 4, 2
• Trifascicular block (bifascicular block with first-degree AV block) indicates more extensive conduction system involvement 4
• The disease slowly progresses to third-degree AV block in patients with chronic bifascicular block 4

Clinical Significance and Prognosis

LBBB Implications

• Benign LBBB is rare; disease usually becomes manifest over time 3
• Newly acquired LBBB carries a 10-fold increase in mortality compared to preexisting block 3
• LBBB affects patient diagnosis (primary conduction disease versus secondary to underlying pathology), treatment decisions (cardiac resynchronization therapy eligibility), and prognosis 1

RBBB Implications

• Isolated RBBB in patients with normal hearts does not appear to reflect adverse outcomes 4
• In patients with myocardial infarction receiving thrombolytic therapy, BBB identifies a subset at high risk 4
• The most frequent cause of sudden cardiac death in patients with bifascicular block is ventricular tachyarrhythmia, mainly occurring in those with coronary artery disease, heart failure, and/or advanced age 4

Management Approach in Older Adults with HTN/CAD

Initial Evaluation

In patients with newly detected LBBB, transthoracic echocardiography to exclude structural heart disease is mandatory (Class I recommendation). 4, 6

• For RBBB with suspected structural heart disease, transthoracic echocardiography is reasonable (Class IIa) 4
• Advanced imaging (cardiac MRI, CT, or nuclear studies) is reasonable when echocardiography is unrevealing but structural disease is suspected 4, 6
• Stress testing with imaging may be considered in asymptomatic LBBB patients when ischemic heart disease is suspected 4, 6

Symptom Assessment

• In symptomatic patients with conduction system disease where AV block is suspected, ambulatory electrocardiographic monitoring is useful 4, 6
• Electrophysiology study (EPS) is reasonable in patients with symptoms suggestive of intermittent bradycardia (lightheadedness, syncope) with conduction system disease on ECG 4, 6
• Syncope in patients with bundle branch block predicts abnormal conduction properties and warrants EPS 7

Pacing Indications

Permanent pacing is indicated (Class I) for bundle branch block with syncope when EPS demonstrates HV interval ≥70 ms or frank infranodal block. 4, 7, 6

• Alternating bundle branch block requires permanent pacing due to high risk of sudden complete heart block 4, 7, 6
• Bifascicular or trifascicular block with intermittent second- or third-degree AV block warrants permanent pacing 4
• Isolated asymptomatic bundle branch block with 1:1 AV conduction does NOT require pacing (Class III: Harm). 7, 6

Critical Pitfalls to Avoid

• Do not assume all bundle branch block patterns are benign; always evaluate for underlying structural heart disease, especially when new-onset 7
• Avoid unnecessary permanent pacing for isolated bundle branch block without symptoms or other conduction abnormalities 7
• In patients with bundle branch block and syncope who have normal HV conduction time, recognize that most syncopal recurrences are due to prolonged asystolic pauses from sudden-onset paroxysmal AV block 4
• The most frequent cause of sudden cardiac death in these patients is ventricular tachyarrhythmia rather than bradyarrhythmia, particularly in those with coronary artery disease and heart failure 4