What is the management of left bundle branch block (LBBB)?

Management of Left Bundle Branch Block (LBBB)

All patients with newly detected LBBB require transthoracic echocardiography to exclude structural heart disease and assess left ventricular function, followed by risk stratification to determine need for pacing or cardiac resynchronization therapy. 1, 2

Initial Diagnostic Workup

Mandatory Testing

• Transthoracic echocardiography is the first-line test (Class I, Level B-NR) for all patients with newly detected LBBB to evaluate for structural heart disease and measure left ventricular ejection fraction (LVEF). 1, 2
• Obtain laboratory testing based on clinical suspicion to identify reversible causes (electrolyte abnormalities, thyroid dysfunction, inflammatory markers). 1
• Review prior ECGs to determine if LBBB is truly new versus "not known to be old"—this distinction is critical as new LBBB may indicate acute myocardial infarction. 3

Additional Imaging When Indicated

• Advanced imaging with cardiac MRI, CT, or nuclear studies is reasonable (Class IIa, Level C-LD) when echocardiography is unrevealing but structural disease remains suspected. 1, 2
• If ischemic heart disease is suspected, use vasodilator stress testing (adenosine or dipyridamole) with myocardial perfusion imaging rather than exercise stress testing—exercise causes false-positive septal perfusion defects in LBBB. 2

Risk Stratification Based on Symptoms

Symptomatic Patients (Syncope, Presyncope, Extreme Fatigue)

• Ambulatory ECG monitoring is mandatory (Class I, Level C-LD) in symptomatic patients to detect intermittent high-degree AV block. 1
• Electrophysiology study (EPS) is reasonable (Class IIa, Level B-NR) when symptoms suggest intermittent bradycardia with conduction system disease. 1
• If EPS reveals HV interval ≥70 ms or infranodal block, permanent pacing is indicated (Class I, Level C-LD). 1, 2

Asymptomatic Patients

• Permanent pacing is NOT indicated (Class III: Harm, Level B-NR) in asymptomatic patients with isolated LBBB and 1:1 AV conduction. 1, 2
• Educate patients about warning symptoms (syncope, presyncope, extreme fatigue, significant dizziness) that indicate progression to higher-degree heart block. 1, 2

Special Clinical Scenarios

LBBB in Acute Myocardial Infarction

• New or presumably new LBBB in the setting of acute MI should be managed like ST-segment elevation MI and considered for immediate reperfusion therapy. 3, 1, 2
• However, LBBB at presentation should not be considered diagnostic of acute MI in isolation—most cases are "not known to be old" due to lack of prior ECG for comparison. 3
• Consider using Sgarbossa criteria or modified Smith criteria for ECG diagnosis of acute STEMI in the setting of LBBB. 3

LBBB with Heart Failure

• Cardiac resynchronization therapy (CRT) may be considered (Class IIb, Level C-LD) in patients with heart failure, LVEF 36%-50%, and LBBB with QRS ≥150 ms. 1
• LBBB causes immediate electrical and mechanical dyssynchrony, reducing LVEF to approximately 55% even in otherwise normal hearts, with progressive deterioration over time from HFpEF to HFmrEF to HFrEF over 5-21 years. 4
• CRT is currently guideline-indicated primarily for HFrEF with LBBB, though emerging evidence suggests benefit in HFmrEF and potentially HFpEF. 4

Alternating Bundle Branch Block

• Permanent pacing is recommended (Class I, Level C-LD) for patients with alternating bundle branch block due to high risk of developing complete AV block. 1

LBBB in Specific Disorders

• For patients with Kearns-Sayre syndrome and LBBB, permanent pacing is reasonable (Class IIa, Level C-LD), with consideration of additional defibrillator capability if appropriate. 1, 2
• Extended monitoring up to 14 days is recommended for new LBBB after transcatheter aortic valve implantation (TAVI). 2

Follow-Up Strategy

Ongoing Monitoring

• Educate all patients about red flag symptoms: syncope, presyncope, extreme fatigue, or significant dizziness. 1, 2
• If symptoms develop, perform prompt evaluation with ambulatory monitoring or electrophysiology study. 1
• Serial echocardiography to monitor for progressive LV dysfunction, particularly in patients with underlying structural heart disease. 5

Emerging Therapies

• Conduction system pacing (left bundle branch area pacing) is an emerging strategy that may reverse and forestall the deleterious effects of LBBB, though not yet incorporated into standard guidelines. 4

Common Pitfalls to Avoid

• Do not delay evaluation in patients with preexisting LBBB who develop complete heart block during right heart catheterization or endomyocardial biopsy—temporary pacing may be required. 1
• Do not use exercise stress testing in LBBB—it produces false-positive septal perfusion defects; use vasodilator stress instead. 2
• Do not assume LBBB is benign in asymptomatic patients—it shortens median survival by 5.5 years in HFmrEF and causes progressive adverse remodeling. 4
• Do not place prophylactic temporary pacemakers routinely for surgery in asymptomatic LBBB, but have equipment immediately available. 6