Clinical Implications of Bundle Branch Blocks

Diagnosis and Management

The American College of Cardiology recommends that transthoracic echocardiography is mandatory in all newly detected LBBB to exclude structural heart disease, as LBBB markedly increases the likelihood of left ventricular systolic dysfunction 3, 2, 4
LBBB is strongly associated with coronary artery disease and heart failure development, unlike RBBB 1, 2
Advanced imaging (cardiac MRI, CT, or nuclear studies) is reasonable if echocardiogram is unrevealing but structural disease is still suspected 3, 2, 4
Stress testing with imaging may be considered in asymptomatic patients when ischemic heart disease is suspected 2, 4
Echocardiography is reasonable if structural heart disease is suspected in RBBB, but the threshold for imaging is lower than with LBBB 2
RBBB has increased risk of left ventricular dysfunction compared to normal ECGs, but significantly less than LBBB 1, 2
RBBB patients had 64% increased odds of in-hospital death in acute MI settings, compared to 34% for LBBB, suggesting RBBB may indicate more extensive disease when MI occurs 5

Alternating bundle branch block requires immediate permanent pacing due to high risk of sudden complete heart block 6, 7
Syncope with bundle branch block AND HV interval ≥70 ms or infranodal block on electrophysiology study is an indication for permanent pacing (Class I) 6, 7
Symptoms suggesting intermittent AV block warrant diagnostic evaluation and possible pacing 6, 7

Ambulatory ECG monitoring is useful in symptomatic patients with conduction system disease when AV block is suspected 3, 2
Electrophysiology study is reasonable in patients with symptoms suggestive of intermittent bradycardia when ambulatory monitoring is unrevealing 3, 2
Ambulatory monitoring may be considered in asymptomatic patients with extensive conduction disease to document suspected higher-degree AV block 2, 4
Serial ECGs should monitor for progression of conduction disease 4

Approximately 10% of LBBB patients with acute MI present without typical symptoms 4
Both RBBB and LBBB patients are significantly undertreated for acute MI, with only 32% of RBBB and 16.7% of LBBB patients receiving fibrinolytic therapy compared to 65.5% without bundle branch block 5