What is the management plan for a patient with a new onset Right Bundle Branch Block (RBBB) on an electrocardiogram (EKG)?

Management of New Onset Right Bundle Branch Block

Immediately obtain a transthoracic echocardiogram to exclude structural heart disease, perform a focused history and physical examination for symptoms of bradycardia or acute coronary syndrome, and consider ambulatory ECG monitoring if symptoms suggest intermittent conduction abnormalities. 1, 2, 3

Immediate Diagnostic Workup

Clinical Assessment

• Assess for chest pain characteristics and timing, as new RBBB in the setting of acute chest pain may indicate acute myocardial infarction with complete coronary occlusion, even without classic ST-segment elevations 3, 4, 5
• Evaluate for symptoms of bradycardia including syncope, presyncope, lightheadedness, or dizziness, which warrant more extensive evaluation for intermittent high-degree AV block 2, 3
• Screen for pulmonary embolism risk factors, as newly emerged RBBB can indicate massive pulmonary trunk obstruction in 80% of cases with main trunk PE 6
• Review cardiac risk factors, family history, and current medications to stratify overall cardiovascular risk 3

Electrocardiographic Confirmation

• Confirm RBBB diagnosis with QRS duration ≥120 ms, RSR' pattern in V1-V2, S wave greater than R wave or >40 ms in leads I and V6, and R peak time >50 ms in V1 3
• Identify high-risk conduction patterns including alternating bundle branch block, bifascicular block (RBBB + left anterior or posterior hemiblock), or first-degree AV block combined with RBBB 3

Mandatory Imaging

• Transthoracic echocardiography is reasonable for all new RBBB to assess for structural heart disease and left ventricular dysfunction, though the threshold for imaging is lower than with LBBB 1, 2, 3
• RBBB carries 64% increased odds of in-hospital death in acute MI settings, suggesting more extensive disease when MI occurs 1

Risk Stratification and Special Scenarios

Acute Coronary Syndrome Context

• New RBBB with chest pain and positive troponin warrants urgent coronary angiography, as RBBB can obscure ST-segment analysis and complete coronary occlusion may be present without classic STEMI criteria 3, 4, 5
• TIMI flow 0 occurs in 51.7% of AMI patients with RBBB, higher than the 39.4% seen with LBBB 5
• In-hospital mortality is highest (18.8%) among patients with new or presumably new RBBB, exceeding even new LBBB (13.2%) 5
• 26% of acute left main coronary artery occlusions present with RBBB (mostly with left anterior hemiblock) 5

High-Risk Features Requiring Immediate Intervention

• Alternating bundle branch block requires immediate permanent pacing due to high risk of sudden complete heart block 1, 3
• Syncope with RBBB and HV interval ≥70 ms or infranodal block on electrophysiology study is a Class I indication for permanent pacing 1, 2, 3
• Symptomatic second-degree Mobitz type II or third-degree AV block requires immediate permanent pacing 3

Monitoring and Follow-Up Strategy

Symptomatic Patients

• Ambulatory ECG monitoring (24-48 hour Holter) is useful to detect intermittent higher-degree AV block when symptoms suggest intermittent bradycardia 1, 2
• Electrophysiology study is reasonable when symptoms suggest intermittent bradycardia but ambulatory monitoring is unrevealing 1, 2, 3

Asymptomatic Patients with Isolated RBBB

• Annual clinical evaluation with ECG is recommended, including reassessment for symptom development and monitoring for progression to higher-degree conduction disease 2, 3
• Asymptomatic patients with isolated RBBB and 1:1 AV conduction have a benign prognosis and do not require permanent pacing 2
• Stress testing with imaging is reasonable if ischemic heart disease is suspected, as RBBB can mask ischemic ECG changes requiring an imaging component for accurate assessment 1, 2, 3

Critical Diagnostic Pitfalls

• RBBB patients are significantly undertreated for acute MI, with only 32% receiving fibrinolytic therapy compared to 65.5% without bundle branch block 1
• RBBB can mask ST-segment changes indicating myocardial ischemia, and more than 50% of patients with chest pain and RBBB will have a diagnosis other than MI 2
• Do not dismiss new RBBB as benign without excluding acute coronary occlusion, pulmonary embolism, and structural heart disease 4, 5, 6