Right Bundle Branch Block (RBBB): Diagnostic Criteria and Clinical Significance

Diagnostic ECG Criteria for Complete RBBB

The American College of Cardiology defines complete RBBB as a heart block in the right bundle branch of the electrical conduction system, characterized by QRS duration ≥120 ms in adults, an rSR' pattern in leads V1-V2, and S waves of greater duration than R waves in leads I and V6 1, 2
QRS duration ≥120 ms in adults (>100 ms in children 4-16 years, >90 ms in children <4 years) is a diagnostic criterion for complete RBBB 2
rSR', rsR', or rSR pattern in leads V1 or V2, with the R' deflection usually wider than the initial R wave, is a characteristic ECG finding in complete RBBB 2
S wave of greater duration than R wave or >40 ms in leads I and V6 is a diagnostic criterion for complete RBBB 2
Normal R peak time in leads V5 and V6 but >50 ms in lead V1 is a characteristic ECG finding in complete RBBB 2

RBBB occurs when conduction is delayed or blocked in the right bundle branch of the His-Purkinje system, according to the American College of Cardiology 3, 4
The normal conduction axis consists of the sinus node, atrial muscle, atrioventricular node, His bundle, bundle branches, fascicles, Purkinje fibers, and ventricular muscle, as described by the American College of Cardiology 3

Complete RBBB has a prevalence of approximately 1% in the general population, according to the American College of Cardiology 2
In young adult athletes, the prevalence of complete RBBB ranges from 0.5% to 2.5%, as reported by the American College of Cardiology 2
RBBB may be an isolated and clinically benign finding or associated with underlying cardiovascular disorders, such as coronary artery disease or cardiomyopathy, as noted by the American College of Cardiology 2
RBBB is commonly seen after repair of tetralogy of Fallot and in Ebstein's anomaly, according to the American College of Cardiology 2

In patients with newly detected RBBB, a transthoracic echocardiogram is reasonable if structural heart disease is suspected, as recommended by the American College of Cardiology 3
In symptomatic patients with conduction system disease where atrioventricular block is suspected, ambulatory electrocardiographic monitoring is useful, according to the American College of Cardiology 3
The European Society of Cardiology recommends that demonstration of complete bundle branch block should lead to a cardiological work-up including exercise testing, 24-hour ECG monitoring, and imaging 2

Preexisting RBBB does not invalidate interpretation of the exercise ECG, except in the anterior precordial leads (V1, V2, and V3), as noted by the American Heart Association 5, 6
RBBB has been associated with underlying coronary artery disease, particularly with obstructive disease affecting the left anterior descending artery, though this association has been questioned, according to the American Heart Association 5, 6

The European Society of Cardiology states that RBBB usually will not hamper interpretation of ST-segment elevation in the context of acute myocardial infarction 7, 8
RBBB preserves ST-segment interpretation, unlike left bundle branch block (LBBB), which significantly complicates ECG diagnosis of acute MI 7, 8

The European Society of Cardiology recommends that patients with myocardial infarction and RBBB have a poor prognosis, and prompt management should be considered when persistent ischemic symptoms occur in the presence of RBBB, regardless of whether the RBBB is new or previously known 7, 8
The American College of Cardiology notes that the morphology of RBBB explains why ST segments remain interpretable, with the slurred S wave appearing in lateral leads (I, V6), not in the leads where you're primarily looking for ST elevation (precordial leads V1-V4 for anterior MI, or inferior leads II, III, aVF) 9, 10

The European Society of Cardiology guidelines note that in the presence of LBBB, the ECG diagnosis of acute myocardial infarction is difficult and requires complex algorithms that don't provide diagnostic certainty 7, 8
Concordant ST elevation in LBBB (ST elevation in leads with positive QRS deflections) is one of the best indicators of ongoing MI with an occluded infarct artery 7, 8

The European Society of Cardiology recommends measuring ST segments normally, applying standard STEMI criteria (≥0.1 mV in limb leads, ≥0.2 mV in precordial leads for men >40 years) 8
The European Society of Cardiology advises against being falsely reassured by RBBB presence, as the conduction abnormality doesn't protect against MI and may actually indicate worse prognosis 7, 8
Consider emergency angiography if persistent ischemic symptoms are present with RBBB, even without diagnostic ST elevation 7, 8
Compare to prior ECGs when available, as new RBBB in the setting of chest pain should raise suspicion for acute MI 7, 8