What are the causes of incomplete right bundle branch block in adults with a history of heart conditions?

Causes of Incomplete Right Bundle Branch Block

Primary Etiologic Categories

Incomplete right bundle branch block (iRBBB) results from delayed conduction through the right bundle branch, with causes ranging from benign normal variants to serious underlying cardiovascular disease including structural heart disease, congenital abnormalities, pulmonary conditions, and infiltrative processes. 1

Benign and Physiologic Causes

• Normal variant in young individuals and athletes is the most common benign cause, occurring in 0.5-2.5% of young adult athletes and considered a normal variant of athletic cardiac remodeling when isolated and asymptomatic 2, 1
• Crista supraventricularis (CSV) pattern represents late activation of the right ventricular crest, one of the last structures depolarized by the Purkinje network, and may result from posterior apex deviation or subpulmonic area delay 3
• Technical factors including higher placement of V1 and V2 electrodes can create an iRBBB pattern, particularly when the terminal rightward deflection is less than 20 ms 4, 3
• Pectus excavatum can produce an iRBBB pattern with negative P waves due to altered chest anatomy 3

Structural Heart Disease

• Congenital heart disease is a major cause, both in unoperated and postoperative patients, with atrial septal defect (particularly ostium secundum) being the classic association presenting with iRBBB and fixed splitting of S2 on examination 2, 1
• Ischemic heart disease, particularly anterior myocardial infarction with persistent intraventricular conduction disturbances, carries an unfavorable prognosis 1
• Cardiomyopathies of various types including hypertensive heart disease can produce iRBBB 1
• Ebstein's anomaly of the tricuspoid valve characteristically displays prolonged PR interval and wide RBBB pattern 1

Right Ventricular Strain and Pressure Overload

• Pulmonary hypertension and right ventricular pressure overload can manifest as iRBBB, representing right heart strain 2, 5
• Pulmonary embolism may present with iRBBB as an ECG sign of right ventricular overload, usually seen in more severe cases 2
• Right ventricular diastolic overload from conditions like mild atrial septal defects can produce iRBBB with normal QRS width 6

Degenerative and Infiltrative Processes

• Primary degenerative lesions of the specialized conducting tissue occur particularly in older individuals as an isolated phenomenon 1
• Sarcoidosis is an infiltrative cause requiring prophylactic pacing consideration even if AV block is transient due to disease progression risk 1
• Amyloidosis may cause iRBBB and requires prophylactic pacing consideration 1

Infectious and Inflammatory Causes

• Myocarditis represents an inflammatory cause of iRBBB 1
• Chagas' disease is an infectious cause of iRBBB 1
• Lyme disease can cause AV block during the acute phase, though this typically resolves and does not require permanent pacing 1

Genetic and Neuromuscular Conditions

• Lenegre disease (progressive cardiac conduction disease) is an autosomal dominant condition linked to SCN5A gene mutations affecting cardiac sodium channels, presenting with various conduction defects including RBBB in young individuals 1
• Neuromuscular diseases may cause iRBBB and require prophylactic pacing consideration due to progression risk 1

Critical Diagnostic Pitfalls

When iRBBB Signals Serious Disease

• Bifascicular block (iRBBB with left anterior or posterior hemiblock) carries increased risk of progression to complete AV block and requires comprehensive evaluation 1
• Arrhythmogenic right ventricular cardiomyopathy (ARVC) shows localized QRS prolongation in right precordial leads (V1-V3) with epsilon waves and should be considered in the differential diagnosis, especially with family history of sudden death or ventricular arrhythmias 1
• Brugada pattern (iRBBB with ST-elevation in V1-V3) requires immediate specialized evaluation due to sudden cardiac death risk 1
• Symptomatic iRBBB (syncope, presyncope, dizziness, fatigue, exercise intolerance) requires urgent evaluation for arrhythmic etiology 2, 1

Differential Diagnosis Considerations

• Distinguish from type-2 Brugada ECG pattern, right ventricular enlargement, ARVC, ventricular preexcitation (Wolff-Parkinson-White syndrome), and hyperkalemia 3
• Evaluate for atrial septal defect by auscultating for fixed splitting of the second heart sound, as RBBB is a common finding in ostium secundum ASD 2, 3

Mandatory Evaluation Approach

• Assess for associated symptoms including syncope, presyncope, dizziness, fatigue, or exercise intolerance 2
• Perform transthoracic echocardiography as the first-line diagnostic test to exclude structural heart disease, particularly right ventricular enlargement, atrial septal defects, pulmonary hypertension, and valvular abnormalities 2
• Determine if iRBBB is isolated or associated with other conduction abnormalities (e.g., left anterior or posterior hemiblock, first-degree AV block) 2
• Evaluate family history for premature cardiac disease or sudden cardiac death, which warrants further cardiac evaluation 2