Right Bundle Branch Block (RBBB): Electrocardiographic Features and Clinical Significance
Right bundle branch block (RBBB) is characterized by specific ECG findings including 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
Diagnostic ECG Criteria for Complete RBBB
- QRS duration ≥120 ms in adults (>100 ms in children 4-16 years, >90 ms in children <4 years) 2, 1
- rSR', rsR', or rSR pattern in leads V1 or V2, with the R' deflection usually wider than the initial R wave 2, 1
- S wave of greater duration than R wave or >40 ms in leads I and V6 in adults 2, 1
- Normal R peak time in leads V5 and V6 but >50 ms in lead V1 2, 1
Morphological Variations
- The classic RBBB pattern shows an rSR' configuration in right precordial leads (V1-V2) 1
- In some cases, a wide and often notched R wave pattern may be seen in leads V1 and/or V2 instead of the typical rSR' pattern 2, 1
- RBBB reduces the amplitude of the S wave in the right precordial leads 1
Incomplete RBBB
- Defined by QRS duration between 110 and 120 ms in adults, between 90 and 100 ms in children between 4 and 16 years of age, and between 86 and 90 ms in children less than 8 years of age 2
- Other criteria are the same as for complete RBBB 2
- IRBBB is a common ECG finding at all ages, more frequent in men and athletes 3
- Usually does not need further evaluation unless abnormalities are found on clinical examination 3
Pathophysiology
- RBBB occurs when conduction is delayed or blocked in the right bundle branch of the His-Purkinje system 4
- This leads to delayed activation of the right ventricle, creating the characteristic ECG pattern 4
Clinical Significance and Prevalence
- Complete RBBB has a prevalence of approximately 1% in the general population 4
- In young adult athletes, the prevalence of complete RBBB ranges from 0.5% to 2.5% 1, 4
- RBBB may be an isolated and clinically benign finding or associated with underlying cardiovascular disorders 2, 4
- RBBB is commonly seen after repair of tetralogy of Fallot and in Ebstein's anomaly 4
- RBBB with a QR pattern in V1 has been associated with high-risk pulmonary embolism 5
Evaluation Recommendations
- Demonstration of complete bundle branch block should lead to a cardiological work-up including exercise testing, 24-hour ECG monitoring, and imaging to evaluate for underlying pathological causes 2, 1
- In patients with newly detected RBBB, a transthoracic echocardiogram is reasonable if structural heart disease is suspected 4
- Special attention should be paid to the splitting of the second heart sound, as RBBB is a common finding in ostium secundum atrial septal defect 3
Special Considerations
- RBBB is associated with significant reduction in "left ventricular" QRS amplitudes on the standard ECG 6
- Combined voltages used for left ventricular hypertrophy (LVH) criteria are significantly reduced by RBBB, which may affect the sensitivity of standard LVH criteria 6
- Special criteria for LVH in the presence of RBBB include S V1 >2 mm (0.2 mV), R V5,6 >15 mm (1.5 mV), and QRS axis to the left of -30° 1
- In patients with paced rhythm and a RBBB-like pattern, displacement of leads V1-V2 to the sixth intercostal space can help identify true right ventricular pacing 7
Differential Diagnosis
- RBBB must be differentiated from incomplete RBBB 2
- It's necessary to differentiate IRBBB from pathological patterns such as type-2 Brugada ECG pattern, right ventricular enlargement, arrhythmogenic right ventricular cardiomyopathy, and ventricular preexcitation 3
- In arrhythmogenic right ventricular cardiomyopathy, RBBB ventricular tachycardia can originate from both ventricles, with most (62%) originating from the right ventricle 8