RSR' Pattern in V1: Right Bundle Branch Block Characteristics and Significance
An RSR' pattern in lead V1 on an electrocardiogram is a characteristic finding of right bundle branch block (RBBB), consisting of an initial small R wave, followed by an S wave, and then a second R wave (R'), where the R' deflection is typically wider than the initial R wave. 1
Diagnostic Criteria for Complete RBBB
- QRS duration ≥120 ms in adults, >100 ms in children ages 4-16 years, and >90 ms in children <4 years of age 2
- RSR', rsR', rSR', or rarely a qR pattern in leads V1 or V2 2
- S wave of greater duration than R wave or >40 ms in leads I and V6 2
- Normal R peak time in leads V5 and V6 but >50 ms in lead V1 2
Diagnostic Criteria for Incomplete RBBB
- Same QRS morphology criteria as complete RBBB but with QRS duration between 110-119 ms in adults 2
- In children, incomplete RBBB may be diagnosed when the terminal rightward deflection is <40 ms but ≥20 ms 2
- The ECG pattern of incomplete RBBB may be present in the absence of heart disease, particularly when lead V1 is recorded higher than normal position 2
Normal Variant Considerations
- In children, an RSR' pattern in V1 and V2 with a normal QRS duration is considered a normal variant 2
- The terms "RSR" and "normal RSR" are not recommended to describe such patterns due to potential misinterpretation 2
- In athletes, an RSR' pattern with normal QRS duration is often considered benign 2
Clinical Significance and Implications
- Complete RBBB indicates conduction tissue disease affecting the right bundle branch 2
- RBBB with a QR pattern in V1 has a high positive predictive value for diagnosing cardiac arrest caused by high-risk pulmonary embolism 3
- Masquerading bundle branch block (RBBB pattern in precordial leads with LBBB pattern in limb leads) indicates severe and diffuse conduction system disease with poor prognosis 4
- Incomplete RBBB requires differentiation from pathological patterns such as Brugada syndrome, right ventricular enlargement, and arrhythmogenic right ventricular cardiomyopathy 5
Features Suggesting Pathological vs. Normal Variant RSR'
- Age: Older individuals with RSR' pattern are more likely to have pathological RBBB 6
- S wave characteristics: Diminution of S wave depth and inversion of SV1 > SV2 ratio often precede progression to complete RBBB 6
- QRS duration: QRS ≥100 ms more commonly associated with pathological RBBB 6
- Hereditary considerations: In hereditary bundle branch defect, RSR' pattern may indicate mutation carrier status, especially with broad r wave in aVR and s in V6 7
Monitoring and Follow-up
- Patients with incomplete RBBB should be monitored if they have symptoms, abnormal clinical exam findings, or family history of cardiac disease 5
- In hereditary bundle branch defect, 19% of patients with RSR' pattern may progress to complete fascicular block 7
- Males with hereditary predisposition demonstrate conduction blocks more frequently than females (75% vs 50%) 7