Examples of rSR' Pattern in Lead V1
The rSR' pattern in lead V1 is most commonly associated with right bundle branch block (RBBB), but can also appear in several other cardiac conditions and even as a normal variant in certain populations.
Right Bundle Branch Block (RBBB)
The classic rSR' pattern in V1 is a hallmark of RBBB, characterized by:
- An initial small r wave
- A subsequent S wave
- A terminal R' wave (often wider than the initial r wave)
According to the American Heart Association/American College of Cardiology/Heart Rhythm Society guidelines, complete RBBB shows:
- QRS duration ≥120 ms in adults (>100 ms in children 4-16 years, >90 ms in children <4 years)
- rSR', rsR', or rSR' pattern in leads V1 or V2, where the R' or r' deflection is usually wider than the initial R wave 1
- S wave of greater duration than R wave or >40 ms in leads I and V6
- Normal R peak time in leads V5 and V6 but >50 ms in lead V1 1
Incomplete Right Bundle Branch Block
Incomplete RBBB presents with:
- Similar morphology to complete RBBB
- QRS duration between 110-119 ms in adults
- In children, terminal rightward deflection <40 ms but ≥20 ms 1
Normal Variant in Children
In children, an rSR' pattern in V1 and V2 with normal QRS duration is considered a normal variant 1. This is particularly important to recognize to avoid unnecessary investigations.
Atrial Septal Defect (ASD)
The rSR' pattern is seen in approximately:
- 26% of all pediatric patients with secundum ASD
- 54% of patients with large ASDs (>5 mm) 2
In patients with ASD, the presence of rSR' correlates with:
- Lower probability of spontaneous closure (7% vs 36%)
- Higher likelihood of requiring device or surgical closure (71% vs 38%) 2
Accessory Pathways
An rSR' complex in lead V1 with QRS duration <110 ms can be seen in:
- Left-sided accessory pathways (pseudo partial right bundle branch block)
- This may be the sole manifestation of a left-sided accessory pathway in sinus rhythm 3
Supraventricular Tachycardia
During supraventricular tachycardia, an rSR' pattern with QRS <110 ms may be observed in:
- Atrioventricular nodal reentrant tachycardia (AVNRT)
- Orthodromic atrioventricular reciprocating tachycardia with left-sided accessory pathway 4
Other Conditions
The rSR' pattern in V1 may also be associated with:
- Right ventricular hypertrophy
- Right ventricular outflow tract abnormalities
- Brugada syndrome (with specific ST elevation characteristics)
- Arrhythmogenic right ventricular dysplasia/cardiomyopathy 5
Diagnostic Approach
When evaluating an rSR' pattern in V1, consider:
- QRS duration (≥120 ms suggests complete RBBB)
- Patient age (normal variant in children)
- S wave characteristics in leads I and V6
- Associated symptoms or clinical context
- Other ECG findings (axis deviation, ST-T changes)
Important Considerations
- Not all rSR' patterns represent bundle branch blocks; nonspecific intraventricular conduction delays are common 6
- The American College of Cardiology recommends against assuming all wide QRS complexes are bundle branch blocks 6
- In patients with rSR' pattern and QRS <120 ms, evaluating the SV1/SV2 ratio can help distinguish incomplete RBBB from normal variants (SV1/SV2 >1.0 more likely represents incomplete RBBB) 7