Clinical Significance of Persistent S Wave in V5 and V6
Persistent S waves in leads V5 and V6 are clinically significant markers that indicate right ventricular hypertrophy (RVH), suggest biventricular hypertrophy when combined with left ventricular hypertrophy (LVH) criteria, and serve as important prognostic indicators in specific cardiac conditions including pulmonary hypertension, heart failure, and cardiac resynchronization therapy response.
Primary Diagnostic Significance
Right Ventricular Hypertrophy and Biventricular Hypertrophy
The most established significance comes from the AHA/ACCF/HRS guidelines, which identify prominent S waves in V5 or V6 as useful signs that RVH may be present, particularly when seen alongside ECG criteria for LVH 1. This pattern suggests biventricular hypertrophy, where the increased QRS vectors from both ventricles create this characteristic finding 1, 2.
The guidelines specifically recommend that right axis deviation in the presence of electrocardiographic LVH and tall biphasic R/S complexes in several leads should be recognized as suggestive of biventricular hypertrophy 1. This is particularly important because biventricular hypertrophy has notoriously low ECG sensitivity due to vector cancellation between the two hypertrophied ventricles 1.
Age-Related Considerations
In pediatric populations, persistent S waves in V6 have specific diagnostic thresholds that vary by age. For children ≥5 years, an S wave amplitude ≥4mm in V6 suggests RVH 1, 2. This age-related interpretation is critical to avoid misdiagnosis.
Prognostic Significance in Specific Conditions
Pulmonary Hypertension
Deeper S waves in lead V5 are independent predictors of pulmonary hypertension, with a cut-off value of 0.42 mV demonstrating clinical utility for screening 3. In non-high-risk pulmonary embolism patients, S-wave depth in lead V5 <0.15 mV independently predicts early discharge (OR 0.137), making it a practical risk stratification tool 4.
Heart Failure and Cardiac Resynchronization Therapy
The presence of S waves in V5 and V6 has opposite prognostic implications depending on the clinical context:
In patients with complete left bundle branch block (CLBBB) receiving standard CRT: An S wave in V6 predicts poor response to therapy. Patients with S waves in both V5 and V6 had only a 38.5% response rate compared to 85.2% in those without S waves in either lead 5. This finding was independently associated with CRT nonresponse (HR 0.33) and higher rates of heart failure rehospitalization or death 5.
In patients receiving left bundle branch area pacing (LBBAP): The presence of S waves in V5/V6 after LBBAP predicts better clinical outcomes, with a 77.8% reduction in risk of the composite endpoint (HR 0.222) and lower non-response rates (22.58% vs 58.82%) 6. This reflects successful left bundle branch capture 7.
Clinical Algorithm for Interpretation
When encountering persistent S waves in V5/V6, evaluate systematically:
Check for LVH criteria: If present, strongly consider biventricular hypertrophy, especially with right axis deviation 1
Assess clinical context:
- Suspected pulmonary disease → Measure S-wave depth in V5 (>0.42 mV suggests pulmonary hypertension) 3
- Acute pulmonary embolism → S-V5 <0.15 mV predicts favorable early discharge 4
- Pre-CRT evaluation with CLBBB → S wave in V6 predicts poor response to standard CRT 5
- Post-LBBAP → S waves in V5/V6 confirm successful capture and predict better outcomes 6
Consider age: Apply pediatric-specific criteria if patient <18 years 1
Common Pitfalls
- Do not assume acute pathology: Persistent S waves may represent chronic structural changes, not acute events
- Context matters critically: The same ECG finding (S wave in V6) predicts opposite outcomes in standard CRT versus LBBAP
- Low sensitivity caveat: The absence of S waves in V5/V6 does NOT exclude RVH or biventricular hypertrophy, as ECG sensitivity for these conditions is inherently low 1
- Avoid isolated interpretation: Always integrate with clinical probability of congenital heart disease, valvular disease, or chronic pulmonary disease 2