What does a deep S wave in leads V1 and V2 on an electrocardiogram (ECG) indicate?

Deep S Wave in Leads V1 and V2: Clinical Significance and Interpretation

Deep S waves in leads V1 and V2 on an electrocardiogram (ECG) are most commonly a normal finding but can also indicate left ventricular hypertrophy, left bundle branch block, or other cardiac conditions depending on associated ECG findings and clinical context.

Normal Variant vs. Pathological Finding

Deep S waves in the right precordial leads (V1 and V2) are often part of normal ventricular depolarization patterns, representing the normal left-to-right activation sequence of the ventricles. However, they can also be associated with several cardiac conditions:

Normal Finding When:

• Present without other ECG abnormalities
• QRS duration is normal (<120 ms in adults)
• No associated symptoms or clinical concerns

Potential Pathological Indications:

1. Left Ventricular Hypertrophy (LVH)

   • Deep S waves in V1-V2 combined with tall R waves in V5-V6
   • According to the American College of Cardiology guidelines, the Sokolow-Lyon criteria (S in V1 + R in V5 or V6 > 35 mm) is a validated measure for LVH 1
   • Consider multiple criteria rather than relying on a single criterion for diagnosing LVH

2. Left Bundle Branch Block (LBBB)

   • When accompanied by:
     • QRS duration ≥120 ms in adults
     • Broad notched or slurred R waves in leads I, aVL, V5, and V6
     • Absent q waves in leads I, V5, and V6
     • R peak time >60 ms in leads V5 and V6 2

3. Dilated Cardiomyopathy

   • Deep S waves in V1-V4 with reduced QRS voltage in other leads
   • Often accompanied by lack of R wave progression from V1 to V4 and ST-T abnormalities 3

4. Right Ventricular Hypertrophy (RVH) Considerations

   • In the presence of biventricular hypertrophy, deep S waves in V5 or V6 with right axis deviation may suggest RVH alongside LVH 2

Diagnostic Algorithm

1. Evaluate QRS Duration:

   • Normal (<120 ms): Consider normal variant, LVH, or early cardiomyopathy
   • Prolonged (≥120 ms): Consider LBBB or other conduction disorders

2. Check for Associated ECG Findings:

   • Tall R waves in V5-V6: Suggests LVH
   • Notched/slurred R waves in lateral leads: Suggests LBBB
   • Q waves in specific distributions: May indicate prior myocardial infarction 2
   • Right axis deviation with deep S waves: Consider biventricular hypertrophy

3. Consider Patient Demographics:

   • Age: QRS voltage tends to decline with increasing age 1
   • Gender: Women have lower upper limits of QRS voltage than men 1
   • Body habitus: Obesity can mask voltage criteria by reducing QRS amplitude 1

Clinical Pitfalls to Avoid

1. Overinterpretation of Isolated Finding

   • Deep S waves alone without other criteria should not be diagnosed as pathological
   • The American College of Cardiology recommends using multiple validated criteria rather than relying on a single criterion 1

2. Failure to Consider Athletic Heart

   • Athletes commonly show increased QRS voltage that can mimic pathological conditions 4
   • Distinguish from pathological conditions through comprehensive evaluation

3. Ignoring Conduction Abnormalities

   • Modified criteria are needed when conduction disorders are present 1
   • In RBBB, S wave amplitude in right precordial leads may be reduced 1

4. Neglecting Clinical Context

   • ECG findings should always be interpreted in the context of the patient's clinical presentation
   • The ECG by itself is often insufficient to diagnose cardiac conditions 2

Deep S waves in V1 and V2 require careful interpretation within the broader clinical and ECG context to determine their significance and guide appropriate management decisions.