Overview:

• S wave: 1st negative deflection after R wave

S waves in precordial leads: [1]

• Right precordial leads (V1-V2):
• Term newborn: S waves prominent (up to 23 mm in V1) despite RV dominance
• 1 week to 1 month of age: S waves ↓ to minimum
• S waves gradually ↑ with age & ↑ LV mass

• Mid-precordial leads (V3-V4):
• Birth: S waves prominent (up to 28 mm)
• Gradual ↓ with age (but remains more prominent than V5-V6)

• Left-lateral precordial leads (V5-V6):
• Birth: often prominent (up to 10 mm in V6)
• Gradual ↓ with age & ↑ LV mass

REFERENCES

1. Davignon A, Rautaharju P, Boisselle E, et al. Normal ECG standards for infants and children. Ped Cardiol 1:123, 1979.