What does normal morphology of the P wave, QRS complex, ST segment, and T wave in leads V1 through V6 on an electrocardiogram (ECG) indicate?

Normal ECG Morphology in Leads V1-V6

Normal P wave, QRS complex, ST segment, and T wave morphology in leads V1 through V6 indicates normal cardiac electrical conduction through the ventricles without evidence of conduction disturbances, ischemia, or structural heart disease. 1

Normal P Wave Morphology

• In leads V1-V6, normal P waves should be upright, smooth, and rounded with amplitude less than 0.25 mV and duration less than 120 ms 1
• In V1, the P wave may normally have a biphasic appearance (positive then negative) reflecting right and left atrial activation 1
• P waves should precede each QRS complex with a constant PR interval (120-200 ms) unless there is atrioventricular block 1

Normal QRS Complex Morphology

• Normal QRS duration is less than 110 ms in adults, less than 90 ms in children 8-16 years, and less than 80 ms in children under 8 years 1
• Lead V1: Small r wave followed by deep S wave (rS pattern) 1, 2
• Lead V2: r wave slightly larger than in V1, still with deep S wave (rS pattern) 1, 2
• Lead V3: Transitional lead with R and S waves of approximately equal amplitude (RS pattern) 1, 2
• Leads V4-V6: Dominant R wave with small or absent S wave (R or Rs pattern) 1, 2
• R wave amplitude progressively increases from V1 to V5, then slightly decreases in V6 2, 3

Normal ST Segment Morphology

• ST segment should be isoelectric (at baseline) in all precordial leads 1
• Some ST elevation at the J point is normal, especially in leads V2-V3 1
• Normal J-point elevation thresholds 1:
  • Men ≥40 years: up to 0.2 mV (2 mm) in V2-V3; up to 0.1 mV (1 mm) in other leads
  • Men <40 years: up to 0.25 mV (2.5 mm) in V2-V3
  • Women: up to 0.15 mV (1.5 mm) in V2-V3; up to 0.1 mV (1 mm) in other leads
  • For both men and women: up to 0.05 mV (0.5 mm) in V4-V5 (except males <30 years: up to 0.1 mV)

Normal T Wave Morphology

• T waves should be upright in leads V3-V6 1
• In V1, the T wave may be upright or inverted in adults 1
• In V2, the T wave is typically upright in adults but may be inverted in adolescents and young adults under 20 years 1
• T wave amplitude is normally highest in leads V2 or V3 1
• Normal T wave amplitude thresholds 1:
  • Men: up to 1.0-1.4 mV (up to 1.6 mV in 18-29 year age group)
  • Women: up to 0.7-1.0 mV

Common Variants and Pitfalls

• RSR' pattern in V1-V2 with normal QRS duration (<110 ms) is a normal variant, especially in children 1, 2, 4
• Juvenile T-wave pattern: T-wave inversion in V1-V3 is normal in children and may persist in young adults 1
• Early repolarization: ST elevation at J point with upward concavity and prominent T waves, most common in young males 1
• T-wave inversions in V1-V2 may be normal in adults, but T-wave inversion in V5-V6 is always abnormal 1

Clinical Significance

• Normal ECG morphology in leads V1-V6 rules out:
  • Bundle branch blocks (QRS duration would be ≥120 ms) 1
  • Ventricular hypertrophy (would show increased voltage criteria) 1, 5
  • Myocardial ischemia/infarction (would show ST-T abnormalities) 1
  • Conduction disorders like fascicular blocks 1

Key Distinguishing Features from Abnormal Patterns

• Complete RBBB: QRS ≥120 ms with RSR' pattern in V1-V2 and wide S wave in I and V6 1
• Complete LBBB: QRS ≥120 ms with broad notched R waves in I, aVL, V5-V6 and absent Q waves 1
• Incomplete RBBB: QRS 110-119 ms with RSR' pattern in V1-V2 1
• Incomplete LBBB: QRS 110-119 ms with LVH pattern and R peak time >60 ms in V4-V6 1
• Myocardial ischemia: ST depression or T wave inversion 1

Normal ECG morphology in leads V1-V6 is an important baseline finding that indicates normal ventricular depolarization and repolarization, suggesting absence of structural heart disease, conduction abnormalities, or ischemic changes.