ST segment:

• From end of QRS complex to beginning of T wave
• Represents electrically neutral period b/t ventricular depolarization (QRS) & ventricular repolarization (T wave)
• Period in which ventricular contraction is maintained to expel blood from ventricles
• Typically located at baseline

Junction (J) point:

• Located at end of QRS complex & beginning of ST segment (ie, start of ST segment)
• Not always discernible due to STE

Isoelectric line:

• Often difficult to make out true isoelectric line on pediatric ECG due to:
  • (1) Faster heart rates (hence, P wave falls on preceding T wave)
  • (2) Atrial repolarization (affects PR segment)
• PR segment still typically used to assess level of ST segment

ST-segment deviation:

• STD or STE >1 mm: rare in normal children
• STE in normal children: most common in precordial leads (esp. at transition of T wave)
• STE-related early repolarization (“fishhook”) pattern:
  • Gender specific: ↑ prevalence in adolescent males [1]
  • Male pattern: J point elevation >1mm & ST angle >20° [2]

REFERENCES

1. Bidoggia H, Maciel JP, Capalozza N, et al. Sex-dependent electrocardiographic pattern of cardiac repolarization. Am Heart J 140:430, 2000.

2. Surawicz B, Parikh SR. Prevalence of male and female patterns of early ventricular repolarization in the normal ECG of males and females from childhood to old age. J Am Coll Cardiol 40:1870, 2002.