Overview:

• PR interval: period from beginning of P wave to beginning of QRS (ie, P wave + PR segment)
• Cardiac event: transmission from atrium (adjacent to sinus node) to ventricle (adjacent to Purkinje-network fibers)

PR interval duration:

• In general: ↑ PR interval with ↑ age [1]
• Average based on age:
  • 18-22 weeks GA: 102 ms
  • Term: 110 ms
  • Birth: 107 ms
  • 1 month: 98 ms
• ↓ PR interval from birth-to-1 month primarily due to autonomic factors [1]
• ↑ PR interval after 1-month due to slowing of AV nodal conduction related to intrinsic changes in AV node & ↑ in atrial size
• Lower limit of normal:
  • Children: 90 ms
  • Adults: 120 ms
• Upper limit of normal:
  • Young infants: 140 ms
  • Adolescents: 180 ms
  • Adults: 200 ms

Short PR interval:
Ventricular preexcitation

• Due to conduction over (1) accessory AV connection (more common) or (2) fasciculoventricular pathway [3]
• May be difficult to recognize with short PR interval
• Suspect if: [2]
  • PR interval <100 ms
  • No Q waves in left-lateral precordial leads (V5-V6)
  • LAD (QRS in frontal plane)

Prolonged PR interval:
1st-degree AV block

• Due to conduction slowing at atrium, AV node, or His-Purkinje system in children [4]
• Occurs at only one of these sites in children with heart disease [5]

REFERENCES

1. Chia EL, Ho TF, Rauff M, et al. Cardiac time intervals of normal fetuses using noninvasive fetal electrocardiography. PrenatDiagn 25:546, 2005.

2. Perry JC, Giuffre, Garson A Jr. Clues to the electrocardiographic diagnosis of subtle Wolff-Parkinson-White syndrome in children. J Pediatr 117:871, 1990.

3. Sallee D III, Van Hare GF. Preexcitation secondary to fasciculoventricular pathways in children: a report of three cases. J Cardiovasc Electrophysiol. 10:36, 1999.

4. Sarubbi B, Mercurio B, Ducceschi V, et al. A “multisite” atrioventricular block. Ital Heart J 5:64, 2004.

5. Sherron P, Torres-Arraut E, Tamer D, et al. Site of conduction delay and electrophysiologic significance of first degree atrioventricular block in children with heart disease. Am J Cardiol 55:1323, 1985.