- P wave duration gradually increases with age in children [1,2,3]
- No significant age-related differences in P wave duration or amplitude to define LAE in children; thus, adult LAE diagnostic criteria applied for all ages
- Assumes sinus rhythm present
- V1 (negative portion of P wave): [depth (mm)] x [duration (s)] ≥ -0.04 mm∙s
- II: [notched P waves] + [P wave duration >95th percentile for age]
- 95th percentile: 65 ms (birth); 95 ms (12-16 y/o) 
- Limited sensitivity (44%); good positive predictive value (85%) 
- Macruz Index = ratio of P wave duration to PR segment duration
- Little value in pediatrics due large normal variation
- ↑ index in children (likely 2/2 to faster AV conduction) vs. adults 
1. Liebman J. Atrial hypertrophy. In: Liebman J, Plonsey R, Gillette P (eds): Pediatric Electrocardiography. Baltimore, Williams & Wilkins, 1982, p 140.
2. Chia EL, Ho TF, Rauff M, et al. Cardiac time intervals of normal fetuses using noninvasive fetal electrocardiography. Prenat Diagn 25:546, 2005.
3. Kose S, Kilic A, Iyisoy A, et al. P wave duration and P dispersion in healthy children. Turk J Pediatr 45:133, 2003.
4. Maok J, Krongrad E. Assessment of electrocardiographic criteria for left atrial enlargement in childhood. Am J Cardiol 53:215, 1984.