- Normal standard variations occur with age (most rapidly during 1st year of life) , ethnicity, racial background [2,3] (limited race-specific data), & body mass index 
- Most significant variations occur in QRS voltage in scalar ECGs & vectorcardiograms 
- With improved technology in fetal ECG, normal fetal values being established [6,7]
1. Davignon A, Rautaharju P, Boisselle E, et al. Normal ECG standards for infants and children. Ped Cardiol 1:123, 1979.
2. Rao PS, Thapar MK, Harp RJ. Racial variations in electrocardiograms and vectorcardiograms between black and white children and their genesis. J Electrocardiol 17:239, 1984.
3. Rao PS. Racial differences in electrocardiograms and vectorcardiograms between black and white adolescents. J Electrocardiol 18:309, 1985.
4. Ito S, Okuni M, Hosaki J, et al. Effects of fatness on the electrocardiogram in children aged 12-15 years. PediatrCardiol 6:249, 1986.
5. Perry LW, Pipberger HV, Pipberger HA, et al. Scalar, planar, and spatial measurements of the Frank vectorcardiogram in normal infants and children. Am Heart J 111:721, 1986.
6. Taylor MJ, Smith MJ, Thomas M, et al. Non-invasive fetal electrocardiography in singleton and multiple pregnancies. BJOG 110:668, 2003.
7. Chia EL, Ho TF, Rauff M, et al. Cardiac time intervals of normal fetuses using noninvasive fetal electrocardiography. PrenatDiagn 25:546, 2005.