The ECGs of 104 normal children from a few hours old to 5 years of age were studied. These ECGs consisted of the standard limb leads, the aV limb leads and six precordial leads: V4R, V1, V2, V4, V5 and V6.
While the number of cases in each group are small, the following conclusions are suggested by this study:
1. ECGs of the newborn infant present important variations from those seen in later life. This is especially true during the first week of life. Thereafter the contour evolves [SEE FIG. 2 IN SOURCE PDF] in a definite manner until the adult-like pattern is reached.
2. The vertical and semivertical "electric" positions were the most frequently encountered in this age group.
3. P-waves present a rather permanent pattern in this age range:
a. is usually upright in lead 1 and 2, aVF, V4, V5 and V6.
b. is usually inverted in lead 2 and aVR.
c. is either upright, inverted or diphasic in lead 3, aVL, V4R, V1 and V2.
4. The P-R interval varies from 0.10 sec. minimum to 0.16 sec. maximum with the average being 0.12 sec. in this age range. It tends to become greater in the older age groups.
5. QRS duration is shorter in the younger age groups and increases slowly with age.
6. Polyphasic, M-shaped or slurred QRS complexes are not uncommon in the ECGs of normal children in this age range.
7. A Q wave is frequently absent in lead 1 and in all chest leads during the first week of life. Thereafter up to 5 years of age the pattern of the Q wave is as follows:
a. Q is generally absent in lead 1, V4R, V1, V2 and V4.
b. Q is generally present in lead 3, V4R, aVF, V5 and V6.
8. There is a distinct pattern of right ventricular dominance in leads from the sternum and to its right at birth. This pattern gradually undergoes involution, probably related to normal physiologic development, until the left ventricle becomes dominant. Thus the evolution of the S-wave parallels a gradual involution of the R-wave in right precordial leads and probably also in aVR. This dominance of the left ventricle over the entire precordium is usual by about 3 years, but may be delayed normally until 5 years of age.
9. The T-wave is upright or diphasic in V4R, V1, and V2 and inverted in V5 and V6 for the first 24 hours of life; it gradually alters so that by the fourth day it is inverted in V4R, V1 and V2 and upright in V5 and V6 and thereafter.
10. The transition zone of QRS varies from one age group to another and tends in some ages to be broad. In some instances no real transition zone can be determined.