Repolarization in Infants and Children

Jerome Liebman, M.D.
University Hospital, Case Western University, Cleveland, Ohio

Abstract: There is no evidence that the principles of the electrophysiology of repolarization in infants and children are any different from that of any other age.  However, there is no question that it is clinically different.  The differences begin in the newborn period.  A number of early studies noted many changes in normals in the first days if life, but by 72 hours to one week, the T wave was markedly posterior.  The most comprehensive analysis was by Hait and Gasul ⁽¹⁾ who noted that at birth the T was always directed to the left, and anterior.  By six hours of age, the T vector transiently was anterior and to the right and by three days was again to the left, but could be anterior or posterior.  Then by seven days, the T vector was reliably to the left and posterior.  This posterior direction of the T is very reliable throughout childhood, only becoming reliably anterior well into adolescence and young adulthood although there are occasional anterior T waves before that in normals.  Mechanisms of the above have been postulated but there is no data.  In fact if the T vector prior to adolescence is anterior and to the left, then the ECG is diagnosed as showing RVH.

The second major issue related to repolarization early in life is the misnamed concept of “early repolarization”.  Studies utilizing body surface potential surface maps ^(2,3,4) have given insight into this issue.  Spach^(2,3) has shown that in childhood and adolescents that at the end of the QRS a significant amount of repolarization can be recognized.  Widman⁽⁴⁾ in young adults documented the same phenomenon.  In addition, it was also documented that there could be so much repolarization near the end of the QRS that the QRS is distorted.  Obviously, since in normal, depolarization begins early in the endocardium, repolarization begins very early in the QRS.  Thus the repolarization which often distorts the QRS is not early in repolarization, but is clearly a manifestation of the normal biological variation, manifested late in repolarization.  The more repolarization seen late in the QRS the more likely there will be clearly visible distortion of the QRS.  Why there is so much more repolarization late in the QRS often of high magnitude in adolescents and young adults is not known.

 

REFERENCES

[1] Hait G, Gasul BM, “The evolution and significance of T wave changes in the normal newborn during the first seven days of life”.  Am. J. Cardiol 1963; 12: 494.

[2]  Widman LE,  Liebman J, et al, “Electrocardiographic body surface potential maps of  the QRS and T of  normal young men.  Qualitative description and selected quantifications”. J. Electrocardiol. 1988; 21: 121-136.

[3]   Spach MS, Barr RC, Warren RB et al, “Isopotential body surface mapping in subjects of all ages:emphasis on low level potentials with analysis of the method”.  Circulation 1979; 59: 805-821.

[4]   Spach MS, Barr RC, Benson W, “Body surface low level potentials during ventricular  repolarization with analysis of the ST segments.  Variability in normal subjects”  Circulation 1979; 59: 822-836.