A Study on Electrocardiograms of Healthy Japanese Children

Abstract

The purpose of this study is to obtain the normal ranges of electrocardiograms of Japanese elementary school children and to compare with each group separated by age and sex. Materials and Methods The subjects were 984 healthy children (506 boys and 478 girls) selected at random from all children (3532 boys and girls) in an elementary school in Nagoya, Japan. They were accepted as healthy children on the basis of their daily unrestricted activity and through a series of medical examinations. The subjects were sub-divided into twelve groups by sex and age for further analysis of their electrocardiograms. The 12 conventional leads and Lead V₃R were recorded for all subjects. The amplitudes and intervals of electrocardiographic deflections were carefully measured in each lead. In this paper 95 percentile of frequency distribution was accepted as a normal range for each component of the record. Results and Discussion RR interval was longer with increasing age both in boys and girls. The increasing rate of RR interval was more prominent in the boys than in the girls, and the difference of mean RR intervals reached a statistical significant level in the groups of 10 and 11 years old. According to above data, it was concluded that the normal range of RR interval should be set up separately; 0.48 to 1.00sec. for 6-9 years, and 0.54 to 1.08 sec. for 10-11 years. Although PQ interval also increased along with age, no significant difference was found for boys and girls. The normal ranges of PQ interval were 0.12 to 0.18 sec. for 6-9 years and 0.13 to 0.19sec. for 10-11 years respectively. The increasing rate of QT interval was less remarkable than RR or PQ intervals, and the mean of boys was significantly longer than that of girls in elder age group. A single normal range could be accepted for QT intervals as 0.28 to 0.40sec. for the all age groups. Though PQ interval tended to be longer with increasing RR interval except in the group with tachycardia, no significant correlation was observed for PQ and RR intervals. Correlation coefficients of RR with QT intervals were very high and proved statistically significant both in boys and girls and for all age groups.