Constitutional and echocardiographic variability of the normal electrocardiogram in children.

To understand better the normal electrocardiogram and to improve the diagnosis of left ventricular hypertrophy (LVH), the authors examined RV5 and SV1 + RV5, using a special computational technique, in relation to body size, heart size, and the distance between the heart and the chest wall in 7-year-old normal subjects. Boys and girls were analyzed separately. Using multiple regression analysis with a total of 16 constitutional and echocardiographic parameters as the predictor variable, the authors selected a minimum set of parameters and found that the greater the left ventricular mass (LVM) and the left ventricular cavity and the shorter the distance between the heart and the chest wall, the greater the RV5 and SV1 + RV5. In subjects with LVH in whom these parameters vary, SV1 + RV5 is preferable to RV5 for the electrocardiographic diagnosis of LVH, because LVM correlates more significantly with SV1 + RV5. In a similar analysis, using principal components as the predictor variable, no significance level was reached for the first principal component that represented size. This indicates that RV5 and SV1 + RV5 are in a constant range, irrespective of the body size and accompanying heart size.