Normal values and methodologic recommendations for signal-averaged electrocardiography in children and adolescents

Signal-averaged electrocardiography was performed in 153 normal children and adolescents (1 day to 18.3 years old) to examine the effects of age, sex, and race on different electrocardiographic variables, and to evaluate whether the current methods for analysis of the signal-averaged electrocardiogram are applicable to small children. Tracings with inaccurate automatic determination of the QRS end point or high noise levels were excluded. Filtered QRS duration, root-meansquare voltage, and low-amplitude signal duration were measured using 25, 40, and 80 Hz filters. All variables were significantly different (p < 0.01) in infants compared with subjects aged >15 years. These differences gradually resolved with increasing age. Sex differences were present for some variables in adolescents only, and there was no significant race-related difference. Because of the shorter QRS duration, the terminal activities were more accurately reflected at the terminal duration of 30 ms in infants and 35 ms in children aged at least 1 year to <6 years. Normative data for filtered QRS duration, root-mean-square voltage, and low-amplitude signal duration are provided for different age groups.