Normal values of signal-averaged electrocardiographic parameters and QT dispersion in infants and children

Ventricular late potentials, and dispersion of the QT interval, are markers for risk of ventricular arrhythmias. Normal values for these parameters ar e well established in adults, but may not apply for children. This study ha s investigated the age dependency of signal averaged electrocardiographic p arameters and QT dispersion in 111 normal children aged from 5 days to 16 y ears. The results indicate that parameters change with age: duration of fil tered QRS and low amplitude (< 40 mu V) terminal signal increase with age, especially in the younger patients. Filtered QRS is 88.9 +/- 7.87 ms in inf ants, and increases to 108.7 +/- 8.51 in teenagers (p < 0.001). Low amplitu de terminal signals are 17.0 +/- 3.44 ms in infants, and 24.5 +/- 5.64 ms i n teenagers (p < 0.001). Root mean square of the last 40 ms decreases with age, but remains stable after the age of 10 years (122.4 +/- 33.30 mu V in infants, 60.9 +/- 31.27 in teenagers, p < 0.001). QT dispersion, on the oth er hand, does not change significantly with age. The mean value for the who le group is 36 +/- 13.7 ms. A weak but significant correlation exists betwe en QT dispersion and filtered QRS. Thus, age must be taken into considerati on when interpreting signal-averaged electrocardiograms, but not when measu ring QT dispersion.