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 are well established in adults, but may not apply for children. This study has investigated the age dependency of signal averaged electrocardiographic parameters and QT dispersion in 111 normal children aged from 5 days to 16 years. The results indicate that parameters change with age: duration of filtered QRS and low amplitude (< 40 microV) terminal signal increase with age, especially in the younger patients. Filtered QRS is 88.9 +/- 7.87 ms in infants, and increases to 108.7 +/- 8.51 in teenagers (p<0.001). Low amplitude terminal signals are 17.0 +/- 3.44 ms in infants, and 24.5 +/- 5.64 ms in 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 microV in infants, 60.9 +/- 31.27 in teenagers, p<0.001). QT dispersion, on the other hand, does not change significantly with age. The mean value for the whole group is 36 +/- 13.7 ms. A weak but significant correlation exists between QT dispersion and filtered QRS. Thus, age must be taken into consideration when interpreting signal-averaged electrocardiograms, but not when measuring QT dispersion.