The Authors report their experience with the QRS duration among children requiring RV apical pacing.  They demonstrate, not unexpectedly, that the mean QRS duration increases with advancing age groups.  These are descriptive but interesting observations.   These observations call into question the use of the QRS duration as a criterion for CRT in children.

There are a few points that must be mentioned as relates to CRT. 

First, the title of the manuscript is somewhat misleading.  The title suggests that the QRS duration was measured serially and longitudinally in this population. Rather, these data reflect the mean duration for advancing age groups.

Second, these data do not help with defining the criterion of the appropriate QRS duration for CRT selection in children.  No measures of LV function were included.   In addition, no mention of functional classification is given.  Thus, these data do not allow us to conclude that there is or is not a threshold value of QRS duration that predicts a positive response to CRT in children.  The Authors should be very careful to include this as a significant limitation.

Extensive experience in pacing and CRT in adults and children