Individually Rate Corrected QTc Intervals in Children and Adolescents

Abstract

Accurate evaluation of the appearance of QTc sex differences during childhood and adolescence is intricate. Inter-subject differences of individual QT/RR patterns make generic heart rate corrections inaccurate because of fast resting heart rates in children. The study investigated 527 healthy children and adolescents aged 4–19 years (268 females, 50.9%). All underwent continuous ECG 12-lead monitoring while performing postural changes during a 70-min investigative protocol to obtain QT interval measurements at different heart rates. On average, more than 1200 ECG measurements (QT interval and its 5-min history of preceding RR intervals) were made in each subject. Curvilinear QT/RR regression involving intra-individual correction for QT/RR hysteresis were calculated in each subject. The projection of the QT/RR regressions to the heart rate of 60 beats per minute defined individually corrected QTc intervals. In males, gradual QTc shortening by about 15 ms appeared during the ages of 13–19 years synchronously with the incidence of secondary sex signs ( p = 0.016). On the contrary, whilst gradual QTc prolongation by about 10 ms appeared in females, it occurred only during ages 16–19 years and was not related to the incidence of secondary sex signs ( p = 0.18). The study also showed that in children and adolescents, linear QT/RR models fit the intra-subject data significantly more closely than the log-linear models ( p < 0.001). The study speculates that hormonal shifts during puberty might be directly responsible for the QTc shortening in males but that QTc prolongation in females is likely more complex since it was noted to follow the appearance of secondary sex signs only after a considerable delay.

Physiologic heart rate dependency of the PQ interval and its sex differences

“…Verification of such a concept is clearly beyond the possibilities offered by our data as no hormonal measurements were included in the source clinical studies. In addition to future studies with detailed hormonal measurements, it would also seem appropriate to replicate these analyses in ECG data of children and adolescents 33 to answer the question of when in life the sex difference appears. In addition, similar to the QT/RR hysteresis which, as shown, exhibits opposite age influence and sex differences, PQ/RR hysteresis might likely be under autonomic control also contributing to both sex and age influences 34 .…”

Problems with Bazett QTc Correction in Paediatric Screening of Prolonged QTc Interval

“…The investigated population was reported in detail before [13]. In brief, continuous 12-lead ECGs sampled at 1000 Hz were obtained in 345 healthy children and adolescents aged from above 4 to below 15 years (174 girls).…”

“…As previously described [13], the complete recordings were divided into consecutive 10-second ECG segments and in each segment, heart rate was measured based on the average of all RR intervals.…”

“…In each segment, representative median beat was also constructed, and QT interval duration was measured using previously published procedures [14,15] in the image of the representative beats of all 12 leads superimposed on the same isoelectric axis. As previously described [13], appropriate validation including the measurements including systematic morphological interpretation [16] was employed.…”

“…Nevertheless, the properties of the Bazett formula should also be considered when evaluating paediatric recordings since the erroneously prolonged QTc values at increased heart rate might lead to an increased number of false positive LQTS diagnoses. To investigate this potential problem, we have studied Bazett corrected QTc intervals in a large set of long-term ECG recordings obtained in children during postural provocative manoeuvres [13].…”