Maximum QTc on Holter electrocardiography in children.

Background: Corrected QT interval (QTc) on electrocardiography (ECG) at rest and after exercise in a short daytime recording period may be insufficient for the diagnosis and management of long QT syndrome (LQTS), especially for LQTS type 2 and 3. Therefore, examination of QTc on Holter ECG is important. We designed a method of analyzing QTc on Holter ECG that can be performed in daily clinical practice by combining automatic and manual measurements.

Methods: We reviewed the charts of healthy children (n = 210) and LQTS patients (n = 35) aged <16 years and analyzed QTc at rest and after exercise, and the maximum QTc on Holter ECG.

Results: The QTc (Fridericia's correction) of most controls and LQTS patients reached the maximum at night or early in the morning. QTc differed according to sex and age. In the control group, QTc on ECG of all three types tended to lengthen with age. QTc after exercise was slightly longer than QTc at rest, and the maximum QTc on Holter ECG was much longer than both, reaching >450 ms in boys and 500 ms in girls. In most LQTS type 1 patients, QTc after exercise and that on Holter ECG tended to be long. In most LQTS type 2 and 3 patients, QTc at rest and that after exercise was long, and that on Holter ECG tended to be much longer.

Conclusions: The present method of analyzing QTc on Holter ECG, in which automatic and manual measurements are combined, is practical and may be useful for diagnosis and risk stratification of LQTS.