QT hysteresis in long-QT syndrome children with exercise testing

Area of Science:

• Pediatric Cardiology
• Clinical Electrophysiology
• Genetics

Background:

• Congenital long QT syndrome (LQTS) is an inherited cardiac disorder affecting ion channels, leading to abnormal heart repolarization.
• LQTS can cause syncope and sudden cardiac death, characterized by a prolonged QT interval and polymorphic ventricular tachycardia.
• Adult studies suggest LQTS patients exhibit altered QT adaptation to heart rate changes, forming a 'hysteresis loop'.

Purpose of the Study:

• To investigate QT interval changes during exercise testing in pediatric LQTS patients.
• To explore the potential of QT hysteresis as a diagnostic marker for LQTS in children.

Main Methods:

• Subjects were categorized into definite LQTS (n=17), middle (n=16), and normal control (n=18) groups based on 1993 LQTS criteria.
• All participants underwent treadmill exercise testing with continuous ECG monitoring during exercise and recovery.
• DeltaQT was calculated by subtracting the QT interval during recovery from the QT interval at a similar heart rate during exercise.

Main Results:

• While QT intervals shortened with increased heart rate in all groups, QTc remained stable.
• The LQTS group exhibited significantly greater DeltaQT values during the first 1, 2, and 4 minutes of recovery compared to control groups.
• A significant QT hysteresis loop was observed in the LQTS group during the recovery phase, where the QT interval remained shortened despite decreasing heart rate.

Conclusions:

• Pediatric LQTS patients demonstrate significant QT hysteresis during exercise test recovery.
• The QT hysteresis loop during exercise recovery may serve as a valuable tool for the early diagnosis of LQTS in children.