ABNORMAL RESPONSE TO EXERCISE, FACE IMMERSION, AND ISOPROTERENOL IN CHILDREN WITH THE LONG QT SYNDROME

The present study was performed to observe the change of QT interval b y sympathetic stimulations in patients with the long QT syndrome (LQTS ). The study group consisted of 6 children with LQTS and 6 healthy chi ldren without QT prolongation. All LQTS patients had syncopal episodes . The QT(c) and Delta QT(c)% ([QT(c) interval after examination - QT(c ) interval at rest]/QT(c) interval at rest X 200) by treadmill testing , face immersion, and isoproterenol were examined. One minute after pe ak exercise of treadmill testing, the changes in the QT(c) interval we re not significant in either group, but Delta QT(c)% was larger in the LQTS group than in the control group (+11.0 +/- 12.1% vs -2.6 +/- 3.2 %; P = 0.02). The QT(c) interval at the shortest RR interval during f ace immersion was prolonged in the LQTS group (0.47 +/- 0.01 s to 0.51 +/- 0.04 s; P = 0.02), but there were no significant changes in the c ontrol group (0.40 +/- 0.03 s to 0.41 +/- 0.03 s; P = NS). Delta QT(c) % was larger in the LQTS group than in the control group (+10.0 +/- 7. 3% vs +1.1 +/- 5.5%; P = 0.04). In the LQTS group, the RR interval was shortened (P = 0.009) and QT(c) interval was prolonged (P = 0.0008) a fter isoproterenol infusion. These sympathetic stimulations amplified the TU abnormality in the LQTS group. By observing the TU changes caus ed by face immersion, we hoped to find a possible new method with whic h to diagnose LQTS. The combination of these examinations may be helpf ul in screening the borderline cases of TU abnormalities.