Multi-undulant T-U-wave, sinus bradycardia and long QT syndrome: a possible phenotype of mutant genes controlling the inward potassium rectifiers.

Abstract

Inward rectifying potassium currents (Ikr and Iks) during phase 3 repolarization of the myocyte from the beginning to the end of repolarization of the myocardial syncytium will inscribe a T-U-wave on the surface electrocardiogram (ECG). Type two congenital long QT syndrome (LQT2) is a phenotype of human ether-a-go-go-related gene (HERG) mutation on the chromosome 7q 35-36. Type one congenital long QT syndrome (LQT1) is a phenotype of KvLQT1 mutation on the chromosome 11p15.5. Both LQT1 and LQT2 relate with inward rectifying potassium currents and is repolarization related, therefore, it is speculate that patients of LQT1 and LQT2 may have an abnormal T-U-wave on their surface ECG. To two probands of congenital LQT, 8 patients of structural heart disease treated by open heart surgery, 13 patients of structural heart disease without open-heart surgery, and 10 patients of normal controls, 24 hour-Holter monitoring was performed from July to December 1996. Their corrected QT interval (QTc) as well as the RR interval of every heart beat was calculated by a computer. The results showed that all 33 patients exhibited beat-by-beat fluctuation of their QTc and RR daily. The RR intervals of these two probands of congenital LQT were somewhile more than 1200 ms during circadian waking time, while 31 cases without LQT showed their RR prolongation only during the circadian sleeping time. A multi-undulant T-U-wave, or a beat-to-beat changing of vectors or amplitudes of their T-U-wave observed in these two probands of congenital LQT, were not observable in those 31 patients without congenital LQT. Therefore, we concluded that multi-undulant T-U-wave, sinus bradycardia and a longer QTc was a phenotype of the mutated genes which control the inward rectifying potassium currents during phase 3 repolarization.