LQT1 patients have augmented response of repolarization dispersion following atropine induced heart rate increase...

The long QT syndrome type 1 (LQT1) is caused by loss-of-function mutations affecting the potassium channel current I_Ks important for repolarization adaptation at heart rate (HR) increase. We therefore compared changes in three global VR dispersion parameters following a rapid, atropine-induced HR increase in LQT1 patients versus healthy controls applying Frank vectorcardiography. The adaptation patterns, magnitudes, and changing rates of T amplitude, T area, and the ventricular gradient were assessed during 5 min following injection. Twenty-one LQT1 patients and 31 controls were enrolled. HR increased similarly within ~23 s. The majority had a tri-phasic VR dispersion adaptation pattern: a rapid decrease to a minimum, a slower return to a slightly higher level, and a very slow almost horizontal decrease. In the LQT1 group, all three dispersion parameters had a longer lasting rapid phase and larger overshoot reaction, although statistically significant only for T amplitude. In conclusion, LQT1 was associated with an augmented adaptation of global dispersion parameters to a rapid HR increase versus healthy controls. Further studies are needed to determine how these observations relate to arrhythmogenesis and if the atropine test of QT interval and dispersion adaptation can be used in risk assessment on the individual level.