[Dynamic changes in the QT interval during the head-up tilt test in patients with vasovagal syncope]

Dynamic changes of the QT and QTc interval as well as QT dispersion and QTc dispersion during the head-up tilt test were investigated in 15 patients (8 men, mean age 32 years) with vasovagal syncope (VVS) and a positive head-up tilt test and in a control group of 15 patients with syncope in the case-history and a negative head-up tilt test (9 men, mean age 33 years). The value at rest of the QT interval did not differ in patients with VVS and controls. In controls at the beginning of HUT shortening of QT occurred (0.447 sec. vs. 0.419 sec. p = 0.0002), subsequently the QT did not change significantly. In patients with VVS during the beginning of the test only an insignificant shortening of QT occurred, while during the development of the syncope QT was prolonged (0.394 sec. vs. 0.420 sec. p < 0.0001). QT corrected for the pulse rate (QTc) did not change significantly during HUT. QTc dispersion was in patients with VVS significantly lower 3 minutes before the development of the syncope (0.067 sec. vs. 0.085 sec. p = 0.03), which may indicate the decline of the sympathetic and increase of the parasympathetic tonus which subsequently leads to the development of vasovagal syncope. QTc dispersion before the test was higher in patients with VVS as compared with controls (0.087 sec. vs. 0.063 sec., p = 0.03), which suggests an increase in the baseline sympathetic tonus in patients with VVS.