Spontaneous onset of torsade de pointes in long-QT syndrome and the role of sympathovagal imbalance

The net effects of sympathetic and vagal activity on the QT interval and th e mode of spontaneous onset of torsade de pointes (TdP) are still unclear i n long-QT syndrome. Two patients with long-QT syndrome had syncope while un dergoing Holter ECG investigation, The spontaneous onset of UP in these pat ients was analyzed with respect to the relation between the RR and QT inter vals. Both patients were high-school students (16- and 17-year-old boys) wh o had been diagnosed as long-QT syndrome and followed up without medical tr eatment because they had had neither a history of syncope nor arrhythmia in duction by treadmill exercise tests. The first episode of syncope in both p atients occurred during ordinary daily life and was not related to exercise or psychological stress. The dynamic changes between the RR and QT interva ls associated with the spontaneous onset of TdP were analyzed by Holter ECG , Both patients showed sinus tachycardia followed by abrupt sinus bradycard ia immediately before the onset of TdP. The enhanced rate of the adaptive r esponse of the QT interval that occurred during the deceleration of the hea rt rate preceded the onset of UP. These observations suggest that the compl ex situation that follows sympathovagal imbalance may have an important rol e in the dynamic change in the QT interval and initiation of UP in patients with long-QT syndrome.