THE EFFECTS OF MIDAZOLAM FOLLOWED BY ADMINISTRATION OF EITHER VECURONIUM OR ATRACURIUM ON THE QT INTERVAL IN HUMANS

Prolongation of the QT interval may produce potentially hazardous dysr hythmias. The effects on the QT interval of midazolam followed by admi nistration of either vecuronium or atracurium have been investigated. Thirty patients, ASA I or II, without cardiovascular problems, electro lyte abnormalities or receiving any medication were studied. All patie nts were premedicated with midazolam 0.08 mg kg(-1) i.m. 30-60 min bef ore surgery. Anaesthesia was induced with midazolam 0.4 mg kg(-1). ECG recordings as well as heart rate and arterial pressure measurements w ere obtained before induction of anaesthesia and 1, 3 and 5 min after midazolam administration. Further recordings were obtained at 1,3 and 5 min after either vecuronium 0.1 mg kg(-1) (15 patients) or atracuriu m 0.5 mg kg(-1) (15 patients). Further recordings were obtained immedi ately after tracheal intubation and at 1, 3 and 5 min later. Midazolam followed by administration of either vecuronium or atracurium did not produce any significant change in QT(c) interval (QT interval correct ed for heart rate). Statistically sig significant prolongation of QT,w as observed in both groups after intubation, although the mean QT(c) v alues did not exceed the upper limits of normal. Heart rate and arteri al pressure were also increased significantly in both groups after int ubation.