Anaesthesia and the QT interval in humans: effects of halothane and isoflurane in premedicated children

The effects of halothane and isoflurane followed by subsequent administrati on of vecuronium on the QT interval have been investigated during the induc tion of anaesthesia. Fifty-eight children, ASA I, without cardiovascular an d electrolyte abnormalities and not receiving any medication were studied. Anaesthesia was induced with either halothane (n = 28) or isoflurane (n = 3 0), and was maintained until the end of the study with end-tidal concentrat ions of 2.5-3%. Recordings of EGG, heart rate and systolic arterial pressur e were obtained at the following times: prior to induction of anaesthesia; 1 and 3 min after stable end-tidal concentrations of the induction agent ha d been reached; 1 and 3 min following vecuronium administration; at the tim e of tracheal intubation; 1 and 3 min later. Halothane significantly shorte ned the QTc interval (P < 0.05); isoflurane prolonged it (P < 0.001). Heart rate decreased significantly after halothane administration (P < 0.01); in contrast, heart rate increased after induction of anaesthesia with isoflur ane (P < 0.05), increasing fur ther after laryngoscopy and tracheal intubat ion (P < 0.001). Systolic arterial pressure decreased significantly (P < 0. 001) in both groups after induction of anaesthesia and remained decreased u ntil the end of the study. It is concluded that halothane may be a better c hoice than isoflurane for children with a long QT interval.