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

The effects of halothane and isoflurane followed by subsequent administration of vecuronium on the QT interval have been investigated during the induction of anaesthesia. Fifty-eight children, ASA I, without cardiovascular and electrolyte abnormalities and not receiving any medication were studied. Anaesthesia was induced with either halothane (n = 28) or isoflurane (n = 30), and was maintained until the end of the study with end-tidal concentrations of 2.5-3%. Recordings of ECG, heart rate and systolic arterial pressure were obtained at the following times: prior to induction of anaesthesia; 1 and 3 min after stable end-tidal concentrations of the induction agent had been reached; 1 and 3 min following vecuronium administration; at the time of tracheal intubation; 1 and 3 min later. Halothane significantly shortened 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 isoflurane (P < 0.05), increasing further after laryngoscopy and tracheal intubation (P < 0.001). Systolic arterial pressure decreased significantly (P < 0.001) in both groups after induction of anaesthesia and remained decreased until the end of the study. It is concluded that halothane may be a better choice than isoflurane for children with a long QT interval.