ANESTHESIA AND THE QT INTERVAL IN HUMANS - THE EFFECTS OF ISOFLURANE AND HALOTHANE

Prolongation of the QT interval may cat!se potentially hazardous arrhy thmias. The effects on the QT interval (QTc, collected for heart rate) of isoflurane and halothane followed by vecuronium have been investig ated during induction of anaesthesia in 51 patients. All patients were ASA 1 or 2, without cardiovascular problems or electrolyte abnormalit ies and were not receiving medication. Midazolam 0.08 mg.kg(-1) was ad ministered intramuscularly for premedication. Anaesthesia was induced with either isoflurane (n=26) ol halothane (n=25), and the inspired co ncentration increased to reach an end-tidal concentration of 2.5% to 3 %. Recordings of ECG, heart rate, systolic and diastolic arterial pres sure were obtained at the following times: prior to induction of anaes thesia; 1 min and 3 min after a stable end-tidal concentration had bee n reached; 1 min and 3 min following vecuronium administration, at the time of tracheal intubation and 1 min and 3 min later. Halothane sign ificantly shortened QTc (p<0.05 to p<0.001), in contrast to isoflurane which prolonged if (p<0.01). The heart I ate decreased (p<0.01 to p<0 .001) after induction of anaesthesia with halothane and returned to pr e-induction values after tracheal intubation. In contrast, heart rate increased after. induction with isoflurane and increased further after laryngoscopy and tracheal intubation (p<0.001). In the isoflurane gro up, ST depression was noticed in seven patients and nodal rhythm in tw o, while in the halothane group seven patients developed nodal I rhyth m and, in two patients, ventricular ectopics were recorded. There were no sequelae. In both groups, systolic and diastolic arterial pressure decreased after induction of anaesthesia (p<0.01 to p<0.001), increas ing again after intubation.