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.