Role of halothane in QT-time prolongation and dysrhythmias during microlaryngoscopy

To study the mechanism of dysrhythmias during microlaryngoscopy, heart rate-corrected QT-times (QTc) were measured in three different methods of anaesthesia. A balanced anaesthesia was induced by Althesin in 96 patients, or by thiopentone in 68 patients. Halothane anaesthesia was induced by Althesin in 23 patients. In all groups the mean QTc-time was significantly longer during the manipulation of vocal cords than before the induction of anaesthesia. Dysrhythmias are also most common during the procedure. With the Althesin-halothane combination, however, the prolongation of QTc-time was most pronounced: Control X +/- SE 408.4 +/- 5.5 msec, manipulation 432.3 +/- 6.7 msec, p less than 0.001. Among those patients who had dysrhythmias during the procedure, only the patients in the Althesin-halothane group had significantly longer QTc-time than before anaesthesia. In patients with supra-ventricular dysrhythmias, differences of QTc-time did not reach significant level. Significant prolongation of QTc-time occurred in patients with ventricular ectopic beats (p less than 0.05) and junctional rhythm (p less than 0.02) but only in the Althesin-halothane group.