Succinylcholine does not worsen bupivacaine-induced cardiotoxicity in pentobarbital-anaesthetized dogs

The intravascular injection of a large dose of bupivacaine induces electrophysiological cardiac impairment, mainly by slowing ventricular conduction velocity, and haemodynamic depression, by a decrease in myocardial contractility. When cardiotoxicity occurs, succinylcholine rapidly stops convulsions. However, the possible interactions between bupivacaine and succinylcholine on cardiac electrophysiology and haemodynamic status have never been investigated. Thus, we used an experimental electrophysiological model involving closedchest dogs. Three groups (n = 6) of pentobarbitalanaesthetized dogs were given 0.2 mg · kg−1 atropine iv. Dogs in Group 1 were given saline. The others received 4 mg · kg−1 bupivacaine iv over ten seconds. Dogs in Group 2 were then given saline and those in Group 3 were then given 2 mg · kg−1 succinylcholine iv from one to two minutes after the administration of bupivacaine. The following electrophysiological variables were measured: heart rate represented by RR interval (RR), PR, atria-His (AH), and Hisventricle (HV) intervals, QRS duration, and QT interval corrected for heart rate (QTc). The following haemodynamic variables were measured: mean aortic pressure (MAoP), the peak of the first derivative of left ventricular pressure (LVdP/dt max), and LV end diastolic pressure (LVEDP). Comparison between Groups 1 and 2 showed that bupivacaine induced more than 100% HV interval lengthening and QRS widening (P < 0.01), prolonged QTc interval by more than 25% (P <0.01), and decreased LV dP/dt max by more than 50% (P < 0.01). The only difference between Groups 2 and 3 was a transient shortening of QRS in the group given succinylcholine at four and five minutes (P <0.05) and a shortening of QTc throughout the study period (P < 0.05 at two and three min, P <0.01 at four to 30 min after the end of bupivacaine administration). We conclude that 2 mg · kg−1 succinylcholine did not worsen the previously impaired electrophysiological or a haemodynamic variables produced by a high dose of bupivacaine in anaesthetized dogs.