Comparison of Effects of Three Anesthetic Agents

The effects of three anesthetic agents on the inducibility of ventricular tachycardia by programmed stimulation were investigated in dogs with a surgically induced left ventricular infarct. Endocardial catheter electrodes were placed at the right ventricular apex under general anesthesia at least 2 weeks after infarction, and the dogs were allowed to recover for 24 hours before undergoing programmed stimulation in the conscious state on two occasions 2 hours apart. A protocol of programmed stimulation with up to seven ventricular extrastimuli was used. In 15 animals, ventricular tachycardia was inducible on both occasions with 3.4+± 0.4 (mean SEM; range, 1-5) extrastimuli. Two hours after baseline conscious induction, the dogs were anesthetized with either halothane, pentobarbital, or a fixed combination of fentanyldroperidol plus nitrous oxide. Halothane prolonged the PR interval from 99 4 to 117 6 msec (p =0.001) and the ventricular effective refractory period from 140 4 to 157 6 msec (p=0.008). The ability to induce ventricular tachycardia was abolished in five of 10 animals (p<0.05). In the animals that remained inducible, the cycle length of tachycardia increased from 153±10 to 168±10 msec (p = 0.015), while the number of extrastimuli required was unaltered. Pentobarbital prolonged the PR interval from 104 6 to 124 6 msec (p= 0.004) and the QT, interval from 270+10 to 310 6 msec (p = 0.006). Ventricular tachycardia remained inducible in only six of 10 dogs (p<0.05) with no change in cycle length or the number of extrastimuli required. Ventricular fibrillation was inducible in an additional three dogs with a number of extrastimuli similar to that required to induce ventricular tachycardia before anesthesia. The neuroleptic combination of fentanyl-droperidol plus nitrous oxide caused no change in basic electrocardiographic intervals or refractoriness. Ventricular tachycardia remained inducible in nine of 10 dogs with no significant change in the cycle length or number of extrastimuli required. We conclude that of the three agents, the fentanyl-droperidol combination is the most successful in permitting reproducible induction of ventricular tachycardia by programmed stimulation. Both halothane and pentobarbital suppress the inducibility of ventricular tachycardia. In addition, halothane slows the tachycardia, while pentobarbital promotes the induction of ventricular fibrillation. (Circulation 1988;78:221-226)