EFFECTS OF ISOFLURANE ON ELECTROPHYSIOLOGICAL MEASUREMENTS IN CHILDREN WITH THE WOLFF-PARKINSON-WHITE SYNDROME

This study was designed to assess the effects of isoflurane (ISO) on t he electrophysiological properties of the accessory pathway, atrium, v entricle, and AV node in children with the Wolff-Parkinson-White (WPW) syndrome. The results of programmed electrical stimulation were analy zed in 51 patients (4 months to 17 years of age) with WPW. The study p opulation was divided into two groups. Twenty-seven patients received local anesthesia and intramuscular injection of meperidine, promethazi ne, and chlorpromazine (MPC group). Twenty-four patients received gene ral anesthesia with ISO inhalation (ISO group). We compared the antegr ade effective refractory period of the accessory pathway (antegrade AP ERP), ventricular effective refractory period (VERP), atrial effective refractory period (AERP), AH interval, and cycle length of circus mov ement tachycardia (CMT-CL) in 12 pairs of age and sex matched patients selected from the MPC and ISO groups. Of the 12 pairs of age and sex matched patients, antegrade APERP in patients who received ISO (299 +/ - 17 ms, mean +/- SEM) was significantly longer as compared with match ed patients in the MPC group (262 +/- 5 ms, P < 0.025). The VERP and A ERP in patients from the ISO group were significantly prolonged compar ed with the MPC patients (239 +/- 7 vs 210 +/- 8 ms, P < 0.025, and 22 8 +/- 12 vs 180 +/- 6 ms, P < 0.01, respectively). There was no signif icant difference in the AH interval or CMT-CL between the two subgroup s. Thus, ISO prolongs the antegrade APERPs as well as the effective re fractory periods of atrial and ventricular muscle in children with WPW while the AH interval and CMT-CL appear to be unaffected. Care must b e taken in interpreting measurements of the antegrade APERP made in pa tients under general anesthesia for RF ablation of accessory pathways.