Effects of Propofol or Isoflurane Anesthesia on Cardiac Conduction in Children Undergoing Radiofrequency Catheter Ablation for Tachydysrhythmias

Approval from the institution's Committee on Clinical Investigation and informed consent from the parents were obtained before initiating this study. Only patients with SVT and a structurally normal heart were included in this study. Twenty consecutive patients presenting for RFCA were included and were randomly assigned to receive one of two anesthetics: propofol or isoflurane. All antidysrhythmic medication had been discontinued 10 days before the procedure.

The patients were premedicated with 0.1 mg *symbol* kg sup -1 intravenous midazolam if deemed necessary. Monitors consisted of electrocardiography, noninvasive and invasive arterial blood pressure, pulse oximetry, capnography, and temperature probe. For both groups, anesthesia was induced with 20 micro gram *symbol* kg sup -1 alfentanil, 4 mg *symbol* kg sup -1 thiopental, and 0.1-0.15 mg *symbol* kg sup -1 pancuronium, followed by an infusion of alfentanil at a rate of 1 micro gram *symbol* kg sup -1 *symbol* min sup -1. Positive-pressure ventilation was instituted after induction of anesthesia, and a mixture of 70% N²O in 30% O²was used throughout the procedure as well as 0.1 mg *symbol* kg sup -1 *symbol* h sup -1) pancuronium. After venous cannulation, an electrophysiology study (EPS) was performed under this baseline anesthetized state.

In the EPS portion of the RFCA procedure, catheters are introduced percutaneously through the femoral veins and/or the internal jugular or subclavian vein to different positions in the heart: right atrium, right ventricle, and coronary sinus. A brief hemodynamic study was performed to confirm the echocardiographic diagnosis of a structurally normal heart, and venous oxygen saturation from the superior vena cava was measured to grossly estimate cardiac output. All were within normal limits. Electrograms from the intracardiac catheters were recorded on a multichannel recording system. Mapping was done initially with the patient in sinus rhythm and later after induction of tachydysrhythmias. Once this preliminary mapping was performed, a specialized ablation catheter was advanced to the heart for more precise mapping.

At the completion of the baseline EPS, alfentanil was discontinued, and patients randomly received either 0.8-1.2% isoflurane (group 1) or 2 mg *symbol* kg sup -1 propofol bolus plus an infusion of 150 micro gram *symbol* kg sup -1 *symbol* min sup -1 (group 2). After 30 min of equilibration, the patients underwent a repeat EPS. The following electrophysiologic parameters were compared to baseline: cycle length (CL), atrial-His interval (AH, atrioventricular node conduction time), His-ventricle interval (HV, conduction time between the bundle of His and the right ventricle), corrected sinus node recovery time (CSNRT, time to first sinus beat escape after termination of pacing, corrected to the patient's intrinsic rate), AV node effective refractory period (AVNERP, longest interval between two impulses that fail to conduct through the atrioventricular node), and atrial effective refractory period (ATERP, longest interval between two atrial impulses that fail to result in atrial depolarization). Ablation was then performed. After a period of observation in the electrophysiology laboratory to exclude delayed recovery of the ablated tract, the patients were awakened. After tracheal extubation, they were transferred to the postanesthesia care unit.

For statistical analysis, the electrophysiologic parameters described above were compared between baseline anesthesia and propofol or isoflurane using paired Student's t tests. Results are expressed as mean plus/minus SD. Statistical significance was accepted as P < 0.05.

Twenty consecutive ASA physical status 2 patients presenting for RFCA were studied. Of the 20 patients, 17 had accessory pathways (manifest Wolff-Parkinson-White syndrome in 9 of 17, concealed accessory pathway in 8 of 17), 1 had permanent junctional reciprocating tachycardia, and 2 had classic "slow fast" AV node reentry tachycardia. All patients had been considered to have a normally structured heart by transthoracic echocardiography. Ten patients received propofol, and 10 others received isoflurane. The demographic data for both groups are shown in Table 1. There was no significant difference between both groups with regard to age, weight, gender, and ASA physical status.

The effects of propofol and isoflurane on cardiac conduction are shown in Table 2. Electrophysiologic values during propofol and isoflurane anesthesia were compared to baseline anesthesia and are represented as mean plus/minus SD. As demonstrated in Table 2, neither propofol nor isoflurane significantly altered electrophysiologic parameters when compared to continuous alfentanil infusion with pancuronium for muscle relaxation. Specifically, heart rate (cycle length) did not change between baseline anesthesia with propofol or isoflurane. In all patients, conduction through accessory pathways was induced without difficulty, allowing for accurate mapping and location during the course of this study. There were no changes in superior vena cava saturation in any patient, indicating no major change in cardiac output.

Since radiofrequency catheter ablation was first introduced in 1987 in adults, it has largely replaced surgical ablation and transcatheter ablation with direct current. [9,10]The safety and efficacy of RFCA in the pediatric population has been assessed recently by the Pediatric Electrophysiology Society. [11]This multicenter study reports an overall success rate of 83% and complication rate of 4.8%. In our institution, the overall success rate for accessory pathway ablation is 96%. These encouraging results have prompted cardiologists to apply this technique to patients with complex congenital heart disease. Indications for RFCA include life-threatening symptoms, medically refractory tachycardia, adverse drug effects, tachycardia-induced ventricular dysfunction, impending surgery, and patient's choice.

Although the sample size in this study is small, neither isoflurane nor propofol was shown to alter cardiac conduction when compared to baseline values obtained during anesthesia with alfentanil and midazolam in pediatric patients with SVT undergoing RFCA. These results agree with those of Romano et al., [4]who performed a more limited electrophysiologic study using propofol in healthy adults. They compared the results of transesophageal pacing in awake patients with those of non-intubated spontaneously breathing patients receiving propofol anesthesia and found that propofol does not increase sinus node recovery time. However, our results obtained during isoflurane anesthesia differ significantly from those of Sharpe et al., who found that isoflurane prolonged the refractory period within accessory and atrioventricular pathways. [8]There are some differences between our study and that by Sharpe et al. First, most of the patients in our study were teenagers undergoing catheter ablation, as opposed to adults submitted to surgical ablation requiring a sternotomy. Second, intracardiac electrophysiologic measurements were used in the current study, as compared with epicardial measurements in the study by Sharpe et al. Such baseline electrophysiologic parameters taken after sternotomy may reflect an increased sympathetic tone. The stress response is less during RFCA, as opposed to surgical ablation, which may explain why no effect on cardiac conduction was demonstrated in our patient population.

None of the agents used for baseline anesthetic have been shown to alter the conduction pathways. Previous studies have shown that alfentanil/midazolam had no effects upon the normal conduction system or accessory pathways in adult patients with Wolff-Parkinson-White syndrome. [12]Nitrous oxide and pancuronium were used throughout the baseline anesthetic and the study period. Nitrous oxide may increase sympathetic tone but has no effect on conduction, and pancuronium decreases vagal tone.

Radiofrequency catheter ablation is not a very painful procedure, the most stimulating event being the percutaneous introduction of catheters at the beginning of the procedure. Therefore, general anesthesia is not always required, such as for surgical ablation via sternotomy. However, patients in the pediatric age group and those undergoing prolonged procedures may benefit from general anesthesia. The ideal anesthetic should not alter impulse propagation or refractoriness and should not prevent triggering of the offending dysrhythmia. It also should allow rapid awakening to assess complications. The results of this study should allow anesthesiologists to make a more appropriate choice of anesthetics for RFCA. We conclude that propofol and isoflurane after baseline anesthesia with alfentanil, nitrous oxide, and pancuronium do not alter cardiac conduction in pediatric patients with SVT undergoing radiofrequency catheter ablation. A substantially larger study would be needed to assess the safety of these techniques.