Barbara J. Knick

Radiofrequency catheter ablation of incessant, medically resistant supraventricular tachycardia in infants and small children

OBJECTIVES This study retrospectively evaluates initial experience with radiofrequency catheter ablation in a group of seven infants and small children with a history of incessant, medically resistant supraventricular tachycardia. METHODS Before attempted catheter ablation, all patients had had unsuccessful conventional medical therapy (with digoxin or propranolol, or both) and, in addition, each continued to have daily episodes of supraventricular tachycardia while taking amiodarone or a class IC antiarrhythmic agent alone or in combination. The average patient age was 10 months (range 1 to 27) and the average patient weight was 6 kg (range 3 to 13). Electrophysiologic diagnosis included reentrant supraventricular tachycardia in six patients and atrial ectopic tachycardia in one patient. RESULTS These seven patients underwent a total of nine catheter ablation procedures. The atrial approach to ablation was employed in eight of the nine procedures. Overall, radiofrequency catheter ablation was totally successful in five of the seven patients, partially successful in one patient and unsuccessful in the remaining patient. The combination of radiofrequency catheter ablation and surgical ablation was successful in controlling tachycardia in all patients; with at least 5 months of follow-up study, no patient has had a recurrence of supraventricular tachycardia or reappearance of a delta wave. CONCLUSIONS Surgical ablation of arrhythmogenic substrates in the pediatric age group, although rarely indicated, has been found in the past to be safe and effective. Our initial experience with radiofrequency catheter ablation in infants and small children demonstrates that this procedure is a promising nonpharmacologic therapeutic alternative to surgical ablation.

Catheter Tip Cooling during radiofrequency ablation of intra-atrial reentry: Effects on power, temperature, and impedance

Catheter Tip Cooling. Introduction: Cooling the catheter tip either passively with increased tip size or actively during radiofrequency catheter ablation (RFCA) has been shown in canine thigh preparations to create larger lesions than standard catheter tips, yielding a theoretical advantage for improving the outcome of RFCA for intra‐atrial reentrant tachycardia (IART).

Learning curve for radiofrequency catheter ablation in pediatrics at a single institution

We examined the learning curve for radiofrequency ablation in pediatrics at a single institution. The first 146 cases were retrospectively reviewed, including patients < or = 21 years old with a single tachycardia diagnosis who were undergoing radiofrequency ablation for the first time. Data regarding demographics, electrophysiologic properties of the tachycardia, and procedural characteristics were tabulated. Data were then analyzed for evidence of association between these characteristics, success, and experience. Results revealed that success rates improved significantly with experience, reaching 85% success for all cases after < 100 cases attempted. Success for accessory pathway tachycardias alone reached > 93%. The number of cases of nonpathway tachycardias undertaken significantly increased as experience was gained. Fluoroscopy time improved to 34 +/- 27 minutes after < 100 cases. In conclusion, as experience was gained, (1) success rates showed a steep improvement; (2) the population undergoing radiofrequency ablation clearly shifted to include more difficult diagnoses; and (3) fluoroscopy time significantly decreased.

Ventricular Tachycardia in Nonpostoperative Pediatric Patients: Role of Radiofrequency Catheter Ablation

Experience concerning radiofrequency catheter ablation (RFCA) of ventricular tachycardia (VT) in pediatric patients is limited. In adults, success rates vary widely based on the etiology of the VT. Highest success rates have been achieved in patients without structural heart disease. Between March 1998 and December 1999, five young patients (age, 5 months to 15 years; body weight, 5.5–61.6 kg) underwent RFCA for VT at our institution [structurally normal heart (n = 4), preoperative tetralogy of Fallot (n = 1)]. Monomorphic VT was present in four children, and an infant with MIDAS syndrome had polymorphic VT. Clinical presentation varied: palpitations, n = 2, congestive heart failure, n = 3. All patients had been proven to be unresponsive to one to six (median, three) antiarrhythmic drugs. In all five patients, VT could be successfully eliminated by RFCA after a total of nine (range, 1–4) procedures. Activation mapping and pace mapping were used to identify the anatomical substrate, which was located in the right ventricle/right ventricular outflow tract in all four patients with monomorphic VT and in the left ventricular septum/left ventricular free wall in the infant with polymorphic VT. There were no significant complications in any patient. During follow-up (20–42 months), all patients are in normal sinus rhythm. Left ventricular function recovered in all three patients who had initially presented with congestive heart failure. RFCA can be effective, safe, and life saving in children with medically resistant VT who have not been operated on for congenital heart disease, even when the VT is polymorphic. Although the number of patients is small, RFCA may be the treatment of choice for symptomatic VT in pediatric patients.

Frequency of atrioventricular valve dysfunction after radiofrequency catheter ablation via the atrial approach in children

Abstract Unlike the retrograde approach, the atrial approach has not been associated with significant postprocedure valvular dysfunction. Given equal efficacy of both methods, this study might indicate that the atrial approach would be preferable.

High-Dose Narcotic Anesthesia Using Sufentanil in Swine for Cardiac Catheterization and Electrophysiologic Studies

A protocol for high-dose narcotic anesthesia using sufentanil by intravenous infusion was developed in swine undergoing cardiac catheterization and intracardiac electrophysiologic studies. In experiments involving cardiac conduction system ablation, nine swine received intramuscular ketamine, 33 mg/kg, and intramuscular acepromazine, 1.1 mg/kg, as premedication. An infusion of sufentanil (15 mcg/kg/h) was started followed by a loading dose of sufentanil (7 mcg/kg) given as a bolus intravenously. A continuous infusion of sufentanil (15-30 mcg/kg/h) was used for maintenance anesthesia. Since the development of this protocol, we have been able to achieve stable hemodynamics and cardiac rhythms for intracardiac electrophysiologic studies.

A Technique for Conducting Noninvasive Cardiac Electrophysiology Studies in Conscious Swine

A noninvasive method was developed in swine for conducting cardiac electrophysiology (EP) studies without the potential confounding effects of sedatives or anesthetics. Following a 1-week conditioning regimen in the EP laboratory, 1-month-old Hanford miniature swine underwent transvenous pacemaker (PM) implantation under isoflurane anesthesia. Two bipolar screw-in pacing leads were inserted into the left external jugular vein, with one positioned in the right atrial appendage and one in the myocardium at the right ventricular apex. The leads were attached to a multiprogrammable pulse generator, and the pacing system was placed in a subcutaneous pocket. At weekly intervals following implantation, conscious, unsedated swine were remained in a sling for noninvasive programmed stimulation (NIPS) using a programmable telemetry system. A NIPS protocol to induce arrhythmias was performed separately for the atrium and ventricle. Data for this model are reported. Complications occurred in 6 of 26 animals studied and included one infection of the PM pocket, three cases of dislodgement of the atrial lead, and rotation of the generator within the pocket in two animals, preventing communication with the PM. This technique has been used to perform EP studies successfully in swine and has been utilized in a variety of studies of the cardiac conduction system.

Comparison of medical care costs between successful radiofrequency catheter ablation and surgical ablation of accessory pathways in the pediatric age group

Short-term follow-up of radiofrequency catheter ablation (RFCA) has shown that it is a safe and effective procedure for the treatment of medically resistant supraventricular tachycardia in both adults and children. 1–3 Before the advent of RFCA, the most common technique for ablation of supraventricular substrates involved open-chest surgery. An important advantage of RFCA over surgical ablation (SA) is the anticipated reduction in medical costs associated with a catheter procedure versus an open-chest surgical procedure. This study compares the cost of radiofrequency catheter ablation with those of surgical ablation for the treatment of supraventricular tachycardia in a pediatric population.

Lack of proarrhythmia as assessed by Holter monitor after atrial radiofrequency ablation of supraventricular tachycardia in children.

The purpose of this study was to assess the short-term arrhythmogenicity of atrial radiofrequency (RF) ablation lesions in children. Patients with the greatest exposure to RF energy comprised the study group. Holter data on 35 RF ablation procedures in 31 patients with a median age of 13.2 years (range 3 months to 20 years) was retrospectively analyzed. Patients received an average of 19.9 (SD = 13.6) RF lesions, all delivered by an atrial approach. Supraventricular ectopy and ventricular ectopy were compared immediately before and after and 4 to 9 weeks after RF ablation by serial Holter monitoring. Factors thought to possibly predispose patients to a proarrhythmic effect were used to define subgroups for separate analysis. No increase in ambient supraventricular ectopy or ventricular ectopy was observed either immediately after or 4 to 9 weeks after RF ablation compared with the baseline Holter recordings. Children exposed to relatively large doses of RF energy may demonstrate transient and asymptomatic nonsustained tachycardias in the short term. However, no new sustained tachycardias and no increase in supraventricular or ventricular ambient ectopy are detected by short-term Holter monitoring.

Sinoatrial Node Reentrant Tachycardia in Infants With Congenital Heart Disease

T exact nature of sinoatrial node reentrant tachycardia (SANRT) is debated, but has been reported to occur as a clinical entity in 1.8% to 16.9% of adults undergoing electrophysiologic evaluation for supraventricular tachycardia (SVT). Although SANRT has been occasionally mentioned in reports of pediatric SVT, the reports are few in number and sparse in data. –11 SANRT has electrocardiographic features that are similar to sinus tachycardia, and it may be easily misdiagnosed, particularly when there is a high likelihood of sympathetic and/or catecholaminergic stimulation. Because SANRT has a high association with structural heart disease and has been noted to cause hemodynamic embarrassment, situations may arise when the diagnosis of SANRT rather than sinus tachycardia may be critical for patient management (e.g., after surgery for congenital heart disease). The purpose of this study was to assess the relative incidence and clinical characteristics of SANRT in a pediatric population. • • • The pediatric electrophysiologic study database at the Medical University of South Carolina was reviewed for cases of SANRT in children 0 to 18 years of age diagnosed by intracardiac, transesophageal, or epicardial pacing wire electrophysiologic study performed to investigate a previously documented clinical SVT between January 1999 and November 2000. Studies were performed before initiation of any antiarrhythmic therapy or after therapy had begun. Studies were generally performed on an elective basis unless they were performed for postoperative arrhythmia evaluation, in which case they were performed as close to presentation as possible. Transesophageal electrophysiologic studies were performed with administration of midazolam and/or fentanyl. Intracardiac studies were usually performed with the patient under deep sedation or general anesthesia, and epicardial pacing wire studies were typically performed without sedation. All studies were performed in the fasting state. Study protocols consisted of single and double atrial extrastimuli after either sensed atrial rhythm and/or a fixed atrial drive train (500 and 400 ms, if underlying rhythm permitting, or 30 ms below baseline rhythm cycle length), followed by rapid atrial pacing. Ventricular stimulation was used when possible to investigate retrograde conduction. Because all of the studies were not intracardiac, all previously described criteria of SANRT could not be demonstrated (Table 1). 3–6,9 Thus, for the purposes of this study, SANRT was defined as a paroxysmal or reproducibly inducible and terminable tachycardia, with a P-wave axis and morphology in all 12 surface leads nearly identical to sinus rhythm. The reentrant mechanism of the tachycardia was confirmed by the ability to initiate the tachycardia with programmed atrial stimulation. Tachycardia response to adenosine, when available, was used to support the diagnosis of an atrial arrhythmia. Demographic and electrophysiologic variables as well as short-term management and follow-up are noted in the review. Because of the small number of subjects, variables are described as median and range unless otherwise noted. Group comparisons are made with Yates’ coefficient. Of the 106 patients, aged 1 day to 18 years, who underwent electrophysiologic study for documented SVT during the study period, 7 male patients (6.6%) met this study’s criteria for SANRT (Figures 1A and 1B). All identified patients were infants with structural heart disease (Table 2). Of the 6 patients with congenital heart disease, 5 had undergone surgical repair or palliation within the past 0 to 11 days (median 5) before presentation, 4 of those for palliation of hypoplastic left heart syndrome. One patient had a dilated cardiomyopathy. The incidence of structural heart disease and congenital heart disease was much greater in those with SANRT than in the remaining 99 patients with other SVT mechanisms (100% vs 26%, p 0.0003; 86% vs 24%, p 0.002, respectively). However, if only infants are considered, differences between the SANRT and non-SANRT groups in the incidence of structural heart disease and congenital heart disease do not reach statistical significance (100% vs 60%, p 0.14; 86% vs 53%, p 0.3, respectively). This may be a reflection of the fact that the proportion of infants in the SANRT group was From the Children’s Heart Program of South Carolina–Medical University of South Carolina, Charleston, South Carolina. Dr. Blaufox is supported by National Institutes of Health Training Grant T32 HL07710-06, Bethesda, Maryland. Dr. Blaufox’s address is: Children’s Heart Program of South Carolina–MUSC, 165 Ashley Avenue, PO Box 250915, Charleston, South Carolina 29425. E-mail: Blaufoad@musc.edu. Manuscript received April 25, 2001; revised manuscript received and accepted June 21, 2001. TABLE 1 Previously Described Criteria for SANRT