© 2004 by European Society of Cardiology
Radiofrequency catheter ablation of atrioventricular nodal reentrant tachycardia in children aided by the LocaLisa mapping system
aUniversity Medical Center Utrecht, The Netherlands; bUniversity of Cologne Germany
Manuscript submitted 9 October 2003. Accepted after revision 8 February 2004.
*Corresponding author. Department of Pediatric Cardiology, University Hospital Cologne, Jozef Stelzmann Straße 9, 50924 Cologne, Germany. Tel.: +49-221-478-86301; fax: +49-221-478-86302. E-mail address: n.sreeram{at}uni-koeln.de (N. Sreeram).
 |
Abstract |
|---|
 Top Abstract IntroductionPatients and methodsResultsDiscussionReferences |
|---|
AIMS: In young patients, slow pathway ablation for treatment of atrioventricular nodal reentrant tachycardia (AVNRT) carries a small but definite risk of permanent AV block. The aim was to assess the efficacy of slow pathway ablation aided by the LocaLisa mapping system.
PATIENTS AND METHODS: Radiofrequency (RF) modification of the slow AV nodal pathway was performed in 26 children <19 years of age (median age 9.8 years, range 3–18.9). Three measures to limit the risk of AV block were applied: (1) use of LocaLisa, a non-fluoroscopic mapping system, to determine and mark the location of the AV node/His bundle axis, and monitor ablation catheter position, (2) continuous atrial stimulation during RF delivery to monitor AV conduction, and (3) gradual increase of RF power during RF ablation.
RESULTS: AVNRT was rendered non-inducible in all patients. Dual AV physiology was abolished in 24/26 patients; 2 patients had single atrial echoes at the end of the procedure. At follow-up, AVNRT recurred in 3 patients (including the above 2), necessitating a second procedure. The median number of RF applications was 4 (3–8); median fluoroscopy time was 16 (7–33) min. One patient developed transient second-degree AV block, with full recovery within 6 weeks of the procedure.
CONCLUSIONS: RF modification of the slow AV nodal pathway in children can be safely accomplished, achieving the ideal end-point of abolishing dual AV physiology, aided by use of the LocaLisa mapping system.
Key Words: AVNRT, radiofrequency ablation, electroanatomical mapping, paediatrics
|
Introduction |
|---|
|
TopAbstractIntroductionPatients and methodsResultsDiscussionReferences |
|---|
Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common form of supraventricular tachyarrhythmia in young adults [1]
. It accounts for 11–13% of SVT in infants and 13–23% in the whole paediatric population [2,3]. In AVNRT, there are multiple AV nodal pathways, which are functionally and anatomically distinct, forming the electrophysiological basis for reentry within the AV node. During the last decade radiofrequency (RF) catheter ablation modification of the slow pathway has become the method of choice for curative therapy of AVNRT in symptomatic patients. Most studies have been performed in adult populations demonstrating success rates in excess of 95% [4]. Of concern in the paediatric population is the risk of inadvertent AV block during AV node modification, with the potential requirement for lifelong pacemaker therapy [5,6]. In this study we present the experience with catheter ablation of AVNRT in children using the LocaLisa mapping system [7–9]. |
Patients and methods |
|---|
|
TopAbstractIntroductionPatients and methodsResultsDiscussionReferences |
|---|
Patients
Twenty-six consecutive patients aged <19 years (17 females, 9 males) with AVNRT underwent RF slow pathway modification at our institution (29 procedures). Their median age was 9.8 years (range 3–18.9), and median weight 42 kg (15.0–59). All children had a structurally normal heart confirmed on echocardiography. Surface 12 lead electrocardiograms at rest were normal in all. The median duration of symptoms prior to ablation was 14 (11–54) months, and all patients had undergone a trial of antiarrhythmic drug therapy (median of 2 drugs/day). Indication for ablation was based on patient or parent preference in all cases. All medical and electrophysiological (EP) records were reviewed for procedural details, complications, and follow-up.
Electrophysiological studies
All but 2 of the procedures were performed under general anaesthesia, after written consent was obtained. Antiarrhythmic therapy was discontinued for at least 5 half-lives prior to ablation. Electrode catheters were introduced via the femoral vein, and positioned in a standard manner in the right atrium, ventricle, and coronary sinus. The His bundle location was entirely mapped out using a standard temperature controlled mapping/ablation catheter, and displayed on the LocaLisa monitor (Fig. 1). The right ventricular catheter was used as the reference catheter for the LocaLisa mapping system. Using a standard extrastimulus protocol, dual AV physiology (defined as a 
50 ms increase in the A2–H2 interval with a 10-ms decrement in the A1–A2 interval or 50 ms increase in the A–H interval with a 10-ms decrease in the atrial paced cycle length) was demonstrated in all patients, and sustained AVNRT (defined by the criteria of Ross et al. [10]) was induced either at baseline state (17 patients, 19 procedures) or with the use of isoprenaline by infusion (0.02 µg/kg/min; 9 patients, 10 procedures). The slow pathway was targeted for ablation in all patients.
|
LocaLisa mapping system
This system, which is commercially available (Medtronic, Minneapolis, MN, USA), allows continuous monitoring of intracardiac electrodes. Previous clinical studies have confirmed the efficacy and accuracy of this mapping system [7–
9]. All studies described here were performed using the LocaLisa system.
Ablation
Ablation was commenced approximately 12 mm (range 11–15) below (inferior to) the location of the proximal His bundle, on the atrial aspect of the tricuspid valve annulus; the latter landmark being based on the appearance of an atrial potential on the distal electrogram of the ablation catheter. This approach was identical to that used in adult patients also during the same timeframe. The localization of the His bundle is based on the steepest bipolar His potential while moving the catheter supero-inferiorly around the His bundle area. By doing so at progressively more posterior sites, one can follow and mark on the LocaLisa screen the His bundle from its distal to its most proximal extent (antero-posterior extent) (Fig. 1). The filter settings for the intracardiac electrograms (Prucka), to eliminate far-field signals, were 50–500 Hz bandpass filtering for bipolar electrograms and 0.05–500 Hz for unipolar electrograms. The LocaLisa system used a 1.5–2 s averaging to correct for respiratory variations. Slow pathway potentials were not routinely sought, but when they were observed (n=7 patients), they were seen as a "slow" hump, usually positive on the bipolar electrogram. Analysis of the location of the slow pathway potential in these 7 patients confirmed that they could be identified between 5 and 10 mm inferior to the His bundle and between 0 and 5 mm posterior to the tricuspid valve annulus. Sites, at which these potentials were seen, were targeted for ablation. The compact node could not be identified on the basis of the electrograms, but we take the proximal extent of the His bundle, as marked on the LocaLisa screen, to be the superior/anterior margin of the AV node. RF application was performed during continuous atrial pacing, to ensure the presence of AV conduction during each RF application. Pacing was commenced at a cycle length slightly above the resting sinus cycle length (usually at cycle lengths between 500 and 600 ms). The measured sinus cycle lengths prior to commencing atrial pacing were between 513 and 832 ms. Junctional ectopy during RF delivery, which was used as a marker of proximity to the optimal target area, could be reliably identified. With the occurrence of junctional ectopy the atrial pacing rate was increased to re-enable monitoring of antegrade conduction. Sustained junctional tachycardia during RF application was seen in only 5 patients, at cycle lengths between 445 and 526 ms, and in all cases pacing at rates higher than the junctional rhythm was possible. Continuous atrial pacing, or changes in pacing rate during RF application did not result in catheter tip instability, or influence the need to terminate lesion application in any patient.
Retrograde conduction of the junctional ectopic beats to monitor retrograde fast pathway conduction was not routinely performed. At sites where junctional ectopy was observed during RF application, the application was continued for up to 60 s. The power output of the RF generator was slowly increased, starting at 5 W, and increasing gradually to achieve tip electrode temperature in excess of 50 °C. When high grade junctional ectopy, or sustained junctional tachycardia (cycle length > 600 ms) was observed at moderate RF power levels (10–20 W) this was taken as indicating extreme proximity to the AV node, and ablation at these sites was discontinued, and recommenced at a greater distance from the AV node.
After each RF application during which accelerated junctional rhythm was present, the atrial pacing protocol was repeated to demonstrate either dual AV physiology, or reinduction of tachyarrhythmia. If either of these was present, lesions were progressively made closer to the His bundle recording sites, as shown on LocaLisa (Fig. 1). The new site was chosen at between 1 and 4 mm from the previous RF application site, as measured from the LocaLisa system. The end-point of the procedure was absence of dual AV physiology in 24 of 26 patients. In 2 patients, both early in our experience (patients 7 and 8, respectively, in Table 1), dual AV physiology and single atrial echoes were present at termination of the procedure, but AVNRT was non-inducible which was accepted as the end-point.
|
|
Results |
|---|
|
TopAbstractIntroductionPatients and methodsResultsDiscussionReferences |
|---|
RF catheter ablation
Catheter modification of the slow pathway resulting in non-inducibility of AVNRT was accomplished in all 26 patients. During each RF application, the distance from the ablation site to the most proximal His bundle electrogram was recorded. The median distance of the last RF application site to the His bundle was 7 (5–11) mm. In this patient cohort with a large age range, no differences were observed with regard to the age of the patient and the distance of the successful ablation location from the proximal His bundle electrogram. Two patients had evidence of persisting dual AV physiology and single atrial echo beats. As mentioned previously, early in our experience with children, this was chosen to be the end-point for the procedure in these 2 cases. None of the other patients had evidence of dual AV physiology at termination of the procedure. The median number of RF applications was 4 (3–8); the median fluoroscopy time was 16 (7–33) min. The A–H interval remained virtually unchanged (72±12 ms pre-ablation versus 79±21 ms post-ablation). There was 1 episode of second-degree AV block in a 5 year old girl, with fixed 2:1 AV conduction (confirmed at various atrial pacing rates) following slow pathway ablation, and absence of retrograde AV conduction. A total of 4 RF pulses had been delivered in this patient, at a median distance of 7 (5–8) mm from the His bundle. During the last RF application, there had been no evidence of catheter instability. No isoprenaline or atropine was administered to assess AV conduction, and no corticosteroids were administered. The patient was as usual 24 h post-procedure, on oral aspirin therapy. Overnight telemetry had confirmed ventricular rates of >60/min throughout. At outpatient follow-up 5 weeks later, normal 1:1 AV conduction was documented. Three months post-ablation, transoesophageal atrial pacing performed in this patient confirmed a Wenkebach cycle length of 340 ms, which was considered to indicate restoration of functional integrity of the AV node. Apart from that in this patient, no episodes of AV block occurred during any of the RF applications, and none of the other patients had any procedure-related complications. Patients were discharged on the following day, on oral aspirin therapy (5 mg/kg/day) for 6 weeks.
Recurrence rate
In 3 patients, AVNRT recurred within 3 months of the initial ablation procedure (Table 1). This included both patients with evidence of persisting dual AV physiology. The third patient did not demonstrate dual AV physiology at the end of the initial ablation procedure, but had documented AVNRT during a second EP study. All 3 patients underwent a second ablation procedure at 3, 3 and 6 months after the initial procedure. In both patients with dual AV physiology demonstrated at restudy, this was abolished. The third patient showed progressive A–H prolongation during atrial extrastimulus pacing, with induction of AVNRT, but without a classical A–H jump. The slow pathway was again modified, using the techniques described above. None of these 3 patients has had recurrence of tachyarrhythmia at follow-up of >12 months.
Follow-up
The median follow-up duration was 25 (3–61) months after the last ablation procedure. Serial Holter recordings at 6 months (n=19) and at 12 months (n=11) post-ablation did not demonstrate any AV conduction disturbances.
|
Discussion |
|---|
|
TopAbstractIntroductionPatients and methodsResultsDiscussionReferences |
|---|
Catheter ablation by RF current application is presently the accepted treatment modality for AVNRT in adults. The frequency of this arrhythmia appears to be age-dependent, although it is increasingly diagnosed in childhood [11]
. Of particular concern is the risk of inadvertent AV block during slow pathway modification. In a review of 314 children and adolescents with AVNRT, 5 (1.6%) developed advanced second- or third-degree AV block as a complication of the procedure [5]. This rate did not differ from the 1% risk of AV block reported in adult series of patients with AVNRT. More recent follow-up studies in children reveal a complication rate for AVNRT ablation that appears to be age-dependent, varying from 18% in patients <5 years of age to 3% in patients aged between 5 and 21 years [6]. Fluoroscopy times and radiation exposure is another important issue when dealing with children. The fluoroscopy times in our series (median 16 min, range 7–33 min) compare favourably with that reported in the Pediatric Radiofrequency Ablation Registry (29.3±25.7 min) [6].
The potential risk of RF lesion growth resulting in late onset AV block should also be considered during ablation procedures close to the AV node in young patients [12]. In this report we present 26 children with symptomatic AVNRT who underwent RF catheter modification of the slow AV nodal pathway as a curative therapy. The results are comparable with those in adults. Moreover, none of the treated children developed permanent AV conduction disturbances at follow-up.
There are no clear recommendations concerning the end-point AVNRT ablation. The end-point of non-inducibility of AVNRT even in the presence of dual AV physiology and single atrial echo beats is generally accepted, and has been shown to be associated with long-term success in adults. Unlike most previous reports of AV node modification, we attempted to abolish dual AV physiology during the ablation procedure in the majority of patients. This aggressive approach was aided by the use of the LocaLisa mapping system which enabled the location of the ablation catheter electrodes to be precisely monitored, and the distance from the His bundle to be measured. Ancillary precautions that were taken during RF energy application included incremental AV pacing, and energy delivery starting at low power output, with progressive increase in output to achieve the desired catheter tip temperature. Both patients in whom the desired end-point was not achieved, and non-inducibility of AVNRT was used as a measure of success, had recurrence of the original tachyarrhythmia within 3 months of the ablation procedure, necessitating a second procedure. The only other patient with a documented recurrence did not have classical dual AV physiology during the second EP procedure, as described above, although the arrhythmia had all the characteristics of AVNRT.
One of the potential limitations of this study is that patients were not randomised to ablation with and without the use of LocaLisa, so that direct comparisons between the 2 subgroups from the same institution cannot be made. Recurrence rates following initial ablation (3/26 patients, or 12%) were rather high, although in 2 of the 3 patients non-inducibility of AVNRT with persistent dual AV physiology was the end-point used. The ideal end-point of abolition of dual AV physiology was eventually successfully accomplished in all patients, unlike all previous reports of AVNRT ablation [13]. This end-point was achieved with fluoroscopy times comparable with, or less than, that reported for other series [4–6,13]. With a relatively small cohort of patients and a modest follow-up interval, it is not possible to make recommendations concerning the ideal end-point for AVNRT ablation in children.
In conclusion, continuous electrode localization, in combination with the ability to measure the distance from the AV node/His bundle axis, improves the safety and efficacy of catheter modification of the AV node in young patients with AVNRT.
|
References |
|---|
|
TopAbstractIntroductionPatients and methodsResultsDiscussionReferences |
|---|
[1] Akhtar M, Jazayeri MR, Sra J, Blank Z, Deshpande S, Dhala A. Atrioventricular nodal reentry: clinical, electrophysiological and therapeutic considerations. Circulation 1993; 88: 282–295.
[2] Ko JK, Deal B, Strasburger J, Benson DW Jr. Supraventricular tachycardia mechanisms and their age distribution in pediatric patients. Am J Cardiol 1992; 69: 1028–1032.[CrossRef][Web of Science][Medline]
[3] Crosson JE, Hesslein PS, Thilenius OG, Dunnigan A. AV node reentry tachycardia in infants. Pacing Clin Electrophysiol 1995; 18: 2144–2149.[Medline]
[4] Calkins H, Young P, Miller JM, et al. Catheter ablation of accessory pathways, atrioventricular nodal reentrant tachycardia, and the atrioventricular junction: final results of a prospective, multicenter clinical trial. The Atakr Multicenter Investigators Group. Circulation 1999; 99: 262–270.
[5] Schaffer MS, Silka MJ, Ross BA, Kugler JD. Inadvertent atrioventricular block during radiofrequency catheter ablation: results of the pediatric radiofrequency ablation frequency. Circulation 1996; 94: 3214–3220.
[6] Kugler JD, Danford DA, Houston KA, Felix BS. Pediatric radiofrequency catheter ablation registry success, fluoroscopy time, and complication rate for supraventricular tachycardia: comparison of early and recent eras. J Cardiovasc Electrophysiol 2002; 13: 336–341.[CrossRef][Web of Science][Medline]
[7] Wittkampf FHM. inventor. Catheter mapping system and method. US patent 5697377; December 16, 1997.
[8] Wittkampf FHM, Wever EFD, Derksen R, et al. LocaLisa. New technique for real-time 3-dimensional localization of regular intracardiac electrodes. Circulation 1999; 99: 1312–1317.
[9] Molenschot M, Ramanna H, Hoorntje T, et al. Catheter ablation of incisional atrial tachycardia using a novel mapping system: LocaLisa. Pacing Clin Electrophysiol 2001; 24: 1616–1622.[CrossRef][Medline]
[10] Ross DL, Johnson DC, Denniss AR, et al. Curative surgery for atrioventricular junctional (AV nodal) reentrant tachycardia. J Am Coll Cardiol 1985; 6: 1383–1392.[Abstract]
[11] Van Hare GF, Chiesa NA, Campbell RM, Kanter RJ, Cecchin F. Atrioventricular nodal reentrant tachycardia in children: effect of slow pathway ablation on fast pathway function. J Cardiovasc Electrophysiol 2002; 13: 203–209.[Medline]
[12] Saul JP, Hulse JE, Papagiannis J, et al. Late enlargement of radiofrequency lesions in infant lambs. Implications for ablation procedures in small children. Circulation 1994; 90: 492–499.
[13] Teixeira OH, Balaji S, Case CL, et al. Radiofrequency catheter ablation of atrioventricular nodal reentrant tachycardia in children. Pacing Clin Electrophysiol 1994; 17: 1621–1626.[Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||