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Radiofrequency ablation for supraventricular and ventricular tachycardia in young patients
International
Journal
of
cardiology ELSEVIER
International Journal of Cardiology 54 (1996) 33-40
Radiofrequency ablation for supraventricular and ventricular tachycardia in young patients I-Chang Hsieh, San-Jou Yeh, Ming-Shien Wen, Chun-Chieh Wang, Fun-Chung Lin, Delon Wu* Second Section of Cardiology, Deparhnent of Medicine, Chang Gung Memorial Hospital, Chang Gung Medical College, Taipei, Taiwan Received 5 July 1995; accepted 16 January 1996
Abstract Radiofrequency ablation therapy was conductedin 86 consecutive children and young patients with a mean age of 14 ? 3 years (range = 3-18). Fifty-two patients had Wolff-Parkinson-White syndrome, one had re-entry tachycardia incorporating a nodoventricular fiber, 22 had atrioventricular node re-entry tachycardia, two had atrial tachycardia and nine had idiopathic ventricular tachycardia. Radiofrequency ablation was successfulin 50 of the 52 patients (96%) with Wolff-Parkinson-White syndrome and the one with nodoventricular fiber. Radiofrequency modification of the atrioventricular node using the inferior approachwas successfulin eliminating atrioventricular node re-entry tachycardia in 20 of the 22 patients (91%). Radiofrequency ablation in the two patients with atria1tachycardia was unsuccessful.Of the nine patients with idiopathic ventricular tachycardia, eight from the left ventricle and one from the right ventricular outflow tract, eight were successfully ablated (88%). Follow-up over a period ranging from 1 to 46 months (21 + 13) revealed a recurrence of tachycardia in seven patients; a late electrophysiological study in 38 patients revealed the induction of tachycardia in 11 patients (seven with accessorypathway-mediatedtachycardia, three with atrioventricular node re-entry tachycardia and one with idiopathic ventricular tachycardia). All 11 patients were successfully ablated by a secondtrial. In conclusion, radiofrequency ablation therapy is effective and safe in pediatric patients with supraventncular and ventricular tachycardia and should be considered as the therapy of choice in this group of patients. Keywords:
Radiofrequency ablation; Children
1. Introduction Symptomatic supraventticular or ventricular tachycardia in children or young patients is usually managed by antiarrhythmic agents [ 11. However, *Corresponding author, Chang Gung Memorial Hospital, 199
Tung Hwa North Road, Taipei, Taiwan. Tel.: 886 3 3281200; fax: 886 3 3285636.
chronic drug administration poses an inconvenience to the patients as well as to the families, and is associated with the potential risk of serious side effects. Surgery used to be the only option in patients with drug-resistant or troublesome tachycardias [2,3]. Radiofrequency ablation therapy is the current therapy of choice in adults with some types of supraventricular and ventricular tachycardias [4-lo]. In this study, racliofrequency ablation
0167-5273/96/$1.5.00 0 1996 Elsevier Science Ireland Ltd. All rights reserved PII SO167-5273(96)02575-2
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therapy on atrioventricular (AV) re-entry tachycardia incorporating an accessory pathway, re-entry tachycardia incorporating a Mahaim fiber, AV node re-entry tachycardia, atria1 tachycardia, and idiopathic ventricular tachycardia in children and young patients is conducted to evaluate the efficacy and safety of this therapeutic procedure from a single institution. 2. Materials
and methods
2.1. Patients
From June 1991 to May 1995, 86 consecutive children were referred to this laboratory for consideration of radiofrequency ablation therapy because of troublesome supraventricular or ventricular tachycardias. There were 47 males and 39 females with a mean age of 14 ? 3 years (range 3-18). Seventynine showed no evidence of structural heart disease, two revealed a ventricular septal defect, one had Ebstein anomaly and atrial septal defect, one demonstrated atria1 septal defect, two had dilated cardiomyopathy, and the other exhibited a rightsided aortic arch. All 86 patients suffered from palpitations with electrocardiographic documentation of supraventricular or ventricular tachycardia, eight experienced recurrent syncope or nearsyncope and 28 had dizziness. All 86 patients had received two or more anti-arrhythmic agents for control of tachyarrhytbmia prior to referral and were considered to be unsatisfactory by the referral physician. All 86 patients underwent an electrophysiologic study that was followed by radiofrequency ablation. The procedure was reviewed and approved by the hospital review board and was in accordance with local ethical standards. A written informed consent for the procedure was obtained from parents of all patients. 2.2. Electrophysiologic
study
The electrophysiologic study was performed in the supine position after discontinuation of cardioactive drugs for at least three half-lives. Small children were premedicatedwith meperidine hydrochloride 0.5-2 mg/kg, promethazine hydrochloride
0.3-0.8 mg/kg, and chlorpromazine hydrochloride 0.2-0.4 mg/kg. Oral diazepam 2-5 mg was administered before the electrophysiologic study. Heparin sodium 50 units/kg was given intravenously after insertion of the arterial catheter. In most patients, two 6F quadripolar electrode catheters (USC1 002943; Bard, Galway, Ireland) and one 6F tripolar electrode catheter (USC1 002854; Bard) were introduced percutaneously into right and left femoral veins and advanced to the right atrium. These catheterswere positioned respectively in the high right atrium, acrossthe tricuspid valve, in the coronary sinus or the right ventricular apex, for recordings of the intracardiac electrogram and pacing. In patients older than 15 years, a fourth 6F quadripolar electrode catheter was introduced percutaneously into the right internal jugular vein and advanced into the coronary sinus for recording of the left atria1 electrogram, whereas in the two younger patients aged 3 and 5 years, only two catheters were used. Electrocardiographic leads I, AVF and VI as well as intracardiac electrograms from different sites were simultaneously displayed and recorded on a multichannel oscilloscopic recorder (Electronics for Medicine, VR 16 White Plains, New York) at a paper speedof 100 or 150 mm/set. The pacing stimuli were approximately twice the diastolic threshold in strength and 2 msec in duration and were provided by a digital programmable stimulator (Bloom and associates,DTU-200, Reading, PA). All patients underwent a complete anterogradeand retrograde electrophysiologic study using incremental pacing and extrastimulus testing techniques. 2.3. Radiofrequency ablation
For ablation of a right-sided accessorypathway or modification of the atrioventricular node, one of the quadripolar or tripolar electrode catheters was replaced by a 6F quadripolar steerable electrode catheter with a 4-mm bulbous distal electrode and a 2-mm interelectrode spacing between the two distal electrodes (Mansfield-EP, Watertown, MA). The catheter was advanced to the atrial aspect of the tricuspid annulus for ablation of the accessory pathway and to the region of Koch’s triangle for modification of the atrioventricular node. For abla-
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Journal of Cardiology 54 (1996) 33-40
tion of a left-sided accessory pathway, the steerable catheter was introduced percutaneously through the femoral artery, advanced to the left ventricle and positioned at the ventricular or atrial aspect of the mitral annulus. The radiofrequency current was supplied as a continuous unmodulated sine-wave energy at a frequency of 500 kHz by a commercially available electrosurgical unit (model RFG-3C; Radionics, Burlington, MA). It was delivered between the tip electrode and a dispersive cutaneous pad that was applied to the left posterior chest. The delivery of the radiofrequency current was performed under continuous digital monitoring of the power level and the impedance. The ablation procedure was discontinued immediately if atrioventricular block, chest pain, hypotension, severe bradycardia or a rise in impedance occurred. The technique and the selection of the ablation site for accessory pathway were performed as previously described [ 11,121. The ablation of the AV node re-entry tachycardia was conducted by the inferior approach [6,13]. The ablation of idiopathic ventricular tachycardia was conducted by the activation and pace-mapping techniques [8-lo]. Following successful ablation, electrophysiologic studies were repeated with isoproterenol infusion to achieve a 20% increase in sinus rate to ensure the success of ablation. The patients were observed in the hospital for 3 days with measurements of serum creatinine phosphokinase, 24-h Holter monitoring, and a two-dimensional echocardiographic examination. They were then followed in the clinic with a late electrophysiologic study scheduled 2 or 3 months later. Thirty-eight of the 86 patients underwent a repeat electrophysiologic study.
3. Results Fifty-two patients had AV re-entry tachycardia incorporating a retrograde accessory pathway, one patient had re-entry tachycardia using a nodoventricular fiber (Mahaim fiber) for anterograde and the normal pathway for retrograde conduction, 22 patients had AV node re-entry tachycardia, two patients had atria1 tachycardia, whereas nine patients had idiopathic ventricular tachycardia. The initial success of radiofrequency ablation was noted
35
in 79 of the 86 patients (92%). Eleven patients, seven with AV re-entry tachycardia, three with AV node re-entry tachycardia and one with idiopathic ventricular tachycardia, exhibited a recurrence of tachycardia induction at a late follow-up electrophysiologic study. They underwent a second trial and were successfully ablated. 3.1. Ablation of the accessory pathway and Mahaim jiber A total of 56 accessory pathways was found in the 52 patients with Wolff-Parkinson-White syndrome (four patients had two accessory pathways and 48 patients had a single accessory pathway). Thirty-one were manifest and 25 were concealed accessory pathways. All 52 patients had electrical induction of orthodromic AV re-entry tachycardia during electrophysiologic study. The tachycardia cycle length was 330 ? 47 msec (range 230-445). The accessory pathway was located in the left free wall in 28, the right wall in 17, the anteroseptal area in three, the midseptal area in two and the posteroseptal area in six. Radiofrequency ablation was successful in 54 of the 56 accessory pathways (96%) or in 50 of the 52 (96%) patients, and failed in two patients. One patient had re-entry tachycardia with pre-excited QRS complex of left bundle branch block pattern using a nodoventricular fiber for anterograde and the normal pathway for retrograde conduction. The nodoventricular fiber was successfully ablated. This patient was reported previously [ 141. Successful ablation required a mean of 10 2 11 (range l-44; median 5) applications, a power level of 28 + 4 watts (range 15-35), an application duration of 20 t 8 set (range 5-35), a fluoroscopic exposure time of 37 + 27 min (range 8-l 16.5), and a total procedure time of 128 t 54 min (range 60-300). One of the two patients whose ablation was unsuccessful had a midseptal accessory pathway (para-Hisian) and the other a posteroseptal accessory pathway. In these two patients, the ablation procedure was discontinued due to the occurrence of a transient AV block during delivery of the radiofrequency current in one and after 41 applications with a fluoroscopic exposure time of 117 min in the other.
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The follow-up duration was 24 ? 13 months (range 3-46). Resumption of accessory pathway conduction was noted in four patients within 2 months after successful ablation and three of them had recurrent tachycardia. A repeat electrophysiologic study was performed in 28 patients with successfulablation including the four patients with resumption of accessorypathway conduction and/or recurrence of tachycardia. Seven patients, including the four with clinical recurrence, showed induction of AV re-entry tachycardia whereas the others showed no induction of tachycardia or echoes. Six of these patients had a right-sided accessory pathway and the other had a left-sided accessory pathway. These seven patients were successfully ablated by a secondtrial. Both patients in whom the initial radiofrequency ablation was unsuccessfulcontinued to manifest with pre-excitation, but only the patient with a posteroseptal accessorypathway exhibited a recurrence of supraventricular tachycardia. The other who displayed a transient AV block during delivery of the radiofrequency current experienced no recurrence of tachycardia during follow-up.
patients. The number of applications was 5 2 7 (range l-25; median l), the power level was 24 + 4 watts (range 18-29), the application duration was 11 + 3 set (range 7-20), the fluoroscopic exposure time was 21 5 9 min (range 7-41), and the total procedure time was 112 + 34 min (range 70-180). In the two patients in whom the ablation was unsuccessful, one had multiple form tachycardias and the other had slow-fast form tachycardia. In the former patient, it was not possible to eradicate the fast-slow form tachycardia despite successful ablation of other tachycardias. The follow-up duration was 14 ? 12 months (range l-44). Three patients were noted to have recurrence of supraventricular tachycardia within 4 months after ablation. Eight patients, including the three with clinical recurrent tachycardia underwent a repeat electrophysiologic study 4 + 1 months (range 2-5) after the initial ablation and three showed induction of AV node re-entry tachycardia. All three were successfully ablated by a second trial.
3.2. Ablation of the AVnode re-entry tachycardia
Two patients had atrial tachycardia, one with adenosine-sensitive atria1 tachycardias from two different foci (one at the low right atrium and the other at the high right atrium), and the other with incessant automatic atria1 tachycardia from the posterior septum of the left atrium. Ablation therapy was unsuccessful in both patients.
Of the 22 patients with AV node re-entry tachycardia, 17 showed the common slow-fast form, one displayed the fast-intermediate form [15], and four revealed multiple form tachycardias. The cycle length of the slow-fast form tachycardia was 310 + 38 msec (range 240-410), the fast-intermediate form tachycardia was 330 msec, and the multiple form tachycardias were 350-430 msec. Anterograde dual pathway physiology was noted in 21 patients; retrograde dual pathway physiology was noted in the three patients with multiple form tachycardias, whereas retrograde triple pathway physiology was noted in the two patients with fast-intermediate or multiple form tachycardias. Radiofrequency ablation was successful in 20 of the 22 patients (91%). It resulted in selective ablation or modification of the slow pathway conduction in 16 patients, ablation of both the slow and the intermediate pathway conductions in two patients, and ablation of both the slow pathway and the retrograde fast pathway conductions in two
3.3. Ablation of the atria1 tachycardia
3.4. Ablation of the idiopathic ventricular tachycardia Nine patients had idiopathic ventricular tachycardia, eight from the left ventricle and one from the right ventricular outflow tract. Of the eight patients with idiopathic left ventricular tachycardia, five exhibited a QRS morphology of right bundle branch block and left axis deviation and three with an indeterminate axis. In all eight patients, the tachycardia was electrically inducible and responsive to verapamil. The cycle length of the tachycardia was 344 2 41 msec (range 280-400). The ventricular tachycardia was successfully ablated in seven of the eight patients (88%). The ablation site
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in the seven patients with successful ablation was located at the inferior apical septum in five patients and at the midseptal area in two patients. The one patient with the tachycardia from the right ventricular outflow tract displayed a QRS morphology of left bundle branch block and right axis deviation. The tachycardia could be triggered by exercise and isoproterenol infusion, was electrically inducible and responsive to verapamil. The cycle length of tachycardia was 300 msec. The tachycardia was ablated successfully in this patient. The number of applications, the power level, the application duration, the fluoroscopic exposure time, and the total procedure time in the eight patients with a successful ablation were 11 2 7 (range l-59; median 3), 26 2 1 watts (range 22-29), 15 If: 2 set (range lo-30), 33 “_ 6 min (range 6-69), and 165 f 20 min (range 90-290), respectively. The follow-up duration was 17 +- 7 months (range 8-30). One patient had recurrent tachycardia 1 month after ablation and was successfully ablated by a second session. Another patient with right ventricular outflow tract tachycardia underwent a follow-up electrophysiologic study 2 months after ablation and the tachycardia was noninducible. Two patients who suffered from incessanttachycardia before ablation demonstrated a marked improvement of left ventricular ejection fraction (as evaluated by 2Dechocardiography) from 35 to 60% 6 months after successful ablation. 3.5. Complications
One patient with a midseptal accessorypathway developedtransient AV block during delivery of the radiofrequency current. In this patient, the AV conduction resumed immediately after discontinuance of radiofrequency ablation. Four patients with AV node re-entry tachycardia developed transient AV nodal Wenckebachblock during manipulation of the bulbous-tip ablation catheter in the junctional area before delivery of the radiofrequency current. In these four patients, the AV conduction resumed spontaneouslyafter reposition of the ablation catheter without interfering with subsequent radiofrequency modification of the AV node. A fracture of the introducer sheathin the right femoral vein occurred in one patient; the fractured sheath
37
was removed surgically. Mild per&dial effusion was noted on a routine post-ablation two-dimensional echocardiographic examination in another patient. This patient was asymptomatic and the pericardial effusion disappearedspontaneouslyduring subsequentfollow-up echocardiographicexaminations.
4. Discussion 4.1. Supraventricular young patients
tachycardia in children and
Supraventricular tachycardia is the most common symptomatic tachyarrhythmia in pediatric patients [l]. The majority of these tachycardiasresults from re-entry incorporating an accessory pathway. Others include ectopic atrial tachycardia, automatic junctional tachycardia, AV node re-entry tachycardia, and the permanentform of junctional tachycardia. Idiopathic ventricular tachycardia without the presence of structural heart disease also occurs in children and young adolescents [8-lo]. Drug therapy used to be the optional choice of treatment in these patients. Surgical intervention with an incision of the accessorypathway, ablation of the arrhythmia focus, or interruption of the His bundle were the other options in patients with drug-resistant or troublesome arrhythmias [2,3]. Transcatheter ablation using DC shocks has been attemptedin several patients with automatic junctional tachycardia, automatic atrial tachycardia, the permanent form of junctional tachycardia, and accessory pathway-mediated tachycardia [16-191. However, the result was less than satisfactory. The patients frequently exhibited heart block requiring implantation of a permanent pacemaker.In addition, delivery of DC shocks requires general anesthesiaand is associatedwith a risk of serious side effects due to arcing and gas formation. 4.2. Radiofrequency ablation in children and young patients
Substantial experienceof radiofrequency ablation therapy in adult patients with supraventricular or ventricular tachycardia have been reported from
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several institutions [4-lo], the experience of this therapeutic modality in children and young patients from a single institution is still limited in case numbers. Van Hare et al. [20] reported 17 patients with various types of supraventricular tachycardia, aged from 10 months to 17 years, undergoing radiofrequency therapy. Twelve patients exhibited accessory-mediated tachycardia, four revealed atrioventricular node re-entry tachycardia, and one displayed ectopic junctional tachycardia. A total of 19 procedures were conducted and resulted in successful ablation of the tachycardia in 14 patients (82%), including 10 of the 12 patients (83%) with accessory pathway-mediated tachycardia, three of the four patients with AV node re-entry tachycardia, and one patient with ectopic junctional tachycardia. Dick et al. [21] reported 19 patients with accessory pathway-mediated tachycardia, aged from 3 to 18 years (median of 12.5 years), undergoing radiofrequency ablation. Initial success was noted in 13 patients (68%), whereas final success was noted in 14 patients (74%). Case et al. [22] reported seven patients with a body weight of less than 15 kg, aged from 1 to 27 months, undergoing radiofi-equency ablation for accessory pathway-mediated tachycardia (six patients) or ectopic atrial tachycardia (one patient). A total of nine procedures was conducted and resulted in a successful ablation in five patients (71%). Saul et al. [23] reported their experience of radiofrequency ablation therapy in 71 young or adult patients, aged from 1 month to 55 years (median of 14 years). A total of 83 accessory pathways, including eight concealed slowly conducting accessory pathways, were found in the 71 patients. Successful ablation was noted in 77 of the 83 accessory pathways (93%). Van Hare et al. [24] recently reported their follow-up data in 100 consecutive pediatric patients undergoing radiofrequency ablation and showed a 93% overall initial success rate and a 1.6% complication rate. The mean fluoroscopic time was 54.2 min and a 6month recurrent rate was 13.7%. Silka et al. [25] conducted radiofrequency modification of the slow pathway in 18 children or young adolescents with AV node re-entry tachycardia. They noted that after the initial modification of the slow pathway, AV node re-entry tachycardia with 2:l block distal to
the His bundle recording site was inducible in seven patients and the atypical fast-slow form AV node re-entry tachycardia was inducible in nine patients. These nine patients required a secondary modification of the slow pathway. During a followup of 9.8 + 3 months, one patient had the recurrence of the initial tachycardia and two other patients developed the atypical fast-slow form tachycardia. The above data on radiofrequency ablation in children or young patients tend to show a lower success rate and longer procedure times as compared with the adult population. However, the complication rate appears to be similar. The Registry Study of the Pediatric Electrophysiology Society of North America [26] collected 652 patients undergoing 725 radiofrequency ablation procedures from 24 centers. The average early success rate was 83% and ranged from 67 to 100% (83% for ablation of accessory pathway and AV node re-entry tachycardia) in various supraventricular tachycardias. Success rate was higher in centers with higher numbers of ablation in accessory pathway located in the left free wall, and in tachyarrhythmia of atria1 ectopic focus. The followup data with life table analysis displayed a freedom from recurrence of tachycardia or pre-excitation after ablation ranging from 50 to 78% dependent on several factors. Recurrences were likely to occur in a right free wall accessory pathway, in patients with underlying heart disease, and in patients with high body weight. The fluoroscopic time ranged from 45.9 + 34 to 79.6 + 51.7 min depending upon accessory pathway location and type of tachyarrhythmia. The complication rate at the time of ablation was 3.7% and the total complication rate including the late complications was 4.8%. The success rate of 92% (96% in accessory pathway-mediated tachycardia, 91% in atrioventricular node re-entry tachycardia, 0% in atria1 tachycardia and 88% in idiopathic ventricular tachycardia) in the present study is comparable to the large series by Van Hare et al. [24] from a single institution, but is better than most of the reported pediatric series [21-23,25-271 and is identical to the results in the adult population. No special techniques were used for ablation of the accessory pathway in this study compared with
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others [23,27]. The complications that were encountered by Silka et al. [25] in ablation of the slow-fast form AV node re-entry tachycardia were not noted in this study. The procedure time, fluoroscopic time, power level of current, application duration, number of applications, complications, and recurrence rate of the present study are not different from those of the adult population. The higher success rate, lower complication rate and shorter fluoroscopic time in this study are likely to result from the substantial experience of radiofrequency ablation in this laboratory. During the study period, 620 patients with accessory pathway-mediated arrhythmia, 595 patients with AV node re-entry tachycardia, 27 patients with atria1 tachycardia and 81 patients with idiopathic ventricular tachycardia had received radiofrequency ablation therapy in this institution. However, the fact that only seven of the 86 patients (8%) in this study were suffering from underlying heart disease compared to 16% of the patients in the Registry Study may in part account for the difference.
Acknowledgments
Supported in part by grants from the National Health Research Institute (DOH83-HR-205) and the National Science Council (NSC84-2331-B-l 82009 and NSC84-233l-B-182-003) of the Republic of China, Taipei, Taiwan.
References [l] Campbell RM, Dick M, Rosenthal A. Cardiac arrhythmias in children. Ann Rev Med 1984; 35: 397-410. [2] Holmes DR, Danielson OK, Gersh BJ et al. Surgical treatment of accessory atrioventricular pathways and symptomatic tachycardia in children and young adults. Am J Cardiol 1985; 55: 1509-1512. [3] Case CL, Crawford FA, Gillette PC et al. Management strategies for surgical treatment of dysrhythmias in infants and children. Am J Cardiol 1989; 63: 1069-1073. [4] Calkins H, Sousa J, El-Atassi R et al. Diagnosis and cure of the Wolff-Parkinson-White syndrome or paroxysmal supraventricular tachycardias during a single electrophysiologic test. N Engl J Med 1991; 324: 1612-1618.
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[5] Jackman WM, Wang X, Friday KJ et al. Catheter ablation of accessory atrioventricular pathways (Wolff-ParkinsonWhite syndrome) by radiofrequency current. N Engl J Med 1991; 324: 1605-1611. [6] Wu D, Yeh SJ, Wang CC et al. A simple technique for selective radiofrequency ablation of the slow pathway in atrioventricular node re-entrant tachycardia. J Am Co11 Cardiol 1993; 21: 1612-1621. [7] Chen SA, Chiang CE, Yang CJ et al. Radiofrequency catheter ablation of sustained intra-atrial reentrant tachycardia in adult patients. Circulation 1993; 88: 578-587. [8] Klein LS, Shih HT, Hackelt FK et al. Radiofrequency catheter ablation of ventricular tachycardia in patients without structural heart disease. Circulation 1992; 85: 1666-1674. [9] Nakagawa H, Beckman KJ, McClelland JH et al. Radiofrequency catheter ablation of idiopathic left ventricular tachycardia guided by a Purkinje potential. Circulation 1993; 88: 2607-2617. lo] Wen MS, Yeh SJ, Wang CC et al. Radiofrequency ablation therapy in idiopathic left ventricular tachycardia with no obvious structural heart disease. Circulation 1994; 89: 1690-1696. 1l] Yeh SJ, Wang CC, Wen MS et al. Radiofrequency ablation in multiple accessory pathways and the physiologic implications. Am J Cardiol 1993; 71: 1174-1180. 121 Yeh SJ, Wang CC, Wen MS et al. Characteristics and radiofrequency ablation therapy of intermediate septal accessory pathway. Am J Cardiol 1994; 73: 50-56. 131 Wu D, Yeh SJ, Wang CC et al. Nature of dual atrioventricular node pathways and the tachycardia circuit as defined by radiofrequency ablation technique. J Am Co11 Cardiol 1992; 20: 884-895. [14] Wen MS, Yeh SJ, Wang CC et al. Successful radiofrequency ablation in reentrant tachycardia incorporating a nodoventricular tract. Am Heart J 1994; 127: 1413-1419. [15] Wu, Yeh SJ, Wang CC et al. Double loop figure-of-8 reentry as the mechanism of multiple atrioventricular node reentry tachycardias. Am Heart J 1994; 127: 83-95. [16] Gillette PC, Garson A Jr, Porter CJ et al. Junctional automatic ectopic tachycardia: new proposed treatment by transcatheter His bundle ablation. Am Heart J 1983; 106: 619-623. [17] Gillette PC, Wampler DG, Garson A Jr et al. Treatment of atrial automatic tachycardia by ablation procedures. J Am Co11 Cardiol 1985; 6: 405-409. [18] Smith RT, Gillette PC, Massumi A et al. Transcather ablative techniques for treatment of the permanent form of junctional reciprocating tachycardia in young patients. J Am Co11 Cardiol 1986; 8: 385-390. [19] Bromberg BI, Dick M, Scott WA et al. Transcatheter electrical ablation of accessory pathway in children. PACE 1989; 12: 1787-1796. [20] Van Hare GF, Lesh MD, Scheinman M et al. Percutaneous radiofrequency catheter ablation for supraventricular arrhythmias in children. J Am Co11 Cardiol 1991; 17: 16131620.
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[21] Dick M, O’Connor BK, Serwer GA et al. Use of radiofrequency current to ablate accessorypathway connection in children. Circulation 1991; 84: 2318-2324. [22] Case CL, Gillette PC, Oslizlok PC et al. Radiofrequency catheter ablation of incessantmedically resistant supraventricular tachycardia in infants and small children. J Am Co11Cardiol 1992; 20: 1405-1410. [23] Saul JP, Hulse E, De W et al. Catheter ablation of accessoryatrioventticular pathways in young patients: use of long vascular sheaths, the transeptal approach and a retrograde left posterior parallel approach. J Am Co11 Cardiol 1993; 21: 571-583. [24] Van Hare GF, Witherell CL, Lesh MD. Follow-up of radiofrequency catheter ablation in children: Results in 100 consecutive patients. J Am Co11Cardiol 1994; 23: 16511659.
[25] Silka MJ, Kron J, Park JK et al. Atypical forms of supraventricular tachycardia due to atrioventricular node reentry in children after radiofrequency modification of slow pathway conduction. J Am Co11Cardiol 1994; 23: 1363-1369. [26] Kugler JD, Danford DA, Deal BJ et al. Radiofrequency catheter ablation for tachyarrhythmias in children and adolescents.N Engl J Med 1994; 21: 1481-1487. [27] Schhiter M, Kuck KH. Radiofrequencycurrent for catheter ablation of accessory atrioventricular connections in children and adolescents. Emphasis on the single-catheter technique. Pediatrics 1992; 89: 930-935.
Journal
of
cardiology ELSEVIER
International Journal of Cardiology 54 (1996) 33-40
Radiofrequency ablation for supraventricular and ventricular tachycardia in young patients I-Chang Hsieh, San-Jou Yeh, Ming-Shien Wen, Chun-Chieh Wang, Fun-Chung Lin, Delon Wu* Second Section of Cardiology, Deparhnent of Medicine, Chang Gung Memorial Hospital, Chang Gung Medical College, Taipei, Taiwan Received 5 July 1995; accepted 16 January 1996
Abstract Radiofrequency ablation therapy was conductedin 86 consecutive children and young patients with a mean age of 14 ? 3 years (range = 3-18). Fifty-two patients had Wolff-Parkinson-White syndrome, one had re-entry tachycardia incorporating a nodoventricular fiber, 22 had atrioventricular node re-entry tachycardia, two had atrial tachycardia and nine had idiopathic ventricular tachycardia. Radiofrequency ablation was successfulin 50 of the 52 patients (96%) with Wolff-Parkinson-White syndrome and the one with nodoventricular fiber. Radiofrequency modification of the atrioventricular node using the inferior approachwas successfulin eliminating atrioventricular node re-entry tachycardia in 20 of the 22 patients (91%). Radiofrequency ablation in the two patients with atria1tachycardia was unsuccessful.Of the nine patients with idiopathic ventricular tachycardia, eight from the left ventricle and one from the right ventricular outflow tract, eight were successfully ablated (88%). Follow-up over a period ranging from 1 to 46 months (21 + 13) revealed a recurrence of tachycardia in seven patients; a late electrophysiological study in 38 patients revealed the induction of tachycardia in 11 patients (seven with accessorypathway-mediatedtachycardia, three with atrioventricular node re-entry tachycardia and one with idiopathic ventricular tachycardia). All 11 patients were successfully ablated by a secondtrial. In conclusion, radiofrequency ablation therapy is effective and safe in pediatric patients with supraventncular and ventricular tachycardia and should be considered as the therapy of choice in this group of patients. Keywords:
Radiofrequency ablation; Children
1. Introduction Symptomatic supraventticular or ventricular tachycardia in children or young patients is usually managed by antiarrhythmic agents [ 11. However, *Corresponding author, Chang Gung Memorial Hospital, 199
Tung Hwa North Road, Taipei, Taiwan. Tel.: 886 3 3281200; fax: 886 3 3285636.
chronic drug administration poses an inconvenience to the patients as well as to the families, and is associated with the potential risk of serious side effects. Surgery used to be the only option in patients with drug-resistant or troublesome tachycardias [2,3]. Radiofrequency ablation therapy is the current therapy of choice in adults with some types of supraventricular and ventricular tachycardias [4-lo]. In this study, racliofrequency ablation
0167-5273/96/$1.5.00 0 1996 Elsevier Science Ireland Ltd. All rights reserved PII SO167-5273(96)02575-2
34
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Journal of Cardiology 54 (1996) 33-40
therapy on atrioventricular (AV) re-entry tachycardia incorporating an accessory pathway, re-entry tachycardia incorporating a Mahaim fiber, AV node re-entry tachycardia, atria1 tachycardia, and idiopathic ventricular tachycardia in children and young patients is conducted to evaluate the efficacy and safety of this therapeutic procedure from a single institution. 2. Materials
and methods
2.1. Patients
From June 1991 to May 1995, 86 consecutive children were referred to this laboratory for consideration of radiofrequency ablation therapy because of troublesome supraventricular or ventricular tachycardias. There were 47 males and 39 females with a mean age of 14 ? 3 years (range 3-18). Seventynine showed no evidence of structural heart disease, two revealed a ventricular septal defect, one had Ebstein anomaly and atrial septal defect, one demonstrated atria1 septal defect, two had dilated cardiomyopathy, and the other exhibited a rightsided aortic arch. All 86 patients suffered from palpitations with electrocardiographic documentation of supraventricular or ventricular tachycardia, eight experienced recurrent syncope or nearsyncope and 28 had dizziness. All 86 patients had received two or more anti-arrhythmic agents for control of tachyarrhytbmia prior to referral and were considered to be unsatisfactory by the referral physician. All 86 patients underwent an electrophysiologic study that was followed by radiofrequency ablation. The procedure was reviewed and approved by the hospital review board and was in accordance with local ethical standards. A written informed consent for the procedure was obtained from parents of all patients. 2.2. Electrophysiologic
study
The electrophysiologic study was performed in the supine position after discontinuation of cardioactive drugs for at least three half-lives. Small children were premedicatedwith meperidine hydrochloride 0.5-2 mg/kg, promethazine hydrochloride
0.3-0.8 mg/kg, and chlorpromazine hydrochloride 0.2-0.4 mg/kg. Oral diazepam 2-5 mg was administered before the electrophysiologic study. Heparin sodium 50 units/kg was given intravenously after insertion of the arterial catheter. In most patients, two 6F quadripolar electrode catheters (USC1 002943; Bard, Galway, Ireland) and one 6F tripolar electrode catheter (USC1 002854; Bard) were introduced percutaneously into right and left femoral veins and advanced to the right atrium. These catheterswere positioned respectively in the high right atrium, acrossthe tricuspid valve, in the coronary sinus or the right ventricular apex, for recordings of the intracardiac electrogram and pacing. In patients older than 15 years, a fourth 6F quadripolar electrode catheter was introduced percutaneously into the right internal jugular vein and advanced into the coronary sinus for recording of the left atria1 electrogram, whereas in the two younger patients aged 3 and 5 years, only two catheters were used. Electrocardiographic leads I, AVF and VI as well as intracardiac electrograms from different sites were simultaneously displayed and recorded on a multichannel oscilloscopic recorder (Electronics for Medicine, VR 16 White Plains, New York) at a paper speedof 100 or 150 mm/set. The pacing stimuli were approximately twice the diastolic threshold in strength and 2 msec in duration and were provided by a digital programmable stimulator (Bloom and associates,DTU-200, Reading, PA). All patients underwent a complete anterogradeand retrograde electrophysiologic study using incremental pacing and extrastimulus testing techniques. 2.3. Radiofrequency ablation
For ablation of a right-sided accessorypathway or modification of the atrioventricular node, one of the quadripolar or tripolar electrode catheters was replaced by a 6F quadripolar steerable electrode catheter with a 4-mm bulbous distal electrode and a 2-mm interelectrode spacing between the two distal electrodes (Mansfield-EP, Watertown, MA). The catheter was advanced to the atrial aspect of the tricuspid annulus for ablation of the accessory pathway and to the region of Koch’s triangle for modification of the atrioventricular node. For abla-
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tion of a left-sided accessory pathway, the steerable catheter was introduced percutaneously through the femoral artery, advanced to the left ventricle and positioned at the ventricular or atrial aspect of the mitral annulus. The radiofrequency current was supplied as a continuous unmodulated sine-wave energy at a frequency of 500 kHz by a commercially available electrosurgical unit (model RFG-3C; Radionics, Burlington, MA). It was delivered between the tip electrode and a dispersive cutaneous pad that was applied to the left posterior chest. The delivery of the radiofrequency current was performed under continuous digital monitoring of the power level and the impedance. The ablation procedure was discontinued immediately if atrioventricular block, chest pain, hypotension, severe bradycardia or a rise in impedance occurred. The technique and the selection of the ablation site for accessory pathway were performed as previously described [ 11,121. The ablation of the AV node re-entry tachycardia was conducted by the inferior approach [6,13]. The ablation of idiopathic ventricular tachycardia was conducted by the activation and pace-mapping techniques [8-lo]. Following successful ablation, electrophysiologic studies were repeated with isoproterenol infusion to achieve a 20% increase in sinus rate to ensure the success of ablation. The patients were observed in the hospital for 3 days with measurements of serum creatinine phosphokinase, 24-h Holter monitoring, and a two-dimensional echocardiographic examination. They were then followed in the clinic with a late electrophysiologic study scheduled 2 or 3 months later. Thirty-eight of the 86 patients underwent a repeat electrophysiologic study.
3. Results Fifty-two patients had AV re-entry tachycardia incorporating a retrograde accessory pathway, one patient had re-entry tachycardia using a nodoventricular fiber (Mahaim fiber) for anterograde and the normal pathway for retrograde conduction, 22 patients had AV node re-entry tachycardia, two patients had atria1 tachycardia, whereas nine patients had idiopathic ventricular tachycardia. The initial success of radiofrequency ablation was noted
35
in 79 of the 86 patients (92%). Eleven patients, seven with AV re-entry tachycardia, three with AV node re-entry tachycardia and one with idiopathic ventricular tachycardia, exhibited a recurrence of tachycardia induction at a late follow-up electrophysiologic study. They underwent a second trial and were successfully ablated. 3.1. Ablation of the accessory pathway and Mahaim jiber A total of 56 accessory pathways was found in the 52 patients with Wolff-Parkinson-White syndrome (four patients had two accessory pathways and 48 patients had a single accessory pathway). Thirty-one were manifest and 25 were concealed accessory pathways. All 52 patients had electrical induction of orthodromic AV re-entry tachycardia during electrophysiologic study. The tachycardia cycle length was 330 ? 47 msec (range 230-445). The accessory pathway was located in the left free wall in 28, the right wall in 17, the anteroseptal area in three, the midseptal area in two and the posteroseptal area in six. Radiofrequency ablation was successful in 54 of the 56 accessory pathways (96%) or in 50 of the 52 (96%) patients, and failed in two patients. One patient had re-entry tachycardia with pre-excited QRS complex of left bundle branch block pattern using a nodoventricular fiber for anterograde and the normal pathway for retrograde conduction. The nodoventricular fiber was successfully ablated. This patient was reported previously [ 141. Successful ablation required a mean of 10 2 11 (range l-44; median 5) applications, a power level of 28 + 4 watts (range 15-35), an application duration of 20 t 8 set (range 5-35), a fluoroscopic exposure time of 37 + 27 min (range 8-l 16.5), and a total procedure time of 128 t 54 min (range 60-300). One of the two patients whose ablation was unsuccessful had a midseptal accessory pathway (para-Hisian) and the other a posteroseptal accessory pathway. In these two patients, the ablation procedure was discontinued due to the occurrence of a transient AV block during delivery of the radiofrequency current in one and after 41 applications with a fluoroscopic exposure time of 117 min in the other.
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The follow-up duration was 24 ? 13 months (range 3-46). Resumption of accessory pathway conduction was noted in four patients within 2 months after successful ablation and three of them had recurrent tachycardia. A repeat electrophysiologic study was performed in 28 patients with successfulablation including the four patients with resumption of accessorypathway conduction and/or recurrence of tachycardia. Seven patients, including the four with clinical recurrence, showed induction of AV re-entry tachycardia whereas the others showed no induction of tachycardia or echoes. Six of these patients had a right-sided accessory pathway and the other had a left-sided accessory pathway. These seven patients were successfully ablated by a secondtrial. Both patients in whom the initial radiofrequency ablation was unsuccessfulcontinued to manifest with pre-excitation, but only the patient with a posteroseptal accessorypathway exhibited a recurrence of supraventricular tachycardia. The other who displayed a transient AV block during delivery of the radiofrequency current experienced no recurrence of tachycardia during follow-up.
patients. The number of applications was 5 2 7 (range l-25; median l), the power level was 24 + 4 watts (range 18-29), the application duration was 11 + 3 set (range 7-20), the fluoroscopic exposure time was 21 5 9 min (range 7-41), and the total procedure time was 112 + 34 min (range 70-180). In the two patients in whom the ablation was unsuccessful, one had multiple form tachycardias and the other had slow-fast form tachycardia. In the former patient, it was not possible to eradicate the fast-slow form tachycardia despite successful ablation of other tachycardias. The follow-up duration was 14 ? 12 months (range l-44). Three patients were noted to have recurrence of supraventricular tachycardia within 4 months after ablation. Eight patients, including the three with clinical recurrent tachycardia underwent a repeat electrophysiologic study 4 + 1 months (range 2-5) after the initial ablation and three showed induction of AV node re-entry tachycardia. All three were successfully ablated by a second trial.
3.2. Ablation of the AVnode re-entry tachycardia
Two patients had atrial tachycardia, one with adenosine-sensitive atria1 tachycardias from two different foci (one at the low right atrium and the other at the high right atrium), and the other with incessant automatic atria1 tachycardia from the posterior septum of the left atrium. Ablation therapy was unsuccessful in both patients.
Of the 22 patients with AV node re-entry tachycardia, 17 showed the common slow-fast form, one displayed the fast-intermediate form [15], and four revealed multiple form tachycardias. The cycle length of the slow-fast form tachycardia was 310 + 38 msec (range 240-410), the fast-intermediate form tachycardia was 330 msec, and the multiple form tachycardias were 350-430 msec. Anterograde dual pathway physiology was noted in 21 patients; retrograde dual pathway physiology was noted in the three patients with multiple form tachycardias, whereas retrograde triple pathway physiology was noted in the two patients with fast-intermediate or multiple form tachycardias. Radiofrequency ablation was successful in 20 of the 22 patients (91%). It resulted in selective ablation or modification of the slow pathway conduction in 16 patients, ablation of both the slow and the intermediate pathway conductions in two patients, and ablation of both the slow pathway and the retrograde fast pathway conductions in two
3.3. Ablation of the atria1 tachycardia
3.4. Ablation of the idiopathic ventricular tachycardia Nine patients had idiopathic ventricular tachycardia, eight from the left ventricle and one from the right ventricular outflow tract. Of the eight patients with idiopathic left ventricular tachycardia, five exhibited a QRS morphology of right bundle branch block and left axis deviation and three with an indeterminate axis. In all eight patients, the tachycardia was electrically inducible and responsive to verapamil. The cycle length of the tachycardia was 344 2 41 msec (range 280-400). The ventricular tachycardia was successfully ablated in seven of the eight patients (88%). The ablation site
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in the seven patients with successful ablation was located at the inferior apical septum in five patients and at the midseptal area in two patients. The one patient with the tachycardia from the right ventricular outflow tract displayed a QRS morphology of left bundle branch block and right axis deviation. The tachycardia could be triggered by exercise and isoproterenol infusion, was electrically inducible and responsive to verapamil. The cycle length of tachycardia was 300 msec. The tachycardia was ablated successfully in this patient. The number of applications, the power level, the application duration, the fluoroscopic exposure time, and the total procedure time in the eight patients with a successful ablation were 11 2 7 (range l-59; median 3), 26 2 1 watts (range 22-29), 15 If: 2 set (range lo-30), 33 “_ 6 min (range 6-69), and 165 f 20 min (range 90-290), respectively. The follow-up duration was 17 +- 7 months (range 8-30). One patient had recurrent tachycardia 1 month after ablation and was successfully ablated by a second session. Another patient with right ventricular outflow tract tachycardia underwent a follow-up electrophysiologic study 2 months after ablation and the tachycardia was noninducible. Two patients who suffered from incessanttachycardia before ablation demonstrated a marked improvement of left ventricular ejection fraction (as evaluated by 2Dechocardiography) from 35 to 60% 6 months after successful ablation. 3.5. Complications
One patient with a midseptal accessorypathway developedtransient AV block during delivery of the radiofrequency current. In this patient, the AV conduction resumed immediately after discontinuance of radiofrequency ablation. Four patients with AV node re-entry tachycardia developed transient AV nodal Wenckebachblock during manipulation of the bulbous-tip ablation catheter in the junctional area before delivery of the radiofrequency current. In these four patients, the AV conduction resumed spontaneouslyafter reposition of the ablation catheter without interfering with subsequent radiofrequency modification of the AV node. A fracture of the introducer sheathin the right femoral vein occurred in one patient; the fractured sheath
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was removed surgically. Mild per&dial effusion was noted on a routine post-ablation two-dimensional echocardiographic examination in another patient. This patient was asymptomatic and the pericardial effusion disappearedspontaneouslyduring subsequentfollow-up echocardiographicexaminations.
4. Discussion 4.1. Supraventricular young patients
tachycardia in children and
Supraventricular tachycardia is the most common symptomatic tachyarrhythmia in pediatric patients [l]. The majority of these tachycardiasresults from re-entry incorporating an accessory pathway. Others include ectopic atrial tachycardia, automatic junctional tachycardia, AV node re-entry tachycardia, and the permanentform of junctional tachycardia. Idiopathic ventricular tachycardia without the presence of structural heart disease also occurs in children and young adolescents [8-lo]. Drug therapy used to be the optional choice of treatment in these patients. Surgical intervention with an incision of the accessorypathway, ablation of the arrhythmia focus, or interruption of the His bundle were the other options in patients with drug-resistant or troublesome arrhythmias [2,3]. Transcatheter ablation using DC shocks has been attemptedin several patients with automatic junctional tachycardia, automatic atrial tachycardia, the permanent form of junctional tachycardia, and accessory pathway-mediated tachycardia [16-191. However, the result was less than satisfactory. The patients frequently exhibited heart block requiring implantation of a permanent pacemaker.In addition, delivery of DC shocks requires general anesthesiaand is associatedwith a risk of serious side effects due to arcing and gas formation. 4.2. Radiofrequency ablation in children and young patients
Substantial experienceof radiofrequency ablation therapy in adult patients with supraventricular or ventricular tachycardia have been reported from
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several institutions [4-lo], the experience of this therapeutic modality in children and young patients from a single institution is still limited in case numbers. Van Hare et al. [20] reported 17 patients with various types of supraventricular tachycardia, aged from 10 months to 17 years, undergoing radiofrequency therapy. Twelve patients exhibited accessory-mediated tachycardia, four revealed atrioventricular node re-entry tachycardia, and one displayed ectopic junctional tachycardia. A total of 19 procedures were conducted and resulted in successful ablation of the tachycardia in 14 patients (82%), including 10 of the 12 patients (83%) with accessory pathway-mediated tachycardia, three of the four patients with AV node re-entry tachycardia, and one patient with ectopic junctional tachycardia. Dick et al. [21] reported 19 patients with accessory pathway-mediated tachycardia, aged from 3 to 18 years (median of 12.5 years), undergoing radiofrequency ablation. Initial success was noted in 13 patients (68%), whereas final success was noted in 14 patients (74%). Case et al. [22] reported seven patients with a body weight of less than 15 kg, aged from 1 to 27 months, undergoing radiofi-equency ablation for accessory pathway-mediated tachycardia (six patients) or ectopic atrial tachycardia (one patient). A total of nine procedures was conducted and resulted in a successful ablation in five patients (71%). Saul et al. [23] reported their experience of radiofrequency ablation therapy in 71 young or adult patients, aged from 1 month to 55 years (median of 14 years). A total of 83 accessory pathways, including eight concealed slowly conducting accessory pathways, were found in the 71 patients. Successful ablation was noted in 77 of the 83 accessory pathways (93%). Van Hare et al. [24] recently reported their follow-up data in 100 consecutive pediatric patients undergoing radiofrequency ablation and showed a 93% overall initial success rate and a 1.6% complication rate. The mean fluoroscopic time was 54.2 min and a 6month recurrent rate was 13.7%. Silka et al. [25] conducted radiofrequency modification of the slow pathway in 18 children or young adolescents with AV node re-entry tachycardia. They noted that after the initial modification of the slow pathway, AV node re-entry tachycardia with 2:l block distal to
the His bundle recording site was inducible in seven patients and the atypical fast-slow form AV node re-entry tachycardia was inducible in nine patients. These nine patients required a secondary modification of the slow pathway. During a followup of 9.8 + 3 months, one patient had the recurrence of the initial tachycardia and two other patients developed the atypical fast-slow form tachycardia. The above data on radiofrequency ablation in children or young patients tend to show a lower success rate and longer procedure times as compared with the adult population. However, the complication rate appears to be similar. The Registry Study of the Pediatric Electrophysiology Society of North America [26] collected 652 patients undergoing 725 radiofrequency ablation procedures from 24 centers. The average early success rate was 83% and ranged from 67 to 100% (83% for ablation of accessory pathway and AV node re-entry tachycardia) in various supraventricular tachycardias. Success rate was higher in centers with higher numbers of ablation in accessory pathway located in the left free wall, and in tachyarrhythmia of atria1 ectopic focus. The followup data with life table analysis displayed a freedom from recurrence of tachycardia or pre-excitation after ablation ranging from 50 to 78% dependent on several factors. Recurrences were likely to occur in a right free wall accessory pathway, in patients with underlying heart disease, and in patients with high body weight. The fluoroscopic time ranged from 45.9 + 34 to 79.6 + 51.7 min depending upon accessory pathway location and type of tachyarrhythmia. The complication rate at the time of ablation was 3.7% and the total complication rate including the late complications was 4.8%. The success rate of 92% (96% in accessory pathway-mediated tachycardia, 91% in atrioventricular node re-entry tachycardia, 0% in atria1 tachycardia and 88% in idiopathic ventricular tachycardia) in the present study is comparable to the large series by Van Hare et al. [24] from a single institution, but is better than most of the reported pediatric series [21-23,25-271 and is identical to the results in the adult population. No special techniques were used for ablation of the accessory pathway in this study compared with
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others [23,27]. The complications that were encountered by Silka et al. [25] in ablation of the slow-fast form AV node re-entry tachycardia were not noted in this study. The procedure time, fluoroscopic time, power level of current, application duration, number of applications, complications, and recurrence rate of the present study are not different from those of the adult population. The higher success rate, lower complication rate and shorter fluoroscopic time in this study are likely to result from the substantial experience of radiofrequency ablation in this laboratory. During the study period, 620 patients with accessory pathway-mediated arrhythmia, 595 patients with AV node re-entry tachycardia, 27 patients with atria1 tachycardia and 81 patients with idiopathic ventricular tachycardia had received radiofrequency ablation therapy in this institution. However, the fact that only seven of the 86 patients (8%) in this study were suffering from underlying heart disease compared to 16% of the patients in the Registry Study may in part account for the difference.
Acknowledgments
Supported in part by grants from the National Health Research Institute (DOH83-HR-205) and the National Science Council (NSC84-2331-B-l 82009 and NSC84-233l-B-182-003) of the Republic of China, Taipei, Taiwan.
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[5] Jackman WM, Wang X, Friday KJ et al. Catheter ablation of accessory atrioventricular pathways (Wolff-ParkinsonWhite syndrome) by radiofrequency current. N Engl J Med 1991; 324: 1605-1611. [6] Wu D, Yeh SJ, Wang CC et al. A simple technique for selective radiofrequency ablation of the slow pathway in atrioventricular node re-entrant tachycardia. J Am Co11 Cardiol 1993; 21: 1612-1621. [7] Chen SA, Chiang CE, Yang CJ et al. Radiofrequency catheter ablation of sustained intra-atrial reentrant tachycardia in adult patients. Circulation 1993; 88: 578-587. [8] Klein LS, Shih HT, Hackelt FK et al. Radiofrequency catheter ablation of ventricular tachycardia in patients without structural heart disease. Circulation 1992; 85: 1666-1674. [9] Nakagawa H, Beckman KJ, McClelland JH et al. Radiofrequency catheter ablation of idiopathic left ventricular tachycardia guided by a Purkinje potential. Circulation 1993; 88: 2607-2617. lo] Wen MS, Yeh SJ, Wang CC et al. Radiofrequency ablation therapy in idiopathic left ventricular tachycardia with no obvious structural heart disease. Circulation 1994; 89: 1690-1696. 1l] Yeh SJ, Wang CC, Wen MS et al. Radiofrequency ablation in multiple accessory pathways and the physiologic implications. Am J Cardiol 1993; 71: 1174-1180. 121 Yeh SJ, Wang CC, Wen MS et al. Characteristics and radiofrequency ablation therapy of intermediate septal accessory pathway. Am J Cardiol 1994; 73: 50-56. 131 Wu D, Yeh SJ, Wang CC et al. Nature of dual atrioventricular node pathways and the tachycardia circuit as defined by radiofrequency ablation technique. J Am Co11 Cardiol 1992; 20: 884-895. [14] Wen MS, Yeh SJ, Wang CC et al. Successful radiofrequency ablation in reentrant tachycardia incorporating a nodoventricular tract. Am Heart J 1994; 127: 1413-1419. [15] Wu, Yeh SJ, Wang CC et al. Double loop figure-of-8 reentry as the mechanism of multiple atrioventricular node reentry tachycardias. Am Heart J 1994; 127: 83-95. [16] Gillette PC, Garson A Jr, Porter CJ et al. Junctional automatic ectopic tachycardia: new proposed treatment by transcatheter His bundle ablation. Am Heart J 1983; 106: 619-623. [17] Gillette PC, Wampler DG, Garson A Jr et al. Treatment of atrial automatic tachycardia by ablation procedures. J Am Co11 Cardiol 1985; 6: 405-409. [18] Smith RT, Gillette PC, Massumi A et al. Transcather ablative techniques for treatment of the permanent form of junctional reciprocating tachycardia in young patients. J Am Co11 Cardiol 1986; 8: 385-390. [19] Bromberg BI, Dick M, Scott WA et al. Transcatheter electrical ablation of accessory pathway in children. PACE 1989; 12: 1787-1796. [20] Van Hare GF, Lesh MD, Scheinman M et al. Percutaneous radiofrequency catheter ablation for supraventricular arrhythmias in children. J Am Co11 Cardiol 1991; 17: 16131620.
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[21] Dick M, O’Connor BK, Serwer GA et al. Use of radiofrequency current to ablate accessorypathway connection in children. Circulation 1991; 84: 2318-2324. [22] Case CL, Gillette PC, Oslizlok PC et al. Radiofrequency catheter ablation of incessantmedically resistant supraventricular tachycardia in infants and small children. J Am Co11Cardiol 1992; 20: 1405-1410. [23] Saul JP, Hulse E, De W et al. Catheter ablation of accessoryatrioventticular pathways in young patients: use of long vascular sheaths, the transeptal approach and a retrograde left posterior parallel approach. J Am Co11 Cardiol 1993; 21: 571-583. [24] Van Hare GF, Witherell CL, Lesh MD. Follow-up of radiofrequency catheter ablation in children: Results in 100 consecutive patients. J Am Co11Cardiol 1994; 23: 16511659.
[25] Silka MJ, Kron J, Park JK et al. Atypical forms of supraventricular tachycardia due to atrioventricular node reentry in children after radiofrequency modification of slow pathway conduction. J Am Co11Cardiol 1994; 23: 1363-1369. [26] Kugler JD, Danford DA, Deal BJ et al. Radiofrequency catheter ablation for tachyarrhythmias in children and adolescents.N Engl J Med 1994; 21: 1481-1487. [27] Schhiter M, Kuck KH. Radiofrequencycurrent for catheter ablation of accessory atrioventricular connections in children and adolescents. Emphasis on the single-catheter technique. Pediatrics 1992; 89: 930-935.