Paroxysmal supraventricular tachycardia incidence is approximately 1–3 cases per 1000 persons. The incidence rate of the WPW pattern on ECG tracings is 0.1–0.3% in the general population, although not all patients develop SVT . In a population-based study, the prevalence of paroxysmal supraventricular tachycardia was 2.25 cases per 1000 persons, with an incidence of 35 cases per 100,000 person-years . AVNRT is more common in patients who are of middle age or older, while adolescents are more likely to have SVT mediated by an accessory pathway. Paroxysmal supraventricular tachycardia is not only observed in healthy individuals, it is also common in patients with previous myocardial infarction, mitral valve prolapse, rheumatic heart disease, pericarditis, pneumonia, chronic lung disease, and current alcohol intoxication. Digoxin toxicity also may be associated with paroxysmal supraventricular tachycardia .
Radiofrequency (RF) catheter ablation is a well established approach in treating several types of cardiac arrhythmias whether supraventricular or ventricular and is in many cases the first choice therapy. Radiofrequency ablation has been shown to be effective and safe with a success rates ranging from 80% to 100% in patients with atrial flutter and exceeding 90–95% in patients with atrioventricular nodal re-entrant tachycardia (AVNRT) or atrioventricular re-entrant tachycardia (AVRT) due to accessory pathways [4,5].
The incidence of procedural complications ranges from 25% to 6% in different cases series [6–8].
Despite such encouraging data, the interventional approach in treating cardiac arrhythmia has not been widely adopted in elderly people, even though it may be particularly useful in this kind of patient, in whom antiarrhythmic drugs are often poorly tolerated .
Indeed, the age related structural modification of the heart; the higher prevalence of structural heart disease and the higher thromboembolic risk are believed to increase of procedural complications in the elderly patients in comparison with young adults .
Furthermore, few studies had investigated the efficacy and safety of catheter ablation in elderly patients and pediatrics patients [11,12].
Aim of this study
This study is prospective evaluation of the safety and efficacy of radiofrequency ablation of regular narrow complex supraventricular tachycardia in both age extremes, elderly and pediatric patients.
The study included 30 patients, 19 patients >60 years [group I] and 11 pediatric patients <14 years [group II], referred to National Heart Institute and Critical Care Department at Kasre AL-Ainy Cairo University hospital from October 2008 to October 2009 who underwent electrophysiology study and radiofrequency catheter ablation to variable indications. The inclusion criteria were: life-threatening symptomatic supraventricular tachyarrhythmia, medically refractory tachycardia, adverse drug effects, impending surgery, and the patient's choice.
All patients included in the study were subjected to the following
- Full history taking with special emphasis on the history of dysrrhythmias.
- Full clinical examination.
- 12 – leads resting ECG.
- Twenty-four hour – dynamic ECG monitoring [Holter] to document the presence of dysrrhythmias.
- Transthoracic echocardiography [TTE] for assessment of the cardiac dimensions, evaluation of the presence of any anatomical abnormalities and assessment of LV systolic and diastolic function.
- Routine laboratory investigations including complete blood picture, liver and kidney function tests, lipid profile, thyroid function tests and hepatitis markers.
- Radiofrequency catheter ablation:
- Patients were brought to the electrophysiology laboratory in the post – absorptive state and always off antiarrhythmic drugs for five half lifes.
- In all cases, 6 French quadpolar catheters were inserted through right and left femoral veins and positioned in the his bundle region and the right ventricular apex.
- A 6 French quadpolar catheter was then inserted through the left subclavian vein and positioned in the coronary sinus.
- In the atrial flutter ablation procedure, a 7 French Halo catheter was inserted through the left femoral vein and positioned in the right atrium.
- Detailed electrophysiological evaluation using standard recording by general electric-PRUCA engineering and simulation techniques by Micropace, EPS 320, cardiac stimulator (Cordis) was performed to confirm diagnosis and to identify the target site for radiofrequency delivery.
- Radiofrequency energy was applied through a 7-french 4-mm tip catheter in procedures for AVNRT, AVRT and AT and through a 7-french 8-mm tip catheter in cases of atrial flutter.
- The ablating catheter was inserted through the right femoral vein in procedures for AVNRT, right accessory pathways and AT.
- The patients with left accessory pathways, the ablating catheter was inserted through the right femoral artery, atrial septal puncture and left atrial approach was used in case of retrograde approach failure.
- Radiofrequency energy was applied by using an RF current generator for a time ranging from 30 to 120 s, with a maximum tip temperature of 60–65 °C and a power output of 50 W, ablator: ST 1642 – EP – Shuttle-Stockert (Cordis).
Clinical characteristics: group I had a significantly higher prevalence of cardiovascular and non-cardiovascular comorbid conditions (P < 0.05) Table 1, Figs. 1 and 2.
Table 2 showed that the most commonly used drug therapy was calcium channel blockers then beta blockers. The incidence of the use of Cordarone, B-blockers and aspirin were significantly higher among group I than that of group II (P < 0.05).
The mean tachycardia duration were significantly higher in group I than that of group II (P < 0.001).
Frequency of dysrrhythmia per year in the two groups
There was no significant different as regards frequency of dysrrhythmia of both groups (Table 3) and (Fig. 3)
Table 4 show that the AVRT is more frequent in higher age group; however the AVNRT is almost equally distributed in both age group.
Table 5 show that: slow pathway ablation was the only site for AVNRT ablation in both groups but the left lateral accessory pathway was the target of ablation in most AVRT patients in both groups, and only two patients in group 1 need antiarrhythmics for non-specific atrial tachycardia after ablation.
Fluoroscopy time was more prolonged in group I and ablation duration was longer also in group I (with significant P value): Table 6, Figs. 4 and 5.
No complications recorded in group I and in group II apart from complete heart block in 1 patient that required permanent pacemaker insertion (Table 7).
No recurrence rate recorded in group II at 1 or 6 months follow- up period in group II while in group I the recurrence occurred in 2 patients at 6 months follow up (10.53%) (Table 8).
The following Figs. 6–8 show intracardiac tracing for patients with AVRT and AVNRT during radiofrequency ablation.
Accessory pathway mediated tachycardias constitute 80% of all the tachyarrhythmias during infancy. In some infants, some tachycardias they resolve as the child grows. Most SVTs beyond the age of 5 tend to recur and may need to undergo RF ablation. Ectopic atrial tachycardia and atrial flutter represent 10–15% of SVTs in infancy, of which some may not ever recur .
Radiofrequency ablation is uncommonly performed under 5 years of age. This is because some SVTs resolve spontaneously. Also, arrhythmias may get suppressed under the influence of anesthesia at the time of RF ablation. Patient size poses limitations in using multiple electrode catheters and there is an increased possibility of cardiac/valve damage with ablation. The risks of ablation are acceptable only if the child has recurrent, drug-resistant SVT especially if it results in tachycardiomyopathy or life-threatening cardiovascular compromise .
Cardiac arrhythmias are relatively uncommon in the younger population, accounting for approximately 5% of all emergency cardiac admissions. Paroxysmal supraventricular tachycardia (SVT) like atrio-ventricular reciprocating tachycardia (AVRT), ectopic atrial tachycardia, and atrio-ventricular nodal reentrant tachycardia are the most common. In those patients who have undergone operations for congenital heart disease, junctional ectopic tachycardia and atrial flutter are more common. Symptoms of arrhythmias depend on the age, presence of structural heart disease, and the state of the left ventricular function apart from the nature, severity, and duration of arrhythmia .
Atrioventricular nodal re-entry is the most common cause of regular narrow complex SVT. In our study, 70% of SVT are due to atrioventricular nodal re-entry. If AVNRT are less frequent and responsive to therapy with beta blocker or calcium channel blocker, then RFA can be deferred .
Supraventricular tachycardias are the most frequent forms of symptomatic tachyarrhythmias in infants, children and adolescents. Clinical symptoms depend on age and underlying cardiac anatomy. Newborn babies and infants with paroxysmal atrioventricular reentrant tachycardias usually present with signs of congestive heart failure due to rapid heart rate .
Failure to discriminate among AF, atrial flutter, and othersupraventricular arrhythmias has complicated the precise definition of this arrhythmia in the general population. The estimated prevalence of paroxysmal supraventricular tachycardia (PSVT) in a 3.5% sample of medical records in the Marshfield (Wisconsin) Epidemiologic Study Area (MESA) was 2.25 per 1000. The incidence of PSVT in this survey was 35 per 100 000 person-years .
In our study, we conducted a prospective clinical trial in the National Heart Institute and critical care department at Kasr Al-Ainy Cairo University hospital in order to evaluate the safety and the efficacy of radiofrequency ablation in both age extremes, elderly and pediatric patients.
Our study included 30 patients; 19 patients >60 years of age (group I) and 11 pediatric patients (group II).
Group I included 19 patients, their age ranged between 61 and 71 years with a mean age of 67.5 ± 5.1 years, they were 9 males (47.4%) and 10 females (52.6%) while in group II, their mean age was 12.5 ± 3.5 years and they were 6 males (54.5%) and 5 females (45.6%). There was no significant difference between the 2 groups regarding their sex distribution (P > 0.05). The heart rate was significantly higher among group II than that of group I but the systolic and diastolic blood pressure was significantly higher among group II than that of group I (P < 0.05).
Results of the current study showed that group I had a significantly higher prevalence of cardiovascular and non-cardiovascular comorbid conditions (P < 0.05).
Results of the current study showed the most commonly used drug therapy was calcium channel blockers then beta blockers. The incidence of the use of Cordarone, B-blockers and aspirin were significantly higher among group I than that of group II (P < 0.05).
Results of the current study showed the mean tachycardia duration were significantly higher than in group I than that of group II (P < 0.001).
Results of our study showed that no complications recorded in group I and in group II the only recorded complication was complete heart block in 1 patient that required permanent pacemaker insertion.
In our study there was no recurrence rate recorded in group II at 1 and 6 months follow up in group II, while in group I the recurrence occurred in 2 patients at 6 months follow up (10.53%).
However in patients with frequent episodes or hemodynamic intolerance or those who refuse prolonged medication, RFA is a safe and cost effective treatment modality. The success rate is more than 96% and the risk of damaging the compact AV node is <1% and the recurrence rate is also <3% . But in our study may be explained by small number of patients and the recurrence rate in AVNRT has been very low because it had been part of our protocol to look for slow junctional rhythm during RFA and to insure with isoproteronol the tachycardia could no longer be reinduced once RFA had been done. The presence of a junctional rhythm during slow-pathway ablation has been indisputably considered to be the most sensitive but non-specific marker of successful ablation.
In our study we found that RF ablation was safe in children with a very high success rate and very low complication rate and these results are not in agreement with Hsieh et al.  who stated that children were not considered for radiofrequency ablation because is not very safe in this age and cryo-ablation is a preferable option for AVNRT.
Our results are different from the study of Shuenn-Nan et al.  who studied 27 patients (17 males, 10 females) underwent RFA at an age less than 6 years. All of his patients had drug-refractory SVT or tachycardia-induced cardiomyopathy. They found that immediate success rate was 92.6%, with low early (3.7%) and late recurrence (7.4%) after 5.4 ± 3.7 years follow-up. Tachycardia-induced cardiomyopathy was noted in 4 and resolved in all after RFA. Procedure-related complications included complete atrioventricular block in 1. No other risk factors for outcomes were noted, even with low body weight. He concluded that the outcome of RFA for medically refractory SVT, even associated with tachycardia-induced cardiomyopathy, in infants is favorable . The higher recurrence rate and lower success rate in their study may be because they included younger patients and longer follow up period.
Results of our study showed that RF ablation of young children was a good and safe way of management of patients with SVT and these results agreed with that reported by Van Hare,  who stated that long-term management of AVRT in infancy and childhood is age dependent. In newborn babies and infants, pharmacological therapy is advised due to the high spontaneous cessation rate of those tachycardias at the end of the first year of life. In contrast to this, the probability of spontaneous cessation of tachycardia in children >1 year of age is very low. Therefore, radiofrequency catheter ablation of the anatomical substrate of the tachycardia is a rational alternative to long-lasting antiarrhythmic therapy.
Our results are also in agreement with the study of Aiyagari et al. 2005  who found that RFA in children with a structurally normal heart are comparable to those achieved in adults.
Paul et al.  supported our conclusion in that pharmacological therapy is often not sufficient to control the tachycardia. In addition, underlying sinus node dysfunction may be aggravated in a considerable portion of the patients affected.
Also Baine et el.  supported our conclusion as supraventricular arrhythmias are relatively common, often repetitive, occasionally persistent, and rarely life threatening. The precipitants of supraventricular arrhythmias vary with age, sex, and associated comorbidity .
Age exerts an influence on the occurrence of SVT. The mean agent the time of PSVT onset in the MESA (Multi Ethnic Study of Atherosclerosis) cohort was 57 years (ranging from infancy to more than 90 years old) . In the MESA population, compared with those with other cardiovascular disease, “lone” (no cardiac structural disease) PSVT patients were younger (mean age equals 37 versus 69 years), had faster heart rates (186 versus 155 beats per minute [bpm]), and were more likely to present first to an emergency room (69% versus 30%). The age of tachycardia onset is higher for AVNRT (32 plus or minus 18 years) than for AVRT (23 plus or minus 14 years) .
Gender plays a role in the epidemiology of SVT. Female residents in the MESA population had a two-fold greater relative risk (RR) of PSVT (RR equals 2.0; 95% confidence interval equals 1.0–4.2) compared with males .
In our study we targeted the slow pathway along the posterolateral region of the tricuspid annulus which yielded a high success rate and a low complication rate (only one patient had complete heart block, and our results are in agreement with that reported by Fuster et al.  who mentioned that targeting the slow pathway along the posteroseptal region of the tricuspid annulus markedly reduces the risk of heart block and is the preferable approach. Advantages of slow-pathway ablation include a lower incidence of complete AV block (1% versus 8%) and the absence of the hemodynamic consequences of marked prolongation of the PR interval. Hence, slow pathway ablation is always used initially and fast pathway ablation is considered only when slow pathway ablation fails.
Our results are also in agreement with the NASPE prospective catheter ablation registry which included 1197 patients who underwent AV-nodal modification for AVNRT. Success was achieved in 96.1%, and the only significant complication was a 1% incidence of second-degree or third-degree AV block . These data have been confirmed by Clague et al. . Atrioventricular block may complicate slow-pathway ablation caused by posterior displacement of the fast pathway, superior displacement of the slow pathway (and coronary sinus), or inadvertent anterior displacement of the catheter during RF application. Pre-existing first-degree AV block does not appear to increase appreciably the risk of developing complete AV block, although caution is advised. The recurrence rate after ablation is approximately 3–7% .
Ablation of the slow pathway may be performed in patients with documented SVT (which is morphologically consistent with AVNRT) but in whom only dual AV-nodal physiology (but not tachycardia) is demonstrated during electrophysiological study .
Slow-pathway ablation may be considered at the discretion of the physician when sustained (more than 30 s) AVNRT is induced incidentally during an ablation procedure directed at a different clinical tachycardia .
Indications for ablation depend on clinical judgment and patient preference. Factors that contribute to the therapeutic decision include the frequency and duration of tachycardia, tolerance of symptoms, effectiveness and tolerance of antiarrhythmic drugs, the need for lifelong drug therapy, and the presence of concomitant structural heart disease. Catheter ablation has become the preferred therapy, over long-term pharmacologic therapy, for management of patients with AVNRT. The decision to ablate or proceed with drug therapy as initial therapy is, however, often patient specific, related to lifestyle issues (e.g., planned pregnancy, competitive athlete, recreational pilot), affected by individual inclinations or aversions with regard to an invasive procedure or the chronicity of drug therapy, and influenced by the availability of an experienced center for ablation. Because drug efficacy is in the range of 30–50%, catheter ablation may be offered as first-line therapy for patients with frequent episodes of tachycardia. Patients considering RF ablation must be willing to accept the risk of AV block and pacemaker implantation .
Catheter ablation of accessory pathways is performed in conjunction with a diagnostic electrophysiological test. The purposes of the electrophysiological test are to confirm the presence of an accessory pathway, determine its conduction characteristics, and define its role in the patient's clinical arrhythmia. Once the arrhythmia is identified, ablation is performed using a steerable ablation catheter. There have been no prospective, randomized clinical trials that have evaluated the safety and efficacy of catheter ablation of accessory pathways versus pharmacological treatment, however, the results of catheter ablation of accessory pathways have been reported in a large number of single-center trials, one multicenter trial  and several prospective registries . The initial efficacy of catheter ablation of accessory pathways is approximately 95% in most series . The success rate for catheter ablation of left free-wall accessory pathways is slightly higher than for catheter ablation of accessory pathways in other locations. After an initially successful procedure, resolution of the inflammation or edema associated with the initial injury allows recurrence of accessory pathway conduction in approximately 5% of patients. Accessory pathways that recur can usually be successfully ablated during a second session .
Complications associated with catheter ablation of accessory pathways result from radiation exposure, vascular access (e.g., hematomas, deep venous thrombosis, arterial perforation, arteriovenous fistula, pneumothorax), catheter manipulation (e.g., valvular damage, microemboli, perforation of the coronary sinus or myocardial wall, coronary artery dissection, thrombosis), or delivery of RF energy (e.g., AV block, myocardial perforation, coronary artery spasm or occlusion, transient ischemic attacks, or cerebrovascular accidents). The procedure-related mortality reported for catheter ablation of accessory pathways ranges from 0% to 0.2% . The voluntary Multicenter European Radiofrequency Survey (MERFS) reported data from 2222 patients who underwent catheter ablation of an accessory pathway. The overall complication rate was 4.4%, including 3 deaths (0.13%). The 1995 NASPE survey of 5427 patients who underwent catheter ablations of an accessory pathway reported a total of 99 (1.82%) significant complications, including 4 procedure-related deaths (0.08%). Among the 500 patients who underwent catheter ablation of an accessory pathway as part of a prospective, multicenter clinical trial, there was 1 death (0.2%). This patient died of dissection of the left main coronary artery during an attempt at catheter ablation of a left free-wall accessory pathway .
The most common major complications are complete AV block and cardiac tamponade. The incidence of in advertent complete AV block ranges from 0.17% to 1.0%. Most occur in the setting of attempted ablation of septal accessory pathways located close to the AV junction. The frequency of cardiac tamponade varies between 0.13% and 1.1%.
The higher incidence of complications in the previously mentioned study could be explained by that, they included a larger number of patients and at longer duration of the study as well as the bigger number of operators.
Catheter ablation of supraventricular tachycardia is a very good option for management of patients with drug resistant SVT in both young and old patients.
The success rate was very high almost with no complications and very low recurrence rate in the elderly and no recurrence in the young during the 6 months follow-up.
Older patients had more comorbid conditions with longer duration of ablation and higher energy frequency as well as more fluoroscopic time.
 Trohman Richard G. Supraventricular tachycardia
implications for the intensivist. Crit Care Med 2000;28(10):129 [N 135].
 Orejarena LA, Vidaillet Jr H, De Stefano F, et al. Paroxysmal supraventricular tachycardia
in the general population. J Am Coll Cardiol 1998;31(1):150-157.
 Josephson ME. Clinical cardiac electrophysiology: techniques and interpretations. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2002.
 Maggi R, Quartieri F, Donateo P, Bottoni N, Solano A, Lolli G, et al. Seven-year follow-up after catheter ablation of atrioventricular nodal re-entrant tachycardia. J Cardiovasc Med 2006;7:39-44.
 Bohnen Marius, Stevenson William G, Tedrow Usha B, Michaud Gregory F, John Roy M, Epstein Laurence M. Increase and predictors of major complications from catheter ablation to treat. Heart Rhythm 2011;8:1661-1666.
 Jackman WM, Beckman KJ, Mc Clelland JH, et al. Treatment of supraventricular tachycardia
due to atrioventricular nodal reentry by radiofrequency catheter ablation of slow-pathway conduction. N Engl J Med 1992;327(5):313-318.
 Chen SH, Chiang CE, Tai CT, Cheng CC, Chiou CW, Lee SM, et al. Complication of diagnostic electrophysiologic studies and radiofrequency catheter ablation in patients with tachyarrhythmia. Am J Cardiol 1996;77:41-46.
 Cappato R, Calkins H, Chen SH, Davies W, Lesaka Y, Kalman J, et al. Worldwide survey on the methods, efficacy and safety of catheter ablation for human. Ciculation 2005;111:1100-1105.
 Oral H, Chugh A, Ozadyin M, Good E, Fortino J, Sankaran S, et al. Risk of throboembolic events after percutanous left atrial radiofrequency ablation
. Circulation 2006;114:759-765.
 Epstein LM, Chiesa N, Wong NM, Lee RJ, Griffin JC, Scheinman MM, et al. Radiofrequency catheter ablation in the treatment of supraventricular tachycardia
in the elderly. J Am Coll Cardiol 1994;23:1356-1362.
 Zado E, Callans D, Gottlieb CD, Kutalek SP, Wilbur SL, Samuels FL, et al. Efficacy and safety of catheter ablation in octogenarians. J Am Coll Cardiol 2000;35:458-462.
 Rostock T, Risius T, Ventura R, Klemm HU, Weiss C, Keitel A, et al. Efficacy and safety of radiofrequency ablation
of atrioventricular nodal re-entrant tachycardia in the elderly. J Cardiovasc Electrophysiol 2005;16:608-610.
 Perry James C, Arthur Garson JR. Supraventricular tachycardia
due to wolff - Parkinson - white syndrome in children: early disappearance and late white syndrome in children: early disappearance and late recurrence. J Am Coll Cardiol 1990;16(5):1215-1220.
 Lee Change, Hwang Betau, Chen Shih-Ann. The results of radiofrequency catheter ablation of supraventricular tachycardia
in children - pacing and clinical electrophysiology 2007;30(5):655-661.
 Vora Amit, Lokhandwala Yash, Sheth Chirag, Dalvi Bharat. Radiofrequency ablation
in an infant with recurrent supraventricular tachycardia
and cyanosis. Am J Cardiol 2009;2(2):156-158.
 Jentzer JH, Goyal R, Williamson BD, et al. Analysis of junctional ectopy during radiofrequency ablation
of the slow pathway in patients with atrioventricular nodal reentrant tachycardia. Circulation 1994;90(6):2820-2826.
 Paul T, Guccione P, Garson Jr A. Relation of syncope in young patients with Wolff-Parkinson-White syndrome to rapid ventricular response during atrial fibrillation. Am J Cardiol 1990;65(5):318-321.
 Fuster V, Ryden LE, Asinger RW, et al. ACC/AHA/ESC guidelines for the management of patients with atrial fibrillation: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines and Policy Conferences (Committee to Develop Guidelines for the Management of patients with atrial fibrillation) developed in collaboration with the North American Society of pacing and electrophysiology. Circulation 2001;104:2118-2150.
 Kimman GP, Theuns DAMJ, Szili T, Torok MF, Scholter JC, Res LJ, Jordaens CRAVT. A prospective, randomized study comparing transvenous cryothermal and radiofrequency ablation
in atrioventricular nodal re-entrant tachycardia. Eur Soc Cardiol 2004; http://dx.doi.org/10.1016/J.ehj
 Hsieh MH, Chen SA. Catheter ablats of focal. In: Zipes AT, Haissaguerre DP, editors. Catheter ablats of arrhythmia 2002. Armonk, NY: Futura publishing Co. Inc.; 2004. p. 185-204.
 Shuenn Nan Chiu, Chih Wei Lu, Chi Wei Chang, Ming Tailin, Jou Kou Wan, Mei Hwan Wu. Radiofrequency catheter ablation of supraventricular tachycardia
in infants and toddlers. Circul J Official J Jap Circul Soc 2009;73(9):1717.
 Van Hare GF. Indications for radiofrequency ablation
in the pediatric population. J Cardiovasc Electrophysiol 1997;8:952-962.
 Aiyagari R, Saarel EV, Etheridge SD, Fischbach PS. Radiofrequency ablation
for supraventricular tachycardia
in children ≤15 kg is safe and effective. J Pediatric Cardiol 2005;26(5):622-626.
 Baine WB, Yu W, Weis KA. Trends and outcomes in the hospitalization of older Americans for cardiac conduction disorders or arrhythmias, 1991-1998. J Am Geriatr Soc 2001;49(6):763-770.
 Scheinman MM, Huang S. The NASPE prospective catheter ablation registry. Pacing Clin Electrophysiol 1998;2000(23):1020-1028.
 Clague JR, Dagres N, Kottkamp H, Breithardt G, Borggrefe M. Targeting the slow pathway for atrioventricular nodal reentrant tachyardial initial results and long-term follow-up in 379 consecutive patients. Eur Heart J 2001;22(1):82-88, doi: 10.1053.
 Calkins H, Yong 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(2):262-270.