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Background Although radiofrequency catheter ablation has been used extensively to treat refractory supraventricular tachycardia in adults, few data are available on its safety and efficacy in children and adolescents. We reviewed registry data obtained from 24 centers to evaluate the indications, early results, complications, and short-term follow-up data in young patients who underwent this procedure.
Methods Standardized data were submitted for 652 patients who underwent 725 procedures between January 1, 1991, and September 1, 1992. The mean length of follow-up was 13.5 months.
Results The median age of the patients was 13.5 years, and 84 percent of them had structurally normal hearts. The initial success rates for ablation of atrioventricular accessory pathways (508 of 615 procedures) and atrioventricular-node reentry (63 of 76 procedures) were both 83 percent. Greater institutional experience in performing ablation in children and location of the accessory pathway in the left free wall correlated with greater likelihood of sustained success. Conversely, a right free-wall pathway, the presence of other heart disease, and higher body weight were all associated with a lesser chance of sustained success. Recurrences of arrhythmia accounted for 45 percent of the failures overall in the series. Atrial ectopic-focus tachycardia had the highest recurrence rate. The total complication rate was 4.8 percent (35 of 725 procedures), and the only variables that independently correlated with a higher complication rate were very low weight and less institutional experience.
Conclusions These early results suggest that radiofrequency catheter ablation has a good success rate and a low complication rate in pediatric patients, especially when it is carried out in experienced pediatric cardiology centers.
Only a small number of children and adolescents were included in the reports of large series of adult patients, and only a few single-center reports have focused on pediatric patients8,9,10,11,12,13. Accordingly, the Pediatric Radiofrequency Ablation Registry was established in November 1990 by the Pediatric Electrophysiology Society to gather data on the use of this procedure in this population. We summarize the initial findings from the registry regarding the safety and efficacy of radiofrequency catheter ablation in children and adolescents and report the results of short-term follow-up of a large cohort.
Methods
Patients and Procedures
Twenty-four centers (see the Appendix) contributed data on 652 patients who underwent 725 procedures involving radiofrequency catheter ablation (69 patients underwent 2 procedures each, and 2 underwent 3 procedures each) between January 1, 1991, and September 1, 1992. The median number of procedures per center was 13.5 (25th and 75th percentiles, 6 and 32, respectively); 76 percent of the procedures were performed at eight centers.
Criteria for Participation
Any member of the Pediatric Electrophysiology Society could participate in the registry by submitting data on children who had undergone radiofrequency catheter ablation. Although the goal of the registry was to study all such patients treated at each center, no center was excluded because of incomplete participation. After the interval set for data collection, a survey revealed that the registry comprised 97 percent of all pediatric patients who underwent ablation at the participating centers during that time. A follow-up form was completed (May 1993) and submitted (June 1993) once for each patient by each participating center to provide information about late complications (i.e., complications not detected at the time of ablation), recurrences of clinical tachycardia or preexcitation (follow-up cardiac catheterizations were not routinely performed) and the time of recurrence (<4, 4 to 12, or >12 months after ablation), and medications and their effectiveness. At the time of follow-up, data were current for 89 percent of patients in the registry. Patients were registered if 21 years of age or younger, according to the definition of the American Academy of Pediatrics14.
Collection and Analysis of Data
Each registration form recorded the patient's demographic characteristics, the indications for ablation, procedural data (e.g., fluoroscopy time), the results of treatment (success or failure), and complications. After the forms were returned to the coordinating center (University of Nebraska Medical Center), the data were entered by means of a relational-data-base program.
Univariate and multivariate analyses were performed with the Statistical Analysis System (SAS Institute, Cary, N.C.) to identify variables associated with three measures of outcome: the result of ablation (presence of tachycardia or preexcitation, vs. its absence), fluoroscopy time, and complications (absence vs. presence).
Outcome was evaluated in relation to the following variables: age, very young age ( 
3 years), weight, extremes of body weight ( 15 and 
80 kg), presence of heart disease, number of ablation procedures previously performed in children at the institution, and location of the accessory pathway (defined below) or the mechanism of tachyarrhythmia (e.g., atrioventricular-node reentry or atrial ectopic-focus tachycardia).
Categorical variables were analyzed for their univariate relation to outcome by means of the chi-square test. Each continuous variable was tested by generating a regression model to predict outcome, with only one continuous variable being incorporated at a time. All variables with at least a fair correlation with outcome on univariate analysis (P<0.10) were entered into a multivariate analysis. They were added to the model by forward-selection logistic regression (for dichotomous outcome measures, early success, and complications) or stepwise multiple linear regression (for fluoroscopy time) until the model showed no statistically significant improvement (alpha = 0.05). Patients for whom data on risk factors or outcome were incomplete were excluded from the multivariate analyses; thus, the results of treatment and complications in 96 percent of the patients were analyzed, and the data on fluoroscopy time in 85 percent.
Life-table analysis using the Kaplan-Meier method was applied to estimate the probability of freedom from tachycardia or preexcitation (or both) as a function of the time elapsed since ablation. Data on patients lost to follow-up were censored at the midpoint of the interval during which follow-up data became unavailable. Recurrences of tachycardia or preexcitation were counted from the midpoint of the interval during which the recurrence was noted. The "midpoint" of a follow-up interval of more than 12 months was estimated as the mean duration of follow-up in patients followed for more than 12 months. Patients not followed for more than 12 months who had undergone ablation more than 24 months previously were considered lost to follow-up during the time after the 12-month interval. The analysis was stratified according to the categorical variables evaluated for their relation to other outcome measures and according to the median number of ablations previously performed in children at the study center (<30 vs. 30). The Kaplan-Meier curves generated for each variable were compared by the Wilcoxon test.
Indications for Ablation
Of the following indications for ablation listed on the registry form, only one was accepted for each procedure: (1) life-threatening symptoms -- tachyarrhythmia associated with syncope, near syncope, seizures, or resuscitation from cardiac arrest; (2) medically refractory tachycardia -- tachyarrhythmia not effectively controlled by one or more antiarrhythmic medications; (3) adverse drug effects -- any problems attributed to the use of one or more antiarrhythmic medications; (4) tachycardia-induced ventricular dysfunction -- ventricular dysfunction associated with incessant tachycardia; (5) impending surgery -- planned cardiac surgery whose risks could be reduced by catheter ablation; and (6) the patient's choice -- an indication accepted only when none of the above indications applied. Although the patient's choice (or the family's choice for young patients) was a practical consideration in virtually all procedures, it was regarded as the indication only when it was the sole reason for ablation. Specific reasons for the choice were not sought or analyzed. Moreover, each of these definitions probably varied from center to center (e.g., what one center defined as medically refractory tachycardia might have been defined as the patient's choice at another center). Therefore, the selection of patients for radiofrequency catheter ablation also probably differed somewhat among centers.
Study Definitions
Atrioventricular Accessory Pathway
To maintain the consistency of the definition of the location of the accessory atrioventricular pathway among the study centers, arbitrary borders were shown on the registry form in a diagram representing the left anterior oblique view of the tricuspid-valve annulus and the mitral-valve annulus. The anatomical sections on the diagram were assigned numbers to facilitate identification of the specific area of ablation. Although this system facilitated data collection and analysis, it might have introduced some anatomical inconsistencies.
Slow and Fast Pathways in Atrioventricular-Node Reentry
Patients with atrioventricular nodal reentry tachycardia underwent ablation of either the "fast" pathway or the "slow" pathway5,6. (Five patients underwent ablation of both pathways after ablation of one pathway was unsuccessful.) The fast pathway was defined as the anterior or superior atrioventricular nodal pathway, whereas the slow pathway was the posterior or inferior atrioventricular nodal pathway5,6.
Treatment Success
Ablation was considered successful if conduction through a pathway (e.g., preexcitation) was abolished, tachyarrhythmia (e.g., atrioventricular-node reentry) could not be induced, or tachyarrhythmia (e.g., ectopic-focus tachycardia) was absent. In patients with two or more pathways or types of tachycardia, success was determined with respect to each pathway or diagnosis. Success was also determined with respect to each diagnosis regardless of complications. For example, if a pathway was successfully ablated but complete atrioventricular block was produced, the pathway was considered successfully ablated but with a complication.
Recurrence
For each patient and for each pathway or type of tachycardia, only documentation of preexcitation, tachycardia, or both was considered to represent a recurrence. Palpitations were not considered to represent recurrences if they were not associated with documented tachyarrhythmia or if they were associated with a tachyarrhythmia different from that identified before ablation.
Complications
Complications were included in this report if they met one or both of the following criteria: the problem required emergency or ongoing treatment or follow-up; or residual effects interfered with normal function.
Results
Characteristics of the Patients
Patients ranged in age from 20 days to 20.9 years at the time of ablation (median, 13.5 years; mean, 12.4); their distribution according to age is shown in Figure 1. Their weight ranged from 3.2 to 124 kg (median, 50).
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Indications
Thirty-nine percent of the patients underwent ablation for medically refractory tachycardia, 30 percent by choice, 13 percent for life-threatening symptoms, 6 percent for adverse drug effects, 5 percent for tachycardia-induced ventricular dysfunction, 5 percent for unknown reasons, and 2 percent because of impending surgery.
Fluoroscopy Time
Multivariate analysis revealed four factors independently associated with fluoroscopy time. Fluoroscopy took longer if the accessory pathway was in the right free wall (
= 18.89; 95 percent confidence interval, 9.91 to 27.87; P<0.001) or body weight was higher ( = 0.17; 95 percent confidence interval, 0.03 to 0.31; P = 0.047). Fluoroscopy was shorter if the number of ablation procedures previously performed at the institution was higher ( = -0.18; 95 percent confidence interval, -0.27 to -0.08; P<0.001) or the mechanism of tachyarrhythmia was atrioventricular-node reentry ( = -15.62; 95 percent confidence interval, -26.76 to -4.48; P = 0.005). (In these and subsequent analyses, negative coefficients represent inverse associations, and positive coefficients, direct associations).
Early Success of Ablation
Five factors were found to be independently associated with early success of ablation. Success rates were lower if heart disease was present ( = -0.68; 95 percent confidence interval, -1.19 to -0.17; P = 0.007) or body weight was 80 kg or more ( = -0.84; 95 percent confidence interval, -1.49 to -0.18; P = 0.011). Success rates were higher if the number of ablation procedures previously performed at the institution was higher ( = 0.014; 95 percent confidence interval, 0.008 to 0.020; P<0.001), the accessory pathway was in the left free wall ( = 1.10; 95 percent confidence interval, 0.62 to 1.59; P<0.001), or the mechanism of tachyarrhythmia was atrial ectopic-focus tachycardia ( = 2.08; 95 percent confidence interval, 0.56 to 3.60; P = 0.006).
Success rates are shown in Table 1 according to the pathway or type of tachycardia.
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Variables associated with success of ablation over time were an accessory pathway in the left free wall and greater institutional experience (Figure 2). Failure over time was associated with a pathway in the right free wall, underlying heart disease, and high body weight. Figure 2 shows the results of 725 procedures over time as a function of pathway location, institutional experience with ablation, heart disease other than tachyarrhythmia, and body weight. Of 603 patients who were free from tachycardia early after the procedure and eligible for follow-up, 39 were lost to follow-up before four months. Of 491 eligible patients without recurrence at 4 months, 32 were lost to follow-up by 12 months. Seven of 431 eligible patients without recurrence were lost to follow-up before 24 months. The mean duration of follow-up was 13.5 months among the patients who remained free of tachycardia or preexcitation. Among the patients with early or late treatment failure, 70 patients required medication for recurrent tachycardia, which was successfully controlled in 57 (81 percent).
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Complications
The complication rate at the time of ablation was 3.7 percent (27 of 725 procedures), and the total rate of complications (including those detected during follow-up) was 4.8 percent (35 procedures) (Table 2). The multivariate analysis showed that body weight of less than 15 kg was an independent risk factor for complications ( = 1.16; 95 percent confidence interval, 0.30 to 2.02; P = 0.007). If the number of ablations previously performed in children at a study center was higher, the rate of complications was lower ( = -0.012; 95 percent confidence interval, -0.024 to 0; P = 0.043). The complication rate among children weighing less than 15 kg was 10 percent.
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Four patients died at different times after ablation. Because of the low number, statistical analysis of the deaths was not carried out. However, observational data are shown in Table 3.
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In this report from a multicenter registry, we have addressed the safety and efficacy of radiofrequency catheter ablation for supraventricular tachyarrhythmias in children and adolescents. The success rate of this procedure among patients with supraventricular tachycardia treated at individual centers has been quite variable, ranging from 50 to 96 percent among children and adolescents8,9,10,11,12,13,15,16,17 to 82 to 99 percent among adults1,2,3,4,5,6. Such studies alone could not establish with certainty the reasons for the differences in reported success rates within each of these two age groups or between them.
Although the extensive experience represented by our registry data allowed better assessment of the results of radiofrequency catheter ablation in the pediatric population, it is difficult to compare our results with those in adult patients because multicenter registry data for the latter have not been reported. Higher reported success rates among adults may reflect several possible influences other than the age and size of the patients. First, the studies in adults were conducted in series of patients from single institutions and thus would be more subject to selection bias than studies of a large registry of patients from many centers. Second, some of the series of adults with higher success rates include disproportionately more patients with left-sided free-wall accessory atrioventricular pathways1,2 and fewer patients with right-sided free-wall pathways1,2. In both the children in our report and the children and adults in reports from individual centers, the chances of initial success were greater among patients with left-sided free-wall accessory atrioventricular pathways and lower among those with right-sided pathways3,4,8,9,16,17. Even with apparent early success, our data and those of others show that right-sided free-wall pathways are prone to the recurrence of preexcitation, tachycardia, or both1,3,6,16,17,18,19. Third, as would be expected in a pediatric population, a relatively high proportion of our patients had underlying heart disease, as compared with most of the series of adult patients2,3,4. Our analysis demonstrated that treatment failure over time was associated with the presence of such disease.
Prolonged exposure to radiation during fluoroscopy is a concern20,21. Both an accessory pathway in the right free wall and higher body weight were associated with longer fluoroscopy time. Technical challenges in mapping and ablation of right free-wall pathways are probably related to the longer fluoroscopy times required.
A higher number of ablation procedures previously performed in children at a study center was associated with a higher success rate, a shorter fluoroscopy time, and a lower complication rate. Although individual centers have reported that their results improved as their studies progressed,3,9 our findings document a learning curve for procedural safety and efficacy that is independent of other confounding variables.
The rate of early complications (3.7 percent) was similar to rates reported in the individual series of adult patients (1.3 to 8 percent)1,2,3,4,5,6 and children (0 to 10 percent)8,9,10,11,12,13,15,16,17. Few reports have included late complications, making it difficult to compare their rates with our total rate (for early and late complications combined, 4.8 percent). These rates are only slightly higher than that of pediatric cardiac catheterization in general22,23.
Late recurrence of tachycardia or preexcitation after apparent initial success has involved all pathway locations and mechanisms of tachycardia. This phenomenon is particularly frequent with respect to atrial ectopic-focus tachycardia, possibly because this type of tachycardia may arise from multiple foci24 and thus present during follow-up as a "recurrence." Our follow-up has not been long enough to permit estimation of the lifetime risk of recurrence; however, the likelihood of recurrence appears to diminish with time.
Deaths were very infrequent, but observational details provide common findings that suggest ways to try to reduce the risks of mortality further. Because three of the four patients who died had noncardiac diseases and two had peripheral thrombosis after catheterization, it appears prudent to evaluate patients carefully for noncardiac diseases and to recommend the use of anticoagulation during and after the procedure.
The main limitation of this study applies to any uncontrolled, voluntary registry25. Because 97 percent of all pediatric patients who underwent radiofrequency ablation at the participating centers were entered into the registry, bias introduced by selective reporting was probably small. However, the results reported here are not necessarily representative of those that might be expected in children treated outside centers with expertise in pediatric electrophysiologic programs. It may be argued that ablation in adolescents has more in common with the procedure in adults than with ablation in younger children, and that the inclusion of adolescents might obscure important conclusions about the procedure in small children and infants. Careful attention to the independent effects of age and body weight on outcome show that patients with very low weight have a higher complication rate, and that very heavy patients have a lower success rate. Otherwise, adolescents do not differ enough from younger children to warrant separate consideration. Because only weights (and not heights) were available for our study, the influence of body-surface area and body-mass index is not known.
Early results suggest that radiofrequency catheter ablation is becoming an acceptable mode of treatment for supraventricular tachycardia in children. The low risk of complications and the high success rate (despite learning curves) demonstrate its safety and efficacy. The fact that 30 percent of the procedures were performed with the patient's choice serving as the indication is evidence of its acceptability to physicians and patients. However, because low weight was an independent risk factor for complications and because three of the four deaths occurred in very small, young patients and all four patients had underlying heart disease, it is prudent to emphasize that the procedure poses a higher risk to patients with these features. Together with data on the natural history of tachyarrhythmias, the maintenance and analysis of long-term follow-up data from the registry should help determine whether or not radiofrequency catheter ablation is the treatment of choice for pediatric patients with certain supraventricular tachyarrhythmias.
We are indebted to Kris Gerken Houston, R.N., B.S.N., M.A., for entering the registry data; to Gary Felix, B.A., for developing and customizing the computer system and assisting in the data analysis; and to Louise Larsen for assistance in preparing the manuscript.
Source Information
From the Section of Pediatric Cardiology, University of Nebraska Medical Center, Omaha (J.D.K., D.A.D.); Children's Memorial Hospital, Chicago (B.J.D.); South Carolina Children's Heart Center, Charleston (P.C.G.); Texas Children's Hospital, Houston (J.C.P.); Oregon Health Sciences University, Portland (M.J.S.); University of California at San Francisco, San Francisco (G.F.V.H.); and Children's Hospital, Boston (E.P.W.). The other members of the Pediatric Electrophysiology Society who participated in this study are listed in the Appendix according to their study centers (Dr. Danford is not a member).
Address reprint requests to Dr. Kugler at the Section of Pediatric Cardiology, University of Nebraska Medical Center, 600 S. 42nd St., Omaha NE 68198-2166.
References
The following members of the Pediatric Electrophysiology Society participated in this study. Arkansas Children's Hospital, Little Rock -- C. Erickson; Atlanta Children's Heart Center, Atlanta -- R. Campbell and J.E. Hulse; Children's Hospital, Boston -- J.P. Saul; Children's Hospital of the King's Daughters, Norfolk, Va., -- B. Ross; Children's Memorial Hospital, Chicago -- D.W. Benson, Jr.; Cleveland Clinic Foundation, Cleveland -- R. Sterba; Columbia University Babies Hospital, New York -- A.J. Hordoff; Denver Children's Hospital, Denver -- M.S. Schaffer; Duke University Medical Center, Durham, N.C. -- R.J. Kanter; University of Florida College of Medicine, Gainesville -- M. Epstein; Geisinger Medical Center, Danville, Pa. -- M. Cohen; Georgetown University Hospital, Washington, D.C. -- K. Kuehl and S. Beder; University of Iowa, Iowa City -- D. Atkins; Loma Linda University Medical Center, Loma Linda, Calif. -- J. McCormack; Long Island Jewish Medical Center/Schneider Children's Hospital, New Hyde Park, N.Y. -- C. Kurer; University of Miami School of Medicine, Miami -- G. Wolff and M.-L. Young; South Carolina Children's Heart Center, Charleston -- C. Case; St. Louis Children's Hospital, St. Louis -- B. Bromberg; Texas Children's Hospital, Houston -- R. Friedman; Toronto Hospital for Sick Children, Toronto -- R. Hamilton and R. Gow; and Vanderbilt University, Nashville -- F. Fish.
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