Catheter Ablation of Accessory Pathways, Atrioventricular Nodal Reentrant Tachycardia, and the Atrioventricular Junction
Final Results of a Prospective, Multicenter Clinical Trial
Background—The purpose of this study was to evaluate the safety and efficacy of a temperature-controlled radiofrequency catheter ablation system.
Methods and Results—The patient population included 1050 patients who had undergone ablation of atrioventricular nodal reentrant tachycardia (AVNRT), an accessory pathway (AP), or the atrioventricular junction (AVJ). Ablation was successful in 996 patients. The probability of success was highest among patients who had undergone ablation of the AVJ, lowest in patients who had undergone ablation of an AP, and in between for patients who had undergone ablation of AVNRT. A major complication occurred in 32 patients. Four variables predicted ablation success (AVJ, AVNRT, or left free wall AP ablation and an experienced center). Four factors predicted arrhythmia recurrence (right free wall, posteroseptal, septal, and multiple APs). Two variables predicted development of a complication (structural heart disease and the presence of multiple targets), and 3 variables predicted an increased risk of death (heart disease, lower ejection fraction, and AVJ ablation).
Conclusions—These findings may serve as a guide to clinicians considering therapeutic options in patients who are candidates for ablation.
Since its introduction in the early 1990s, a number of studies have reported the results of radiofrequency (RF) catheter ablation in the treatment of atrioventricular nodal reentrant tachycardia (AVNRT)1 2 3 4 5 6 7 8 and arrhythmias that involve accessory atrioventricular connections (accessory pathways, AP),8 9 10 11 12 13 14 15 16 17 and ablation of the atrioventricular junction (AVJ).18 19 20 The favorable results of these studies have fueled enthusiasm for catheter ablation, with the number of ablation procedures increasing from 500 procedures per year in 1991 to >15 000 in 1993.21 22 However, limitations of those studies include the fact that data often were not collected in a prospective standardized fashion, relatively small numbers of patients were involved, and the data represented the experience of single institutions. The purpose of the present prospective multicenter study was to evaluate the safety and efficacy of an RF catheter ablation system in a large, consecutively screened patient population.
The patient population included 1050 patients who participated in the Atakr Ablation System (Medtronic CardioRhythm) clinical trial and had undergone catheter ablation of AVNRT, an AP, or the AVJ at 1 of 18 institutions between 1992 and 1995.23 A total of 1136 ablation procedures were performed.
Patient Evaluation, Electrophysiology Testing, and Catheter Ablation
Before the ablation procedure, each patient gave informed consent. A history and physical examination, ECG, and echocardiogram were also obtained. Catheter ablation of AVNRT was performed with the posterior approach. An initial attempt at catheter ablation was made with the investigational ablation system (RF Ablatr or RF Marinr, Medtronic CardioRhythm) as previously reported.23 If successful ablation was not achieved, an alternate system could be used. Pacemaker implantation was performed in all patients who had undergone successful ablation of the AVJ. The programmed pacing rate after the procedure was at the discretion of the physician.
Each patient was evaluated 1, 3, 6, 12, and 24 months after ablation. Patients who experienced palpitations underwent transtelephonic monitoring. Of the 776 patients enrolled in this study who underwent successful ablation of AVNRT or an AP with the investigational ablation system, 457 (59%) underwent a follow-up electrophysiological study a mean of 2.5±0.9 months after ablation. The median duration of follow-up was 6.3 months.
There were 5 predetermined outcomes: ablation success, development of major complications, development of new echocardiographic abnormalities, arrhythmia recurrence, and death. Catheter ablation procedures were classified at the completion of the procedure as acutely successful or unsuccessful on the basis of whether all ablation targets had been successfully eliminated.
Complications were classified as major or minor. Major complications were defined as those that resulted in permanent injury or death, required an intervention for treatment, or prolonged the duration of hospitalization. An asymptomatic increase in the degree of valvular regurgitation by 2 or more echocardiographic grades (ie, mild to severe) was also classified as a major complication. Paired echocardiograms (before and after the procedure) were requested as part of the clinical protocol in all patients and were available for analysis in 972 patients (93%).Differences in the echocardiograms were classified as demonstrating a major change if a thrombus, new wall-motion abnormality, ≥15% change in estimated ejection fraction, an increase in valvular regurgitation by ≥2 grades, or the presence of a pericardial effusion was detected. A minor change in the findings on echocardiography was determined to be present if there was a 5% to 15% change in the estimated ejection fraction or if a 1-grade increase in valvular regurgitation was observed.
With the use of long-term follow-up data, patients were further classified as having a recurrence or not and as dead or alive. Analysis of arrhythmia recurrence was confined to the 887 patients in whom successful ablation was achieved with the investigational ablation system.
All tests were 2-sided, and P values <0.05 were considered significant. Regression models were used to identify variables associated with the acute result of the ablation procedure and the development of major complications (as defined above). Variables that were evaluated as potential predictors of outcome are shown in Table 1⇓. Repeated analyses were also performed with the ablation centers grouped as high- or low-volume centers on the basis of whether ≥40 patients had been enrolled in the protocol, and also with the centers classified either as predominantly a pediatric center or predominantly an adult center. Each variable was tested by generation of a logistic regression model to predict outcome, with only 1 variable being incorporated at a time. Variables were jointly assessed for predictive power with a forward-selection multivariate, stepwise logistic regression model.
Recurrence survival rates were estimated with the Kaplan-Meier method. Cox proportional hazards models were used to assess which factors were associated with the risk of recurrence and the risk of death.
The patient population consisted of 489 males and 561 females ranging in age from 8 months to 90 years (mean age, 37±18 years). Among the entire group, 133 (13%) were <13 years of age, and 193 (18%) were between 13 and 20 years of age. Underlying heart disease was present in 270 patients (125 had hypertension, 80 had coronary artery disease, 47 had congestive heart failure, 33 had congenital heart disease, 59 had valvular heart disease, and 44 had a cardiomyopathy). The mean ejection fraction was 63±11%.
Five hundred patients underwent ablation of a single AP, 373 underwent ablation of AVNRT, and 121 underwent ablation of the AVJ. An additional 56 patients had >1 type of ablation target. Among those patients who underwent ablation of a single AP, 270 procedures involved the left free wall, 92 involved the right free wall, 98 were posteroseptal, and 40 were septal. Patients who underwent ablation of an AP were significantly younger (mean age, 27±17 years) than patients with AVNRT (44±18 years) or patients who underwent ablation of the AVJ (64±15 years; P<0.0001; Figure 1⇓). Patients who underwent ablation of AVNRT were more likely to be female (70%) than were patients who underwent ablation of an AP (42%) or the AVJ (52%; P<0.001).
Acute Success of Catheter Ablation
Catheter ablation was acutely successful with either the investigational or noninvestigational ablation system in 996 patients (95%; Table 2⇓). The median number of RF applications was 6 (range, 1 to 98). Two ablation sessions were required in 42 patients. The success rate of catheter ablation was lower among patients who underwent ablation of an AP (93%) and highest among patients who underwent catheter ablation of the AVJ (100%), with the success rate for AVNRT falling in between (97%; P<0.001). Among patients with an AP, success rates were lower during ablation of right free wall and posteroseptal APs (90% and 88%, respectively) than during ablation of left free wall APs (95%; P=0.03). It is interesting to note that the greater difficulty of ablation of APs, particularly posteroseptal and right free wall APs, is also reflected in an increased proportion of patients who required a second ablation procedure (Table 2⇓). Success with the investigational ablation system was achieved in 889 patients (85%; Table 2⇓).
When separate logistic regression models were used to assess the odds of success among the variables of interest, 9 predictors of ablation success were individually significant (P<0.05): the ablation target (AVNRT, right free wall AP, posteroseptal AP, multiple accessory APs, or AVJ), the ejection fraction, whether or not a center had ≥40 patients enrolled in the study, and several specific ablation centers (Table 1⇑).
Table 3⇓ presents the results of multivariate logistic regression analysis. Catheter ablation of the AVJ was 100% successful. Because it was a perfect predictor, it could not be included in the statistical model. Three additional factors were identified as jointly predictive of successful ablation, including the ablation target (AVNRT and left free wall APs) and the experience of the ablation center.
A major complication occurred within 1 month after ablation in 32 patients (3%), and minor complications developed in 87 patients (8.2%). The type and distribution of complications are shown in Table 4⇓. The most significant complications included 3 patient deaths, 2 strokes, 1 myocardial infarction, and 10 cases of complete AV block that required placement of a permanent pacemaker.
The most common complications were the development of transient first- or second-degree AV block in 21 patients (2%) and development of complete heart block, which required pacemaker implantation, in 10 patients (1%). The development of complete heart block was related to the type of ablation procedure and occurred in 5 of 373 patients who had undergone ablation of AVNRT (1.3%) compared with 5 (1%) of 500 patients who underwent ablation of an AP. The development of complete heart block during ablation of an AP was most commonly observed after ablation of septal (1 of 40, 2.5%) and posteroseptal (3 of 98, 3%) APs but also occurred in 1 (0.3%) of 270 patients who undergone ablation of a left free wall AP. Two patients had a stroke (0.2%), 1 after ablation of a left-side AP with a transeptal approach and the second after ablation of the AVJ with a retrograde aortic approach. There were 3 deaths (within 30 days of the procedure). One patient died on the day of the ablation procedure; this 56-year-old woman, who had known coronary artery disease and an ejection fraction of 38% with a left lateral AP, died during the procedure as a result of a dissected left main coronary artery. A second patient died on the seventh day after the procedure; this 74-year-old man with an ischemic dilated cardiomyopathy (ejection fraction, 17%) had undergone an AVJ ablation and placement of a pacemaker. He died suddenly 1 week later. Ventricular fibrillation was documented by the emergency medical technicians. The third patient was a 49-year-old woman with a dilated cardiomyopathy who had undergone an AVJ ablation and pacemaker implantation after a failed attempt at ablation of atrial flutter. She died on the 14th day after the procedure. The patient was reported to be choking and was found to be in electromechanical dissociation on the arrival of paramedics. It is presumed that the patient died of a pulmonary embolus.
As identified with separate logistic regression analyses, the 3 predictors that influenced the odds of a major complication were patient age, the presence of structural heart disease, and the presence of multiple ablation targets. Table 5⇓ presents the results of multivariate logistic regression analysis. The 2 factors found to be jointly associated with the development of a major complication were the presence of multiple ablation targets and the presence of structural heart disease.
Echocardiograms were performed before and after catheter ablation in 972 patients. Six of these patients developed clinical evidence of tamponade during the ablation procedure that was subsequently confirmed with echocardiography. Among the 966 patients in whom an echocardiogram was performed solely for the purposes of this study, there was no significant change in 805 patients, a minor change in 139 patients (13%), and a major change in 22 patients (2%). The type of ablation target associated with these echocardiographic findings is shown in Table 6⇓. Little correlation was noted between changes in valvular function and the specific ablation target and approach used for ablation. For example, although an increase in aortic insufficiency was observed in 20 patients, only 4 had undergone ablation via the retrograde aortic approach.
After a successful ablation procedure, 56 (6%) of the 889 patients in whom success was achieved with the investigational ablation system developed a recurrence: 31 patients (7.8%) who had undergone ablation of an AP, 16 (4.6%) who had undergone ablation of AVNRT, and 2 (1.9%) who had undergone ablation of the AVJ (P<0.01; Table 2⇑). The median time to recurrence was 35 days (range, 0 to 244 days). Figure 2⇓ shows Kaplan-Meier curves for recurrence based on the ablation target and also on AP location. When separate Cox proportional hazards models were used to assess the risk of a recurrence, 8 predictors were individually significant (P<0.05): whether the ablation center was pediatric or adult, patient age, the ablation target (left free wall, right free wall, septal, or multiple APs), and 2 specific ablation centers (Table 1⇑). Table 7⇓ presents the results of the stepwise Cox proportional hazards multivariate regression analysis. The 4 factors found to be jointly predictive of the risk of recurrence were the presence of a septal, posteroseptal, or right free wall AP and the presence of multiple APs.
Twenty-three patients died either in the periprocedural period or during a median follow-up of 6.3 months. Of the 23 deaths, 9 had a noncardiac cause, 8 were classified as cardiac nonarrhythmic death, 5 were classified as sudden cardiac death (including the patient who died on day 7), and 1 was due to a presumed pulmonary embolus (as described above). Of the 5 sudden deaths, 4 were known to be due to ventricular fibrillation, and the fifth was unwitnessed. The ablation target was the AVJ in each of these patients. One of these patients died suddenly 7 days after the ablation procedure, another died suddenly 10 weeks after ablation, and the remaining 3 died suddenly >5 months after ablation.
Total survival was estimated by the Kaplan-Meier method. Overall, 98% of patients were alive at 1 year of follow-up. Significant differences were observed in patient survival when analyzed according to their ablation target. Patients who had undergone ablation of the AVJ had a lower 1-year survival (86%) compared with patients who had undergone ablation of an AP or AVNRT (99% 1-year survival, P<0.001, Figure 3⇓). As identified with separate Cox proportional hazards regressions, the 4 predictors of risk of death were patient age, the presence of structural heart disease, the ejection fraction percentage (analyzed as a continuous variable or dichotomized on the basis of a cutoff of 35%), and the AVJ as the ablation target (Table 1⇑). The 3 factors found to be jointly predictive of the risk of death were the ejection fraction, the presence of structural heart disease, and the AVJ as the ablation target (Table 8⇓).
The present study is the first report on the safety and efficacy of catheter ablation of supraventricular arrhythmias based on the results of a prospective, multicenter clinical trial. This study is also unique because of its large size and the inclusion of data from children and adults. The results of the present study demonstrate that catheter ablation of APs, AVNRT, and the AVJ can be performed with a high level of success (95%), a low recurrence rate (6%), and a relatively low incidence of major complications (3%). This study also identifies 4 clinical variables that are jointly predictive of ablation success (AVJ, AVNRT, or left free wall AP ablation and an experienced ablation center), 4 factors that jointly predict an increased risk of arrhythmia recurrence (right free wall, posteroseptal, septal, and multiple APs), 2 clinical variables that jointly predict development of a complication (structural heart disease and the presence of multiple ablation targets), and 3 clinical variables that predict an increased risk of death (structural heart disease, lower ejection fraction, and AVJ ablation).
Factors Affecting Ablation Success and Recurrence
Successful ablation of tissue responsible for an arrhythmia with RF energy requires accurate mapping and adequate tissue heating. Catheter ablation of the AVJ was associated with the highest efficacy, followed by ablation of AVNRT and then by ablation of APs. Among APs, greater success was achieved during ablation of left free wall APs than ablation of multiple APs, posteroseptal APs, and right free wall APs. These findings can be understood if one considers the increasingly well-recognized target-dependent differences that exist in the ease of mapping and the effectiveness of tissue heating.23 24 25 26 27 Given the technical expertise required to map arrhythmias accurately and to maintain adequate catheter-tissue contact to achieve adequate tissue heating, it is perhaps not unexpected that success was more likely at more experienced ablation centers. It is also important to note that no age-related differences in ablation success were observed.
The probability of arrhythmia recurrence after a successful ablation procedure was strongly influenced by the ablation target, with recurrence being more likely after ablation of right free wall, posteroseptal, and septal APs and with multiple APs. These differences in the likelihood of arrhythmia recurrence can be explained, in large part, by the target-dependent differences in the effectiveness of tissue heating noted above.23 24 25
The incidence of major complications in this study was 3%, and the incidence of less serious complications was 8%. The most significant major complications included 3 patient deaths, 2 stroke, 1 myocardial infarction, and 10 cases of complete heart block that required placement of a permanent pacemaker. Of the 3 patient deaths, only 1 occurred as an immediate result of the ablation procedure; sudden death occurred in the other 2 patients after hospital discharge as a result of ventricular fibrillation or a presumed massive pulmonary embolus. The finding that heart block was at least as common during ablation of posteroseptal and septal APs as during ablation of AVNRT is an important reminder that ablation anywhere along the septal aspect of the tricuspid valve may result in heart block.28 The 2 factors that were identified as independent predictors of a major complication were structural heart disease and multiple ablation targets. Although the importance of structural heart disease is not surprising, the basis for the link between multiple ablation targets and complication cannot be readily explained but may reflect longer procedures, greater catheter manipulation, and physician fatigue. The results of the present study also provide evidence that catheter ablation does not result in significant valvular damage and that echocardiograms do not need to be routinely performed after ablation procedures.
The 1-year survival rate after catheter ablation was 98%. Patients who underwent ablation of the AVJ had a much lower 1-year survival rate (86%) than patients who underwent ablation of AVNRT or an AP (99%). The 3 factors identified as independent predictors of increased risk of death included ablation of the AVJ, the presence of structural heart disease, and a lower ejection fraction. The importance of ablation of the AVJ as an independent predictor of mortality is consistent with the findings of prior studies that have reported on the development of sudden cardiac death after ablation of the AVJ.20 29 30 31 It is notable that the prevalence of sudden cardiac death after ablation of the AVJ with the use of RF energy in the present study (5 of 121, 4%) was somewhat higher than was originally reported with the use of DC shock energy in the Percutaneous Cardiac Mapping and Ablation Registry (8 of 499, 1.6%).29 These findings suggest that the development of sudden cardiac death after ablation of the AVJ cannot be attributed solely to proarrhythmic effects of DC shock ablation but extend also to RF ablation. A better understanding of the specific cause of this type of complication and identification of methods to prevent late sudden cardiac death are needed before AVJ ablation becomes more widely performed. The findings from several recent studies31 32 33 suggest that the early development of malignant ventricular arrhythmias after ablation of the AVJ are pause or bradycardia dependent. Geelen and colleagues31 reported a 6% incidence of ventricular fibrillation or sudden cardiac death within 1 month after RF ablation of the AVJ when pacing rates were set to 60 bpm compared with a 0% incidence of sudden cardiac death when pacing rates were programmed to 90 bpm for the first 1 to 3 months after the procedure, with subsequent reductions of the pacing rate to 70 bpm. Although pacing rates were left to the physician’s discretion in the present study and are unavailable for analysis, it is important to note that sudden cardiac death occurred within 1 month of the ablation procedure in only 1 of the 5 patients who died suddenly after ablation of the AVJ in this series.
Role of Temperature Monitoring
Because patients were not randomized to either power or temperature control, we were unable to determine whether closed-loop temperature control per se results in improved efficacy or a lower incidence of complications than catheter ablation with power control alone. However, we previously reported that applications of RF energy delivered with closed-loop temperature control are associated with a 3-fold reduction in the incidence of coagulum development compared with those delivered with the power-control mode.23 We suspect that this reduction in the likelihood of coagulum development would translate to a decrease in the incidence of thromboembolic complications.
The 95% overall success rate in the present study reflects an 85% success rate with the investigational ablation system and a need for an alternate ablation system in 10% of patients. This finding is consistent with the well-recognized clinical observation that a variety of ablation catheters are often required to achieve catheter stability and ablation success because of differences in heart size and shape and depending on the ablation target.
Comparison With Prior Reports
During the past several years, a number of studies have been published reporting the results of catheter ablation of supraventricular arrhythmias. The success, frequency of arrhythmia recurrence, and incidence of major complications reported in the present study are similar to results from prior reports of catheter ablation in adults.1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 22 In contrast, the success rates reported in the present study are higher than have previously been reported in children and adolescents according to the pediatric ablation registry.34 This difference may reflect the learning curve involved with ablation procedures as well as the vast experience of the 2 pediatric centers that participated in the present study.
The results of this study may serve as a guide to clinicians considering therapeutic options in patients who are candidates for ablation. Because we identified factors that are predictive of outcome, this study also identifies subgroups of patients most likely to have a favorable result in whom it would be reasonable for clinicians to recommend catheter ablation as first-line therapy. It is hoped that the identification of a group of patients at increased risk of death after catheter ablation will stimulate further investigation of the potential mechanisms of this important complication and lead to its resolution. The absence of a difference in the outcome of catheter ablation in children and adults provides further evidence that ablation should be considered an important therapeutic tool in children and adults34 35 36 ; however, infants are an exception, because a body weight <15 kg has been demonstrated to be associated with a higher incidence of complications.34
Atakr Investigators and Institutions
J. Philip Saul, MD; Edward Walsh, MD—Childrens Hospital, Boston, Mass. Marcus Wharton, MD; Ronald Kanter, MD; Robert Sorrentino, MD; Ruth Ann Greenfield, MD—Duke University Medical Center, Durham, NC. David Cannom, MD; Anil Bhandari, MD; Robert Lerman, MD; Kelly Tucker, MD—Good Samaritan Hospital, Los Angeles, Calif. Hugh Calkins, MD; Jack Lawrence, MD; Gordon Tomaselli, MD; Ronald Berger, MD—Johns Hopkins Hospital, Baltimore, Md. Lawrence S. Klein, MD; Kevin Hackett, MD; William Miles, MD; Doug Zipes, MD—Krannert Institute, Indianapolis, Ind. Brian Olshansky, MD; Andrew Telfer, MD—Loyola University Medical Center, Maywood, Il. Douglas Packer, MD; Stephen Hammill, MD; Win K. Shen, MD; Michael Osborn, MD; Marshall Stanton, MD; Thomas Munger, MD—Mayo Clinic, Rochester, Minn. Paul Gillette, MD; Christopher Case, MD—Medical University of South Carolina, Charleston. Eric Prystowsky, MD; Joseph Evans, MD—Northside Cardiology, Indianapolis, Ind. John Swartz, MD—St. Francis Hospital, Tulsa, Okla. Robert Bernstein, MD; John Herre, MD; John Onufer, MD—Sentara Norfolk General Hospital, Norfolk, Va. L. Bing Liem, DO; Ruey Sung, MD; Charlie Young, MD—Stanford University Medical Center, Stanford, Calif. Arjun Sharma, MD; Padraig G. O’Neil, MD; Stephen Stark, MD; Stanley Henjum, MD; Larry Wolff, MD—Sutter Memorial Hospital, Sacramento, Calif. John M. Miller, MD; Alfred Buxton, MD; Henry Hsia, MD—Temple University Medical Center, Philadelphia, Pa; G. Neal Kay, MD; Sharon Dailey, MD; Andrew Epstein, MD; Vance Plumb, MD—University of Alabama at Birmingham, University Hospital, Birmingham, Ala. Mark Carlson, MD; Albert Waldo, MD; Lee Biblo, MD; Nancy Johnson, MD; David Rosenbaum, MD—University Hospital of Cleveland, Cleveland, Ohio. Shoei K. Stephen Huang, MD; Robert Mittleman, MD; Alan Wagshal, MD; Trevor Greene, MD—University of Massachusetts Medical Center, Worcester, Mass. James Baker, MD; Frank Fish, MD; John Lee, MD; Katherine Murray, MD; Mark Wathen, MD—Vanderbilt University Medical Center, Nashville, Tenn.
This study was supported in part by grant AR-20610 from the National Institutes of Health (to Dr Bloch).
↵1 A list of principal investigators and participating centers is provided in the Appendix.
- Received April 15, 1998.
- Revision received September 10, 1998.
- Accepted October 1, 1998.
- Copyright © 1999 by American Heart Association
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Tanel RE, Walsh EP, Triedman JK, Epstein MR, Bergau DM, Saul JP. Five-year experience with radiofrequency catheter ablation: implications for management of arrhythmias in pediatric and young adult patients. J Pediatr. 1997;131:878–887.This study reports the safety and efficacy of catheter ablation of atrioventricular nodal reentrant tachycardia, an accessory pathway, or the atrioventricular junction in 1050 patients as part of a prospective, multicenter clinical trial. Catheter ablation was successful in 95% of patients. A recurrence developed in 6% of patients, and 3% of patients developed a major complication.