Multicenter Clinical Trial of Catheter Ablation
April 1, 1999 4 minutes read
Multicenter Clinical Trial of Catheter Ablation
ABSTRACT & COMMENTARY
Synopsis: Between 1992 and 1995, catheter ablation had matured to be a standard procedure with a high success rate and an acceptable risk.
Source: Calkins H, et al. For the Atakr Multicenter Investigators Group. Circulation 1999;99:262-270.
In this report, calkins and colleagues report the results of catheter ablation procedures during a large multicenter study performed during the clinical investigation of a new temperature-controlled ablation system. The studies were performed at 18 adult and pediatric institutions between 1992 and 1995. A total of 1136 ablation procedures were performed in 1050 patients. As part of the investigational protocol to test the efficacy and complications associated with this ablation system, Calkins et al tabulated clinical variables, success rates, arrhythmia recurrence rates after the procedure, and early and late complications.
The patient population consisted of 489 males and 561 females with a mean age of 37 ± 18 years. Among the entire group, 13% were younger than 13 years of age and an additional 18% were between 13 and 20 years of age. Five hundred patients underwent ablation of a single accessory pathway, 373 underwent ablation for AV node reentrant tachycardia, and 121 underwent ablation of the AV junction. An additional 56 patients had more than one type of ablation procedure. In keeping with the natural history of these disorders, patients who underwent ablation of an accessory pathway were younger than patients with AV node reentrant tachycardia, who, in turn, were younger than those who underwent ablation of the AV junction. Catheter ablation was successful in 95% of the patients. Two ablation sessions were required in 42 patients. Second ablation sessions were more commonly required in patients with right free wall or posteroseptal accessory pathways and in patients with either multiple accessory pathways or multiple targets. There was a higher success rate with ablation of left free wall accessory pathways (95%) compared to right free wall and posteroseptal accessory pathways (90% and 80%, respectively).
Major complications occurred within one month of the ablation procedure in 32 (3%) patients, with minor complications noted in an additional 87 patients. There were three patient deaths, two strokes, one myocardial infarction, 10 cases of inadvertent complete AV block, and six cases of tamponade. The three deaths were due to dissection of a coronary artery, ventricular fibrillation seven days after AV junctional ablation, and an apparent pulmonary embolus 14 days after AV junctional ablation. The three predictors of a major complication were: increased patient age, the presence of structural heart disease, and the presence of multiple ablation targets.
Echocardiograms were performed before and after catheter ablation in 972 patients. In addition to the six patients who developed clinical evidence of tamponade, an additional 20 patients had pericardial effusions after the procedures. Although some changes in valvular regurgitation were noted, these were felt not to be directly due to the ablation procedure itself.
After an initially successful ablation procedure, 6% of the patients developed recurrent arrhythmias. Recurrence was more common among patients who had undergone ablation of an accessory pathway (7.8%) compared to those who had undergone ablation for AV nodal reentrant tachycardia (4.6%) or those who had undergone ablation of the AV junction (1.9%). Recurrence was more common with septal, posteroseptal, or right free wall accessory pathways and in patients who had multiple accessory pathways.
During long-term follow-up, there were 23 deaths. Of these, five were classified as sudden cardiac death and one was due to a pulmonary embolus that was presumed to be a late complication of the procedure. The four predictors of death were patient age, the presence of structural heart disease, a lower ejection fraction, and AV junctional ablation.
Calkins et al conclude that between 1992 and 1995, catheter ablation had matured to be a standard procedure with a high success rate and an acceptable risk. Their data may serve as a useful guide to clinicians considering therapeutic options for patients who have arrhythmias susceptible to catheter ablation.
Comment by John P. DiMarco, MD, PhD
Catheter ablation has progressed rapidly as a technique for managing arrhythmias since it was first introduced almost 20 years ago. Initially, DC shock was used to ablate the AV junction, posteroseptal accessory pathways, and ventricular tachycardia. The development of radiofrequency ablation made the procedure considerably more attractive and more than 20,000 radiofrequency ablation procedures are performed annually in the United States. Although previous reports on the success and complications of radiofrequency ablation have been published, they have either represented single laboratory reports or voluntary registry data. The latter likely underreport complications and the former may not represent the efficacy rate in usual practice. Few prior studies had extensive data about late recurrence. This study, since it involved the clinical trial of an investigational ablation system, provided a uniform method for data collection and follow-up and, therefore, represents probably the most accurate assessment of radiofrequency catheter ablation yet available.
The major limitation to this paper is that the data were obtained between 1992 and 1995. This period was still early in the learning curve for many centers. Calkins et al identified the number of procedures performed at a center as a predictor of success. By now, however, any large center should have performed hundreds of catheter ablation procedures, not just the number (40) that were associated with a higher rate of success in this study. However, as more electrophysiologists have been trained in this technique, many now practice in relatively low-volume centers and data about the number of procedures required to maintain a high level of success are not available. In addition, this paper does not include data about the success rates or complication rates for ablation of atrial tachycardias, ventricular tachycardias, atrial flutter, or atrial fibrillation. Ablation for these arrhythmias is often more complicated, and up-to-date data about the success and complications during ablation attempts with these arrhythmias would be valuable.
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