AV Node Ablation for Atrial Fibrillation
Abstract & Commentary
Synopsis: Survival among patients with atrial fibrillation after ablation of the atrioventricular node is similar whether they receive ablation or drug therapy and is strongly influenced by the presence of underlying heart disease.
Source: Ozcan C, et al. N Engl J Med. 2001;344:1043-1051.
Ozcan and colleagues reviewed data from the Mayo Clinic to assess the effects of atrioventricular (AV) nodal ablation and implantation of a permanent pacemaker on survival in patients with atrial fibrillation. During the period between July 1990 and December 1998, 350 patients (185 men and 165 women) underwent AV junctional ablation and had a pacemaker implanted at the Mayo Clinic. Data from these patients were then compared to 2 control groups. The first control group was calculated on the basis of age- and sex-specific mortality rates for the Minnesota population during the period between 1970 and 1990. A second control group was constructed from a group of consecutive patients who received drug therapy for atrial fibrillation at the Mayo Clinic in calendar year 1993. All patient data were retrieved from a centralized repository maintained at the Mayo Clinic. Follow-up ended in January 1999 or at the time of death.
A total of 350 patients with atrial fibrillation were included in the study. Complete AV block was achieved with radio frequency energy application in all patients. Seven patients (2%) required a left sided approach. A repeat procedure, because of the recurrence of AV conduction, was required in 24 patients (6.9%). Patients in permanent atrial fibrillation received a single-chamber pacemaker (55%) while patients in sinus rhythm at the time of the procedure received a dual chamber pacemaker (45%). The age at the time of ablation was 68 ± 11 years. Patients in the ablation group had failed a mean of 4.3 ± 2 antiarrhythmic drugs. Their mean left ventricular ejection fraction was 47 ± 17%. Twenty-seven percent of the patients had suffered a previous myocardial infarction, and 21% had a history of congestive heart failure. Previous cerebrovascular accidents or transient ischemic attacks had been documented in 19% of the patients. Diabetes mellitus and chronic obstructive lung disease were seen in 20% and 32% of the ablation patients, respectively. A history of hypertension was present in 46%. The drug therapy control group was similar in many respects but did have a slightly higher percentage of males (66% vs 53%), a lower frequency of prior myocardial infarction (17% vs 27%), and had failed fewer antiarrhythmic drugs (2.0 ± 1 vs 4.3 ± 2).
When compared to expected values for age- and sex-matched members of the general Minnesota population, survival was significantly worse for the ablation group due to the increased prevalence of cardiovascular disease in the latter. There was no difference in survival between the ablation and the drug therapy groups that had more similar rates of cardiovascular disease. Similarly, in subgroups of patients with congestive heart failure or coronary artery disease, there was no difference in survival between the group of patients treated with ablation and the drug therapy group.
Univariate and multivariate predictors of death were analyzed. Multivariate analysis showed that previous myocardial infarction, a history of congestive heart failure, and the need for cardiac drugs after ablation were independent predictors of death. However, among the 121 patients who had no heart failure, no history of prior myocardial infarction, and were not treated with cardiac medications after the ablation, survival was the same as the expected rate in the general population. Finally, survival among 26 patients with lone atrial fibrillation was examined. None of these patients died during a mean follow-up period of 37 ± 27 months.
Ozcan et al concluded that survival among patients with atrial fibrillation after ablation of the AV node is similar whether they receive ablation or drug therapy and is strongly influenced by the presence of underlying heart disease.
Comment by John P. DiMarco, MD, PhD
Ablation of the atrioventricular node and implantation of a pacemaker in patients with atrial fibrillation was first described about 20 years ago. Earlier studies have shown that cardiac symptoms are decreased and quality of life improves in highly symptomatic patients with atrial fibrillation who undergo this procedure. This study shows that these benefits are not won at the price of an increased late mortality.
The comparison with the group of drug-treated patients is particularly valuable. Ablation of the AV node is a permanent intervention. The data presented here suggest that it neither improves or adversely affects survival. Therefore, if patients remain symptomatic because of either recurrent episodes of paroxysmal atrial fibrillation or poor rate control in permanent atrial fibrillation, AV junctional ablation may be safely used. Rate control is often a simpler therapeutic strategy, and many patients cannot be maintained in sinus rhythm with currently available antiarrhythmic drugs. These drugs also produce side effects frequently.
AV junctional ablation with pacemaker implantation provides a certain method of maintaining ventricular rate control in patients with atrial fibrillation. If pharmacologic rate control provides a similar result, then an approach that assured adequate rate control with anticoagulation would eliminate any excess mortality associated with atrial fibrillation. This question is now being addressed in several large randomized trials including the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study, which is nearing completion.
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