Initiation of Atrial Fibrillation By Pulmonary Veins Ectopic Beats
ABSTRACT & COMMENTARY
Synopsis: Focal atrial ectopic beats are a required precursor of atrial fibrillation in selected patients.
Source: Haissaguerre M, et al. N Engl J Med 1998; 339:659-666.
The search for an electrical approach to atrial fibrillation continues with this study. A group of French investigators describe their experience with 45 patients with recurrent atrial fibrillation. The patients were a select group of patients presenting with episodic atrial fibrillation for 6 ± 6 years. Each had frequent episodes of atrial fibrillation with self-terminating episodes occurring at least once every two days. Most had multiple daily episodes. The patients were also required to have frequent isolated atrial ectopic beats when they were in sinus rhythm. The study group included 35 men and 10 women with a mean age of 54 years. All patients had failed drug therapy. Only 14 of the 45 patients had structural heart disease, and 21 of 45 had undergone a previous ablation of atrial flutter. All patients were chronically anticoagulated before the study. Twelve-lead electrocardiograms were available in all patients to document the morphologic features of the atrial ectopic beats that preceded clinical episodes of atrial fibrillation.
Electrophysiologic studies were performed with multi-electrode catheters placed in both the right and left atria. Attempts were made to map the earliest atrial activity associated with the onset of ectopic atrial beats. Particular attention was paid to the pulmonary veins as they entered into the left atrium. If a site of origin for the atrial ectopic beats was identified, attempts were made to eliminate the focus with radiofrequency ablation. After the ablation procedure, patients were followed on telemetry and with 24-hour ambulatory ECG monitoring. Patients in whom the ablation was thought to be successful were followed off antiarrhythmic drugs.
Twenty-nine patients had a single point of origin identified for their ectopic beats. Two origins were identified in nine patients, three in six patients, and four in one patient. In four patients, the point of origin was in atrial muscle. In the remaining 41 patients, the ectopic foci were located in the pulmonary veins near their insertions into the left atrium. Most sites were in the right or left superior pulmonary veins.
The mapping procedure was complicated. Haissaguerre and colleagues describe difficulties including the unpredictable spontaneous occurrence of ectopic beats and atrial fibrillation, and episodes of sustained atrial fibrillation of variable duration that precluded further mapping while present. Specific electrophysiologic findings were seen at the sites of origin of the atrial premature beats. The local electrograms often had sharp spikes preceding the onset of the surface P wave by 40-160 msec. Atrial fibrillation was initiated by bursts of two or more repetitive focal discharges from these sites in most patients, with a few patients requiring only a single focal discharge to initiate atrial fibrillation. Radiofrequency ablation of the atrial and venous ectopic foci was attempted in all patients. Two sessions were required in 25 patients, and three sessions were required in six patients because of recurrence after ablation or the emergence of new foci. Ablation was thought to be clinically successful in 38 of 65 patients. These patients showed a marked decrease in frequency of ectopic beats on Holter monitoring. During 6-8 months of follow-up, 28 of 45 patients had complete elimination of symptomatic atrial fibrillation.
Haissaguerre et al conclude that focal atrial ectopic beats are a required precursor of atrial fibrillation in selected patients. The sites of origin of these beats are frequently in the proximal portion of the pulmonary veins. Ablation of focal atrial sites of origin of these beats may lead to elimination or improved control of atrial fibrillation.
COMMENT BY JOHN P. DiMARCO, MD, PhD
Atrial fibrillation is the most common sustained cardiac arrhythmia. Although not usually considered to be a life-threatening arrhythmia, it may be highly disabling. In the last decade, the use of radiofrequency ablation to selectively target critical parts of the heart required for arrhythmia circuits has revolutionized the way we manage many arrhythmias. Atrial fibrillation, however, because of the complexity of the multiple circuits involved during sustained arrhythmia and our prior inability to define a single critical region, has so far resisted most simple catheter ablation approaches.
In this paper, Haissaguerre et al focus on the factors that initiate atrial fibrillation. This group of patients is certainly not representative of all patients with atrial fibrillation. They had characteristic ambulatory monitors with frequent atrial premature beats from single foci and usually did not have severe structural heart disease. The major lesson from this paper is that clinicians should consider ambulatory monitoring in young patients or patients with mild forms of heart disease who present with repetitive episodes of atrial fibrillation. If frequent atrial premature beats with a single morphology during periods when the patient is not in atrial fibrillation are identified, an effective ablation procedure that maintains sinus rhythm may be possible.
The pulmonary veins were the most frequent site of origin of the atrial ectopy that initiated atrial fibrillation in these patients. Although Haissaguerre et al report no complications with ablation in this series, anecdotal evidence that pulmonary venous hypertension may be produced by multiple ablations in the pulmonary veins is now merging. Longer term follow-up is clearly needed to fully define the safety of ablation approaches in these small venous structures.
This is an exciting paper for those of us who have been frustrated with attempts to manage atrial fibrillation. Drug therapy is frequently unsuccessful, and the agents available produce frequent toxicity. Identification of a subset of atrial fibrillation patients whose arrhythmia can be eliminated without drug therapy is an important breakthrough.
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