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Ablation of atrial fibrillation: What can we tell our patients?

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ABSTRACTAlthough catheter-based radiofrequency ablation is no longer experimental, it is not yet the first-line treatment for most patients. The authors describe how this procedure works, its indications, benefits, and limitations, and important points to communicate to potential candidates for this procedure.

KEY POINTS

  • During the procedure, scar tissue is created in rings around the ostia of the pulmonary veins and in other locations in the left atrium to electrically isolate triggers of fibrillation and areas that maintain it.
  • Results of the procedure are superior to those of drug therapy. Success rates are higher for those with paroxysmal atrial fibrillation than for those with persistent atrial fibrillation.
  • The main indication for this procedure is failure of drug therapy or inability to tolerate drug therapy.
  • Patients must understand that ablation therapy will not eliminate the need to take anticoagulant drugs.


 

References

More patients with atrial fibrillation are asking their physicians about catheter-based radiofrequency ablation as a treatment option.

Indeed, in the mere 10 years or so since this procedure was introduced, it has shown promising clinical results. Still, it is not yet available at many medical centers, and it is not yet considered the first-line treatment for atrial fibrillation.1 Moreover, some patients may have unrealistic expectations about it, such as being able to stop taking anticoagulant drugs afterward. It is therefore important for health care professionals not only to recognize which patients may benefit from catheter-based treatment, but also to educate them about it so they have reasonable expectations.

See related editorial and patient information at http://my.clevelandclinic.org/heart/services/tests/procedures/ablation.aspx

In this article, we briefly review the mechanisms of catheter ablation of atrial fibrillation and discuss its current indications, with an emphasis on how to determine which patients with atrial fibrillation are candidates for this new procedure.

NUMBERS ARE RISING, AND DRUG THERAPY HAS LIMITATIONS

Atrial fibrillation is a disease of the elderly: about 70% of patients are between the ages of 65 and 85.2 As the elderly segment of the US population increases, the number of people with atrial fibrillation is expected to more than double by the year 2050.3

This growing prevalence and the increasing socioeconomic burden are two reasons people are looking to new treatments such as catheter and surgical ablation.

Several randomized clinical trials,4–7 most importantly the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) trial,7 found that attempting to restore and maintain sinus rhythm with antiarrhythmic drugs imparts no significant benefit in terms of survival compared with a strategy of controlling the heart rate only. However, recent studies, including an analysis by the AFFIRM investigators,8 suggest that if sinus rhythm could be achieved without the adverse effects of antiarrythmic drugs, then rhythm control may have a survival benefit over rate control. These studies, combined with improving techniques and tools for catheter ablation of atrial fibrillation, have made ablative treatment an attractive option and an emerging trend.

HOW ATRIAL FIBRILLATION STARTS AND HOW IT IS MAINTAINED

Figure 1.

Atrial fibrillation is a supraventricular arrhythmia characterized by chaotic and uncoordinated contraction of the atrium.1 Multiple models have been proposed for its mechanism. The current view is the “dual-substrate model,” ie, that atrial fibrillation often arises from a focal source, usually in one of the pulmonary veins, and that it is maintained by abnormalities in the atria (Figure 1).

Several studies9–11 showed that left atrial myocardial cells extend into the pulmonary veins. These “myocardial sleeves,” which vary in extent between individuals, have short refractory periods and can cause conduction delays, which may create the conditions needed for arrhythmias.12,13

In landmark studies in the 1990s, Haïssaguerre et al14 and Jais et al15 showed that most focal triggers are in the myocardial sleeves at the junction of the pulmonary vein and the left atrium. These investigators went on to show that catheter-based ablation of these ectopic foci could eliminate atrial fibrillation in some patients.

Ectopic foci in the pulmonary veins fire rapidly and chaotically, generating impulses that enter the left atrium and begin to generate wavelets of reentry. These wavelets may be perpetuated if the conduction velocity is slow, the refractory period is short, and atrial mass is high.1,16,17

Some experts thought that by surgically interrupting the path of these wavelets and reducing the atrial mass, one could terminate atrial fibrillation. This model is the basis of the surgical maze procedure developed by Cox et al in the 1990s,18 which planted the seed for catheter ablation of atrial fibrillation.

DEFINITIONS OF ATRIAL FIBRILLATION

A 2007 consensus document1 prepared jointly by several heart societies emphasizes the need to classify the types of atrial fibrillation consistently, as recommendations for different treatments are based primarily on the type of atrial fibrillation. Although some patients may have atrial fibrillation that falls into more than one of these categories, it should be categorized by its most frequent pattern. These definitions apply only to episodes that last at least 30 seconds and have no identifiable reversible cause, such as acute pulmonary disease or hyperthyroidism.

Paroxysmal atrial fibrillation is defined as at least two episodes that terminate spontaneously within 7 days.

Persistent atrial fibrillation is defined as lasting more than 7 days, or lasting less than 7 days but necessitating pharmacologic or electrical cardioversion.

Permanent atrial fibrillation is defined as lasting more than 1 year.

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