Ablation of atrial fibrillation: What can we tell our patients?
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.
THE TECHNIQUE
Catheter ablation is usually done as an outpatient procedure. As the procedure can take 3 to 5 hours, most patients receive conscious sedation or general anesthesia. A catheter is inserted into a femoral vein and advanced into the right atrium. Then, the atrial septum is punctured to gain access to the left atrium, and a radiofrequency ablation catheter and a mapping catheter are inserted (Figure 1).
What to ablate?
Various approaches are being used in catheter-based ablation of atrial fibrillation.1,12,19–29
Since most of the triggers of atrial fibrillation are located within the pulmonary veins, one can use an empiric anatomic approach, creating a ring of ablation lesions around the outside of the ostium of each of the four pulmonary veins (but not within the vein itself), or a single ring around the ostia of the two left pulmonary veins and another around the two right pulmonary veins. The aim is to electrically isolate these veins.
Refinements to this procedure involve making additional lines of lesions in the atrium, similar to those in the Cox maze procedure; a line across the roof of the left atrium connecting the ring of lesions around the left and right superior pulmonary veins; a line across the mitral isthmus (between the mitral valve and the left inferior pulmonary vein); and a line connecting either the roof line or the left or right circumferential lesion to the mitral annulus anteriorly. The aim of these additional lesions is to interrupt the re-entrant circuits that keep atrial fibrillation going, and they may make the procedure more effective in cases of persistent or permanent atrial fibrillation than it would be without these lesions.
An electrophysiologic approach involves using intracardiac electrocardiography to locate specific drivers of fibrillation and areas of complex fractionated atrial electrograms, which can be ablated. This is a more tailored approach, and it may be more effective. In addition, one can ablate, then attempt to induce fibrillation electrically or with drugs, and then, if fibrillation ensues, do more ablation.
Fluoroscopy vs intracardiac echocardiography
Fluoroscopy, intracardiac echocardiography, three-dimensional mapping, and pulmonary venography have all been used to guide left atrial pulmonary vein ablation.
Until recently, electrophysiologists used fluoroscopy, but now most use intracardiac echocardiography and other imaging techniques. Intracardiac echocardiography provides information that fluoroscopy cannot. It can show, from moment to moment, the anatomic structures, the position of the catheter, and if there are thrombi in the left atrium. It can also help optimize the use of radiofrequency energy by monitoring for microbubbles, which represent tissue overheating.1
Three-dimensional mapping and navigation techniques help define the anatomy and help guide the catheter, especially with previously acquired computed tomography (CT) or magnetic resonance imaging (MRI).30–32 Likewise, pulmonary venography can also show the shape and size of the pulmonary ostia. This modality can guide catheter manipulation and assessment for pulmonary venous stenosis resulting from prior ablation.1
INDICATIONS FOR CATHETER ABLATION
An absolute contraindication to catheter ablation is left atrial thrombus. Because of the risk of dislodging an existing thrombus during the procedure and causing a stroke, the committee recommends that patients with persistent atrial fibrillation who are in atrial fibrillation at the time of the procedure undergo transesophageal echocardiography to screen for thrombus.
An individualized decision
The decision to proceed with catheter ablation must be individualized on the basis of the risk of complications, the likely benefits, and the likelihood of success.1
Factors that increase the risk of iatrogenic complications such as myocardial perforation and thromboembolism include older age and comorbid conditions.
Factors that increase the chance of significant benefit include more severe symptoms and heart failure. Hsu et al33 found that the ejection fraction increased by 21 plus or minus 13 percentage points in heart failure patients who underwent the procedure.
Success rates for catheter-based ablation are lower in patients with persistent atrial fibrillation than in those with paroxysmal atrial fibrillation. Oral and colleagues34 reported that the recurrence rate in patients with persistent atrial fibrillation was 75%, compared with 29% in patients with paroxysmal atrial fibrillation. In addition, the chances of a successful outcome are lower in those with marked dilation of the left atrium.
Lifelong anticoagulation is still needed
When weighing the pros and cons of catheter-based procedures, health care providers need to also emphasize to patients that the procedure does not allow them to forgo anticoagulation. Even after ablation, patients with atrial fibrillation still face a formidable risk of thromboembolic events, and most electrophysiologists suggest lifelong anticoagulation, especially in patients with other risk factors for stroke. We discuss the guidelines for anticoagulation later in this review.
