Why Has Ablating Atrial fibrillation Been So Difficult?Most cardiac arrhythmias are caused by a small, localized area somewhere within the heart that produces an electrical disruption of the normal heart rhythm. For most arrhythmias, then, ablation simply requires locating that small abnormal area and cauterizing it. In contrast, the electrical disruptions associated with atrial fibrillation are much more extensive - essentially encompassing most of the left and right atria. (Read about the cardiac chambers.)
So early efforts at ablating atrial fibrillation were aimed at creating a "maze" of complex, linear scars throughout the atria, to disrupt this extensive abnormal electrical activity. This approach (which has been called the maze procedure) works reasonably well when performed by very experienced surgeons in the operating room - but it requires major open-heart surgery, with all the associated risks. Creating this maze of linear scars is nearly impossible to perform with a catheterization procedure.
A Different Approach: Going After the TriggersIn recent years, electrophysiologists (heart rhythm doctors) have had more success ablating atrial fibrillation using a different approach. Rather than trying to attack the mechanism of atrial fibrillation itself by establishing a maze of linear scars, doctor are now aiming their efforts at ablating the "triggers" of the arrhythmia - namely the PACs (premature beats arising in the atria) that often trigger atrial fibrillation.
Studies have now shown that in up to 90% of patients with atrial fibrillation, the PACs that trigger the arrhythmia arise from specific areas within the left atrium, namely, near the openings of the four pulmonary veins. (The pulmonary veins are the blood vessels that deliver oxygenated blood from the lungs to the heart.) If the opening of the veins can be electrically isolated from the rest of the left atrium (by using a catheter to create just two or three strategically-placed linear scars), atrial fibrillation can often be reduced in frequency or even eliminated.
Recently, new and very advanced (and very expensive) three-dimensional mapping systems have been developed for use in ablation procedures in the catheterization lab. These new mapping systems allow doctors to create ablation scars with a level of precision unknown just a few years ago. And this new technology has made the ablation of atrial fibrillation much more feasible than it used to be.
But it is still a lengthy and difficult procedure, and its results are less than perfect. Even with modern mapping systems, ablation procedures work best in patients who have relatively brief episodes of atrial fibrillation - so called "paroxysmal" atrial fibrillation. Ablation works much less well in patients who have chronic or persistent atrial fibrillation, or who have signficant underlying cardiac disease such as heart failure, or heart valve disease.
Even with patients who appear to be ideal candidates for ablation of atrial fibrillation, the arrhythmia recurs in at least 15 - 20% within one year, and in 25 - 50% within three to five years. Furthermore, even when an ablation procedures appears to be successful, the risk of stroke (the most dreaded complication of atrial fibrillation) remains elevated. So it is important to continue with therapy to prevent strokes.
ComplicationsThe risks of catheter ablation for atrial fibrillation are somewhat higher than with catheter ablation for other cardiac arrhythmias. This is because the duration of the ablation procedure tends to be much longer with atrial fibrillation, the extent of the scar that must be produced is much greater, and the location of the scars that are produced (i.e., near the pulmonary veins), can cause problems with the pulmonary veins themselves.
Procedure-related death occurs in roughly one in 1,000 patients having ablation for atrial fibrillation. Stroke occurs in up to 2%. Damage to a pulmonary vein (which can produce lung problems leading to severe shortness of breath, cough, and recurrent pneumonia) occurs in up to 3%. Damage to other blood vessels (the vessels through which the catheters are inserted) occurs in 1 or 2%. All of these complications appear to be more common in patients over 75 years of age, and in women.
In general, both the success of the procedure and the risk of complications improve when the ablation is conducted by an electrophysiologist with extensive experience in ablating atrial fibrillation.
The Bottom Line
Before the ablation of atrial fibrillation can become a routine procedure, the technology needs to be further refined to reduce the time it takes to perform the procedure, and to reduce or eliminate the risk of neurological complications and of damage to the pulmonary veins. While some experts maintain that we have already reached this point, most disagree, and want to see hard evidence that: a) the procedure is effective enough, b) the procedure is safe enough, and c) that clinical outcomes of patients subjected to this procedure are substantially improved.
If you are considering an ablation procedure for atrial fibrillation, you need to make sure you're aware of all your treatment options for this arrhythmia.
European Heart Rhythm Association (EHRA), European Cardiac Arrhythmia Scoiety (ECAS), American College of Cardiology (ACC), et al. HRS/EHRA/ECAS expert Consensus Statement on catheter and surgical ablation of atrial fibrillation: recommendations for personnel, policy, procedures and follow-up. A report of the Heart Rhythm Society (HRS) Task Force on catheter and surgical ablation of atrial fibrillation. Heart Rhythm 2007; 4:816.