Catheter Ablation for Atrial Fibrillation
Catheter ablation is a common treatment done by a specialized cardiologist, called an electrophysiologist, who deals with heart rhythms. It is a minimally-invasive procedure that has been successful in treating many cardiac arrhythmias, but historically has not been as successful in treating atrial fibrillation, particularly persistent and permanent afib.
It is done on a beating heart in a closed chest. A small puncture is made in the groin area and thin, flexible tubes called catheters are inserted into the femoral vein and threaded up to the heart. Once there, the catheter's tip punctures the wall between the left and right atria (septal wall), and is positioned at the left superior vena cava, one of the pulmonary veins.
Once positioned, the area that is the source of the irregular heartbeats is destroyed using an energy source, such as intense cold or radio waves. That energy source creates a lesion of scar tissue, called a conduction block, which keeps the errant electrical signals caused by atrial fibrillation from being transmitted from the pulmonary veins into the heart.
Evolution of Catheter Ablation
Catheter Ablation
Image courtesy of AtriCure, Inc.
Catheter ablation originated in the 1980s for treating cardiac arrhythmias and was used for atrial fibrillation starting in the 1990s. Variations of the procedure have evolved over time.
One catheter ablation procedure that has been done for years, but is less commonly done today, is catheter ablation of the AV node, sometimes called AV junctional ablation. The atrio-ventricular node sends electrical signals from the upper to the lower chambers of the heart. In this procedure, the AV node is frozen or cauterized to stop electrical signals from being transmitted and a permanent pacemaker is implanted to control the heart's electrical system. This procedure doesn't cure afib, and the patient keeps having afib, but the signals don't get transmitted. So, with afib continuing, the patient is still at risk for blood clots and stroke and must stay on anticoagulants. In addition, the heart doesn't work effectively, so patients will still feel tired. This works best in patients that already have a pacemaker, or need one for other reasons.
A large study, with data from 181 centers worldwide, showed the evolution over time of different catheter ablation techniques. Most frequently used during the following time periods were: 1
- 1995 to 1997 — right atrial compartmentalization
- 1998 to 1999 — ablation of the triggering focus (hotspots for errant electrical signals)
- 2000 to 2002 — electrical disconnection of multiple pulmonary veins (pulmonary vein isolation)
Most commonly done today is some variation of pulmonary vein isolation (PVI), also called pulmonary vein antrum isolation (PVAI) or pulmonary vein ablation (PVA), to eliminate the irregular heartbeats that research has shown originate from the four pulmonary veins.
Catheter ablation is not yet approved by the US Food and Drug Administration (FDA) for treating atrial fibrillation, but clinical trials are ongoing to determine the efficacy of it.
Catheter Ablation Success Rates
Though this procedure works for some, it isn't effective for all. A number of studies have been done, and success rates to date have been low.
A study published in 2005 using data from 1995–2002 at 181 centers throughout the world indicated that 52% of patients having catheter ablations did not have symptoms and did not need antiarrhythmic drugs. An additional 23.9% also didn't have symptoms, but were still on their antiarrhythmic drugs, which incidentally did not work prior to the ablation. To get these results required a second procedure for 24.3% of patients and a third procedure for 3.1% of patients. Pulmonary vein electrical disconnection was a contributor to two thirds of these results. Results were independent of the technique used and of the type of afib. Success rates were higher in high-volume centers. Very significantly, this study also found a very high number of major complications, at 6%. 1
A 2006 study focused on longer-term outcomes of one to two years, much longer than the six months used for many other studies, and found a 28% success rate, with patients not having symptoms and taking no antiarrhythmic medication. About one-third of the original patients received a second procedure, and 42% of those were successful long-term. 2
Many cardiologists who do the procedure today insist that the accuracy and effectiveness is much better, especially among those who have done more procedures. Various centers cite success rates as high as 80%–85% for first ablations and 95% for second ablations.
Still, one statistic seems concerning — electrical reconnection of pulmonary veins following catheter ablation. In one study, RF lesions to the pulmonary veins reconnected themselves in 80% of cases within just 4 months after the catheter ablation, and similar results were seen just 5 months after reablation, explaining why catheter ablation may be only a temporary fix for some patients. 3 Perhaps some of the currently ongoing clinical studies will show new results.
Catheter Ablation Risks
Catheter ablation has risks, including blood clots, strokes, blockage or perforation of the pulmonary veins or heart, and other risks.
The 2005 worldwide study mentioned above that gathered data from 181 centers found a 6% rate of major complications from catheter ablation, which is quite high. Of the 8,745 patients in the study, four died, 20 suffered strokes, 47 had transient ischemic attacks (TIAs), and 107 had dangerous fluid buildup around the heart (cardiac tamponade), likely due to perforation of the heart or a pulmonary vein. In addition, there was significant narrowing of the pulmonary veins (pulmonary vein stenosis) in 117 pulmonary veins. New atrial flutter occurred in 3.9% of the patients. 1
In another 2005 study, published in The Journal of Cardiovascular Electrophysiology in January of 2006, patients who had pulmonary vein isolation (PVI) using catheter ablation were given a follow up MRI using high-sensitivity diffusion-weighted magnetic resonance imaging (DW-MRI) to identify blood clots (thromboembolisms) from the procedure. Out of 20 patients, two (10%) had ischemic strokes, neither of which had ischemic strokes prior to catheter ablation. And one of the two suffered irreversible brain damage. 4
In this study, the procedure was done using an irrigated radiofrequency catheter, which was supposed to reduce the risk of clots. One theory among researchers is that the body's blood clotting system kicks in during the catheter ablation procedure. 4
Opinion
One very recent opinion piece, "Catheter ablation should not be first-line therapy for atrial fibrillation", which was published in early 2007 in Nature Clinical Practice Cardiovascular Medicine, was written by a professor of medicine at the Johns Hopkins University School of Medicine who is also Director of the Electrophysiology Laboratory at the Johns Hopkins Hospital. It was very illuminating regarding catheter ablation. 5
It dealt with the current suggestion in the EP community that catheter ablation be considered first line of treatment for some afib patients. The current state of affairs is that without large, multicenter clinical trials, the effectiveness of catheter ablation for afib is unknown. In addition, while much progress is being made in new catheters, new energy sources, and new understanding of ablation strategies, many now believe that isolation of the pulmonary veins may not even be necessary. Research is ongoing into other strategies, such as treating the ganglia plexi. 5
What the author felt was most important is the state of affairs regarding complications. Though complications decrease with experience, even the most experienced EPs are discovering new complications. In addition to some of the complications listed above, the risk of lethal perforation of the esophagus is very real — twenty patients worldwide have died from esophageal perforation. In addition, a number of patients have also experienced acute pyloric spasm. And the incidence of silent strokes pointed out by the study listed above makes recommending this as first-line treatment very premature.5 This opinion piece raises significant causes for concern when considering catheter ablation.
To learn more about catheter ablation, see What to Expect From Catheter Ablation.
1 Cappato, Riccardo, MD, et al, "Worldwide Survey on the Methods, Efficacy, and Safety of Catheter Ablation for Human Atrial Fibrillation" <http://circ.ahajournals.org/cgi/content/full/111/9/1100>, Circulation: 2005;111:1100-1105.
2 Cheema, Aamir, et al, "Long-term single procedure efficacy of catheter ablation of atrial fibrillation" <http://www.springerlink.com/content/m414473846828q57/>, Journal of Interventional Cardiology and Electrophysiology, Copyright, 2006; 15:145-155.
3 Cappato, Riccardo, et al, "Prospective Assessment of Late Conduction Recurrence Across Radiofrequency Lesions Producing Electrical Disconnection at the Pulmonary Vein Ostium in Patients With Atrial Fibrillation" <http://circ.ahajournals.org/cgi/content/full/108/13/1599?ijkey=84d63d895f09f284f7ef969d68fde35e2522e733>, Circulation: 2003;108:1599.
4 Lickfett, Lars, MD., et al, "Cerebral Diffusion-Weighted Magnetic Resonance Imaging: A Tool to Monitor the Thrombogenicity of Left Atrial Catheter Ablation" <http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=16426390&dopt=Abstract>, Journal of Cardiovascular Electrophysiology, Vol. 17, pp. 1-7, January 2006.
5 Calkins, Hugh, "Catheter ablation should not be first-line therapy for atrial fibrillation" <http://www.nature.com/ncpcardio/journal/v4/n1/full/ncpcardio0741.html>, Nature Clinical Practice Cardiovascular Medicine: 2007; 4, 4-5
