Catheter Ablation vs Antiarrhythmic Drug Therapy in Atrial Fibrillation: CABANA – What Did We Learn?
Catheter Ablation vs Antiarrhythmic Drug Therapy in Atrial Fibrillation: CABANA – What Did We Learn?
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Dr. Wazni: Good morning. I'm Oussama Wazni. I'm the Section Head of Cardiac Electrophysiology at the Cleveland Clinic. With me here is Dr. Lindsay, the past Section Head, the immediate Past Section Head, of Cardiac Electrophysiology at the Cleveland Clinic. Also, Dr. Lindsey was a past president of Heart Rhythm Society. Both of us are thrilled to be here this morning to talk about the CABANA trial and its implications on our clinical everyday work in EP. Dr. Lindsay will take the lead and I will be discussing with him the study in detail.
Dr. Lindsay: CABANA is a very interesting trial. It was one that really was designed to look at additional benefits from going through an ablation. What I mean by that is that most patients come to us for ablation procedures because they have symptomatic atrial fibrillation. Many of them, either medicines have failed to control their arrhythmias or were not tolerated. Then they came to us because they needed relief from the kind of symptoms they had. For many people atrial fibrillation has a significant burden on quality of life. In some instances, patients also looked at the risks of taking medicines and just didn't want to take them. That's really why we do ablation procedures, to improve quality of life.
The question really that CABANA focused on is whether it reduces the risks of death, stroke, bleeding, or cardiac arrest. That was a combined endpoint that they looked at to see whether it would make a difference. They also looked at all-cause mortality and hospitalization, recurrence to atrial fibrillation, and certain other secondary endpoints. In doing this trial, it was difficult. To put it in perspective, we had a great challenge in recruiting patients for it because they came to us because they were symptomatic. They wanted to have something done, and they didn't want to be randomized to a drug limb, which maybe they had already failed. Right there you have an immediate challenge in doing a study like this. It was known what there would be a big crossover from one treatment limb to the other. Dr. Packer and the statisticians tried to account for that in designing the clinical trial. It was a difficult trial to do and I think it will evoke controversy over the next five or six years as we analyze results. I mainly want to give you a perspective.
Dr. Wazni: This was a challenging time from all aspects, even with the enrollment roles. The enrollment role started with about five thousand patients. That was about down to about three thousand and even less when the trial was finally concluded. Nevertheless, Dr. Lindsay, tell us about the overall findings of the study and how these findings can apply to our daily activity with our patients.
Dr. Lindsay: In round numbers, there were two thousand patients enrolled in the study, a thousand each limb. One limb got medical therapy and the other limb underwent ablation procedures. About 20% of the patients who went through ablations required a second ablation. The problem was this. About 9% of the patients who were supposed to get ablations never did. It's not quite clear why, whether there were financial issues or whether they changed their mind or could they have been too sick? That's a problem because it would bias the results. On the other side, there were a substantial number of patients, if I recall correctly about 27%, who crossed over from drug therapy to ablation. That was a little higher crossover than, I think, was anticipated in this study. Whenever you do an intention-to-treat analysis, it's very difficult when there's a big crossover and people really didn't get exactly the treatment they were supposed to get.
Nonetheless, in looking at these parameters by an intention-to-treat analysis, the all-cause mortality was ... There were modest reductions. All-cause mortality was about 6% less with ablation therapy. A very modest reduction in absolute terms. There was a substantial reduction in the time to recurrence of atrial fibrillation. This is something we've seen in the past. Ablation tends to be more effective. Again, to put this in perspective, about 47% of the patients had persistent as opposed to paroxysmal atrial fibrillation. Maybe 9% or 10% had longstanding persistent. Persistent is a very broad definition. It covers people who had atrial fibrillation anywhere from a week to months. That in itself raises some issues. Nonetheless, it was a distribution of patients commonly seen in the office.
Dr. Wazni: Actually, for me, I thought the results were very encouraging. Taking the intention-to-treat analysis and all the statistic analyses aside, this was a big study that showed that actually ablation works. It keeps people in sinus rhythm more than medical treatment. It also showed that ablation is a safe strategy in these patients. The complication rate was very, very, low. If we take into account subgroup analysis, for example, younger patients and patients who have heart failure, those patients tended to do much better when they had ablation versus medical treatment. Especially with regards to the patients who have heart failure, it corroborates the findings from CASTLE-AF Afib study in which patients were randomized to either ablation versus medical therapy in patients who had heart failure. The ones who had an ablation did a lot better.
In that sense, I think CABANA is very encouraging. Unfortunately, again, this was a very challenging study to enroll in. Even when patients were enrolled, it was very hard to get patients to stick to the arm of treatment. Frankly, it was the fact that a lot of patients who were supposed to get medical therapy ended up getting ablation even through they were in the study. It means that medical therapy is not something that patients want to stick with for the long run.
Dr. Lindsay: To put this in perspective, though, it's difficult to know what to do with an intention-to-treat analysis where there's so much crossover. If you took the patients as to what they were actually treated with, there was a reduction in cardiovascular mortality. There was a substantial reduction in hospitalizations for cardiovascular problems. The primary endpoint was reduced by a relative 23%. Where the debate will occur over the next years is what do you do with a trial with this much crossover? If you go by what the patients were actually treated with, some would argue that there is benefit from actually being treated with an ablation procedure. I think that's the debate as to whether that's a valid way to do it. I think part of it is we need to better understand the demographics of the patients who were originally supposed to get an ablation but didn't and some of the other things that would help us to determine these changes. That's where the debate will occur.
It shouldn't detract us from why patients go through these ablations in the first place. They go through the ablation to alleviate symptoms. That hasn't changed. This study wasn't about that. If any, it would support it because the recurrence rates were lower in people who had ablations. The real question is, is there additional benefit? The answer, I suppose, is maybe. This study will provoke a lot of discussion over that very subject.
Dr. Wazni: Yeah. At the clinic we have been looking very hard to determine the subgroup patients, a group of patients who would benefit from ablation, especially if it's done sooner than later. Our research is consistent that the sooner we intervene with an ablation, the better the overall outcomes, especially in younger patients and in patients who have heart failure. Actually, I am very, very, encouraged with the results from CABANA. I think in the future there will be studies that will be on a smaller scale. I think we're going to be able to do such a large study, first of all because people have learned the lesson that such a study is very difficult to manage and to conduct in the first place. I think, overall, you will continue to have data, even if it's retrospective analysis, that will show that ablation is here to stay, first for symptom relieve. Secondly, I think patients will do better overall by getting an ablation or, at least, suppressing atrial fibrillation somehow without the bad side effects that the patients have from medication.
Dr. Lindsay: I think it's important for patients and physicians to understand that it's a progressive disorder. As Oussama has pointed out, earlier intervention, according to our data, seems to offer better outcomes than if you wait too long in the course of disease where patients get progressive changes in their HA, which are harder to reverse. There is data from CASTLE trial and other data suggesting that, for patients who have heart failure, you can reduce the rate of hospitalization by getting them back to a normal rhythm. There's a lot of judgment and selection in making these kinds of decisions. Some people who are doing well didn't need to go through this necessarily. For those who do have symptoms, or in whom management would be difficult because of progressive heart failure, I think that's where it's more clear that the ablation procedure offers a benefit. As for these other parameter that we've discussed, we'll see what the debate brings us over the next five or six years.
Dr. Wazni: In our practice, Dr. Lindsay, how would you describe the patient that we now typically will offer them an ablation?
Dr. Lindsay: For me, it tends to be patients who come from around the country who have been tried on medications. They have a lot of symptoms. They aren't doing very well. Those aren't the ones that I can randomized to one versus the other. That was one of the challenges that I had in recruiting patients for CABANA. There are also patients who've read about the risks of taking antiarrhythmic medications and also recognize that the efficacy of these medicines is relatively low. There the discussion centers on the fact that ablation procedures aren't perfect either, but this is what the potential benefits are in alleviating their symptoms.
Then there's a small percentage of patients who may want to go through the ablation procedure to come off of anticoagulation. What I explain to those patients is that that's generally not the reason to go through an ablation procedure. There's a consensus that, because of the relatively high recurrence rates related to atrial fibrillation after ablation, in somebody who has a significant stroke risk you can't just stop the anticoagulation. In people with lower stroke risk, if they're monitored repeatedly and say they're a year out, then I could have that discussion. They continue to require close followup and monitoring. There are now a lot of devices that they can use with their cell phones to check their rhythm and see what that is. That provides a potential opportunity for those patients, although it's not real well proven as to whether that's the best thing to do. Perhaps you have some other perspective.
Dr. Wazni: There's one more group of patients that I would also consider ablation on. That's the patient who may not be very symptomatic but it's very clear that their left ventricular function is starting to suffer, either the LV is starting to dilate or the ejection fraction is starting to drop. In those patients, even through they would say that they might be asymptomatic, I would offer then an ablation in order to control the Afib. There has been a study recently, the Cameron Afib Study which was published in Jan, that showed even in controlled atrial fibrillation, any patient can develop LV dysfunction. If we can restore normal rhythm, then their LV dysfunction improves, especially if there's no scar on MRI. I think that's a subset of patients that I would consider for an ablation sooner than later, even if they're not that symptomatic.
Dr. Lindsay: That's a good point. Many patients that are referred to us come from heart failure doctors where they're having difficulty managing it and feel that if we could help them get the patients back into sinus rhythm it would be beneficial. Also, to put this in perspective, treatment of atrial fibrillation is not that it's only ablation or only medications. All our data and our goals are based on getting people back to a normal rhythm and getting them off of medications, but there's some in whom a combined approach is necessary. That's just reality. If we can get somebody who's struggling with atrial fibrillation, even if they're not completely cured, if we can reduce the burden of atrial fibrillation or perhaps control it with medications, they'll come back to us saying that their quality of life is much better.
Dr. Wazni: I want to thank you, Dr. Lindsay, as always. The discussion has always been great. I think the summary is we still have a lot of patients that need our help with an ablation, either because they can't tolerate the medications, the medications are not working, they want to come off an anticoagulant, or because they're developing heart failure. I want to thank you again for a great discussion. I always learn a lot by sitting here and hearing from you. Thank you.
Dr. Lindsay: One of the advantages we have is we get to bounce ideas off of each other. Thanks very much.
Dr. Wazni: Thank you.
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