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Mini Maze Procedure for Atrial Fibrillation More Effective, But With More Complications, Than Catheter Ablation

By Christine Welniak

  • Summary: A randomized trial showed that minimally invasive (mini maze) surgical ablation was more effective, but with more complications, than catheter ablation at treating atrial fibrillation patients who had failed a previous catheter ablation or had an enlarged left atrium.
  • Reading time: Approximately 8–10 minutes

January 9, 2012 — According to a recent study, minimally invasive surgical ablation, often called the mini maze procedure, was more effective than catheter ablation in treating atrial fibrillation patients who had previously failed a catheter ablation or who had an enlarged left atrium. Dr. Lucas Boersma, of St. Antonius Hospital in the Netherlands, presented the results of the FAST study (Atrial Fibrillation Catheter Ablation versus Surgical Ablation Treatment: A Multicenter Randomized Clinical Trial) at the American Heart Association meeting in November. The results also appeared in the on-line version of Circulation on November 14, 2011 and in the printed edition, dated January 3, 2012.

FAST enrolled 124 patients at two centers in Europe, St. Antonius Hospital in the Netherlands and the Hospital Clinic in Barcelona, Spain. FAST is the first randomized trial to compare the safety and effectiveness of minimally invasive afib surgery (mini maze) and catheter ablation.

Mini maze surgery and catheter ablation are both minimally invasive procedures used to treat afib when a patient’s symptoms are not controlled by medication. Catheter ablation is effective for most patients, though multiple procedures may be needed to achieve reported success rates of 70% or more for patients with paroxysmal atrial fibrillation and 50% or more for patients with persistent afib.

Mini maze is a term that is often used to describe minimally invasive surgical ablation. It doesn’t create a true “maze” to keep the heart’s electrical impulses on the appropriate path through the left and right atria as most mini maze procedures are performed only in the left atrium. In addition, the ablation lines may vary by physician, which can lead to misunderstandings between doctors and patients and can make a big difference in the rate of freedom from afib after ablation. For the remainder of this article, we will refer to this procedure as minimally invasive surgical ablation or surgery.

Patients, Protocol, and Techniques

Since many patients undergoing catheter ablation need a second procedure to obtain normal sinus rhythm, one of FAST’s objectives was to determine which ablation type—catheter or minimally invasive surgical—offered better freedom from afib rates for these patients. Nearly 70% of the patients in FAST had failed previous catheter ablations. Other patients had an enlarged left atrium, and some had high blood pressure. Two-thirds of patients had paroxysmal atrial fibrillation, and the remaining one-third had persistent afib.

Patients were randomized to receive either minimally invasive surgical ablation or catheter ablation. Both are closed-chest procedures. In minimally invasive surgical ablation, tissue on the outside of the heart is ablated through small incisions made on both sides of the chest. In catheter ablation, tissue on the inside of the heart is ablated through a small puncture in the groin.

Surgical ablation arm
Patients received pulmonary vein isolation, which is ablation of the area around the pulmonary veins, and ablation of the ganglionated plexi using the AtriCure Synergy bipolar radiofrequency (RF) clamp and Coolrail pen. About 30% of patients received additional ablation lines based on the doctor’s discretion. (Of note, conduction block wasn’t verified for all additional ablation lines.)

The doctors used a thoracoscope, which is a small camera inserted into the chest cavity, to directly see the heart and guide where to make ablation lines. Because a thoracoscope is integral to minimally invasive surgical ablation, you may hear some surgeons call this procedure thoracopscopic afib surgery or thoracoscopic afib ablation.

The left atrial appendage was removed in all surgery patients. The left atrial appendage is a small pouch attached to the left atrium. It is thought to lead to stroke for many afib patients, as blood clots can form within the appendage. If the clots detach, they can travel through the bloodstream and cause a stroke.

Catheter ablation arm
Patients received pulmonary vein antrum isolation using a single tip radiofrequency catheter. Patients treated at the Hospital Clinic in Barcelona were ablated with an irrigated RF catheter whereas patients at St. Antonius Hospital in the Netherlands received ablation using a non-irrigated RF catheter. A circular mapping catheter was used in all patients at both hospitals to verify that pulmonary vein isolation had been achieved.

The two centers also differed in terms of ablation lines. Patients treated at St. Antonius Hospital in the Netherlands received only pulmonary vein antrum isolation. Patients treated at the Hospital Clinic in Barcelona, however, could receive additional ablation lines based on the doctor’s discretion. In fact, nearly 50% of patients treated at the Hospital Clinic received an ablation line along the roof of the left atrium, 27% received an ablation line along the mitral isthmus, and 23% of patients had both the roof of the left atrium and the mitral isthmus ablated. The left atrial appendage was not removed in any of the patients as that is not possible during a catheter ablation procedure.

At both hospitals, doctors used fluoroscopy (x-ray) and a 3D electroanatomic mapping system to help position the catheter and guide where to make ablation lines. At St. Antonius Hospital in the Netherlands, the NavX mapping and navigation system was used; at the Hospital Clinic in Barcelona, the CARTO mapping and navigation system was used.

The study’s endpoint was freedom from atrial fibrillation, atrial flutter, and antiarrhythmic medication at 12 months. Any episode of afib or atrial flutter lasting longer than 30 seconds was considered a failure, which is in accordance with the Heart Rhythm Society recommendations for afib ablation clinical trials. Interestingly, the FAST study was designed a year before the Heart Rhythm Society guidelines were published. Patients were evaluated at one month, three months, six months and 12 months and had a seven-day Holter monitor at six and 12 months. This follow up monitoring is more rigorous than the Heart Rhythm Society guidelines.

Effectiveness Results

Minimally invasive surgical ablation was shown to be more effective than catheter ablation at stopping atrial fibrillation. Specifically, 65.6% of patients in the surgery group were free of atrial fibrillation, flutter, and antiarrhythmic drugs at 12 months compared to only 36.5% of patients in the catheter ablation group.

Dr. Boersma, who was a principal investigator of the FAST trial and lead author of the published study, commented, “It seems surprising that the efficacy of catheter ablation was so low, but we have to remember that most of the patients in the FAST trial already had failed catheter ablation. Second catheter ablation procedures only boost success by 25%-30%, so I think doctors may have been overestimating the effectiveness of second procedures.”

Dr. Ralph Damiano, Chief of Cardiothoracic Surgery at Barnes-Jewish Hospital in St. Louis, who was not involved in the study, wasn’t surprised by the results. He commented, “The efficacy of catheter ablation was what I would have expected in patients who already have failed a catheter procedure. FAST results suggest that a minimally invasive surgical ablation should be considered for these patients.”

In the published Circulation article, the authors hypothesize that having failed one catheter ablation procedure, some patients could be pre-disposed to failing a second catheter ablation. Alternatively, the authors indicate that minimally invasive surgical ablation, in which ablation is performed on the outside of the heart using a bipolar RF clamp, may be better able to achieve permanent conduction block.

Afib type
The type of atrial fibrillation could have lowered catheter ablation’s success rates, according to Dr. Boersma. The catheter ablation group had more patients with persistent atrial fibrillation than the surgery arm did. Over 40% of patients randomized to catheter ablation had persistent afib whereas only about 26% of patients who had minimally invasive surgical ablation had persistent afib. This may have affected the overall effectiveness comparison between the treatment groups, as persistent atrial fibrillation is more difficult to treat than paroxysmal afib.

“Patients in the catheter ablation group were allowed to receive extra ablation lines but this was not systematically done, and it’s possible that we didn’t ablate enough tissue. In other words, persistent patients may have been undertreated,” says Dr. Boersma.

Looking at afib type, 68.9% of surgical patients with paroxysmal atrial fibrillation met the study’s endpoint versus only 35.1% of patients in the catheter ablation group. Patients with persistent atrial fibrillation also had higher success rates with minimally invasive surgical ablation, at 56% versus 36% for catheter ablation.

Safety

Minimally invasive surgery had more early adverse events (complications) than catheter ablation, though the rate over longer-term follow up was comparable.

The major early complication rate was 23.0% for surgery compared to only 3.2% for catheter ablation. In total, there were 14 early complications in the surgery group, and two early complications in the catheter ablation group. There was one stroke in the surgery group, and one transient ischemic attack (“mini stroke”) in the catheter ablation group. Two surgery patients needed a pacemaker. In the catheter ablation group, one patient experienced pericardial effusion, which is a dangerous fluid buildup around the heart. One patient in the surgery group experienced cardiac tamponade, which is when pericardial effusion begins to compress the heart.

The magnitude, or seriousness, of early complications should be considered. About 45% of the complications in the surgery group were for a collapsed lung. Dr. Damiano commented, “Thoracoscopic afib surgery is more invasive than catheter ablation, so a higher complication rate isn’t surprising. In general, surgeons consider a collapsed lung to be a relatively minor complication that is easily fixed and only modestly affects recovery.” If a lung collapses, the surgeon will insert a chest tube into the lung to re-inflate it.

The FAST study protocol mandated that a collapsed lung be considered an early adverse event even though it is easily treated. If the six instances of collapsed lung were considered as minor safety events in comparison to a stroke, the surgery group’s early complication rate would be about 13%. In addition, some might question classifying pacemaker implantation as a complication of the same magnitude as a stroke. If the two pacemaker implantations were additionally classified as minor events, the surgery group’s early complication rate would be 9.8%, as compared to the reported 23.0% rate.

The adverse event rate during the longer-term follow up of 12 months was similar for catheter and surgical ablation, at 12.7% and 11.5%, respectively. Among those having catheter ablation, there was one death related to a cerebral hemorrhage in a patient who was taking Coumadin. There was also one stroke and another transient ischemic attack. Among those having surgical ablation, there were no deaths or strokes, though two patients had fluid build up in the chest cavity (hydrothorax), and one of those had to have the fluid drained.

Here again, if the magnitude of complications in longer-term follow up is considered, the catheter ablation group had one death, one stroke and one mini stroke and the surgery group had two instances of hydrothorax, one of which required draining.

Criticism of the FAST Trial

Since the presentation of FAST results at the American Heart Association meeting, there have been various criticisms of the trial. These include:

Success rates lower than published literature. The freedom from atrial fibrillation rate was 65.6% for afib surgery and 36.5% for catheter ablation, both of which are lower than the 70% or higher success rates in published studies of both treatment types. However, comparing FAST results to other studies is faulty. When comparing clinical trials, the first step is to compare the type of patients who were enrolled in the trials. If the patient characteristics are not similar, the trials—and the trials’ results—cannot be directly compared. FAST is the first study to focus on patients who have already failed a catheter ablation. In other words, the majority of patients enrolled in the FAST trial are not comparable to patients involved in other clinical studies. In addition, the follow up monitoring used in FAST was more rigorous than many early studies of both catheter ablation and afib surgery. Because a seven-day Holter monitor was used at six and 12 months, it’s likely that more arrhythmias (afib and atrial flutter) were detected compared to earlier studies.

Afib type. There were more patients with persistent atrial fibrillation in the catheter ablation group (over 40%) than in the afib surgery group (about 26%). Since persistent atrial fibrillation is more difficult to treat, some people believe catheter ablation’s effectiveness was skewed to be lower than the afib surgery group. Dr. Boersma indicated the FAST investigators “did not observe a significant effect” based on the type of atrial fibrillation. In addition, he noted that the FAST trial was not designed to investigate the influence of afib type on procedure outcome.

Ablation lines. There are two opposing criticisms related to ablation (lesion) lines between the surgery and catheter ablation groups. On the one hand, some critics contend that the design of the FAST trial “stacked the deck” in favor of minimally invasive surgical ablation from the outset. Their rationale is based on the surgery patients receiving more ablation, which presumably would equate to a higher freedom from afib rate. Conversely, some observers focus on the lesion lines in the catheter ablation group. These critics contend that the additional lesion lines made in patients treated at the Hospital Clinic could have reduced the number of catheter ablation patients meeting the study’s endpoint (freedom from afib and atrial flutter). Their rationale is based on the fact that ablation can lead to atrial flutter, which would have signified failure to meet the endpoint.

As a reminder, surgery patients had ablation of the ganglionated plexi (GP) as well as additional ablation lines based on the doctor’s discretion. Ablation of these GP may be a factor in surgery’s higher effectiveness rate, however, there have not been any randomized clinical trials proving this to be the case.

With regard to the differing protocols for catheter ablation at St. Antonius Hospital and the Hospital Clinic, the FAST investigators indicated that the effectiveness results were not significantly different. In other words, the placement of additional ablation lines at the Hospital Clinic in Barcelona did not significantly improve patients’ freedom from afib rates compared to patients who were treated at St. Antonius Hospital in the Netherlands.

Catheter type. Some observers have cited the use of a non-irrigated (conventional) RF catheter as a reason why catheter ablation’s effectiveness was lower than that for minimally invasive afib surgery. The FAST investigators did not find any notable difference between the freedom from afib rates for patients treated at St. Antonius Hospital (conventional RF catheter) and the Hospital Clinic (irrigated RF catheter).

What Does FAST Mean for Patients?

The FAST trial is the first randomized study to compare treatments for patients who have already received catheter ablation but who continue to have atrial fibrillation, or who have an enlarged left atrium. It adds to the body of medical knowledge of which type of patient is best suited for which type of treatment. Its results should not be interpreted that one type of treatment—be it catheter ablation or minimally invasive surgery—is superior for treating all afib patients.

The FAST trial results demonstrated that minimally invasive surgical ablation may be a better option for patients who have failed a previous catheter ablation or who have an enlarged left atrium. However, the higher rate of effectiveness of minimally invasive afib surgery comes at the cost of higher early complications, although most of these are considered “minor” by surgeons.

Patients should discuss the risks and benefits of both procedures with their doctor to determine which procedure is best suited for them. In addition, not all heart surgeons perform minimally invasive afib surgery. It’s always important to have an experienced doctor perform procedures, as greater experience is generally associated with better outcomes.

Mellanie’s Comments:

The higher early complication rate has led some critics to conclude that minimally invasive surgical ablation is not safe, and that you have a one in four chance of major complications from having one. However, most of the early complications from surgery were not considered serious and were easily fixed, and later complications were mostly insignificant. On the other hand, later complications from catheter ablation were more serious (a death, a stroke, and a mini stroke). While those may have been related to anticoagulation, they may also have been related to the procedure itself.

It’s true that afib surgery is more invasive than catheter ablation and so it’s not surprising that there were more complications, especially early on. However, I don’t believe the complications in the surgery group were as dire as some detractors suggest.

Some critics have also suggested that the study shows that minimally invasive surgical ablation is not effective. I cannot see how anyone can come to that conclusion when there was a 66% success rate, with very rigorous monitoring and high failure standards, among a population that had failed a previous catheter ablation, thus making them more challenging.

From the FAST trial results, I conclude that, contrary to what others may say, minimally invasive surgical ablation is safe and efficacious. It is worth consideration by those who have failed previous catheter ablations or who wish to decrease their stroke risk by eliminating their left atrial appendage.

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Disclaimer: Patients come first at StopAfib.org, and we do not compromise on that. For transparency, we note that StopAfib.org has received grants from AtriCure to support our patient education efforts. This article was written by an independent observer and was not reviewed by the company prior to publication.