In 1987, Dr. James Cox pioneered an open-heart surgical procedure to cure atrial fibrillation. The Cox maze procedure involved making incisions in a maze-like pattern on the left and right atria (the heart’s upper chambers). When these incisions healed, the resulting scar tissue blocked erratic electrical impulses. In effect, the scar tissue created a barrier so that the abnormal electrical impulses could no longer be conducted throughout the heart.
The first maze pattern was used for 32 patients, 56% of whom had paroxysmal atrial fibrillation. Although 90.6% of patients were free from afib after three months1, Dr. Cox and his colleagues found that the patients couldn’t achieve an optimal heart rate during exercise tests. The researchers found that the initial maze pattern affected the normal function of the sinus (sinoatrial) node. They reconfigured the placement of some incisions (the Cox maze II), which was performed on just 15 patients because the procedure was complicated.
A subsequent incision pattern became known as the Cox maze III procedure. In long-term follow-up, 97% of patients were free from atrial fibrillation.1 Because of its high effectiveness rate, the Cox maze III procedure became the gold standard for surgical treatment of atrial fibrillation.
In addition to being the first procedure to stop atrial fibrillation, three things are important about the Cox maze procedure. First, the incisions create a “maze” that keeps the heart’s electrical impulses on the appropriate path so that the atria and ventricles open and contract at the right time and in the correct order. Second, incisions are bi-atrial, on both the left and right atria, not just in the left atrium. Third, the incisions are transmural. Transmural simply means that all layers of tissue have been penetrated. Transmurality is essential to permanently block abnormal electrical impulses.
Removing the left atrial appendage is another crucial part of the Cox maze procedure as that may decrease an afib patient’s stroke risk. The left atrial appendage is a small, tongue-shaped sac attached to the left atrium. When blood is caught in the left atrial appendage, clots can form. If clots detach from inside the left atrial appendage, they can travel through the bloodstream and cause a stroke.
Because over 90% of clots are believed to form in the left atrial appendage, it is thought that removing or cutting off blood flow into the appendage will lower the stroke risk for afib patients. Long-term follow-up on the first 198 Cox maze III patients at Barnes-Jewish Hospital supports this theory as only one patient had a late stroke.2
Some people dispute the high effectiveness rate published by Dr. Cox and colleagues. However, it’s important to remember that these results were published about 10 years before the first Heart Rhythm Society Expert Consensus Statement.3 This consensus statement, issued in 2007, set standards for catheter and surgical ablation clinical studies.
Dr. Cox and colleagues reported a 97% rate of freedom from atrial fibrillation. However, some patients remained on antiarrhythmic medication. Nevertheless, the success rate was 93% when considering only those patients who were free of afib, atrial flutter, and antiarrhythmic drugs.1 Clearly, this was still a high effectiveness rate.
However, effectiveness must be assessed based on a period of time. Today, clinical study effectiveness results are reported at six months, one year, two years, etc. Dr. Cox and colleagues did not use a specific time period for results. Instead, they reported effectiveness results “at last follow up” (in other words, during the patient’s last office visit or telephone interview).
Thus, some patients who were considered successes may have had the Cox maze III procedure only six months previously. In contrast, others may have had the procedure three years earlier. That can make a difference in effectiveness rates. Of note, in later published reports, the effectiveness rate did decrease to 73–80% for the initial Cox maze III patients.2
Some people think the Cox maze III effectiveness rate is overstated because of the follow-up monitoring performed. Specifically, patients were contacted by phone or mail and asked whether they were experiencing any atrial fibrillation.
Today, at a minimum, patients in afib ablation studies have a 24-hour Holter monitor at six and 12 months, and it’s not uncommon for a seven-day Holter monitor to be used. Since some afib episodes are asymptomatic, critics say that basing the effectiveness rate on patient self-reporting doesn’t accurately reflect all afib activity. Because of this, some people believe the actual success rate of the Cox maze III is lower.
The Cox maze III procedure, called the “cut-and-sew maze,” is rarely performed today because of the complexity of the procedure. Still, it remains the gold standard for afib surgery.
Most surgeons who perform afib procedures today use an energy source, such as radiofrequency energy, to ablate the heart tissue instead of making incisions. When done as an open-chest procedure, it is called a Cox maze IV surgical ablation procedure.
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New technologies and techniques have allowed surgeons to perform a simplified Cox maze surgery. Instead of making incisions, the surgeon uses either a probe or a clamp to apply a surgical ablation energy source to heart tissue. Energy sources such as radiofrequency or cryothermy are used to scar tissue in the left and right atria. This is called bi-atrial ablation and is a cornerstone of a “true” Maze procedure. Like the Cox maze III, the Cox maze IV is done with the patient on the cardiopulmonary bypass machine (often called a heart-lung bypass machine).
The Cox maze IV lesion set is similar to the pattern used in the Cox maze III procedure. First, the pulmonary veins are ablated, and additional lines are made to direct electrical activity along the appropriate path in the heart. After the ablated tissue heals, the resulting scar creates a conduction block that stops abnormal electrical impulses from progressing through the atria.
The left atrial appendage is often removed or occluded during the procedure to lower the patient’s stroke risk. The left atrial appendage can be closed manually with the use of a surgical stapler or sutures. However, a study performed at the Cleveland Clinic showed that only 40% of 137 manual left atrial appendage excisions or occlusions using these techniques successfully stopped the blood from flowing into the appendage.4
The FDA approved the AtriClip Gillinov-Cosgrove Left Atrial Appendage Occlusion system in June 2010 for left atrial appendage occlusion (closure) during open-heart surgery. While this device does not have specific FDA approval for afib stroke reduction, it was shown to occlude the left atrial appendage in most patients in clinical studies.
The surgical ablation version, the Cox maze IV, is much faster than the original cut-and-sew Cox maze III procedure and is considered very effective.5 The Cox maze IV may be done as a concomitant procedure when performed during another heart surgery. Or, it may be done as a standalone procedure for afib only.
Surgical ablation is often performed simultaneously with another heart surgery, such as valve replacement or repair or coronary artery bypass (CABG). In fact, the HRS Consensus Statement recommends that afib patients who need heart surgery undergo surgical ablation instead of catheter ablation to treat their afib. When performed simultaneously with another heart surgery, the procedure is called “concomitant ablation.” In addition, per the HRS Consensus Statement, which was updated in 2012, patients do not have to fail antiarrhythmic drugs to be considered for a concomitant procedure.6
Not getting afib treated at the same time as another heart condition reduces life expectancy and increases stroke risk. For instance, the death rate for afib patients who did not receive concomitant ablation during coronary artery bypass grafting (CABG) surgery was more than 20% higher than for those who did. Those patients also experienced double the stroke rate at 10 years. Afib patients who didn’t receive concomitant ablation with aortic valve surgery had worse late survival and a higher stroke rate (25% when afib wasn’t treated versus 10% when it was). For afib patients having mitral valve surgery, untreated afib resulted in an 18% higher death rate than for afib patients ablated during mitral valve repair or replacement.7
Concomitant ablations are generally open-chest Cox maze IV procedures. The ablation pattern (lesion set) can vary by doctor. At a minimum, the pulmonary veins are ablated, and most doctors confirm that the pulmonary veins have been isolated. The left atrial appendage is generally removed or closed during open-chest concomitant procedures.
But, “maze” has become a catch-all term meaning different things to different doctors. For example, some surgeons ablate both the left and right atria; others only ablate the left atrium. The term “maze” is often applied to any surgical ablation, leading to misunderstandings between doctors and patients. For example, some surgeons will refer to doing a “maze” procedure but only make ablation lines in the left atria. If only the left atrium is ablated, then a true “maze” has not been created. If you’re considering a surgical ablation, you will want to know what lesion set will be used, as different ablation patterns have different levels of effectiveness.
Some heart centers now perform concomitant ablation as a minimally invasive, closed-chest procedure. For instance, some surgeons perform closed-chest mitral valve repair and afib ablation using the da Vinci robot.
Some afib patients have surgical ablation when they do not have another heart condition that requires surgery. When surgical ablation is performed in this manner, the procedure is called a standalone Cox maze IV ablation procedure. As with the concomitant procedure, the standalone procedure is done with the chest open and the patient supported by a cardiopulmonary bypass machine.
Since a standalone Cox maze IV ablation procedure may be extreme for those with only afib, the minimally invasive (mini maze) surgical ablation is more commonly performed. It is a closed-chest procedure that typically doesn’t require the cardiopulmonary bypass machine.
If you’re considering a Cox maze IV surgical ablation procedure for your atrial fibrillation, with or without other heart issues, you need to know about Maze Procedure Success Rates, Maze Procedure Risks, and Are You a Candidate for a Maze Procedure.
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