minimaze.org

A few words about terminology

Unfortunately, the terminology of the Maze and "mini" maze procedures for AF can be quite confusing. It's easy to become misinformed by careless or imprecise use of terms.

The history begins during the 1980's. when James Cox, MD, developed the "Maze" or "Cox-Maze" procedure, an open-heart surgical procedure to eliminate atrial fibrillation (see Surgical Maze, below).  He is universally regarded as the dominant figure in the field; his pioneering work is the basis for essentially all curative procedures for atrial fibrillation. The terms "minimaze", "mini-Maze", and "mini Maze" refer to variations on the original Maze procedure, and are used interchangeably.

“Maze” refers to the series of incisions made in the upper chambers of the heart, which are arranged in a maze-like pattern. These incisions were intended to stop AF by blocking the irregular electrical activity by the scars of the incisions, although they may work by other methods as well. This procedure required an incision through the breastbone (median sternotomy), stopping the heart and using the heart-lung machine (cardiopulmonary bypass), and an extensive series of incisions through both upper chambers. It met with success, but had complications as well. A series of improvements were made, culminating in the Cox Maze III procedure in 1992. The Cox Maze III procedure has long been considered the “gold standard” for effective surgical cure of AF, and now, when the Maze procedure is discussed, it is usually the Cox Maze III that is meant.  This procedure goes by other names, including the “Traditional Maze” or the “Cut and Sew Maze”, and others.

A great deal of effort has since been made to equal or exceed the success of the original Maze III, while reducing the complexity and likelihood of complications.  Fewer incisions on the heart, and/or smaller incisions through the chest, led to the use of terms such as “mini-maze”, “minimaze”, and “mini maze” for these procedures.

The mini-maze was first reported in 1999, in an article entitled "Midterm results after the mini-maze procedure" (ref).  It described a procedure similar to the original Cox-Maze III in that it required cardiopulmonary bypass, a median sternotomy, and endocardial incisions, but with fewer incisions on the heart. Dr. Cox also defined the “Mini-Maze” procedure that way in an article published in 2004; in it, he specifically excluded epicardial procedures such as the Wolf MiniMaze or the microwave minimaze:

“In summary, it would appear that placing the following lesions can cure most patients with atrial fibrillation of either type: pulmonary vein encircling incision, left atrial isthmus lesion with its attendant coronary sinus lesion, and the right atrial isthmus lesion. We call this pattern of atrial lesions the “Mini-Maze Procedure” ... None of the present energy sources—including cryotherapy, unipolar radiofrequency, irrigated radiofrequency, bipolar radiofrequency, microwave, and laser energy—are capable of creating the left atrial isthmus lesion from the epicardial surface, because of the necessity of penetrating through the circumflex coronary artery to reach the left atrial wall near the posterior mitral annulus. Therefore, the Mini-Maze Procedure cannot be performed epicardially by means of any presently available energy source.” (ref)

In 2002, however, Saltman performed a completely endoscopic surgical ablation of AF (ref) ; this was performed epicardially, using microwave energy, and did not require cardiopulmonary bypass or a median sternotomy. In 2003 and 2004 he published his results (ref 2003; ref 2004). This procedure is sometimes referred to as the "microwave minimaze".

Shortly thereafter, Randall K. Wolf, MD developed a procedure using radiofrequency energy rather than microwave, and different, slightly larger incisions ("Wolf MiniMaze"). In 2005, he published his results in 27 patients (ref). Now, although the terms “minimaze”, "mini-Maze", and "mini Maze" are still used for open heart, on-pump procedures similar to the Cox Maze, the terms more often refer to the procedure that Saltman developed, and the one Wolf developed, as well as other epicardial minimally invasive surgical procedures for atrial fibrillation. Generally, these "minimaze" procedures are distinguished by:

1. No median sternotomy (vertical incision in the entire breastbone); instead, endoscopes or “mini-thoracotomy” incisions are used (between the ribs).
2. No need for cardiopulmonary bypass (heart-lung machine); instead, these procedures are performed on the beating heart, with few or no actual incisions into the heart itself.  The maze lines are made epicardially (from the outside of the heart) by heating the tissue using radiofrequency, microwave, or ultrasonic energy, or by freezing the tissue.

What curative procedures are currently available?

The Cox-Maze III procedure is still in use, but there are others. The main procedures, in approximate order of number of procedures being performed, include:

• Radiofrequency (RF) catheter ablation, performed using catheters inserted in the veins in the legs, heating and destroying sites from which AF originates
• Cox-Maze III and variations, using a sternal incision, cardiopulmonary bypass, and a series of incisions in the atria
• Epicardial bipolar RF ablation ("Wolf MiniMaze"), using incisions between the ribs, without cardiopulmonary bypass
• Epicardial microwave ablation (microwave minimaze, micromaze), using even smaller incisions between the ribs, without cardiopulmonary bypass. Dr. Saltman provides an excellent description of this procedure at the provided link.
• Variations on the procedures above, sometimes using other ways to destroy tissue such as cryoablation (freezing) or HIFU (sound waves)

A brief history of curative procedures for atrial fibrillation

Surgical Maze: James Cox and colleagues the Maze procedure during the 1980’s, modifying and improving upon it over the years, culminating in the “Maze III” procedure in 1992. Those interested in learning more can read Dr. Cox's description of it here. “Maze” refers to the series of incisions made in the upper chambers of the heart, which are arranged in a “maze-like” pattern. These incisions were intended to stop AF by interrupting the irregular electrical activity by the scars of the incisions. His pioneering work is the basis for essentially all curative procedures for atrial fibrillation, including minimally invasive ones, and even catheter ablation of AF. The Cox Maze III procedure has long been considered the “gold standard” for effective surgical cure of AF.

Recently, Dr. Cox and associates published long-term results in 112 patients receiving the Maze III procedure without other heart surgery at the same time, and 86 who were getting other heart surgery. This is considered by many to be the single best publication in the field, as it is recent (December of 2003) and includes a large number of patients who underwent the Maze procedure alone, without additional heart surgery. That's important because most people interested in catheter ablation or minimally invasive surgery for AF will not be undergoing other heart surgery at the time. This publication is available in its entirety online here. If there is but one publication that you read regarding curative procedures for AF, it is this one; you are strongly encouraged to review it.

They showed that nearly 80% of the patients who received the Maze III procedure alone were free of AF without antiarrhythmic medicines about 5 years later, but 3.6% of the patients died or had a stroke or mini-stroke during surgery, and 8% required pacemakers. They stayed in the hospital about 9 days. 23 of the 112 patients (20.5%) died, received a pacemaker, or had a major complication of some sort by their definition. The authors carefully noted limitations of the study: "The major limitation of this study was that it might have underestimated the failure rate. Electrocardiographic follow-up was not obtained on patients who stated that they were in normal sinus rhythm and had stopped all medications." " Another limitation of any long-term AF study is the possibility that the patient might have had asymptomatic episodes of AF. Our follow-up in many patients was only annual physician visit ECGs, and this might have missed asymptomatic intermittent rare episodes of AF." These limitations plague much of the literature in the field, as it has been clearly demonstrated that longer or more intensified follow-up catches much more recurrent atrial fibrillation (ref). Recently, investigators have been using monitors that the patient wears for one month that can record AF even if it occurs without symptoms; this will likely give us more accurate (but lower) estimates of success of curative procedures.

These results were better than previously published, but not good enough for many doctors and their patients to accept. In addition, the surgery was long, complex, and difficult, and was not widely adopted by heart surgeons. Perhaps the most important aspect of the Maze III procedure is that it has become the benchmark for success to which all other procedures for eliminating AF have been compared. A great deal of effort has recently been made to equal or exceed the success of the Maze III, while reducing the complexity and likelihood of complications.

How successful are these procedures?

Unfortunately, there is little consensus regarding this. Some investigators report extremely high success rates, while others wonder if successes are achieved at all. Procedures continue to evolve rapidly, so direct comparisons with long follow-up cannot accurately reflect current methods. Widely varying ways of reporting success and complication rates have made interpretation of results very difficult. In addition, for procedures that have been used for many years, such as the Cox-Maze III and catheter ablation, there is a great deal of information. However, for some of the newer procedures, such as radiofrequency, microwave, or HIFU ablation, reports are small and preliminary.

Perhaps the biggest problem in reporting of success rates is inconsistent methods of following patients to determine if atrial fibrillation has recurred. It has been clearly demonstrated that longer or more intensified follow-up catches much more recurrent atrial fibrillation (ref), hence will make that procedure appear "less successful". Because of these problems, many have called for standardization of terms and controlled clinical trials, which have yet to be performed, and likely never will.

In the absence of good comparative trials, we suggest a new metric, "Single Procedure Risk-Adjusted Success" (SPRAS), in an attempt to compare different procedures from the standpoint of patient outcome, while controlling for some of the variables that have confounded comparisons. We propose that:

SPRAS = ((Patients documented freedom from AF at one year F/U) - ((deaths * 3) + (strokes * 2) + (other major complications)) / (all patients entering the study).

In addition, SPRAS should be calculated:

• for one procedure only, excluding multiple procedures
• using only multicenter trials with greater than 100 patients
• determination of freedom from AF proven by a method that detects asymptomatic episodes
• F/U of a minimum of 6 months
• major complications defined in a standard way, including requirement for permanent pacemaker, re-operation, TIA or RIND, PV stenosis, anemia requiring transfusion, hemodynamic instability requiring intervention such as balloon pump insertion, cardiac tamponade, acute renal failure.

These data are not available for the procedures of interest today. For that reason we hesitate to make specific claims about these procedures. With those caveats in mind, it can be said that success rates of many of these procedures are likely in the 75% range. Types of complications differ between the procedures. Rare but potentially serious complications of catheter ablation, including death due to perforation of the esophagus, about 1.5% incidence of stroke, and pulmonary vein stenosis (scarring and closure of the vein, which can cause shortness of breath) have been reported with the catheter ablation approach. Complications have been very infrequent with the surgical approach, and there have been no strokes or perforation of the esophagus to date (July 2005) but because only several hundred of these procedures have been performed to date, this must be interpreted cautiously.

Each approach appears to have a role. At this time (September 2005), the surgical procedure seems to be associated with more discomfort (patients have incisional pain for several days, and complete recovery may take two to three weeks) and a longer hospital stay, but may also be associated with higher likelihood of success than other strategies. You will need to discuss with your physician which approach, if any, seems appropriate for you.

Which patients benefit from potentially curative therapies?

Generally, catheter ablation and minimally invasive surgery are appropriate for very similar types of patients; if you are a candidate for one, you are probably a candidate for the other.

Those most likely to have a good outcome have paroxysmal (intermittent) AF, have moderate or severe symptoms, have done poorly with medicines for AF, and have a heart that has not been severely damaged, for instance by heart attacks or leaking valves. Those with severely enlarged atria are unlikely to have a successful result; these procedures are not recommended for such patients.

Those who have undergone previous open heart surgery are probably less likely to have a successful result with minimally invasive surgery, unfortunately. That's because the first operation causes scarring on the outside of the heart and can make it difficult to do the minimaze. Some investigators have reported good results despite prior surgery; you can read about this here.

Are you a candidate for advanced therapy?

Most patients do well with traditional therapy, and only those patients who are likely to benefit from catheter ablation or minimaze should consider them. The flowchart below can give you some idea about this. It should be noted, however, that there are exceptions to these general guidelines, and the guidelines change frequently. Your physician will best be able to determine if you are a good candidate for advanced therapy.

What to expect from here:

If your physician believes you might benefit from advanced therapy of AF, you will be scheduled to see one of the electrophysiologists. Your records will be reviewed, and tests such as EKGs, Holter monitors, or an echocardiogram may be ordered. You will be seen in the office, and a medical history and physical examination will be performed. Therapeutic options and the pros and cons of each that are appropriate for you will be discussed. These may include:

• No change in your current management
• “Rate control plus blood thinner” strategy
• Cardioversion
• Antiarrhythmic medicines
• Pacemaker implantation with or without AV node ablation
• Catheter ablation of atrial flutter (a related rhythm disturbance that may accompany AF)
• Catheter ablation of AF
• Referral to a cardiac surgeon for minimally invasive surgery for AF

Readers interested in learning more can read about catheter ablation and minimally invasive surgery elsewhere on this site. Video of a surgical procedure is available there as well.