The Maze procedure was developed to preclude or interrupt the macro-reentrant drivers that sustain atrial fibrillation (AF). It was first performed clinically in 1987, some 11 years before Haïssaguerre showed that pulmonary vein (PV) triggers induced most episodes of AF. Since that time, improvements have evolved in the lesion patterns and in the surgical tools to create them, but the basic concept of the Maze procedure has not changed. Radiofrequency (RF) energy was introduced for the catheter ablation of arrhythmias other than AF in the early 1990s, but attempts to reproduce the Maze procedure with RF catheters at that time proved to be futile. This was not because of an inadequate energy source but because of the limitations of the catheter technique in creating lesions in the essential areas of the atrium to interrupt the macro-reentrant drivers. The era of catheter ablation for AF began in 1998 when Haïssaguerre demonstrated that PV triggers induced AF and that the number of recurrent episodes of paroxysmal AF (PAF) could be dramatically reduced or completely abolished by isolating the PVs (PV isolation [PVI]) with RF catheters. The use of PVI for more persistent forms of AF was not recommended by Haïssaguerre in that article, but despite this fact, PVI subsequently became widely applied for nonparoxysmal AF (non-PAF) as well. It soon became clear that although catheter PVI for PAF was quite successful, the results of PVI for more persistent forms of AF were dismal.
After Haïssaguerre’s seminal 1998 report, bipolar RF clamps and unipolar RF surgical devices were developed to provide surgeons with an alternative to surgical incisions and linear cryoprobes. The bipolar RF clamps have been quite successful for the treatment of AF when performing either PVI for PAF or in creating lesions of the Maze-III or Maze-IV procedure for more complex forms of AF. There is no reason to expect that surgical PVI is any better than a well-performed catheter PVI for the treatment of non-PAF, but some surgeons were willing to accept the suboptimal results of PVI for non-PAF as long as the procedure could be performed off pump and through smaller chest incisions. This compromise represented a paradigm shift in the primary surgical objective of AF surgery from seeking the best possible outcomes to seeking the least invasive procedures . With rare exceptions, these “minimally invasive” procedures for AF eschewed the use of cardiopulmonary bypass (CPB) even though CPB has been the seminal tool that has allowed cardiac surgery to be performed safely for more than 70 years.
The desire to develop a surgical procedure less invasive than the Maze procedure for AF was, and remains, a laudable goal. However, there is concern that relatively uninformed patients are not always allowed to participate in the decision regarding which approach is to be used for their own surgery (i.e., the traditional “better outcomes” approach or the more recent “less invasive” approach). Nevertheless, the compromise between better outcomes and less invasion led to the development of the Wolf Mini-Maze procedure, the left atrial Maze procedure, the Dallas lesion set, the five-box Maze procedure, and many other unnamed and untested surgical interventions for the treatment of patients with all types of AF. In the process, the term “Maze procedure” became the generic designation for virtually any surgical procedure used to ablate AF. , This generic use of the term “Maze procedure” skews the perception of the success rates of an actual Maze procedure, leading to confusion not only among patients but also among surgeons and cardiologists. ,
Wolf Mini-Maze Procedure
In 2005, Wolf and colleagues reported a series of 27 patients who underwent a minimally invasive surgical procedure for AF performed through bilateral mini-thoracotomies that included PVI with a bipolar RF clamp and occlusion of the left atrial appendage with a stapler ( Fig. 19.1 ). Two-thirds of the patients had PAF, and the patients were followed for an average of 6 months. Of the 25 patients followed for at least 3 months (the usual blanking period), 91% (21 of 23) were free of AF. No mention was made of whether or not the patients were also free of atrial flutter and/or atrial tachycardia, both of which constitute procedural failure. , Nevertheless, this was an exciting initial report of a promising new minimally invasive approach for the treatment of patients with AF.
The original Wolf mini-Maze procedure included isolation of the right pulmonary veins (A), isolation of the left pulmonary veins (B), and occlusion of the left atrial appendage (LAA) using a stapling device (C). In later iterations, the LAA was occluded with an AtriClip and ganglionic plexus ablation was added. Recently an SVC–inferior vena cava (IVC) intercaval lesion was included in which a bipolar radiofrequency clamp is placed on the posterior right atrial and left atrial walls as illustrated (D). LA, Left atrium; LIPV, left inferior pulmonary vein; LSPV, left superior pulmonary vein; RA, right atrium; RIPV, right inferior pulmonary vein; RSPV, right superior pulmonary vein.
According to the current website (wolfminiMaze.com), Wolf has now performed “over 2,000 Wolf Mini-Maze procedures since the first one in 2003, and has demonstrated the procedure to over 800 heart surgeons worldwide.” Unfortunately, there is no evidence in the literature that this large personal series of Wolf mini-Maze procedures, or even a sizeable cohort of it, has ever been subjected to the peer-review process for publication of a scientific article. In a 2007 review article, the success rate for the procedure was again stated to be 91% with no other information on results provided. A two-page update of the procedure published in 2014 contained no patient data but mentioned that ganglionic plexus ablation had been added to the procedure since its original description in 2005. In a separate 2014 perspective article it was stated:
“Recently we reviewed 157 patients who are now 1 to 9 years out from the Wolf procedure. The patients’ ages ranged from 15 to 87 years old. The cure rate for paroxysmal AF was 92%, 85% for persistent AF, and 75% for long-standing persistent AF. The follow-up included 7-day continuous monitoring. There were no deaths (personal review).”
No other information on freedom from recurrent arrhythmias, statistical analysis, or outcomes was provided, and there was no reference for this data summary, leaving one to conclude that even this cohort of 157 patients had not been subjected to the peer-review process. A 2021 review titled “Surgical Treatment of Atrial Fibrillation” published in the Methodist DeBakey Cardiovascular Journal again stated: “The AF-free rate is 92% for paroxysmal AF, 85% for persistent AF, and 75% for long-standing persistent AF.” It was also mentioned that “After more than 1,000 procedures using a stapler to close the LAA, we transitioned to clip closure of the LAA (Atriclip, Atricure, Inc.).”
The only other outcomes mentioned in that 2021 review were those from the biatrial Maze procedure arm of the cardiothoracic surgical trials network (CTSN) Clinical Investigators prospective randomized trial. As described in Chapter 13 , the patients in that trial who had mitral valve (MV) or double valve surgery had persistent or long-standing persistent AF (LSpAF), and the results of concomitant surgical AF ablation are among the poorest in the literature (66% success at 1 year). Because the Wolf mini-Maze procedure is used in patients with stand-alone AF rather than concomitant AF in patients undergoing coronary artery bypass graft or valve surgery, perhaps it would have been appropriate to mention that in 2017, Ad and colleagues reported their results with the minimal invasive CryoMaze-III procedure for stand-alone AF, 78% of which was LSpAF, as being successful in 73% of patients at 5 years. The year after the 2021 review, Damiano’s group reported their results for stand-alone AF, 75% of which was non-PAF, as being successful in 89% of patients at 5 years. It is unfortunate that after performing the Wolf mini-Maze procedure in more than 2000 patients, we still have only the original peer-reviewed report on 27 patients with an average of 6 months of follow-up to compare with the safety and efficacy of other minimally invasive surgical procedures for AF.
Left Atrial Maze Procedure
As mentioned in Chapter 13 , there are several publications in the literature suggesting that the right atrial lesions are unnecessary or that they are only incidental to the success of the Maze procedure for the treatment of patients with AF. Thus, it is understandable that surgeons might choose to delete the right atrial lesions and perform only the left atrial lesions of a Maze procedure, especially when ablating AF caused by left-heart problems such as coronary artery disease or left-sided valve abnormalities. Of course, if lesions are not placed in both atria, the procedure cannot rightfully be called a “Maze procedure” because a complete maze cannot be placed in only half of the contiguous atrial myocardial mass any more than a complete maze can be drawn in only half of a square. Thus the so-called “left atrial Maze” procedure is not a Maze procedure at all, even if every left atrial lesion of a Maze-III or Maze-IV procedure is created and placed perfectly.
The major problem with the concept of performing a “left atrial Maze” procedure in patients with non-PAF is that up to 30% of the macro-reentrant drivers that sustain AF can be located in the right atrium (RA; Fig. 19.2 ). , As described in Chapter 13 , if these potential right atrial drivers are not addressed, they can continue to sustain AF, and the left atrium (LA) will be a passive bystander in the fibrillation ( Fig. 19.3 ).
Sites of documented right atrial macro-reentrant drivers of atrial fibrillation (AF). Up to 30% of all macro-reentrant drivers that can potentially sustain AF are located in the right atrium. See text for discussion.
Preoperative phase map of the atria a patient with non-paroxysmal atrial fibrillation (AF). In this single frame from a video of sustained AF, two active macro-reentrant drivers are clearly visible in the right atrium. Note that the entire left atrium is being passively activated in response to the two right atrial drivers. MV, Mitral valve; TV, tricuspid valve.
In patients who have left-heart abnormalities such as coronary artery disease, aortic and/or MV disease, heart failure, or systemic hypertension causing AF, the location of the AF drivers may be confined to the LA early in the disease process because the RA is still normal and therefore incapable of harboring more than one macro-reentrant circuit at a time because of the long refractory periods in the RA (see Chapter 4 , Figs. 4.14 and 4.15 ). Of course, both atria are fibrillating in these patients, but the RA is fibrillating passively in response to the multiple AF drivers in the LA that are sustaining the AF. Therefore, if a patient with MV regurgitation undergoes MV repair early in the course of the disease before the RA is actively involved in sustaining the AF, it would be expected that ablative lesions confined to the LA would be as effective as biatrial ablative lesions. However, later in the course of the MV regurgitation when the RA is capable of actively sustaining AF drivers, deleting the RA lesions of the Maze procedure ( Fig. 19.4 ) may result in failure of the surgical procedure ( Fig. 19.5 ).
Anterior and posterior views of the atria showing the locations of surgical lesions a “left atrial Maze” procedure for atrial fibrillation. In addition to the left atrial lesions, a right atrial intercaval lesion between the superior vena cava (SVC) and inferior vena cava (IVC) was added for unknown reasons in this particular patient. A coronary sinus lesion, not shown here, was also created in the plane of the mitral line to prevent postoperative peri-mitral flutter. Each of these left atrial lesions is placed in the perfect position, as is the intercaval line in the right atrium (RA). LA, Left atrium; LAA, left atrial appendage.
Failed “left atrial Maze” procedure for non-paroxysmal atrial fibrillation (non-PAF).
These are four frames from a postoperative video of recurrent AF after the left atrial Maze procedure shown in the Fig. 19.4 that demonstrate the importance of including the right atrial lesions in patients with non-PAF. They document that each of the left atrial lesions except the right atrial intercaval lesion is functioning perfectly as a line of bidirectional conduction block:
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The four pulmonary veins and posterior left atrial wall are successfully isolated from the rest of the atrial myocardium by the box lesion (A–D).
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The mitral line blocks conduction in both directions (A and B).
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The LAA line blocks conduction in both directions (A and D).
However, the right atrial intercaval line blocks conduction only from medial to lateral (C) but not from lateral to medial (B), so it has resulted in a unidirectional conduction block only. The drivers that are sustaining AF are clearly documented in all four frames of the video:
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130 ms after the beginning of the video, two macro-reentrant circuits are simultaneously driving AF, one located in the anterior right atrium (RA) and another in the posterior RA.
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The 1415-ms frame shows three simultaneous AF drivers, two in the anterior RA and one in the posterior RA. Note the smooth, passive activation of the left atrium (LA) in response to the active AF drivers in the RA.
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At 1575 ms, the two RA drivers are still apparent, and passive activation of the LA continues.
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At 1965 ms, two drivers are still active in the RA, and a new passive wavefront generated by these two drivers is being conducted passively across the LA.
This series of snapshots from a video of sustained AF after a perfectly performed left atrial Maze procedure demonstrates the importance of performing the RA lesions when treating patients with non-PAF. They also show the futility of trying to use mapping to determine precisely where surgical or catheter lesions should be placed to ablate AF because these drivers change locations every few milliseconds. It is a graphic demonstration of why interventional therapy for AF cannot be map guided reliably even with the ready availability of such sophisticated mapping techniques.
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