Over the past two decades, many different surgical ablation procedures have been proposed to replace the Maze procedure, but the stand-alone Maze procedure for lone atrial fibrillation (AF) remains the best single procedure for rhythm control for all types of AF. The cut-and-sew Maze procedure was originally introduced in 1987 after extensive research and rigid follow-up assessment that included complete electrophysiological studies 6 months postoperatively in the first 69 patients in the original series. In 1997, the minimally invasive CryoMaze-III procedure emerged as the preferred surgical approach for patients with stand-alone AF. When the minimally invasive approach was first developed, cryoablation was the only alternative to the cut-and-sew technique for creating atrial lesions. Even today, the minimally invasive CryoMaze-III procedure under direct vision or endoscopically guided , remains one of the most frequently used surgical techniques for the treatment of patients with stand-alone AF, although the group at Washington University uses a combination of bipolar radiofrequency and cryothermal energy for minimally invasive stand-alone Maze procedures.
Rationale and Surgical Indications
Although catheter ablation is associated with acceptable outcomes for paroxysmal AF with short duration and small left atria, the success rates are much lower for persistent AF and long-standing persistent AF (LSpAF; see Chapter 31 ). Surgical ablation in general, and the Maze procedure in particular, continues to offer the best long-term freedom from AF and atrial flutter in these patients and remains underused. In addition, the Cox-Maze procedure provides the largest reduction in stroke rates. The literature also shows that on-pump procedures such as the Maze procedure are not associated with higher periprocedural morbidity compared with off-pump surgical ablation options.
The hybrid Convergent procedure has demonstrated an absolute increase in freedom from AF and previously failed class I and III antiarrhythmic drugs of 17% when compared with catheter ablation alone for persistent AF and LSpAF. Like all hybrid procedures, the Convergent procedure includes both the initial epicardial ablation and an obligatory follow-up catheter ablation. Totally thoracoscopic (TT) left atrial ablation with or without follow-up catheter ablation is another option for stand-alone AF surgery, although it is suboptimal for persistent and LSpAF because it does not provide consistent transmural lesions because some of the critical left atrial lesions are performed with unipolar radiofrequency. Therefore, the success of off-pump procedures remains limited even after follow-up catheter ablation is performed as part of a planned hybrid procedure. When confronted with patients with a large left atrium (LA) and a long duration of persistent AF or LSpAF, a Cox Maze procedure offers the best single procedure rhythm outcomes with no added perioperative morbidity. Patients who undergo the minimally invasive CryoMaze-III procedure and have a documented recurrence of atrial arrhythmia should be referred for an electrophysiologic study and a touch-up ablation, which has been reported to be extremely successful.
In summary, there are currently several surgical options for patients who have persistent AF or LSpAF, including a traditional open surgical Maze procedure, a minimally invasive or robotic CryoMaze-III procedure, TT left atrial ablation without an obligatory follow-up catheter ablation, thoracoscopic–catheter hybrid procedures, and the Convergent procedure. In our opinion, the minimally invasive CryoMaze-III procedure offers a more comprehensive ablation scheme for the treatment for AF and atrial flutter, and despite requiring 60 to 90 minutes of cardiopulmonary bypass (CPB), morbidity rates are often lower than they are for off-pump hybrid or TT procedures. , Nevertheless, approximately 80% of surgical ablation for AF in the United States is performed off pump, and there is no left atrial appendage (LAA) management in 50% of those patients. By contrast, a full Maze procedure can be performed through a small incision or through a port, with no added morbidity compared with off-pump modalities. Patients should be particularly encouraged to pursue a full Maze procedure for late persistent AF and LSpAF, long duration of AF, and an enlarged LA, the most important predictors of failure after interventional AF therapy.
Screening of Patients
When evaluating a patient for a minimally invasive CryoMaze-III procedure, it is important to document any prior failed catheter ablations or prior off-pump surgical ablations. Echocardiography is important to rule out valvular disease and cardiac catheterization is helpful not only to rule out coronary artery disease but also to identify coronary artery anatomy in the left atrioventricular (AV) groove near the mitral isthmus and LAA and to note whether the patient has a left- or right-dominant circulation. Importantly, 22% of our referred patients had a diagnosis of significant valvular or coronary artery disease that led to a concomitant surgical procedure.
Preoperative evaluation should also include computed tomography angiography (CTA) of the chest, abdomen, and femoral vessels to ensure that femoral access vessels are usable and to determine whether retrograde arterial perfusion during CPB is possible. Patients who are not eligible for retrograde perfusion during CPB because of diseased femoral arteries or aortoiliac disease can be considered for axillary cannulation or direct aortic cannulation through the thoracotomy incision. The diameter of the ascending aorta should also be less than 45 mm and free of significant calcific disease. Rhythm monitors and electrocardiograms are reviewed to determine the type of atrial arrhythmia, although similar to the open surgical Maze-III and Maze-IV procedures, the CryoMaze-III procedure is equally successful in all forms of AF and atrial flutter. Finally, body mass index (BMI) is a factor for consideration. When first initiating a program, it is recommended to limit patient selection to those with a BMI under 30 kg/m², but with more experience, larger BMIs can also be undertaken. Recently, we added an option of implanting a loop recorder preoperatively, which enhances our ability to establish baseline arrhythmia burden and improve our follow-up decision making, especially regarding anticoagulation management.
Thoracotomy Under Direct Vision or Endoscopically Guided
A 3- to 5-cm mini-thoracotomy is placed along the right breast anterolateral fold. This affords a reduction in pain compared to more lateral thoracotomies, and it facilitates performance of the right atrial lesions of the Maze procedure, which are more anteriorly located. We use a special retractor and perform the operation under fibrillatory arrest if the patient has no significant aortic insufficiency, but we provide a description of the operation with use of an aortic cross-clamp and antegrade cardioplegia. If the aorta is cross-clamped, a standard Chitwood clamp or similar clamp (detachable or not) may be used. The advantages of a detachable clamp that can be placed through the incision are that it avoids a separate incision and sometimes offers a lower profile in the chest. Finally, an endo-balloon can also be used to provide aortic occlusion and deliver antegrade cardioplegia.
Principles of Cryoablation
There are two commercially available cryoablation devices that utilize either nitrous oxide or argon gas as the cryogen. Nitrous oxide devices cool the cryoprobe to approximately minus 60°C and argon-based devices usually cool the cryoprobe to approximately minus 160°C. The cryoprobe itself has a hollow shaft and records the probe temperature at its distal tip for the argon-based device and at the proximal end for the nitrous oxide device. The liquid cryogen is stored in a tank and is released through a valve into the shaft of the probe, at which point it converts into a gas. This results in cooling of the probe by the Joule-Thomson effect. Tissue cells are destroyed by direct formation of ice crystals and early and late apoptosis, disrupting the cell membrane as well as cell organelles (see Chapter 14 ). Of note, cryoablation, unlike RF, does not result in destruction of tissue architecture and does not destroy collagen. This is why cryothermia is the only ablative energy that can be safely used to ablate myocardial tissue anywhere in the heart without fear of structural injury. This includes the annulus, leaflets, chordae tendineae, and papillary muscles of cardiac valves and the coronary sinus while performing a Maze procedure. The optimal length of time one should apply a cryoprobe to myocardial tissue varies depending on multiple factors, including the temperature of the cryoprobe as well as the temperature and perfusion status of the target tissue. This topic is discussed in Chapters 14 and 20 and has been described in detail in a 2021 report by Cox and colleagues.
Left Atrial Lesions of the CryoMaze-III Procedure
After CPB is established, the oblique sinus is opened to allow for later creation of the epicardial coronary sinus lesion. After arresting the heart, the LAA can be closed with an epicardial device either at the beginning of the procedure or immediately after the LA lesions are completed and before closure of the LA. The LAA can be closed with endocardial sutures or preferably with an AtriClip (AtriCure, Inc.) passed behind the ascending aorta through the transverse sinus with the aid of a 3-0 pledgeted Prolene suture to help guide the clip to the true base of the LAA. Regardless of the stage when the LAA epicardial AtriClip is placed, the LAA orifice should be examined afterward from inside the LA to ensure that the device has been positioned all the way to the base of the LAA and has left no residual pouch.
Next, the LA is opened and the left atrial lift system is positioned to expose the mitral valve (MV) as the ablation begins with the “mitral line” across the LA isthmus and the accompanying coronary sinus lesion. These lesions must be created in the same plane, so the coronary sinus lesion is performed first, and the resultant left atrial endocardial iceball is marked with methylene blue dye to ensure overlap (see Chapters 14 and 48 ). The mitral line across the left atrial isthmus is then performed, taking care to cross the MV annulus onto the leaflets to ensure that there are no gaps at the annular level that could result in atypical left atrial flutter ( Fig. 38.1 ). There is significant morbidity associated with left atrial peri-mitral flutter as an iatrogenic rhythm because rates can be faster than AF, the rhythm less chemically sensitive to antiarrhythmic medications, and the patient more symptomatic than with AF.
Minimally invasive CryoMaze-III lesions: mitral line–coronary sinus. The surgical left atriotomy is illustrated in red, and the endocardial mitral line cryolesion and epicardial coronary sinus cryolesion are illustrated in cyan . Note that the mitral line and coronary sinus lesions are in the same plane. These two lesions prevent postoperative peri-mitral atrial flutter.
In the 90% of patients with a right-dominant coronary circulation, the mitral line–coronary sinus lesions should be placed in the so-called “watershed area” between the last marginal branch of the circumflex coronary artery and the posterior descending branch of the right coronary artery where there is no coronary artery in the AV groove. Endocardially, the lesions end up being between the P2 and P3 leaflets of the MV. With a left-dominant coronary circulation, they are placed around P3 near the posteromedial commissure. Although cryoablation does not appear to damage coronary arteries, there is some evidence for late intimal hyperplasia, so it is prudent to avoid placing the cryoprobe in direct contact with the coronary artery if possible. However, one clinical study using CTA after the CryoMaze-III procedure revealed no late coronary artery damage resulting from cryoablation near the coronary arteries.
After completion of these lesions, a box lesion that encompasses all four pulmonary veins (PVs) and the intervening posterior left atrial wall is created. We can usually create a complete box lesion with only two applications of the cryoprobe, although massive enlargement of the LA can necessitate a third application. With the first application, the cryoprobe is shaped into a U, and the linear cryolesion is created from the top of the atriotomy, around the left PVs, ending just below the left inferior PV ( Fig. 38.2 ). With the second application, the cryoprobe is shaped more linearly, and the lesion is placed from the atriotomy to just below the left inferior PV, where it overlaps with the first linear cryolesion ( Fig. 38.3 ). After the completion of the box lesion set, the atriotomy is closed, and the LA is de-aired. After de-airing of the heart, the aortic cross-clamp is removed.
Minimally invasive CryoMaze-III lesions: first endocardial cryolesion of the box around the pulmonary veins (PVs). The first linear cryolesion of the left atrial box lesion extends from the upper end of the left atriotomy, across the roof of the left atrium, around the left PVs, and ends below the left inferior pulmonary vein.
