INTRODUCTION
The goals of concomitant treatment of atrial fibrillation (AF) are to achieve high efficacy as measured by late freedom from AF and stroke, to minimize morbidity, and to be efficient so as not to prolong the operative time. When we achieve these goals, we can extend treatment to as many patients as possible. If the procedure is safe, effective, and efficient, then it should be uniformly adopted as recommended by the Society of Thoracic Surgeons Guidelines. Concomitant left atrial appendage occlusion (LAAO) has become the standard of care and should be considered the most basic addition to the primary cardiac operation. Surgical ablation of AF is equally important and adds a late survival advantage to LAAO alone in all types of AF, including paroxysmal AF. It is easier to perform LAAO and concomitant ablation in operations with an open left atrium (LA), generally mitral valve (MV) surgery, than in those in which the LA is not opened (LA closed) such as coronary artery bypass (CAB), aortic valve replacement, and aortic aneurysms. The operations with the LA closed are covered in other chapters (see Chapters 26 and 29 ). This chapter focuses on the details of MV operations with surgical ablation and LAAO. It is common for MV operations to include tricuspid valve operations and CAB. We discuss these additional procedures as well. We report the technique of the modified CryoMaze-III procedure, , which includes epicardial clip closure of the left atrial appendage (LAA). ,
Setup and Exposure
The operation is generally performed through a small incision median sternotomy and can be done through a lower or upper hemisternotomy. It also can be performed through a right thoracotomy, with or without use of a robotic assistance, although placement of the LAA clip can be more challenging through a thoracotomy. This chapter is written as if through a sternotomy approach, and surgeons can adapt the technique to another approach if desired. The technique has been described before.
Prepping and draping the patient are routine. Transesophageal echocardiography (TEE) is standard, and routine measurements are made for the MV repair (length of A2; distance between the septum and coaptation point of the mitral leaflets in systole). Routine examination of all valves, ventricular function, and left ventricular dimensions are performed. The preoperative examination in patients with AF includes LAA thrombus and “smoke” and left atrial and right atrial dimensions with close attention to tricuspid diameter and grade of tricuspid regurgitation. A Swan-Ganz catheter is optional in patients with normal biventricular function and normal preoperative pulmonary artery pressures. A percutaneous wire is placed in the femoral vein (typically on the right) and advanced into the right atrium (RA). If needed for CAB, the saphenous vein is harvested using an endoscopic approach. After sternotomy, the left internal mammary artery (LIMA) is prepared for bypass grafting if desired. The patient is given therapeutic doses of heparin, and the pericardium is opened. The ascending aorta is cannulated in the standard fashion in the distal ascending aorta. A 28-Fr percutaneous multihole venous cannula is advanced from the femoral vein. It is positioned both with the guidance of TEE and by palpation of the RA–inferior vena cava (RA-IVC) junction. The tip of the cannula should be 1 or 2 cm caudal to the junction. Cardiopulmonary bypass with vacuum assistance is initiated, and a 26-Fr right-angle superior vena cava (SVC) cannula is placed. Retrograde cardioplegia is not used; therefore, for an “LA-only” ablation, there are no incision, no perforation, no suturing, and no significant manipulation of the RA. A caval tape is placed around the RA-IVC junction, pulled up, and attached to the drapes inferiorly. This is a standard procedure to optimize MV exposure at the medial commissure. No epicardial dissection is required for a modified CryoMaze-III operation.
The cross-clamp is applied, and 1500 cc of Del Nido cardioplegia is given antegrade (200 cc more if there is mild aortic insufficiency). Cold saline (no ice) is poured on the right ventricle. The LA is opened in the interatrial groove as cardioplegia is infusing. The incision is extended below the SVC and below the IVC as is standard for mitral surgery. No dissection along the left atrial dome is needed to perform the modified CryoMaze-III procedure.
Left Atrial Appendage Occlusion and Left Atrial Ablation
When cardioplegia is complete, the heart is lifted out of the pericardium toward the right chest and held by the surgeon’s left hand with a sponge ( Fig. 27.1 ). The LAA is readily visible and collapsed because the LA is open. In the right hand, the surgeon takes a 35-mm AtriClip ACH2 (AtriCure, Inc.) and opens the clip by squeezing the handle. Because the LAA is deflated, there is no need to measure the base of the appendage. It is like a deflated balloon, and the 35-mm clip can accommodate even a large LAA when it is empty. The clip is opened (the surgeon squeezes the handle) and positioned so the assistant can pull the LAA into the clip using two forceps as the surgeon lowers the clip to the base of the LAA. The surgeon releases tension on the handle to close the clip and inspects the base of the clip. Visually, the surgeon confirms it is at least 2 mm away from the circumflex coronary artery, which is typically visible near the base of the appendage ( Fig. 27.1 , inset ). The surgeon and assistant also inspect the clip placement to look for symmetry. One side or the other may not be as low as desired on the LAA. If so, the clip is reopened and repositioned with traction from the assistant. Most often repositioning is not necessary because placement is very straightforward. When both are satisfied with the clip position, the assistant cuts the sutures, and the surgeon removes the handle to release the clip. The heart is placed back in the pericardium. On average, this whole process from the time of lifting the heart, positioning and releasing the clip, removing the handle, and replacing the heart in the pericardium takes less than 2 minutes.
When cardioplegia is complete and the left atrium (LA) is open, the left ventricle is elevated and tipped to the patient’s right to expose the left atrial appendage (LAA). The LAA is empty, like a deflated balloon, because the LA is open. The surgeon takes a 35-mm AtriClip and squeezes to open the clip for positioning over the LAA while an assistant uses forceps to pull the LAA into the clip and align at the base. After releasing tension on the clip handle, visual confirmation and repositioning are performed to achieve symmetrical placement at least 2 mm from the circumflex artery, and the clip is at the LAA base. The sutures are cut, and the handle is removed to release the clip. The clip will cause tissue necrosis and electrical isolation of the LAA.
If CAB is to be performed with saphenous vein grafts, then the distal anastomoses are performed at this time. This allows for redosing of cardioplegia down the vein graft if desired. The LIMA to left anterior descending (LAD) anastomosis can be performed at this point, or more often, just before removing the cross-clamp. After placing the clip (and CAB distals), attention is returned to the LA. Two self-retaining retractor blades are placed in the same position for the modified CryoMaze-III procedure as for mitral exposure.
Our modification of the minimally invasive CryoMaze-III procedure recreates all of the lesions of the original minimally invasive CryoMaze-III lesion set (see Chapter 14 ), which in turn recreated the lesion pattern of the original cut-and-sew Maze-III procedure (see Chapter 12 ) ( Fig. 27.2 ). However, all of these lesions are created in our modification with only three cryoablation applications in the LA and three cryoablation applications in the RA ( Fig. 27.3 ). This modification simplifies the procedure and shortens the time needed to create the entire biatrial Maze-III lesion pattern. As in all previous iterations of the Maze procedure, the ablation lines should be uniformly transmural, contiguous (no gaps), and anchored to an area that cannot conduct an electrical wavefront (mitral or tricuspid annulus, or SVC/IVC in the RA) ( Fig. 27.4 ). The 10-cm flexible cryoprobe (AtriCure Cryo Flex) can achieve these goals, and the ability to shape the probe to the atrial wall makes it easy to use. The long length of the probe allows a longer ablation line than the shorter reusable probes that were originally used for arrhythmia surgery, including the Maze procedure ( Fig. 27.5 ).
(A) Cut-and-sew Maze-III lesion pattern. Virtually all of the lesions of the original cut-and-sew Maze-III procedure were performed using a knife and/or scissors (red lines). However, there were several specific places in the lesion pattern where cryosurgery was used, those being at the mitral and tricuspid annuli and across the coronary sinus. (B) Minimally invasive CryoMaze-III lesion pattern. In the mid-1990s, the minimally invasive CryoMaze-III procedure replaced the original cut-and-sew Maze-III procedure, but the lesion patterns remained identical. However, with the exception of the two atriotromies performed for exposure purposes, all of the lesions in the CryoMaze-III procedure were performed using nondisposable linear cryoprobes (pale cyan lines). When the modern disposable, flexible, linear cryoprobes became available, they became the tools used to perform the minimally invasive CryoMaze-III procedure.
Modified CryoMaze-III procedure lesion pattern. The modified CryoMaze-III procedure was developed to make the CryoMaze-III procedure quicker and easier to perform. The modern long, flexible, linear cryoprobes can be formed into virtually any desirable shape, which allowed us to use them to create all of the Maze-III lesion pattern with only three cryoablation applications in the left atrium and three cryoablation applications in the right atrium. Comparing this figure with Fig. 27.2 confirms that all of the biatrial Maze-III lesions can be created with these six cryoablation applications.
The modified CryoMaze III procedure consists of three left atrial ablations that reproduce the Cox Maze III lesion set. The cryoablation lines must be transmural, contiguous, and anchored to tissue that cannot conduct an electrical wavefront such as the valve annulus. The lesion set, as drawn, reproduces the box lesion, mitral isthmus line, and coronary sinus ablation (not pictured). The left atrial appendage (LAA) has been closed with an epicardial AtriClip, which induces left atrial necrosis; therefore, the LAA is electrically silent. The ablation line across the dome of the left atrium also crosses the base of the LAA, so there is no need for a separate ablation line to the LAA.
The disposable 10-cm flexible cryoprobes (top) have several advantages over the older, shorter, reusable cryoprobes (bottom). The disposable cryoprobe can easily and rapidly be bent into the proper form for each ablation. It can also be manipulated into a variety of shapes. Pressure on the probe or outside the atrium, pushing atrial tissue onto the probe, allows long, continuous ablation lines with no gaps. The longer length of the probe allows for the creation of long ablation lines with fewer applications than the reusable probes can provide.
The first ablation line outlines the superior portion of the box lesion around the pulmonary veins (PVs) and the LAA ( Fig. 27.6 ). It covers the dome of the LAA and the base of the LAA, and the tip of the probe is usually (depending on LA size) about at the level of P2. For the first line, the probe is bent into a C shape. The base of the probe is positioned at the superior extent of the atriotomy under the SVC. The gentle curve of the probe covers the dome of the LA and, importantly, the LAA. The portion of the probe near the distal end extends along the left side of the LA, midway between the PVs and the mitral annulus. With a small LA, the tip of the probe may extend to P3. The probe may be quickly reshaped and repositioned at the distal end so that it is in good atrial contact and in the correct position between the PVs and mitral annulus. The surgeon pushes the probe into contact with the atrial wall with gentle pressure. Forceps or a sucker tip may help maintain contact and eliminate a small tissue fold. When the probe is in good position, a 3-minute freeze is begun. The probe quickly adheres to the tissue. The surgeon may release the forceps holding the probe in place because the probe sticks to the tissue rapidly and will not move. The assistant can hold the probe in place while the surgeon begins to inspect the MV, so no cross-clamp time is wasted. At 3 minutes the probe is thawed and removed from the tissue. It is important to confirm visually that there were no small folds that could leave a gap in the cryolesion. If so, a “spot” freeze on the gap may be needed, although this is unusual.
