There are essentially three categories of procedures that presently are performed to surgically treat AF: the Cox-Maze procedure, left atrial lesion sets, and pulmonary vein isolation (PVI). Each of these approaches is described in the following.
The Cox-Maze IV Procedure
The original "cut-and-sew" Cox-Maze III procedure is rarely performed today. At most centers, the surgical incisions have been replaced with lines of ablation using a variety of energy sources. At our institution, bipolar RF energy has been used successfully to replace most of the surgical incisions of the Cox-Maze III procedure. Our current RF ablation-assisted procedure, termed the Cox-Maze IV, incorporates the lesions of the Cox-Maze III (Fig. 58-4).52 Our clinical results have shown that this modified procedure has significantly shortened operative time while maintaining the high success rate of the original Cox-Maze III procedure.53,54
The Cox-Maze IV lesion sets. IVC = inferior vena cava; SVC = superior vena cava. (Reproduced with permission from Cox JL, Schuessler RB, D'Agostino HJ Jr, et al: The surgical treatment of atrial fibrillation. III. Development of a definitive surgical procedure. J Thorac Cardiovasc Surg 1991; 101:569-583.)
The Cox-Maze IV procedure is performed on cardiopulmonary bypass. The operation can be done either through a median sternotomy or a less invasive right minithoracotomy. The right and left pulmonary veins (PVs) are bluntly dissected. If the patient is in AF, amiodarone is administered and the patient is electrically cardioverted. Pacing thresholds are obtained from each pulmonary vein. Using a bipolar RF ablation device, the PVs are individually isolated by ablating a cuff of atrial tissue surrounding the right and left PVs. Proof of electrical isolation is confirmed after ablation by demonstrating exit block from each PV.
The right atrial lesion set is performed on the beating heart (Fig. 58-5). A bipolar RF clamp is used to create most of the lesions. A unipolar device, either cryoablation or radiofrequency energy, is used to complete the ablation lines endocardially down to the tricuspid annulus because of the difficulty of clamping in this area.
Illustration of the right atrial lesion set. White lines indicate bipolar RF ablation. Cryoablation or unipolar RF energy is used to complete the ablations line at the tricuspid valve annulus.
The left-sided lesion set (Fig. 58-6) is performed via a standard left atriotomy on the arrested heart. The incision is extended inferiorly around the right inferior PV and superiorly onto the dome of the left atrium. Connecting lesions are made with the bipolar RF device into the left superior and inferior pulmonary veins and a final ablation is performed down toward the mitral annulus. Our group has shown that isolating the entire posterior left atrium with ablation lines into both left pulmonary veins resulted in a better drug-free freedom from AF at 6 and 12 months than a single connection lesion.55 A unipolar device, usually cryoablation, is used to connect the lesion to the mitral annulus and complete the left atrial isthmus line. The left atrial appendage is amputated, and a final ablation is performed through the amputated left atrial appendage into the one of the left pulmonary veins.
Illustration of the left atrial lesion set. White lines indicate RF bipolar ablation. Cryoablation is used to complete the ablation line at the mitral valve annulus.
Over the past decade, there have been a number of new surgical procedures introduced in attempt to cure AF. The results have been variable and have had a wide range of success rates.43,56–63 All of the ablation technologies have been used to create a large number of different lesion patterns. All of these procedures have generally involved some subset of the left atrial lesion set of the Cox-Maze procedure. Results have been dependent on the technology used, the lesion set, and the patient population. From a technical standpoint, all of the approaches have attempted to isolate the pulmonary veins. The importance of the rest of the left atrial Cox-Maze lesion set remains controversial. However, Gillinov et al published a large series demonstrating that the omission of the left atrial isthmus lesion resulted in a significantly higher incidence of recurrent AF in patients with permanent AF.64 To complete this lesion, it is mandatory to also ablate the coronary sinus in line with the endocardial lesion. In addition, our clinical results have shown that it is important to isolate the entire posterior left atrium.55
Pulmonary vein isolation is an attractive therapeutic strategy because the procedure can be done without cardiopulmonary bypass and with minimally invasive techniques, using either a thoracoscopic approach or small incisions. It can also be easily added to another cardiac surgery intervention (eg, coronary bypass graft or a valve procedure) with minimum increase of time to the case. Based on the original report of Hassaiguerre, it has been well documented that the triggers for paroxysmal AF originate from the pulmonary veins in the majority of cases.65 However, it is important to remember that up to 30% of triggers may originate outside the pulmonary veins.66 To increase efficacy, some investigators have added ablation of the ganglionic plexi (GP).67–69
The pulmonary veins can be isolated separately or as a box (Fig. 58-7). The most common approach for treatment of lone AF uses an endoscopic, port-based approach to minimize incision size and pain for the patient. At our center, bipolar RF clamps are favored to isolate the pulmonary veins, but unipolar radiofrequency, cryoablation, and HIFU devices have also been used.49,70,71
Diagram illustrating the methods to isolate the pulmonary veins, either separately (A), with a connecting lesion (B), or as a box isolation of the entire posterior left atrium (C).
Patient preparation begins with double-lumen endotracheal intubation. A transesophageal echocardiogram is performed to confirm the absence of thrombus in the left atrial appendage. If a thrombus is found, the procedure is either aborted or converted to an open procedure, in which the risk of systemic thromboembolism from left atrial clot can be minimized. External defibrillator pads are placed on the patient and the patient is positioned with the right side turned upward 45 to 60 degrees and the right arm positioned above the head to expose the right axilla.
An initial port for the thoracoscopic camera is placed at the sixth intercostal space. Under thoracoscopic vision, a small working port can then be placed in either the third or fourth intercostal space at the midaxillary line depending on surgeon preference and patient anatomy. The right phrenic nerve is identified to avoid injury to this structure. An incision is made in the pericardium, anterior and parallel to the phrenic nerve, to expose the heart from the superior vena cava to the diaphragm. Through this pericardiotomy, the space above and below the right pulmonary veins is dissected to allow enough room for insertion of a specialized thoracoscopic dissector. This includes opening into the oblique sinus and dissecting the space between the right superior PV and the right pulmonary artery. The dissector and a guiding sheath is introduced through a second port, either lateral or medial to the scope port, and guided into the space between the right superior pulmonary vein and right pulmonary artery. After the dissector is carefully removed from the chest, the sheath remains in place as a guide for the insertion of the bipolar RF clamp. At this point, the patient is cardioverted into sinus rhythm so that pacing thresholds can be obtained. As with a Cox-Maze IV procedure, it is critical to document pacing thresholds from the pulmonary veins before isolation. Some surgeons also use the opportunity provided by surgical exposure to test and ablate ganglionated plexi.
The sheath is attached to the lower jaw of a bipolar RF clamp. The clamp is introduced into the chest, and the left atrium surrounding the pulmonary veins is clamped and ablated. After confirmation of exit block by pacing, the instruments are removed from the right chest and the right chest ports are closed.
The approach to the left chest is similar to the right. The patient is repositioned such that the left chest is elevated 45 to 60 degrees and the left arm is held up to expose the left axilla. A port for the thoracoscopic camera is placed in the sixth intercostal space, slightly more posterior than on the right side. With thoracoscopic visualization, a left-sided working port is created in the third or fourth intercostal space (Fig. 58-8). The left phrenic nerve is identified, and the pericardium is opened posterior to the course of the nerve. The ligament of Marshall is identified and divided. The dissector is then introduced through a second port, also in the sixth intercostal space. This port site is placed to allow for a straight line introduction of the dissector around the pulmonary veins. The guiding sheath is used to position the RF clamp around the left pulmonary veins, and they are isolated. Again, conduction block is confirmed with pacing.
Patient after left atrial pulmonary vein isolation approach.
The procedure is not complete until the left atrial appendage has been addressed. Traditionally, this has been done by stapling across the base of the left atrial appendage with an endoscopic stapler. This requires careful surgical technique and attention because it can result in tears and bleeding.72 There are clip devices in development designed to address this difficulty.73,74 Further investigation is needed to determine their efficacy and safety for this purpose. After ablation of the left pulmonary veins and exclusion of the left atrial appendage, the left side of the pericardium is closed.