Several off-pump, minimally invasive surgical procedures were developed in the early 2000s for the treatment of patients with stand-alone atrial fibrillation (AF) in an effort to make AF surgery less invasive and more accessible to a larger number of cardiac surgeons. The minimally invasive, off-pump procedures incorporated epicardial lesions only and were performed either via bilateral mini-thoracotomies or totally thoracoscopically with or without video assistance. , In 2007, Dr. Andy Kiser described a novel approach to surgical AF ablation called the “Ex-Maze” (extra-cardiac Maze) procedure in which a small midline incision was made in the upper abdomen and a specially designed pericardioscope was inserted into the abdominal cavity. The abdomen was then insufflated to separate the liver from the diaphragm, and the posterior pericardial space was entered through the dome of the diaphragm to expose the posterior left atrium (LA) and pulmonary veins (PVs). He then created multiple epicardial lesions in the left and right atria using radiofrequency (RF) ( Fig. 36.1 ).
Lesions of the original extracardiac Maze (“Ex-Maze”) procedure performed on a beating heart. The back of the heart was accessed by a minimally invasive, trans-abdominal, trans-diaphragmatic route, and all lesions were performed epicardially using a vacuum-assisted unipolar radiofrequency ablation device.
(Reproduced from Kiser AC, Wimmer-Greinecker G, Chitwood WR. Totally extracardiac Maze procedure performed on the beating heart. Ann Thorac Surg. 2007;84:1783–1785.)
This original trans-abdominal, trans-diaphragmatic surgical approach was eventually replaced by a subxiphoid approach as the Ex-Maze procedure evolved into the contemporary Convergent hybrid procedure.
Although left atrial appendage occlusion (LAAO) was not a part of the original Convergent procedure, thoracoscopic LAAO through the left chest has become a common part of the procedure since 2017. Other means of addressing the left atrial appendage (LAA) have also included percutaneous endocardial devices and external suture ligation.
The initial version of Convergent ablation was conducted as a “joint” or same-day procedure, but the addition of LAAO and practical workflow considerations necessitated a “staged” approach in which endocardial catheter ablation is delayed until recovery of the thoracoscopic epicardial lesions. Follow-up catheter ablation in a staged Convergent hybrid procedure can be performed within the same hospitalization or several weeks after the initial thoracoscopic stage.
Role of Posterior Left Atrial Wall Isolation or Ablation in Surgery for Atrial Fibrillation
Although PV isolation remains the cornerstone of all catheter and surgical AF ablation procedures, the posterior left atrial wall between the right and left PVs is also important in the genesis and perpetuation of AF. This area is complex in structure, sharing similar origins developmentally with the PVs and presumably maintaining their propensity to induce episodes of AF. Indeed, failure to isolate this area effectively was the only predictor of poor outcomes in an analysis of the late clinical results of one version of the Cox Maze-IV procedure. The presence of varying myocardial fiber orientation and discrete septo-pulmonary and septo-atrial bands creates anisotropy of conduction, leading to slow conduction (see Chapter 3 , Fig. 3.13 ). The posterior wall of the LA between the right and left PVs is believed to harbor approximately 20% of the atrial triggers responsible for inducing concomitant AF and some 30% of the macro-reentrant drivers responsible for sustaining persistent and long-standing persistent AF (LSpAF) use this area as a part of their reentrant circuit. Therefore, if this area is neither isolated nor ablated, it will result in an obligatory failure rate of at least 20% in patients with paroxysmal AF and at least 30% in patients with non-paroxysmal AF undergoing catheter or surgical ablation of AF (see Chapter 25 ).
Convergent Procedure Technique
Whereas the box lesions of the on-pump surgical Maze-III and Maze-IV procedures are created to isolate the posterior left atrial (LA) wall along with the four PVs, the off-pump hybrid Convergent procedure is designed to ablate the posterior LA wall and isolate the PVs by combining thoracoscopic epicardial ablation and catheter-based endocardial ablation.
Thoracoscopic Closure of the Left Atrial Appendage
The patient is positioned supine with a bump placed under the left thorax toward the spine. Standard anesthetic monitoring includes an arterial line, central venous access, large-bore peripheral intravenous lines, and an oropharyngeal temperature probe positioned under fluoroscopic guidance to monitor esophageal temperature during the epicardial ablation. A bronchial blocker or double-lumen endotracheal tube is commonly used for intubation to allow for single right lung ventilation and left lung decompression during the initial thoracoscopic closure of the LAA. If the LAA is not closed thoracoscopically, a single lumen endotracheal tube can be used. We perform a transesophageal echocardiography (TEE) at the outset of the operation to ensure that there is no thrombus in the LA or atrial appendage and to assess left ventricular function and valvular competency. TEE is also used during the thoracoscopic LAAO to confirm complete LAA exclusion using multiple views, including three-dimensional reconstruction. Although the stages of the surgical procedure can be performed in different orders, our current practice is to perform the thoracoscopic LAAO before the subxiphoid epicardial ablation.
In addition to elevating the left chest, the operating table can be positioned in the reverse Trendelenburg position and tilted to the right to improve visualization. A 5-mm 30-degree scope is inserted in the sixth intercostal space (ICS) along the mid-axillary line, the pleural space is insufflated with carbon dioxide, and all pleural adhesions are divided. A second 5-mm port is inserted in the fourth ICS at the mid-axillary line, and a final 12-mm port in the eighth ICS at the posterior axillary line for delivery of the LAA clip. The phrenic nerve is identified, and the pericardium is incised 1 to 2 cm posterior to it. The pericardiotomy is extended caudally to the mid-ventricular level and cephalad to the main pulmonary artery trunk level. An endo-Kittner is used to expose the LAA through the pericardiotomy, and the Ligament of Marshall is identified and divided with an electrocautery ( Fig. 36.2 ). The LAA is then closed with an AtriClip (AtriCure, Inc.) while proper clip application is confirmed by TEE.
Thoracoscopic exposure and division of the ligament of Marshall (LoM).
In our current practice, we create a partial anterior lesion from the base of the LAA toward the mitral valve epicardially that is completed later endocardially by catheter. This combination of epicardial and endocardial lesions is created to prevent conduction across the so-called “mitral vestibule” (see Chapter 41 , Figs. 41.2 through 41.4 ), also called the “LAA–MV isthmus” (see Chapter 48 , Figs. 48.8 , 48.9 , and Fig. 48.11 through 48.13 ). As demonstrated anatomically in Chapter 41 and described functionally in Chapter 48 , this isthmus of atrial myocardium between the LAA and the mitral valve annulus can potentially participate in postoperative peri-mitral atrial flutter if neither an anterior trigone lesion nor the combined posterior mitral line–coronary sinus lesions are used to prevent postoperative peri-mitral flutter. However, if either of those more traditional measures to prevent postoperative peri-mitral flutter is used, this LAA–MV isthmus lesion is unnecessary.
Subxiphoid Posterior Left Atrial Wall Ablation
A 3- to 4-cm incision is placed over the xiphoid process to expose the pericardium and a 4- to 6-cm transverse pericardiotomy is created to expose the posterior surface of the heart. A SUBTLE cannula (AtriCure, Inc., Mason, OH) is inserted into the pericardial space for suction and irrigation ( Fig. 36.3 ), a 5- to 7-mm 0-degree scope is then inserted through the cannula, and both are positioned behind the heart. The cleft of the cannula is pointed toward the heart, and the beveled tip of the cannula is oriented toward the middle aspect of the posterior pericardial space. Gentle clockwise and counterclockwise twisting of the cannula helps maneuver it within the pericardial space to expose the posterior wall of the LA ( Fig. 36.4 ). The superior PVs are rarely visible given the cephalad extent of the pericardial reflections. After the scope is inserted into the cannula, the first structure that is usually visible is the coronary sinus. With advancement of the cannula to the patient’s right side from the coronary sinus, the LA will then come into view. If the right atrium is identified initially, advancing the cannula to the patient’s left side will successfully guide the surgeon to the posterior left atrial space. Cephalad movement of the cannula will expose the left inferior PV. Sweeping the cannula and focusing on the patient’s right will bring the right inferior PV into view. Ablation can begin after these three landmark structures above have been clearly identified. The EPi-Sense Coagulation Device (AtriCure, Inc., Mason, OH) is then inserted through the cannula ( Fig. 36.5 ).
The SUBTLE cannula and the EPi-Sense monopolar, vacuum-assisted, saline-irrigated radiofrequency ablation system. (See text for further discussion.)
Surgeon’s initial view of the back of the heart through a pericardioscopy placed via the subxiphoid approach. LA, Left atrium.
The EPi-Sense ablation device being positioned on the posterior wall of the left atrium between the right and left pulmonary veins.
Ablation lines are initially created adjacent to the posterior aspect of the right PVs, advancing the cannula as far superior as the pericardial reflections will allow to achieve ablation of a portion of the posterior right superior PV and carina between the right PVs. The ablation catheter is moved in the cephalad direction until resistance is met by pericardial reflections, indicating that the catheter has been placed as far superiorly as possible. Vacuum suction is initiated through the Epi-Sense ablation device to create optimal contact with the posterior left atrial wall. Baseline esophageal temperature is recorded, and saline is infused into the field before ablation is initiated. The ablation catheter coil must always face the heart to avoid inadvertent energy delivery through the posterior pericardium in the oblique sinus where the esophagus resides. For this reason, endoscopic visualization of the guiding markers located along the open ablation face of the catheter is used as an additional visual reference. RF energy is applied at 30 watts for 90 seconds to create each lesion. Sequential ablation lines are created by moving from a cephalad to a caudal direction, ensuring each ablation lesion slightly overlaps the previous lesion. Ablated myocardium has a blanched appearance that assists in the placement of the next lesion ( Fig. 36.6A ). The availability of sensing electrodes on the ablation device is also extremely helpful in identifying residual electrical activity characteristic of incompletely ablated tissue ( Fig. 36.6B . In addition, a “sawtooth” pattern on the sensing electrodes sometimes occurs as a consequence of epicardial fat, further indicating incomplete ablation ( Fig. 36.6C ).
