Anthony B. Mozer and James L. Cox
This chapter is a revision and update of that included in previous editions of the TSRA Review written by Scott D. Johnson (2nd edition) and Chad N. Stasik (1st edition).
Background
In the 1980s, physician- and surgeon-scientists at Washington University in St. Louis began to carefully map the behavior of the cardiac conduction system, profoundly changing our understanding of cardiac electrophysiology and creating an opportunity for surgical correction of symptomatic dysrhythmias. Atrial fibrillation (AF) is the most common arrhythmia in the world, afflicting 2-3 million people in the United States. Symptoms of AF include palpitations, chest discomfort, fatigue, shortness of breath, anxiety, and altered hemodynamics. It is estimated that 20% of all strokes are related to thromboembolism associated with AF and the risk of stroke is approximately 5% per year, or 5 times that compared to those without AF. Further, longitudinal analyses from the original Framingham cohort identified a significant mortality risk associated with AF, independent of other risk factors, that increases with advancing age. In their seminal work based on animal models, Dr. Cox and colleagues demonstrated that regular rhythms are generated by the “atrial pacemaker complex” of the right atrium and superior and inferior vena cavae, which includes but is not limited to the sinoatrial (SA) node. Regular rhythms with rates from below 60 bpm to approximately 100 bpm are conducted as depolarization wavefronts from these tissue areas and are subject to neurohumoral inputs. It is from this understanding of the electrical conduction roadmap that the first arrhythmia surgery, a “maze” of incisions to halt the macro-reentrant circuits that cause AF, was developed and performed in 1987. From this successful principle, iterative improvements in catheter-directed and surgical approaches for the treatment of dysrhythmias have followed.
There are three classifications of AF:
- Paroxysmal: Self-limited (terminates spontaneously), but may be recurrent (2 or more episodes); indicates electrical origin most likely in pulmonary vein and low likelihood of atrial remodeling
- Persistent: Sustained >7 days; may be terminated with chemical or electrical cardioversion
- Permanent: Continuous for at least 6 months, despite efforts at chemical or electrical cardioversion
Chemical antiarrhythmic therapy can provide rate control as well as conversion to a sinus rhythm; however, these medications have around a 50% success rate of achieving a sinus rhythm, with long-term success being closer to 30%.
Cox-Maze procedure
The original Cox-Maze-I, II, and III are iterations of the “cut-and-sew” technique to divide and reapproximate the left and right atria along mapped lesion lines in order to force the atrial electrical conduction to follow a pathway from the SA node to the AV node and limit re-entrant circuits from disrupting sinus rhythm conducted through to the ventricles. Three fundamentals of arrhythmia surgery have been shown to be reproducibly achieved: re-establishment of sinus rhythm, elimination of thromboembolism risk, and facilitation of the typical pattern of atrial conduction.
Lesion sets
The Cox-Maze procedure creates bi-atrial lesion lines, including an endocardial box lesion pulmonary vein isolation (PVI), a left atrial lesion set, and a right atrial lesion set. Patients with intermittent AF generally have an electrical focus around the pulmonary veins, and some data show that the PVI lesion set alone can be up to 70-80% effective at restoring sinus rhythm. However, 10-15% patients undergoing PVI alone develop peri-mitral atrial flutter, and the success rate of PVI drops to 56% or less when performed in patients with persistent AF. The complete left atrial lesion set includes PVI and adds connecting, contiguous endocardial lesions to the mitral isthmus, endocardial and epicardial coronary sinus, and across the “coumadin ridge” to the orifice of the LAA. Clip or suture ligation of the LAA is also added, as up to 90% of thromboemboli are attributed to stasis in the LAA.
The right-sided lesion set includes an endocardial lesion from the SVC to the IVC. A lesion is then made to connect this lesion to the right atrial appendage (RAA). This lesion set is unique in that it can be performed without difficulty on an open right atrium after the aortic crossclamp has been removed. When necessary, it can also be delayed and completed via transcatheter approach in a separate procedural setting.
Indications
STS consensus guidelines from 2017 provide the following indications and recommendations (Class, Level of Evidence) for surgical management of patients with AF:
- To restore sinus rhythm at the time of concomitant mitral valve surgery to (IA)
- To restore sinus rhythm at the time of concomitant aortic valve surgery (AVR), coronary bypass grafting (CABG), or combined AVR/CABG (IB)
- To restore sinus rhythm as a stand-alone surgical ablation for symptomatic AF refractory to antiarrhythmics, catheter ablation, or both (IIA, B)
- As stand-alone ablation for symptomatic persistent or longstanding persistent AF when using the Cox-Maze III/IV lesion set (IIA, B)
- For longitudinal thromboembolic morbidity prevention in AF, it is reasonable to surgically treat the LAA +/- ablation (IIA, C)
Contraindications for operative management include the following:
- Surgical management of AF in the setting of LA enlargement > 4.5 cm or more than moderate mitral regurgitation by PVI alone is not recommended (III, C)
Cox Maze IV
In order to simplify and expedite the maze lesion set as performed in the operating room, the fourth iteration of the procedure (Cox-Maze IV) uses a combination of bipolar radiofrequency (RF), and/or cryothermal (Cryo) ablation to recreate the original cut-and-sew isolation lines. The use of these energy modalities has resulted in an opportunity for surgeons to treat AF more aggressively, with strong data to support the safety and efficacy of Cryo / RF maze concomitant with other coronary and valve operations without increasing morbidity and mortality due to minimal or no additional cross-clamp or cardiopulmonary bypass time.
Radiofrequency ablation
This was the first energy source to be used in the operating room. Dry unipolar devices have been inconsistent, mostly thought to be secondary to the heat sink of circulating blood. Because of this, bipolar devices were developed that shield the energy from the surrounding blood and minimize collateral injury. Downsides of RF are the need to perform multiple clamps for each lesion line to produce a transmural lesion due to tissue thickness and density and the care needed to assure there are no gaps or areas of thermal char between the clamp which can lead to incomplete lesion lines.
Cryoablation
Cryoablation utilizes thermal energy rather than heat to create a transmural lesion. Cryo is the most frequently employed method of performing the maze lesion set. Antifreeze is used to drop the probe to very low temperatures, freezing the contacted tissue, and creating intracellular and extracellular ice crystals that induce cell death. This method is very safe and preserves the fibrous skeleton. The disadvantage of this method is that it takes up to 3 minutes to create an effective, full-thickness lesion. Transmural lesions on a beating heart can also be difficult to create, at times, owing to the “heat sink” effect of circulating blood to tissue variability causing incomplete contact to the epicardial or endocardial surface.
Postoperative care
Patients who have undergone a concomitant operation in addition to their arrhythmia surgery should be cared for as they would had they not had the arrhythmia surgery, including placement of epicardial pacing leads as per institution preference. Specific to the arrhythmia procedure, it is important to be mindful of the potential collateral damage that can be caused, especially injuries to the esophagus and left circumflex coronary artery. As it is common for patients to remain in or develop AF in the immediate postoperative period, medical management involves prophylactic antiarrhythmic medications, anticoagulation, and a strategy for cardioversion if necessary for recurrent AF. In the absence of high-degree AV block in the postoperative period, most patients receive an oral or IV loading dose of amiodarone and are started and maintained on anticoagulation (i.e., coumadin) for 3 months. At this point, EKG and Holter or other outpatient rhythm monitoring is performed, and antiarrhythmics are discontinued if sinus rhythm is maintained. Some surgeons confront the elimination of atrial natriuretic peptide input due to the lesion set by managing volume with spironolactone in addition to loop diuretics in the early postoperative period. Sotalol, propafenone, dofetilide, or other anti-arrhythmia agents may also be used prophylactically in some cases. A period of 4-5 days is often given for rhythm recovery in the setting of AV block before pursuing electrophysiology consult for permanent pacemaker (PPM) placement.
Suggested Readings
- Bhadwar V, Rankin JS, Damiano Jr R, et al. The Society of Thoracic Surgeons 2017 Clinical Practice Guidelines for the Surgical Treatment of Atrial Fibrillation. Ann Thorac Surg. 2017;103:329-41.
- Boineau JP, Canavan TE, Schuessler, RB, et al. Demonstration of a Widely Distributed Atrial Pacemaker Complex in the Human Heart. Circulation. 1988; 77(6):1221-37.
- Cox JL. The First Maze Procedure. J Thor Cardiovasc Surg. 2011; 141(5):1093-97.
- Cox JL, Churyla A, Kislitsina ON, et al. Cardiac Anatomy Pertinent to the Catheter and Surgical Treatment of Atrial Fibrillation. J Cardiovasc Electrophysiol. 2020;31:2118–2127.
- January CT, Wann LS, Calkins H, et al. 2019 AHA/ACC/HRS focused update of the 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. Circulation. 2019;140:e125–e151.
