Surgical Ablation of Atrial Fibrillation

Chapter 98 Surgical Ablation of Atrial Fibrillation

Although atrial fibrillation (AF) is often regarded as an innocuous arrhythmia, it is associated with significant morbidity and mortality secondary to its detrimental sequelae: (1) palpitations resulting in patient discomfort and anxiety; (2) loss of atrioventricular (AV) synchrony, which can compromise cardiac hemodynamics and result in various degrees of ventricular dysfunction or congestive heart failure; (3) stasis of blood flow in the left atrium, increasing the risk of thromboembolism and stroke.110

Because of the shortcomings of the medical treatment of AF, an interest in nonpharmacologic approaches to treat this arrhythmia has led to the development of catheter-based and surgical techniques beginning in the 1980s. Initial attempts were aimed at providing rate control but failed to address the detrimental hemodynamic and thromboembolic sequelae of AF. Early attempts at finding a surgical treatment culminated in the introduction of the Maze procedure in 1987, which became the gold standard for many years.

The following section will briefly describe the historical aspects of surgery for AF.

Historical Aspects

Left Atrial Isolation Procedure

The first procedure designed specifically to eliminate AF was first described in 1980 in the laboratory of Dr. James Cox at Duke University. The left atrial isolation procedure, which confined AF to the left atrium, restored the remainder of the heart to sinus rhythm (Figure 98-1).11 This procedure was significant because it restored a regular ventricular rate without requiring a permanent pacemaker. Since the sinoatrial (SA) node, AV node, and internodal conduction pathways are located in the right atrium and the inter-atrial septum, the left atrial isolation procedure did not affect normal AV conduction. Isolating the left atrium allowed the right atrium and the right ventricle to contract in synchrony, providing a normal right-sided cardiac output. This effectively restored normal cardiac hemodynamics.

By confining AF to the left atrium, the left atrial isolation procedure eliminated two of the three detrimental sequelae of AF: (1) an irregular heartbeat and (2) compromised cardiac hemodynamics. However, it did not eliminate the thromboembolic risk, since the left atrium usually remained in fibrillation. This procedure never achieved clinical acceptance, though it was performed by Dr. Cox in a single patient.

Corridor Procedure

In 1985, Guiraudon et al developed the corridor procedure for the treatment of AF.13 This operation isolated a strip of atrial septum harboring both the SA node and the AV node, allowing the SA node to drive both ventricles. This procedure effectively eliminated the irregular heartbeat associated with AF, but both atria either remained in fibrillation or developed their own asynchronous intrinsic rhythm because they were isolated from the septal “corridor” (Figure 98-2). Furthermore, the atria were isolated from their respective ventricles, thereby precluding the possibility of AV synchrony. The corridor procedure was abandoned because it had no effect on the hemodynamic compromise or the risk of thromboembolism associated with AF.

Atrial Transection Procedure

In 1985, Dr. James Cox and associates described the first procedure that attempted to terminate AF.14 This was different from the earlier surgical procedures that only isolated or confined AF to a certain region of the atria. Using a canine model, Cox’s group found that a single long incision around both atria and down into the septum could terminate AF. This atrial transection procedure prevented the induction and maintenance of AF or atrial flutter in every canine that underwent the operation.15 Unfortunately, this procedure was not effective clinically and was abandoned.

Development of the Cox-Maze Procedure

The Maze procedure was clinically introduced in 1987 by Dr. Cox after extensive animal investigation at Washington University in St. Louis.1517 The Cox-Maze procedure was developed to interrupt any and all macro–re-entrant circuits that were felt to potentially develop in the atria, thereby precluding the ability of the atrium to flutter or fibrillate (Figure 98-3). Unlike earlier procedures, the Cox-Maze procedure successfully restored both AV synchrony and sinus rhythm, thus potentially reducing the risk of thromboembolism and stroke.18 The operation consisted of creating a myriad surgical incisions across both the right and left atria. These incisions were placed so that the SA could still direct the propagation of the sinus impulse throughout both atria. It allowed for most of the atrial myocardium to be activated, resulting in the preservation of atrial transport function in most patients.19

The original version, the Maze I procedure, was modified because of problems with late chronotropic incompetence and a high incidence of pacemaker implantations. The Maze II procedure, however, was extremely difficult to perform technically. It was soon replaced by the Maze III procedure, also known as the Cox-Maze III procedure today (Figure 98-4).20,21

The Cox-Maze III procedure—often referred to as the “cut-and-sew” Maze—became the gold standard for the surgical treatment of AF. In a long-term study of patients who underwent the Cox-Maze III procedure at the authors’ institution, 97% of the patients at late follow-up were free of symptomatic AF.22 These excellent results have been reproduced by other groups worldwide.2325

Although the Cox-Maze III procedure was effective in eliminating AF, it is presently mainly of historical interest. It was technically difficult and invasive, and only a handful of cardiac surgeons still perform this operation today. At most centers around the world, the surgical incisions have been replaced with ablations using a variety of energy sources. These ablation-assisted procedures have greatly expanded the field of AF surgery in the past decade. With the current ablation technology, surgery can be performed with low mortality and often with limited-access incisions.

The indications for surgery have been defined in a recent consensus statement.26 These presently include (1) all symptomatic patients with documented AF undergoing other cardiac surgical procedures, (2) selected asymptomatic patients with AF undergoing cardiac surgery in which the ablation can be performed with minimal risk in experienced centers, and (3) stand-alone AF, which should be considered for symptomatic patients with AF who prefer a surgical approach, have failed one or more attempts at catheter ablation, or are not candidates for catheter ablation.

The referral of patients for surgery with medically refractory, symptomatic AF in lieu of catheter ablation is still being debated. The problem is that no head-to-head comparisons of outcomes with catheter and surgical ablation are available. In these instances, clinical decisions should be made on the basis of the individual institution’s experience with catheter and surgical ablations, the relative outcomes and risks of each in the individual patient, and patient preference. Programs involved in the surgical treatment of AF should develop a team approach to these patients, with the team including both electrophysiologists and surgeons, to ensure appropriate selection of patients.

In the authors’ opinion, relative indications for surgery were not included in the consensus statement. The first is a contraindication to long-term anticoagulation in patients with persistent AF and a high risk for stroke (CHADS score ≥2). Up to one third of patients with AF screened for participation in clinical trials of warfarin were deemed ineligible for chronic anticoagulation, mainly because of a perceived high risk of bleeding complications.27,28 In fact, patients on warfarin have twice the rate of intracerebral hemorrhage and mortality in a dose-dependent relationship.29 In one study, the annual rate of intracranial hemorrhage in anticoagulated patients with AF was 0.9% per year, and the overall major bleeding complications was 2.3% per year.28 The Cox-Maze procedure not only is able to eliminate AF in most patients but also amputates the left atrial appendage. The stroke rate following the procedure off anticoagulation has been remarkably low, even in patients with a CHADS score ≥2. At the authors’ institution, only 5 of 450 patients had a stroke after a mean follow-up of 6.9 ± 5.1 years. No difference in stroke rate was observed in those patients with CHADS scores above or below 2.30 This low risk of stroke following the Cox-Maze procedure has been noted in other series as well.18,31,32

Surgical treatment for AF with amputation of the left atrial appendage also should be considered in patients with chronic AF who have suffered a cerebrovascular accident despite adequate anticoagulation. These patients are at high risk of recurring neurologic events. Anticoagulation with warfarin reduces the risk of ischemic and hemorrhagic strokes by over 60% in patients with AF but does not completely eliminate this serious complication.9,33 At the authors’ institution, 20% of patients who underwent the Cox-Maze III procedure had experienced at least one episode of cerebral thromboembolism that resulted in a significant temporary or permanent neurologic deficit prior to undergoing the operation.22 No late strokes occurred in this population, with 90% of patients off anticoagulation at last follow-up.22

In patients undergoing concomitant valve surgery, studies have shown that adding the Cox-Maze procedure can decrease the late risk of cardiac-related and stroke-related deaths.34,35 However, there have been no prospective or randomized studies demonstrating the survival or other benefits of adding a Cox-Maze procedure in patients with AF. The contraindication to a Cox-Maze procedure in this group would be in asymptomatic patients who have tolerated their AF well and have not had problems with anticoagulation and in whom adding the ablation would increase their surgical risk.

Surgical Ablation Technology

The development of surgical ablation technology has revolutionized the field of AF surgery. It has transformed a technically difficult and time-consuming operation that few surgeons were willing to perform into a procedure that is technically easier, less invasive, and easy to be routinely performed by most surgeons. This section will briefly summarize the various energy sources being used for surgical ablation.

For ablation technology to successfully replace incisions, it must meet several criteria. (1) It must create linear ablation lines that reliably produce bi-directional conduction block. This is the mechanism by which incisions prevent AF, by either blocking macro–re-entrant or micro–re-entrant circuits or isolating trigger foci. The authors’ laboratory and others have shown that this requires a transmural lesion, as even small gaps in ablation lines can conduct both sinus and fibrillatory impulses.36,37 (2) The ablation device must be safe. This requires a precise definition of dose-response curves to limit excessive or inadequate ablation. The surgeon must also have knowledge of the effects of a specific ablation technology on surrounding vital cardiac structures such as the coronary sinus, coronary arteries, and valvular structures. (3) The ablation device should make AF surgery simpler and require less time to perform. This would require the device to create lesions rapidly, be simple to use, and have adequate length and flexibility. (4) The device should be adaptable to a minimally invasive approach. This would include the facility to insert the device through minimal access incisions or ports, and the device should be able to create epicardial transmural lesions on the beating heart. Currently, no device has met all of these criteria. The following sections will briefly summarize the current ablation technologies and their advantages and disadvantages.


Cryoablation technology is unique in that it destroys myocardial tissue by freezing rather than heating. It has the benefit of preserving the fibrous skeleton and collagen and is thus one of the safest energy sources available. The devices work by pumping a refrigerant to the electrode tip, where it undergoes transformation from a liquid state to a gaseous state, releasing energy into the tissue that is in contact with the tip. The formation of intracellular and extracellular ice crystals disrupts the cell membrane and kills the cell. Evidence that the induction of apoptosis plays a role in late lesion expansion is also available. Lesion size depends on the temperature of the probe, thermal conductivity, and the temperature of the tissue.

Currently, two commercially available sources of cryothermal energy are being used in cardiac surgery. The older technology, based on nitrous oxide, is manufactured by AtriCure (Cincinnati, OH). More recently, ATS Medical (Minneapolis, MN.) has developed a device based on argon. At 1 atmosphere of pressure, nitrous oxide is capable of cooling tissue to −89.5° C, while argon has a minimum temperature of −185.7° C. The nitrous oxide technology has a well-defined efficacy and safety profile and is generally safe except around the coronary arteries.38,39 The potential disadvantage of cryoablation, however, is the relatively long time that is needed to create lesions (1 to 3 minutes). Creating lesions on the beating heart is also difficult because of the “heat sink” of the circulating blood volume.40 Furthermore, if blood is frozen during epicardial ablation on the beating heart, it coagulates, creating a potential risk for thromboembolism.

Radiofrequency Energy

Radiofrequency (RF) energy, which has been used for cardiac ablation for many years in the electrophysiology laboratory, was one of the first energy sources to be applied in the operating room.41 RF energy uses alternating current in the range of 100 to 1000 kHz. This frequency is high enough to prevent rapid myocardial depolarization and the induction of ventricular fibrillation, yet low enough to prevent tissue vaporization and perforation. Resistive RF energy can be delivered by either unipolar electrodes or bipolar electrodes, and the electrodes can be either dry or irrigated. With unipolar RF devices, the energy is dispersed between the electrode tip and an indifferent electrode, usually the grounding pad applied to the patient. In bipolar RF devices, alternating current is passed between two closely approximated electrodes embedded in the jaws of a clamp. The lesion size depends on electrode-tissue contact area, the interface temperature, the current and voltage (power), and the duration of delivery. The depth of the lesion can be limited by char formation, epicardial fat, myocardial and endocavity blood flow, and tissue thickness.

Numerous unipolar RF devices have been developed for ablation. These include both dry and irrigated devices and devices that incorporate suction. Although dry unipolar RF has been shown to create transmural lesions on the arrested heart in animals with sufficiently long ablation times, problems have occurred in humans. After 2-minute endocardial ablations during mitral valve surgery, only 20% of the in vivo lesions were transmural.42 Epicardial ablation on the beating heart has been even more problematic. Animal studies have consistently shown that unipolar RF is incapable of creating epicardial transmural lesions on the beating heart.43,44 Epicardial RF ablation in humans resulted in only 10% of the lesions being transmural.45 This deficiency of unipolar RF has been felt to be caused by the heat sink of the circulating blood.46 This has led some groups to examine the addition of both irrigation and suction to improve lesion formation. While these additions have improved the depth of penetration, a device capable of creating reliable transmural lesions on the beating heart is still not available.

To overcome this problem, bipolar RF clamps were developed. With bipolar RF, the electrodes are embedded in the jaws of a clamp to focus the delivery of energy. The electrodes are shielded from the circulating blood pool, and this allows for faster ablation times and limits collateral injury to tissue that is close to the electrodes. Bipolar ablation has been shown to be capable of creating transmural lesions on the beating heart, both in animals and humans, with short ablation times.4749 Three companies (AtriCure; Medtronic, Minneapolis, MN; and Estech, San Ramon, CA) currently market bipolar RF devices.

Another advantage of bipolar RF energy is its safety profile. A number of clinical complications of unipolar RF devices that have been reported include coronary artery injuries, cerebrovascular accidents, and esophageal perforation leading to atrio-esophageal fistula.5053 Bipolar RF technology has eliminated most of this collateral damage, and no injuries have been described with these devices despite extensive clinical use.

High-Intensity Focused Ultrasound

High-intensity focused ultrasound (HIFU) is another modality that is applied clinically for surgical ablation (St. Jude Medical, St. Paul, MN). Ultrasound effectively ablates tissue via mechanical hyperthermia. When ultrasound waves are emitted from the transducer, the resulting wave travels through the tissue causing compression, refraction, and particle movement. This translates into kinetic energy and ultimately thermal coagulative tissue necrosis. HIFU produces rapid, high-concentration energy in a focused area and is reportedly able to create transmural epicardial lesions through epicardial fat in a short time.54

HIFU is unique in that it is able to create noninvasive, noncontact focal ablation in three-dimensional volume without affecting intervening and surrounding tissue. It uses ultrasound beams in the frequency range of 1 to 5 MHz or higher, creating focused lesions quickly by rapidly raising the temperature of the targeted tissue to above 80° C, effectively killing the cells. By focusing the ultrasound waves, HIFU is able to create targeted thermal coagulation of tissue at a very well-defined focus without harming intervening tissue. Its ability to focus the target of ablation at specific depths is its major advantage over other energy modalities.

Another advantage of HIFU technology is its mechanism of thermal ablation. Unlike all other energy sources that heat or cool tissue by thermal conduction, HIFU ablates tissue by directly heating the tissue in the acoustic focal volume and is therefore much less affected by the heat sink of the circulating endocardial blood pool. A few clinical studies using HIFU have shown some encouraging results.5457 However, the efficacy of HIFU devices to reliably create transmural lesions has not been independently verified. The fixed depth of penetration of these devices may be a major problem in pathologically thickened atrial tissue. Moreover, these devices are somewhat bulky and are expensive to manufacture.

In summary, each ablation technology has its own advantages and disadvantages. In the future, it will be imperative for surgeons to develop a more compete understanding of the effects of each surgical ablation technology on atrial hemodynamics, function, and electrophysiology. This will allow for the more appropriate use of devices in the operating room. The inability to create reliable linear lesions on the beating heart remains a shortcoming of most devices and has impeded the development of minimally invasive procedures, especially for patients with longstanding AF and large left atria.

Surgical Techniques

The numerous procedures that are currently performed to surgically ablate AF can be grouped into three broad categories: (1) the Cox-Maze procedure, (2) left atrial lesion sets, and (3) PV isolation. These approaches will be described in the following section.

The Cox-Maze IV Procedure

The original cut-and-sew Cox-Maze III procedure is only rarely performed today. At most centers, the surgical incisions have been replaced with lines of ablation using a variety of energy sources. At the authors’ institution, bipolar RF energy has been used successfully to replace most of the surgical incisions of the Cox-Maze III procedure. The current RF ablation–assisted procedure, termed Cox-Maze IV, incorporates the lesions as does Cox-Maze III (Figure 98-5).58 The authors’ 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.59

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 rhythm is electrically cardioverted. Pacing thresholds are obtained from each PV. 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, entrance block, or both.

The right atrial lesion set is performed on the beating heart, as shown in Figure 98-6. A bipolar RF clamp is used to create most of the lesions. A unipolar device, either cryoablation or RF energy, is used to complete the ablation lines endocardially down to the tricuspid annulus because of the difficulty of clamping in this area.

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Aug 12, 2016 | Posted by in CARDIOLOGY | Comments Off on Surgical Ablation of Atrial Fibrillation

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