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Right arrow Electrophysiology - arrhythmias

Ann Thorac Surg 2007;83:331-340
© 2007 The Society of Thoracic Surgeons

Reviews

Current Strategies in the Surgical Treatment of Atrial Fibrillation: Review of the Literature and Onze Lieve Vrouw Clinic’s Strategy

Ihsan Bakir, MDa, Filip P. Casselman, MD, PhDa,*, Pedro Brugada, MD, PhDb, Peter Geelen, MD, PhDb, Francis Wellens, MDa, Ivan Degrieck, MDa, Frank Van Praet, MDa, Yvette Vermeulen, MSa, Raphael De Geest, MDa,b, Hugo Vanermen, MD, FETCSa,b

a Cardiovascular and Thoracic Surgery Department, Onze Lieve Vrouw Clinic, Aalst, Belgium
b Cardiovascular Research and Teaching Institute, Onze Lieve Vrouw Clinic, Aalst, Belgium

* Address correspondence to Dr Casselman, Onze Lieve Vrouw Clinic, Thoracic and Cardiovascular Surgery Department, Moorselbaan 164, Aalst, 9300 Belgium (Email: filip.casselman{at}olvz-aalst.be).


   Abstract
Top
 Abstract
Introduction
 Material and Methods
 Results of Surgical Treatment...
 Onze Lieve Vrouw Clinic's...
 Comment
 References
 
Atrial fibrillation is the most common rhythm disturbance in clinical practice. It is a major source of stroke and morbidity. Although the Cox maze procedure effectively eliminates atrial fibrillation in most patients, the procedure has not found widespread application. As a consequence, new operations that use alternative sources of energy, such as radiofrequency, microwave, cryothermy, laser, and ultrasound have emerged to surgically create lesion sets to treat atrial fibrillation. This article reviews the fundamentals and current strategies in the surgical treatment of atrial fibrillation.


   Introduction
Top
 Abstract
 Introduction
Material and Methods
 Results of Surgical Treatment...
 Onze Lieve Vrouw Clinic's...
 Comment
 References
 
Atrial fibrillation (AF) is a supraventricular tachyarrhythmia characterized by uncoordinated atrial activation with consequent deterioration of atrial mechanical function [1]. It is the most common cardiac arrhythmia, accounting for about one third of diagnosed rhythm disturbances and is associated with substantial morbidity and mortality [2]. An estimated 2.2 million people in the United States and more than 5 million people worldwide have atrial fibrillation [2, 3]. Atrial fibrillation is present in approximately 1% of the general population and 6 % of those greater than 65 years of age [4].

Atrial fibrillation is related to thromboembolism and stroke or pulmonary embolism due to slow and stagnant blood flow in the atria [2]. The risk of stroke associated with AF is 5% to 8% per year [2, 5]; in other words AF is associated with a fivefold to sevenfold increase in the risk of stroke [3, 6] and increases in health care expenses [7, 8]. According to the United States of America Health Care Finance Administration, AF results in 227,000 hospitalizations costing $6.6 billion annually [2, 4].

Besides pharmacological treatments, the development of minimally invasive, low-risk, cost-effective therapies to overcome AF are evolving and are of great value. This review describes clinical classification, pathophysiology, and nonpharmacological treatment modalities of the most commonly sustained cardiac rhythm disturbance–atrial fibrillation and treatment strategies in our department.


   Material and Methods
Top
 Abstract
 Introduction
 Material and Methods
Results of Surgical Treatment...
 Onze Lieve Vrouw Clinic's...
 Comment
 References
 
An extensive English literature search using the MEDLINE database between 1960 and 2006 was performed. Keywords used for the search included: atrial fibrillation, surgical ablation, Cox maze procedure, cardiac surgery, catheter ablation, surgery, denervation, radiofrequency (RF), microwave, cryothermy, ultrasound, and laser. Additional studies were identified from references cited in identified studies and review articles.

Classification of Atrial Fibrillation
Many conflicting and vague definitions to characterize the clinical patterns of AF have made the comparison of studies and assessment of treatment difficult. Therefore the joint American College of Cardiology/American Heart Association/European Society of Cardiology task force has described a clear nomenclature for classification of AF [1]. According to this guideline, classification starts with the first diagnosed episode of AF. If a patient has two or more episodes, AF is considered recurrent. Recurrent AF is designated as paroxysmal, persistent, or permanent (Fig 1). Permanent AF is defined as a condition in which sinus rhythm can not be sustained after cardioversion or the patient and physician have decided against further efforts to restore sinus rhythm [1, 3].


Figure 1
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  		Fig 1. Classification of atrial fibrillation (AF1). Either paroxysmal or persistent AF may be recurrent AF (AF2). Paroxysmal AF lasts 7 or fewer days and terminates spontaneously (AF3). Persistent AF includes cases of long-standing AF (eg, greater than 1 year), usually leading to permanent AF (AF4). Persistent AF does not terminate spontaneously, but requires electrical or pharmacological cardioversion to restore normal sinus rhythm; if the first-detected episode of AF does not terminate spontaneously, it is also designated persistent.

 
Atrial fibrillation secondary to a precipitating condition such as acute myocardial infarction, cardiac surgery, myocarditis, hyperthyroidism, or acute pulmonary disease is not being considered in this review. In these settings, treatment of the underlying disorder concurrently with management of the episode of AF usually eliminates the arrhythmia [1].

Pathophysiology of Atrial Fibrillation
Atrial fibrillation is a complex rhythm disturbance of incompletely understood pathogenesis [3]. There is a general consensus that AF requires a substrate, a trigger, and modulating factors [7]. The substrate is an atrial abnormality, frequently an inflammation or fibrosis, and causes atrial electrical dysfunction that serves development of AF [3]. Triggers include atrial ectopic foci, changes in atrial wall tension, and alterations in autonomic tone. Although substrate and trigger may vary, experimental and clinical evidence points to the primary importance of the pulmonary veins and left atrium in starting and maintaining AF [3]. Theories of the mechanism of AF involve two main processes: (1) enhanced automaticity in one or several rapidly depolarizing foci (focal AF) and (2) re-entry involving one or more circuits (multiple vavelet concept of AF) [1]. Rapidly firing atrial foci (located in one or several of the pulmonary veins) can initiate AF in susceptible patients [9, 10]. Foci also occur in the right atrium and infrequently in the superior vena cava or coronary sinus.

Haissaguerre and colleagues [9] showed that paroxysmal AF takes origin from ectopic beats in the pulmonary veins in 94% of cases. The focal origin seems to be more important in paroxysmal AF than in persistent AF. Ablation of such foci can be curative [10].

The multiple-wavelet hypothesis as the mechanism of re-entrant AF was suggested by Moe and colleagues [11]. The macro re-entry waves follow different pathways through the atrial myocardium resulting in random depolarization of the atrial myocytes and irregular stimulation of the atrioventricular node [12]. The role of modulating factors (ie, autonomic nervous system) in AF has long been recognized. Although the autonomic tone has clearly been shown to play a role in AF, the extent of that role remains controversial. Much of the controversy could be explained by the time frame during which the measurements were recorded and possibly the differential effect of the autonomic changes on the substrate versus the trigger [13].

A recent study of endocardial mapping of ganglionated plexuses during catheter ablation also showed that ablation of substrate or trigger alone, or both, without modification of the modulating factor (autonomic tone), may be sufficient for succesful ablation of AF [14]. Ultimately, a better knowledge of electrophysiological mechanisms is necessary for the development of effective preventive measures [15].

Treatment
The main aim of treating atrial fibrillation is restoration of a regular rhythm so that optimal cardiac output is sustained and the risk of stroke is reduced. The ideal end result is to restore normal sinus rhythm to patients to prevent tachycardia-induced myocardial remodelling and heart failure. Due to the inadequate efficacy and pro-arrhythmic risks of anti-arrhythmic drug therapy, physicians may choose one or more of the following nonpharmacologic therapies for treatment of AF [2]: (1) cardioversion, (2) implantable devices, (3) catheter ablation, and (4) surgical ablation. Because cardioversion and implantable devices were out of the scope of this review, they were not discussed in detail.

Catheter Ablation
The catheter ablation techniques use transvenous radiofrequency and cryoablation catheters to ablate triggers in the atria, destroying myocardial cells that contribute critically to the initiation of an atrial fibrillation. Based on the success of surgical approaches to AF, several catheter ablation strategies have been designed to produce similar effects [16]. Ablation strategies limited to the right atrium produce marginal improvement, whereas linear ablation in the left atrium has been more successful [1]. The recognition that foci triggering AF often originate within the pulmonary veins has led to ablation strategies that target this zone or electrically isolate the pulmonary veins from the left atrium. Other sites of arrhythmogenic foci have been found in the superior vena cava, the right atrium and the left atrium, and the coronary sinus [9]. Ablation of these foci eliminates the frequency of AF in more than 60% of patients, but the risk of recurrent AF after a focal ablation procedure is still 30% to 50% for the first year and even higher when more than one pulmonary vein is involved [1]. Thus many patients continue to require anti-arrhythmic drug regimen after catheter-based ablative therapy of AF [17].

A recent comparative study of catheter ablation of AF between different centers demonstrated that achieved freedom from atrial fibrillation is significantly better for paroxysmal AF (59% to 85%) compared with permanent-persistent AF (5% to 25%) [18]. However the experience reported by pioneering centers for the last 2 to 3 years is encouraging, with success rates in the absence of anti-arrhythmic drugs of 72% to 90% [19–21]. Rather than focusing only on ablating triggers (ie, pulmonary vein potentials) of AF, catheter ablation has evolved toward modification of the left atrial tissue substrate [22].

Potential complications of catheter ablation for AF consist of pulmonary vein stenosis, systemic embolism, pericardial effusion, phrenic nerve paralysis, and cardiac tamponade [1]. Thus, although these procedures have produced promising results, the length of these procedures, potential complications, and roentgenogram exposure still pose a challenge to physicians today [23].

Surgical Ablation
Many procedures have been advanced since the early 1980s for surgical treatment of AF [24]. Guiraudon and colleagues [25] described the corridor procedure in 1985. He created a corridor between the sinus node and atrioventricular node that restored regular rhythm. However, success with the corridor operation was limited by loss of atrial transport function, as the majority of atrial muscle was still fibrillating [24]. Based on mapping studies of animal and human AF, Cox and colleagues [35] developed a surgical procedure (Cox maze procedure) that controls AF in more than 90% of selected patients. In the original procedure atrial appendages are excised and the pulmonary veins are isolated. Appropriately placed atrial incisions not only interrupt the conduction routes of the most common re-entrant circuits, but they also direct the sinus impulse from the surgical ablation node to the atrioventricular node along a specified route [26, 27]. Although encouraging and succesful results were obtained, the original surgical technique, the Cox maze I procedure, was modified to become the Cox maze II procedure because of late chronotropic problems with the surgical ablation node and intra-atrial conduction delays that resulted in diminished left atrial contraction. However the Cox maze II procedure proved to be technically difficult to perform. As a result, it was modified to become the Cox maze III procedure, which soon became the surgical technique of choice for the treatment of medically resistant AF [27, 28].

Although the presence of atrial transport function has been shown in most patients after the maze operation, more important is whether the amount of mechanical function is enough to provide sufficient atrial contraction and eliminate the risk of systemic thromboembolism. It is hypothesized that the isolation of the posterior left atrium, discordant activation in certain adjacent left atrial segments, and the potential atrial ischemia beyond the incision are the main mechanisms causing insufficient left atrial transport function after the maze operation [29]. Therefore Nitta and colleaques [30] created a new concept of surgical treatment for AF (ie, the radial approach) in which atrial incisions radiate from the sinus node toward the atrioventricular annular margins to allow a more physiologic atrial activation sequence and to parallel the atrial branches of coronary arteries to preserve the blood supply to most atrial segments. The radial approach has been shown to preserve greater atrial transport function than the Cox maze procedure in the early postoperative period. However, serial change in the postoperative atrial transport function has not been examined in detail and long-term follow-up is still mandatory [31, 32]. In spite of some studies reporting that the left atrial transport function after Cox maze surgery recovers slowly, it remains at an unsatisfactory level during long-term follow-up [32–34] (Table 1). Cox and colleagues [35] have reported excellent results at 8 years follow-up with a 2% mortality rate and 99% restoration of sinus rhythm. Temporary postoperative AF was frequent, presenting in 38% of patients. This problem was related to a shortened atrial refractory period during the procedure and did not preclude long-term success. Successful ablation treatment of AF was independent of mitral valve disease, type of AF, and left atrial size [3, 35]. Their studies have demonstrated that strokes were not common. When the atrium is fibrillating, extreme stagnation of blood in the left atrial appendage is often present, which is one of the important factors generating thrombus in the atrial appendage. The Cox maze procedure not only diminished the rate of stroke but nearly eliminated the risk of stroke after the operation [36, 37].


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  		Table 1. Results of Corridor, Cox Maze III Procedure and Radial Approach
 
Other centers have reported their results with the Cox maze III procedure [38, 39]. The efficiency has been less than that published by Cox and colleagues [35]. Although concomitant organic heart disease did not decrease the effectiveness of the Cox maze III procedure in the series of Cox and colleagues [40], others demonstrated decreased success rate in their studies (Table 1). In most series, concomitant mitral valve surgery with the Cox maze III procedure cured AF in 75% to 82% of patients [3, 41, 42].

Although shown to be highly effective, the Cox maze III procedure, even after the latest modifications, has been discussed by others for being a difficult and long procedure, making it less suitable for combined procedures [24]. Therefore other efforts have been made to develop faster and simpler procedures for the treatment of AF.


   Results of Surgical Treatment of AF With Alternative Energy Sources
Top
 Abstract
 Introduction
 Material and Methods
 Results of Surgical Treatment...
Onze Lieve Vrouw Clinic's...
 Comment
 References
 
The theoretically anticipated events, after the surgical treatment of AF, consist of abolition of AF, the restoration of the atrial contractility with associated atrial kick, optimization of the cardiac output, improved quality of life, and survival and a decrease in cerebral vascular accidents [43]. To achieve these goals, today the cut-and-sew Cox maze procedure is refreshed by other procedures that use alternative energy sources (ie, RF, microwave, ultrasound, laser, and cryothermy) to produce lines of conduction block speedily with minor risk of bleeding [24, 44].

Energy Sources
The mechanism of action and limitations of different energy sources that have been used today are depicted in Tables 2 and 3. Go Surgeons who use energy sources that produce thermal lesions should be cautious against injury to surrounding structures, especially the esophagus. The transesophageal echocardiographic probe should be withdrawn during endocardial ablation procedure [3]. Esophageal injury has been published with RF ablation, but not with microwave ablation [41, 45]. The currently available energy sources (ie, RF, microwave, cryothermy, ultrasound, and laser) are detailed in this article.


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  		Table 2. Mechanism of Action in Different Energy Sources
 

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  		Table 3. Limitations of Different Energy Sources
 
Radiofrequency
Radiofrequency energy uses alternating current of 350 kHz to 1 MHz to heat tissue [3]. Experimental data show that heating tissue for approximately 1 minute at 70°C to 80°C with a maximal power output of 150 W creates lesions 3 to 6 mm depth, usually enough to produce a transmural line of conduction block [3, 46]. However in clinical practice the size of lesions is also very dependent on the size of the electrode, the use of irrigation, and whether power, temperature, or impedance is used to control ablation. Several different RF catheter systems are used for surgical application [46, 47]. The probes may be applied on either endocardial or epicardial surfaces of the heart [3, 46]. Epicardial placement allows off-pump or beating heart AF ablation [48]. Saline-cooled unipolar RF systems may augment lesion depth while relieving surface char [3]. Irrigation prevents the accumulation of char on the ablating surface as can occur with standard unipolar systems. Irrigation with saline cools the tissue and drives the focus (hottest point) of energy deeper, which allows creation of deeper lesions [49]. The energy disperses from a single element and there is a possibilty of damaging the adjacent structures (ie, esophagus). The bipolar RF clamp confounds these disadvantages, creating precise and controlled transmural lesions [3, 24, 43, 49]. The bipolar system monitors tissue impedance, ablating until a plateau in the impedance is reached, which indicates the point of lesion transmurality [50]. The structure of most importance is the circumflex artery, which could potentially be damaged during the epicardial ablation procedures. The circumflex artery is lodged in fat in the atrioventricular groove. Fat is a superb insulator of RF energy, and it would be difficult to damage the circumflex artery with the RF ablation procedure of the mitral valve annulus [46]. Surgeons have innovated a variety of lesion sets for RF ablation of AF that invariably involves isolation of the four pulmonary veins [46–48, 51, 52]. Creation of left-sided lesion sets generally takes 10 to 20 minutes [24, 46, 47]. This time frame in is opposition with the 1 hour or longer time required to complete the Cox maze III procedure [53, 54]. Some reports describe the lesions produced with various probes [55], but there are no clinical data comparing lesions produced from the epicardial or endocardial surface with unipolar and bipolar devices [50]. A recent report about surgical ablation of AF with a novel bipolar RF device has demonstrated a sinus rhythm restoration rate of 79% at 3 months, 87% at 6 months, and 89% at 1 year [56]. Although lesion sets generated with RF energy differ, the results are similar; the AF is ablated in 70% to 80% of patients [3, 41, 46, 47].

Microwave
There is a growing interest in microwave energy for creating lines of conduction block by thermal damage and successive scar formation [3]. Microwave energy creates electromagnetic radiation that induces oscillation of dipoles such as water molecules in tissue, transforming electromagnetic energy into kinetic energy, and heat. Microwave energy has a benefit over unipolar RF ablation, because the volume and depth of heated tissue are bigger, resulting in a higher possibility of transmural lesions [3]. However a recent postmortem histologic study showed that in the majority of samples the lesions were not transmural and the extent of myocardial damage was highly variable [57]. Microwave energy does not char the endocardial surface (as long as appropriate ablation factors are used), which may diminish the detrimental effect of thromboembolism [41]. Lesion sets generated with microwave energy are identical to those generated with RF ablation, generally involving pulmonary vein isolation (PVI) [3, 41]. Approximately 80% of patients can be cured of chronic AF by microwave ablation [3, 58]. In one series of Knaut and colleagues [59], 90 patients with chronic AF underwent an endocardial microwave maze procedure accompanying cardiac surgery. On follow-up after 1 year, 67% of the patients had sustained sinus rhythm. Microwave ablation is now being considered as an epicardial ablation tool during minimally invasive cardiac surgery [59]. Transmurality is still in debate in microwave created lesions. To obtain a complete isolation, online electrophysiologic evaluation during microwave ablation is necessary to optimize the results [60].

Cryothermy
Cryoablation is a well-documented technique in arrhythmia surgery and an important element of the Cox maze III procedure [26, 35, 61]. Use of a nitrous oxide-based cryoablation probe on atrial tissue for 2 minutes duration at –60°C creates a transmural lesion that can be visually verified [3]. Although thawing the tissue architecture seems to be preserved, cells within the frozen tissue become irreversibly damaged and are subsequently replaced by fibrotic tissue [62, 63]. Recently cryoablation has been found to be available for percutaneous transvascular mapping and ablation of cardiac arrhythmias [62–64].

Transmural lesions created by the energy sources differ. Although the cut and sew technique and endocardial cryothermy ensure transmural lesions, epicardially used unipolar RF and microwave on a beating heart may not guarantee the necessary lesion depth. In a caprine study of right atrial free-wall linear percutaneous cryoablation, Keane and colleagues [65] demonstrated that endocardial cryoablation could create linear conduction block in the beating heart. Sueda and colleagues [66] reported successful endocardial cryoablation of AF in 78% of patients. Others have reported that isolation of the pulmonary veins with endocardial cryoablation terminated AF in 70% of patients [67]. There are several obstacles to the use of cryothermy epicardially, mostly related to the heat sink effect of endocardial blood, which is frequently observed in other unipolar energy sources as well. Several recent modifications (ie, argon-based and helium-based cryo systems) have been introduced that will hopefully increase the efficacy of these sources in beating heart applications [49].

Ultrasound
Ultrasound involves the propagation of sound waves at a frequency of 2 to 20 MHz. A transducer with a piezoelectric crystal vibrates at a fixed frequency when electrical energy is applied. The energy is propagated as a mechanical wave by the motion of particles within the medium. Absorption of the motion results in heating of the medium. At high power, ultrasound can disrupt cell membranes, alter physical properties, and result in thermal heating. The advantages of ultrasound are that it can be collimated and has a long depth of penetration [62, 68]. In one single center series, an ultrasound balloon was deployed in 15 patients in the superior and left inferior pulmonary veins [69]. Over a 35-week clinical follow-up period, 9 of 15 patients remained in sinus rhythm. In a recent multicenter study [70], epicardial high-intensity focused ultrasound was clinically evaluated and the initial results were assessed at the 6-month follow-up visit. The study showed that freedom from AF was 85% in the entire study group (80% in patients with permanent AF, 88% in 35 patients who had the additional mitral line, and 100% in patients with paroxysmal AF). A pacemaker was implanted in 8 of 103 patients.

The extent of epicardial fat makes RF the least effective source on account of its lack of depth of penetration. Ultrasound energy seems to be particularly advantageous. The advantages arise from the characteristics of ultrasound to be contact forgiving, its ability to be focused at variable tissue depths, as well as its propensity to remain collimated over distance. Nevertheless mid-term and long-term results are necessary for wide clinical application of this new energy source [62].

Laser
Laser produces a monochromatic, phase coherent beam of a specific wavelength that can be delivered in a highly focused beam of energy of specified duration and intensity. As the laser energy passes through a medium it is absorbed, resulting in heating or scattering, which results in lesion enlargement [62]. Earlier studies of laser cardiac ablation used high-energy pulsed laser and carried a risk of crater formation. More recently, diode laser has been pursued as a means of providing continuous low-energy ablation. The pre-clinical laboratory work of Williams and colleagues [49] demonstrated that laser energy created 100% transmural lesions in canines from an endocardial approach. Recently developed laser-based probes (Edwards Lifesciences, LLC, Irvine, CA) have been specifically designed for thoracoscopic AF ablation [71]. The initial clinical work has been promising, although the number of patients treated remains small [49].

Alternative techniques such as new cryotechnologies, laser application, and ultrasound energy need to be evaluated with further clinical trials for effectiveness and safety [62].


   Onze Lieve Vrouw Clinic’s Strategy for Surgical Treatment of AF
Top
 Abstract
 Introduction
 Material and Methods
 Results of Surgical Treatment...
 Onze Lieve Vrouw Clinic's...
Comment
 References
 
The concept of "hybrid therapy" is that a combination of treatment modalities might be used in a given patient so as to produce a synergistic effect, with each technology improving the efficacy of the other [72]. It is known that addition of right atrial catheter ablation to a regimen of previously ineffective anti-arrhytmic drugs is associated with a significant reduction in the frequency, duration, and severity of AF episodes and symptoms [73]. In this sense, hybrid therapy with RF catheter ablation of right atrium and surgical techniques may be an effective therapeutic approach for treatment of AF. Combined surgical and percutaneous approach necessitates close collaboration between the surgeon and electrophysiologist. The available data in the literature suggest that a combined surgical and percutaneous approach could be the strategy of choice for treatment of AF [74]. Our current strategy for surgical treatment of AF in our center is summarized in Table 4.


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  		Table 4. Current Options for Surgical Treatment of Atrial Fibrillation in Onze Lieve Vrouw Clinic
 
Lone AF
The surgical treatment modality of lone AF at our center is the robotically enhanced (da Vinci Surgical System [Intuitive Surgical Inc, Sunnyvale, CA]) microwave ablation technique. Although promising innovations are obtained in laser and ultrasound technology, microwave is the only device available in Europe at this time for robotic application. This program was started in October 2004, but since then it has seemed to be a promising tool in the minimally invasive treatment of lone AF. Indication for surgery was symptomatic, drug refractory paroxysmal AF, or recurrence after percutaneous treatment. The surgical procedure was performed off-pump as an isolated right chest approach. All procedures were performed using the Flex 10 microwave ablator (Guidant, Indianapolis, IN). A lesion, encircling the pulmonary veins, is performed by the microwave ablator (65 W for 90 seconds) and is repeated. The postoperative drug regimen included a beta blocker (sotalol) and anticoagulation for at least 6 months, depending on the clinical evolution. All patients had a 6-week follow-up visit and were further re-evaluated at 3 and 6 months postoperatively and then again at 1 year postoperatively, and then annually thereafter. All follow-up visits included an electrocardiogram, transthoracic echocardiogram, and 7-day Holter monitoring (except at the 6th week visit). Mean follow-up time was 8.5 ± 3.4 months (and all patients are beyond the 6-month follow-up) [75]. Thirteen patients underwent robotically enhanced PVI. Recently updated follow-up results are depicted in Table 5 [75]. There was one intraoperative conversion to sternotomy due to a bleeding complication. During the follow-up none of the patients experienced a major adverse cardiac event (eg, anticoagulation problems, stroke, or nonfatal myocardial infarction). One patient required a left atrial flutter ablation and another patient required a right atrial flutter ablation during follow-up. The patient with left flutter ablation subsequently went into continuous AF requiring a minimally invasive left atrial cryo-maze procedure. Since then this patient has been free of AF (follow-up, 8 months). All patients in sinus rhythm are off anticoagulation and antiarrythmic drugs. Recently, Jansens and colleagues [76] reported their series of robotic PVI for symptomatic paroxysmal AF. Within their series, 6 patients underwent successful endoscopic PVI. In 1 patient the operation was converted into a small right thoracotomy. Operative assessment of the ablation line showed a successful electric block in every patient. Three months after the procedure, the first 5 patients were in permanent sinus rhythm. Although long-term results are not available yet, we believe that robotically enhanced microwave ablation is both a feasible and efficacious treatment option for paroxysmal lone AF.


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  		Table 5. Rhythm Follow-Up in Robotic Pulmonary Vein Isolation (n = 13)
 
AF Accompanied by Coronary Artery Bypass Grafting or Aortic Valve Replacement or Both
A small number of patients presenting for coronary artery bypass surgery have AF [77]. In our center, surgical strategy of AF treatment in accompanying coronary artery bypass grafting or aortic valve replacement surgery, or both, is bilateral bipolar PVI with or without left atrial appendage exclusion with or without partial cardiac denervation. An overview of this surgical strategy accompanied by AF treatment in our center is summarized in Table 6.


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  		Table 6. Results of Surgical Ablation for Atrial Fibrillation Accompanied by Coronary Artery Bypass Grafting and/or Aortic Valve Replacement
 
Cardiac denervation was widely performed in the 1970s for the prevention of coronary artery spasms. Amano and colleagues [78] studied the effects of intrapericardial cardiac denervation on coronary artery bypass flows and reported its beneficial effect on systemic hemodynamics and coronary circulation. In partial denervation, the fat pad around the aorta is dissected first. In the second step, the superior vena cava is completely liberated and freed from the right pulmonary artery. Then the interatrial groove, the region of Bachmann’s bundle, the roof of the left atrium, and the ligament of Marshall are dissected. In a recent study of Melo and associates [79], 207 patients undergoing low-risk coronary artery surgery had ventral cardiac denervation. Their results indicate that ventral cardiac denervation is a fast and low-risk procedure. Its use significantly reduces the incidence and severity of AF after routine coronary artery bypass surgery.

AF Accompanied by Valvular Disease With or Without Ischemic Heart Disease
About 40% to 60% of patients undergoing mitral valve surgery have AF at the time of the operation [47, 54, 80]. The study of Crijns and colleagues [81] investigated which patient may benefit from additional surgery for the cure of AF performed in combination with valve surgery. The study demonstrated that patients scheduled for mitral valve surgery with a history of chronic AF should be considered candidates for additional surgery for AF concomitantly performed during valve surgery.

Our surgical approach for treatment of concomitant AF, aortic valve replacement (or coronary artery bypass grafting), and mitral valve disease is the conventional approach through a standard sternotomy. However our surgical strategy for concomitant treatment of AF and mitral valve disease with or without tricuspid valve disease is the thoracoscopic approach through a port access. Since January 1999, 103 patients underwent minimally invasive mitral valve surgery with a concomitant PVI performed with unipolar RF.

The mini-maze procedure was performed after the completion of the mitral valve repair or the insertion of the prosthesis. Intra-atrial ablation lines were created by using a saline irrigated tip unipolar radiofrequency pen (Cardioblate [Medtronic Inc, Minneapolis, MN]). Lines of electric isolation were positioned around the four pulmonary veins ostia and were connected with the atriotomy line to complete the isolation (Fig 2). Another line was created to connect the mitral annulus, starting in the region of P3, with the line isolating the pulmonary veins [82].


Figure 2
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  		Fig 2. Lesion set generated in our center. Pulmonary veins are isolated by a line of ablation around the ostiums and connected to the atriotomy incision line. Another line is created towards the mitral P3 region. (LAA = left atrial appendage).

 
In our group of patients, 41.2% were known to have intermittent AF and 58.8% were known to have continuous AF. At the time of surgery 67.7% of the patients were in AF. Mitral valve surgery included mitral valve repair in 71.8% and mitral valve replacement in 26.2%. Tricuspid annuloplasty was performed in 22 patients. Major complications were mortality (1%), cerebrovascular accident and transient ischemic accident (1.9%), and permanent pacemaker placement (5.9%). At the time of discharge 71.9% of patients were in sinus rhythm, 21.9% were in AF, 1% was in atrial flutter, and 5.2% were in pace rhythm. Follow-up was performed in 100 patients with a mean follow-up time of 17.4 ± 14.1 months with 69.7% of the patients in sinus rhythm, 28.3% who were in AF, and 2% who were pacemaker-dependent.

Our results indicate that concomitant mitral valve surgery and left-sided maze (isolation of the all pulmonary veins from the left atrium) with unipolar RF performed through a minimally invasive approach is a safe and feasible technique with low morbidity and satisfactory early-term and mid-term clinical success (Table 7), for intermittent and continuous AF. Further follow-up is necessary to assess the long-term efficacy of this approach [82].


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  		Table 7. Intermediate-Term Follow-Up Results in Port Access Surgery
 

   Comment
Top
 Abstract
 Introduction
 Material and Methods
 Results of Surgical Treatment...
 Onze Lieve Vrouw Clinic's...
 Comment
References
 
In conclusion, AF is an extremely important rhythm disturbance that is associated with substantial morbidity, mortality, and a tremendous amount of health care expenses. There are different treatment options for AF. In 1991 Cox and colleagues described the maze 1 procedure and later the maze 2 and maze 3 procedures [4, 26, 27]. The maze 3 procedure not only sustained sinus rhythm, but it also maintained atrial transport function and became the gold standard for surgical treatment of AF. The maze procedure controls AF in more than 90% of selected patients. However this procedure never became a widespread technique.

Different energy sources became available in the surgical armamentarium as alternatives to the cut-and-sew method. New technologies (ie, RF, microwave, cryothermy, ultrasound, and laser) in the surgical management of AF and the creation of new left atrium lesion sets are being developed to potentially match the results to the maze procedure while performing less complicated and extensive surgery. Although encouraging and promising results are obtained with these new techniques, the success rate did not reach the maze 3 procedure yet. This may have been caused by the difficulties in achieving consistent transmurality and mostly using these alternative enrgy sources (in the setting of ablation) limited to the left atrium.

Our strategy in AF treatment is based on patient profile. We are adapting new technologies (ie, RF, microwave, cryothermy, ultrasound and laser) and minimally invasive innovations and approaches (ie, robotically enhanced PVI and port access mini-maze) according to pathology (lone AF, AF accompanied by coronary artery bypass grafting, or mitral valve disease, and so forth) and indication (paroxysmal or permanent AF) as depicted in Table 4. Although long-term results are not available yet, robotically enhanced microwave ablation seems both an efficacious and feasible treatment option for paroxysmal lone AF and may be an alternative choice to percutaneous ablation procedures. Our encouraging results also show that using unipolar RF energy to perform a mini-maze during minimally invasive mitral valve surgery with or without tricuspid valve surgery is a safe procedure and is associated with good early-term outcomes.

However, hardly any alternative procedure matches the results of the Cox maze procedure to date. Therefore, long-term follow-up results of pioneering institutions and further extensive researches in the field of energy sources are still mandatory.


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 Abstract
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 Material and Methods
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 Onze Lieve Vrouw Clinic's...
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