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Ann Thorac Surg 2002;74:2165-2168
© 2002 The Society of Thoracic Surgeons
a The Center for Atrial Fibrillation, The Cleveland Clinic Foundation, Cleveland, Ohio, USA
Accepted for publication September 9, 2002.
* Address reprint requests to Dr Gillinov, Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation/F25, 9500 Euclid Avenue, Cleveland, OH 44195, USA.
e-mail: gillinom{at}ccf.org
Abstract
PURPOSE: This work reports our initial evaluation and clinical experience with the Atricure bipolar radiofrequency (RF) system for intraoperative ablation of atrial fibrillation (AF).
DESCRIPTION: The Atricure system includes a bipolar RF clamp and an RF generator. Lines of conduction block are created by delivery of RF energy (75 volts, 750 milliamps) to tissue compressed between the jaws of the clamp. Energy delivery is continued until the lesion is transmural, indicated by steady and reduced conductance between electrodes in the clamp.
EVALUATION: The Atricure device was used for intraoperative treatment of AF in 120 patients. Lesion sets varied, as the device was used for pulmonary vein isolation, creation of right atrial lesions, or both. There were no device-related complications. Initial incomplete pulmonary vein isolation, identified by pacing, was uncommon, occurring with very thick atrial tissue and when tightening the clamp caused tissue to become folded upon itself in the jaws or to extrude beyond the jaws of the clamp. In such cases, reapplication of the RF clamp produced complete pulmonary vein isolation.
CONCLUSIONS: The Atricure bipolar RF system facilitates surgical treatment of AF. Proper application of the clamp is essential to ensure continuous transmural lesions.
There is a resurgence of interest in direct surgical ablation of atrial fibrillation (AF), fueled by the pioneering work of Cox and colleagues [1, 2], recent technological advances, and demonstration that the pulmonary veins and posterior left atrium are the drivers of AF in most patients [1–4]. Alternate energy sources used to simplify the surgical procedure and to replace incisions of the Cox-Maze III procedure include radiofrequency (RF), microwave, cryothermy, and laser [5–9]. Recent development of a bipolar RF system that includes a mechanism for transmurality assessment represents an important advance in the surgical treatment of AF [10]. We report our initial evaluation and clinical experience with the Atricure (West Chester, OH) bipolar RF system.
For editorial comment see pages 1899 and 1901.
Technology
Radiofrequency energy uses alternating current to heat tissue, creating thermal injury that results in a line of conduction block. In unipolar systems, grounding is achieved by an indifferent electrode applied to the skin (usually the back), and current flows from the tip of the RF catheter and resistively heats tissue in tip contact [10]. With the Atricure bipolar system, electrodes reside in the jaws of an atraumatic clamp (Fig 1). The operator depresses a foot pedal, and RF energy is delivered to the tissue between the jaws of the clamp at 75 volts and 750 milliamps (mA). The RF generator monitors voltage, current, temperature, time, and tissue conductance (Fig 2). Energy delivery is continued until tissue conductance between electrodes in the jaws of the clamp decreases and reaches a steady state for 2 seconds. This algorithm based upon tissue conductance is designed to ensure transmural ablation and conduction block.
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In this initial experience, the Atricure clamp was used to create a variety of lesion patterns on the atria and pulmonary veins.
Left atrial and pulmonary vein ablation
The Atricure clamp is well suited for intraoperative pulmonary vein ablation. The pulmonary veins may be isolated either on or off pump, with the heart arrested or beating.
The right pulmonary veins are prepared by mobilizing the superior and inferior venae cavae and by dissecting the right pulmonary artery from the right superior pulmonary vein. The clamp is then placed around the right pulmonary veins, initially directed from the inferior pulmonary vein toward the superior pulmonary vein (Fig 3A). The operator slides the clamp onto the left atrial tissue adjacent to the pulmonary veins, thereby preventing injury to the pulmonary vein ostia. As the clamp is closed, care is taken to prevent tissue from extruding beyond the tip of the clamp or from folding or bunching up within the jaws. The foot pedal is depressed, and RF energy is delivered. When the generator emits a chirping sound, conductance is low and steady, and ablation is complete. Each application takes 10 to 30 seconds. The clamp is then repositioned for a second application to the right pulmonary veins, this time starting cephalad and engaging the right superior pulmonary vein first. An overlapping RF lesion is thus created, ensuring a continuous transmural line to isolate the right pulmonary veins. The left pulmonary veins are ablated in similar fashion (Fig 3B).
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Right atrial lesions
Right atrial lesion are created on cardiopulmonary bypass with the heart either beating or arrested. If desired, the three right atrial incisions of the Maze procedure can be virtually duplicated with the Atricure device. Lesions may be created on the right atrium either by introducing one jaw of the clamp through small stab incisions or, alternatively, after making a caudal incision (the "T" incision of the Maze procedure) in the right atrium. The Atricure device may be used to create a linear lesion from the superior vena cava to the inferior vena cava, a lesion from the right atrial appendage to the atrioventricular groove, and a caudal right atrial lesion from the atrioventricular groove to the interatrial septum. We have not used the Atricure device to extend these lesions to the tricuspid annulus, as this could endanger the right coronary artery.
Assessment of conduction block
Conduction block across the pulmonary veins was assessed by pacing in 10 patients who were on cardiopulmonary bypass with a beating heart. After pulmonary vein isolation, a bipolar pacing catheter was positioned on each set of pulmonary veins distal to the ablation line. Inability to pace the heart from this site using a stimulus strength up to 10 mA confirmed conduction block.
Choice of lesion set and alternate energy sources
Lesion sets varied, as choice of lesion set was at the surgeon’s discretion and was tailored to treat the patient’s underlying rhythm. Although patients with paroxysmal AF were frequently treated by pulmonary vein isolation alone, patients with persistent or permanent AF usually received additional left atrial lesions. Some patients, particularly those with history of atrial flutter, received right atrial lesions. In many cases, cryolesions were created at the mitral or tricuspid annuli.
Clinical experience
From November 2001, through July 2002, the Atricure bipolar clamp was used to create lesions during AF surgery in 120 patients. The device is versatile and can be used to create a variety of different lesion sets. Most patients had pulmonary vein isolation; in addition, many patients had right atrial lesions patterned after those of the Maze procedure. The left atrial appendage was excised or oversewn in all patients. Most patients had concomitant procedures, including mitral valve repair or replacement, coronary artery bypass grafting, or aortic valve repair or replacement.
Of the 10 patients who had assessment of conduction block at the pulmonary veins, 3 had initial conduction across the ablation line after a single application of the Atricure clamp. In each of these cases, repeat application of the clamp resulted in conduction block. After this observation, all pulmonary vein lesions were created twice in an overlapping fashion. Using this protocol, we achieved conduction block in the next 7 patients assessed by pacing.
Comment
This report describes our initial evaluation and application of the Atricure bipolar RF clamp in patients with AF. The device is particularly well suited to pulmonary vein isolation, as the shape of the clamp allows easy placement around these structures. Two applications to each set of pulmonary veins ensures a complete line of conduction block. The algorithm for transmurality assessment is an important feature, ensuring ablation from the epicardium to the endocardium.
The trends in surgical treatment of AF include use of alternate energy sources to create lines of conduction block and concentration of lesions on the pulmonary veins and posterior left atrium [5–9]. Advantages to alternate energy sources include rapid application, preserved tissue integrity, and reduced risk of bleeding. Lines of conduction block may be created with heat-based energy sources (RF, microwave, laser) or cryothermy. The ideal device creates a lesion rapidly, minimizes risk to adjacent structures, and affords assessment of transmurality. The Atricure bipolar RF clamp satisfies these criteria.
The optimal lesion set has not yet been defined. Catheter-based pulmonary vein ablation cures AF in most patients with paroxysmal AF and in many patients with persistent and permanent AF [3]. These results are useful to guide surgical approaches. Isolation of the pulmonary veins and excision of the left atrial appendage are mandatory. A variety of approaches that include these components have corrected AF in 70% to 90% of patients [6–9]. The importance of connecting lesions in the left atrium (eg, between the right and left pulmonary veins or from the left pulmonary veins to the mitral annulus) is uncertain. Atrial fibrillation arising from the right atrium is uncommon; right atrial lesions may be necessary only in patients with atrial flutter [9]. Thus, pulmonary vein isolation combined with left atrial appendage excision may represent the appropriate operation in most patients with AF. Further study is necessary to test this hypothesis.
In this study, we report our initial experience with the Atricure bipolar RF system. The device is versatile and can be used to achieve simple and rapid pulmonary vein isolation, to perform a full Maze lesion set, or to perform a modified procedure including some of the incisions of the Maze procedure. This initial experience includes a diverse patient population with a variety of lesion sets and recent surgery; we have developed a technique to ensure transmural and continuous lesions, and we have demonstrated the safety of the device. However, we do not yet have data documenting the long term efficacy of these approaches. Additional experience and close patient follow-up are necessary to determine the late success rate and the optimal lesion pattern. This sort of technology, coupled with improved understanding of the pathogenesis of AF, is likely to lead to minimally invasive, off-pump procedures that may be offered to patients with lone AF and no other indication for cardiac surgery.
Disclosures and freedom of investigation
The generators and Atricure clamps were purchased by The Cleveland Clinic Foundation. The authors have performed a free and independent evaluation of this new technology. Doctors Gillinov and McCarthy have no financial relationship with Atricure, but both have been asked to become consultants to Atricure.
Footnotes
The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article.
References
This article has been cited by other articles:
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