Ann Thorac Surg 2006;82:1876-1879
© 2006 The Society of Thoracic Surgeons
New Technology
Epicardial Beating Heart "Off-Pump" Ablation of Atrial Fibrillation in Non-Mitral Valve Patients Using New Irrigated Bipolar Radiofrequency Technology
Piotr Suwalski, MDa,
Grzegorz Suwalski, MDa,
Nicolas Doll, MD, PhDb,*,
Franciszek Majstrak, MDa,
Andrzej Kurowski, MDa,
Kazimierz B. Suwalski, MD, PhDa
a Cardiac Surgery Department, Warsaw Medical University, Warsaw, Poland
b Department of Cardiac Surgery, Heart Center, University of Leipzig, Leipzig, Germany
Accepted for publication March 7, 2006.
* Address correspondence to Dr Doll, Heart Center Leipzig, Department of Cardiac Surgery, University of Leipzig, Strümpellstrasse 39, Leipzig, 04289 Germany. (Email: dolln{at}medizin.uni-leipzig.de).
 |
Abstract
|
|---|
PURPOSE: We evaluated the use of a novel irrigated bipolar radiofrequency system for the treatment of nonmitral paroxysmal atrial fibrillation.
DESCRIPTION: Between December 2003 and July 2005, 24 patients with paroxysmal atrial fibrillation underwent nonmitral cardiac procedures (coronary artery bypass grafting, n = 14; aortic valve replacement, n = 6; aortic valve replacement and coronary artery bypass grafting, n = 3; Bentall procedure, n = 1). In 12 of 14 of the coronary artery bypass graft patients, the procedure was performed off pump. All patients additionally underwent pulmonary vein isolation using the Medtronic Cardioblate BP system (Medtronic, Minneapolis, MN). Acute conduction block was evaluated in 16 patients.
EVALUATION: Patients were followed-up for 6 months. Major adverse events include 1 patient death and 1 patient requiring implantation of a pacemaker. At discharge 19 of 22 patients (86.3%) were in stable sinus rhythm. After 3 months, stable sinus rhythm was found in 15 of 21 patients (71%). After 6 months, 15 of 15 patients (100%) were in stable sinus rhythm. Complete conduction block was accomplished in 29 of 32 pulmonary vein pairs (91%) after a single radiofrequency ablation and in 31 of 32 pairs (97%) after a second application.
CONCLUSIONS: Pulmonary vein isolation with the use of this irrigated bipolar radiofrequency device is feasible, safe, and gains high experimental and clinical efficacy, including use during off-pump surgery.
|
Introduction
|
|---|
Surgical techniques, such as off-pump surgery, and expanding indications for ablation, have resulted in development of epicardial approaches for surgical atrial fibrillation (AF) ablation [1]. A number of ablation systems have been used for the epicardial treatment of AF. However, experimental studies have questioned the transmurality of the scar created by unipolar devices [1, 2]. Conversely, bipolar ablation devices have been more reliable in achieving transmurality on the cardioplegic arrested heart and epicardially on the beating heart with or without the use of the extracorporeal circulation [1, 2].
We report the use of a novel, irrigated bipolar radiofrequency (RF) system for the treatment of nonmitral paroxysmal AF including off-pump coronary artery bypass surgery, describing early electrophysiological and follow-up results.
|
Technology
|
|---|
Patients and Methods
Between December 2003 and July 2005, 38 nonmitral patients underwent concomitant AF treatment with an irrigated bipolar RF device. A subgroup of 24 patients with paroxysmal AF (duration of greater than 6 months) refractory to standard antiarrhythmic therapy was selected for the analysis. Patients were treated with surgical pulmonary vein isolation concomitant to the primary procedures (Table 1). In 12 of 14 (85.7%) coronary artery bypass graft patients the procedure was performed in off-pump technique (OPCAB). The mean Euroscore was 10.4%, (±1.5).
The study was approved by the local ethics committee. Each enrolled patient signed an informed consent form for the procedure and the follow-up visits.
|
Technique
|
|---|
The main objectives of the study were to evaluate the efficacy and safety of the bipolar device to create pulmonary vein encircling lesions during on-pump and off-pump procedures, to evaluate the impact of this procedure on atrial rhythm, to assess the ability of the device to create acute conduction block from the pulmonary veins, and to assess the intraoperative use of the device and its efficacy in OPCAB surgery.
Preoperative data are summarized in Table 2.
All ablations were performed using an irrigated bipolar RF ablation system (Cardioblate BP, Model 60821 [Medtronic, Minneapolis, MN]) (Fig 1). The system consists of a disposable handpiece and a power generator. The head can be rotated 300 degrees and angulated up to 90 degrees, allowing proper adjustment and facilitating placement in the surgical field. The malleable jaws allow shaping such that they conform to the anatomy of the target tissue and the shape of the desired lesion. During ablation the surface of the tissue is continously irrigated with saline through the porous polymer electrodes located within the 5-cm long jaws. Power is supplied by a stepwise-increasing algorithm until a plateau in impedance, predicting transmurality, is achieved [1].
View larger version (29K):
[in this window]
[in a new window]
|
Fig 1. Medtronic Cardioblate BP (Medtronic, Minneapolis, MN) irrigated bipolar radiofrequency ablation device.
|
|
Pulmonary vein isolation was performed in all patients. After dissection of pericardial reflections and eventually the interatrial groove, the bipolar device was clamped around the atrial cuff containing the inflow of the right pulmonary veins (Fig 2). Radiofrequency energy was delivered and the encircling ablation line was created. On the left side, after the heart was lifted, the encircling line was created in a similar manner. The ligament of Marshall was surgically dissected. Intraoperative conduction block was assessed in 16 patients. In 22 of 24 cases the pulmonary vein isolation was performed off-pump, and in the other 2 patients it was performed on-pump while the heart was beating. Due to safety considerations the procedure was usually performed after completing the bypass grafting in OPCAB patients.
View larger version (119K):
[in this window]
[in a new window]
|
Fig 2. Right pulmonary vein isolation using irrigated bipolar radiofrequency device. The ability to rotate and articulate the head facilitates easy placement within the thoracic cavity. The malleable jaws enable positioning of the electrodes on the atrial cuff and off of the venous tissue.
|
|
Conduction Block Validation
Electrical isolation of right and left pulmonary vein couples was acutely assessed in 16 patients, including 10 of 12 OPCAB patients. Two monopolar electrodes (Medtronic, Minneapolis, MN) were attached to the intrapericardial portion of each pulmonary vein pair and paced prior to and after ablation. Successful ablation was defined as the inability to pace the heart at a stimulation level of 20 mA.
Postoperative Management and Follow-Up
A 24-hour Holter electrocardiogram and echocardiography were peformed prior to surgery in all patients. Cardiac rhythm was continuously monitored during the intensive care unit stay. In cases of perioperative AF, medical therapy with amiodarone or with beta-blockers, or both, or electrical cardioversion was performed. If a patient experienced further rhythm instability (ie, more than 2 AF episodes) amiodarone therapy was continued for a maximum of 3 months. At discharge, 24-hour Holter electrocardiogram and echocardiography were peformed in all patients. All patients received anticoagulation therapy for a minimum of 3 months. Patients in stable sinus rhythm without antiarrhythmic drugs (AAD) at 3 months were weaned from warfarin. At 3 and 6 months post-surgery, 24-hour Holter-electrocardiograms, echocardiography, physical examinations, and interviews were carried out in all patients.
Statistical Analysis
Statistical analysis was performed using Statistica (StatSoft, Inc, Tulsa, OK). The data are expressed as mean ± SD.
|
Clinical Experience
|
|---|
Preoperative patient characteristics are listed in Table 1. There were no ablation device-related complications. There was no conversion from OPCAB to conventional coronary artery bypass grafting. Major hospital morbidity occurred in 2 patients, including abdominal ischemia and a reoperation for bleeding. There was 1 in-hospital patient death from severe respiratory disorder. The time of the ablation procedure ranged from 3 to 11 minutes. Mean ablation duration was 15.2 ± 2.2 seconds. Follow-up was 100% complete. No thromboembolic events were recorded and 1 patient died 6 months after surgery due to severe heart failure.
Conduction Block Validation
At baseline, pacing at 5 mA was effective in all 32 vein pairs that were tested. After a single ablation, pacing at 20 mA showed complete conduction block (no atrial capture) in 29 of 32 (91%) pulmonary vein couples. All ineffective ablations were located on the right side. In two right pulmonary couples a repeat application was necessary to achieve conduction block. In 1 patient, despite multiple applications, capture persisted, although the theshold was higher than 10 mA. In this patient there were unique anatomical conditions in the area of the right pulmonary veins. Three large veins came directly off the atrial chamber, which made it difficult to clamp the entire pulmonary vein cuff. In addition, the atrial muscle seemed to be significantly thicker than usual in this area.
Rhythm Outcome
Rhythm follow-up data is shown in Figure 3
and Table 1. All patients were free from AF at the time of intensive care unit arrival. In the intensive care unit, 16 of 24 patients (67%) required electrical (10 patients) or pharmacological (6 patients) cardioversion for AF at least once. One patient (6%) required pacemaker implantation due to sick sinus syndrome. Right or left atrial flutter and pulmonary vein stenosis (clinical or echocardiographic signs) were not identified in any patient throughout the course of follow-up. None of the patients were treated with antiarrhythmic drugs after the 3-month follow-up.
View larger version (36K):
[in this window]
[in a new window]
|
Fig 3. Bar graph showing stable sinus rhythm rate in follow-up. (SR = sinus rhythm; ICU = intensive care unit.)
|
|
Atrial transport function was evaluated in patients sustaining sinus rhythm at each point of follow-up (ie, at 3 months and at 6 months) using transthoracic echocardiography with Doppler analysis of mitral and tricuspid flows. Left and right atrial transport function, defined as a transmitral and transtricuspid A-wave velocity greater than 0.2 m/s, was detected in all patients at each follow-up time point.
|
Comment
|
|---|
In spite of reported good clinical results, experimental data shows that none of the available unipolar devices are able to predictably create a transmural lesion epicardially, especially on the beating heart [1–3]. In this context, bipolar RF energy is very attractive. Clamping the target structures prevents the so-called "heat sink effect," which is due to convective endocardial cooling by flowing blood within the heart chambers. Another advantage is that compression of the atrial wall improves contact and reduces the overall tissue thickness. The ability of bipolar RF devices to create reliably transmural lesions in pigs was shown acutely and with short-term follow-up [4–6]. There is growing experimental evidence that bipolar energy may have higher rates of transmurality than any unipolar device [7].
In Bugge and colleagues' [7] study, the inability to entrain the left atrium from the pulmonary veins significantly predicted transmurality. That is why we strongly recommend performing the double ablation, which resulted in a very high probability of gaining a transmural lesion. The validation of the conduction block also touches on the problem of the transmurality indication by bipolar systems. Today's bipolar devices are based on impedance measurements and are highly reliable. Although they represent a significant step toward the ideal ablation instrument, they may fall short during difficult anatomical conditions like diseased, hypetrophied atria (thicker than 5 mm), areas of trabeculation, or simply folded muscle tissue. In these instances, repeated ablation may be useful and requires only 15 to 20 seconds of additional procedure time. Similar results were shown by Gillinov and McCarthy [8] using a dry bipolar device.
Moreover, bipolar devices have very good safety profiles. The RF current flows in the path of least resistance, which is from one electrode to the other. As a result, collateral damage to structures surrounding the heart is highly unlikely, the heat spread is confined, and there is no current flow through the body of a patient [9].
The ablation system used in this study is customizable and surgeon-friendly in use. The "swan neck"-like handpiece is practical, especially in off-pump surgery, and allows one to put the lifted heart down immediately after the the left pulmonary veins have been clamped, allowing completion of the ablation on a normal positioned heart. This flexibility minimizes rhythm and hemodynamic disturbaces. This facilitates additional possibilities to use the tool in lone AF patients or after a failed catheter ablation.
Electrophysiologists have shown that the origin of paroxysmal atrial fibrillation resides from the pulmonary veins as focal triggers [10]. These triggers can easily be eliminated by isolation of the pulmonary veins. On average 20% of paroxysmal AF degenerates to persistent AF. After 1 year, persistent AF converts to permanent AF in the majority of cases. There is growing evidence that the substrate of permanent AF must be treated differently than paroxysmal AF. To treat permanent AF connecting lines between the mitral annulus and the pulmonary veins may be necessary to control postoperative arrhythmias such as atrial flutter or supraventricular tachycardia [11]. These arrhythmias may be less tolerated by the patient than AF itself. Due to the presence of the circumflex artery in this area [12], the unquestioned challenge for the future is how to create the connecting lines, especially the one leading to the mitral annulus, in a safe mannner without placing the patient on-pump.
In conclusion, the use of this irrigated bipolar radiofrequency device is feasible and safe. Pulmonary vein isolation with use of bipolar ablation results in high clinical efficacy including use during off-pump surgery. The double ablation is recommended in order to optimize the results.
|
Disclosures and Freedom of Investigation
|
|---|
The ablation system was purchased by the Medical Academy of Warsaw. The authors have performed a free and independent evaluation of this new technology. The authors have no financial relationship with the company Medtronic.
|
Footnotes
|
|---|
Disclaimer 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
|
|---|
- Maessen JG, Nijs JF, Smeets JL, et al. Beating-heart surgical treatment of atrial fibrillation with microwave ablation Ann Thorac Surg 2002;74:1307-1311.
- Santiago T, Melo J, Gouveia RH, et al. Epicardial radiofrequency ablations: in vitro and in vivo studies on human atrial myocardium Eur J Cardiothoracic Surg 2003;24:481-486.[Abstract/Free Full Text]
- Doll N, Kornherr P, Aupperle H, et al. Epicardial treatment of atrial fibrillation using cryoablation in an acute off-pump sheep model Thorac Cardiov Surg 2003;51:267-273.
- Bonanomi G, Schwartzman D, Francischelli D, et al. A new device for beating heart bipolar radiofrequency atrial ablation J Thorac Cardiovasc Surg 2003;126:1859-1866.[Abstract/Free Full Text]
- Prasad SM, Maniar HS, Diodato, MD, et al. Physiological consequences of bipolar radiofrequency energy on the atria and pulmonary veins: a chronic animal study Ann Thorac Surg 2003;76:836-841.[Abstract/Free Full Text]
- Hamner CE, Potter Jr DD, Cho KR, et al. Irrigated radiofrequency ablation with transmurality feedback reliably produces Cox maze lesions in vivo Ann Thorac Surg 2005;80(6):2263-2270.[Abstract/Free Full Text]
- Bugge E, Nicholson IA, Thomas SP. Comparison of bipolar and unipolar radiofrequency ablation in an in vivo experimental model Eur J Cardiothorac Surg 2005;28:76-82.[Abstract/Free Full Text]
- Gillinov AM, McCarthy PM. Atricure bipolar radiofrequency clamp for intraoperative ablation of atrial fibrillation Ann Thorac Surg 2002;74:2165-2168.[Abstract/Free Full Text]
- Doll N, Borger M, Mohr FW, et al. Esophageal perforation during left atrial radiofrequency ablation: is the risk too high? J Thorac Cardiovasc Surg 2003;125:836-842.[Abstract/Free Full Text]
- Haissaguerre M, Jais P, Shah DC, et al. Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins N Engl J Med 1998;339(10):659-666.[Abstract/Free Full Text]
- Cox JL. The central controversy surrounding the interventional–surgical treatment of atrial fibrillation J Thorac Cardiovasc Surg 2005;129:1-4.[Free Full Text]
- Becker AE. Left atrial isthmus: anatomic aspects relevant for linear catheter ablation procedures in humans J Cardiovasc Electrophysiol 2004;15(7):809-812.[Medline]
This article has been cited by other articles:
|
|
|
|
 
W. Wisser, G. Seebacher, T. Fleck, C. Aigner, C. Khazen, G. Stix, D. Hutschala, and E. Wolner
Permanent Chronic Atrial Fibrillation: Is Pulmonary Vein Isolation Alone Enough?
Ann. Thorac. Surg.,
October 1, 2007;
84(4):
1151 - 1157.
[Abstract]
[Full Text]
[PDF]
|
|
|
Top
Abstract
Introduction
