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Ann Thorac Surg 2002;74:797-804
© 2002 The Society of Thoracic Surgeons
a Department of Surgery, Yale University School of Medicine, Yale-New Haven Hospital, New Haven, Connecticut, USA
b Department of Pediatrics, Yale University School of Medicine, Yale-New Haven Hospital, New Haven, Connecticut, USA
* Address reprint requests to Dr Kopf, Yale University School of Medicine, 333 Cedar St, FMB 121, New Haven, CT 06510, USA
e-mail: gary.kopf{at}yale.edu
Presented at the Thirty-eighth Annual Meeting of The Society of Thoracic Surgeons, Fort Lauderdale, FL, Jan 28–30, 2002.
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Abstract |
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Methods. Six patients aged 6 weeks to 40 years with refractory SVT were referred for reoperation for repair of complex congenital heart disease (transposition of the great vessels, Ebstein’s anomaly, single ventricle, tetralogy of fallot). Intraoperative radiofrequency ablation was performed in the right atrium for refractory SVT as an adjunct to surgical reconstruction (redo Fontan, right atrial reduction plasty, right ventricular outflow tract reconstruction, tricuspid repair). Lesions were made with a radiofrequency probe using temperatures of 70°C for 60 seconds. Lesions were placed between the coronary sinus and the tricuspid valve, between the tricuspid valve and the inferior vena cava, between the atrial septal defect and the superior and inferior vena cava in patients with intraatrial reentry tachycardia/atrial flutter, and at the location of the accessory pathway in a patient with Wolff-Parkinson-White syndrome. The long, flexible probe has multiple independently controlled segments allowing ablation lesions that conform to the atrial morphology.
Results. An average of five intraoperative radiofrequency ablation lesions per patient were made. Average time for ablation was 14 minutes. With up to 25 months’ follow-up, 5 patients are in sinus rhythm, and 1 is in a paced atrial rhythm. The patient with Wolff-Parkinson-White syndrome showed no preexcitation after operation. No complications resulting from intraoperative radiofrequency ablation were encountered.
Conclusions. Intraoperative radiofrequency ablation in the atrium is a safe, effective, and expeditious procedure for control of SVT in patients undergoing reoperation for congenital heart disease with refractory SVT.
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Introduction |
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In the Cox maze operations, lines of conduction block are created usually by a combination of surgical incisions and cryoablation. Recently, intraoperative radiofrequency ablation (IORFA) has been used in place of surgical incisions, cryoablation, or both. The application of IORFA has helped simplify and shorten the classic maze procedure, which in turn has increased general interest in its use [5–7].
Intraoperative ablation for the treatment of SVT in patients with CHD has been successfully applied in select centers. Mavroudis and colleagues [8, 9] have used intraoperative cryoablation during Fontan revisions and other redo operations to treat SVT. They have developed a set of ablation lines based on detailed electrophysiologic (EP) mapping designed to cure as well as to prevent IART ("modified RA maze procedure") [10]. In this modified RA maze operation, the lines of block, or ablation lines, are formed with a combination of cryoablation and incisions. The modified RA maze procedure has yet to become widespread, which may be due in part to the belief that performing a structural repair to assuage hemodynamic issues will alleviate arrhythmias. In addition, after a complex, time-consuming, reoperative congenital cardiac procedure, surgeons may be reluctant to perform an additional procedure whose utility is unclear.
To simplify and shorten intraoperative treatment of SVT in patients with CHD, we began using a malleable radiofrequency (RF) probe to produce ablation lines quickly and reliably according to the modified RA maze procedure. We have also used IORFA to treat other forms of SVT. The purpose of this report is to review our initial short-term experience with this technique.
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Material and methods |
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Surgical technique
Defibrillation pads are placed on the lateral chest wall for emergency defibrillation. Indifferent electrodes are positioned on the patient’s back to ground the RF circuit. Reentry median sternotomy is performed with particular caution, as this is probably the most hazardous part of the operation. Exposure of a groin vessel is routine if it appears that grafts or cardiac structures are tightly adherent to the sternum. Before sternotomy, mediastinal structures are dissected from the inner table starting inferiorly and working upward with the help of upward retraction on the costal margins. If dissection reveals difficult adhesions between the sternum and the cardiac structures or grafts, groin cannulation and partial bypass is used.
After dissection and aortic and bicaval cannulation, cardiopulmonary bypass is commenced with cooling to 25°C. The aorta is clamped and cardioplegia given. A left ventricular vent through the right superior pulmonary vein is used routinely. The inferior vena cava is cannulated directly in as inferior a position as possible so that the atrial-caval junction can be visualized. In 5 of the 6 patients, the RA incision extended to the inferior vena cava. In patient 2 with dextrocardia and levotransposition of the great arteries, the approach was through the left atrium. The enlarged atrium is reduced by extensive resection of the anterior atrial wall and appendage (Fig 1). An adequate cuff along the atrioventricular groove is left to allow atrial closure without causing injury to the right coronary artery. If there is an atriopulmonary connection, it is taken down, and the RA incision is extended to the incised atrial end. Atrial septostomy is performed when necessary for Fontan revision, and the atrial pathology is carefully assessed. Ablation pathways are determined, and IORFA is carried out.
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The location and the number of ablation lesions were similar for each patient undergoing the modified RA maze procedure, but there was some variation because of individual pathology. We used what is known about IART circuits from previously published animal and human EP study data [12–15] as well as the general guidelines established by Mavroudis and co-workers [8, 9] (Fig 3). The isthmus between the inferior vena cava and the tricuspid annulus was ablated by placing lesions between the tricuspid valve and the inferior vena cava and between the coronary sinus and the inferior vena cava. Additional RA lesions were made, after taking into consideration the presence of RA scars, atrial septal defects or patches, and an atriopulmonary connection. Ablation lines were made superior and lateral to the atrial septal defect scar or patch to connect with the superior vena cava or the RA incision. Additional ablations between the atriopulmonary anastomosis and the atrial septal defect, or the RA incision, were made if necessary (Fig 4–6). No scars or incisions were left in an island of viable atrial tissue to avoid reentry circuit formation. In general, an unablated pathway between the sinus and the atrioventricular nodes remained, although this is not essential in the patient with a single ventricle where the right atrium becomes essentially nonfunctional and atrial pacing is established. In patients with two ventricles, ablation lines are designed to avoid the creation of electrically isolated areas in the right atrium to preserve RA function.
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Completion surgical procedures
After IORFA, right heart reconstruction was completed. After the right atrium was closed, an external-conduit Fontan procedure was done in 2 patients during rewarming. Atrial resection and closure allows ample room for the external conduit (see Fig 6).
After the patient was weaned from cardiopulmonary bypass, epicardial bipolar, steroid-eluting atrial and ventricular leads were placed in 3 patients (patients 3, 5, and 6) and were connected to a newly implanted abdominal pacemaker generator (patients 3 and 5). Dual-chamber temporary pacing wires were implanted in all patients.
Costs
The disposable RF probe costs $1,495, and there is an additional $100 per operation cost for grounding pads and RF cables. The one-time cost of the RF generator is $22,500. The same equipment is used widely for creation of left atrial ablations in association with mitral valve surgical procedures.
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Results |
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Cardiac rhythm before and after operation and throughout follow-up are shown in Table 1. The immediate postoperative rhythm was sinus rhythm in 5 of the 6 patients and atrial pacing in the other (patient 4). During the first 24 hours, episodes of SVT were documented in patients 1, and 2. Patient 2 had a single episode of atrial flutter that required cardioversion to restore sinus rhythm. Patient 1 had sustained episodes of atrioventricular node-dependent reentrant SVT that was subsequently controlled with propranolol hydrochloride. This nodal-dependent reentrant pathway had not manifested itself preoperatively. Patient 5 had rare nonsustained atrial flutter. At discharge, 5 patients remained in sinus rhythm, and 1 was in a paced atrial rhythm.
Follow-up ranges from 10 to 25 months. Patient 2 continues to experience rare episodes (one to three per month) of nonsustained atrial flutter (longest episode, less than 35 beats). Patients 1, 2, and 5 are receiving antiarrhythmic medications.
All patients survived hospitalization. There was one late death 4 months postoperatively. Patient 4 was undergoing a noncardiac procedure and sustained respiratory arrest under conscious sedation. This patient also had a history of Kawasaki disease, and postmortem examination showed severe coronary artery disease.
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Comment |
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Surgical approaches for the treatment of SVT have been well established. Theodoro and associates [18] at the Mayo Clinic effectively used the classic Cox maze procedure for the right atrium to control SVT in a group of patients most of whom had tricuspid repair for Ebstein’s anomaly. Patients with IART have undergone reconstruction of the Fontan operation not combined with ablation procedures. A redo Fontan operation can result in clinical improvement, but SVT persists in a large segment of patients [19–21]. Mavroudis and coauthors [9, 10] have shown that Fontan conversion combined with atrial ablation procedures results in fewer and more easily controlled episodes of arrhythmias. Nevertheless, there are very few reports of the use of intraoperative ablation for Fontan revision, perhaps because of time concerns and perceived complexity of the procedure.
Supraventricular tachycardia associated with long-standing palliated CHD often originates from the scarred, dilated right atrium. The mechanism and pathways of IART have been elegantly studied and are due to reentry circuits within the atrium [3, 10, 12, 13, 22]. The classic Cox maze procedure and its modifications were originally designed for left atrial or biatrial pathology associated with mitral valve or myocardial disease and atrial fibrillation. This operation, although effective, is complex. The modified RA maze procedure is a simplified, safe, and quick approach to manage IART localized to the right atrium.
In none of our patients was the arrhythmia the primary indication for surgical intervention, but all had persistent SVT despite other forms of treatment. Our clinical impression is that operation without arrhythmia ablation would not have resulted in optimum results.
Use of RF
There is little experience with the use of IORFA in congenital heart surgery. In reports on the modified RA maze procedure in Fontan revisions, cryoablation is used extensively [9]. Whether RF ablation is as effective as cryoablation in CHD remains to be proven; however, our initial results are encouraging and warrant further investigation in view of its other possible advantages. A considerable amount of data is being accumulated as to the effectiveness and safety of IORFA in the adult population undergoing maze procedures [5–7].
In our opinion, the RF system has the benefit of a long, malleable multistage electrode that allows the creation of an entire ablation line with one application of the electrode in 1 minute. The ablations generally requires less than 15 minutes. The RF generator requires only alternating current; there is no need of liquid nitrogen and its encumbrances. In our small series, there were no complications attributable to the RF ablation technique. Because ablation is accomplished by tissue desiccation, not charring or cutting, we do not expect major tissue damage to adjacent structures.
Preoperative and intraoperative EP study and mapping
Precise mapping of the IART circuit or circuits was not performed prior to operation in any of our patients. Several patients (patients 1, 3, and 5) underwent limited EP study. The known pathways in the right atrium for reentry circuits in IART are sufficient to identify the ablation sites to interrupt these pathways. The advantage to this approach is that it eliminates the costs, risks, and discomforts of a prolonged EP procedure. Intraoperative endocardial EP mapping is time-consuming and complicated and requires specialized equipment in the operating room. In only a very limited number of patients will the information obtained from intraoperative EP study change the ablation procedure. Together with atrial resection, the ablation lines we used are designed to interrupt all the known reentry pathways in the right atrium. Whether additional ablation is necessary in the left atrium can be determined by limited preoperative EP study and electrocardiographic data. Intraoperative EP study is unnecessary in the vast majority of patients. Although short-term results are favorable, longer follow-up of patients treated without intraoperative EP mapping will determine whether this view is justified.
Role of pacemakers
Patients with CHD, especially those who have undergone operation, are at risk for the development of sinus node dysfunction and bradycardia-induced SVT. In addition, most pharmacologic therapy for SVT frequently has the side effect of bradycardia, thereby indirectly contributing to the arrhythmia. The use of pacing to prevent bradycardia has proved to be an effective method to decrease the frequency of SVT [23]. Permanent epicardial pacing wires were implanted in the majority of our patients at the time of operation. The generator can be implanted immediately or expeditiously at a later date if indicated. The use of pacemakers is an important adjunct to intraoperative arrythmia procedure for long-term control of SVT.
In summary, intraoperative ablation for the treatment of SVT, specifically IART, in patients with structural CHD has been successfully applied but not widely used. With the development of safe, reliable, and easy methods of intraoperative ablation, this procedure may receive more widespread use and can be employed for a variety of arrhythmias affecting patients with CHD [22]. The intraoperative RF ablation probe is easy to use and faster than cryoablation in our experience. There were no complications attributed to the RF ablations. On the basis of our initial experience, we think that intraoperative RF ablation is feasible in almost any patient and adds little to the time or complexity of the operation. Ablation therapy for arrhythmias should be part of the armamentarium of the congenital heart surgeon and should be used more frequently as the number of long-term survivors of CHD operations increases.
For patients with CHD who require surgical intervention to correct underlying hemodynamic or structural problems, the use of intraoperative RF ablation appears to be a safe, effective, and feasible alternative to traditional treatment of IART. Our results are short term, and whether these early successes will be maintained with long-term follow-up remains to be seen. These preliminary results using intraoperative RF ablation to treat SVT in conjunction with structural cardiac repairs are encouraging and warrant further investigation.
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Discussion |
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TopAbstractIntroductionMaterial and methodsResultsCommentDiscussionReferences |
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This report describes a well-thought-out approach to the standardization of surgical ablation of right atrial reentrant tachycardia with limited preoperative electrophysiologic mapping and draws from earlier work in the field by Dr Mavroudis. My only question relates to the safety of using unipolar radiofrequency (RF) ablation in infants. Radiofrequency ablation delivers a higher current than electrocautery, and the current increases as the length of the active electrode increases. The Cobra RF surgical probe is designed for use in adults, and two standard grounding pads on the posterior thorax are recommended to avoid thermal skin injury. This was presumably done in the 5 patients in this series who ranged from 15 to 40 years old. I have concerns that the use of pediatric grounding pads in infants, whose thin skin is more susceptible to thermal injury, could lead to thermal injury because of the higher current density as the surface area of the grounding pad decreases.
Although this study concerns RF ablation in congenital heart disease, only 1 of the patients was an infant. How was the indifferent electrode applied to the skin of the 6 week-old infant? Were multiple coils used simultaneously during ablation? Can the high current detection threshold and automatic shutoff of the electrosurgical unit be relied on to prevent skin injury when smaller surface area grounding pads are used?
Finally, have the authors considered the use of an alternative thermal energy source, such as microwave, in young children to avoid this potential problem? I believe that it is premature to recommend unipolar RF ablation in this very young age group until these issues are addressed.
DR CONSTANTINE MAVROUDIS (Chicago, IL): Congratulations. That was a very nice presentation.
My colleagues and I have used cryoablation and incisional techniques to treat 88 young children, most with congenital heart disease, for various arrhythmias from 1990 to 2002. We were struck during this time by how thick the right atria were, measuring up to 15 to 20 mm, and we questioned whether the technique of RF ablation could actually cause a reliable transmural line of block in light of these thick atria.
The other issue that steered us away from using intraoperative RF ablation was the possibility of injuring structures such as valve leaflets, valve annuli, and coronary arteries. The problems with making lesions in the presence of congenital heart disease are not only the thickness of the atria but also the variance in the anatomy. Cryoablation lesions or ablative lesions can be required in often unrecognized areas where vital structures are. Therefore, we have been keeping away from this technology.
Perhaps the bipolar RF ablation may offer new solutions to these problems. At present, considering the advantages and disadvantages of RF ablation, I offer a note of caution about the use of RF ablation in children, where the vital structures are very close to the proposed lines of block. I am sure that as time goes by the technology will be refined, and one of these or perhaps a combination of these two procedures will develop into the standard.
DR KOPF: Thank you, Dr Kress and Dr Mavroudis, for your comments and questions. I acknowledge Dr Mavroudis’s outstanding contributions to and leadership in the field of arrhythmia surgery in congenital heart disease.
As far as safety in infants is concerned, the alternating current goes from the electrode to the grounding pad in the back, and the larger that grounding pad, the more the current will be spread out over an area on the skin. In this series, used the adult grounding pads so that there was a very large area on the back of the 1 infant. We thought that by using a large grounding pad, the current density would be very, very low over that pad and that that would prevent any skin injury. In fact, the infant sustained no skin injury.
As for the issue of unipolar versus bipolar RF ablation to use a bipolar system you have to have electrodes on both sides of the tissue, that is, with the tissue in between the two electrodes. That works extremely well. The current is limited between the two electrodes, and ablation is absolute. The problem in these complex congenital heart lesions is that it often is not feasible or it is extremely difficult to get the tissue between two electrodes and that to do this would require a lot of extra dissection. Although the bipolar technique is appealing, I do not think it is feasible in many areas in congenital heart disease.
Dr Mavroudis, I share your concern about thick atria. As you said, some of these patients having a redo Fontan operation, have atria 10 mm, 12 mm, or even 15 mm thick. This does require increasing the ablation current and time, although we do not really know exactly what the appropriate settings are. They have yet to be worked out. In very thick atria, I do increase the temperature settings and the time settings to boost the current. However, we do not have any definitive studies to determine whether or not we are actually producing a full transmural block. All we can go by is our clinical results, which, at least initially, appear to be satisfactory.
The problem of injury to nearby cardiac structures, for example, valves and coronary arteries, is a real concern. It is a matter for consideration with cut-and-sew techniques and with cryoablation. We are careful to limit our incisions, but the way the RF energy is set up, it is designed for desiccation, and that is how it kills the tissue. Because of its high frequency, it will not cut tissue, nor will it burn or char tissue, and we think that this provides a margin of safety when we get close to important structures.
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