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Ann Thorac Surg 2002;74:1992-1997
© 2002 The Society of Thoracic Surgeons

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Original article: cardiovascular

Extracardiac conduit with a limited maze procedure for the failing Fontan with atrial tachycardias

^a Department of Paediatric and Congenital Cardiac Surgery, Auckland, New Zealand
^b Department of Paediatric Cardiology, Green Lane Hospital, Auckland, New Zealand

Accepted for publication July 22, 2002.

* Address reprint requests to Dr Finucane, Cardiothoracic Surgical Unit, Green Lane Hospital, Green Lane West R, Epsom, Auckland, New Zealand.
e-mail: kfinucane{at}adhb.govt.nz

	Abstract

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BACKGROUND: Atrial arrhythmias are a frequent late complication of Fontan procedures. Conversion to an extracardiac conduit combined with reducing right atrial size should improve hemodynamics and reduce the development of tachyarrhythmias. More effective control may be achieved by interrupting atrial arrhythmia circuits and atrial pacing.

METHODS: Between May 1997 and October 2001, 6 patients underwent a revision of their intracardiac Fontan anastomosis. The conversion included an extracardiac conduit insertion, limited right atrial maze procedure, and pacemaker placement. Ages ranged from 14 to 34 years (mean, 22.8 years) at an average of 14.6 ± 4.4 years after their original Fontan procedure. All of the patients had medically uncontrollable atrial tachyarrhythmias with markedly reduced exercise tolerance.

RESULTS: All of the patients survived with an average hospital stay of 16.7 days. Exercise tolerance has improved in all 6 patients, and atrial tachycardias have either decreased (n = 2) or disappeared (n = 4). Two patients are taking antiarrhythmic medications other than digoxin. Follow-up is a mean of 28.5 months.

CONCLUSIONS: Limited right atrial maze procedure, atrial size reduction, and pacemaker implantations are worthwhile additions to simple conversion to an extracardiac conduit in the failing Fontan.

	Introduction

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As patients advance in age after the Fontan operation, the morbidity of atrial tachyarrhythmias becomes increasingly evident [1–6]. Arrhythmias have been noted in up to 40% of Fontan patients at 10-year follow-up [3] and are most common among those with an atriopulmonary anastomosis [6]. Ventricular failure and thromboembolic complications contribute to late morbidity and mortality and often occur in the same patients who have the atrial arrhythmias. Atrial tachycardias are often poorly tolerated; resulting in chronically reduced cardiac output and deterioration in exercise tolerance.

In this group of patients, medium-term results of radiofrequency ablation of intraatrial reentrant tachycardias (IART), which form the majority of the tachycardias, have been relatively poor [7, 8], reflecting the large number of tachycardias induced and their multifactorial causes. Although new isochronal electrophysiologic mapping facilities may improve this longer-term success rate for arrhythmia management, when current medical management is failing, therapeutic management is restricted to either performing a cardiac transplantation or revising the Fontan. With the hazards of immunosuppression and the limited number of organ donors in New Zealand, the latter option is preferable if it can improve the patient’s condition. Altering the Fontan circulation to that of an extracardiac conduit has been performed in patients with a failing circuit [9]. Decreasing tension on the atrial tissue, reducing atrial size, maintaining laminar flow, and allowing the pulmonary veins and coronary sinus to decompress may all be factors that allow cardiac function to improve and arrhythmias to regress. However, atrial tachyarrhythmias often recur after this procedure [5, 6]. With the addition of a limited right atrial maze (LRAM) procedure, these patients may have long-lasting relief from their atrial tachyarrhythmias [10–12]. Atrial pacemakers prevent bradycardias, which are caused by the commonly associated sick sinus syndrome. They also allow the use of antiarrhythmic agents that can worsen bradycardia (especially sotalol) if some tachycardias persist postoperatively. We originally reported our experience of this technique in 1999, which helped 2 patients circumvent this problem [13]. The surgical method has progressed since the initial procedures were performed, and we present our results and our current operative technique.

	Material and methods

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We retrospectively reviewed the patient charts and operation notes of the 6 patients who have undergone conversion to an extracardiac Fontan conduit, LRAM, and epicardial pacemaker placement at Green Lane Hospital since 1997. Two patients previously reported (patients 1 and 5) are included in the analysis [13]. The cohort includes 5 women and 1 man aged 14 to 34 years (mean, 22.8 years). All are receiving continued cardiologic follow-up and have been seen and evaluated recently.

Details of diagnoses and patient data, and preoperative and postoperative medication are summarized in Table 1. . Each patient presented with increased fatigue, decreased exercise tolerance, and the development of atrial tachyarrhythmias. In general the tachyarrhythmias were poorly tolerated and were not responsive to medical therapy. A considerable number of side effects to the medications had been encountered.

Presurgical evaluation
Each patient had a detailed cardiovascular assessment including echocardiography, cardiac catheterization (Table 2), and Holter recordings, and patients 5 and 6 had an invasive electrophysiologic study. Nonfluoroscopic electrophysiologic mapping facilities were not available, but in the 2 patients undergoing invasive study, multiple IARTs were induced. In both patients, one of the tachycardias had a critical isthmus at the inferior vena cava–right atrial junction just as in typical atrial flutter. No attempt at ablation was made, but the approximate sites of reentry points, scars, and electrically inactive tissue were recorded and related to the surgeons before and during the operation. Electrophysiologic study was planned but canceled in 1 patient (number 2) because of fear of causing displacement of multiple large right atrial thrombi seen on transesophageal echocardiography.

Cardiac catheterization was performed in all but patient 1, excluding elevated pulmonary vascular resistance and pulmonary arterial abnormalities (Table 2). Transesophageal echocardiography was helpful in revealing atrial thrombi in 2 patients and the precise nature of the subaortic obstruction caused by a restrictive ventricular septal defect in patient 3.

Surgical technique
Bicaval cannulation with moderately hypothermic cardiopulmonary bypass was undertaken in all patients. Several patients had part of the procedure performed under profound hypothermia with circulatory arrest, including 2 patients with bilateral superior vena cavae requiring bidirectional Glenn procedures as a concurrent operation (Table 1). One patient required resection of subaortic stenosis. Antegrade blood cardioplegia was used for myocardial protection at 20-minute intervals.

The technique of incision and cryolesion placement in the LRAM has evolved during the span of the six cases and was adapted to their variable morphology and previous surgical scars. The basic principles in performing the LRAM are described below, and the lesions are outlined in Figure 1. It is important to note that not all of the patients had the complete array of incisions and cryoablations listed below.

View larger version (53K): [in this window] [in a new window]   Fig 1. Right atrial diagram of surgical incisions and cryoablation patterns for the limited right atrial maze procedure. Cross-hatched areas indicate cryolesions, dashed lines are surgical incisions, and lines with slashes are suture lines. The procedure is performed in the following steps: A, excise right atrial appendage (RAA), open the atrium laterally and excise excess tissue, connect incision to superior vena cava (SVC) with cryolesion; B, cryolesion across isthmus; C, incise from initial incision to tricuspid valve and finish with cryolesion; and D, open atrial septal defect (ASD), unroof coronary sinus (CS), or cryolesion between the two. (IVC = inferior vena cava.)

Lesion A
An incision is placed in the anterolateral right atrium for initial entry to the right atrium. Excision of tissue each side of this is used to reduce the right atrial size along with excision of the right atrial appendage. This incision runs to the IVC with cryolesions performed laterally to the superior vena cava avoiding the sinoatrial node.

Lesion B
Cryolesions are placed across the isthmus between the IVC and tricuspid annulus by means of the posterior aspect of the coronary sinus. It is important to note that the tricuspid valve may be nothing more than a simple depression in patients with tricuspid atresia. This lesion must be kept inferior to avoid the atrioventricular node.

Lesion C
A separate incision is placed at a right angle to lesion B, running anteriorly toward the atrioventricular groove and completed with cryoablations up to the tricuspid annulus to avoid injuring the right coronary artery.

Lesion D
The old atrial septal defect patch and associated scar tissue is removed to recreate the atrial septal defect and remove potentially arrhythmogenic foci. The atrial septal defect is then connected to coronary sinus or lesion B by a low incision or cryolesion.

Atrial and ventricular epicardial pacing leads are placed and attached to a generator usually placed in a subcutaneous abdominal pocket. Pacing modes are dependent on atrioventricular node conduction, but in all patients the atrial rate is not allowed to fall below 80 beats per minute. The extracardiac Fontan conduit is performed by using a 22-mm or 24-mm polytetrafluoroethylene graft and anastomosing it to the IVC (end to end) and right pulmonary artery (end to side).

Patients are anticoagulated with warfarin postoperatively once surgical hemostasis is assured. During the postoperative period, routine antiarrhythmic drugs, other than digoxin, were not administered.

	Results

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The size of the polytetrafluoroethylene conduit was either 22 (n = 1) or 24 mm (n = 5). The LRAM procedure was performed with specific incisions, and cryoablative lesions were placed as described above. A right atrial reduction was performed in all patients. None of the patients had a fenestrated Fontan conduit. Concurrent operations included two bilateral bidirectional Glenn procedures and one resection of subaortic stenosis. Cardiopulmonary bypass time averaged 205 ± 37 minutes (range, 176–257 minutes) with an aortic cross-clamp time of 128 ± 32 minutes (range, 79–165 minutes). At the time of conversion 2 patients had circulation arrest times of 38 and 33 minutes to perform their bilateral bidirectional Glenn anastomoses.

One patient had a pacemaker placed 15 months before her Fontan conversion whereas the remainder (n = 5) had them placed at or soon after their operation (1 patient had a generator placed 2 weeks afterward). The pacemaker modes were AAIR (n = 4), AAI (n = 1), or DDDR (n = 1).

The average hospital stay was 16.7 days (range, 7–38 days), and all the patients survived. Patients were in the intensive care unit for an average of 3 days (range, 1–7 days). Follow-up is a mean of 28.5 months (range, 11–46 months).

There were two postoperative returns to the operating room. One patient had an exploration for bleeding. Another patient had an epicardial lead replaced approximately 3 weeks after her operation owing to increasing impedance thought to be caused by early scarring at the point of lead contact. Another patient who had a concurrent subaortic stenosis resection developed postoperative complete heart block, which was anticipated because of the anatomic location of the obstruction. This patient, mentioned earlier with L-transposition of the great arteries, already had preoperative intermittent heart block and is the only patient with dual chamber pacing.

All patients have had a significant improvement in their energy level and well-being. New York Heart Association functional classification has improved in all 6 patients, with 4 patients having no reported physical limitations after the operation (Table 1).

Early in the postoperative course 5 patients had some sort of transient atrial tachyarrhythmia, which responded to antiarrhythmic medications. All were discharged in sinus or atrially paced rhythm. After hospital discharge 3 patients have had no recurrence of atrial arrhythmias. Three patients had recurrence of atrial tachycardias after hospital discharge, which responded to sotalol. Sotalol converted 1 patient to sinus rhythm from atrial fibrillation 2 years after her operation and was subsequently discontinued after a few months. Two patients currently take sotalol regularly, although one of these patients is only 3 months out from her operation and we are optimistic that this medication may be stopped in the near future. The other patient has paroxysmal IART when not taking sotalol.

	Comment

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Common problems in patients undergoing the Fontan operation that occur years after their initial operation include thrombi, bradycardias, tachyarrhythmias, and poor hemodynamics as a result of capacitance effects of the giant right atrium. The onset of atrial tachyarrhythmias may precipitate the development of right atrial thrombus, which can be fatal if left undetected [3]. It is important to bring these arrhythmias under control when first noted. Transesophageal echocardiography has been known to diagnose right atrial thrombi in patients who have had a negative transthoracic echocardiographic study [14], and this was true in two of our cases.

Extracardiac polytetrafluoroethylene Fontan conduit conversion to ameliorate a failing Fontan has been performed by various institutions [15], and seems to be a logical answer to many of the problems encountered in this cohort. The extracardiac conduit improves hemodynamics by maintaining laminar flow with less of a capacitance effect, especially when the pulmonary artery anastomosis is placed away from the bidirectional Glenn superior vena caval inflow [16]. Right atrial reduction and appendage excision means that there are fewer places for thrombi to develop, and no new complex scars are placed in the heart to encourage abnormal arrhythmogenic foci. Nevertheless, this procedure alone frequently fails to bring atrial tachyarrhythmias under control, because it does not eliminate all of their potential causes.

Gandhi and associates [17] have reported that in the canine model, arrhythmias can arise from right atrial suture lines without any other condition present. The damaged tissue around the scar forms a zone of slow conduction, which allows a reentry circuit to stabilize within the atrium, whether or not the atrium is stretched or otherwise damaged. In some cases, the critical point of reentry is tissue that has been damaged through hypoxia or stretch rather than an incision. There are multiple suture lines and areas of myocardial scarring in patients undergoing the Fontan operation. Improving hemodynamics alone will not eliminate these. Our experience and that of others now suggests that when an intracardiac Fontan is taken down, there is a strong argument to routinely perform an LRAM, whether or not there is a history of preoperative atrial tachyarrhythmia [11].

The LRAM procedure prevents IARTs by eliminating potential circuits. Each scar is joined to another or to electrically dead tissue such as the IVC, such that a circuit cannot develop around the scar. A particularly important cryoablation series is between the tricuspid valve, coronary sinus, and IVC, inasmuch as this tissue can itself form a zone of slow conduction and allow a reentrant circuit to be established. The isthmus between the IVC and the tricuspid valve forms the zone of slow conduction for common atrial flutter seen in the unoperated heart. This was proven to be a critical zone for one of the tachycardias in the 2 patients undergoing invasive electrophysiologic study in this series.

The fact that one of our patients can still have IART (without medication) suggests that a potential zone of slow conduction was inadequately treated, or that it arises from the left atrium. We do not know whether the cryoablation lesions always result in complete electrical block. A further refinement in operative technique would be to assess the intraoperative success of the surgical lesions preventing conduction. This is commonly performed after catheter radiofrequency ablation, using computerized nonfluoroscopic electrophysiologic mapping systems.

Silka and associates [18] noted that preventing episodes of bradycardia by pacing significantly decreased supraventricular and ventricular tachyarrhythmias. Sinoatrial node dysfunction is not uncommon after cavopulmonary shunts [19], and atrial tachyarrhythmias do sometimes recur even after the LRAM modification. Preventing bradycardia may thus be an important adjunct to therapy in these patients, supporting the routine placement of atrial pacemakers after the LRAM [18]. The presence of the pacemaker also allows therapeutic doses of sotalol to be administered safely postoperatively if an antiarrhythmic medication is needed. We routinely program the base rate at 90 to 100 beats per minute for the first few postoperative days and reduce it to 70 to 80 beats per minute thereafter.

Despite the routine placement of an atrial pacemaker, our surgical technique attempts to preserve sinus node function, and on postoperative Holter examination all of our patients spend a proportion of time in sinus rhythm rather than just being atrially paced. This at least preserves pacemaker battery life and in some instances allows more physiologic heart rate response with exercise, even though exercise rate responsive atrial pacing is now quite sophisticated.

Even if arrhythmias were not completely eradicated postoperatively, they have become much easier to control. Cox and coworkers [20] have found that with the standard maze procedure for atrial fibrillation, arrhythmias are common (40% to 50%) within the first 3 months with the incidence lowering with time. This has certainly been the case with our cohort as 5 of the 6 patients have had some form of early postoperative atrial arrhythmia. In light of this experience it would now seem reasonable to give the patient a few months of prophylactic sotalol or amiodarone postoperatively. Although 1 or possibly 2 (the second still in the early postoperative period) patients still need sotalol, we contend that all of the patients are a success because the residual arrhythmia is easily controlled medically, and all are vastly improved symptomatically.

With respect to anticoagulation, our patients continue to take postoperative warfarin because of their prosthetic conduits and the known thrombogenic characteristics of Fontan physiology [21, 22].

In the failing Fontan with atrial fibrillation or IART, conversion to an extracardiac conduit with LRAM and pacemaker placement improves patient well-being and brings atrial tachyarrhythmias under control. We await long-term follow-up but these early results are very promising.

	References

Top Abstract Introduction Material and methods Results Comment References

 

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