Early survival after the Fontan operation has improved significantly after staged interventional strategies that have been instrumental in preparing favorable ventricular compliance, pulmonary artery resistance, and systemic venous connections for a lifetime of Fontan circulation [1–5]. High venous pressures are required to drive pulmonary perfusion and cardiac output. While early functional status has been satisfactory in the majority of cases, significant complications occur with age accrual owing to a host of intervening conditions. There is a natural progression of pulmonary artery pressure during the human lifetime that is easily tolerated in two‐ventricle physiology, but is deleterious for single‐ventricle physiology (Fontan circulation). Anatomic/physiologic problems that can occur include obstructions in the venous‐to‐pulmonary artery pathway, pulmonary venous return or ventricular outflow, atrioventricular valve dysfunction (regurgitation), pulmonary arteriovenous malformations, venous thrombosis, and the development of atrial arrhythmias, among others [1, 3, 4]. These complications have been demonstrated in older patients with largely atriopulmonary connections owing to time accrual and unfavorable flow characteristics. It is not clear whether newer reconstructions such as the lateral tunnel or extracardiac connections will show improvement over the long term. These conditions can lead to reduced functional status resulting from decreased cardiac output, cyanosis, protein‐losing enteropathy (PLE), liver/renal dysfunction, plastic bronchitis, cerebral emboli (fenestrated Fontan), and death [1, 3, 4].

Various surgical and catheter interventions aimed at reducing morbidity and mortality have been attempted to treat these identifiable abnormalities. Strategies have included catheter ablation of atrial arrhythmias and antitachycardia pacing, atrioventricular valve replacement/repair [6–9], Fontan conversion to extracardiac conduits with arrhythmia surgery and pacemaker strategies [10–12], hepatic venous flow diversion techniques to treat acquired arteriovenous pulmonary fistulas [13–15], cardiac transplantation [16], and combined cardiac/liver transplantation. Recent advances with ventricular devices have been documented without widespread application [17–19]. The purpose of this chapter is to review the accumulated experience with Fontan conversion and discuss the lessons learned over 20 years.

Evolution of Chronic Fontan Physiology

The modified atriopulmonary anastomosis was designed for tricuspid atresia with a systemic left ventricle, and subsequently more extensive atrial baffling techniques evolved for more complex anatomic substrates, including heterotaxy syndrome and left‐sided valve atresia with a systemic right ventricle. The characteristics of atriopulmonary connections included atrial dispensability and venous compliance, which over time resulted in marked atrial dilatation. The physiologic sequelae of this atriomegaly included increased hepatic pressure, distortion of the atriopulmonary connection resulting in venous obstruction, and compression of pulmonary venous return. Atrial hypertrophy resulted in fibrosis and electrical “scar” or dispersion of electrical conductivity, allowing the development of atrial reentrant arrhythmias. The atrial arrhythmias in turn resulted in increased atrial pressures, loss of atrioventricular synchrony, and decreased cardiac output, with resultant venous stasis and thrombosis. This delicate interplay between hemodynamic and electrical function, initially described by Wong and associates [20] as “electromechanical interaction” in patients with tetralogy of Fallot, is nowhere more important than in the passive venous circulation of Fontan patients. Unlike tetralogy of Fallot, the relatively high mortality associated with initial Fontan operations resulted in reluctance to attempt surgical revisions of the Fontan circulation.

Early Catheter Ablation Techniques

The introduction of catheter ablation techniques for arrhythmia therapy coincided with the first generation of adolescent and young adult survivors of early atriopulmonary Fontan repairs. Advances with transcatheter techniques improved the arrhythmia burden, but catheter ablation for atrial arrhythmias in the Fontan substrate is associated with high arrhythmia recurrence and allows for progressive hemodynamic decline. The implantation of transvenous or transmural atrial pacemaker leads to deliver antitachycardia therapy was not, surprisingly enough, associated with increased risk of major venous thrombosis.

Introduction of Fontan Revision

The introduction of Fontan revision for hemodynamic indications led to the speculation that repair of pathway obstruction, valve dysfunction, and atriomegaly could help treat arrhythmias, the idea being that improved hemodynamics would result in arrhythmia ablation. For patients with tetralogy of Fallot, a surgical strategy of improving hemodynamics was associated with reduction in ventricular arrhythmias [6, 8, 21–23]. However, atrial arrhythmias were not eliminated by Fontan revision, and early postoperative atrial arrhythmias severely compromised cardiac output. Surgical mortality for Fontan revision without arrhythmia surgery was associated with a higher mortality [6, 8]. A retrospective comparison of patients who underwent Fontan revision without arrhythmia surgery and patients who underwent Fontan conversion to extracardiac connections, arrhythmia surgery, and pacemaker implantation [24] demonstrated improved outcomes with the inclusion of arrhythmia surgery. While intuitively obvious, this study showed that repair of both arrhythmia and anatomic/physiologic problems was necessary for effective hemodynamic treatment and arrhythmia reduction.

Introduction of Fontan Conversion

At this time, we introduced a nomenclature distinction between Fontan revision and Fontan conversion. Fontan revision was used to identify patients undergoing Fontan reoperations and address hemodynamic problems without including arrhythmia surgery. We decided to term our contribution Fontan conversion to account for the three major parts of the new Fontan reoperation, namely revision of atriopulmonary to extracardiac Fontan connections, atrial arrhythmia surgery, and pacemaker implantation [25–27]. While it is important to stress that the majority of patients had conversion from atriopulmonary to extracardiac connections, a significant number of patients had conversion of lateral tunnel to extracardiac connections. In our experience, atrial pacemaker therapy provides atrioventricular synchrony and reduces premature atrial contractions that can trigger atrial reentry tachycardia. This is particularly important in the perioperative time period, when any instability is to be avoided. In addition, some patients who have had Fontan reoperations with arrhythmia surgery and no pacemaker may need pacemaker implantation shortly after the operation that will require resternotomy. Atrial and ventricular lead implantation at the time of Fontan conversion avoids the need for late reoperation, and allows for rate responsiveness and atrial antitachycardia pacing algorithms should they become necessary.

Fontan Conversion with Associated Procedures

In time, associated interventions were added to Fontan conversion. This innovative approach resulted in a series of manuscripts that documented the progression of atrial resection and better defined atrial cryoablation lesions that would be necessary to effectively treat atrial reentry tachycardia, focal tachycardia, and atrial fibrillation [9, 11, 26–35]. As this experience matured, patients with higher‐risk factors were treated. Fontan conversion was coupled with valve repair/replacement, aneurysmectomy/aortic reconstruction, extensive pulmonary artery reconstruction, and pulmonary venous pathway resolution without an increase in morbidity or mortality. Careful patient selection criteria were used to avoid extensive surgery in patients with ventricular dysfunction not related to arrhythmias or arrhythmia medications, or patients with important end‐organ dysfunction. The team approach to these patients was not an insignificant factor in determining excellent outcomes. Direct operating room participation by electrophysiologists, two experienced surgeons performing the operation, meticulous surgical technique with hemostasis, increased intraoperative perfusion pressures, conscientious application of cryoablation lesions, and favorable epicardial pacemaker lead placement were determinants of favorable results.

Conduct of Fontan Conversion

Three basic types of existing first‐time anatomic connections undergoing revision are atrial compartmentalization with right atrium to pulmonary artery anastomosis, classic right Glenn operation and an atrium–left pulmonary artery anastomosis, and a total cavopulmonary artery reconstruction.

At the time of Fontan conversion, or any redo congenital heart operation, adhesions from previous operations, dilated right atria, long‐standing abnormal physiology of the atriopulmonary circuit, and right ventricular to pulmonary artery conduit or anterior aorta all contribute to the difficulty of sternal reentry [24]. In rare cases, the femoral vessels can be dissected before the resternotomy for rapid cannulation and institution of cardiopulmonary bypass when there is high risk for cavitary entry. Early identification of the aorta and atrium is achieved so that rapid institution of cardiopulmonary bypass can be accomplished in the event of unwanted mishaps during dissection. To avoid injury to the phrenic nerves, the dissection plane should remain medial to the pericardium and entry into the cardiac chambers is to be avoided, to reduce the risk of paradoxic air embolus occurring through residual intracardiac shunts. Careful preoperative planning and extreme caution during the resternotomy should insure a safe outcome for the patient [36].

Once the sternum is opened, we proceed to aortic and direct vena cava cannulation using right‐angled cannulas inserted high in the superior caval vein and straight cannulas in the inferior caval vein [11]. After the commencement of cardiopulmonary bypass, the inferior caval vein is transected and anastomosed to a 24 mm Gore‐Tex (W.L. Gore, Flagstaff, AZ, USA) tube graft. A vent is placed in the right superior pulmonary vein, the aorta is cross‐clamped, and cold‐blood cardioplegia is delivered. With the heart arrested, an atrial septectomy and resection of the right atrial appendage are performed. Linear cryoablation lesions for the right‐sided maze procedure are placed with a Surgifrost device (CryoCath, Kirkland, Quebec, Canada) applied at −160 °C for 1 minute. The lesions extend from the base of the right atrial appendage to the cut edge of the atrial septal defect, across the crista terminalis from the cut edge of the atrium to the atrial septal defect, and from the transected inferior caval vein to the coronary sinus. In addition, if a tricuspid valvar orifice is present, a lesion is created from the inferior caval vein to the annulus of the tricuspid valve. A lesion is placed to prevent macro reentrant circuits extending from the coronary sinus to the edge of the atrial septal defect. In patients with atrial fibrillation, the Cox‐maze III procedure is performed. The left atrial appendage is excised and an encircling pulmonary venous isolation is performed using cryoablation and/or incisional techniques. A cryoablation lesion is placed from the cut portion of the excised left atrial appendage to the confluence of the pulmonary veins. An additional lesion is placed from the encircling atriotomy lesion to the annulus of the mitral valve, directing it at the inferomedial scallop. A circular lesion, created for 2 minutes, is placed on the epicardial surface of the coronary sinus directly opposite the endocardial lesion involving the mitral valve. At the conclusion of the Cox‐maze III procedure, the right atrium is closed with running polypropylene, the heart de‐aired, and the cross‐clamp removed. This sequence can be altered in the event that other left‐sided lesions require surgical repair.

For patients with atriopulmonary anastomoses, a standard total cavopulmonary artery connection is accomplished using a lateral tunnel or an extracardiac technique [37–40]. Pulmonary artery reconstruction, when necessary, is performed at that time. In patients with a prior right Glenn procedure and an atrium–left pulmonary artery anastomosis, more creative pulmonary artery reconstructions are required. Left‐sided (systemic circulation) procedures are performed under cardioplegic arrest; they include prosthetic atrial patch resection, valvar reconstructions, and completion of left atrial cryoablative lesions when needed. After atriorrhaphy and removal of the aortic cross‐clamp, total cavopulmonary connection is then completed, using a polytetrafluoroethylene conduit for the inferior caval vein connection to the pulmonary artery. Earlier in our experience, transmural atrial wires were implanted using the technique reported by Hoyer and associates [41, 42]. Presently the epicardial approach is used for the atrial pacemaker leads. Initially, an atrial antitachycardia pacemaker was used. With subsequent use of the more extensive modified right atrial maze procedure, tachycardia recurrence is rare, and an atrial rate‐responsive pacemaker is preferred. Separation from cardiopulmonary bypass is followed by transesophageal echocardiographic assessment.

Pacemaker Implantation

Achievement of acceptable pacing thresholds in the atrium may be challenging because of the extensive resection, reconstruction, and ablative lesions [11, 29]. Typically, epicardial bipolar steroid eluting leads are placed on the right atrium near the atrioventricular groove anterior to the atriotomy. The technique of lead implantation is illustrated in Figures 28.1 and 28.2 [43]. It is important to find a portion of atrium relatively free of adhesions. In difficult situations, these leads can be placed on the dome of the left atrium or at the base of the left atrial appendage. Device selection has evolved over the years to the current use of epicardial dual‐chamber antitachycardia pacing systems. Ventricular leads are placed on the ventricular diaphragmatic surface or the anterior ventricular wall, according to optimal threshold measurements. Placement of ventricular leads will minimize the effects of atrial lead far‐field R wave sensing, and will provide the capability of dual‐chamber pacing should atrioventricular block develop with time. For the ventricular lead we have tried to use the steroid eluting bipolar epicardial leads, but when there is a large amount of scar tissue or fat on the ventricle, we have used two screw‐in leads attached in a “Y” configuration for bipolar sensing. Multisite ventricular pacing has been used in the setting of marked QRS prolongation to achieve ventricular synchrony and improved cardiac function [26, 29]. In the rare setting of prior cardiac arrest because of ventricular arrhythmia, implantation of epicardial defibrillator patches or subcutaneous coils has been performed.

Anatomic and Electrophysiologic Variations of Fontan Conversion

Takedown of Right Atrial–Right Ventricular Bjork Modification

In the setting of surgical conversion of a Bjork–Fontan modification to a total cavopulmonary artery connection, the dilemma arises of what to do with the right ventricle [29]. Disconnecting the main pulmonary artery and leaving the right ventricle, however small, without an egress of blood flow has the potential problems of right ventricular dilatation and leftward interventricular septal deviation caused by accumulation of thebesian blood flow. We have performed Fontan conversion with arrhythmia surgery on 14 patients (14/109; 12.8%) with tricuspid atresia (n = 13) and unbalanced atrioventricular canal (n = 1) who had a previous right atrial–right ventricular Bjork–Fontan connection with (Figure 28.3; n = 2) and without (Figure 28.4; n = 12) an interposition bioprosthetic valve [29]. The distinct surgical considerations in this setting are (i) takedown of the Bjork–Fontan anastomosis, and (ii) management of the right ventricle. Most of the patients without the bioprosthetic valve interposition graft had a communication that was formed by a posterior reversed right atrial flap and an anterior prosthetic patch that formed the right atrial–right ventricular connection. Takedown of these connections involves a careful and extensive dissection of the right atrioventricular groove to facilitate right atrial appendage amputation, right atrial wall reduction, epicardial pacemaker lead placement, and adequate right ventricular wall patch closure. The dissection of the right atrioventricular groove is commenced near the ascending aorta where an undissected plane is readily achieved (Figures 28.5 and 28.6). The dissection is continued as far as possible toward the posteroseptal area as long as the dissection plane safely allows (Figure 28.7). Care must be taken not to enter the right coronary artery, which occurred in two patients in this series (1.8%). Because the injury was caused by electrocautery dissection in one, cardioplegic arrest and Gore‐Tex patch arterioplasty were performed without sequelae. The other injury was caused by sharp dissection and was repaired with cardioplegic arrest and interrupted suture technique without sequelae. Our approach to the remaining right ventricle is to preserve the right ventricular to main pulmonary artery connection to allow easy egress of blood into the pulmonary arteries (Figures 28.8 and 28.9). We have found that the developed right ventricular pressure is low under these circumstances because of decreased right ventricular preload, and does not affect the nonpulsatile blood flow established by the extracardiac total cavopulmonary connection (TCPC). Figure 28.10 shows a right ventricular patch and right atrial closure in association with the extracardiac TCPC. The extensive atrioventricular groove dissection has aided the right atrial wall reduction and allowed for unscarred atrial wall for optimal epicardial pacemaker lead placement.

Takedown of Atrioventricular Valve Isolation Patch for Right‐Sided Maze Procedure

In the developing era of Fontan procedures for complex diagnoses such as double‐inlet ventricles, criss‐cross hearts, and straddling atrioventricular valves, the smaller right‐sided atrioventricular valve was oftentimes isolated with a patch when the left‐sided atrioventricular valve was large enough and functional [11, 29]. Patching of this valve accomplished separation of the circulations by performing an atriopulmonary connection together with an atrial septal defect closure. The important anatomic and electrophysiologic considerations relate to the distance of the patch to the annulus and the partitioning of the coronary sinus. Oftentimes, the isolation was performed to leave the coronary sinus on the ventricular side to avoid complete heart block (Figure 28.11), which means that the right‐sided arrhythmia circuit might be partitioned to the pulmonary venous atrium. Under these circumstances, the right‐sided maze cannot be safely performed because the traditional landmarks, namely the coronary sinus and the tricuspid valve, are not exposed. Therefore, the patch must be removed to accomplish the cryoablation procedure. Figure 28.12 shows the techniques of tricuspid valve and atrial septal patch removal. Figure 28.13 depicts the dissection plane associated with tricuspid valve patch removal. The cryoablation lesions can now be performed with adequate landmark identification, which will insure transmural cryoablation (Figure 28.14). This part of the operation would have been in question if the cryoablation lesions were made on top of the prosthetic patch material. If the tricuspid valve is competent by bulb syringe testing, one can elect to allow the valve to function normally. If there is any question of valve competency or if there was antecedent valve dysfunction or injury, the valve can be isolated again with a Gore‐Tex patch anchored to the leaflets of the tricuspid valve near the annulus (Figure 28.15).

Right Atrial Cannulation in the Presence of a Right Atrial Clot

Approximately 5% of patients undergoing atriopulmonary to total cavopulmonary artery Fontan conversion can have right atrial clots, sometimes as a consequence of multiple transcatheter radiofrequency ablation attempts [44]. Fontan conversion in the setting of right atrial thrombus is fraught with hazards because of compromised cardiac output during sternotomy and dissection, the risk of clot dislodgment with cannulation, and the potential for venous catheter occlusion [29]. Preoperative evaluation using magnetic resonance imaging or computed tomography to assess clot size and location can be complemented by epicardial echocardiography to guide safe atrial cannulation. Oftentimes, it is preferable to perform aorto–right atrial bypass to establish adequate cardiopulmonary bypass and improved perfusion while the dissection is completed, which can lead to bicaval cannulation. During this time it is important to place the single atrial catheter away from the clot, as shown in Figure 28.16.

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