INTERVENTIONAL PEDIATRIC CARDIOLOGY

Transcatheter Closure of Atypical Right-to-Left Shunts after Fontan Surgery

Mark H. Hoyer, MD
Mark H. Hoyer, MD
Current treatment strategies for patients with single ventricle physiology are aimed toward Fontan operations. Often, the Fontan completion is performed with an intentional fenestration to allow systemic venous decompression at the expense of mild cyanosis. Studies have shown the augmented cardiac output from right-to-left flow through the fenestration to more than offset the consequent cyanosis and provide greater peripheral systemic oxygen delivery.1,2 However, excessive cyanosis from a large right-to-left shunt generally overrides this augmentation in cardiac output and results in significant exercise intolerance. At our institution, conventional treatment for patients with Fontan fenestrations includes low-level anticoagulation with coumadin, which is discontinued if the fenestration closes spontaneously or is too small to be significant. Tiny unintentional baffle leaks are common and are usually located at the superior end of the anastomosis of polytetrafluoroethylene (PTFE) to the right atrial wall where pectinate muscles result in an irregular sewing surface.3–5 The negligible right-to-left shunts through these leaks do not create noticeable cyanosis. Conversely, large baffle leaks are uncommon and may result from either torn sutures or dehiscence at the anastomotic site. Thesebaffle leaks may be detected by transthoracic echocardiography or discovered during cardiac catheterization when the degree of cyanosis cannot be adequately explained by the fenestration alone. Extracardiac Fontan conduits can be fenestrated as well, either by direct window connection or by interposing a tube graft between the conduit and atrium. Transcatheter closure of Fontan fenestrations is straightforward. However, closure of large unintended baffle leaks is challenging. While information already exists regarding the benefits and timing of Fontan fenestration closure,6 the following cases emphasize the importance of unintended baffle leaks and demonstrate the feasibility of closing various atypical right-to-left shunts after Fontan surgery. Methods. Between April 2001 and March 2002, 4 patients underwent closure of atypical shunts. Devices were implanted before FDA approval, thus informed consent was obtained according to Institutional Review Board guidelines. All catheterizations were performed with general anesthesia, and patients received cefazolin and heparin during the procedure and 3 doses of cefazolin at 8-hour intervals afterward. A femoral venous approach and transesophageal echocardiographic (TEE) guidance were utilized in all but the patient with an atypical tube fenestration in whom the approach was from the right internal jugular vein. Three patients had hypoplastic left heart variants, while the other had tricuspid atresia. Specific diagnoses were: aortic atresia (Patient 1); mitral atresia and double outlet right ventricle (Patient 2); tricuspid atresia (Patient 3); and asymmetric atrioventricular septal defect with hypoplastic left ventricle, double outlet right ventricle and asplenia syndrome (Patient 4). All underwent staged operations to culminate in Fontan physiology. The lateral caval tunnel was fenestrated in 3 patients by placing a 2.5–3 mm punch in the PTFE, while 1 patient underwent interposition of a 6 mm PTFE tube graft between the 18 mm GoreTex conduit and the morphologic right atrium (neo-left atrium). Two patients had a large Fontan baffle leak, one had a large residual fistula between the inferior vena cava and coronary sinus, and the other had the atypical tube fenestration. Balloon sizing was performed with either a NuMed (NuMed, Inc., Hopkinton, New York) or AGA (AGA Medical Corp., Golden Valley, Minnesota) sizing catheter in all but Patient 4 to aid in the selection of device size and confirm the absence of residual flow by color Doppler. Test occlusion of the shunts resulted in an increase of systemic venous pressure from baseline ranging from 0–2 mmHg. Results. Table 1 summarizes the data. Patient 1 was treated with captopril, aspirin and coumadin. Transthoracic echocardiography (TTE) showed a surgical fenestration which could not be found by TEE. Instead, a sizable color flow disturbance was noted at the superior end of the baffle. Angiography showed a superior baffle leak adjacent to the right atrial appendage which is part of the neo-left atrium (Figure 1). The echo suggested a lengthy tunnel rather than the mere absence of a wall, and the superior border of the shunt was the roof of the anatomic right atrial appendage within the neo-left atrium. The stretched tunnel diameter was 12 mm. A 16/14 Amplatzer Duct Occluder (AGA Medical) was delivered through a 10 Fr Cook sheath (Cook Inc., Bloomington, Indiana) and deployed with TEE and fluoroscopic guidance to create an elongated device shape without proximal protrusion into the systemic venous channel (Figure 2). At the latest follow-up, there were no symptoms and the only medications being taken are lisinopril and low-dose aspirin. Patient 2 was lost to follow-up for 3 years after Fontan surgery until she presented with easy fatiguability, marked digital clubbing and oxygen saturation of 60% in the office. TTE showed a small surgical fenestration and a moderate-sized Fontan baffle leak at the inferior end of the lateral tunnel. Baseline systemic oxygen saturation during mechanical ventilation rose to 82%. Angiography showed unobstructed flow to the pulmonary artery, a small surgical fenestration, and a large baffle leak just superior to the mouth of the coronary sinus with contrast refluxing back into the coronary sinus (Figure 3A). Test balloon occlusion of the baffle leak increased systemic oxygen saturation to 95%, thus we chose to attempt closure of the baffle leak only. The defect diameter measured 4.0–4.5 mm at rest and 7 mm with balloon stretching. Temporary occlusion with a balloon wedge catheter helped elucidate the window-like nature of this defect (Figure 3B). A 17 mm CardioSEAL® (NMT Medical, Boston, Massachusetts) was delivered through a 10 Fr sheath with TEE guidance, and the fully deployed device assumed its natural shape to allow unobstructed coronary sinus flow into the systemic venous atrium. Outpatient oxygen saturation was 88% five months later. Cardiac catheterization 15 months after closure of the baffle leak allowed placement of a 4 mm Amplatzer Septal Occluder to close the surgical fenestration (Figure 4). At last follow-up, she remains asymptomatic on digoxin and aspirin, and oxygen saturation is 94%. During the Fontan operation in Patient 3, an unusual fistula from inferior vena cava to coronary sinus was closed to allow the coronary sinus to continue drainage to the right atrium. However, oxygen saturations remained 82%, and she coincidentally developed a chronic slow ventricular tachycardia. A TTE showed a dilated inferior vena cava and coronary sinus and persistent right-to-left shunting from an unknown location by microbubble contrast. Selective angiography in the coronary sinus clarified the origin of the fistula to be from the coronary sinus, near its drainage to the systemic venous atrium. Using combined angiographic and echocardiographic images, an endhole catheter was manipulated into the fistulous connection (Figure 5A). During temporary occlusion of the fistula with a balloon wedge catheter, right atrial angiography from the contralateral femoral vein confirmed complete occlusion of the fistula without compromise of coronary venous return, and oxygen saturation rose from a baseline of 82% to 93–94%. After positioning a delivery sheath, vascular occlusion was achieved by delivering a 12/10 Amplatzer Duct Occluder into the proximal end of the fistula. Final angiography showed no residual shunt through the device and unobstructed coronary venous drainage to the systemic venous atrium (Figure 5B). At last follow-up, the rhythm is sinus, oxygen saturation remains 94%, and medications are aspirin, coumadin, furosemide and amiodarone. Finally, the tube interposition graft for “fenestration” in Patient 4 presented the most straightforward approach. As opposed to the other cases, this was the intended source of right-to-left shunting and resulted in persistent saturations of 76–82%. Despite Fontan completion, this child required coumadin, aspirin, furosemide, captopril and amoxicillin, the latter for asplenia prophylaxis. After diagnostic catheterization 2 months previously, tube length and diameter measurements of 2 cm and 5–6 mm, respectively, allowed the catheter intervention to be planned. The orientation of the PTFE tube favored an internal jugular venous approach, and angiograms demonstrated the tube graft (Figure 6A). After positioning a delivery sheath, a 6/4 Amplatzer Duct Occluder was deployed, allowing the aortic retention disk to be elongated by deformation within the graft. Repeat angiography showed no residual shunt (Figure 6B), and oxygenation improved, but did not completely normalize. Symptoms of easy fatiguability have disappeared, coumadin and furosemide have been discontinued and the oxygen saturation is 92%. In summary, all patients have had decreased symptoms of fatiguability (3 are now asymptomatic), 3 are on fewer medications after closure procedures and all had oxygen saturation increases ranging from 12–34%. Moreover, all devices have remained in stable position without TTE evidence of residual flow or compromise of surrounding cardiac structures. Discussion. Each of these cases represents an atypical right-to-left atrial level shunt following fenestrated Fontan operation. The tube fenestration in Case 4, an unusual method of decompressing the systemic venous atrium, was the only intended surgical shunt, allowing a planned approach. The other cases were unclear until detailed exploration was undertaken at catheterization. The “hunt and search” approach to finding and characterizing these shunts relied heavily on transesophageal echocardiography in conjunction with fluoroscopy and angiography. The different scenarios made it imperative to select a device best suited to each situation, thereby occluding the target area without affecting surrounding cardiac structures or blood drainage patterns. The morphology and location of the defect in Case 1 dictated selection of an Amplatzer Duct Occluder because of the channel length between systemic and pulmonary venous atria. In contrast, Case 2 was a window defect. We speculate that either the surgical anastomosis of the PTFE baffle to the lower atrium dehisced or a suture tore spontaneously in the postoperative period to create such a large right-to-left shunt. Angiography during temporary balloon occlusion provided better understanding of this defect, which, in turn, allowed us to select the proper size and type of device. A longer vascular plug like the Amplatzer Duct Occluder may have extended too far proximally and obstructed coronary venous drainage. Instead, a CardioSEAL provided a better match for the window-like defect. Our surgeons typically leave the coronary sinus to drain into the pulmonary venous atrium following an intracardiac lateral caval tunnel Fontan. Interestingly, after device closure of the defect in Case 2, the coronary sinus now drains to the systemic venous atrium. Finally, it is worth noting that had the recently marketed Amplatzer Vascular Plug (AGA Medical) been available, it would have been considered for Patients 3 and 4 and possibly Patient 1. Closure of residual right to left interatrial communications after Fontan surgery has been reported previously.3–5 The most common defect is at the superior end of the baffle where the intracardiac tunnel is sewn to the pectinate muscles of the right atrium. Other defects include long, tortuous channels arising from the right atrial wall with drainage to the pulmonary venous atrium through a capillary network, as well as leaks of the suture line between the patch material and the right atrial free wall. In most cases, coils have been used to close the residual leaks. In another recent report, multiple leaks along the length of the intracardiac tunnel were closed by placing a covered stent within the tunnel, thereby eliminating blood flow to these areas of leak.7 These cases demonstrate the variety of vascular communications that can present to the interventional pediatric cardiologist after Fontan operations. Details of the surgery are vital to understanding the mechanism of the abnormality. With the help of careful catheter exploration, along with the aid of TEE in most instances, the appropriate type of device and size can be chosen that is best suited for each individual. The examples described here further underscore the need for a wide variety of types of devices to be available to the interventional cardiologist.
References
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