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Eur J Cardiothorac Surg 2000;18:690-695
© 2000 Elsevier Science NL
a Department of Cardiovascular and Thoracic Surgery, German Heart Institute (Deutsches Herzzentrum Berlin), Berlin, Germany
b Department of Congenital Heart Disease, German Heart Institute (Deutsches Herzzentrum Berlin), Berlin, Germany
Received 24 February 2000; received in revised form 6 September 2000; accepted 25 September 2000.
Corresponding author. Tel.: +49-30-4593-2010; fax: +49-30-4593-110
e-mail: alexi{at}dhzb.de
| Abstract |
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Key Words: Extracardiac Fontan operation Inferior vena cava
| 1. Introduction |
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Lack of growth potential and thrombogenicity of the conduit are the major drawbacks and main points of criticism of the ECFO [6]. In the literature there are no data on the optimal size of the conduit in accordance with the patients anthropometric data, diameter of the inferior vena cava (IVC) and distance between the cardiac segment of the IVC and the lower surface of the right pulmonary artery (IVCRPA), where the conduit is usually implanted during ECFO.
Conduit performance seems to be an important issue of the ECFO. Therefore, the purpose of this study was to find out whether optimal dimensions of the conduit could be established before ECFO.
| 2. Patients and methods |
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To control conduit patency and thrombosis, all of the patients underwent follow-up echocardiographic control angiography 130 months (median 8 months) after surgery and eight patients also underwent magnetic resonance imaging (MRI). In all cases the smallest diameter of conduit and conduit proximal and distal anastomoses were measured.
In 50 other non Fontan patients aged between the first day of life and 77 years (median 13 years), body weight from 2.4 to 118 kg (median 43.5 kg) and body surface area between 0.18 and 2.19 m2 (median 1.33 m2) with congenital and coronary heart disease without pulmonary artery hypoplasia, the distance between the cardiac segment of the IVC, just above the diaphragm and the undersurface of the right pulmonary artery, was measured after median sternotomy (31 patients) and during cardiac catheterization (19 patients).
No postoperative anticoagulation treatment except aspirin was used in the studied patients.
2.1. Statistical analysis
Statistical analysis was performed using the linear regression and Spearmans rank correlation using SPSS for Windows 8.0. The difference was considered statistically significant when the P-value was
0.05.
| 3. Results |
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3.4. Conduit thrombosis
We observed two cases of partial conduit thrombosis: one in a 3-year-old child with Ebstein anomaly, who underwent closure of the tricuspid valve as a newborn, together with an atrioseptectomy and central aorta-pulmonary shunt. She underwent ECFO at 3 years of age with a 20 mm conduit, which retrospectively was markedly oversized (2.0 times greater than the actual IVC diameter, Fig. 4A) . Several months later she developed congestive heart failure and protein-losing enteropathy. She underwent surgery at 4 years of age because of partial thrombosis of the conduit detected by angiography and MRI. Conduit replacement with a 16 mm aortic homograft was performed. Intraoperatively partial thrombosis of the conduit was found (Fig. 5)
. She is now free of symptoms. Another case of conduit partial thrombosis was observed in a 27-year-old patient with an interrupted inferior vena cava and an azygous continuation, who underwent surgery early in our series of ECFO, in whom only a short segment of the IVC, where the hepatic veins drained, was connected with a 24 mm GoreTex® tube to the right pulmonary artery (conduit to IVC ratio was 1.9), and the main Fontan pathway was the left-sided azygous vein. Postoperatively the patient received no anticoagulation treatment except aspirin, but when control cardiac angiography and MRI revealed partial conduit thrombosis he was placed on an anticoagulation regimen with warfarin to target the International Normalized Ratio (INR) of 23.
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| 4. Discussion |
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The normal adult IVC expiratory mean diameter is 20.4 mm with variations that range from 10 to 36 mm [7,9,1317] without a strong correlation with age, sex, height, weight or corporeal area. In children, such a correlation exists up to 1415 years of age [8]. However, even a 2-year-old child may have an adult sized IVC or the converse (Fig. 4A,B) [7,8]. The diameter of the IVC is increased in patients with congenital and acquired heart diseases, particularly in the presence of heart failure with increased right atrial pressure [7].
After lateral tunnel Fontan operation, the atriopulmonary anastomosis is often obstructive when compared with some of the caval areas (Fontan area). Therefore, the diameter of GoreTex® tube in children should be equal or somewhat larger than the diameter of the cardiac end of the IVC in order to neutralize the absence of growth potential of the conduit [4]. However, optimal diameter of the conduit has to be determined, despite the fact that ECFO appears to solve the problem of pre-pulmonary stenosis.
The upper limit of critical conduit to IVC diameter ratio is approximately 1.5, without a substantially negative hydrodynamic consequence [5]. In 14 of 20 of our patients the conduit used oversized the IVC diameter by 1.21.5 times (Fig. 3), which is thought to be optimal for hemodynamic performance [5]. Such moderate oversizing can be ignored with respect to the decreased risk of the necessity for conduit replacement in the future but individual variations of the IVC diameter in children and adults prevent the prediction of which size of conduit will become inadequate with a childs growth. Conduits implanted without knowing the actual IVC diameter may result in a discrepancy between conduit to IVC diameter and suboptimal Fontan circulation.
There are two directional growth potential restrictions of the implanted prosthesis: diameter and length. It is doubtless that conduit growth cannot be expected, but it is also doubtful whether implantation of the maximum possible sized conduit is necessary, even in some adults, because of the variable diameter of the IVC.
The optimum conduit length for ECFO also has not yet been established. In a reported large series of ECFO, the lengths of the conduits were not given [2,10,12,18]. There is no data in the anatomical and surgical literature on the IVCRPA distance. Intraoperative measurement of this distance permits the use of a shorter conduit, because the anastomosis of the conduit with the IVC always includes a short rim of the right atrial wall, and thus has longitudinal and transverse growth potential. Thin (usually less than 1000 µm) neointimal ingrowth occurs in the e-PTFE graft [19] and cannot influence conduit performance. Theoretically a conduit that is too short may become the cause of distortion of the right pulmonary artery and compression of the pulmonary veins as the patient grows, but we and others have not observed such complications after ECFO [2,3,10,11,18]. Perhaps the optimal age for ECFO is 24 years, when the mean diameter of the cardiac end of the IVC and RPAIVC distance approaches 6080% of the adult size. The assessment of the actual IVC diameter before ECFO appears to be important so that the implantation of a hemodynamically optimal conduit without significant oversizing can take place. Even conduit of 20 mm diameter can be optimal or oversized in a small child (Fig. 4A,B).
We now prefer implantation of the extracardiac conduits which oversize the diameter of the IVC by no more than 20%. If a patient needs the conduit to be replaced later, this seems to be technically easy and can be performed with partial bypass [20].
Thromboembolic complications are one of the major concerns after all types of Fontan operation, and occur in as many as 20% of cases [2123]. Use of anticoagulation treatment is discussed controversially after Fontan operation [21]. After Fontan operation some groups recommend anticoagulation with Warfarin for at least 12 months, followed by a life-long aspirin regimen [3,11,20,23].
Neointima, which develops in the GoreTex® prosthesis 36 months after experimental replacement of caval veins, is thicker at the anastomosis site and thinner in the middle part (7001000 µm) where sometimes thrombotic focuses develop [19].
In two of six of our patients with considerably oversized conduits, partial thrombosis developed during the first year after surgery. When the left-sided azygous vein bears the main Fontan flow, the conduit size should be adjusted to the size of the IVC entrance into the right atrium to minimize turbulent flow and the risk of thrombosis, which developed in one patient with such an anomaly. Therefore, anticoagulation treatment should be considered in patients with suboptimal Fontan circulation in whom a GoreTex® conduit is implanted.
In conclusion, when considering the inferior vena cava size, ECFO in children may be performed optimally at 24 years of age and at a body weight of 1215 kg when the diameter of the inferior vena cava and the distance between the IVC and the right pulmonary artery approaches 6080% of the adult value and a conduit can be implanted without significant oversizing and negative hemodynamic consequences. Optimization of the conduit dimensions is necessary in relation to the pre- or intraoperatively measured actual IVC diameter and the IVCRPA distance. When an e-PTFE graft conduit is used, considering the absence of true endothelialization of the prosthesis, the use of long-term anticoagulation for at least 6 months after the operation is important to prevent conduit thrombosis, which may develop as early as during first year after surgery, especially in the presence a suboptimal Fontan circulation.
| Acknowledgments |
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| Footnotes |
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| References |
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