Ann Thorac Surg 1997;63:1321-1325
© 1997 The Society of Thoracic Surgeons
Original Article: Cardiovascular
Bidirectional Inferior Vena Cava-Pulmonary Artery Shunt
Loïc Macé, MD,
Patrice Dervanian, MD,
Jean Losay, MD,
Thierry A. Folliguet, MD,
Jean-Michel Grinda, MD,
Sami Abdelmoulah, MD,
Jean-Félix Verrier, MD,
Francesco Santoro, MD,
Jean-Yves Neveux, MD
Department of Cardiovascular and Pediatric Cardiac Surgery, Marie Lannelongue Hospital, Paris-Sud University, Paris, France
Accepted for publication November 26, 1996.
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Abstract
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Background. Bidirectional superior vena cava-pulmonary shunt is widely used as an interim palliation for patients with univentricular hearts. Bidirectional inferior vena cava-pulmonary artery shunt, as an alternative approach of partial Fontan circulation, may offer the advantage of performing the complete Fontan circulation more easily due to the already constructed inferior vena cava lateral tunnel.
Methods. We used bidirectional inferior vena cava-pulmonary artery shunt in 2 patients. Contraindications to a complete Fontan circulation were due to, respectively, a volume-overloaded systemic ventricle and an irregular pulmonary arterial tree.
Results. Postoperative courses were uneventful. There were no significant pleural effusions. Transcutaneous oxygen saturations were 77% and 78%. Pulmonary-to-systemic blood flow ratios were 0.57 and 0.63. A complete Fontan circulation was safely performed 8 and 12 months later, without any "Fontan-related" complications.
Conclusions. Bidirectional inferior vena cava-pulmonary artery shunt can be useful in selected patients with univentricular hearts, although its place in the field of "partial Fontan operations" cannot be determined as yet.
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Introduction
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The concept of "partial Fontan operations" is widely recognized as an interim palliation of univentricular hearts. Irrespective of their own indications and timing for operation, which are still a subject of debate, several procedures correspond to that concept: (1) the bidirectional superior vena cava-pulmonary artery shunt (SCP) [1], (2) the hemi-Fontan procedure [2], (3) the fenestrated Fontan operation [3], and (4) the adjustable Fontan operation [4]. The common interest of such procedures is due to the persistence of a right-to-left shunt, which decreases the pulmonary artery pressure, preserves the cardiac output, and unloads the univentricular heart. As a consequence, partial Fontan operations could be performed at a younger age or safely associated with additional procedures. Conversely, each of these partial Fontan circulations bears its own specificities. Among them, the pulmonary-to-systemic blood flow ratio (Qp/Qs), which reflects the percentage of the venous return flowing through the lungs and the eventual presence of an accessory source of pulmonary blood flow, influences the arterial oxygen saturation [5] and pulmonary artery growth [6]. The ease of performing a complete Fontan circulation has also been taken into account. Partial Fontan operations must be performed with the aim of minimizing the consequences of the second operative step due either to the adverse effects of the cardiopulmonary bypass and aortic cross-clamping or to a redo dissection near the sinus node area [7].
Bidirectional inferior vena cava-pulmonary artery shunt (ICP) may fulfill these latest criteria. This shunt was previously used in a unidirectional form as part of a complete or adjustable Fontan operation [8–10]. An experimental study showed that, when used in a bidirectional fashion, this shunt resulted in improvement in the venous return and cardiac output response curves [11]. The aim of this report is to evaluate the ICP shunt as an interim palliation toward a complete Fontan operation.
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Material and Methods
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Of 57 patients who underwent creation of a partial Fontan circulation from October 1989 to May 1996 in our institution, in 2 children an ICP shunt was performed.
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Patient 1
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A 6-month-old male infant, weighing 6,600 g, was referred to our institution with the diagnosis of double-outlet hypoplastic right ventricle and pulmonary stenosis. He underwent a modified right Blalock-Taussig shunt. Data from catheterization at the age of 3 years 6 months and a weight of 17 kg precluded a biventricular repair. Mean left atrial pressure was 5 mm Hg. Mean pulmonary arterial pressure was 17 mm Hg. The pulmonary artery index was 542 mm2/m2 [12]. Arterial oxygen saturation was 84%. Indication of a partial Fontan circulation was based on the volume-overloaded systemic ventricle as a risk factor for a complete Fontan circulation.
The ICP shunt was performed on March 31, 1993. The operative approach was a midline sternotomy. Mean intraoperative pulmonary arterial and left atrial pressures were 15 mm Hg and 10 mm Hg, respectively. Cardiopulmonary bypass was established between the ascending aorta and both venae cavae. Myocardial protection was obtained using cold crystalloid cardioplegia. The main pulmonary artery and its branches were fully mobilized. The azygos vein was divided and the superior vena cava transected above the level of the sinus node. Its cardiac end was enlarged toward the roof of the right atrium. The main pulmonary artery was divided, its cardiac end closed with a running suture. Its distal part was enlarged toward the inferior aspect of the right pulmonary, and an end-to-end anastomosis with the prepared right atrium was performed. A lateral intraatrial tunnel [13] was constructed, using a polytetrafluoroethylene patch (W. L. Gore & Associates, Inc, Elkton, MD), directing the inferior vena caval blood flow toward the pulmonary bifurcation. The systemic part of the superior vena cava was anastomosed end-to-side to the roof of the left atrium due to a left juxtaposition of the atrial appendages (Fig 1
). After bypass, mean pulmonary arterial and inferior vena caval pressures were 15 mm Hg. Mean superior vena caval and left atrial pressures were 8 mm Hg. The postoperative course was uneventful without inotropic support. The duration of artificial ventilation was 13 hours. The duration of pleural effusions was 3 days (29 ml/kg). Transcutaneous oxygen saturation was between 72% and 77% at discharge.
In April 1994, a new catheterization revealed an excellent angiographic aspect of the inferior vena caval lateral tunnel (Fig 2), a mean pulmonary capillary wedge pressure of 2.5 mm Hg, a mean pulmonary arterial pressure of 8.5 mm Hg, and an arterial oxygen saturation of 74%. The pulmonary arterial resistances were 1.8 indexed Wood units and the Qp/Qs was 0.63. The pulmonary artery index was 419 mm2/m2. The right heart bypass was completed under a circulatory bypass time of 23 minutes, by anastomosing end-to-side the superior vena cava to the right pulmonary artery. Mean pulmonary arterial and left atrial pressures were 16 mm Hg and 5 mm Hg, respectively. No postoperative inotropic support was necessary. The patient was ventilated for 10 hours. The duration of pleural effusions was 3 days (28 mL/kg). Transcutaneous oxygen saturation was greater than 95%. He is doing well 2 years after this operation.
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Fig 2. . Postoperative angiogram of patient 1 showing the bidirectional inferior vena cava-pulmonary artery shunt.
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Patient 2
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A 5-month-old female infant was referred for an increasing cyanosis. She was diagnosed, using color-coded echocardiography and angiography, as having a double-inlet right ventricle with pulmonary atresia and nonconfluent pulmonary arteries arising from the aorta at the isthmic level. She first underwent a left modified Blalock-Taussig shunt, and subsequently, 9 months later, a right modified Blalock-Taussig shunt. When she was 38 months old, weighing 13 kg, a new angiography and cardiac catheterization were performed to assess the possibility of performing a Fontan circulation. The mean right pulmonary arterial pressure was 12 mm Hg, and pressure could not be measured in the left pulmonary artery. The Nakata index was 397 mm2/m2. Pulmonary vascular resistances could not be calculated. The right ventricular end-diastolic pressure was 6 mm Hg. The indication of an ICP shunt was due to the irregularity of the pulmonary arterial tree.
Intraoperative measurements revealed a mean left atrial pressure of 7 mm Hg and a right pulmonary artery pressure of 11 mm Hg. The pulmonary arterial tree was widely dissected, and the systemic-to-pulmonary artery shunts were divided at the beginning of the bypass. The right superior vena cava was divided and the azygos vein ligated. The right pulmonary artery was divided at the level of the shunt (the retro-aortic part of the right pulmonary artery was harvested as a pulmonary artery autograft). The cardiac end of the superior vena cava was anastomosed end-to-end to the right pulmonary artery. The left pulmonary artery was divided at the level of the shunt and anastomosed end-to-end to the pulmonary artery autograft. Then, the reconstructed left pulmonary artery was anastomosed end-to-side to the roof of the right atrium. Through a longitudinal right atriotomy, a lateral tunnel was constructed using a polytetrafluoroethylene patch. The systemic part of the superior vena cava was anastomosed to the right atrial appendage (Fig 3). After bypass, the mean pulmonary arterial and left atrial pressures were 15 mm Hg and 7 mm Hg, respectively. Artificial ventilation and inotropic support with dobutamine were necessary for 5 days. The duration of pleural effusions was 7 days. The volume of pleural drainage was 67 mL/kg. Transcutaneous oxygen saturation was 78% with room air at discharge.
Nine months later, a cardiac catheterization revealed a pulmonary capillary wedge pressure of 2 mm Hg and a mean pulmonary arterial pressure of 4 mm Hg (Fig 4). Arterial oxygen saturation was 75% with a Qp/Qs of 0.57. Pulmonary vascular resistances were 2.7 indexed Wood units. The Nakata index was 271 mm2/m2. The complete right heart bypass was realized under normothermic cardiopulmonary bypass (36 minutes) without aortic cross-clamping. Before bypass, the transpulmonary gradient was 5 mm Hg. The superior vena cava was anastomosed end-to-side with the right pulmonary artery. After completion of the operation, the pulmonary arterial and left atrial pressures were 12 mm Hg and 5 mm Hg, respectively. Transcutaneous oxygen saturation was 100%. The postoperative course was uneventful. The duration of artificial ventilation was 20 hours. The duration of pleural effusions was 2 days (11 mL/kg). Today, 2 years after the last procedure, she enjoys a normal life and activity without cardiac insufficiency.
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Fig 4. . Postoperative angiogram of patient 2 showing the bidirectional inferior vena cava-pulmonary artery shunt.
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Comment
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We performed in 2 patients, with temporary contraindications to a complete Fontan circulation, an ICP shunt to reduce the risks inherent to the completion of a Fontan circulation. The clinical status of the patients was satisfactory without symptoms of cardiac insufficiency. However, their activity was restricted due to the persistent arterial oxygen desaturation. A complete Fontan operation could then be performed easily, without any "Fontan-related" mortality or morbidity.
Hemodynamic assessments revealed that inferior vena caval pressure was less in an ICP shunt than in a complete Fontan circulation, as experimentally predicted [11]. The absence of a postoperative low cardiac output avoided both the risk of hepatic failure [14] and an activation of the renin angiotensin system, which could be responsible for an increase in pleural effusions [15]. Moreover, the fluid dynamics of an ICP shunt seem to be more favorable than those of a complete derivation due to the absence of competitive flows with the superior vena cava [13], thereby decreasing the risks associated with the postural drainage of the inferior vena cava [16].
The Nakata index decreased after ICP shunts, as reported after SCP shunts [6], probably resulting from a decrease in the Qp/Qs. However, the ICP shunt provides a higher transpulmonary blood flow than the SCP shunt, and could therefore promote an additional growth of the pulmonary arteries. However, in our opinion, the construction of an ICP shunt in the very young or along with another source of pulmonary blood flow seems contraindicated and thereby cannot be offered as a definitive palliation measure. The Qp/Qs was close to 0.6, as could be predicted [5]. The resulting level of arterial oxygen saturation, almost identical to an SCP shunt without an accessory source of pulmonary blood flow, was somewhat deceiving. Even though an ICP shunt provides an increase in pulmonary blood flow compared with an SCP shunt, its oxygen delivery remains at a low level. This can be partly explained due to the high venous oxygen saturation of the renal venous blood flow that did not participate in effective pulmonary blood flow (ie, the venous saturation of the inferior vena cava is higher than in the superior vena cava). Exercise of the lower limbs does not modify the flow of the superior vena cava but increases the flow of the inferior vena cava [17], which can be an advantage of the ICP shunt, despite our inability to verify these data.
Regarding the technical aspects of the construction of the inferior vena cava-pulmonary artery connection, use of a lateral atrial tunnel does not preclude the onset of atrial arrhythmias [18]. Therefore, an extracardiac prosthetic conduit could be used to establish the inferior vena cava-pulmonary artery connection. Nevertheless, it could not be performed in the younger children, as for a classic intraatrial tunnel, due to the absence of any growth potential. Anyhow, the most impressive benefit of the ICP shunt is the technical and hemodynamic ease of the second operative step. This could have important consequences on the pulmonary and myocardial functions in the immediate postoperative course and on the occurrence of sinus node dysfunction [7]. In our 2 patients, there were no surgically created conduction or arrhythmias disorders.
Theoretically, the ICP shunt allows the hepatic venous blood flow to go directly through the lungs with the so-called hepatic factor, thereby avoiding the development of arteriovenous fistulas in the lungs [19]. Moreover, there is no risk of collateralization between the inferior vena cava and the hepatic veins. However, this shunt does not prevent of the risk of collateralization between the systemic venous system of the inferior and the superior part of the body. Thus, the azygos and hemiazygos veins must be divided and a preoperative search for anomalies of the systemic or hepatic venous return must be performed.
Although the inferior vena caval pressure was slightly increased in ICP shunts, pleural effusions were minimal due to a low pressure in the superior vena cava and absence of any obstruction to the thoracic duct drainage [20]. Nevertheless, it is important to observe that the pleural effusions were more important, for the second patient, after the ICP shunt than after the completed Fontan circulation, probably because part of the parietal pleural drainage is through the azygos vein [20]. Increased intestinal lymph production and ascites, related to an increase in the inferior vena caval pressure and mild obstruction to thoracic duct drainage by high superior vena caval pressure, has been cited as a possible contributor to the development of protein-losing enteropathy in a few patients after the completed Fontan procedure [20]. Theoretically, the thoracic duct could drain at a low pressure in an ICP situation, which may avoid this late complication.
Today, the place of the ICP shunt among the other types of partial Fontan circulations remains to be determined. It can be offered to patients in need of a first-step procedure before a Fontan operation because its advantages are (1) a fixed Qp/Qs not dependent on the transatrial gradient as for the fenestrated Fontan operation [16, 21], (2) an acceptable level of arterial oxygen saturation, and (3) mainly an increased facility to perform the second step of the Fontan operation. Further clinical experience will be required to determine if it should be applied as a partial Fontan operation.
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Footnotes
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Address reprint requests to Dr Macé, Département de Chirurgie Cardiovasculaire et Cardiaque Pédiatrique, Hôpital Marie Lannelongue, 133, ave de la Résistance, 92350 Le Plessis Robinson, France.
This article has been selected for the open discussion forum on the STS Web site:http://www.sts.org/annals
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Abstract
Introduction
