Asian Cardiovasc Thorac Ann 2001;9:282-285
© 2001 Asia Publishing EXchange Pte Ltd
Pulmonary Blood Distribution After Total Cavopulmonary Connection
Chu Jun Min, MD,
Wu Qing Yu, MD,
Wang Wen Ming, MD1
Department of Cardiovascular Surgery
1 Department of Nuclear Medicine Cardiovascular Institute and Fuwai Hospital Chinese Academy of Medical Sciences and Peking Union Medical College Beijing, People's Republic of China
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For reprint information contact: Chu Jun Min, MD Tel: 86 10 6833 2376 Fax: 86 10 6833 2376 Department of Cardiovascular Surgery, Cardiovascular Institute and Fuwai Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, 167 Beilishi Road, Xicheng Region, Beijing 100037, People's Republic of China.
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ABSTRACT
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From July 1998 to December 2000, the distribution of pulmonary blood flow was evaluated in 34 consecutive surviving patients who had been randomly assigned to one of 4 different modes of total cavopulmonary connection. All patients underwent radionuclide lung perfusion imaging with 99mTc-macroaggregated albumin to determine the distribution of blood from the superior and inferior venae cavae and the total pulmonary flow to each lung. The most physiological distribution of blood between the right and left lungs was obtained when the inferior vena cava anastomosis was widened and slightly offset towards the right pulmonary artery in patients without persistent left superior vena cava. This type of anastomosis should also reduce the incidence of arteriovenous malformations in the lung caused by exclusion of hepatic venous return.
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INTRODUCTION
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Total cavopulmonary connection (TCPC) has been widely used for surgical treatment of tricuspid atresia, single ventricle, and several other complex malformations of the heart, which are unsuitable for a biventricular repair.1 Compared to other Fontan-type operations, TCPC can result in a more streamlined and, thus, energy-efficient blood flow pattern.2,3 It provides excellent hemodynamics with minimal postoperative complications such as atrial arrhythmias.4 However, some controversies remain concerning the method of anastomosis of the inferior vena cava (IVC) and the pulmonary artery (PA), and the potential for arteriovenous malformations in the lung due to exclusion of hepatic venous return. Thus, the optimal surgical design has not been determined. The purpose of this study was to evaluate the caval and total pulmonary blood flow distributions after different types of TCPC.
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PATIENTS AND METHODS
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From July 1998 to December 2000, 34 consecutive survivors of TCPC (23 males and 11 females, aged 5 to 21 years) underwent radionuclide lung perfusion imaging (with the informed consent of the patients or their parents) using 99mTc-macroaggregated albumin. Preoperatively, angiography and cardiac catheterization were used to confirm that the PA was well developed in all patients, and there was no stenosis or collateral circulation. The PA pressure was less than 16 cm H2O, and pulmonary vascular resistance was less than 4 Wood units in all cases. None of the patients had heterotaxia. The patients were randomly assigned to one of 4 different techniques of TCPC. The postoperative courses were uneventful. The patients were divided into 4 groups according to the mode of anastomosis between the IVC and the PA. Diagnoses are shown in Table 1
. Group 1 comprised 10 patients in whom the IVC was connected to the distal end of the transected main PA by an extracardiac conduit (n = 8) or an intraatrial lateral tunnel (n = 2), as shown in Figure 1A. Group 2 was 8 patients who had anastomosis of the superior vena cava (SVC) and IVC directly opposite each other on the right PA, forming a cross shape with an extracardiac conduit (Figure 1B). Group 3 included 11 patients in whom the IVC was connected by a widened anastomosis to the right PA that was slightly offset towards the right (Figure 1C). In the 5 patients in group 4, the IVC was connected to the main PA by an extracardiac conduit to give the bilateral bidirectional cavopulmonary connection illustrated in Figure 1D.
Radionuclide lung perfusion scans were performed in the supine position under adequate sedation 30 days after TCPC. An intravenous line was placed in a right arm vein, and a bolus dose of 99mTc-macroaggregated albumin (50 to l00 Ci•kg–1) was injected slowly. Relative lung perfusion was determined by radionuclide counts of 500,000 from posterior images. After 3 days, lung perfusion was reassessed by injection of 99mTc-macroaggregated albumin via a lower limb vein. In group 4, lung per-fusion scans were also carried out by injection of 99mTc-macroaggregated albumin via a left arm vein. The percentages contributed by the IVC and SVC to the total pulmonary blood flow (physiologically, these should be 35% from the SVC and 65% from the IVC) were determined, as well as the distribution of blood from the SVC, IVC, and the total pulmonary flow to each lung.
The unpaired Student t test was used to compare blood flow from the SVC, IVC, and the total flow to both lungs in each group. Values were expressed as mean ± standard deviation. A p value 
0.05 was considered statistically significant.
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RESULTS
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The distribution of blood flow to the right and left lungs from the SVC, IVC, and the total pulmonary flow is summarized in Table 2. In group 1, IVC flow went pre-dominantly or completely to the left lung, SVC flow went mainly to the right lung, and the left lung received 61% of the total pulmonary flow, which is not in accordance with the physiological distribution (considered to be 55% to the right lung and 45% to the left). In group 2, blood flow from the SVC and IVC mixed in the middle of the junction and was distributed equally to both lungs; the total pulmonary blood flow also perfused both lungs equally. In group 3, flow from the SVC dispersed to both lungs equally, but a major proportion of the IVC flow went to the right lung; the total pulmonary blood flow went predominantly to the right lung, and corresponded to the physiological distribution. In group 4, all flow from the right SVC went to the right lung, and all left SVC flow went to the left lung, while the IVC flow went mainly to the left lung.
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DISCUSSION
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In 1964, Wagner and colleagues5 studied normal vena caval blood distribution quantitatively and qualitatively with 131I-labeled macroaggregated human albumin. Recently, Cloutier and colleagues6 used this technique in a detailed study of pulmonary blood flow after Glenn and Fontan operations, which demonstrated abnormal patterns in some patients. Seliem and colleagues7 reported that 27% of patients had a normal distribution of pulmonary blood flow after a Glenn shunt, 16% had mildly decreased flow to the left lung, and 27% had severely decreased flow to the left lung. There have been several studies of pulmonary blood distribution after TCPC, but they are limited to a computer numeric model, in-vitro investigations, and magnetic resonance imaging.8–14 There have been no animal studies or quantitative clinical findings reported previously. This clinical study used radionuclide lung perfusion scanning which is a convenient, noninvasive, accurate, and reproducible technique that allows quantitative analysis of the distribution of blood flow.
Based on a computer numeric model, flow was found to be symmetrically distributed after TCPC in a cross formation, with complete mixing of blood from the IVC and SVC.8 When the IVC was offset to the left, flow separation occurred and IVC flow was directed more towards the left PA; the separation was more pronounced when the IVC was shifted further to the left.8 A similar separation phenomenon was found in this clinical study. After examining flow following TCPC by computational fluid dynamics, de Leval and colleagues10 concluded that the best flow distribution between the left and right lungs was obtained with an IVC anastomosis offset 0.5 to 0.7 cm towards the right PA. When the IVC anastomosis was offset towards the left PA, there was a greater proportion of flow to the left lung, which is contrary to the physiological distribution. In a bidirectional cavo-pulmonary connection model, most or all of the SVC flow went to the right lung, and most or all of the IVC flow went to the left lung; the proportion of total pulmonary flow in the left lung was greater than that in the right lung. This was similar to the results in this study.
In in-vitro flow experiments, Sharma and colleagues11 demonstrated that anastomosis of the IVC and SVC directly opposite each other on the right PA caused mixing of the SVC and IVC flows and equal distribution to both lungs. When the IVC anastomosis was offset to the right, the IVC flow went completely to the right lung. This separation phenomenon has also been demonstrated clinically by angiography.15,16 Another in-vitro study showed that symmetrical anastomosis of the IVC and SVC to the right PA caused blood flow from both venae cavae to mix at the junction and distribute equally to the right and left PA.9 When the IVC anastomosis was offset to the right, 78% of its flow went to the right lung and 22% to the left lung, while 100% of the SVC flow went to left lung. This pattern is not in line with the physiological distribution. The findings in this clinical study confirm that such shifts occurred postoperatively.
The cause of the flow separation due to offsetting the IVC connection was investigated by Sharma and colleagues11 who found a vigorous vortex at the anastomosis site. The vortex appeared to cushion the caval flow and prevent the diversion of flow to either the right or left lung. This caused separation of blood flow from the IVC and SVC. Kim and colleagues13 also reported that a significant area of stagnation was created in the middle of the offset region. In classic TCPC, dissipative energy losses are believed to be high at the site of collision of caval flows. In a fluid dynamics study, minimal loss of energy was obtained by angling the IVC connection towards the right PA and widening the anastomosis to 2.5 cm; this design gave the most physiological flow distribution between the left and right lungs.10 In group 3, we observed similar results: 56% of the total pulmonary blood flow went to the right lung, and 44% to the left lung.
There have been several studies convincingly demon-strating that exclusion of hepatic venous blood from a lung can result in the development of pulmonary arteriovenous fistulae.17–20 With hepatic venous blood distributed to both lungs, a decrease in the incidence of pulmonary arteriovenous fistulae could be expected. It was concluded that the various designs of TCPC give different pulmonary blood flow distributions. The best distribution of flow between the left and right lungs was obtained when the IVC anastomosis was widened and offset towards the right PA in patients without persistent left SVC.
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ABSTRACT
INTRODUCTION
