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Ann Thorac Surg 2000;70:711-716
© 2000 The Society of Thoracic Surgeons

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Original articles: cardiovascular

Are bilateral superior vena cavae a risk factor for single ventricle palliation?

^a Division of Cardiovascular Surgery, The University of Toronto, The Hospital for Sick Children, Toronto, Ontario, Canada
^b Division of Cardiology, The University of Toronto, The Hospital for Sick Children, Toronto, Ontario, Canada

Address reprint requests to Dr Van Arsdell, Division of Cardiac Surgery, The Hospital for Sick Children, 555 University Ave, Toronto, ON M5G 1X8, Canada
e-mail: glen.vanarsdell{at}sickkids.on.ca

Presented at the Poster Session of the Thirty-fifth Annual Meeting of The Society of Thoracic Surgeons, San Antonio, TX, Jan 25–27, 1999.

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. Performing superior vena cava-to-pulmonary artery anastomosis, in the presence of bilateral superior vena cavae, can be technically challenging. Our clinical observation has been that bilateral superior vena cavae are a risk factor for poor outcome in children needing single ventricle palliation.

Methods. Detailed operative, angiographic, and follow-up data were analyzed in 39 children undergoing bilateral cavopulmonary anastomosis (b-CPA). Overall outcome was compared to 274 children having a unilateral cavopulmonary anastomoses (u-CPA).

Results. Nine patients (23%) with bilateral superior vena cavae were found to have thrombus in the cavopulmonary circulation after the b-CPA. Postoperative mean arterial oxygen saturation was significantly lower in those who had thrombus [69% ± 10% versus 82% ± 7%, (p < 0.01)]. Thrombus formation was associated with mortality. The indexed superior vena cavae size was not a risk factor for thrombosis. In follow-up studies the connecting pulmonary artery segment between the two cavopulmonary anastomosis was smaller than the pulmonary arteries adjacent to the hilum. Survivors of a b-CPA were less frequently converted to a Fontan circulation at 5 years of follow up (Kaplan-Meier 5-year estimates, 39% for b-CPA versus 74% for u-CPA [p = 0.02]).

Conclusions. Bilateral superior vena cava-to-pulmonary artery anastomosis is associated with an increased risk of thrombus formation and unfavorable growth in the central pulmonary arteries. Modifications of surgical technique may alter flow patterns, thereby optimizing growth and diminishing the risk of thrombus formation. Anticoagulation therapy may be an important adjunct in children undergoing a b-CPA.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Systemic venous anomalies were once thought to be a contraindication to the Fontan procedure [1]. Application of the concepts for the Fontan circulation have evolved whereby nearly all patients with single ventricle physiology, including those with abnormalities of the systemic venous return [1–5], are palliated on what has become known as the "Fontan tract." Although the initial results for the extension of the indications for the Fontan procedure were not always favorable [1], more recent studies have shown improvement [6, 7].

Performing a cavopulmonary connection as a stage to the Fontan procedure has been used as a method to normalize volume loading of the single ventricle at an earlier age. Normalization of volume loading is thought to reduce the risk for a Fontan procedure, particularly in children with high-risk complex lesions [8, 9]. The presence of bilateral superior vena cava, however, may pose a technical challenge to the performance of a cavopulmonary connection. It also results in a different flow pattern in the central pulmonary arteries when compared to a standard bidirectional cavopulmonary connection.

No studies have reported on outcomes in children who undergo bilateral cavopulmonary anastomosis (b-CPA). We describe patient characteristics, management, and outcomes related to the creation of b-CPAs, and then compare overall outcome to children receiving a unilateral cavopulmonary anastomosis (u-CPA).

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
All patients who underwent a cavopulmonary anastomosis between July 1982 and October 1998 at The Hospital for Sick Children, Toronto, were identified by performing a search of the Division of Cardiovascular Surgery’s database. Three hundred thirteen children were identified who underwent a cavopulmonary anastomosis as a separate procedure from a Fontan operation. The children were divided into two groups based on the presence or absence of bilateral superior vena cava. Bilateral superior vena cava were present in 42 children of which 39 had b-CPAs. Of the 3 children with bilateral superior vena cava who did not have a b-CPA, 2 had the left superior vena cava (LSVC) ligated and in 1 child the LSVC was left alone. These 3 children had a flow pattern in the cavopulmonary circulation, after the cavopulmonary anastomosis, that was similar to children who have a unilateral superior vena cava and a u-CPA; therefore, they were included in the u-CPA group. Patients who underwent a hemi-Fontan connection of the right superior vena cava-to-the right pulmonary artery and a direct connection of the left superior vena cava to the left pulmonary artery were included in the b-CPA group.

Data were collected by reviewing hospital and clinic records. All patients were followed by contacting the family physician, the referring cardiologist, or family members. More detailed data collection and in-depth analysis was performed for the b-CPA group. Patient characteristics for both groups are in Table 1.

Procedure
All bidirectional cavopulmonary shunts were performed using a median sternotomy and standard cardiopulmonary bypass techniques. Cold-blood cardioplegia was given to patients who had associated intracardiac procedures. Previous systemic-to-pulmonary artery shunts were disrupted, as was known antegrade flow in the main pulmonary artery, by division or ligation.

In patients with a single superior vena cava (SVC) (n = 274), the vena cava was divided and anastomosed to the ipsilateral pulmonary artery in an end-to-side manner in 232 patients (85%), an end-to-end manner in 19 patients (7%), and side-to-side in 4 patients (1%). A hemi-Fontan connection was used in 19 patients (7%).

In those children having bilateral SVC (n = 39), the LSVC was occluded while the pressure in the cephalad side in that SVC was monitored. If the pressure was higher than 20 mm Hg, the LSVC was cannulated for cardiopulmonary bypass. This was necessary in 6 patients (15%). If the pressure was less than 20 mm Hg, the procedure was completed with the LSVC occluded as needed. The cavopulmonary connections were created by a bilateral end-to-side anastomosis in 35 children (90%). A right-sided hemi-Fontan connection and a left-sided bidirectional cavopulmonary anastomosis was performed in 4 children (10%).

The median weight at the time of the b-CPA was 8.3 kg (range, 3.8 to 57 kg) and the median total cardiopulmonary bypass time was 134 minutes (range, 39 to 281 minutes). In 12 children an aortic cross-clamp was used for a median time of 43 minutes (range, 11 to 53 minutes).

Angiographic measurements
A review of all available angiograms for each patient with bilateral SVC, was performed (FPD). Detailed measurements for angiograms obtained before the b-CPA (n = 29), after the b-CPA (n = 25), and after the Fontan repair (n = 9) were made. The data is summarized in Table 2.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
Early results of children having a bilateral cavopulmonary anastomosis
Intraoperative arterial oxygen saturation after repair (n = 37) was 79% ± 10%. There were 6 early deaths (15%) after operation. Median length of stay in the intensive care unit and total length of stay was 3 days (range, 1 to 15 days; n = 31) and 12 days (range, 5 to 76 days; n = 34) for those surviving the operation. Postoperative complications occurred in 17 patients (44%). They included vocal cord paralysis in 1 patient (3%), reoperation in 7 (18%) (bleeding in 3 [8%], requirement for sternal reopening in 4 [10%]), chylothorax in 5 (13%), respiratory complications in 5 (13%), low cardiac output in 4 (10%), seizures in 1 (3%), and postoperative arrhythmias in 6 (15%).

Outcomes during follow-up
During follow-up, 20 of the 33 survivors of the b-CPA had no further operation. Eleven children had a Fontan operation. The reasons for not having a Fontan procedure were as follows: too early after b-CPA (n = 9), too high a risk for a Fontan (n = 6), and 1 each a one-and-a-half ventricle repair, an orthotopic heart transplant, and late death (total n = 29).

Three late deaths occurred. One child was 10 months of age and had an unbalanced atrioventricular septal defect, pulmonary atresia, and nonconfluent pulmonary arteries. Unifocalization and pulmonary artery reconstruction with aortic homograft tissue had been performed. This infant was readmitted 108 days after the repair with low oxygen saturations. The postmortem examination revealed extensive thrombosis throughout the homograft and right and left pulmonary arteries. Two patients died early after the Fontan procedure.

Operative measurements
Intraoperative measurements (mean ± standard deviation) of the diameters of the SVCs and branch pulmonary arteries were as follows: right superior vena cava (RSVC) (n = 20), 8 ± 3 mm; LSVC (n = 22), 8 ± 3 mm; right pulmonary artery (n = 23), 9 ± 3 mm; left pulmonary artery (n = 24), 8 ± 2 mm. Mean postrepair pressure measurements in both cava were performed: RSVC (n = 24), 16 ± 5 mm Hg; LSVC (n = 25), 17 ± 6 mm Hg; right pulmonary artery (n = 13), 15 ± 5 mm Hg, and left pulmonary artery (n = 13), 15 ± 5 mm Hg.

Changes in vascular dimensions
An attempt to characterize growth or dimensional changes in the studied structures was made by following ratios and indices over time as described in the Methods section. The diameter ratio of the right-to-left SVC remained equal over time (Table 2). There appeared to be adequate growth of the pulmonary arteries, as indicated by the lack of significant changes over time in both the Nakata and McGoon indices. The ratio of the diameter of the SVC to the respective pulmonary arteries remained stable. The normalized dimensions of the superior vena cavae appeared to decrease with time, consistent with a decreasing contribution of systemic venous return from the head and upper extremities with increasing patient age and body size.

After the b-CPA, the intervening connecting pulmonary artery segment between the two cavopulmonary anastomosis was smaller than either the right or left branch pulmonary artery adjacent to the hilum suggesting growth failure of the central segment of the pulmonary arteries (Table 2 and Fig 1).

View larger version (115K): [in this window] [in a new window]   Fig 1. Pulmonary angiogram showing the narrowed intervening segment of the central pulmonary artery. Other views in the cine demonstrate that this angiographic finding is not related to competitive flow from the other superior vena cava.

Stenoses of the SVC or the branch pulmonary arteries were detected at some point after the b-CPA in 15 of 37 immediate operative survivors (41%). The stenosis was located in the anastomosis of the SVC to the pulmonary artery (RSVC to right pulmonary artery in 6 patients, LSVC to left pulmonary artery anastomosis in 4, and at both anastomoses in 5 patients). These stenoses were managed with transcatheter balloon dilatation in 11 children and by placement of an endovascular stent in 6 children. Figure 2 shows the freedom from transcatheter intervention for vascular stenosis in the cavopulmonary circuit after b-CPAs. Use of Cox’s proportionate hazard modeling identified no significant risk factor for reintervention, including patient characteristics and cardiac anatomy, previous operations, or vascular measurements derived from the cardiac catheterizations.

View larger version (19K): [in this window] [in a new window]   Fig 2. Kaplan-Meier plot of freedom from transcatheter intervention for vascular stenoses in the cavopulmonary circuit. Vertical lines represent 95% confidence interval.

Patient characteristics and outcomes comparing the bilateral cavopulmonary anastomosis group to the unilateral cavopulmonary anastomosis group
Patient characteristics and outcomes for children undergoing a cavopulmonary anastomosis in the presence of either unilateral or bilateral SVC are outlined in Table 1. Children with bilateral SVC were more likely to have dominant right ventricular morphology and were more likely to have atrial isomerism. There was no difference between the groups with regard to previous operations. Kaplan-Meier intermediate term estimates of survival did not differ significantly between those with single and bilateral cavae (log rank test, p = 0.16; Wilcoxon test, p = 0.08 (Fig 3); however, Kaplan-Meier 5-year estimates for conversion to a Fontan were 39% for those who survived a b-CPA and 74% for those in the u-CPA group (p = 0.02). The trend persisted through 10 years but the numbers are small.

View larger version (19K): [in this window] [in a new window]   Fig 3. Kaplan-Meier plot of survival after cavopulmonary connections (CPS). Solid line indicates single cavopulmonary connection; broken line indicates bilateral cavopulmonary connection. Vertical lines represent 95% confidence interval. The difference is not significant.

	Comment

Top Abstract Introduction Patients and methods Results Comment References

As a group, there was a higher prevalence of right ventricular morphology and atrial isomerism in those children who had bilateral SVC than in those who had a unilateral SVC. These differences partially, but not completely, explain the reasons for the less favorable operative outcome in children with b-CPAs. The two significant findings of this study further delineate causes for a less favorable outcome in children with bilateral SVCs: cavopulmonary circulation thrombosis and subsequent failure of growth in the pulmonary artery segment between the two cavopulmonary anastomosis.

Thrombosis of the cavopulmonary circuit
The clinical impact of thrombosis in the cavopulmonary circulation in the present report was a higher risk of death after b-CPA or an increased hospitalization time. Reports of thrombosis after cavopulmonary anastomosis have been few [10–13]; however, Forbes and colleagues [13] have shown that the presence of bilateral SVC was a risk factor for cavopulmonary circulation thrombosis.

We identified two significant risk factors associated with thrombosis in children having a b-CPA: (1) a size discrepancy between the two SVCs, and (2) a low mean oxygen saturation immediately after operation. In both situations thrombosis is likely related to low flow. In the first situation our analysis demonstrated that relative size between the two cavae, not caval size indexed to body surface area, was a risk for thrombosis, indicating that relative flow, not indexed size, was the important determinant of risk for thrombosis. In the second situation, a lower mean oxygen saturation is a reflector of lower flow across the pulmonary vasculature.

Other factors potentially associated with thrombosis of the cavopulmonary circulation could be hypercoagulable states and the use of internal jugular lines. Our data did not permit study of the precise role of internal jugular lines or coagulation status to thrombosis; nevertheless, avoiding central venous lines involving the SVCs may be beneficial.

Changes in pulmonary artery size over time
Previous reports of pulmonary artery size after a b-CPA vary from no increase in size to an increase in size [14, 15] or to a decrease in size on the contralateral side of the anastomosis [16]. Reddy and colleagues [17] noted that distal pulmonary artery growth is better in patients with bilateral bidirectional cavopulmonary shunts than in those with a unilateral connection. Children in our series demonstrated adequate growth of the pulmonary arteries, as indicated by lack of significant changes over time in the Nakata and McGoon indices. However, we found that the pulmonary artery segment between the two anastomoses was smaller than either the right or left pulmonary artery adjacent the hilum. The lack of growth in the connecting portion of the central pulmonary artery is likely due to selective blood flow to the corresponding lung resulting in stagnation and a predisposition to thrombosis in the central pulmonary artery.

Preventing thrombosis
Because of the severe sequelae to thrombosis, modification of treatment techniques may be necessary. First, central venous lines involving the cavae should be avoided; second, postoperative anticoagulation may be beneficial; third, surgical techniques that minimize the technical risks to the venous anastomosis and abnormal pulmonary artery flow patterns are imperative.

Maintaining patency in small venous anastomosis can be difficult. Meticulous surgical technique using interrupted sutures for the anastomosis and, when indicated, augmenting the anastomotic confluence with autologous pericardium may diminish local stricture.

Surgical solutions to the problems defined in this study need to ensure obligate flow through the central pulmonary arteries. Ligation of the smaller of the two SVCs in the presence of a sizable bridging vein would preserve normal u-CPA flow patterns (we have occasionally done this). Extending this concept to include ligation of the smaller SVC in the presence of small bridging veins and a low SVC pressure on test occlusion before bypass may need to be explored. Most children, however, will need bilateral connections and therefore, will need a surgical solution. One solution might be to place the two cavopulmonary anastomosis nearly adjacent to each other, thereby eliminating the intervening central pulmonary artery segment. An alternative method that eliminates one of the troublesome cavopulmonary anastomosis is a right-sided hemi-Fontan and a left-sided cavopulmonary anastomoses. Flow patterns in a hemi-Fontan, by necessity, involve the central portion of the connecting pulmonary artery, which may also promote growth. The connecting pulmonary artery segment might also be more permanently enlarged by a leftward extension of the intraatrial right hemi-Fontan patch. The net affect of this approach is to enlarge the intervening pulmonary artery inferiorly into the atrium.

A more radical solution may be to perform an inferior vena cava-to-pulmonary artery cavopulmonary connection (upside down cavopulmonary anastomosis) as the first stage to a Fontan and later complete the Fontan by performing a b-CPA. There would be some technical problems with an inferior vena cava-to-pulmonary artery connection but flow distribution to the pulmonary arteries would be closer to that of a u-CPA.

In conclusion, patients who undergo b-CPAs have a higher mortality and lower conversion rate to a Fontan procedure than those who have a u-CPA. The incidence of thrombosis and reintervention for stenoses in these patients is high. Central pulmonary artery growth between the two cavopulmonary anastomosis is poor. Altering surgical techniques to minimize thrombotic risk and to create obligate flow patterns to the central portion of the pulmonary artery may be beneficial. Postoperative anticoagulation in children with b-CPAs needs to be explored.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

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