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J Am Coll Cardiol, 1998; 32:502-508 © 1998 by the American College of Cardiology Foundation |





* Departments of Pediatrics, Surgery and Diagnostic Imaging, The Hospital for Sick Children and the University of Toronto Faculty of Medicine, Toronto, Canada
Divisions of Cardiology and Cardiovascular Surgery, The Hospital for Sick Children and the University of Toronto Faculty of Medicine, Toronto, Canada
Variety Club Cardiac Catheterization Laboratories, The Hospital for Sick Children and the University of Toronto Faculty of Medicine, Toronto, Canada
Manuscript received September 8, 1997; revised manuscript received March 26, 1998, accepted April 17, 1998.
Address for correspondence: Dr. Robert M. Freedom, The Hospital for Sick Children, 555 University Avenue, Toronto, Canada, M5G 1X8
| Abstract |
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Background. Systemic venous collaterals have been found after cavopulmonary anastomosis.
Methods. Cardiac catheterization was performed in 103 patients before and after a bidirectional cavopulmonary anastomosis.
Results. After surgery, 51 venous collaterals were identified in 32 patients (31%). Collateral development was associated with an abnormal superior vena caval connection (56% incidence vs. 26% with a single right superior vena cava, p = 0.01) and postoperative factors including pulmonary artery distortion (53% incidence vs. 22% without distortion, p = 0.002); increased superior vena caval mean pressure (14 ± 5 mm Hg versus 11 ± 4 mm Hg with no collaterals, p = 0.0002); increased pulmonary artery mean pressure (13 ± 4 mm Hg vs. 11 ± 4 mm Hg with no collaterals, p = 0.02); lower right atrial mean pressure (5 ± 2 mm Hg vs. 6 ± 3 mm Hg with no collaterals, p = 0.04); and increased mean gradient between superior vena cava and right atrium (8 ± 3 mm Hg vs. 5 ± 4 mm Hg with no collaterals, p = 0.0002). Using multiple logistic regression, only this last factor was independently associated with collateral development with an odds ratio per 1 mm Hg of 1.33 (95% CI 1.121.58, p = 0.001) for their presence.
Conclusions. Systemic venous collaterals occur frequently after a bidirectional cavopulmonary anastomosis and are found postoperatively when a significant pressure gradient occurs between cava and right atrium.
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After a "classic" Glenn anastomosis (end-to-end anastomosis of the superior vena cava [SVC] to the pulmonary artery [PA]), the development of venous connections between the superior and the inferior caval veins or right atrium can lead to progressive cyanosis (4,5) due to reduction in effective pulmonary blood flow, coupled with the increasing oxygen demands with growth. Systemic venous to hepatic collaterals have also been reported after the BCPA (6), particularly in the setting of left atrial isomerism (7), and may also result in profound and progressive cyanosis. Such collateral vessels may develop in the absence of mechanical obstruction, and represent "run-off" from the higher pressure caval venous system to the lower pressure atrium or hepatic vein. Recent reports have also highlighted the development of systemic venous collaterals after the Fontan procedure (8).
The aims of this study were to review those patients who had been palliated with a BCPA to determine the prevalence and morphology of such systemic venous channels, whether their presence was disadvantageous, and if anatomical and hemodynamic factors were associated with their presence.
| Methods |
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Because some PAs were distorted due to previous arterial shunts or constriction of ductal tissue, an attempt was made to categorize the degree of distortion: 1) no distortion, 2) mild distortion of one or both PAs not requiring intervention, 3) severe distortion of one PA requiring intervention either before or at the time of the next surgery, and 4) severe distortion of both PAs.
While most postoperative catheterizations were performed as scheduled assessments, a number were performed early after surgery in patients with low saturations and/or high SVC pressures. At the time of the postoperative assessment, the Nakata index was remeasured, the presence or absence of pulsatile flow in the pulmonary circuit was noted, and PA distortion was characterized as above.
Systemic venous collaterals were defined as venous channels allowing flow from the BCPA circuit to the inferior vena cava (IVC), atrium, or pulmonary veins, and could represent reversal of flow within an existing vessel or opening of a new channel. The location, origin, and course of such channels were recorded and subdivided into those running in the anterior, mid, or posterior mediastinum from lateral angiographic views.
Analysis of hemodynamics. Oxygen saturations were obtained in the aorta and the SVC, and the inspired oxygen concentration was noted. The majority of patients were breathing room air, however, several of those studied in the immediate postoperative setting were ventilated in an enriched oxygen mixture. Mean pressures were recorded in the SVC, the right atrium, and the main or branch PAs, together with the end-diastolic pressure of the dominant ventricle. Stenosis of the anastomosis was detected by both mean pullback pressures between the PA and SVC and by the angiographic appearance. Cardiac index was calculated using measured oxygen consumption in patients breathing room air. In those situations where it was possible to measure pulmonary blood flow (single source flow), the pulmonary arterial resistance index was calculated.
Surgical data. The cavopulmonary anastomosis was performed on cardiopulmonary bypass following a midline sternotomy. An end-to-side anastomosis of the SVC to the PA was constructed using interrupted sutures with 6-0 Prolene (Ethicon, Johnson and Johnson). The atrium was closed in two layers also using 6-0 Prolene. The type of cavopulmonary anastomosis, whether unilateral or bilateral, was noted. Excluding cases of left atrial isomerism with azygous continuation of the IVC, the azygous vein was ligated in all but seven patients by the surgeons preference. In one patient the azygous vein could not be identified. An atrial septectomy was required in 11 patients, the remainder having unrestrictive atrial septal defects.
Summary of risk factors. Possible preanastomosis risk factors for the development of systemic venous collaterals and those associated with the presence of collaterals postanastomosis are summarized in Table 2. Ventricular function and degree of atrioventricular valve regurgitation were not included in the analysis, as this information was qualitative and thought to be of limited validity.
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| Results |
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The morphology of the dominant ventricle was left in 64 patients (62%), right in 38 patients (37%) and in one patient both ventricles were of equal size (1%). The SVC connection was single in 85 patients (82%) and bilateral in 18 patients (18%) (the left SVC draining into the coronary sinus in nine patients and to the roof of a common atrium in nine patients). Four of these patients underwent ligation of the left SVC, 13 underwent bilateral BCPA, and in one patient with left atrial isomerism, the left SVC was left in continuity with the heart.
Postoperative PA flow appeared pulsatile during angiography in 49 patients (48%), either having the main PA in continuity with the heart (n = 36) or having a systemic arterial shunt (n = 13). Postoperative angiography showed that 73 patients had no PA distortion (71%), 15 patients had mild distortion (14%), 11 patients had severe distortion affecting one PA (11%) and four patients had severe distortion affecting both PAs (4%).
Prevalence and types of collaterals. No abnormal systemic venous channels were identified at the time of preoperative catheterization. At the time of postoperative catheterization, a total of 51 sites of collateral venous drainage were identified in 32 patients (31%). Types of channels are summarized in Table 3.
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Management of collaterals. Twelve patients with collaterals required treatment (38%). Coil occlusion during cardiac catheterization was performed in four patients, one of whom also underwent dilatation of a previously implanted endovascular stent at the anastomotic site and another who underwent placement of an endovascular stent within a narrowed left PA. One patient underwent successful balloon angioplasty of the anastomotic site and of a narrowed distal left PA with disappearance of collateral flow, and one patient underwent endovascular stent placement within the left PA with similar reduction in collateral flow. Collaterals in two patients were ligated at the time of Fontan completion, and one patient underwent successful surgical revision for BCPA stenosis with subsequent reduction in collateral flow.
There were three deaths: one patient after attempted thrombolysis for widespread thrombosis following homograft reconstruction of disconnected PAs and bilateral BCPA; one patient after attempted balloon occlusion of a large hemi-azygous vein, and one patient during attempted surgical decompression for SVC syndrome.
Hemodynamics.
Hemodynamic measurements before and after BCPA are given in Table 4. Only the SVC and aortic saturations, the PA pressures and the Nakata index changed significantly. Saturation data collected while patients were receiving enriched oxygen (FiO2
0.25) were not included for analysis. The difference in pulmonary arteriolar resistance was not assessed as pulmonary blood flow could not be calculated in the majority of preoperative studies.
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3 mm Hg (range 39 mm Hg), however, these gradients were not associated with collateral development (p = 0.1). No preoperative hemodynamic factors predicted the development of collaterals, although mean PA pressure tended to be higher at 14 ± 4 mm Hg versus 12 ± 4 mm Hg for no collaterals (p = 0.1). Regression analysis. When these predictors were tested using multiple logistic regression, only the postoperative gradient between the SVC and right atrium emerged as independent for collateral development. The odds ratio per 1 mm Hg was 1.33 (95% CI 1.12 to 1.58, p = 0.001).
| Discussion |
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All patients in this series had acceptable preoperative PA pressures, none had pulmonary venous obstruction, and eight demonstrated obstruction at the anastomotic site, but this factor alone did not predict the appearance of venous anomalies. An elevated ventricular end-diastolic pressure, which can reflect ventricular diastolic dysfunction, was also not independently associated with their development. In any case, such an elevation in pressure sufficient to result in collateral development would not be compatible with single ventricle physiology. In our series, the only anatomical factors associated with the presence of collaterals were postoperative PA distortion and the presence of bilateral SVCs, although the mechanism for the latter would not appear to be due to ligation of one caval vein. As previously reported (12), the Nakata index fell significantly after the BCPA, however, a lower postoperative Nakata index was not associated with the presence of collaterals.
Obstruction to vena caval flow can also lead to systemic venous decompression after atrial repair of transposition of the great arteries (13,14), and pulmonary venous decompression has been described after repair of sinus venosus atrial septal defect (15). An anomalous systemic venous to left atrial channel has also been described between the SVC to left atrium in a case of tricuspid atresia and restrictive interatrial communication (16). Thus, a variety of obstructive lesions can form the substrate for the development of a host of possible decompressing channels.
Mechanism of development. The etiology of such anomalies is unsettled, representing angiogenesis de novo or the reopening of previously existing channels. To this end, the embryological development of the IVC (described in detail by McClure and Butler in 1925 [17]), has helped elucidate the considerable variations found in the adult. During the course of its development, many venous channels are known to "disappear." We postulate that such channels reappear when the cavae are subjected to elevated pressures. This was underscored in our population with the reopening of the anterior and/or posterior cardinal systems from the innominate vein via the superior intercostal vein. The speed at which collaterals appear also suggests the reopening of preexisting channels.
Physiological effects. The physiologic effect of this collateralization takes two forms, either systemic venous to systemic venous connections, or systemic venous to pulmonary venous or left atrial connections. Increased cyanosis could therefore result from either a reduced effective pulmonary blood flow or increased admixture of pulmonary venous return. Clinically, the overall presence of systemic venous run-off was not associated with significant systemic desaturation, presumably as several were small and represented an insignificant right to left shunt or reduction in effective pulmonary blood flow at rest. Large collaterals did result in clinically unacceptable desaturation and required intervention. In many cases, it was safe to leave anomalous veins draining from superior to inferior vena cava, as this shunt would be negated after completion of the Fontan circuit, unless they were so large as to seriously reduce effective pulmonary blood flow in the short term. However, channels draining to the pulmonary veins or common atrium required occlusion.
No hemodynamic risk factors could be identified from the preoperative catheterization data, however, in many cases pulmonary vascular resistance could not be estimated as there were two sources of pulmonary blood flow. In addition, hemodynamic measurements during catheterization only represent a snapshot of prevailing conditions. It may be that collateral channels develop in hemodynamically borderline situations and are markers for a poor long-term outcomes. It is intriguing to speculate that these same patients may develop new collaterals after completion of the Fontan circulation and/or further collaterals after occlusion.
Conclusions. Systemic venous collaterals are frequently found after the bidirectional cavopulmonary anastomosis, the majority drain to the inferior vena cava, and they are related to a pressure gradient between the cava and right atrium. Collaterals probably represent reverse flow in the azygous or hemiazygous systems or reopening of channels present during embryonic development.
| Acknowledgments |
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| References |
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