Ann Thorac Surg 2001;71:1537-1540
© 2001 The Society of Thoracic Surgeons
Original article: cardiovascular
Saphenous vein homograft: a superior conduit for the systemic arterial shunt in the Norwood operation
Vincent K.H Tam, MDa,*,
Kathy Murphy, MSNa,
W.James Parks, MDb,
Anthony A Raviele, MDb,
Robert N Vincent, MDb,
Margaret Strieper, DOb,
Angel R Cuadrado, MDb
a Section of Cardiothoracic Surgery, Emory University School of Medicine, Atlanta, Georgia, USA
b The Children’s Heart Center, Atlanta Children’s Healthcare at Egleston, Atlanta, Georgia, USA
* Address reprint requests to Dr Tam, Section of Cardiothoracic Surgery, The Emory Clinic, Building A, 1365 Clifton Rd, Atlanta, GA 30322 (Email: vtam01{at}emory.edu).
Presented at the Forty-sixth Annual Meeting of the Southern Thoracic Surgical Association, San Juan, Puerto Rico, Nov 4–6, 1999.
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Abstract
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Background. Excessive pulmonary blood flow increases ventricular volume work in the face of inadequate systemic cardiac output, low diastolic blood pressure, and inadequate coronary perfusion. Using the smallest available 3-mm polytetrafluoroethylene shunts have been successful, although catastrophic shunt thrombosis has occasionally been observed. To avoid thrombosis with a smaller conduit, saphenous vein homografts (SVG) were used to construct the modified Blalock–Taussig (BT) shunts.
Methods. From January 1998 to April 1999, 25 patients weighing 3.1 kg (3.0 kg or less, n = 9), at a mean age of 8.9 days, underwent stage I Norwood using an SVG BT shunt. Common heart defects were aortic atresia (n = 8), mitral atresia and double-outlet right ventricle (n = 5), and unbalanced AVC (n = 5). Mean BT shunt size was 3.2 mm, with 12 patients having shunts that were 3 mm or smaller.
Results. Thirty-day hospital mortality was 8% (2 of 25). No shunt thrombosis was seen, despite banding the BT shunt in 3 patients. One patient had BT revision because of an anatomic issue not directly related to the shunt material.
Conclusions. Excellent results may be achieved using SVG BT shunts in the Norwood operation. This conduit seems less likely to thrombose, both acutely and chronically, allowing the use of appropriately smaller-sized shunts in small neonates.
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Introduction
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The Norwood operation continues to be the procedure of choice for the treatment of infants with hypoplastic left heart syndrome and its variants in many institutions. Since its conception and introduction, many refinements have occurred, with continued improvement in outcome. In our practice, excessive pulmonary blood flow in the postoperative infant has generally been poorly tolerated. Our perioperative management scheme has been detailed elsewhere [1]. By using the smaller available 3- and 3.5-mm polytetrafluoroethylene (PTFE) conduits to construct the systemic arterial shunts, we have had a moderate degree of success. However, catastrophic shunt thromboses have been observed with the 3-mm PTFE shunts, particularly when platelet transfusions were given in attempts to correct the severe coagulopathic state seen after cardiopulmonary bypass. Occasionally, when smaller infants (less than 3 kg) are encountered, a smaller conduit would seem to be appropriate. In an effort to avoid shunt thrombosis seen with the 3-mm PTFE conduit, saphenous vein homografts have been used since January 1998. Favorable experience with saphenous vein homograft-constructed systemic arterial shunts have been reported for the treatment of children with a variety of heart defects, resulting in ductal-dependent or inadequate pulmonary circulation [3, 4]. We report our entire experience using saphenous vein homograft-constructed modified Blalock–Taussig (BT) shunts as part of the Norwood operation for hypoplastic left heart syndrome and its variants.
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Material and methods
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From January 1998 to April 1999, 25 infants underwent stage I Norwood palliation using a saphenous vein homograft-constructed modified BT shunt. All infants accepted for the Norwood operation by the first author were included. Mean age was 8.9 ± 10.7 days and mean weight was 3.1 ± 0.5 kg, with 9 patients weighing 3 kg or less. Common heart defects were aortic atresia, mitral atresia or stenosis and double-outlet right ventricle, and unbalanced atrioventricular septal defect (Table 1). The operative technique was modeled after Dr Norwood’s technique. The proximal anastomosis for the BT shunt at the distal innominate artery was constructed either during circulatory arrest or before initiation of cardiopulmonary bypass. The distal anastomosis to the pulmonary artery confluence was constructed during the early rewarming period (Fig 1). The distal anastomosis was inspected through the defect in the pulmonary artery confluence before closing this defect. Saphenous vein homografts were supplied by Cryolife (Kennesaw, GA). All saphenous vein homografts were blood type O, Rh negative. Storage and thawing of homograft tissue was in accordance to guidelines from the supplier. Generally, a 3.5-mm graft was used for an infant 3.5 kg or larger, a 3-mm graft for an infant weighing 2.6 to 3.4 kg, and a 2.5-mm graft for infants weighing 2.5 kg or less. Choice of the BT shunt size was also dependent on the absence or presence of increased pulmonary vascular resistance, source of inflow, and perceived ventricular function.
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Fig 1. Angiogram demonstrating a centrally placed modified Blalock–Taussig shunt with good branch pulmonary arterial growth.
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Results
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No shunt thrombosis was seen in the acute perioperative period, despite the routine practice of platelet and cryoprecipitate administration after cardiopulmonary bypass. Twelve patients had a 3.0-mm or smaller saphenous vein homograft placed as the modified BT shunt. Mean shunt size was 3.2 ± 0.3 mm for the group. The average length of hospital stay was 23 ± 13 days after the initial Norwood operation. Thirty-day hospital mortality was 2 of 25 (8%), with neither death related to the systemic arterial to pulmonary artery shunt. Complications included vascular catheter-related sepsis (n = 3), sternal wound infection (n = 1), and necrotizing enterocolitis (n = 5) treated successfully without abdominal operation.
Three patients had their systemic arterial shunts "banded" to reduce pulmonary blood flow. There were 5 other pulmonary blood flow related complications. Patient no. 13 had her modified Blalock shunt revised because of stenosis of the distal anatomosis, at 20 days after her initial operation. Patients no. 9 and 17 were discovered to have innominate artery stenosis, treated successfully by transcatheter balloon dilation, at approximately 2 months following their Norwood operation. At one week postoperatively, patient no. 17 was found to have stenosis of the origin of the right branch pulmonary artery, which was successfully treated by division of adventitial fibrous bands. Patient no. 25 had patch enlargement of her proximal right pulmonary artery 17 days after the Norwood operation.
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Comment
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Although saphenous vein homograft has proved to be an acceptable conduit for arterial reconstruction since initial description of its use [4, 5], many authors have become less enthusiastic because of suboptimal long-term outcome, probably related to chronic rejection of the donor graft [6, 7]. More recently, however, Danilowicz and colleagues [2], Bogats and associates [3], and Alexander (James Alexander, MD, personal communication, 1997) have reported the successful use of saphenous vein homograft as a systemic arterial to pulmonary artery shunt in the palliation of cyanotic heart defects in children. Because most children are now palliated for a brief period, generally a few months, we think that it was a reasonable conduit for the modified BT shunt. Samples of the explanted grafts at 6 months have demonstrated lack of inflammation and an intact endothelium (Figs 2–4).
There was no incidence of aneurysmal dilatation in children palliated up to 7 months in our experience. Long-term palliation with a saphenous vein BT shunt has been reported by Bogats and coworkers [3].
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Fig 2. Histomicrograph of a freshly thawed saphenous vein homograft. (Hematoxylin and eosin; x400 before 50% reduction.)
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Fig 3. Histomicrograph of explanted saphenous vein homograft 6 months later. Note lack of inflammatory cells and intact endothelium. (Hematoxylin and eosin; x100 before 50% reduction.)
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Fig 4. Histomicrograph of explanted saphenous vein homograft. (Hematoxylin and eosin; x400 before 50% reduction.)
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Saphenous vein homograft offers many theoretical advantages over the more commonly used PTFE grafts. Its lack of thrombogenicity is a major advantage in this application as part of the Norwood palliation. Administration of platelets in this group of patients has not resulted in shunt thrombosis, whereas shunt thrombosis had previously been observed occasionally with the PTFE grafts, particularly with rapid correction of postoperative coagulopathy. In the 3-month period before January 1998, 2 neonates had acute clotting of their BT shunts. These events led ultimately to their deaths. This anecdotal experience would suggest that the saphenous vein homograft shunts are more resistant to acute thrombosis with rapid correction of the infant’s coagulopathy after cardiopulmonary bypass. This diminished thrombogenicity also allows further "adjustment" of the shunt after its initial placement. "Banding" of the modified BT shunt in 3 patients successfully reduced their pulmonary blood flow (Fig 5). Occasionally, in the smaller neonates whose pulmonary vascular resistance is not elevated, one may be faced with excessive pulmonary blood flow at the expense of systemic cardiac output. In these instances, we have been able to narrow the saphenous vein homograft, with less concern for shunt thrombosis. This "banding" process may be rendered more objective by using a small segment of PTFE graft. For example, if a 3.5-mm BT shunt had been placed during the Norwood procedure, and this size provided excessive pulmonary blood flow in the postoperative period, the surgeon may narrow the BT shunt by placing a short segment of a 4-mm PTFE graft around the existing saphenous vein homograft. The PTFE graft is cut longitudinally and placed around the saphenous vein graft. By reapproximating the cut edges of the PTFE graft, the surgeon would force the external diameter of the saphenous vein to become close to 4.0 mm. Cryolife has stated that the external diameter of the vein graft is 1 mm larger than the luminal size. This sizing guideline is generally consistent with our experience. This procedure effectively reduces the luminal size of the BT shunt to be closer to a 3.0-mm graft. As expected, the thawed cryopreserved grafts handle and behave like normal human saphenous vein and their anastomoses are much more hemostatic than the usual PTFE graft. Theoretically, smaller vein grafts should be available, offering an appropriately smaller conduit for the smaller neonates, while synthetic grafts are 3 mm or larger. Lastly, in the occasional occurrence of bacteremic infection, we speculate that the homograft may be much less likely to become a source of persistent infection. In the great majority of patients, the lumen of the saphenous vein homograft contains no pseudointimal deposition, as is seen with a PTFE graft, when the BT shunt is taken down a few months later during conversion to a bidirectional Glenn shunt.
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Fig 5. Angiogram of a "banded" saphenous vein graft modified Blalock–Taussig shunt at 3 months’ follow-up.
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There are some distinct disadvantages to using the saphenous vein homograft for the BT shunt. Availability of the appropriate size may not always be possible. Because the supplier had largely preserved these grafts for use in adults, there is a tendency to undersize these grafts. On close scrutiny, a vein graft labeled as 3 mm may be a 3.5-mm graft. This error of 0.5 mm is unacceptable in our practice. This inaccuracy in sizing had led to further subsequent shunt interventions in some of our patients, particularly early in our experience. Leaving the defect in the pulmonary artery confluence until after completion of the distal shunt anastomosis allows examination and validation of the internal lumen of the graft. Lastly, our hospital is charged more for the saphenous vein homograft than a PTFE graft.
Despite these disadvantages, our experience suggests that the saphenous vein homograft is an acceptable conduit for the modified Blalock shunt as part of the Norwood operation. With further experience and improved, more accurate sizing and description, the saphenous vein homograft will likely become the superior graft material for construction of the Blalock shunt for the Norwood operation, particularly in the smaller infants.
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Discussion
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DR JOHN H. CALHOON (San Antonio, TX): Doctor Tam, congratulations on a very nice article describing some excellent results. Three quick questions. With what material do you band the shunt, or do you use a stitch? Do you use aspirin or ibuprofen postoperatively for any period of time? And how do you size the shunt for your Norwoods? In other words, is there a size range where you would want to get a shunt that is 2-
or 3, is there a size that you would go for a shunt that is 3 or 3-, et cetera?
Thank you.
DR TAM: The size of the shunt in my practice, as I said, is determined mainly by the size of the patient plus the presence or absence of increased pulmonary vascular resistance. We occasionally will see patients that may not have an innominate artery, in which case the shunt is taken from the right common carotid. In that instance I would tend to upsize the shunt about 0.5 mm. Typically for an infant under 3.5 kg I would use a 3-mm shunt. When you get to below 2.5 kg I would try to use a 2.5-mm shunt.
We do routinely put patients on aspirin, but typically that is after the initial 5 or 6 days or so in the ICU.
Lastly, in the few infants in whom pulmonary blood flow seemed to be excessive, in whom reducing pulmonary blood flow seemed to be advantageous, what we have done is to use a short length of Gore-Tex to band the saphenous vein so that you have some control over the final size of the modified BT shunt.
DR THEODORE C. KOUTLAS (Greenville, NC): Doctor Tam, congratulations on an outstanding series. I just want to know, are you using this shunt in diagnoses other than hypoplastic left heart syndrome?
DR TAM: Yes, I have. I did not have time to mention the two other articles that had previously been published for other heart defects with inadequate or ductal-dependent pulmonary circulation, and also Dr Jim Alexander has been using the saphenous vein homograft in occasional patients for the last 3 or 4 years. I do not know the exact details because his data have not been published.
Before I started using the saphenous vein homografts for the hypoplasts, I used them for other newborns who needed shunts, particularly the smaller infants in the 1- to 2-kg range.
DR J. MARK REDMOND (Baltimore, MD): I would also like to echo the comments of the other speakers; the excellent results are plain for us to see. I have two questions for you. First, how exactly do you size the saphenous vein graft when you are in the operating room? As you know, when you inflate the graft, it enlarges significantly, or that is what I have found. Is the cryopreserved saphenous vein less likely to stretch than a freshly harvested saphenous vein? And my second question is, I assume several of these patients have reached the second stage of your palliation. How many of them have had arteriograms or shuntograms and how do they look? The one that you showed us looked to me as if the vein graft had narrowed proximally. Does that just happen to be a quirk of the arteriogram or is that something that you have seen before? Thank you.
DR TAM: The angiogram that I had shown is a child who had his BT shunt banded, so that is why that shunt is narrowed. All of the children in this series have had subsequent angiograms. We have not seen any narrowing in the saphenous vein conduits aside from the instances in which the conduit was intentionally narrowed to control pulmonary blood flow.
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Footnotes
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This article has been selected for the open discussion forum on the STS Web site: http://www.sts.org/section/atsdiscussion/
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References
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- Tam VKH, Emge FC, Miller B, Bailey J, Cuadrado AR. Postoperative management & hemodynamics of infants after first stage Norwood operations. Proceeding of the Second World Congress of Pediatric Cardiology and Cardiac Surgery, Honolulu, HI, May 11–15, 1997. Armonk, NY: Futura, 555–6.
- Danilowicz D, Ishmael RG, Doyle EF, Isom OW, Colvin SB, Greco MA. Use of saphenous vein allografts for aortopulmonary artery anastomoses in neonates with complex cyanotic congenital heart disease Pediatr Cardiol 1984;5:13-17.[Medline]
- Bogats G, Kertesz E, Toszegi A, Kovacs GS. Modified Blalock–Taussig shunt using allograft saphenous vein. six years’ experience. Ann Thorac Surg 1996;61:58-62.[Abstract/Free Full Text]
- Jackson DR. Living homologous saphenous vein; a new graft conduit for use in arterial reconstruction Angiology 1970;21:I-II.[Medline]
- Tice DA, Santoni E. Use of saphenous vein homografts for arterial reconstruction. a preliminary report. Surgery 1970;67:493-498.[Medline]
- Ochsner JL, Lawson JD, Esking SJ, Mills NL, DeCamp PT. Homologous veins as an arterial substitute. long-term results. J Vasc Surg 1984;1:306-313.[Medline]
- Carpenter JP, Tomaszewski JE. Human saphenous vein allograft bypass grafts. immune response. J Vasc Surg 1998;27:392-399.[Medline]
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Abstract
Introduction
