Venous prostheses: Improved patency with external stents

JOURNAL

OF SURGICAL

RESEARCH

Venous

36,

306-3

Prostheses:

11 (1984)

Improved

Patency

ROBERT J. ROBISON, M.D., PAMELA WILLIAM P. DESCHNER, M.D., NICHOLAS HAROLD Department

KING,

of Surgery,

Presented

M.D.,

S. BEIGH,

AND

J. SEARS, JOHN W.

with M.D., M.D., BROWN,

Section of Cardiothoracic Surgery, Indiana Center, Indianapolis, Indiana 44223

External

Stents

ANDREW

C. FIORE,

J. STEVEN M.D.’ University

at the Annual Meeting of the Association for Academic Syracuse, New York, November 2-5, 1983

WHITAKER,

Medical

Surgery,

A uniformly successful prosthesis for replacement in the venous system has not been developed. This study assesses the effect of external stents on the patency of polytetrafluoroethylene (PTPE) grafts in the infrarenal vena cava. Under general anesthesia, 2 I mongrel dogs underwent midline laparotomy. The infrarenal vena cava was resected and replaced by a standard segment (8 cm X 10 mm) of stented PTPE (12 dogs) and nonstented PTFE (9 dogs). Patency was assessed by contrast venography and the results compared between the two groups. The 7-, 30-, and 90&y patency was 12/12, 10/12, and 9/12, respectively, for stented PTPE and 6/9, 2/9, and 2/9, respectively, for nonstented PTPE. The patency of externally stented PTFE at 30 and 90 days was significantly better than grafts fashioned from PTPE alone (P < 0.05 by chi-square analysis). These data demonstrate that external stenting improves the early patency of PTFE prostheses in the infrarenal vena cava. Consideration should bc given to the clinical use of externally stented PTPE when prosthetic replacement in the venous system is required.

INTRODUCTION

A consistently successfulprosthesis for the replacement in the venous system, unlike the arterial system, has not as yet emerged [2, 3, 8, 14, 21, 251. Failure of prosthetic grafts has been attributed to the phasic venous flow and external graft compression.The useof external graft support with stents [ 171 and a thromboresistant luminal surface of PTFE [23] have been suggestedas methods to improve graft patency. Using a canine model, Fiore et al. [6] demonstrated that externally stentcd PTFE achieved a patency rate equal to autologous vein as a thoracic caval substitute. The infrarenal vena cava, because of its lower flow and positive intraabdominal pressure, has proved to be a stringent test for venous substitutes. The purpose of this study was to (1) assessthe effect of external stenting on the patency of PTFE (Gore-Tex’) grafts, and (2) ’ Author to whom requests for reprints should bc addressed * Gore-Tex is a registered trademark of the W. L. Gore and Associates, Inc. in Elkton, Maryland. 0022-4804/84 Copyright All ri&u

!§1.50

0 1984 by Academic Press, Inc. of reproduction in any form resewed.

306

determine if graft patency could be achieved in the difficult infrarenal vena cava position. METHODS

Twenty-one mongrel dogs ( 18-22 kg) were anesthetized with intravenous thiopental sodium (25 mg/kg) and mechanically ventilated with oxygen and halothane through an endotracheal tube. The infrarenal vena cava was exposedthrough a midline abdominal incision and isolated from the renal veins superiorly to the confluence of the common iliac veins inferiorly. The lumbar and right gonadal veins were ligated. After systemic heparinization (1.5 mg/kg) occluding clamps were applied. The infrarenal vena cava was resectedand replaced with a standard segment ( 10 mm X 8 cm) of externally stented PTFE in 12 dogs and nonstented PTFE in 9 dogs (Figs. 1, 2). Prophylactic antibiotics (cefamandole) were given prior to the procedure and for 5 days postoperatively. No postoperative anticoagulants or antiplatelet agents were used. The PTFE pore size was 30 pm in both groups.

ROBISON

FIG. 1. Technique: (A) Excision externally stented PTFE.

ET

of infmrenal

AL.:

VENOUS

inferior

Graft patency was assessed by contrast venography using 50% sodium diatrizoate (Hypaque) at 7, 30, and 90 days postoperatively

FIG. 2. Grafts:

(A) Externally

stented

307

PROSTHESES

vena cava. (B) Replacement

with

10 mm X 8 cm

(Fig. 3). The animals were sacrificed and the excised grafts were examined grossly and histologically. The difference in patency rates be-

PTFE.

(B) Nonstented

PTFE.

308

JOURNAL

FIG. 3. Venography: Patent the infrarenal vena cava.

OF SURGICAL

externally

stented

RESEARCH:

PTFE in

tween groups was assessed for statistical significance using chi-square analysis. RESULTS

Venography results are tabulated in Table 1. At 7 days, all of the stented grafts were patent, while 6 of 9 of the nonstented grafts remained open. At 30 days, 10 of the 12 stented grafts remained patent, while only 2 of the 9 nonstented grafts were open. By 90 days, 1 more stented graft occluded, while the 2 nonstented grafts remained patent. The difference in the patency rates between the two groups was not significant at 7 days (P < 0.2), but achieved significance at 30 and 90 days (P < 0.05).

Gross evaluation of occluded grafts revealed thrombus formation within the grafts, while patent grafts developed a smooth neointimal lining (Fig. 4). Histologically, occluded grafts developed thick, intraluminal linings composed of thrombus and neointima, while patent grafts developed a thin, nonfenestrated neointimal surface (Fig. 5). DISCUSSION

Venous replacement quired following tumor

is occasionally reresection [ 1, 4, 2 11,

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1984

penetrating trauma [20], and venous reconstruction. Autologous vein has been the graft of choice, but adequate vein is not always available or convenient to harvest. Research efforts have been directed toward development of the ideal venous prosthesis. Causes for poor patency include (1) phasic venous flow, (2) anastomotic narrowing, and (3) external graft compression. The phasic flow in the venous system predisposes to graft thrombosis. Efforts directed to prevent thrombosis include increasing flow velocity with an arteriovenous fistula, reducing blood coagulability, and increasing the thromboresistance of the graft’s intraluminal surface. Mitsuoka et al. [ 191 improved inferior vena caval graft patency from 12 to 60% by creating a femoral arteriovenous fistulae. The potential morbidity of this procedure, however, limits the clinical application. Antithrombotic agents, in particular those affecting platelet aggregation, have been used primarily in the arterial system [5, 16, 181. Improved patency has also been demonstrated, however, in the venous system [7, 9, 10, 241. Thomas et al. [24] found an improved inferior vena caval patency (16 vs 90%) using platelet inhibition with phenylbutazone. These studies have been performed in animal models and their effect on graft patency in humans has not been tested. The thromboresistance of the graft material is an important factor affecting patency. PTFE has shown the highest patency rates when compared to other prosthetic materials in animal models. Smith et al. [23] had a 3-month patency rate of 83% using nonstented PTFE to replace the suprarenal inferior vena cava as compared to 57% for lypholized homograft and 14% for fibrocollogenous tubes. PTFE is TABLE

I

PROSTHETICPATENCYASDETERMINED BYCONTRASTVENOGRAPHY Group

7 days

30 days

90 days

Stented Nonstented P

12112 619 10.2

10/12 219 <0.05

9112 219 -co.05

ROBISON ET AL.: VENOUS

PROSTHESI

FIG. 4. Gross evaluation: (A) Thin neointima in patent externally stented PTFE graft. (B) Thrombus in clotted nonstented PTFE graft.

an inert, synthetic polymer with electronegative pores that may impede thrombosis. PTFF pore size appears to influence the early patency. Heydorn et al. [ 12, 131 demonstrated improved results in PTFE grafts with 30-pm pores, when compared to grafts of 5- or 90pm porosity. They demonstrated that the 30pm size was associated with a thinner neointima and sufficient incorporation into the graft by the host tissue. The 5-pm porosity grafts failed to develop an adequate neointima and host incorporation, while the 90-pm pore grafts were associated with increased tissue ingrowth and transmural fibrosis. We used 30pm pore PTFE for this study, considering it to have the most desirable properties for this application. Prosthetic seeding with endothelial cells appears to increase the thromboresistance of the prosthetic graft. Herring et al. [ 1 l] demonstrated a reduced clot formation (76 vs 32%) in seeded Dacron arterial grafts. Similar studies are being conducted for grafts in the venous system, but results are not yet available.

Anastomotic irregularities also influence graft patency. Horsch et al. [ 151 demonstrated that slow intraoperative graft flow, secondary to obstruction, correlated with poor postoperative patency. The venous graft anastomoses were the sites of neointimal hyperplasia in grafts that occluded. The use of an external stent may be a major factor in the improved patency of our stented grafts. External graft compression by positive extraluminal pressures may be the single most important determinant of prosthetic failure in the venous system. External graft support with stenting prevents graft collapse. External graft stenting has been used by others with variable success [6, 17, 221. Fiore et al. [6] compared the 30&y patency of Dacron, glutaraldehydefixed pericardium, nonstented PTFE and externally stented PTFE grafts to autologous vein as a thoracic caval substitute in dogs. While the patency of autologous vein was 1OO%,both Dacron and glutaraldehyde-fixed pericardial grafts had significantly lower patency rates of 0 and 50%, respectively. Nonstented PTFE

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l*

.

.

FIG. 5. Histology: (A) Longitudinal section of a patent externally stented PTFE graft demonstrating a thin nonfenestrated neointimal surface. V = vein. G = graft. (hematoxylin and eosin). (B) Longitudinal section of an occluded nonstented PTFE graft demonstrating a thick, intraluminal lining of thrombus and neointima.

grafts had a patency rate similar to autologous vein (75%), while the patency of externally stented FTFE equaled that of autologous vein. In this study, we elected to assessexternally stented PTFE in the more difficult position of the infrarenal cava. Previous studies have demonstrated that graft patency in this lo-

cation is lower than that of the thoracic vena cava. Better patency in the thoracic cava has been attributed to the negative intrathoracic pressure tending to keep the grafts patent, while the positive intraabdominal pressure tends to compress unsupported grafts [3]. A readily available prosthesis in various

ROBISON ET AL.: VENOUS

sizes is needed for clinical venous replacement. The poor patency of arterial prostheses placed in the venous system has discouraged their use and has favored modified grafts of autologous vein. Previous studies from our laboratory have shown that externally stented PTFE is comparable to autogenous vein in the thoracic cava of dogs. Our current study demonstrates that external stenting of PTFE grafts significantly improves the patency of this material in the difficult infrarenal vena cava (75 vs 22% at 90 days). Consideration should be given to the use of externally stented PTFE when prosthetic replacement in the venous system is required. ACKNOWLEDGMENTS Special thanks to Ms. Vickie Trump, Mr. Manuel Mpinga, Mr. Andrew Hun&z, and Mr. Greg Hegi for their technical assistance and Mrs. Janean Pennington for secretarial assistance for this project. REFERENCES 1. Chiu, C. J., Terzis, J., and MacRae, M. C. Replacement of superior vena cava with the spiral composite vein graft. Ann. Thorac. Surg. 17: 555, 1982. 2. Collins, H. A., Burrus, G., and De Bakey, M. E. Experimental evaluation of grafts in the canine inferior vena cava. Amer. J. Surg. 99: 40, 1960. 3. Dale, W. A., and Scott, H. W. Grafts of the venous system. Surgery 53: 52, 1963. 4. Doty, D. B. Bypass of superior vena cava. J. Thorac. Cardiovasc. Surg. 83: 326, 1982. 5. Feins, R. H., Roedersheimer, R., Green, R. M., and DeWeese, J. A. Platelet aggregation inhibition in human umbilical vein grafts and negatively charged bovine heterografts. Surgery 85: 395, 1979. 6. Fiore, A. C., Brown, J. W., Cromartie, R. S., Peigh, P. S., Ofstein, L. C., Deschner, W. P., Sears, N. J., and King, H. Prosthetic replacement for the thoracic vena cava.J. Thorac. Cardiovasc. Surg. 84: 560, 1982. 7. Friedman, E. W., Frank, H. A., and Ponn, R. Patency of venous grafts in small veins. Arch. Surg. 112: 1072, 1977. 8. Haimovici, H., Hoffert, P. W., Zinicola, N., and Steinman, C. An experimental and clinical evaluation of grafts in the venous system. Surg. Gynecol. Obstet. 131: 1173, 1970. 9. Haimovici, H., Zinicola, N., Noorani, M., and Hoffert, P. W. Vein grafts in the venous system.Arch. Surg. 87: 542, 1963. 10. Hasegawa, T., Matsumoto, H., Yamamoto, M., Fuse, K., Mizuno, A., and Saigusa, M. Prosthetic replace-

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ment of superior vena cava. Anti-platelet-adhesive drug influence. Arch. Surg. 106: 848, 1973. 11. Herring, M. B., Dihey, R. S., Gardner, A. L., and Glover, J. L. Seeding of mechanically derived endothelium on arterial prostheses. Biologic and Synthetic Vascular Prostheses. New York: Grune & Stratton, 1982. 12. Heydom, W. H., Geasling, J. W., Moores, W. Y., Lollini, L. O., and Gomez, A. C. Changes in the manufacture of expanded microporous polytetrafluoroethylene: Effects on patency and histological behavior when used to replace the superior vena cava. Ann. Thorac. Surg. 27: 173, 1979. 13. Heydom, W. H., Zajtchuk, R., Miller, J., and Schuchmann, F. Gore-Tex grafts for replacement of the superior vena cava. Ann. Thorac. Surg. 23: 539, 1977. 14. Hiratzka, L. F., and Wright, C. B. Experimental and clinical results of grafts inthe venous system:A current review. J. Surg. Rex 25: 542, 1978. 15. Horscb, S., Pichlmaier, H., Walter, P., and Landes, T. Replacement of the inferior vena cava and iliac veins with heterologous grafts in animal tests.Surgery 84, 644, 1978. 16. Josa, M., Lie, J. T., Bianco, R. L., and Kaye, M. P. Reduction of thrombosis in canine coronary bypass vein grafts with Dipyridamole and Aspirin. Amer. J. Cardiol. 47: 1248, 1981. 17. Leshnower, A. C., Schumacker, H. B., and Shariatzadeh, A. N. Experimental studies with synthetic venous bypass grafts, including a new experimental model. Amer. J. Surg. 128: 392, 1974. 18. McCann, R. L., and Fuchs, J. C. A. Aspirin and Dipyridamole decrease intimal hyperplasia in experimental vein grafts. Ann. Surg. 191: 238, 1980. 19. Mitsuoka, H. and Howard, J. M. Experimental grafting of the inferior vena cava. J. Cardiovasc. Surg. 9: 190, 1968. 20. Rich, N. M., Hughes, C. W., and Bat&, J. H. Management of venous inferior. Ann. Surg. 171: 724, 1970. 21. Scherck, J. R., Kerstein, M. D., and Stansel, H. C. The current status of vena caval replacement. Surgery 76: 209, 1974. 22. Shore, J. M., Greenstone, S. M., Massell, T. B., Heringman, E. C., and Wagner, K. A comparative study of canine venous autografts. J. Cardiovasc. Surg. 5: 67, 1964. 23. Smith, D. E., Hammon, J., Anane-Sefah, J., Richardson, R. S., and Trimble, C. Segmental venous replacement. A comparison of biological and synthetic substitutes. J. Thorac. Cardiovasc. Surg. 69: 589, 1975. 24. Thomas, J. M., Price, Glynn, M. F. X., Rickwood, A. M. K., and Gough, M. H. Grafting of the major veins: The value of anti-thrombotic drugs to maintain patency. Brit. J. Surg. 63: 189, 1976. 25. Todd, R. S., Sive, E. B., DeJode, L. R., Danese, C., and Howard, J. M. Replacement of segments of the venous system. Arch. Surg. 87: 998, 1963.