Physical Characteristics of Implanted Polytetrafluoroethylene Grafts A

Preliminary Report

Kempczinski, MD \s=b\ Despite the widespread clinical use of polytetrafluoroethylene (PTFE) grafts, few reports dealing with their physical prop-

Richard F.

erties have appeared in the literature. In the past 20 months, 17 such grafts have been implanted into 15 patients threatened with limb loss, with an 88% immediate graft patency. Postoperatively, all patients underwent periodic evaluations; arteriograms were obtained in four. The effect of knee flexion on graft function was also studied. All grafts were found capable of withstanding cuff pressures in excess of 300 mm Hg without occlusion. With 90\s=deg\ flexion, the grafts kinked crossing the knee joint but a pressure gradient or decrease in pulsatile blood flow did not develop. This remarkable resistance to external compression should render these grafts especially valuable for extra-anatomic bypass.

(Arch Surg 114:917-919, 1979)

first clinical use of polytetrafluoroethylene (PTFE) as a vascular graft was in the portal venous system.1 Early experimental results as an arterial substitute were equally encouraging.- Since then, the manufacturer (W. L. Gore & Associates Ine) estimates that more than 60,000 such grafts have been implanted in humans. Despite such widespread application, there have been no reports describ¬ ing the unique physical characteristics of this material

The

following implantation.

MATERIAL AND METHODS In the past 20 months, 6-mm straight, tube grafts of PTFE were inserted into 17 legs of 15 patients at the Veterans Administration Hospital, Denver. All patients were facing impending limb loss and a suitable autogenous saphenous vein was not available. In all cases, the proximal anastomosis was to the common femoral artery or to the limb of a previous aortofemoral graft. The distal anastomosis was to the popliteal artery below the knee (ten) or to individual calf arteries (seven). All grafts were placed in a subsartorial tunnel and crossed the popliteal fossa between the heads of the gastrocnemius muscle. The length of each graft was carefully tailored so that with the knee fully extended there was no tension on either anastomosis and the graft lay, without redundancy, close to the course of the normal vessel. In the recovery room, all patients received aspirin suppositories (650 mg) twice daily. When they were able to take medication orally, they were given aspirin (325 mg) twice daily and sulflnpyrazone (200 mg) four times daily. This therapy was continued for six months.

Laboratory Studies All patients were seen in the vascular diagnostic laboratory preoperatively and at regular postoperative intervals. Studies included segmental limb pressure (SLP) and pulse volume record¬ ing (PRV) at the thigh, calf, and ankle of each leg. The technical details of such studies have been previously described.' Vascular

for publication Feb 2, 1979. From the Department of Surgery, University of Colorado School of Medicine and the Veterans Administration Hospital, Denver. Reprint requests to Department of Surgery, Veterans Administration Hospital, 1055 Clermont St, Denver, CO 80220 (Dr Kempczinski).

Accepted

In addition to these standard determinations, the knee was flexed 90° and a repeated measurement of the calf SLP and PVR was obtained on patients with patent PTFE grafts.

Arteriography Standard, biplane, translumbar arteriograms were obtained for all patients preoperatively. Following completion of the distal anastomosis and passage of the graft through its subsartorial tunnel, intraoperative arteriograms were obtained to confirm the adequacy of the anastomosis and to assess distal runoff. Four legs with patent PTFE grafts were studied arteriographically at intervals ranging from two weeks to two months postim¬ plantation. In addition to posteroanterior (PA) views, the knee of the grafted leg was flexed 90° and lateral arteriograms were obtained. In one leg with

36a PTFE femoropopliteal graft, a large (18 bladder) pneumatic cuff was placed around the thigh prior to arteriography. The cuff was inflated to 300 mm Hg and a PA arteriogram was obtained. One of our cases was uniquely informative and is described in cm

detail.

REPORT OF A CASE

67-year-old

with chronic atrial fibrillation and no his¬ to his family physician with the sudden onset of a cold, painful, right leg. He was treated expectantly for four months despite severe, progressive pain at rest. When cyanosis of the foot developed, he was referred to the vascular service. Arteriograms were obtained shortly after admission and de¬ monstrated complete occlusion of the right superficial femoral, popliteal, and proximal tibial arteries. The remaining vessels in the abdomen and lower left leg were patent and remarkably free of atherosclerosis. Rather than proceeding immediately with a graft to the small, distal, anterior tibial artery, which was the only patent vessel demonstrated below the knee, the popliteal artery was explored. It was soft, but filled with thrombus. Despite the chronicity of the embolus and the extent of the distal thrombosis, it was decided to attempt balloon catheter thromboembolectomy through a popliteal arteriotomy. Following multiple passes of the catheter, both distally into each of the tibial arteries and proximally to the common femoral artery, a large amount of thrombus was recov¬ ered and blood flow was restored. However, the arterial thrombus had begun to organize and could not be completely removed. An intraoperative arteriogram of the superficial femoral artery demonstrated multiple, small filling defects along its course. Since this vessel was unlikely to remain patent, it was decided to proceed with a PTFE femoropopliteal graft. The patient's own superficial femoral artery was not ligated. Postoperatively, pedal pulses were easily palpable and the right foot was free of pain. To prevent further emboli from his heart, the patient received full-dose heparin therapy for five days, and then therapy was converted to warfarin sodium. Arteriograms were obtained two weeks later and demonstrated patency of both of PTFE graft as well as the patient's own artery (Fig 1 to 3). Despite this competitive flow, the graft remained A

man

tory of claudication

came

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Fig 1.—Right femoral gram PTFE

demonstrating

arterio¬ a

patent

femoropopliteal bypass graft (arrows) and patent super¬

ficial femoral artery.

Fig 2.—Femoral arteriogram with pneumatic cuff around thigh (ar¬ rows) inflated to 300 mm Hg. All

Fig 3.—Arteriogram with right knee flexed 90°. Top, Early phase of injection showing rapid flow in femoral artery (A) that crosses joint without kinking. Bottom, Several seconds later, artery is now emptying and PTFE graft (G) is opacified, demonstrating obvious kink at knee joint.

normal arterial flow is occluded by cuff but continues through PTFE graft.

patent for

more than three months, as confirmed by vascular laboratory studies. When the patient returned for his six month postoperative checkup, he was asymptomatic and pedal pulses were still palpable in his right foot. However, the SLP of his right thigh, which had previously been > 300 mm Hg, was now only 155 mm Hg. And arteriogram confirmed graft occlusion.

Two months later, the distal popliteal artery on the right occluded, but the leg remained free of pain at rest. Since the patient was not severely limited by his claudication, further

revascularization

was

not undertaken.

RESULTS

Eighty-eight percent (15/17)

of PTFE grafts

were

patent at the time of discharge, and all of these legs were

salvaged. The remaining two grafts were to isolated, small tibial arteries in desperate clinical situations. Both occluded within 24 hours and the legs required amputation. Followup is presently inadequate to draw meaningful conclusions on long-term graft patency. Segmental limb systolic pressures in all patients with patent PTFE grafts demonstrated incompressibility of the graft in the thigh despite cuff pressures up to 300 mm Hg. This observation was confirmed arteriographically (Fig 2), where the graft was seen to collapse centrally but maintain parallel, patent channels peripherally. This finding was

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vein.*·9 Its ability to remain patent in one of our patients for more than three months despite competitive, parallel flow in the superficial femoral artery suggests a remark¬ able degree of thromboresistance. This thromboresistance has been attributed to several characteristics. Internodal pore size, which can be altered during graft fabrication, was quickly found to be critical. When it averaged 22 µ or less, there was complete fibroblastic ingrowth thru the graft with formation of a thin, adherent neointima, resulting in a graft patency of 88%.7 Greater average pore size led to a precipitous decrease in

patency. The PTFE is remarkably inert and provokes little surrounding inflammation. In addition, the pores have a strong, electronegative potential. Both features are believed important in the graft's resistance to thrombo¬

Fig 4.—Arteriogram of right femoropopliteal PTFE graft on anoth¬ er patient two months after implantation. There is kink (arrow) in graft as it crosses knee, but flow does not appear to be impeded.

sis.' Several authors'1" have described a progressive neointi¬ mal fibrous hyperplasia in canine PTFE grafts that could be suppressed by pretreating the animals with antiplatelet drugs."' All of our patients have received aspirin and sulfinpyrazone immediately postoperatively, and have been maintained on this regimen for six months. We have not yet had the opportunity to examine any long-term grafts histologically to evaluate the efficiency of this

regimen.

Fig 5.—Segmental calf systolic pressure (SLP) and PVR in the patient whose arteriogram is shown in Fig 4 demonstrating no change in pressure or flow across the knee when it is flexed 90°. Left, Knee straight, SLP 130 mm Hg. Right, 90° flexion, SLP 125 mm Hg.

present in the immediate postoperative period and has persisted in our longest followup period (ten months). In addition, 29% (2/7) of the femorotibial bypass grafts were to the distal part of the lower leg, thus completely spanning the area beneath the calf cuff. In both cases, the postoper¬

ative calf cuff pressure was > 300 mm Hg, indicating a similar inability to occlude graft flow. All four legs in which postoperative arteriograms were obtained demonstrated obvious kinking of the graft as it crossed the flexed knee (Fig 3). This finding persisted unchanged as late as two months postimplantation (Fig 4). However, in no case did this kink appear to impede blood flow as verified by the absence of a pressure gradient or an alteration in the PVR across the flexed knee (Fig 5). COMMENT

The PTFE grafts are composed of expanded Teflon arranged as nodules connected by thin fibrils. This materi¬ al was originally developed for industrial use as sealing tape for pipe fittings, but, with suitable modification, is now finding widespread use as a vascular substitute in a variety of challenging clinical situations. In'··"' addition to and portal successful replacement of the vena cava1 vein," it has been used as a small arterial substitute in dogs with excellent patency.- Based on such encouraging experimental results, it was used clinically in limb salvage situations in which autogenous vein was not available, and early life table analysis of such patients indicates patency rates comparable with those achieved with saphenous '

The marked resistance to pneumatic compression of PTFE grafts in the leg is a characteristic unique to this material and one that we have not observed with either Dacron or autogenous vein in a similar position. Further¬ more, although these grafts kinked when crossing the flexed knee, a pressure gradient or decrease in pulsatile blood flow across this area was not demonstrable. This physical characteristic should render PTFE especially suit¬ able for extra-anatomic bypasses in which the grafts lie in a subcutaneous tunnel and are vulnerable to extrinsic

compression. Although the precise explanation for the remarkable thromboresistance of PTFE grafts has not been defined, it is clear that they possess several, unique physical charac¬ teristics that warrant continued clinical trial. References 1. Soyer T, Lempinen M, Cooper P, et al: A new venous prosthesis. Surgery 72:864-872, 1972. 2. Matsumoto H, Hasegawa T, Fuse K, et al: A new vascular prosthesis for a small caliber artery. Surgery 74:519-523, 1973. 3. Kempczinski RF, Rutherford RB: Current status of the vascular diagnostic laboratory, in Rob C (ed): Advances in Surgery. Chicago, Year

Book Medical Publishers, Inc, 1978. 4. Fujiwara Y, Cohn LH, Adams D, et al: Use of Gortex grafts for replacement of the superior and inferior venae cavae. J Thorac Cardiovasc Surg 67:774-779, 1974. 5. Smith DE, Hammon J, Anane-Sefah J, et al: Segmental venous replacement: A comparison of biological and synethetic substitutes. J Thorac Cardiovasc Surg 69:589-598, 1975. 6. Norton L, Eiseman B: Replacement of portal vein during pancreatectomy for carcinoma. Surgery 77:280-284, 1975. 7. Campbell CD, Goldfarb D, Roe R: A small arterial substitute:

Expanded microporous polytetrafluoroethylene: Patency versus porosity. Ann Surg 182:138-143, 1975. 8. Burnham SJ, Flanigan DP, Goodreau JJ, et al: Nonvein bypass in below-knee reoperation for lower limb ischemia. Surgery 84:417-424, 1978. 9. Fry PD, Robertson ME: Initial experience with the polytetrafluoroethylene graft for limb salvage. Am J Surg 136:193-197, 1978. 10. Oblath RW, Buckley FO Jr, Green RM, et al: Prevention of platelet aggregation and adherence to prosthetic vascular grafts by aspirin and dipyridamole. Surgery 84:37-43, 1978.

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Physical characteristics of implanted polytetrafluoroethylene grafts: a preliminary report.

Physical Characteristics of Implanted Polytetrafluoroethylene Grafts A Preliminary Report Kempczinski, MD \s=b\ Despite the widespread clinical use...
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