Effects of a venous cuff at the venous anastomosis of polytetrafluoroethylene grafts for hemodialysis vascular access☆☆☆

Article Outline

• Abstract
• Patients and methods
  • Patients
  • Operative procedure
  • Follow-up
  • Analysis
• Results
  • Patient characteristics, trial end points, patency rates, complications, and interventions
  • Results of duplex scanning and fistulography at 3 months
  • Analysis of risk factors
• Discussion
• References
• Copyright

Abstract 

Introduction and Methods: The most frequent complication of polytetrafluoroethylene (PTFE) arteriovenous grafts for hemodialysis is thrombotic occlusion due to stenosis caused by intimal hyperplasia. This complication is also known for peripheral bypass grafts. Because the use of a venous cuff at the distal anastomosis improves the patency of peripheral bypass grafts, we considered that it might also improve the patency of PTFE arteriovenous grafts. Therefore, a randomized multicenter trial was carried out to study the effect of a venous cuff at the venous anastomosis of PTFE arteriovenous grafts on the development of stenoses and the patency rates. Results: Of the 120 included patients, 59 were randomized for a venous cuff. The incidence of thrombotic occlusion was lower in the cuff group (0.68 per patient-year) than in the no-cuff group (0.88 per patient-year; P = .0007). However, the primary and secondary patency rates were comparable. The cuff group tended to have fewer stenoses at the venous and arterial anastomoses when examined with duplex scan. Graft failure was higher in patients with an initial anastomosing vein diameter smaller than 4 mm (7 of 18 [39%]) than in those with a vein diameter of 4 mm or larger (16 of 88 [18%]; P = .052). Local edema, skin atrophy, and obesity yielded a higher risk on graft failure (23% vs 11%). Conclusion: A venous cuff at the venous anastomosis of PTFE arteriovenous grafts for hemodialysis reduced the incidence of thrombotic occlusions; stenosis at the venous anastomosis was reduced. However, this did not result in a better patency rate. Therefore, the venous cuff should not be used routinely. Initial vein diameter and local problems (edema, obesity, or skin atrophy) appear to be the most important risk factors for graft failure. (J Vasc Surg 2000;32:1155-63.)

Please see related commentary by Dr Julie A. Freischlag on pages 1235-6.

Although a radiocephalic arteriovenous fistula is still the method of first choice as vascular access for hemodialysis, polytetrafluoroethylene (PTFE) grafts are increasingly used as secondary access because of failure or the impossibility to create a radiocephalic arteriovenous fistula. This is due to the increase in the age and number of the population undergoing hemodialysis.¹, ² Older patients have a higher number of comorbidities like diabetes mellitus and cardiac disease and are more likely to have vascular problems.

The incidence of thrombotic occlusion of PTFE arteriovenous grafts is high and leads to graft failure rate of about 30% within the first year after implantation. Eighty percent of the thrombotic complications are caused by stenosis, which develops at the venous anastomosis or in the efferent vein.³, ⁴, ⁵ This stenosis consists of intimal hyperplasia (IH), an accumulation of medial smooth muscle cells in the intima that proliferates and deposits an extracellular matrix. This thickening of the vessel wall leads to critical stenosis, which jeopardizes graft flow.⁶ Much research has been conducted to reveal the causes of IH. Hemodynamic factors like compliance mismatch and high and low shear stress trigger the release of cellular and humoral factors from the endothelial cells and blood components.⁷, ⁸, ⁹, ¹⁰, ¹¹, ¹², ¹³, ¹⁴, ¹⁵ They induce vascular smooth muscle cell proliferation, migration, and matrix deposition, which results in IH.

Implantation of a venous patch or cuff at the distal anastomosis of prosthetic femorodistal bypass grafts leads to a decrease in graft thrombosis and an increased patency rate.¹⁶, ¹⁷, ¹⁸, ¹⁹ The cuff might improve flow hemodynamics at the graft-native vessel junction and could lead to less IH. We hypothesized that these cuffs or patches could also have a beneficial effect on the thrombosis and patency rate of PTFE graft fistulas. Therefore, a prospective, randomized study was performed, in which the incidence of stenoses and the number of complications and patency rates were compared in patients who received PTFE graft arteriovenous fistulas with or without a venous cuff implantation at the venous anastomosis.

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Patients and methods 

Patients 

A prospective, randomized trial was conducted between October 1994 and June 1998 in six hemodialysis centers. Patients who were considered for secondary access surgery or who had no suitable vessels for primary access were included, and all patients entered the study once. During the same study period, 346 nonrandomized access procedures were performed with native arteriovenous fistulas and upper arm grafts. Patients were randomized for a PTFE arteriovenous graft with or without a venous cuff by means of computerized randomization. Patient characteristics and the use of drugs were registered. The study was approved by the Ethics Committee of the hospitals concerned, and informed consent was obtained from each patient.

Operative procedure 

Thin-walled stretch PTFE grafts (Gore-Tex; W. L. Gore & Assoc, Flagstaff, Ariz) with an internal diameter of 6 mm and a wall thickness of 0.4 mm were positioned in a subcutaneous loop fashion in the forearm between the brachial artery and a suitable elbow vein, after the diameter of the vessels was measured with coronary probes that were calibrated with 0.5-mm increments. The minimum acceptable vein diameter for anastomosing was 2 mm. The vein segment was taken from the basilic vein in the forearm in 35 patients, from an upper arm vein in 4 patients, and from the greater saphenous vein in the ankle in 16 patients. In four patients in the cuff group, no suitable vein could be found to use as a cuff. These patients were analyzed in the cuff group according to the intention-to-treat principle, although we also performed an analysis without these patients, which left 55 patients in the cuff group. The results of both analyses were comparable; therefore, we only present the results of the whole group. The venous cuff was created according to the technique initially described by Tyrrell and Wolfe.²⁰ A vein segment of 6 cm was derived from the arm or ankle and was opened lengthwise and trimmed to a 5-mm width. A 1.5-cm long incision was made in the elbow vein, and the short side of the cuff was anastomosed to the proximal part of the venotomy. Subsequently, the long side of the cuff was sutured circumferentially to both sides of the venotomy. Finally, the abundant vein was trimmed and sutured to the proximal vein cuff. To enlarge the cuff opening, we partially opened the heel of the cuff with scissors. After vein cuff completion, the prosthesis was anastomosed to the cuff. Arterial and venous anastomoses were performed with running 7 × 0 polypropylene (Prolene) sutures. Prophylactic antibiotic therapy was given during each procedure. Coumarin was given postoperatively to all patients in a dosage that was sufficient for an adequate anticoagulation (international normalized ratio > 2.5).

Follow-up 

Duplex scan examination was performed 3 months postoperatively. The patients were examined while they were in the supine position by means of B-mode imaging and Doppler scan spectrum measurement of the brachial artery in the upper arm, the arterial anastomosis, the graft, the venous anastomosis, and the efferent vein up to the subclavian vein. Peak systolic velocity (PSV), end-diastolic velocity, and diameter were measured at defined sites and saved as video prints. Significant stenoses with a diameter reduction of 50% (75% area reduction) or more were diagnosed according to previously outlined criteria.²¹ Also, volume flow was measured in the brachial artery and the PTFE prosthesis.

Fistulography of the PTFE arteriovenous grafts was performed 3 months postoperatively. Contrast was injected through the dialysis needle into the graft. The graft, venous anastomosis, and outflow tract were depicted, and visualization of the arterial anastomosis and the brachial artery was obtained with a proximal occluding cuff.²² The percentage of diameter reduction was calculated by dividing the diameter in the stenosis by the diameter of the adjacent normal vessel. Only stenoses with a diameter reduction of 50% or more were included for analysis. Complications were treated according to local customs of the hospital where the patient was. Early and late complications were registered, and interventional and surgical revisions were noticed.

Analysis 

Statistical analysis of the clinical patient variables was performed with the χ² test. The patency rates were calculated with life table analysis and compared with the log-rank test. Primary patency rate was defined as the percentage of grafts that functioned well without any surgical or catheter intervention after implantation. Primary assisted patency was defined as the percentage of grafts that functioned well without graft occlusion more than 24 hours after surgery. In this definition, grafts needing intervention for postoperative bleeding or occlusion due to postoperative hypotension or technical failures occurring within 24 hours after graft implantation were considered patent. Also, grafts needing intervention for stenosis to prevent occlusion were considered patent. Interventions for other reasons were scored as an event. For calculation of the thrombosis-free patency, only thrombotic occlusions were scored as an event. Secondary patency was defined as the proportion of patent grafts still in use for hemodialysis, including those requiring elective intervention or intervention for graft failure. Patients with a patent graft who died, who received a transplant, or who withdrew from hemodialysis therapy alive were censored. Clinical risk factors were defined as a body mass index above 30, significant pitting edema, and skin atrophy that were seen during physical examination of the patient. End points were reached in case of irreversible graft failure, death, transplantation, or transfer to continuous ambulatory peritoneal dialysis treatment.

The incidence rate was defined as the number of complications or interventions per patient-year, and the rate was analyzed with Poisson regression analysis. Risk factors, end points, duplex scan parameters, and fistulography findings in the two groups were compared by means of the χ² test and correlated with patency by means of the Pearson correlation coefficient. Means were compared by use of the Student t test. Differences between the groups were considered to be statistically significant when the P value was less than .05.

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Results 

Patient characteristics, trial end points, patency rates, complications, and interventions 

A total of 120 patients were enrolled in the study, with 61 patients randomized for no cuff and 59 for a cuff. Patient characteristics are summarized in Table I. More men entered the no-cuff group (48%) than the cuff group (29%, P = .034). Other risk factors like age, duration of kidney failure, previous vascular access, arterial and venous diameter, and medical history were equally distributed. Forty patients (34%) received a graft because of failure of the radiocephalic fistula, 23 (17%) because of secondary access failure, and 57 (49%) because primary creation of a radiocephalic fistula was not possible. Total follow-up was 84.0 patient-years (range, 7 days–3.4 years; median, 1.4 years) for the no-cuff group and 77.5 patient-years (range, 0 days–3.6 years; median, 1.3 years) for the cuff group. Forty-nine percent of the patients in each group had a patent graft at the end of the study. Twenty-five patients with a patent fistula died of complications of their kidney failure. Ten patients received a kidney transplantation. In one patient, the transplantation failed within 1 week, and this patient remained in the study. Two patients with a patent graft turned to continuous ambulatory peritoneal dialysis treatment.

Table I. Patient characteristics*

Life table analysis showed all patency rates to be comparable between the two groups. There was a primary patency of 69% at 6 months, 56% at 1 year, 42% at 18 months, and 34% at 2 years in the no-cuff group and 62%, 43%, 30%, and 19%, respectively, in the cuff group (P = .097, Fig 1).

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• Fig. 1. 

  Primary patency rates. Number of patients is presented in the graph. When less then eight patients entered the analysis, the graph was no longer statistically reliable.

The primary assisted patency was 76% at 6 months, 62% at 1 year, 52% at 18 months, and 43% at 2 years without a cuff and 71%, 60%, 53%, and 41%, respectively, with a cuff (P = .53). The secondary patency was 86% at 6 months, 84% at 1 year, 79% at 18 months, and 79% at 2 years without a cuff and 89%, 81%, 76%, and 65%, respectively, with a cuff (P = .42, Fig 2).

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• Fig. 2. 

  Secondary patency rates. Number of patients is presented in the graph. When less than eight patients entered the analysis, the graph was no longer statistically reliable.

The effect of the cuff on thrombosis-free patency was assessed with exclusion of the four patients who had no suitable vein to create a cuff. The primary patency in the no-cuff group was 60% at 1 year and 42% at 2 years. In the cuff group, the primary patency was 55% at 1 year and 37% at 2 years (P = .49). Patency rates in patients with cuffs taken either from the forearm or upper arm basilic vein and saphenous vein from the ankle were similar.

In the overall group, 35 patients (57%) without cuffs underwent 94 interventions, and in 36 patients (61%) with cuffs, 92 interventions were performed (Table II).

Table II. Indications for interventions

Early occlusion was successfully treated with thrombectomy in five patients (8%) in the no-cuff group and in four patients in the cuff group (7%, P = .77). Late complications were noticed in 33 patients (54%) without cuffs and in 35 patients (59%) with cuffs (P = .56). By far the most frequent complication was thrombosis, which occurred 74 times (0.88 per patient-year) in 28 patients in the no-cuff group and 53 times (0.68 per patient-year, P = .0007) in 22 patients in the cuff group. The main intervention for thrombosis was surgical thrombectomy with revision (0.43 per patient-year without cuff and 0.36 per patient-year with cuff) or without revision (0.43 per patient-year without cuff and 0.34 per patient-year with cuff). Occasionally, fibrinolysis was performed with percutaneous transluminal angioplasty (PTA) (0.02 per patient-year without cuff) or without PTA (0.02 per patient-year without cuff).

Stenosis was the second most frequent complication for which intervention was necessary: 12 times (0.14 per patient-year) in 11 patients in the no-cuff group and 17 times (0.22 per patient-year, P = .77) in 12 patients in the cuff group. It was treated with PTA nine times (0.11 per patient-year) in eight patients in the no-cuff group and 13 times (0.17 per patient-year) in 11 patients in the cuff group. In the other cases, surgical revision was carried out because of the extension of the stenosis. Infection was seen once (0.01 per patient-year) in the no-cuff group and five times (0.06 per patient-year; P = .45) in five patients in the cuff group. The operative procedure with a venous cuff usually took about half an hour longer than a normal procedure; however, most infections occurred more than 2 months after surgery. This suggests that the infections are not due to perioperative contamination but are caused by repetitive puncture. In three patients in the cuff group, explantation of the graft was necessary (0.04 per patient-year). The other grafts were salvaged with partial excision and jump graft (0.01 per patient-year in the no-cuff group and 0.03 per patient-year in the cuff group). Hemorrhage occurred once (0.01 per patient-year) in the no-cuff group after puncture and 8 times (0.10 per patient-year) in 6 patients in the cuff group, 3 times after intervention and 5 times after puncture. All patients received coumarin postoperatively, and the hemorrhage was not located in the cuff area. Hemorrhage was treated with surgical closure of the bleeding site. Pseudoaneurysms were excised twice (0.02 per patient-year) in 2 patients in the no-cuff group and 3 times (0.04 per patient-year; P = .97) in 3 patients in the cuff group. Three interventions (0.04 per patient-year) were performed in two patients with ischemia of the hand. In one patient, banding was attempted to reduce the complaints, without success. In both patients, the graft was ligated. In one patient, the ischemic damage was irreversible and required arm amputation. Venous hypertension occurred in one patient (0.01 per patient-year) in the no-cuff group, and the graft was ligated. In each group, three interventions (0.04 per patient-year) were undertaken for excessive oozing of the graft, which caused severe edema of the arm. Fibrin glue (Tissuecol) was used three times to seal the graft, without success. All three grafts were explanted.

Results of duplex scanning and fistulography at 3 months 

Duplex scan examination was performed in 59 patients (29 without cuffs and 30 with cuffs) 3 months postoperatively (Table III).

Table III. Number and locations of > 50% stenoses detected with duplex (D) scan examination and fistulography (X) at 3 months (n = 59)

A total of 48 stenoses were found in the no-cuff group compared to 34 stenoses in the cuff group (P = .066). These stenoses occurred in 21 patients in both groups. There was no difference in the distribution of the stenoses, although the group without cuffs tended to have more anastomotic stenoses than the group with cuffs (14 vs 8 at the arterial anastomosis, P = .097; 14 vs 8 at the venous anastomosis, P = .097). Comparison of hemodynamic parameters, measured with duplex scan examination, revealed no difference between the two groups (Table IV).

Table IV. Hemodynamic parameters from duplex scan examination at 3 months (n = 59)

No significant correlation was found between the volume flow in the brachial artery or prosthesis and the primary and secondary patency.

At 3 months, a fistulography was performed in 59 patients (30 without cuffs and 29 with cuffs). Fewer significant stenoses (> 50%) were revealed by fistulography than by duplex scanning. Most stenoses were located in the venous anastomosis and the efferent vein. No significant differences were found in the distribution of the stenoses between the groups without and with cuff.

Analysis of risk factors 

No correlation was found between the presence of risk factors listed in Table I and the occurrence of graft failure. Additional analysis was performed on the occurrence of graft failure and the use of erythropoietin, acetylsalicylic acid, and angiotensin-converting enzyme–inhibitors, which showed no correlation. In 102 patients, the presence of edema, skin atrophy, or obesity of the arm was scored. The presence of one of these problems tended to impose a higher risk on graft failure (11 [23%] of 47) than without local problems (graft failure 6 [11%] of 55; P = .091). Of the 106 veins in which the diameter was measured with coronary probes, seven (39%) of the 18 fistulas connected to a vein of 3.5-mm diameter or smaller occluded, whereas only 16 (18%) of the 88 fistulas connected to a vein of 4 mm or larger occluded (P = .052). The diameters measured with duplex ultrasound scan at 3 months were not correlated with fistula failure.

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Discussion 

In the current randomized study, the incidence of thrombotic occlusions was less in the group with a venous cuff at the venous anastomosis of PTFE arteriovenous grafts. This was probably due to a lower number of stenoses found with duplex scan examination, although the total number of patients with stenoses was comparable. The decrease in thrombotic occlusions did not result in a better patency in the cuff group, because in the cuff group fewer recurrent occlusions occurred, whereas the total number of patients with thrombotic occlusions was the same as in the no-cuff group. The 1-year patency rates are comparable to the results reported in the literature, varying from 40% to 57% for primary patency and 62% to 78% for secondary patency.³, ²³, ²⁴, ²⁵, ²⁶, ²⁷, ²⁸, ²⁹ The most frequent complication needing intervention was thrombosis, followed by interventions for stenosis that caused impaired fistula function. The cuff group had more interventions for infections (0.06 per patient-year vs 0.01 per patient-year in the no-cuff group), but they are still well below the 0.21 to 0.37 per patient-year and the incidence of 11% to 34% reported by others.³, ²⁴, ²⁶, ²⁷, ²⁸, ²⁹ No correlation was found between risk factors such as age, sex, smoking, diabetes, cardiovascular disease, and cerebrovascular disease and the occurrence of fistula failure. Erythropoietin increases the hemoglobin value and hematocrit and may result in a higher number of thromboses.³⁰ However, many studies, including this one, could not confirm this.³¹, ³², ³³, ³⁴, ³⁵ Acetylsalicylic acid³⁶, ³⁷, ³⁸ and angiotensin-converting enzyme–inhibitors³⁹, ⁴⁰, ⁴¹ have both been indicated as possible inhibitors of IH. In the current study, patients using these drugs did not have less graft failure.

Local thickness of the arm due to edema or obesity hampers palpation of the graft. Apart from the problems this poses for graft puncture, it also decreases the possibility to detect stenoses or even occlusion by palpation of the graft. Atrophy of the skin increases the risk on wound healing problems. We found that patients with local problems had more graft failures.

The importance of vessel diameter was already recognized for the development and patency of Brescia-Cimino (BC) fistulas. Wong et al⁴² found that BC fistulas created with vessels with a diameter less than 1.6 mm, which were measured with preoperative duplex scan examination, failed to mature. Our study shows that the diameter of the efferent vein is an important factor for the patency of PTFE arteriovenous grafts, too. Of the fistulas with a diameter of 3.5 mm or less, seven (39%) of 18 failed, whereas only 16 (18%) of 88 of the fistulas with a vein diameter of 4 mm or more failed. A smaller efferent vein poses a higher resistance to flow, and this could reduce the flow through the fistula. Moreover, a large transition of diameter at the anastomosis induces great flow disturbances. This would predispose a smaller vein to a greater hyperplastic reaction than a larger vein, compromising the flow even more.

PTFE is generally regarded as the material of choice for secondary access surgery, when a BC fistula has failed or its construction is not possible.⁴³ However, PTFE arteriovenous grafts have significantly more complications than BC fistulas.²⁴, ²⁷, ²⁸ Thrombotic occlusion in PTFE arteriovenous grafts occurs with an incidence of 0.54 to 0.95 per patient-year,², ⁵, ²⁴, ²⁹ requiring intervention to reestablish patency or even implantation of a new graft. The key event in the occurrence of thrombotic complications in PTFE arteriovenous grafts for hemodialysis is IH.⁶ Stenoses due to IH also develop at the distal anastomosis of peripheral arterial bypass grafts and cause a decrease of patency. In an attempt to improve patency rates of peripheral bypass grafts, Siegman⁴⁴ created a venous cuff between the prosthesis and the native vessel to facilitate the anastomosis. After Miller et al’s¹⁸ publication of improved patency rates with the use of this venous cuff, the cuffed anastomosis was internationally accepted. The improved patency rates of the Miller cuff were ascribed to the better transition of elastic properties and the insertion of venous endothelium, which might serve as a source for humoral factors preventing IH.⁴⁵ Since then, several different types of cuffs and patches were developed, accompanied with reports of improved patencies in retrospective studies.²⁰, ⁴⁶, ⁴⁷, ⁴⁸

In an in vitro model, the hemodynamic changes induced by the venous cuff were examined to explain the beneficial effect of a venous cuff in the development of IH. In the venous cuff, unidirectional vortices originated with relatively high velocities. This high velocity would exert a high shear stress on the vessel wall, inhibiting IH.⁴⁹ However, in this model, flows were comparable to those in arterial bypass grafts, and it is questionable whether the results can be extrapolated to the high flow system like the arteriovenous fistula. On the contrary, in previous studies performed in our institute, we could prove that initial high shear stress resulted in significantly more stenoses.⁵⁰ Also, we showed a correlation among high shear stress, endothelial denudation of the vessel wall, and IH.⁵¹ Moreover, a recent randomized trial showed that the Miller cuff had no effect on the patency of supragenual bypass grafts. In infragenual bypass grafts, a better patency was obtained, but this was ascribed to facilitation of the anastomosing technique between a stiff prosthesis and a small-caliber crural vessel, and not to mechanical or humoral effects of the cuff.⁵² In the creation of PTFE arteriovenous loop grafts in the arm, the efferent vein in the elbow is usually easily accessible and has a diameter greater than 2 mm. Therefore, PTFE arteriovenous grafts may not benefit from this technical advantage of the cuff. Nevertheless, a recent presentation of the results of a nonrandomized study of PTFE arteriovenous grafts, in which a kind of Linton PTFE patch at the venous anastomosis was used, showed an improved patency rate (88% after 48 months) compared with 4- to 7-mm tapered grafts (66% after 36 months; P = .047).⁵³ Also, a new type of PTFE prosthesis was designed with a cuffed or hooded venous end and used to create PTFE arteriovenous grafts. Early reports are promising, with an improved 4-month secondary patency of 100% versus 59% for the 4- to 7-mm tapered graft. This study was not randomized either, and the patency of the tapered graft seems to be very low.⁵⁴

In this prospective, randomized study, we found that a venous cuff at the venous anastomosis of PTFE arteriovenous grafts for hemodialysis reduces the incidence of thrombotic occlusions through a reduction of stenosis at the venous anastomosis. However, this did not result in a better patency rate. Therefore, the venous cuff should not be used routinely. Initial vein diameter and local risk factors (edema, obesity, or skin atrophy) appear to be the most important risk factors for graft failure.

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