The effect of wall mechanical properties on patency of arterial grafts

Normal arteries have properties which match the low output impedance of the heart to the high peripheral impedance. These properties can be assessed in terms of compliance (% diameter change per unit pressure change) as well as by other haemodynamic parameters. Experiments were designed using vein, Dacron and expanded polytetrafluoroethylene (PTFE) in a low flow canine femoral artery bypass model. No graft group achieved perfect patency. At twelve weeks 80% of vein grafts, 30% of Dacron grafts, and 15% of PTFE grafts remained patent. The compliance of vein grafts was maintained despite marked thickening of the wall. Patency was correlated at a highly significant level with compliance. The studies demonstrate that the matching of the mechanical properties of grafts to host arteries is important in the design of successful synthetic arterial grafts.     

The effect of vein diameter on patency of in situ grafts

In an attempt to evaluate the effect of vein diameter on early patency and long-term durability of in situ lower limb bypasses, we evaluated 195 femoral-distal, popliteal, and/or tibial bypasses constructed in 189 patients (153 men, 36 women), consisting of tibial bypasses in 116 (60%), and popliteal in 79 (40%). The operative angiograms were reviewed and the vein diameter was measured to the nearest 0.5 mm. Postoperative follow-up consisted of visits every three months where graft patency was assessed by physical examination and measurement of graft flow velocity and ankle-brachial indices. Conduits less than 3 mm had a higher rate of occlusion in the 0-30 day interval, but following that period performed satisfactorily. No conduit less than 2 mm was successfully utilized, because of inability to incise valves without injury in these tiny conduits. Following the perioperative period, conduit diameter does not affect the long-term durability of in situ bypass grafts.     

Does 111indium-platelet deposition predict patency in prosthetic arterial grafts?

The relationship between the rate of 111In-platelet deposition on vascular grafts and subsequent thrombosis has been examined in patients undergoing femoropopliteal by-pass. Sixty-seven patients undergoing femoropopliteal by-pass using vein, Dacron or PTFE were randomized to aspirin plus dipyridamole (ASA/DPM) or placebo. Autologous 111In-platelets were injected in the second postoperative week and Thrombogenicity Index (TI) calculated as the mean daily rise in the ratio of radioactivity graft/contralateral thigh. Graft patency was assessed to 1 year. Mean (+s.e.m.) TI at 1 week in 21 grafts that occluded within 12 months was 0.19 +/- 0.018 compared with 0.07 +/- 0.009 in the 38 that remained patient (P less than 0.001). Grafts with a TI less or greater than the median had a 90 per cent or 39 per cent cumulative 1-year patency, respectively (P less than 0.001). In the prosthetic grafts ASA/DPM reduced mean TI from 0.17 +/- 0.02 to 0.11 +/- 0.01 (P less than 0.02) and enhanced 1-year patency from 36 to 67 per cent (P less than 0.05). Following femoropopliteal by-pass TI related to subsequent graft patency. Radiolabelled platelet deposition therefore provides a guide as to how new materials or antithrombotic drugs may influence clinical graft thrombosis. Platelet inhibition reduced both graft thrombogenicity and subsequent occlusion.     

Effect of defibrinogenation on the early patency rate of experimental small calibre arterial grafts

The effect of defibrinogenation with Arvin was studied in a new animal model of early thrombosis of a 3 mm diameter polytetrafluoroethylene (PTFE) graft with a poor run-off. Fifteen control animals were compared with fourteen animals treated with subcutaneous Arvin 20 units kg-1 body weight day-1, starting 2 days before surgery and continuing for 2 days postoperatively. The peroperative fibrinogen level in the controls was 2.8 +/- 0.9 gl-1 compared with 0.4 +/- 0.3 gl-1 in the treated group. There was no significant difference in the peroperative or postoperative platelet count or haematocrit value between the two groups. Plasma viscosity and whole blood viscosity (at a low shear rate of 0.7s-1) were significantly less during and after surgery in the defibrinogenated group. The degree of defibrinogenation in these animals produced no problems with haemostasis during surgery or in the postoperative period. The cumulative patency rates of the controls at 24 h, 48 h, and 4 days were 43 per cent, 28 per cent and 28 per cent compared with 86 per cent (P less than 0.05), 73 per cent (P less than 0.05) and 73 per cent (P less than 0.05) respectively in the defibrinogenated group. In this model of a narrow PTFE graft with a poor run-off, defibrinogenation was a safe and effective method of improving early patency of small calibre arterial grafts.     

Microvascular grafts: effect of diameter discrepancy on patency rates

This study examined the effects of diameter discrepancy between interpositional vein grafts within a range of 0.25 to 2 mm. One hundred rats underwent isolation of a 10 mm segment of the femoral artery, from which a 4 mm segment was removed. Venous grafts measuring 8 +/- 2 mm were interposed. The rats were categorized by their graft to artery diameter ratios. Patency was assessed upon completion and 4-6 days postoperatively. All surgical specimens were submitted to the pathology department for microscopic evaluation. Results showed Group I: graft to artery ratio 1:1, patency rate 90% (18/20); Group II: ratio 0.75:1, patency rate 80% (16/20); Group III: ratio 0.5:1, patency rate 60% (12/20), Group IV: ratio 0.25:1, patency rate 20% (4/20); Group V: ratio 2:1, patency rate 60% (12/20). It is concluded that 1:1 venous graft to artery ratios are optimal. When this is impossible, diameter discrepancies should be at least 0.75:1 for acceptable patency rates to be attained in microvascular grafting.     

Influence of endothelial cell seeding on platelet deposition and patency in small-diameter Dacron arterial grafts

Serial platelet deposition, surface topography, and patency were evaluated in control (N = 28) and endothelial cell-seeded (N = 28) small-diameter (4 mm inner diameter) USCI Dacron grafts implanted in the carotid and femoral arteries of dogs. All dogs received aspirin (325 mg) daily for 2 weeks starting 24 hours prior to graft implantation. Endothelial cell seeding was performed by mixing suspensions of autologous endothelial cells that had been enzymatically harvested from segments of external jugular vein with blood that was used to preclot the prostheses. The platelet deposition on each graft was quantitated by means of indium 111-labeled platelets and technetium 99m-labeled red cells in a dual-isotope platelet-imaging technique. Platelet deposition on seeded grafts 24 hours after implantation was significantly higher than on the controls (p less than 0.05). Two weeks after implantation platelet deposition on seeded prostheses had decreased to a level significantly lower than that on the controls and continued to decline on serial studies up to 7 months. In contrast to seeded grafts, platelet accumulation on control grafts dramatically increased after the withdrawal of aspirin therapy and was associated with a sharp rise in control graft thromboses. Gross and scanning electron microscopic evaluation of endothelial cell-seeded grafts after 1 month indicated complete neointimal coverage, whereas none of the control grafts explanted at 1 month or later exhibited a continuous neointimal lining. Cumulative 7-month patency for seeded prostheses was significantly higher than for the controls (96% and 29%, respectively; p less than 0.001). We conclude that endothelial cell seeding in combination with short-term aspirin therapy is a simple, reliable diameter Dacron prostheses. Abrupt withdrawal of aspirin therapy may be contraindicated in nonseeded control grafts because it results in increased platelet deposition and thrombosis.     

The effect of continued cigarette smoking on the patency of synthetic vascular grafts in Leriche syndrome.

The effects of continued smoking were studied in 187 consecutive patients who underwent aorto-iliac or aorto-femoral grafting because of Leriche disease and who left the hospital with well-functioning grafts. The patients were divided into the following groups: (1) never smoked, (2) stopped smoking after the operation, (3) continued to smoke less than a pack a day and (4) continued to smoke more than a pack a day. The patency of the grafts was evaluated at regular intervals during a follow-up period ranging from 6 months to 10 years. A significant difference in the patency in the favor of the nonsmokers was found, with the "more than one pack a day" group having more than triple the occlusion rate of the nonsmokers, both absolutely and in month-patency time. We recommend that the surgeon make a most sincere effect to induce patients undergoing vascular operations for occlusive vascular diseases to give up smoking. Failure to promise to stop the smoking habit should be regarded as a relatively strong contraindication for surgery in patients not directly threatened with loss of an extremity.     

Effect of cryopreservation on patency and histological changes of arterial isogeneic and allogeneic grafts in the rat model

Vascular grafting is used frequently in the management of length discrepancies between blood vessels. Cryopreservation permits vascular graft storage and aids availability; however, long-term patency of cryopreserved arterial allografts is not well established. Fifty Fisher and 55 Wistar rats were used in the study. Thirty-eight cryopreserved Fisher femoral arterial grafts were transplanted into the femoral arteries of 15 Fisher (cryoisografts) and 23 Wistar rats (cryoallografts). Thirty-two fresh Fisher arterial grafts were implanted into 32 Wistar femoral arteries (fresh allografts). The animals were killed at 1, 4, and 8 months in each group, and graft patency was assessed. One-month graft patency was 100% in all groups. At 4 months, graft patencies were 86%, 100%, and 75% in the cryoisografts, cryoallografts, and fresh allografts respectively. All cryoisografts and fresh allografts were patent, whereas all the cryoallografts were occluded at 8 months ( < 0.01). Cryopreserved rat arterial allografts offered satisfactory graft patency up to 4 months after implantation and may therefore be applicable clinically in selected cases.     

Predictive factors for the intermediate-term patency of arterial grafts in aorta no-touch off-pump coronary revascularization.

OBJECTIVE: Graft flow is one of the important determinants of the arterial graft patency. To establish the optimal graft design, we examined detailed characteristics of the arterial composite and sequential grafts, and sought to delineate the risk factors of graft occlusion due to insufficient bypass flow. METHODS: Angiograms of 2547 bypass grafts in 677 consecutive patients who underwent total arterial off-pump CABG without aortic manipulation followed by early postoperative angiography since December 2000 were reviewed. The angiographic flow was graded as A (antegrade), B (competitive), C (reversal), and O (occlusion). RESULTS: The overall early graft patency rate was 98.2% (2502/2547). The rate of grade A was 91.3% (2325/2547), while the rates of grades B and C were 2.9% (73/2547) and 4.1% (104/2547), respectively. For the main trunk of the anterior descending branch (LAD), the graft patency rate was 99.3% (674/679). The grade A rate of the internal thoracic artery (ITA) grafts to LAD in an individual fashion was 99.5% (203/204), being comparable with that in the sequential or composite grafting which had two distal anastomoses (98.1%, 159/162; p=0.33). The actuarial patency rates at 3 years were 84.7% for the bypass grafts with grade A flow and 33.9% for those with grade B/C flow, respectively (p<0.0001). The multivariate Cox-regression analysis demonstrated that grade B/C (p<0.0001, HR=4.19) and 51-75% stenosis of the native coronary artery (p=0.02, HR=2.86) were significant predictors of graft occlusion. CONCLUSIONS: For the LAD, the results of graft flow in sequential ITA grafting or composite grafting with two distal anastomoses were comparable with that in individual ITA grafting. Prediction and prevention of competitive and reverse flow are mandatory for achieving the advantages of the arterial materials.     

Lack of diameter effect on short-term patency of size-matched Dacron aortobifemoral grafts.

This study examined the relationship between graft diameter and subsequent patency in 79 patients who received Dacron aortobifemoral bypass grafts for aortoiliac occlusive disease between 1985 and 1989. Sixty-five percent of these patients were men, 25% were diabetic, and 94% were smokers, with an average age of 62 years. Patients were followed for a mean interval of 24 months. Life-table survival was 92% at 3 years. All surviving patients showed "significant" postoperative improvement by use of Society for Vascular Surgery/International Society for Cardiovascular Surgery combined clinical and vascular laboratory criteria. There were three early and five late graft thromboses. Primary and secondary life-table patencies were 85% and 92%, respectively, at 3 years. Dacron bifurcation grafts were selected to match the size of native arteries. Patients receiving small diameter grafts, defined as 12 mm (n = 9) and 14 mm (n = 39), were compared with patients receiving large diameter grafts of 16 mm (n = 26) and 18 mm (n = 5). Small diameter grafts were more likely to be used in women (p less than 0.01), but patient groups were otherwise comparable with respect to age, smoking history, diabetes, outflow status, operative indications, type of proximal anastomosis (end-to-end or end-to-side), location of distal anastomosis (common femoral vs deep femoral), type of graft construction (knitted vs woven), and functional result. Graft diameter did not influence life-table patency, which was 84% for small and 87% for large diameter grafts at 3 years (p = 0.74). Furthermore, none of the other variables listed above influenced graft patency.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of preformed confluent endothelial cell monolayers on the patency and thrombogenicity of small calibre vascular grafts

Endothelial cell seeding has been proposed as a method to improve the patency rates in small calibre prosthetic vascular grafts. The seeding methods used at present leave much of the graft luminal surface devoid of endothelial cells and thus still significantly thrombogenic. We have developed a method to preform confluent endothelial cell monolayers, on the grafts prior to implantation, and this study investigates the effect of these monolayers on the early thrombogenicity and patency of polytetrafluoroethylene (PTFE) grafts. Small diameter PTFE grafts were seeded with canine endothelial cells obtained from the external jugular vein. Each of five dogs then received a graft seeded with its own cells and a contralateral, non-seeded control graft. At 1 and 10 weeks after graft implantation graft thrombogenicity was assessed by the use of Indium labelled platelets. The thrombogenicity index (TI) of each graft was determined from counts of gamma activity recorded over a period of 7 days. Grafts were subsequently removed at 12 weeks. At 1 week the mean TI for the seeded grafts was 0.123 (SD 0.019) and that for the controls 0.183 (SD 0.017) (p = 0.005). At 10 weeks only the seeded grafts could be assessed because all of the control grafts had occluded. At this point in time the seeded grafts had a mean TI of 0.159 (SD 0.011) (p = 0.047 vs. seeded at 1 week). By the time of removal at 12 weeks, all control grafts were occluded but only one of the seeded grafts had occluded (p = 0.025). In conclusion, the use of preformed, confluent endothelial cell monolayers for seeding prosthetic grafts significantly reduces the early graft thrombogenicity and improves graft patency. It does not, however, completely halt the increase in thrombogenicity which occurs during the early post-implantation period.     

Improving patency of coronary conduits "valveless" veins and/or arterial grafts

BACKGROUND: Veins used for coronary artery bypass operation have a well-documented limited long-term patency. Internal thoracic artery (ITA) grafts have shown exceptional "durability." Assumptions were made that other arterial conduits have similar characteristics. AIM OF THE STUDY: The purpose of this article is to compare different conduits long-term patency including saphenous veins to other available arterial conduits: inferior epigastric artery (IE), right gastroepiploic artery (RGEA), and radial artery (RA). METHODS: Recent studies have shown that radial artery bypasses have lower patency rate than saphenous veins. Flow patterns, physiological flow characteristics are reviewed including native vessel disease and area of myocardium supplied. In the case of venous bypasses, the primary culprit of failure seemed to be the quality of the vein itself and the reverse venous valves in the conduit resulting in: (a) trapping-hypertension, (b) thrombosis, (c) turbulence, (d) intimal damage, (e) mismatching in size. RESULTS: Clinical follow-up of our patients up to 8 to 11 years (average 8.9 years) have proved the superior characteristics of the so-called "good veins." In a retrospective study of 436 patients sequential, valveless veins patency was 88.6% versus 72% of reversed valvular segments (p < 0.01). Patients' survival seemed to be significantly improved if these veins were combined with ITA grafts. Patients' survival with one valveless limb HS + ITA was 78% versus HS + SV 52% (p < or = 0.0017) and HS + ITA versus HS + ITA + SV (p < 0.0057). CONCLUSION: Selective decision-making of the surgeon at the time of the operation is required to choose the best conduit to be able to perform the best operation with the best long-term result.     

The effect of anti-thrombotic drugs on prosthetic grafts in the canine inferios vena cava.

The effect of phenylbutazone, an anti-thrombotic agent, on the occlusion rate of knitted Dacron grafts placed in the infrarenal inferior vena cava of dogs was studied. Grafts places in dogs treated with phenylbutazone remained patent significantly longer than those in untreated animals. All the grafts in the untreated group occluded, but 2 remained patent in the treated animals.     

联合动静脉瘘对流出道不良患者动脉旁路术通畅率的影响

目的通过对流出道不良患者行动脉旁路术联合动静脉瘘通畅率的分析,强调对流出道不良患者积极手术抢救患肢的重要性,并探讨合理的手术方式。方法回顾性分析行动脉旁路术(ePTFE)联合动静脉瘘手术治疗的26例下肢流出道严重不良患者的临床资料。结果26例(28条肢体)患者中,有14例行浅组(膝部大隐静脉)动静脉瘘,有12例联合行深组(腘、胫腓干、胫后静脉)动静脉瘘。24例获随访,平均随访8个月,近期通畅率两组均为78·6%,远期通畅率深组为78·6%,浅组为57·1%。结论动脉旁路术联合动静脉瘘可提高流出道不良的下肢缺血患者术后通畅率。     

The effect of a venous anastomosis Tyrell vein collar on the primary patency of arteriovenous grafts in patients undergoing hemodialysis

PURPOSE: Vein collars and patches are used at the distal anastomoses of infrainguinal prosthetic grafts to improve graft patency. We initiated a randomized, prospective study to determine whether a Tyrell vein collar at the venous anastomosis of forearm loop arteriovenous grafts (AVGs) would improve patency. METHODS: Patients who required new forearm AVGs were randomized to (1) a standard end-to-side graft-vein anastomosis (control group) or (2) a Tyrell vein collar between the graft and the vein (study group). End points were (1) graft thrombosis, (2) graft removal and ligation, or (3) inadequate graft function. Randomization of 75 subjects was planned. The study was terminated early for ethical reasons. RESULTS: Seventeen patients (eight men, nine women) with a mean age of 52.8 years (range, 31-79 years) had 17 grafts placed (control group, n = 10; study group, n = 7). Comorbidities were not different between the groups (P>.05). Six (86%) of seven study grafts failed by 9 months (mean, 4.6 months). Four (66%) failed study grafts had venous outflow tract stenosis from intimal hyperplasia. This was confirmed at surgery in three and by angiography in one. The 9-month primary patency was 80% for the control group versus 17% for the study group (P =.015). Smaller outflow vein diameter in the study group (P =. 048) did not account for this inferior graft patency. CONCLUSION: A Tyrell vein collar at the venous anastomosis of a forearm AVG resulted in premature graft failure. The use of a Tyrell vein collar may accelerate venous anastomosis intimal hyperplasia.     

The effect of thromboxane receptor blockade versus thromboxane synthase inhibition on canine arterial graft patency

This study compared the effects of a thromboxane synthase inhibitor, thromboxane receptor antagonist, and cyclooxygenase inhibitor in a canine arterial graft patency model. Fifty-six dogs were divided into a control (no treatment) and five treatment groups: thromboxane synthase inhibitor (U63557A; 15 mg/kg/tid); thromboxane receptor antagonist (SQ29548; 0.02 mg/kg/hr); high-dose aspirin (325 mg/day; low-dose aspirin (1 mg/kd/day; and aspirin plus dipyridamole (325 mg/day aspirin; 3 mg/kg/day dipyridamole). Drugs were orally administered except for thromboxane receptor antagonist, which was delivered intravenously by minosmotic pumps. After 24 hours of drug treatment, bilateral femoral artery prosthetic grafts (4 mm diameter x 7 cm; 1 polytetrafluoroethylene and 1 Dacron) were implanted. Patency was determined after 1 week. Dogs were classified before operation according to their epinephrine-enhanced arachidonate-stimulated platelet aggregation response. Polytetrafluoroethylene and Dacron graft patency rates were equivalent in all groups. Overall graft patency was significantly improved from 42% (control) to 94% by both high-dose aspirin and thromboxane receptor antagonist (p less than 0.001). Aspirin-dipyridamole also improved patency (83%; p less than 0.01 versus control), whereas thromboxane synthase inhibitor and low-dose aspirin were not effective. Baseline platelet aggregation was not predictive of patency. The drugs that promoted graft patency in this model either suppressed both thromboxane A2 and prostaglandin H2 formation (high-dose aspirin) or blocked their combined platelet receptor (thromboxane receptor antagonist). Thromboxane synthase inhibitor may be ineffective because prostaglandin H2 production is allowed. These data suggest that activation of the platelet thromboxane A2-prostaglandin H2 receptor is an essential event in early arterial graft thrombosis.     

The influence of quality on the long-term patency of arterial grafts: the surgeon's key role in improving results in medium and small caliber vessels

The long-term patency of small and medium caliber grafts is directly affected by the surgeon's informed selection. In addition, when knitted synthetics are the appropriate choice, the methods used to preclot them for implantation will have a direct effect on their function.