Terms Of Patency Research Articles

Does a skeletonized or pedicled left internal thoracic artery give the best graft patency?☆

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether skeletonization of the internal thoracic artery (ITA) improves graft patency in coronary artery bypass grafting (CABG). Altogether >60 papers were found using the reported search, of which 17 papers represented the best evidence to answer the clinical question. Grafts used were either as single ITAs (left or right, LITA or RITA) or bilateral ITAs (BITAs). The author, journal, date and country of publication, patient group studied, study type, relevant outcomes and results are tabulated. We acknowledge that evidence is limited in this area of cardiac surgery. The skeletonized ITA has not been used long enough to establish whether a decline in patency will occur after several years. The follow-up data was not long-term with only two studies providing patency rates beyond five years. Also, only 4 out of 17 papers were comparative studies (skeletonized conduits vs. pedicled conduits). However, the available evidence demonstrates that short- and medium-term patency rates of both skeletonized and pedicled conduits are excellent. In the four comparative studies, skeletonization patency was at least comparable to pedicled conduits and in two studies even higher. Patency was assessed with the use of angiography, performed on average within four years of CABG surgery. Patency rates exceeded 95% in the 10 non-comparative studies where angiographic follow-up was within three years of surgery. This is an important finding because it justifies further use of skeletonized technique for CABG surgery. It adds also to a growing field of evidence that skeletonized ITA grafts are preferable to pedicled grafts because they may cause less degree of devascularization of the sternum and consequently reduction of sternal wound infection. The evidence presented here demonstrates that in terms of patency, skeletonized and pedicled left internal thoracic arteries provide excellent patency rates.

Lower-extremity Arteriovenous Access for Haemodialysis: A Systematic Review

The lower extremity is increasingly used as an access site in end-stage renal disease patients. However, reports present conflicting results, creating confusion regarding the feasibility and outcomes. Our objective is to review the available literature and analyse the patency rates and complications of various types of lower-extremity arteriovenous access. An Internet-based literature search was performed using MEDLINE to identify all published reports on lower-extremity vascular access. The analysis involved studies comprising at least 10 arteriovenous accesses with both inflow and outflow vessels in the lower extremity, and reporting on patency rates and access-related complications. The weighted mean patency rates were calculated, and the chi-square (chi(2)) test was used to evaluate the differences in the complication rates in the subgroups of patients identified. Three main types of lower-extremity vascular access were identified: the upper thigh prosthetic, the mid-thigh prosthetic and the femoral vein transposition arteriovenous access. There are limited data on saphenous vein loop grafts, which report poor results. The weighted mean primary patency rates at 12 months were 48%, 43% and 83%, respectively. The weighted mean secondary patency rates at 12 months were 69%, 67% and 93%, respectively. Access loss as a result of infection was more common in upper thigh and mid-thigh grafts than femoral vein transposition arteriovenous access (18.40%, 18.33% vs. 1.61%; P<0.05). Ischaemic complications rates were higher in autologous than prosthetic arteriovenous access (20.97% vs. 7.18%, P<0.05). Lower-extremity vascular access has acceptable results in terms of patency, with femoral vein transposition having better patency rates than femoral grafts. Autologous access is associated with less infective complications, however, at the expense of increased ischaemic complications rates. Further research with randomised trials is required to assess the outcomes of lower-extremity vascular access.

Tissue-Engineered Blood Vessel Graft Produced by Self-Derived Cells and Allogenic Acellular Matrix

Current prosthetic alternatives to autologous vascular grafts remain poor in terms of patency. Growing biologic blood vessels has been proposed as an alternative. In this work, the authors demonstrate a method for producing a tissue-engineered vascular graft (TEVG) with self-derived endothelial cells, smooth muscle cells, and allogenic acellular matrix in vitro. The aim of this study was to find out if the graft is suitable as the carotid artery substitute. A canine model was developed for this study. Endothelial and smooth muscle cells were used as seeding cells, and allogenic acellular matrix was used as scaffold to produce the TEVG. Endothelial and smooth muscle cells from the saphenous vein were harvested by trypsin and collagenase digestion respectively. These isolated cells were cultured and expanded by routine cell culture technique. The common carotid artery was harvested from other fresh dog cadavers and processed by a multistep decellularizing technique to remove original cells and preserve elastic and collagen fibers. Then, the inner surface of the acellular matrix as a scaffold was sequentially seeded with cells. Smooth muscle cells were seeded onto the scaffold. It was placed in bioreactors filled Dulbecco modified Eagle medium supplemented with growth factors. After 4 weeks, the vessels were harvested from the bioreactors and seeded with endothelial cells at the lumen for 7 days. Finally, the cell-seeded graft was transplanted to the cell-donated dog to substitute part of the native common carotid artery (2 cm in length). All animals were followed up for 6 months. Twenty-four dogs were divided into 3 groups randomly: group A (native artery graft), group B (allogenic acellular matrix graft only), and group C (acellular allogenic matrix coated with endothelial and smooth muscle cells). These grafts were subjected to regular echocardiography at 1, 3, and 6 months postoperatively. Then, the TEVG were harvested for histologic evaluation at 6 months after transplantation. The vascular luminal surfaces were observed by electronic scanning microscopy. The TEVG showed good functional performance demonstrated by regular Doppler ultrasonography at 1, 3, and 6 months postoperatively, compared with that of native arteries. All vascular grafts in group A and C provided patent rates of 100%; however, the patency rate of group B was 50% at 3 and 6 months postoperatively. The TEVG had a similar macroscopic appearance to that of native vessels. Histologic and immunohistochemical analyses indicated the presence of high cell density and development of a highly organized structure of ECM. Cultured self-derived endothelial and smooth muscle cells could be used as seeding cells and allogenic acellularized matrix could be used as scaffold in producing the TEVG. The TEVG had histologic and functional properties consistent with native arteries.

Revascularization to an isolated (“blind”) popliteal artery segment: A viable procedure for critical limb ischemia

The purpose of this study was to analyze our experience of bypass procedures to an isolated ("blind") popliteal artery segment (IPAS) to revascularize the perigeniculate arteries in patients with critical limb ischemia (CLI), to establish whether such revascularizations could yield acceptable results in terms of patency and limb salvage (LS) rates. Over a decade, 347 above-knee arterial revascularizations were performed in 293 patients and in 51 (14.7%) of these the outflow vessels were the perigeniculate arteries arising from an IPAS, through a reversed saphenous vein or spliced veins (n = 30, 58.8%; group I) or polytetrafluoroethylene (n = 21, 41.2%; group II) prosthetic grafts. Patency, LS, and survival rates were assessed using Kaplan-Meier life-table analysis. A complete follow-up (range, 0.1-10.4 years; mean, 5.6 years) was obtained in 49 patients. The IPAS was chosen as the last resort in 39 patients (76.5%) because no other infrapopliteal artery was identified as being available at angiography; in 12 patients (23.5%) it was chosen because of an invasive foot infection or ischemic necrosis overlying the dorsalis pedis or the posterior tibial arteries. The study series was mainly male, with significantly more younger patients in group I (72 +/- 1 years vs 74 +/- 5 years, P = .037). Group I had a statistically higher incidence of diabetes mellitus (76.6% vs 47.6%, P = .033), insulin dependence (56.7% vs 28.6%, P = .047) and history of smoking (80% vs 47.6%, P = .016) than group II. None of the patients died in the perioperative period. There were 3 early graft failures (2 in group I), prompting 3 major amputations. Kaplan-Meier analysis identified 5-year patency and LS rates of 51.4 +/- 9.6% and 90 +/- 4.3%, respectively, in the series as a whole, and the 2 groups had comparable 5-year patency, LS and survival rates. Revascularizations to an IPAS can be performed with acceptable results in terms of patency and LS rates, even when there is no infrapopliteal runoff vessel. Finding perigeniculate arteries arising from an IPAS with no tibio-peroneal vessel reconstitution at arteriography does not justify a pessimistic attitude to the performance of such revascularizations for LS.

Two-stage aural atresia and stenosis surgery with the use of synthetic skin substitute

Conclusion: With this technique, patency rates achieved in congenital external ear canal (EAC) atresia/stenosis and improvement in hearing were evaluated as ‘good’ and ‘satisfactory’, respectively. Objectives: We aimed to test the efficacy of a novel two-stage technique in preventing restenosis following atresioplasty. Patients and methods: Nine patients with congenital EAC atresia/stenosis comprised our cases. We performed 10 atresioplasties using the two-stage technique described below. In the first stage, the ear canal is drilled and its wall is covered with a synthetic skin replacement that induces proliferation of a soft tissue; in the second stage this is lined underneath with split thickness skin graft. Operations were complemented with tympanoplasties in five of the patients. Results: Nine (91%) of 10 operations carried out with the technique were largely successful in terms of patency. The achieved average hearing gain was air conduction/bone conduction (Ac/Bc): 31.33/9.44 dBHL (21.89 in the air-bone gap), while the postoperative air-bone conduction gap was changed to <30 dBHL in eight (88.9%) of the patients.

Comparison of Bilateral Internal Thoracic Artery Revascularization Using In Situ or Y Graft Configurations

Bilateral internal thoracic arteries (BITA) demonstrated superiority over other grafts to the left coronary system in terms of patency and survival benefit. Several BITA configurations are proposed for left-sided myocardial revascularization, but the ideal BITA assemblage is still unidentified. From 03/2003 to 08/2006, 1297 consecutive patients underwent isolated bypass surgery in our institution. 481 patients met the inclusion criteria for randomization, and 304 (64%) were randomized. Patients were allocated to BITA in situ grafting (n=147) or Y configuration (n=152) then evaluated for clinical, functional, and angiographic outcome after 6 months and 3 years. Patient telephone interviews were conducted every 3 months and a stress test performed twice yearly under the referring cardiologist's supervision. Angiographic follow-up was performed 6 months after surgery. The primary and secondary end points were, respectively, major adverse cerebrocardiovascular events (MACCE) and the proportion of ITA grafts that were completely occluded at follow-up angiography. More arterial anastomoses were performed in patients randomized to the Y than the in situ configuration (3.2 versus 2.4; P<0.001). No significant difference between the 2 groups in terms of hospital mortality or morbidity was found. At follow-up, there was no significant difference in any MACCE rate between the 2 groups. 450 out of 464 anastomosis (97%) in the BITA Y group and 287 of 295 (97%) in the BITA in situ group were controlled patent (P=0.99). Excellent patency rates were achieved using both BITA configurations with no significant differences in terms of MACCE up to 19 months postoperatively, but longer-term results remain to be established.

Infrapopliteal arterial revascularization for critical limb ischemia: Is the peroneal artery at the distal third a suitable outflow vessel?

Though the peroneal artery (PA) often remains patent despite disease or occlusion of other infrapopliteal arteries, there is skepticism about using the terminal PA as the outflow tract in distal revascularizations for limb salvage, especially when a patent inframalleolar artery is available. We analyzed our experience of using the distal PA and inframalleolar or pedal branches arteries as outflow tracts in revascularizations for critical limb ischemia. Over a decade, among 651 infrapopliteal arterial reconstructions performed in 597 patients, the PA was the outflow vessel in 214, its distal third being involved in 69 vein revascularizations (study group). During the same period, 187 vein bypass grafts were performed to 179 inframalleolar and 8 pedal branches arteries (control group). Patency, limb salvage and survival rates were assessed using Kaplan-Meier life-table analysis. Complete follow-up (range, 0.1-10.2 years; mean, 5.8 years) was obtained in 245 (95.7%) patients (66 were in the study group). The distal PA was chosen as the target vessel: (1) because the proximal, mid-PA was occluded or severely diseased and no other adequate inframalleolar or pedal branches arteries were identified preoperatively (n = 30; 43.5%); (2) because an alternative inframalleolar target vessel was present but severely diseased (n = 9; 13%); (3) because of the length limitations of the available vein (n = 12; 17.4%; or (4) because of the presence of invasive infection or necrosis overlying the dorsalis pedis or posterior tibial arteries (n = 18; 26.1%). The study group was significantly younger than the control group (68 +/- 7 years vs 70 +/- 6 years, P = .039), and included significantly more patients with diabetes mellitus (65.2% vs 50.2%, P = .033) and insulin dependence (52.2% vs 37.9%, P = .041), dialysis-dependent chronic kidney disease (5.8% vs 1.1%, P = .047), and history of smoking (75.3% vs 58.2%, P = .012). None of the patients died in the perioperative period. Although the overall need for minor amputation was statistically higher in the PA group (78.2% vs 63.1%, P = .022), especially as concerns partial calcanectomy (8.7% vs 2.1%, P = .026), the proportion of wounds completely healed during the follow-up and the mean time to wound healing were comparable in the two groups. Kaplan-Meier analysis showed comparable long-term patency, limb salvage, and survival rates in the two groups. Revascularization to the distal third of the PA can achieve much the same outcome in terms of patency and limb salvage rates, wound healing rate and timing, as when other inframalleolar or pedal branches are used. The skepticism surrounding use of the terminal PA as an outflow vessel appears to be unwarranted.

Randomized Comparative Study Between Buccal Mucosal and Acellular Bladder Matrix Grafts in Complex Anterior Urethral Strictures

Urethral strictures have been a reconstructive dilemma for many years due to the limited availability of tissue substitutes and incidence of recurrence. Buccal mucosal grafts have been a favored material in instances where penile skin is unavailable due to its durability and excellent graft survival. Recently collagen based matrices derived from the bladder have been used successfully in patients with stricture disease and hypospadias. We performed a randomized comparative study to assess the outcome of the acellular bladder matrix compared to buccal mucosa in patients with complex urethral strictures. Human demineralized bone matrix, obtained from cadaveric donors, was processed and prepared for use as an off-the-shelf material. Thirty patients with stricture 21 to 59 years old (mean 36.2) were enrolled and assessed using a standard protocol. The stricture length ranged from 2 to 18 cm (mean 6.9), of which 11 patients had bulbar, 7 had pendulous and 12 had combined bulbopendulous strictures. Of the 30 patients 7 had received no previous intervention while the remaining 23 had undergone 1 to 7 procedures (mean 1.9). All patients were randomized and alternatively assigned to receive either buccal mucosa or decellularized bladder [corrected] matrix and underwent an onlay procedure. All patients except 2 who were lost during followup were followed for 18 to 36 months (mean 25). In patients with a healthy urethral bed (less than 2 prior operations) the success rate of buccal mucosa grafts (10 of 10) was similar to the bladder matrix grafts (8 of 9) in terms of patency. In patients with an unhealthy urethral bed (more than 2 prior operations) only 2 of 6 patients with a bladder matrix graft were successful, whereas all 5 patients with a buccal mucosa graft had a patent urethra. Postoperative uroflowmetry showed significant voiding improvement in both groups. Histology of the graft biopsies showed normal urethral tissue characteristics. This study demonstrates that the use of acellular bladder matrix is a viable option for urethral repair. Demineralized bone matrix as an off-the-shelf biomaterial achieves the best results in patients with a healthy urethral bed, no spongiofibrosis and good urethral mucosa.

Abstract 2879: Comparison of Bilateral Internal Thoracic Artery Revascularization Using Pedicled or Y Graft Configurations: A Prospective Randomized Clinical, Functional and Angiographic Mid-term Evaluation.

For the left coronary system, bilateral internal thoracic arteries (BITA) have demonstrated their superiority over all others types of grafts in terms of patency and survival benefit. Several configurations of BITA have been proposed to achieve left-sided myocardial revascularization. Because the ideal BITA assembling has not yet been found, we have prospectively randomized two types of BITA configurations to evaluate at 6 months and 3 years the clinical, functional and angiographic outcome.From 03/2003 to 08/2006, 1297 consecutive patients underwent isolated bypass surgery in our institution. Of this group, 481 patients met the entrance criteria for randomization and 304 (64%) patients were randomized. BITA grafting was performed with a pedicled configuration in 147 patients and with a Y configuration in 152. Patients were interviewed by telephone every 3 months and had a systematic stress test twice a year performed under supervision of their referring cardiologists. Systematic angiographic follow-up was performed 6 months after surgery. The primary and secondary end point was respectively the major adverse cerebro-cardiovascular events (MACCE) and the proportion of ITA grafts that were completely occluded at follow-up angiography. More arterial anastomoses were performed in patients randomized in the Y than in the pedicled configuration (3.2 versus 2.4; p&lt; 0.001). There were no significant differences between the 2 groups in terms of hospital mortality or morbidity. Clinical follow-up is 100 % complete with a mean of 16 ± 11 months. At follow-up there is no significant difference in any MACCE rate between the 2 groups. Angiographic follow-up is 90% complete with a mean of 6.5 months. 432 out of 446 anastomosis in the BITA Y group and 278 out of 286 in the BITA pedicled group were controled patent (p=0.96).Excellent patency rates were achieved in both groups with no significant difference in terms of MACCE or patency. Whether the higher number of ITA distal anastomoses in the Y configuration group will translate in better long-term results remains to be established.

Radiological evaluation of covered self-expandable metallic stents used for palliation in patients with malignant esophageal strictures

To study the role of self-expandable metallic stents in malignant esophageal strictures in terms of patency, improved dysphagia score, and possible associated complications. Twenty-two patients with inoperable carcinoma of the esophagus underwent stent placement. Four different varieties of covered stents were used. Stenting was performed under fluoroscopic guidance and local pharyngeal anesthesia. During follow-up, patients were examined clinically and radiologically to assess the effectiveness of stents in relieving dysphagia, to check the stent position, patency, and possible complications. Fluoroscopic placement of the stent was successful and well tolerated in all patients without any serious complications. Accurate stent placement was possible in 95% of cases. The mean dysphagia score prior to stenting was 3.5 and poststent 1.2, with an improvement of 2.3 degrees. In two patients with associated fistulas, complete closure was seen after stent insertion. There was poor stent expansion in three patients. Significant tumor overgrowth occurred in two patients, and a second overlapping stent was deployed in one case. Three patients developed food impaction, which needed endoscopic removal of impacted food in two cases. Fluoroscopic placement of self-expandable metallic stents is a safe and effective method of palliating severe dysphagia and fistulas in patients with inoperable esophageal carcinoma. However, complications such as tumor overgrowth and food impaction may require reintervention after stent placement.

Outcome after hypogastric artery bypass and embolization during endovascular aneurysm repair

Multiple strategies have been devised to extend the applicability of endovascular aneurysm repair (EVAR) in patients with common iliac artery (CIA) aneurysms. This study was designed to examine outcome in patients undergoing EVAR with either hypogastric artery embolization or common iliac artery bifurcation advancement by hypogastric bypass. A retrospective review of all patients undergoing EVAR since the inception of our program (1997-2006) was performed. Data were prospectively collected in an EVAR registry. Patients with large common iliac artery aneurysms (> or = 20 mm) and patent hypogastric arteries not amenable to a cuff or "bell bottom" technique were treated with coil embolization (EMBO) and/or hypogastric revascularization (BYPASS). The perioperative and mid-term outcomes were compared with the larger group of patients undergoing EVAR that did not require either treatment (CTRL). Bilateral common iliac artery aneurysms were treated with unilateral coil embolization and contralateral bypass. Common iliac artery aneurysms were present in 137 (31%) of the 444 patients undergoing EVAR, but only 57 (42%) of 137 required direct management. This included hypogastric artery embolization alone (EMBO) in 31 or hypogastric artery revascularization (BYPASS) in 26, with and without contralateral embolization (both revascularization/embolization in 46%). The procedure length (CTRL, 159 +/- 72 minutes; EMBO, 153 +/- 39 minutes; BYPASS, 283 +/- 75 minutes) and estimated blood loss (CTRL, 251 +/- 313 mL; EMBO, 233 +/- 158 mL; BYPASS, 400 +/- 287 mL) were significantly greater (P < .05) in the BYPASS group. The incidence of any postoperative complication (CTRL, 26%; EMBO, 68%; BYPASS, 54%), any ischemic complication (CTRL, 6%; EMBO, 55%; BYPASS, 27%), and new-onset buttock claudication (CTRL, 3%; EMBO, 39%; BYPASS, 27%) were all significantly greater in the BYPASS and EMBO group relative to the control (CTRL) group (n = 387). The incidence of new-onset buttock claudication ipsilateral to the hypogastric bypass was 4%; the balance of the new onset claudication in the BYPASS group was due to the contralateral embolization. The primary hypogastric artery bypass patency was 91 +/- 11% (SE) at 36 months by life-table analysis. Despite its increased complexity, hypogastric artery bypass is an excellent alternative to embolization in terms of patency and freedom from ischemic symptoms for patients with large common iliac artery aneurysms undergoing EVAR.

Significance of differences in patency among cranial sutures.

To evaluate the gross external characteristics of the coronal, lambdoid, and sagittal sutures in human cadaver skulls and determine if a difference exists in terms of patency, sex, and age. The coronal, lambdoid, and sagittal sutures were described using a modified grading scale to quantify sutural patency. An open suture was graded as 0, a fused suture as 1, and an obliterated suture as 2, 3, or 4, depending on the extent of obliteration. Thirty-six skulls were examined, including 17 female and 19 male (age range, 56-101 y). When compared with the sagittal suture, the lambdoid suture was significantly more likely to be patent and least likely to be obliterated. No significant difference in suture grades was found between female and male skulls, and no significant difference was found between age and suture grade. The prolonged patency of the lambdoid suture may be due to external forces, such as the greater number of muscles affecting the lambdoid suture when compared with the sagittal suture.

Comparison of Carbon-impregnated and Standard ePTFE Prostheses in Extra-anatomical Anterior Tibial Artery Bypass: A Prospective Randomized Multicenter Study

Objectives The aim of this study was to find out whether carbon impregnated ePTFE vascular grafts have better long-term patency or limb salvage rates than Standard ePTFE vascular grafts in crural revascularization in patients with chronic critical ischemia. Design Prospective randomized multicenter trial. Study endpoints were 36 months follow-up, major amputation or death. Materials We used 6 mm carbon ePTFE (Carboflo ®) and 6 mm standard ePTFE vascular grafts (both C.R. BARD Inc./IMPRA). Methods From June 1995 to November 1998, 283 patients were randomly assigned either to carbon (C) ( n=140) or to standard (St) ePTFE ( n=143) vascular grafts at 19 centres. A standard protocol was used with lateral extra-anatomic course of the graft to the anterior tibial artery and of a distal vein patch or cuff. More than 90% of the patients had rest pain or gangrene. Results Two hundred and sixty-five (C=130; St=135) patients could be analysed in the intention-to-treat (ITT) group. Primary patency, secondary patency and limb salvage rates after 36 months were 33, 43 and 67% in the carbon– and 30, 38 and 58% in the standard PTFE group, respectively, (log-rank test: p=0.20, 0.12 and 0.16). Additional analyses were made per protocol (PP) and as-treated (AT). The retrospective power of the study was calculated as 79 and 83%. Conclusion The ITT, PP and AT analysis, showed no statistically significant advantage of the carbon ePTFE vascular graft in terms of patency or limb salvage over the standard ePTFE vascular graft at 36 months.

Pigtail Catheters Used for Percutaneous Fluid Drainage: Comparison of Performance Characteristics

To compare the performance characteristics of various single-lumen all-purpose pigtail drainage catheters. The following parameters were compared: flow rates between catheters of the same size, whether changing the fluid viscosity has any effect on catheter comparisons, the effect on flow of leaving an open three-way stopcock in the drainage pathway, the tendency of the catheters to kink, and catheter patency after kinking, as measured according to flow. All-purpose 8.0-, 8.3-, and 8.5-F (collectively referred to as 8-F); 10.0-, 10.2-, and 10.3-F (collectively referred to as 10-F); and 12.0-F pigtail drainage catheters from three manufacturers were evaluated. Data were compared by using two-tailed t tests after normal distributions were confirmed. P < .05 was considered to represent a significant difference. At comparison of the 8-F catheters, the C.R. Bard catheters demonstrated better flow rates than the Cook and Boston Scientific devices. Among the 10-F catheters, there were no significant differences in the flow rates of fluid with viscosity equivalent to that of water between the C.R. Bard and Boston Scientific catheters; however, both these catheter types demonstrated significantly (P < .05) better flow rates than the Cook devices. Among the 12-F catheters, the C.R. Bard catheters demonstrated significantly (P < .05) better flow rates than the other two catheter types. Changing the fluid viscosity caused no changes in comparison results. In all catheter groups, the presence of a stopcock significantly (P < .05) impaired flow. None of the evaluated catheters demonstrated a clear advantage in terms of patency or susceptibility to kinking. At comparison of the in vitro performances of catheters from different manufacturers, the C.R. Bard 8.0-F and Cook 10.2-F catheters had comparable flow rates, and flow rates through the C.R. Bard and Boston Scientific 10.0-F catheters were comparable to flow rates through the Cook and Boston Scientific 12.0-F catheters. Varying viscosity had no effect on comparisons of catheter flow rates; however, a stopcock between the vacuum source and the catheter was noted to impair flow rates in all brands and sizes of evaluated catheters.

Tissue engineering of blood vessels

Tissue engineering techniques have been employed successfully in the management of wounds, burns and cartilage repair. Current prosthetic alternatives to autologous vascular bypass grafts remain poor in terms of patency and infection risk. Growing biological blood vessels has been proposed as an alternative. This review is based on a literature search using Medline, PubMed, ISIS and CAS of original articles and reviews, and unpublished material and abstracts. Complete incorporation into host tissues and the maintenance of a viable and self-renewing endothelial layer are the fundamental goals to be achieved when developing a tissue-engineered blood vessel. Sourcing of cells and modulating their interaction with extracellular matrix and supporting scaffold have been the focus of intense research. Although the use of tissue-engineered blood vessels in humans is so far limited, advances in our knowledge of stem cell precursors and the development of new biomaterials should enable this technology to reach routine clinical practice within a decade.

Coil-reinforced hydrogel tubes promote nerve regeneration equivalent to that of nerve autografts

Despite spontaneous sprouting of peripheral axons after transection injury, peripheral regeneration is incomplete and limited to short gaps, even with the use of autograft tissue, which is considered to be the “gold” standard. In an attempt to obviate some of the problems associated with autografts, including limited donor tissue and donor site morbidity, we aimed to synthesize a synthetic nerve guidance channel that would perform as well as the nerve autograft. Given that the patency of the nerve guidance channel is critical for repair, we investigated a series of nerve guidance channel designs where patency and the resulting regenerative capacity were compared in a transected rat sciatic nerve injury model. Three tube designs were compared to autograft tissue: plain, corrugated and coil-reinforced tubes of poly(2-hydroxyethyl methacrylate- co-methyl methacrylate). Of the three designs, the coil-reinforced tubes demonstrated superior performance in terms of patency. By electrophysiology and histomorphometry, the coil-reinforced tubes demonstrated outcomes that were comparable to autografts after both 8 and 16 weeks of implantation. The nerve action potential (NAP) velocity and muscle action potential (MAP) velocity for the coil-reinforced PHEMA-MMA tube was 54.6±10.1 and 10.9±1.3 m/s, respectively at 16 weeks, which was statistically equivalent to those of the autograft at 37.5±7.9 and 11.3±2.0 m/s. The axon density in the coil-reinforced tube was 2.16±0.61×10 4 axons/mm 2, which was statistically similar to that of the autograft of 2.41±0.62×10 4 axons/mm 2 at 16 weeks. These coil-reinforced tubes demonstrated equivalence to autografts for nerve regeneration, demonstrating the importance of channel design to regenerative capacity and more specifically the impact of patency to regeneration.

Interventionelle Endoskopie bei benignen und malignen Gallengangsstenosen

During the past years several endoscopic and interventional techniques have been developed for the treatment of bile duct strictures and have had a strong impact on therapeutic regimens. Benign stenoses of the bile duct are mainly caused by cholecystectomy or liver resection or by inflammatory diseases. Insertion of an endoprosthesis insertion or balloon dilation is clinically successful in 60 to 90 % of these patients and will result in adequate opening of the stricture. To date, only bile duct stenosis in chronic pancreatitis are not improved satisfactorily by endoscopy. The insertion of an endoprosthesis is a cornerstone in the treatment of malignant obstructive jaundice in patients with cancer. Several comparative studies have demonstrated the advantages of self-expanding metal stents (SEMS) over plastic prostheses in terms of patency. A selective use of SEMS is mandatory, as the costs for SEMS are high and many patients with malignant jaundice will die with their first plastic prosthesis in situ without stent occlusion. In patients with hilar cholangiocarcinoma, the combination of photodynamic therapy and endoprosthesis insertion might result in a survival advantage. The use of bioabsorbable stent materials or coating of the stent with antiproliferative drugs will improve the treatment results in the future.

New murine model of spontaneous autologous tissue engineering, combining an arteriovenous pedicle with matrix materials.

The authors previously described a model of tissue engineering in rats that involves the insertion of a vascular pedicle and matrix material into a semirigid closed chamber, which is buried subcutaneously. The purpose of this study was to develop a comparable model in mice, which could enable genetic mutants to be used to more extensively study the mechanisms of the angiogenesis, matrix production, and cellular migration and differentiation that occur in these models. A model that involves placing a split silicone tube around blood vessels in the mouse groin was developed and was demonstrated to successfully induce the formation of new vascularized tissue. Two vessel configurations, namely, a flow-through pedicle (n = 18 for three time points) and a ligated vascular pedicle (n = 18), were compared. The suitability of chambers constructed from either polycarbonate or silicone and the effects of incorporating either Matrigel equivalent (n = 18) or poly(DL-lactic-co-glycolic acid) (n = 18) on angiogenesis and tissue production were also tested. Empty chambers, chambers with vessels only, and chambers with matrix only served as control chambers. The results demonstrated that a flow-through type of vascular pedicle, rather than a ligated pedicle, was more reliable in terms of patency, angiogenesis, and tissue production, as were silicone chambers, compared with polycarbonate chambers. Marked angiogenesis occurred with both types of extracellular matrix scaffolds, and there was evidence that native cells could migrate into and survive within the added matrix, generating a vascularized three-dimensional construct. When Matrigel was used as the matrix, the chambers filled with adipose tissue, creating a highly vascularized fat flap. In some cases, new breast-like acini and duct tissue appeared within the fat. When poly(dl-lactic-co-glycolic acid) was used, the chambers filled with granulation and fibrous tissue but no fat or breast tissue was observed. No significant amount of tissue was generated in the control chambers. Operative times were short (25 minutes), and two chambers could be inserted into each mouse. In summary, the authors have developed an in vivo murine model for studying angiogenesis and tissue-engineering applications that is technically simple and quick to establish, has a high patency rate, and is well tolerated by the animals.

Vascular access survival and incidence of revisions: A comparison of prosthetic grafts, simple autogenous fistulas, and venous transposition fistulas from the United States Renal Data System Dialysis Morbidity and Mortality Study

Objective: The study's aim was to evaluate access patency and incidence of revisions in patients initiating hemodialysis and to determine differences in access performance by type of access among patient subgroups. Methods: The study used data from the United States Renal Data System Dialysis Morbidity and Mortality Study Wave 2, which contained a random sample of dialysis patients initiating dialysis in 1996 and early 1997. Failures and revisions were evaluated among 2247 newly placed hemodialysis accesses by using Cox proportional hazards regression model and Poisson regression. Primary and secondary patency rates were estimated using the Kaplan-Meier method. Results: Fifteen hundred seventy-four prosthetic grafts, 492 simple autogenous fistulas, and 181 venous transposition fistulas were available for evaluation. Prosthetic grafts had a 41% greater risk of primary failure compared with simple fistulas (relative risk, 1.41; 95% CI, 1.22-1.64; P <.001) and a 91% higher incidence of revision (relative risk, 1.91; 95% CI, 1.60-2.28; P <.001). At 2 years, autogenous fistulas demonstrated superior primary patency (39.8% versus 24.6%, P <.001) and equivalent secondary patency (64.3% versus 59.5%, P =.24) compared with prosthetic grafts. When compared with simple fistulas, vein transpositions demonstrated equivalent secondary patency at 2 years (61.5% versus 64.3%, P =.43) but inferior primary patency (27.7% versus 39.8%, P =.008) and had a 32% increased incidence of revision (P =.04). Autogenous fistulas had superior primary patency compared with prosthetic grafts in all patient subgroups except for patients with previously failed access. Vein transpositions showed the greatest benefit in terms of patency and incidence of revision in women and in patients with previously failed access. Conclusions: The preferential placement of autogenous fistulas may increase primary patency and decrease the incidence of revisions. Vein transpositions had similar secondary patency compared with simple fistulas, but required more revisions. The greatest benefit of a vein transposition fistula was seen in women and in patients with a history of access failure. (J Vasc Surg 2001;34:694-700.)

PALLIATIVE TREATMENT OF INOPERABLE MALIGNANT ESOPHAGEAL STRICTURES WITH CONICALLY SHAPED COVERED SELF-EXPANDING STENTS

To investigate the effectiveness of conically shaped covered self-expanding (Flamingo) stents in palliative treatment of malignant esophagogastric strictures in terms of patency, improved dysphagia score and survival. Flamingo stents were placed under fluoroscopic guidance between August 1998 and December 1999 for palliation of malignant dysphagia in 33 cases. There were 21 males and 12 females aged 40--80 years (average 64.2 years). Stent placement was successful in all patients, with good symptomatic control and no procedure-related complications. Spontaneous esophago-respiratory fistula and perforation accompanying malignant esophageal stricture in a total of 4 cases (12.2%) were successfully closed. In 1 case, tumor ingrowth was detected from the distal uncovered segment of the stent. In 2 cases with esophago-respiratory fistula, gastrointestinal bleeding occurred. The cause of hemorrhage could not be found by angiography. The mean survival time in 17 patients, later deceased, was 129 days (range 9--360), and the mean observation time in 16 patients still alive is 180 days (range 18--365). Flamingo stents provide an effective and safe choice of palliative therapy in inoperable malignant esophagogastric strictures.