Fluid transfer as a mechanism leading to endotension.

Some abdominal aortic aneurysms bridged with a minimally invasively introduced stent graft prosthesis increase in size without any diagnosable evidence of endoleakage (endotension). There are three possible pathways proposed through which undetectable low rates of blood flow may cause an aneurysm sac to be refilled: through the thrombus at the prosthesis attachment sites, through the clotted collaterals and through the clotted stent graft wall. If the inflow is more rapid than any drainage through the wall of the aneurysm is re-pressurised. However, critical magnitudes for the permeability of the clotted graft and the geometry of the thrombus at the aneurysm, necessary to inhibit endotension, are not known. The aim of this study was to determine which boundary conditions prevent endotension. An analytical model based on Darcy's Law was used to estimate the pressure in the aneurysm sac due to fluid transfer. Experimentally determined time- and pressure-dependent permeability of red and intraluminal thrombus, and of clotted graft materials were input into the model. The computational analysis showed that endotension is unlikely to be caused by fluid transfer from the collaterals or via the prosthesis attachment sites, but rather due to flow through the stent graft wall. Based on this study it can be stated that grafts with a permeability below 2e-13 mm(2) should diminish the occurrence of endotension.

[General surgery under discussion. From the viewpoint of vascular surgery]. / Allgemeinchirurgie in der Diskussion. Aus Sicht der Gefäbchirurgie.

Vascular diseases are common and their frequency is rising. Statistics show that 15% of the German population over 65 display some kind of peripheral arterial pathology. Even aneurysmatic degeneration and cardiac and visceral perfusion disorders are being observed more frequently, while peak age is dropping. Therapeutic surgical options are accordingly being continually advanced and refined. Additionally the range of interventional therapies and new conservative options has substantially increased vascular surgeons' armamentarium. Updates in surgical training have responded to this increase in such disorders, and the diversification of therapeutic modalities has resulted in the elevation of vascular surgery from specialized techniques to a fully accredited specialty equal in standing to the other seven surgical disciplines. Controversy exists however about the new accredition, beginning with the question of advancement from basic surgical training while excluding important elements of general surgery. Since those training for this specialty will branch off immediately after 2 years of basic surgical training, their final accreditation in the new classification would exclude essential skills that remain part of the training as general surgeons.

Certification of vascular centers - a project of the German Society for Vascular Surgery.

OBJECTIVES: Due to the progress vascular medicine has made in conventional vascular surgery, endovascular procedures, and conservative therapy close, interdisciplinary cooperation is required. In order to assure the contextual and structural quality of vascular centers, the German Society for Vascular Surgery established a list of criteria for certification of each interdisciplinary vascular center. MATERIAL AND METHODS: Between July 2002 and December 2005, 77 centers have submitted a written application and have been audited by the commission for quality assurance of the German Society for Vascular Surgery, 59 vascular centers were certified for a period of 3 years with one center in each in Austria and in Switzerland, 13 centers were not certified (16.8%), and the applications of 5 centers are still pending. This analysis is based on 57 German certified vascular centers. RESULTS: Each center treats a median of 1149 inpatients (11% of these are emergency admissions) and 2,159 outpatients per year. Sixty percent of the patients treated have an arterial disease. All centers have vascular surgery and radiology departments. In 11 out of 57 centers, angiology services are offered in cooperation with affiliated physicians. Each vascular center has an average of 4.2 vascular surgeons, 3 radiologists and 1 angiologist. All centers offer radiological and ultrasound diagnostics (CT angiography in 100%, MRT in 95%, duplex sonography in 100%). Each clinic executes a median of 521 (233-1436) arterial operations and 263 (37-1055) arterial interventions. In addition, they execute varicose surgeries (n=217), shunt applications/revisions (n=58), minor amputations (n=57) and major amputations (n=42). They conduct 338 (92-3606) conservative therapies per year (POAD, diabetic foot, phlebothrombosis, chronic venous insufficiency). CONCLUSIONS: The certification of interdisciplinary vascular centers is a new approach to assure the contextual and structural quality of interdisciplinary vascular centers.

[Results of the certification of vascular centers by the German Society for Vascular Surgery]. / Ergebnisse der Zertifizierung von Gefässzentren durch die Deutsche Gesellschaft für Gefässchirurgie.

INTRODUCTION: Advances in conventional vascular surgery, endovascular procedures and conservative treatment require close interdisciplinary cooperation. The term Vascular Centre indicates to patients and referring doctors optimal professional and organisational competence. METHODS: 73 applications by vascular centres for certification were made between June 2002 and December 2005, of which after audit 54 were successful for three years, including one centre each in Austria and Switzerland. 13 centres were not accepted and six are still under consideration. This analysis is based on the data of 52 certified centres in the Federal Republic of Germany. RESULTS: A mean of 1149 patients were hospitalized in these centres per year (12 % emergency admissions) and 2159 patients per year were treated as outpatients, 60 % with arterial vascular disease. All centres have vascular surgery and radiology department, 10 of the 52 centres cooperate with specialists in private practice to provide an angiology service. A mean of 460 arterial vascular operations and 239 arterial interventional procedures were performed at each centre annually. In addition there were operations for varicose veins (n = 217), shunt operations (n = 58) and major amputations (n = 42). Inpatient or outpatient conservative treatment (for peripheral vascular disease, diabetic foot syndrome, phlebothrombosis or chronic venous insufficiency) was given to a mean of 338 patients annually. CONCLUSIONS: Certification of interdisciplinary vascular centres provides structural and medical data and the beginnings of comparing such centres. A future task will be standardization of documentation and continuing assessment of the quality of results.

[Adjusting a surgery department to new conditions in the German health service: day surgery, short-stay surgery, vascular centers and wound centers]. / Anpassung einer chirurgischen Klinik an die Herausforderungen im GesundheitswesenDie Tageschirurgie, die Kurzzeitchirurgie, das Gefässzentrum und die Wundsprechstunde.

In April 1994, after the preconditions for ambulatory surgery came into effect, the day surgery ward was opened in the Hamburg-Harburg General Hospital. Besides ambulatory operations, this ward provides all surgical pre- and postoperative care. In addition to the surgical sections, different departments (urology, gynecology, dentistry, radiology, ophthalmology) take advantage of the ward. As preoperative diagnostics also could be completed ambulatorily, we were then able to establish a short-stay surgery department. This ward was opened in June 1996. One year later, the vascular center ("Gefässcentrum Harburg") was established by the departments for surgery, radiology, and angiology. This structure has been integrated into the day and short-stay surgery wards functionally and spatially. With the organizational structures mentioned and by setting up a wound consultation service, it is possible to optimize the capacity for admissions, operations, and beds. Government and health insurance demands for better processing can be filled and efficiency is increased.

What can we learn from explanted endovascular devices?

OBJECTIVE: To examine the durability of the Stentor and Vanguard endovascular devices in human implants. METHODS: The textile covering, the polypropylene ligatures and the stent metal of 34 devices (25 Stentor, 9 Vanguard) with a mean duration of implantation of 28.8 +/- 16 months was examined by means of stereomicroscopy and scanning electron microscopy. RESULTS: The polyester textile covering showed gaps along the sutured seam and isolated holes in the fabric. All of the examined polypropylene ligatures were worn, some ruptured. Four different types of stent corrosion were classified--pits (100%), bizarre craters (68%), large deficiencies (14%) and fractures (32%). CONCLUSION: Holes in the polyester fabric and frame dislocations are specific for the design of Stentor and Vanguard grafts. The early corrosion of the stent metal Nitinol in these devices is surprising. Until more experience is gained with other devices, we have to be reminded, that the "gold standard" for the long-term durability of artificial vascular grafts is still "today's" conventional graft.

[Injury of polyester grafts by vascular clamps]. / Schädigung von Polyestergefässprothesen durch Gefässklemmen.

UNLABELLED: Protected vascular clamps are not new. Clamp associated damage of human arteries has already been published over 20 years ago. The necessity of protective clamps seems to have been forgotten. In our explant archive (230 explants) we have observed an accumulation of graft ruptures in the groin (13 of 25 ruptures). We presume a multifactorial process. Clamp damage could be part of it. The aim of this study is to prove the clamp induced damage of polyester vascular grafts and to examine whether protected clamps can reduce this. METHOD: Five unprotected (Aesculap(R) FB512R, FB502, FB517, Ulrich CC1235, CV3535) and 5 protected vascular clamp types (Aesculap(R) FB667, FB668, Edwards(R) - formally Baxter(R) - Fogarty(R) CV5050, CV5201, Edwards(R) Cosgrove(R) CV1033) were tested. A longitudinal burst test was performed after maximal clamp closure on 6 different, multifilament polyester yarns of 2 different vascular grafts manufacturers (B. Braun(R), Edwards(R)). RESULTS: The yarn tests with protected clamps showed no difference to those of the unclamped yarns. After clamping with unprotected vascular clamps the stress-strain-diagrams differed significantly. The mean, maximum burst strength was up to 75 % lower. Video documentation revealed filament ruptures. Damage of the yarn surface was seen on a simple woven graft in scanning electron microscopy (SEM). DISCUSSION: The application of unprotected vascular clamps on polyester vascular grafts is common in Germany (56 %). The observed damage of multifilament polyester yarns makes it necessary to re-consider the use of unprotected vascular clamps. The benefit for biological vessels has already been shown.

Corroded nitinol wires in explanted aortic endografts: an important mechanism of failure?

PURPOSE: To analyze surface alterations and fractures observed in the nitinol stent wires of explanted endovascular grafts used for treatment of abdominal aortic aneurysm. METHODS: Twenty-one explanted Stentor devices and 1 Cragg stent were received from investigators in Germany and France. After macroscopy and photography, the explants were cleaned and the polyester coating removed. The frame was examined completely by stereomicroscopy, and irregularities were assayed by scanning electron microscopy and energy dispersive x-ray analysis (EDAX). The observed alterations were classified according to stereomicroscopic and electron microscopic morphology. RESULTS: The mean implantation interval for the endografts was 29.1 +/- 13.2 months (range 5-46). All examined explants, even those retrieved after only a few months in situ, showed pitlike surface damage 10-25 microm in diameter. Larger, irregularly shaped surface alterations were observed in approximately 70% of the explants. Older explants (age >32 months) presented vast regions of decay, with bending of the wire and stress cracks in some areas. EDAX examination revealed decreased nickel concentration in the corroded regions. CONCLUSIONS: Corrosion of the nitinol wire in endovascular grafts is confirmed. Presumably, the observed pitting and irregularly shaped corrosion defects are the precursors of material failure. They weaken the thin wire, which leads to stress cracks and eventually fracture of the stent wire under circulatory pulsation. Cell-induced electrochemical corrosion and active cellular destruction of surfaces are well-known mechanisms that must be investigated for their possible roles in the corrosion of stent metals.

[The giant, pendulant goiter. A case report]. / Die Struma gigantea pendulans - Ein Fallbericht -

A 48-year-old woman with a monstrous goiter was referred to our hospital. She noticed a growth of the goiter for about 20 years, until now she did not undergo surgery because she was afraid of the operation. In September 1999 she suffered from a cardiac decompensation because of a hyperthyreosis, so she decided to be operated. The examination showed a giant goiter, placed in front of the sternum. After a detailed check of risk factors, we resected the goiter in general anaesthesia. The thyroid gland weighed 5 100 grams, in the histologic examination no signs of malignancy were found. Postoperatively, a hypocalcaemia occurred, without clinical symptoms. The patient was discharged on the 6th postoperative day.

Longitudinal ruptures of polyester knitted vascular prostheses.

AIM: The purpose of the study was the characterization of a type of rupture occurring on warp-knitted polyester vascular prostheses. MATERIALS AND METHODS: We studied 20 cases of warp-knitted polyester vascular prostheses that were explanted from humans that showed a longitudinal rupture as a part of a collaborative retrieval program. All the prostheses were immediately fixed in a 10% formaldehyde solution after their explantation in the operating room. The clinical data of these cases were recorded. The explants were photographed, washed to eliminate the surrounding tissues, and photographed again. The ruptures were characterized with macroscopic examination, optical stereomicroscopy, and scanning electron microscopy. RESULTS: The mean duration of implantation of the prostheses was 16.0 +/- 3.3 years (range, 9-20.7 years). The prostheses were Cooley Double Velour (n = 15) and Microvel Double Velour (n = 5). There were 16 aortobifemoral bypass grafts, 1 aorto-biiliac, 1 aorto-aortic, 1 iliofemoral, and 1 axillobifemoral. The longitudinal ruptures occurred on two specific parts of the prostheses: the guide line (6 cases) and the remeshing line (11 cases). In three cases both lines were affected. Scanning electron microscopy showed major degradation of the trilobar filaments of the velour and gradual ruptures of the flat filaments of the remeshing and guide lines. CONCLUSIONS: In this study, we have identified a specific mechanism of late (9-20 years) longitudinal rupture of knitted polyester prostheses consisting of degradation of the polyester filaments along the remeshing and guide lines that run the length of the graft.

Vascular tumors simulating occlusive disease.

Two cases of vascular tumors of large vessels with intraluminal growth simulating venous thrombosis and arterial occlusive disease are reported. One was a borderline malignant epithelioid hemangioendothelioma of the femoral vein and the other a malignant epithelioid angiosarcoma of the carotid artery. Immunohistochemical studies permitted to classify the tumors. Treatment consisted in surgical resection. No recurrence and no metastasis are noted at 24 months. Uncertainty regarding biological behaviour of vascular tumors and treatment persists.

[Late complications after alloplastic vascular replacement]. / Spätkomplikationen nach alloplastischem Gefässersatz.

The follow-up of 273 AAA patients operated 1981-1985 showed a mean dilation of polyester grafts of 17.4% in 12 days and 34.8% in 3 years. This early dilation is due to mesh expansion of the warp knitted grafts. It has no clinical relevance. In contrary the late dilation after approximately 10 years is due to degradation. The evaluation of 436 explanted grafts attained from 75 hospitals showed graft rupture to be the cause of the explanation for 42/255 (16%) polyester grafts and 2/42 (5%) PTFE grafts. The most ruptures were observed in the surrounding of the inguinal ligament after 10 to 20 years of duration. In comparison to modern endovascular grafts the conventional polyester and PTFE grafts still are the gold standard of durability.

[Stent wire fractures and mesh loosening in explanted endovascular prosthesis]. / Stentdrahtbrüche und Maschenlockerungen explantierter, endovaskulärer Prothesen.

UNLABELLED: Vascular grafts are available since the middle of the 50's. Explant retrieval studies still reveal not published material degradation today, after over 40 years of product development. Endovascular grafts exist since the beginning of the 90's. New developments and modifications have lead to numerous devices. The importance of explant retrieval studies grows. MATERIALS AND METHODS: Among 33 stentgrafts, retrieved 5 to 43 months after implantation, the majority were 18 MinTec devices (17 Stentor, 1 Cragg). These 18 explants were examined by endoscopy, stereomicroscopy and scanning electron microscopy. RESULTS: The following material degradation was observed. The textile coating showed holes along the longitudinal seam, the ligatures in-between the stentframes burst, allowing the frames to dislocate. Occasional fractures of the stent wire were seen accompanied by bowl-shaped alterations of the surface. CONCLUSION: The Stentor device is, since its modification 1996, not available any longer. It was one of the most applied devices world-wide. The possible material deficiencies must be known by those performing patient follow-up. The occurrence of alterations within 43 months shows the importance of a continued follow-up besides clinical trials.

The effect of autoclave resterilisation on polyester vascular grafts.

OBJECTIVES: polyester grafts are expensive, single-use items. Some manufacturers of uncoated, woven grafts include instructions for autoclave resterilisation to be performed at the surgeon's own request. Others warn against such manipulation. Theoretically, the glass transition point of polyester at 70-80 degrees C and the possible acceleration of hydrolysis suggest that autoclave resterilisation at 135 degrees C might be a problem. MATERIALS AND METHODS: a DeBakey Soft Woven Dacron Vascular Prosthesis (Bard) and a Woven Double Velour Dacron Graft (Meadox) were autoclave-resterilised 0 to 20 times, having been weighed before and after sterilisation. Tactile testing was performed. Mechanical properties were examined by probe puncture and single-filament testing, the surface was examined by scanning electron microscopy and the degree of hydrolysis by infra-red spectroscopy. RESULTS: tactile testing revealed a change of feeling with increasing cycles of resterilisation. Investigation of weight, textile strength, single-filament strength, electron microscopy of the surface and infra-red spectroscopy showed no change of the material. CONCLUSIONS: changes felt are presumably a surface phenomenon, not measurably affecting strength or chemistry of material after autoclave resterilisation. We therefore feel that it is safe to use once-autoclave-resterilised surplus uncoated polyester grafts, provided that sterility is guaranteed.

Aortobifemoral prosthetic infection treated by cryopreserved arterial homografts of the European Homograft Bank.

The excision of an infected aortobifemoral Dacron graft 9 years after implantation and bilateral axillofemoral Dacron bypass reconstruction led to reinfection of the extra-anatomic bypass grafts. A new aortobifemoral reconstruction was performed using cryopreserved homografts delivered by the European Homograft Bank in Brussels and both axillo-femoral prostheses were removed. No signs of infection and no alterations of the homografts can be detected 3 years later.