Safety Evaluation of Unibody Endografts for Abdominal Aortic Aneurysm Repair: A Systematic Review and Meta-Analysis.

BACKGROUND: The unibody bifurcated aortic endograft (AFX/AFX2) has emerged as a treatment option for abdominal aortic aneurysms (AAAs). This systematic review and meta-analysis aimed to evaluate the safety of the unibody endograft. METHODS: A literature search was conducted in Cochrane Library, Scopus, Web of Science, and PubMed. Studies assessing the unibody endograft for AAA repair between 2014 and 2023 were included. The defined primary outcomes were the incidences of type I, II, and III endoleaks. The secondary outcomes were access site problems, aneurysm-related mortality, aneurysm rupture, all-cause mortality, aneurysm sac growth, limb occlusion, stent graft migration, and technical success rate. RESULTS: Fourteen studies including 12 observational studies and 2 randomized controlled trials were included in the systematic review. The meta-analysis included 10 studies with 12,690 patients that reported the measured outcomes, and excluded 4 studies that did not. Type II endoleaks had the highest incidence of 12% (95% confidence interval [CI]: 4-20%), followed by type III endoleaks with an incidence of 3% (95% CI: 1-5%). The incidence of type I endoleaks was 1% (95% CI: 0-2%). A subgroup analysis by follow-up duration showed that type II endoleak incidence was higher after 1 to 2 years of follow-up than 3 to 4 years of follow-up. The incidence of aneurysmal mortality was 2% (95% CI: 0-7%), limb occlusion was 1% (95% CI: 0-1%), stent graft migration was 1% (95% CI: 0-2%), aneurysmal rupture was 6% (95% CI: 2-11%), access site problems were 7% (95% CI: 2-13%), aneurysm sac growth was 2% (95% CI: 0-4%), all-cause mortality was 21% (95% CI: 4-38%), and technical success rate was 100% (95% CI: 98-100%). CONCLUSIONS: The unibody endograft is a safe and minimally invasive approach for AAA repair. However, potential complications necessitate close patient follow-up after the intervention.

Evidence-Based Complementary Benefit of the Vascular Surgeon Among the Team of Renal Transplantation; a Single Center Experience.

BACKGROUND: In a kidney transplant tertiary referral center; we compared 3 operating team configurations of different surgical specialties to highlight the effect of the operating surgeon's specialty on various operative details and procedural outcome. METHODS: A total of 50 cases of living donor transplantations were divided into 3 main groups according to the operating surgeons' specialty, the first group (A) includes 12 patients exclusively operated on by urologists with advanced training in transplantation, the second group (B) includes 35 patients operated by combined surgical specialties; a urologist and a vascular surgeon both with advanced transplantation training, and a third group (C) includes 3 cases where the transplant operation commenced with operating urologists as in group (A) but required intraoperative urgent notification of a vascular surgeon to manage unexpected intraoperative technical difficulties or major complications. Cases were studied according to operative details, anastomosis techniques, ischemia times, total procedure time, recovery of urinary output, intensive care unit (ICU) stay, postoperative surgical complications and serum creatinine level for up to 3 years of follow-up. RESULTS: Study of operative details revealed that total duration of graft ischemia was significantly shorter in group (B) and significantly longer in group (C) (P value 0.001), Total procedural duration also varied significantly between the 3 groups, group (B) being the shortest while group (C) was the longest (P value less than 0.001). Technically; group (A) used only end to end arterial anastomosis as a standard technique, while group (B) used both end-to-end and end-to-side anastomoses as required per each case. End to side anastomosis in group (B) yielded better immediate graft response in the form of change in color, texture, earlier and more profuse postoperative urine volumes (P value 0.025). Furthermore, anastomosis to common and external iliac arteries (group B) yielded earlier and higher urine volumes than the internal iliac artery (P values 0.024 and 0.031 respectively). Group (B) recorded significantly less postoperative perigraft hematomas and lymphoceles compared to the other 2 groups. Equal rates of urine leaks, ICU stay, creatinine levels, patient and grafts survival rates among groups (A) and (B), while postoperative recovery and ICU stay duration were more lengthy in the complicated group (C). CONCLUSIONS: A vascular surgeon operating in a transplantation team would deal comfortably and efficiently with various vascular related challenges and complications, thus avoiding unnecessary time waste, complications and costs.

One-year results of stent graft repair for carotid artery pseudo-aneurysm in patients with Behcet's disease.

OBJECTIVES: Behcet's disease is a multisystem disorder of unknown etiology with vascular complications. This study reviewed the mid-term outcome of Behcet's disease patients with carotid artery pseudo-aneurysms treated by endovascular stent-graft repair at our unit. METHODS: During a period of 11 years, six cases were included. Postoperative ultrasound duplex results were recorded along with computed tomography angiography report done a year after intervention. RESULTS: The mean age (±SD) was 38 (±5.2) years. The mean (±SD) pseudo-aneurysm size was 33 (±12.2) mm. Technical success was 83%; failed cannulation of the internal carotid artery was encountered in one case. On day 2 post-operative, a duplex ultrasound revealed complete exclusion and thrombosis of the false aneurysm in all cases. A year later, a computed tomography angiography revealed a primary patency rate of 80%, and only one case had a recurrent pseudo-aneurysm at the distal margin of the stent graft. All cases, however, had complete thrombosis in the pseudo-aneurysms lumen with a mean (±SD) regression in size of 18 (±6) mm. The mean (±SD) percentage of in-stent stenosis was 34.5% (±11.73%). CONCLUSIONS: Stent graft repair for carotid artery pseudo-aneurysm in Behcet's disease patients might be the preferable first line of treatment since it had a high technical success and mid-term primary patency rates, with additional fact that it obviously avoids the hazardous complications of surgery.

Evaluation of Tissue Perfusion by Wound Blush and 2D Color-Coded Digital Subtraction Angiography During Endovascular Intervention and Its Impact on Limb Salvage in Critical Limb Ischemia.

PURPOSE: Critical limb ischemia (CLI) is an entity with high mortality if not properly treated. The primary aim of CLI revascularization is to enhance wound healing, which greatly depends on microvascular circulation. The available tools for assessment of revascularization success are deficient in the evaluation of local microvascular tissue perfusion, that wound blush (WB) reflects. A reliable technique that assesses capillary flow to foot lesions is needed. This study aims to assess WB angiographically at sites of interest in the foot after revascularization and its impact on limb salvage in CLI. MATERIALS AND METHODS: 198 CLI patients (Rutherford category 5/6) with infrainguinal atherosclerotic lesions amenable for endovascular revascularization (EVR) were included. Limbs were directly or indirectly revascularized by EVR. Direct revascularization meant that successful revascularization of the area of interest according to the angiosome concept was achieved. A completion angiographic run was taken to assess WB. Patients were divided into 2 groups; positive and negative WB groups. In the event of a disagreement between the observational investigators, the digital subtraction angiography (DSA) series was analyzed for hemodynamic changes with a computerized 2D color-coded DSA (Syngo iFlow). RESULTS: 176 limbs had successful revascularization in 157 patients. The successful revascularization rate was 88.9% (176/198), with technical failure encountered in 22 limbs. 121 patients had positive WB and 55 patients had negative WB. Direct revascularization of target areas was obtained in 98 limbs (55.7%). There was a significant difference in the rate of achieving direct flow to the lesion between the positive WB and negative WB groups (36.4% vs 19.3%, p≤0.001). We noticed a nonsignificant difference between patients who had direct revascularization of the foot lesion(s) and those who had indirect revascularization as regards limb salvage. Patients were followed up for 25.2 ± 12.7 months. By the end of the first year, limb salvage rate was significantly higher in patients who had positive WB (98% vs 63%, p<0.001, after 2 years (97% vs 58%, p<0.001) and after 3 years (94% vs 51.5%, p<0.001). CONCLUSIONS: WB is an important predictor and a prognostic factor for wound healing in CLI patients with soft tissue lesions.

Clinical and hemodynamic outcome of morbidly obese patients with severe chronic venous insufficiency with and without bariatric surgery.

OBJECTIVE: Obesity is associated with several medical problems, including chronic venous insufficiency resistant to usual conservative measures. Venous intervention in patients with a body mass index (BMI) >30 kg/m2 is associated with a higher anesthetic risk and recurrence rate. The aim of the present study was to compare the severity of venous insufficiency in terms of the clinical findings and hemodynamics between morbidly obese patients who had and had not undergone bariatric surgery (BS). METHODS: A total of 123 patients with morbid obesity and severe venous manifestations were included in the present study. The patients were divided into two groups. Group A included 72 patients who had undergone BS, and group B included 51 patients who had not undergone BS. Assessments were performed using both disease-specific and physician-generated tools and duplex ultrasonography. RESULTS: Of the 123 patients, 66% were men. The mean patient age was 44 ± 8.2 years. All the patients were followed up for 1 year. The mean BMI for group A had decreased from 50.1 ± 5.6 kg/m2 to 32.9 ± 4.2 kg/m2 (P = .0001). However, the mean BMI for group B had increased from 49.2 ± 6.1 kg/m2 to 50 ± 5.7 kg/m2 (P = .16). For the patients with a history of venous ulcer, the Charing Cross Venous Ulceration Questionnaire score for group A had decreased 77.5 to 36.8 (P = .0001) compared with a decrease in group B from 77.34 to 75.36 (P = .13). In group A, the median Venous Disability Score had improved from 2 to 0 and the median Venous Clinical Severity Score from 8.6 to 2.1 compared with nonsignificant changes in group B. The number of patients with venous claudication had decreased from 8 to 2 (P = .036) in group A compared with no changes in group B. For group A, the mean 36-item short-form heath survey score had increased from 48 ± 6.8 to 81 ± 4.4 (P = .001) compared with an increase from 52 ± 8.8 to 59 ± 1.2 (P = .52) in group B. The mean common femoral vein diameter had decreased significantly in group A (7.3 ± 1.3 mm) compared with that in group B (8.93 ± 1.08; P = .0001). The peak venous velocity showed higher values for the patients who had undergone BS (group A, 14.9 ± 2.5 cm/s; group B, 10.75 ± 2.05 cm/s; P = .0001). Higher mean velocities and a lower diameter resulted in a higher wall shear stress in group A compared with that in group B (2.2 ± 1.1 dyn/cm2 vs 1.16 ± 0.52 dyn/cm2; P = .0001). CONCLUSIONS: The patients who had lost weight after BS experienced noticeable improvements in chronic venous insufficiency compared with the patients who had not lost weight, including an increased rate of ulcer healing, a decreased incidence of venous claudication, and improved quality of life.

Is atherectomy the best first-line therapy for limb salvage in patients with critical limb ischemia?

OBJECTIVE: To determine the efficacy of atherectomy for limb salvage compared with open bypass in patients with critical limb ischemia. METHODS: Ninety-nine consecutive bypass and atherectomy procedures performed for critical limb ischemia between January 2003 and October 2006 were reviewed. RESULTS: A total of 99 cases involving TASC C (n = 43, 44%) and D (n = 56, 56%) lesions were treated with surgical bypass in 59 patients and atherectomy in 33 patients. Bypass and atherectomy achieved similar 1-year primary patency (64% vs 63%; P = .2). However, the 1-year limb salvage rate was greater in the bypass group (87% vs 69%; P = .004). In the tissue loss subgroup, there was a greater limb salvage rate for bypass patients versus atherectomy (79% vs 60%; P = .04). CONCLUSIONS: Patients with critical limb ischemia may do better with open bypass compared with atherectomy as first-line therapy for limb salvage.

Human carotid plaque calcification and vulnerability. Relationship between degree of plaque calcification, fibrous cap inflammatory gene expression and symptomatology.

BACKGROUND: Inflammation is a key mechanism in human atherosclerotic plaque vulnerability and disruption. The objective was to determine the differential gene expression of pro- and anti-inflammatory factors in the fibrous cap and shoulder region of noncalcified and calcified carotid endarterectomy plaques. METHODS: Thirty carotid endarterectomy plaques were classified as type Va (noncalcified, n = 15) and type Vb (calcified, n = 15) in accordance with the American Heart Association consensus. Using laser capture microdissection, fibrous cap and shoulder regions were excised from frozen sections. Gene expression of pro- [interleukin 1 (IL-1), IL-8 and monocyte chemoattractant protein 1 (MCP-1)] and anti-inflammatory (IL-10) factors, and bone formation (bone morphogenetic protein 6 and osteocalcin) mediators were quantitated by real-time PCR. Protein levels were determined using Western blotting. RESULTS: Mean percent carotid stenosis and calcification area were 79 and 5% in Va-plaques (40% symptomatic) and 77 and 42% in Vb-plaques (20% symptomatic). Macrophages infiltrating the region of the fibrous cap and the shoulder were more numerous in non-calcified plaques compared with calcified plaques (p < 0.01]. mRNA expression of MCP-1 and IL-8, and protein levels of IL-8 were also greater in Va plaques compared to Vb plaques (p < 0.05). Protein levels and mRNA expression of osteocalcin were greater in Vb compared to Va plaques (p < 0.05). CONCLUSIONS: Fibrous cap inflammation is more likely to occur in noncalcified than in calcified plaques. These findings suggest that carotid atherosclerotic plaque calcification is a structural marker of plaque stability.

Reappraisal of velocity criteria for carotid bulb/internal carotid artery stenosis utilizing high-resolution B-mode ultrasound validated with computed tomography angiography.

OBJECTIVE: Reliability of the most commonly used duplex ultrasound (DUS) velocity thresholds for internal carotid artery (ICA) stenosis has been questioned since these thresholds were developed using less precise methods to grade stenosis severity based on angiography. In this study, maximum percent diameter carotid bulb ICA stenosis (European Carotid Surgery Trial [ECST] method) was objectively measured using high resolution B-mode DUS validated with computed tomography angiography (CTA) and used to determine optimum velocity thresholds for > or =50% and > or =80% bulb internal carotid artery stenosis (ICA). METHODS: B-mode DUS and CTA images of 74 bulb ICA stenoses were compared to validate accuracy of the DUS measurements. In 337 mild, moderate, and severe bulb ICA stenoses (n = 232 patients), the minimal residual lumen and the maximum outer bulb/proximal ICA diameter were determined on longitudinal and transverse images. This in contrast to the North American Symptomatic Carotid Endarterectomy Trial (NASCET) method using normal distal ICA lumen diameter as the denominator. Severe calcified carotid segments and patients with contralateral occlusion were excluded. In each study, the highest peak systolic (PSV) and end-diastolic (EDV) velocities as well as ICA/common carotid artery (CCA) ratio were recorded. Using receiver operating characteristic (ROC) analysis, the optimum threshold for each hemodynamic parameter was determined to predict > or =50% (n = 281) and > or =80% (n = 62) bulb ICA stenosis. RESULTS: Patients mean age was 74 +/- 8 years; 49% females. Clinical risk factors for atherosclerosis included coronary artery disease (40%), diabetes mellitus (32%), hypertension (70%), smoking (34%), and hypercholesterolemia (49%). Thirty-three percent of carotid lesions (n = 110) presented with ischemic cerebrovascular symptoms and 67% (n = 227) were asymptomatic. There was an excellent agreement between B-mode DUS and CTA (r = 0.9, P = .002). The inter/intraobserver agreement (kappa) for B-mode imaging measurements were 0.8 and 0.9, respectively, and for CTA measurements 0.8 and 0.9, respectively. When both PSV of > or =155 cm/s and ICA/CCA ratio of > or =2 were combined for the detection of > or =50% bulb ICA stenosis, a positive predictive value (PPV) of 97% and an accuracy of 82% were obtained. For a > or =80% bulb ICA stenosis, an EDV of > or =140 cm/s, a PSV of > or =370 cm/s and an ICA/CCA ratio of > or =6 had acceptable probability values. CONCLUSION: Compared with established velocity thresholds commonly applied in practice, a substantially higher PSV (155 vs 125 cm/s) was more accurate for detecting > or =50% bulb/ICA stenosis. In combination, a PSV of > or =155 cm/s and an ICA/CCA ratio of > or =2 have excellent predictive value for this stenosis category. For > or =80% bulb ICA stenosis (NASCET 60% stenosis), an EDV of 140 cm/s, a PSV of > or =370 cm/s, and an ICA/CCA ratio of > or =6 are equally reliable and do not indicate any major change from the established criteria. Current DUS > or =50% bulb ICA stenosis criteria appear to overestimate carotid bifurcation disease and may predispose patients with asymptomatic carotid disease to untoward costly diagnostic imaging and intervention.

WITHDRAWN: Reappraisal of internal carotid artery stenosis velocity thresholds utilizing high-resolution B-mode ultrasound validated with computed tomography angiography (CTA).

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Transperitoneal versus retroperitoneal suprarenal cross-clamping for repair of abdominal aortic aneurysm with a hostile infrarenal aortic neck.

Infrarenal abdominal aortic aneurysms (AAAs) with a hostile infrarenal aortic neck unfit for endovascular aneurysm repair (EVAR) are more likely to require open repair with suprarenal aortic cross-clamping. We compared the results of the transperitoneal versus retroperitoneal approaches for repair of infrarenal AAA requiring suprarenal cross-clamping and the relative frequency of such techniques after incorporating EVAR into our clinical practice. From January 1998 through September 2005, 478 elective infrarenal aortic aneurysms were repaired. There were 160 (33%) open repairs (71% transperitoneal and 29% retroperitoneal) and 318 (67%) endovascular repairs. In 38 cases (24%) suprarenal cross-clamping was performed (47% transperitoneal and 53% retroperitoneal incisions) for a hostile infrarenal neck. A hostile aortic neck was defined as severe angulation (>60 degrees ), short neck (<15 mm), extensive calcification, or circumferential thrombus. The median age was 70 years; 47% were men; 16% had diabetes mellitus, 29% pulmonary disease, 53% coronary artery disease, and 11% renal insufficiency. The median aneurysm size was 6.0 cm. A retrospective analysis was performed to compare 30-day postoperative outcomes between the trans- and retroperitoneal patient cohorts. The results were determined for two time periods to assess whether open repair with suprarenal cross- clamping was being performed more frequently as a result of increased utilization of EVAR in the contemporary period. After 2002, EVAR increased from 60% to 71% (p = 0.04) while open repair declined from 40% to 29% (p = 0.01). The retroperitoneal approach doubled from 19% to 39%, while the transperitoneal approach decreased from 81% to 61% (p = 0.02). Suprarenal cross-clamping increased by 11% after 2002. There was no significant difference in age, sex, aneurysm size, or comorbidities between the trans- and retroperitoneal groups with suprarenal cross-clamping. The 30-day mortality was 2/38 (5%) and occurred only in the transperitoneal group. The transperitoneal approach was associated with significantly greater blood loss and longer suprarenal cross-clamp times (2,400 vs. 1,800 mL and 38.0 vs. 29.5 min; p = 0.03), but there were no significant differences in 30-day postoperative complications. In our 7 years' experience, there has been a gradual increase in the utilization of EVAR for infrarenal AAAs. At the same time, more infrarenal AAAs with hostile aortic necks requiring suprarenal aortic cross-clamping were encountered. In such instances, the retroperitoneal approach is safer, with less perioperative blood loss and shorter suprarenal cross-clamp time. This is likely attributed to better exposure of the suprarenal abdominal aorta, allowing a more secure proximal anastomosis.

B-mode ultrasonographic characterization of carotid atherosclerotic plaques in symptomatic and asymptomatic patients.

OBJECTIVE: To identify features on B-mode ultrasonography (US) prevalent in symptomatic plaques and correlate these findings with histopathologic markers of plaque instability. METHODS: Carotid endarterectomy (CEA) plaques from symptomatic and asymptomatic patients with critical stenoses (>70%) were qualitatively assessed using preoperative B-mode US for echolucency and calcific acoustic shadowing. US echolucency was quantitated ex vivo using computerized techniques for gray-scale median (GSM) analysis. Histopathologic correlates for US plaque echolucency (percentage of necrotic core area) and acoustic shadowing (percentage of calcification area) were determined. RESULTS: Fifty CEA plaques were collected from 48 patients (46 unilateral and two bilateral); 26 of these plaques were from symptomatic patients. Age, degree of stenosis, and atherosclerotic risk factors were similar for the symptomatic and asymptomatic patients. Using preoperative B-mode US, 58%, 35%, and 7% of symptomatic plaques and 18%, 41%, and 41% of asymptomatic plaques were found to be echolucent, echogenic, and calcific, respectively (P < .05). Using ex-vivo B-mode US and GSM analysis, symptomatic plaques were more echolucent (41 +/- 19) than asymptomatic plaques (60 +/- 13), P < .03. A strong inverse correlation was found between the percent plaque necrotic area core and GSM (R = -0.9, P < .001). Percentage of calcification area in plaques with acoustic shadowing was 66% and only 27% in those without acoustic shadowing (P < .05). CONCLUSIONS: Using B-mode US, symptomatic plaques are more echolucent and less calcified than asymptomatic plaques and are associated with a greater degree of histopathologic plaque necrosis. Such features are indicative of plaque instability and should be considered in the decision-making algorithm when selecting patients with high-grade asymptomatic carotid stenosis for intervention.

Degree of carotid plaque calcification in relation to symptomatic outcome and plaque inflammation.

OBJECTIVE: We undertook this study to quantitate differences in the degree of calcification between symptomatic and asymptomatic plaques removed at carotid endarterectomy (CEA) and to determine associated extent of plaque macrophage infiltration, a histopathologic feature of plaque instability. METHODS: CEA plaques (n = 48) were imaged at 1.25-mm intervals with spiral computed tomography (CT; 10-15 images per plaque). Indications for CEA were transient ischemic attack (n = 16), stroke (n = 5), amaurosis (n = 4), and critical asymptomatic stenosis (n = 23). The percent area calcification for each plaque was determined in spiral CT serial sections and averaged for each plaque. In 31 of 48 plaques macrophage infiltration was quantitated in corresponding histologic sections with immunohistochemical techniques. RESULTS: The mean (+/- SD) age of patients with symptomatic and asymptomatic plaques was 66 +/- 7 years vs 71 +/- 7 years, respectively, and degree of stenosis was 76% versus 82%, respectively (P =.05). Atherosclerosis risk factors were similar between groups. Percent plaque area calcification was twofold greater in asymptomatic versus symptomatic plaques (48% +/- 19% vs 24% +/- 20%, respectively; P <.05). At receiver operating characteristic curve analysis, 80% of symptomatic plaques were below and 87% of asymptomatic plaques were above a cutoff point of 30% plaque area calcification. Macrophage burden was greater in the symptomatic plaques than in the asymptomatic plaques (52% vs 23%; P <.03). A strong inverse relationship between the degree of plaque calcification and macrophage infiltration was found in critical carotid stenoses (r = -0.87; P <.001). CONCLUSIONS: Symptomatic plaques are less calcified and more inflamed than asymptomatic plaques. Regardless of clinical outcome, a strong inverse correlation was found between the extent of carotid plaque calcification and the intensity of plaque fibrous cap inflammation as determined by the degree of macrophage infiltration. Carotid plaque calcification is associated with plaque stability, and is a potential spiral CT in vivo quantitative marker for cerebrovascular ischemic event risk.

Reliability of common femoral artery hemodynamics in assessing the severity of aortoiliac inflow disease.

OBJECTIVES: We investigated the utility of color duplex ultrasound (CDU)-derived common femoral artery (CFA) hemodynamics for detecting significant aortoiliac occlusive disease and predicting its severity. METHODS: From January 1997 to June 2001, 132 consecutive patients with lower extremity arterial insufficiency underwent both femoropopliteal CDU scanning and aortography with runoff studies. CDU-derived CFA waveform contour (monophasic, biphasic, or triphasic), peak systolic velocity (PSV), and acceleration time were recorded for each patient. Severity of aortoiliac occlusive disease was classified by arteriography into three distinct groups: normal or minimal disease (<50%, group 1), significant focal or diffuse stenoses (>/=50%, group 2), or total occlusion (group 3). Using probability and receiver operating characteristic curve analysis, waveform contour and PSV were compared alone and in combination with the arteriographic groups to identify waveform contours and threshold PSV, which may accurately differentiate the three categories of aortoiliac occlusive disease. RESULTS: Of 214 limbs available for study, 112 composed group 1, 70 composed group 2, and 32 composed group 3. Concomitant femoropopliteal disease was present in 47% of limbs in group 1, 53% of limbs in group 2, and 34% of limbs in group III. An abnormal CFA waveform contour (monophasic or biphasic) differentiated group 1 from groups 2 and 3, with 95% sensitivity, 89% specificity, 89% positive predictive value (PPV), 95% negative predictive value (NPV), and 92% accuracy. Mean PSV and acceleration time for monophasic and biphasic waveforms were 39 cm/sec +/- 19, 178 msec +/- 36 vs 95 cm/sec +/- 67, 97 msec +/- 31 respectively (P <.05). In differentiating between groups 2 and 3, the specificity, PPV, and accuracy for CFA PSV of

Transitional flow at the venous anastomosis of an arteriovenous graft: potential activation of the ERK1/2 mechanotransduction pathway.

We present experimental and computational results that describe the level, distribution, and importance of velocity fluctuations within the venous anastomosis of an arteriovenous graft. The motivation of this work is to understand better the importance of biomechanical forces in the development of intimal hyperplasia within these grafts. Steady-flow in vitro studies (Re = 1060 and 1820) were conducted within a graft model that represents the venous anastomosis to measure velocity by means of laser Doppler anemometry. Numerical simulations with the same geometry and flow conditions were conducted by employing the spectral element technique. As flow enters the vein from the graft, the velocity field exhibits flow separation and coherent structures (weak turbulence) that originate from the separation shear layer. We also report results of a porcine animal study in which the distribution and magnitude of vein-wall vibration on the venous anastomosis were measured at the time of graft construction. Preliminary molecular biology studies indicate elevated activity levels of the extracellular regulatory kinase ERK1/2, a mitogen-activated protein kinase involved in mechanotransduction, at regions of increased vein-wall vibration. These findings suggest a potential relationship between the associated turbulence-induced vein-wall vibration and the development of intimal hyperplasia in arteriovenous grafts. Further research is necessary, however, in order to determine if a correlation exists and to differentiate the vibration effect from that of flow related effects.