Infrainguinal vein graft stenosis: Cutting balloon angioplasty as the first-line treatment of choice

ObjectiveThe optimal treatment for hemodynamically significant infrainguinal vein bypass graft stenosis is not known. This study compares three options as first choice for the revision of failing infrainguinal vein grafts: cutting balloon angioplasty (CBA), standard percutaneous transluminal balloon angioplasty (PTA), and open surgical revision (OS).MethodsInfrainguinal vein bypass graft lesions treated in a single institution during a 12-year period were evaluated. Of these, 161 lesions in 124 infrainguinal bypasses (101 patients) were treated with OS (n = 42), PTA (n = 57), or CBA (n = 62). The initial indication for the bypass in these patients was limb salvage in 73% and claudication in 27%. The primary outcome of interest was the development of vein graft occlusion or significant stenosis (≥70%) as detected by surveillance duplex ultrasound scanning or arteriography some time after repair.ResultsThe stenosis-free patency rates at 48 months for OS, CBA, and PTA were 74%, 62%, and 34%, respectively. PTA was associated with an increased risk of treatment failure compared with both OS (hazard ratio [HR], 3.9; P < .0001) and CBA (HR, 3.1; P < .0001). There was no significant difference between OS and CBA (HR, 1.3 for CBA vs OS, P = .6). Pseudoaneurysms developed in two CBA patients. One ruptured and required interposition graft, and one was monitored.ConclusionCutting balloon angioplasty is a reasonable, initial treatment for infrainguinal vein graft stenosis in most patients. It is a safe, minimally invasive, outpatient procedure with patency rates that are comparable to OS and superior to PTA

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

AbstractObjective: 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.

Effect of ethnicity on access and device complications during endovascular aneurysm repair

AbstractIntroductionThere are no published reports on the association between ethnicity and outcome after aortoiliac stent grafting to treat aneurismal disease. Because Hawaii is a state with an ethnically diverse population, we conducted a retrospective study to examine this potential association. We hypothesized that individuals of Asian ancestry may have higher complication rates after endovascular repair compared with non-Asians.MethodsAll endovascular devices placed to treat aneurysm disease from 1996 to 2003 were evaluated in two institutions. The association between ethnicity and access-related and device-related complications, both periprocedural and delayed, was examined with logistic regression analysis.ResultsNinety-two aortoiliac endografts were placed during the study period, including 87 in patients with abdominal aortic aneurysms with or without iliac aneurysm disease, and five patients with isolated iliac artery aneurysms. Forty-four percent of patients were categorized as Asian, 39% as white, 16% as Pacific Islander, and 1% as African American. Access-related and device-related complications (ADRCs) occurred in 11 of 92 (12%) of these patients. The following parameters were significantly associated with ADRCs: Asian ethnicity (P =.015), age greater than 80 years (P = .02), and external iliac diameter smaller than 7.5 mm (P =.01). Asian patients were more likely to have experienced ADRCs than were non-Asian patients (odds ratio, 7.3; 95% confidence interval, 1.5-35.8; P = .015). Asians also had smaller external iliac artery diameters (P = .0003) and more tortuous iliac arteries (P = .03) compared with non-Asians. After adjusting for iliac artery diameter and tortuosity, the association between Asian ethnicity and ARDCs became nonsignificant (P = .074), which suggests that the association between race and complications may be at least in part due to small and tortuous iliac arteries. There was no association between age, gender, or ethnicity and postoperative detection of endoleak.ConclusionOur data indicate that individuals of Asian ancestry are far more likely to experience adverse access-related and device-related complications after aortoiliac stent grafting than are non-Asians. We found that this association is at least partly attributable to the smaller and more tortuous iliac arteries in persons of Asian ancestry

Vein graft lesions: Time of onset and rate of progression

AbstractPurpose: The objectives of this study were to determine the time of onset, location, severity, rate of progression, and subsequent fate of infrainguinal vein graft lesions.Methods: Sixty-one infrainguinal vein grafts were studied serially with duplex ultrasonography to document the location and severity of each lesion. Grafts were studied at 1, 2, 3, 4, 6, 9, 12, and 18 months and then annually.Results: The cumulative secondary graft patency rate at 3 years (life-table analysis) was 93.2%. A total of 158 lesions were detected in 55 of the 61 grafts studied. The degree of diameter reduction at the time of initial detection was as follows: 1% to 19% (29.6%), 20% to 49% (51.0%), 50% to 75% (17.3%), and greater than 75% (3.1%). Forty-eight percent were detected at the first examination, 59.2% within 2 months, and 85.7% within 6 months. Progression was detected in 31.2% of the lesions by 6 and in 39.1% of the lesions by 18 months (life-table analysis). Thrombosis, in the absence of significant changes in ankle-brachial index (≥0.15) or return of symptoms, was not observed in grafts that had lesions with less than 75% diameter reduction.Conclusions: The data support the performance of a duplex scan either during surgery or before discharge from the hospital in addition to frequent surveillance for the first 6 months. Frequent surveillance is appropriate for lesions with less than 75% diameter reduction as long as they remain asymptomatic and without a significant reduction in the ankle-brachial index. (J VASC SURG 1995;22:466-75.

Venous valvular reflux in veins not involved at the time of acute deep vein thrombosis

AbstractPurpose: The aim of this study was to determine whether, in lower extremities with documented episodes of acute deep venous thrombosis (DVT), incompetence develops in veins that were not the site of thrombosis.Methods: Patients were monitored with serial duplex ultrasonography at 1 day, 1 week, 1, 3, 6, 9, and 12 months, and then annually after detection of acute DVT. The following venous segments were analyzed: common femoral, greater saphenous, proximal superficial femoral, deep femoral, popliteal, and posterior tibial. The incidence of reflux development in both thrombosed and uninvolved segments was determined. Reflux was categorized as either transient or permanent.Results: A total of 227 limbs in 188 patients were serially studied. Mean follow-up was 19.9 months (range 1 to 88 months). Overall, 403 of the 1423 segments (28.3% ± 2.3%) developed reflux during the study, of which 118 (29.3% ± 4.4%) had no prior or concurrent history of thrombosis. Considering only the segments that developed incompetence, the percent without prior thrombosis at each level was as follows: common femoral vein (40.0%), greater saphenous vein (53.1%), deep femoral vein (20.6%), proximal superficial femoral vein (23.9%), popliteal vein (8.9%), and posterior tibial vein (31.9%). Valvular insufficiency developing in segments uninvolved with thrombus was more likely to be transient (40.2%) than was the reflux in thrombosed segments (22.6%). This difference was statistically significant (p < 0.05).Conclusions: Permanent venous valvular damage can occur in the absence of thrombosis after DVT. Reflux in uninvolved venous segments has a different anatomic distribution and is more likely to be transient than the incompetence associated with thrombosis.(J VASC SURG 1995;22:524-31.

Early outcome after isolated calf vein thrombosis

AbstractPurpose: The clinical significance of isolated calf vein thrombosis (CVT), particularly with respect to development of the postthrombotic syndrome, remains controversial. The purpose of this study was to define the early natural history of CVT in relation to persistent lower extremity symptoms, propagation, recanalization, and the development of valvular incompetence.Methods: Over a 116-month period, 499 patients with acute deep venous thrombosis (DVT) were referred to our research laboratory, of whom 58 (12%) had thrombosis confined to the calf veins of at least one extremity. The lower extremities of 268 patients (29 with isolated CVT) were followed-up clinically and with duplex ultrasonography at intervals of 1 day, 7 days, 1 month, every 3 months for the first year, and yearly thereafter.Results: Seventy percent of extremities with CVT were symptomatic at presentation. Although the prevalence of clinical signs and symptoms decreased to 29% by 1 month, 23% of patients had persistent pain, edema, or both at 12 months. In contrast, 9% of uninvolved extremities contralateral to a CVT and 54% of extremities with proximal DVT remained symptomatic at 1 year (p = 0.004). Recanalization proceeded rapidly such that the mean thrombus load was reduced by 50% at 1 month and to zero at 1 year. The prevalence of valvular incompetence progressively increased such that reflux was present in 24% of extremities at 1 year. Although its investigation was not a primary goal of this study, pulmonary embolism was diagnosed at presentation and during follow-up in 11% and 3% of patients, respectively.Conclusions: The natural history of CVT is complicated by persistent symptoms and the development of valvular incompetence in approximately one-quarter of patients. This potential for persistent lower extremity symptoms should be considered in evaluating the clinical relevance of isolated calf vein DVT. (J Vasc Surg 1997 26:749-56.

Improving the Catalytic Performance of Cobalt for CO Preferential Oxidation by Stabilizing the Active Phase through Vanadium Promotion

International audiencePreferential oxidation of CO (COPrOx) is a catalytic reaction targeting the removal of trace amounts of CO from hydrogen-rich gas mixtures. Non-noble metal catalysts, such as Cu and Co, can be equally active to Pt for the reaction; however, their commercialization is limited by their poor stability. We have recently shown that CoO is the most active state of cobalt for COPrOx, but under certain reaction conditions, it is readily oxidized to Co3O4 and deactivates. Here, we report a simple method to stabilize the Co2+ state by vanadium addition. The V promoted cobalt catalyst exhibits considerably higher activity and stability than pure cobalt. The nature of the catalytic active sites during COPrOx was established by operando NAP-XPS and NEXAFS, while the stability of the Co2+ state on the surface was verified by in situ NEXAFS at 1 bar pressure. The active phase consists of an ultra-thin cobalt-vanadate surface layer, containing tetrahedral V5+ and octahedral Co2+ cations, with an electronic and geometric structure that is deviating from the standard mixed bulk oxides. In addition, V addition helps to maintain the population of Co2+ species involved in the reaction, inhibiting carbonate species formation that are responsible for the deactivation. The promoting effect of V is discussed in terms of enhancement of CoO redox stability on the surface induced by electronic and structural modifications. These results demonstrate that V-promoted cobalt is a promising COPrOx catalyst and validate the application of in situ spectroscopy to provide the concept for designing better performing catalysts

Effect of manganese promotion on the activity and selectivity of cobalt catalysts for CO preferential oxidation

The preferential oxidation of CO in H2-rich mixtures (COPrOx) is a major catalytic reaction utilized for hydrogen purification. In the exploration of alternatives to noble metals, cobalt-based catalysts appear to be a very promising choice. The activity and stability of cobalt in the COPrOx reaction can be improved by the addition of transition metals and manganese is maybe the most prominent among them. Yet, the arrangement of the two components in the catalytically active state is largely unknown, which hinders in-depth understanding of the manganese promotion effect. Here, we compare pure and Mn-modified cobalt catalysts and correlate their structural and chemical characteristics with their COPrOx performance. The Mn-promoted cobalt catalyst is significantly more active than pure cobalt especially at intermediate reaction temperatures (around 200 °C). The addition of Mn improves the structural stability of the catalyst and helps to maintain higher specific surface areas. Chemical and microstructural analysis using various operando and in situ techniques revealed that Mn promotes CO conversion by partially stabilizing CoO phase during reaction conditions. It is also suggested that at high temperature, Mn suppress CO methanation reaction but promotes H2 oxidation. Apart of the particular interest in COPrOx reaction, in a general context, this work shows how the spatial distribution of the different catalyst components at nanoscopic level, may affect the surface chemistry and consequently control the reactivity