A precious metal alloy for construction of MR imaging-compatible balloon-expandable vascular stents

The authors developed ABI alloy, which mechanically resembles stainless steel 316. The main elements of ABI alloy are palladium and silver. Magnetic resonance (MR) images and radiographs of ABI alloy and stainless steel 316 stent models and of nitinol, tantalum, and Elgiloy stents were compared. ABI alloy showed the least MR imaging artifacts and was more radiopaque than stainless steel 316. ABI alloy has the potential to replace stainless steel 316 for construction of balloon-expandable MR imaging-compatible stents

'Closed' in Situ Vein Infrainguinal Bypass

The autologous greater saphenous vein is considered to be the best bypass material for below knee femoropopliteal and femorocnual arterial reconstructions . . The history of the greater saphenous vein arterial bypass in humans started in 1949, with its first introduction by Kunlin. Upto 1959, when Rob performed the first in situ saphenous vein bypass, the reversed saphenous vein technique of Kunlin was the standard procedure. The first publication about the in situ bypass was written in 1962 by Karl Victor Hall. After tlus preliminary report, several optimistic reports, written by Hall, ConnOlly, May and Samuel followed. Despite the promissing results, the in situ bypass technique only achieved minimal popularity, mainly in Europe. It was not before Leather, Powers and Karmody published their historical publication in 1979 that the in situ bypass really was considered to be a worthy alternative for the "reversed" technique. Their excellent results received worldwide attention and contributed to the adoption of the in situ bypass technique in many major vascular surgery departments during the early eighties (including those in the USA)

Assessment of stenoses in the aortoiliac tract by calculation of a vascular resistance change ratio before and after exercise

Objectives:Intraarterial pressure measurement is the most reliable method to assess haemodynamically significant stenoses in the aortoiliac tract. We have tried to develop a simple and quick, non-invasive method to assess stenoses of this type.Design:Prospective semi-blinded clinical study.Methods:It was postulated that a haemodynamically significant aortoiliac tract stenosis would result in a lesser degree of vascular resistance decrease after vasodilatation, compared to patients only suffering from femorodistal stenoses. We approximated vascular resistance by: (brachial pressure-ankle pressure) / femoral artery mean Doppler velocity. By dividing vascular resistance at rest by vascular resistance after exercise, we calculated the Resistance Change Ratio (RCR).Patients and results:In 34 patients (50 legs) with arterial stenoses, the pressure gradient over the aortoiliac segment was compared to the RCR. Legs were divided in three groups: group 1 consisted of 22 legs that showed a pressure gradient > 10 mmHg at rest; group 2 showed a pressure gradient > 10 mmHg after papaverine; group 3 showed a pressure gradient of 10 mmHg or less. The median RCR was: 0.74 (range: 0.23–4.04) for group 1, 0.71 (range: 0.36–1.80) for group 2 and 0.93 (range 0.36–2.06) for group 3. There was no significant difference between the groups (p = 0.19).Conclusion:The RCR could not be used to accurately detect stenoses in the aortoiliac

The value of pre-operative ultrasound mapping of the greater saphenous vein prior to 'closed' in situ bypass operations

Objective: The aim of this study was to test pre-operative ultrasound mapping for the detection of duplications and narrow vein segments of the greater saphenous vein (GSV) used as bypass for occlusive arterial disease surgery. Patients and methods: In 44 patients pre-operative ultrasound findings of duplications and lumen assessment of the GSV were compared to the per-operative findings. Results: In nine patients (20%) the pre-operative ultrasound examination showed a duplication. Pre-operative ultrasound had missed a duplication in two cases but had instead shown a narrow segment in both. The pre-operative ultrasound assessment of lumen diameter showed a narrow lumen segment in 10 of the 44 patients. In one patient a per-operatively narrow lumen had not been seen on pre-operative ultrasound. Conclusion: Pre-operative ultrasound mapping of the GSV is a sensitive tool for detection of duplications and narrow vein segments. Since these anatomical variations provide important information for the vascular surgeon, before performing a 'closed' in situ bypass operation, pre-operative vein mapping should be considered when planning such a procedure

A Dynamic Network Model to Explain the Development of Excellent Human Performance

Across different domains, from sports to science, some individuals accomplish excellent levels of performance. For over 150 years, researchers have debated the roles of specific nature and nurture components to develop excellence. In this article, we argue that the key to excellence does not reside in specific underlying components, but rather in the ongoing interactions among the components. We propose that excellence emerges out of dynamic networks consisting of idiosyncratic mixtures of interacting components such as genetic endowment, motivation, practice, and coaching. Using computer simulations we demonstrate that the dynamic network model accurately predicts typical properties of excellence reported in the literature, such as the idiosyncratic developmental trajectories leading to excellence and the highly skewed distributions of productivity present in virtually any achievement domain. Based on this novel theoretical perspective on excellent human performance, this article concludes by suggesting policy implications and directions for future research

Shrinkage of the distal renal artery 1 year after stent placement as evidenced with serial intravascular ultrasound

The objective of this study was to determine the quantitative intravascular ultrasound (IVUS) and angiographic changes that occur during 1 year follow-up after renal artery stent placement, given that restenosis continues to be a limitation of renal artery stent placement. 38 consecutive patients with symptomatic renal artery stenosis treated with Palmaz stent placement were studied prospectively. IVUS and angiography were performed at the time of stent placement and at 1 year follow-up. At follow-up, angiographic restenosis was seen in 14% of patients. The lumen area in the stent, seen with IVUS, was significantly decreased from 24+/-5.6 mm(2) to 17+/-5.6 mm(2) (p<0.001) solely due to plaque accumulation. The distal main renal artery showed a significant decrease in lumen area owing to a significant vessel area decrease from 39+/-14.0 mm(2) to 29+/-9.3 mm(2) (p<0.001) without plaque accumulation. Angiographic analysis confirmed this reduction in luminal diameter and showed that the distal renal artery diameter at follow-up was significantly smaller than before stent placement (86+/-23.0% vs 104+/-23.9% of the contralateral renal artery diameter; p=0.003). Besides plaque accumulation in the stent, unexplained shrinkage of the distal main renal artery was evidenced with IVUS and angiography 1 year following stent placement

Intravascular ultrasound evidence for coarctation causing symptomatic renal artery stenosis

BACKGROUND: A recent study of human cadaveric renal arteries revealed that renal artery narrowing could be due not only to atherosclerotic plaque compensated for by adaptive remodeling, but also to hitherto undescribed focal narrowing of an otherwise normal renal arterial wall (ie, coarctation). The present study investigated whether vessel coarctation could be identified in patients with symptomatic renal artery stenosis (RAS). METHODS AND RESULTS: Consecutive symptomatic patients with angiographically proven atherosclerotic RAS who were referred for stent placement were studied by 30-MHz intravascular ultrasound before intervention (n=18) or after predilatation (n=18). Analysis included assessment of the media-bounded area and plaque area (PLA) at the most stenotic site and at a distal reference site (most distal cross-section in the main renal artery with normal appearance). Coarctation was considered present whenever the target/reference media-bounded area was </=85%. Before intervention, coarctation was observed in 9 of 18 patients and adaptive remodeling in 9 of 18 patients. Coarctation lesions had a significantly smaller PLA than adaptive remodeled lesions (P=0.001). Similarly, despite predilatation, coarctation was seen in 8 of 18 patients who had significantly smaller PLAs (P=0. 008) when compared with those patients who had adaptive remodeled lesions. No differences in severity of RAS or angiographic or clinical parameters were observed. CONCLUSIONS: Low-plaque coarctation may cause a considerable proportion of symptomatic RAS, which is angiographically and clinically indistinguishable from plaque-rich RAS