End-to-end Versus End-to-side Distal Anastomosis in Femoropopliteal Bypasses; Results of a Randomized Multicenter Trial

Covered stent grafts for relining of chronically occluded femoro-popliteal bypasses in frail patients

In four high-risk patients with chronically occluded femoro-popliteal bypass suffering from Rutherford 4-5 chronic limb threatening ischemia we performed, as an alternative for redo surgery, endovasculair relining with covered stent grafts. During follow-up (3, 8, 14 and 20 months) one patient had redo percutaneous intervention and eventually below-the-knee amputation.

An in silico study of the influence of vessel wall deformation on neointimal hyperplasia progression in peripheral bypass grafts

Neointimal hyperplasia (NIH) is a major obstacle to graft patency in the peripheral arteries. A complex interaction of biomechanical factors contribute to NIH development and progression, and although haemodynamic markers such as wall shear stress have been linked to the disease, these have so far been insufficient to fully capture its behaviour. Using a computational model linking computational fluid dynamics (CFD) simulations of blood flow with a biochemical model representing NIH growth mechanisms, we analyse the effect of compliance mismatch, due to the presence of surgical stitches and/or to the change in distensibility between artery and vein graft, on the haemodynamics in the lumen and, subsequently, on NIH progression. The model enabled to simulate NIH at proximal and distal anastomoses of three patient-specific end-to-side saphenous vein grafts under two compliance-mismatch configurations, and a rigid wall case for comparison, obtaining values of stenosis similar to those observed in the computed tomography (CT) scans. The maximum difference in time-averaged wall shear stress between the rigid and compliant models was 3.4 Pa, and differences in estimation of NIH progression were only observed in one patient. The impact of compliance on the haemodynamic-driven development of NIH was small in the patient-specific cases considered.

The Ratio of Diameters Between the Target Artery and the Bypass Modifies Hemodynamic Parameters Related to Intimal Hyperplasia in the Distal End-to-Side Anastomosis

Hemodynamics in the distal end-to-side anastomosis is related to early development of intimal hyperplasia and bypass failure. In this study we investigated the effect of diameter ratios between the target artery and the bypass at three different angles of the connection. The pulsatile flow field was visualized using particle image velocimetry in transparent models with three different angles of the connection (25°, 45°, 60°) and the diameter ratio between the bypass and the target artery was 4.6 mm : 6 mm, 6 mm : 6 mm, and 7.5 mm : 6 mm. Six parameters including location and oscillation of the stagnation point, local energy dissipation, wall shear stress (WSS), oscillatory shear index, spatial and temporal gradient of WSS and their distribution in the target artery were calculated from the flow field. In the wider bypass, the stagnation point oscillated in a greater range and was located more proximal to the anastomosis. Energy dissipation was minimal in a wider bypass with a more acute angle. The maximum WSS values were tree times greater in a narrow bypass and concentrated in a smaller circular region at the floor of the anastomosis. The oscillatory shear index increased with wider bypass and more acute angle. The maximum of spatial gradient of WSS concentrated around the floor and toe of the anastomosis and decreased with more acute angle and wider bypass, the temporal gradient of WSS was stretched more towards the side wall. Greater bypass to target vessel ratio and more acute anastomosis angle promote hemodynamics known to reduce formation of intimal hyperplasia.

Why Patencies of Femoropopliteal Bypass Grafts with Distal End-to-End Anastomosis are Comparable with End-to-Side Anastomosis

OBJECTIVE

Despite the theoretical favourable hemodynamic advantage of end-to-end anastomosis (ETE), femoropopliteal bypasses with distal ETE and end-to-side anastomosis (ETS) have comparable clinical patencies. We therefore studied the effects of different in vivo anastomotic configurations on hemodynamics in geometrically realistic ETE and ETS in vitro flow models to explain this phenomenon.

METHODS

Four ETE and two ETS models (30° and 60°) were constructed from in vivo computed tomography angiography data. With flow visualization physiological flow conditions were studied.

RESULTS

In ETS, a flow separation and recirculation zone was apparent at anastomotic edges with a shifting stagnation point between them during systole. Secondary flow patterns developed with flow deceleration and reversal. Slight out of axis geometry of all ETE resulted in flow separation and recirculation areas comparable to ETS. Vertical flow patterns were more stable in wider and longer bevelled ETE.

CONCLUSION

Primary flow disturbances in ETE are comparable to ETS and are related to the typical sites where myointimal hyperplasia develops. In ETS, reduction of anastomosis angle will diminish flow disturbances. To reduce flow disturbances in ETE, the creation of a bulbous spatulation with resulting axial displacement of graft in relation to recipient artery should be prevented.

Numerical analysis of coronary artery bypass grafts: an over view

Arterial bypass grafts tend to fail after some years due to the development of intimal thickening (restenosis). Non-uniform hemodynamics following a bypass operation contributes to restenosis and bypass failure can occur due to the focal development of anastomotic intimal hyperplasia. Additionally, surgical injury aggravated by compliance mismatch between the graft and artery has been suggested as an initiating factor for progress of wall thickening along the suture line Vascular grafts that are small in diameter tend to occlude rapidly. Computational fluid dynamics (CFD) methods have been effectively used to simulate the physical and geometrical parameters characterizing the hemodynamics of various arteries and bypass configurations. The effects of such changes on the pressure and flow characteristics as well as the wall shear stress during a cardiac cycle can be simulated. Recently, utilization of fluid and structure interactions have been used to determine fluid flow parameters and structure forces including stress and strains relationships under steady and transient conditions. In parallel to this, experimental diagnostics techniques such as Laser Doppler Anemometry, Particle Image Velocimetry, Doppler Guide wire and Magnetic Resonance Imaging have been used to provide essential information and to validate the numerical results. Moreover, clinical imaging techniques such as magnetic resonance or computed tomography have assisted considerably in gaining a detailed patient-specific picture of the blood flow and structure dynamics. This paper gives a review of recent numerical investigations of various configurations of coronary artery bypass grafts (CABG). In addition, the paper ends with a summary of the findings and the future directions.

Use of continuous horizontal mattress suture technique in end-to-side microsurgical anastomosis

PURPOSE

The aim of our study was to improve the new suturing method which increases the success rate of end to side microsurgical anastomosis.

METHODS

Thirty-six Sprague-Dawrey rats were randomly divided into three groups that consist of 12 rats in closed envelope method. The end-to-side microsurgical anastomosis procedures were applied by the same surgeon between left main carotid artey and left external jugular vein. The surgical evaluations were performed with anastomosis duration, leakage evaluation, vessels patency, aneurysm improvement and histological assesment.

RESULTS

End-to-side anastomosis, which was applied with Continuous Horizontal Mattress suture, gave significantly better results in terms of leakage, anastomosis openness, aneurysm and histologic assesment. Also anastomosis duration of Continuous Horizontal suture was significantly faster than Simple Intermittent suture.

DISCUSSION

Our study revealed that the Continuous Horizontal Mattress suture technique had the advantages of providing uninterrupted vessel flow in a shorter time, and minimal intraluminal suture material, which increase thrombosis risk. Also 'sac-mouth' effect of Continuous suture technique was prevented by Horizontal Mattress technique.

CT angiography for surgical planning in face transplantation candidates

SUMMARY

Facial allotransplantation replaces missing facial structures with anatomically identical tissues, providing desired functional, esthetic, and psychosocial benefits far superior to those of conventional methods. On the basis of very encouraging initial results, it is likely that more procedures will be performed in the near future. Typical candidates have extremely complex vascular anatomy due to severe injury and/or multiple prior reconstructive attempts; thus, each procedure is uniquely determined by the defects and vascular anatomy of the candidate. We detail CT angiography vascular mapping, noting the clinical relevance of the imaging, the angiosome concept and noninvasive delineation of the key vessels, and current controversies related to the vascular anastomoses.

Effect of Anastomotic Length on the Development of Intimal Hyperplasia in the Distal Anastomosis of Bypass Graft

Many hemodynamic factors have been shown to be associated with increased intimal hyperplasia at the distal anastomosis of arterial bypass graft. However, the relationship between the length of anastomosis and the development of such a complication has not been studied before. The aim of this study was to assess this relationship at the distal anastomosis with a Dacron graft. Iliofemoral bypass using 6 mm Dacron grafts was performed in 10 German shepherd dogs. In accordance with preoperative randomization to individual animal legs, distal anastomoses were reconstructed using four different groups (A, B, C, and D), depending on the length of the arteriotomy: 3.0, 3.5, 4.0, and 4.5 times the internal diameter of the artery, respectively. The vessels were harvested 6 months after the operation, and specimens were processed for histologic and transmission electron microscopic (TEM) studies. Quantitative analysis was performed to assess the extent of intimal hyperplasia at three zones (heel, toe, and midzone of the arterial bed) of the distal anastomosis. Sixteen arterial bypasses were included in this study. Both light and TEM studies revealed evidence of intimal hyperplasia in the four groups. Quantitative analysis showed a significant decrease in intimal hyperplasia with increasing the length of the anastomosis at the heel, toe, or midzone of the arterial bed. Mean (μm ± SD) intimal hyperplasia of the three zones together was significantly higher in group A than group B (585 ± 106 vs 423 ± 8.6, p < .001) and in group B than group C (423 ± 8.6 vs 202 ± 15, p < .001). However, the difference between group C and group D (202 ± 15 vs 162 ± 8.6; p = .13) was statistically insignificant. The present study showed that the length of the anastomosis is one of the hemodynamic factors involved in the development of intimal hyperplasia. Anastomotic techniques that resulted in the least intimal hyperplasia were end to side, with length 4 or 4.5 times the internal diameter of the artery.

Subintimal angioplasty with the aid of a re-entry device for TASC C and D lesions of the SFA

AIM

The aim of this prospective study was to assess the clinical effectiveness and related midterm patency of subintimal angioplasty (SAP) in patients suffering from critical limb ischaemia (CLI) in a single tertiary care university centre. The secondary aim was to evaluate the safety and clinical effectiveness of using a re-entry device when re-canalisation by SAP was unsuccessful.

METHODS

From January 2005 to December 2007, consecutive patients suffering from CLI (Rutherford clinical categories: 4-6) were treated with SAP. All patients included in the study had occluded SFA (TASC C and D) and underwent clinical and ultrasound follow-up examinations at day 30 and at 3, 6, 9 and 12 months, and then yearly. A re-entry device (Outback, Cordis Corporation, Miami Lakes, Florida, USA in all cases) was only used when re-canalisation by simple SAP was unsuccessful, and stenting was used when residual stenosis was >30% or there was a flow-limiting dissection. Factors that could modify the outcome were analysed.

RESULTS

In this study, 145 patients were treated, with a technical success rate of 83.5% (121 of 145) for simple SAP. Stenting was performed in 43% (n=62) of successful SAP procedures. No death occurred in the perioperative period, while the 30-day mortality was 4.8% (7 of 145). The re-entry device (Outback) was used in 24 cases (16.5%). The technical success of the re-entry device was 79% (19 of 24), with a 90% success rate of stent placement at the site of re-entry. Complications occurred in 6.2% of all procedures (n=9) (three arterial perforations (2.1%), three distal embolisations (2.1%), two femoral artery pseudo-aneurysms (1.4%) and one arterio-venous fistula (0.7%)). Factors capable of independently affecting the patency were renal insufficiency (p=0.03), current smoking (p=0.01) and diabetes (p=0.04). The primary patency at 1 and 3 years was 70% and 34% and the secondary patency at 1 and 3 years was 77% and 43%, respectively. At the same time intervals, the limb-salvage rate was 88% and 49%.

CONCLUSIONS

SAP with the aid of a re-entry device for TASC C and D lesions of the SFA seems to be safe and clinically effective in patients suffering from CLI, according to the experience at our centre. Further follow-up and more data are necessary to confirm these findings.

Surgical Feasibility Study of a Novel Polytetrafluoroethylene Graft Design for the Treatment of Peripheral Arterial Disease

Disturbed flow patterns, material mismatch, and surgical injury are often cited as being significant contributors to failure at the distal end of femoropopliteal bypass grafts. The objective of this research is to propose a novel bypass graft design concept which seeks to reduce the incidence of disturbed flow in the bypass junction and to establish the surgical feasibility of the proposed device. A preliminary evaluation of the hemodynamic benefit associated with the proposed device was made using computational fluid dynamics. A prototype of the device was then constructed from commercially available materials, and it was prepared for implantation into the aorta of a pig. The computational model of the proposed device showed that significant flow correction was occurring in the in vitro model due to the geometric configuration of the design. The magnitude of the peak wall shear stress in the recirculation region was noted to decrease by 78%. Surgical feasibility of the proposed device was verified by successful implantation into the aorta of the pig. The pig was sacrificed after 7 weeks, the graft and host artery were excised, and histological examination downstream from the distal junction showed that intimal hyperplasia had developed in the host artery. The proposed device is surgically feasible and may offer a significant hemodynamic advantage over current graft designs.

Remote endarterectomy for occlusive iliac and superficial femoral artery disease

Today's patients increasingly desire a low-risk procedure with rapid return to functional status following surgery. Many patients actively seek a minimally invasive option. During the last decade, minimally invasive surgical and radiological procedures emerged from their infancy to become an integral part of the treatment strategy in both peripheral arterial occlusive disease and aneurysmal arterial disease. The trend towards restoration of luminal patency, using the vessel itself as a conduit, can also be termed restorative intervention. As radiological percutaneous transluminal angioplasty has thus far proven unsuccessful in the long term for iliac and femoropopliteal occlusive lesions exceeding 10 cm, a new endovascular surgical procedure has been developed. A modification to the original ringstripper, used in semiclosed endarterectomy, was made to enable the technique of remote endarterectomy.

Computational investigations of a new prosthetic femoral-popliteal bypass graft design

OBJECTIVE

Prosthetic femoral-popliteal bypasses are performed by using an end-to-side anastomosis, and disease can develop at the distal end; this can lead to poor long-term patency rates. Disturbed flow characteristics are hypothesized as being a major factor in promoting disease development. The objective of this study was to propose a new prosthetic femoral-popliteal bypass graft configuration specifically engineered to reduce or eliminate certain disease-influencing factors that act on the host artery.

METHODS

The proposed device contains a streamlined bifurcation toward its distal end that results in two end-to-end anastomoses, rather than the single end-to-side anastomosis in the traditional procedure. Comparisons are made between idealized representations of it and the traditional end-to-side anastomosis for specific femoral artery flow rates. Qualitative results in the form of velocity vector plots and wall shear stress contour plots are compared, and quantitative results examine the wall shear stress magnitudes and gradients along the bed and roof of each graft model.

RESULTS

Velocity vector plots through each junction suggest that the proposed graft configuration promotes streamlined flow and helps to reduce the magnitude of flow recirculation and separation regions associated with the traditional end-to-side anastomosis. At peak velocity, the flow separation region distal to the toe is eliminated, as evidenced by the change in toe wall shear stress from -0.2 Pa in the traditional anastomosis to +0.5 Pa in the proposed device. Normal fully developed flow occurs sooner in the distal host artery, approximately 15 mm downstream from the toe, unlike 20 mm in the conventional case. The proposed design results in reductions of up to 58% in peak wall shear stress and 86% in peak wall shear stress gradient during the decelerative phase of the femoral pulse in the vicinity of the artery bed below the toe.

CONCLUSIONS

In vitro tests on the proposed device suggest that the streamlined nature of blood flow through the junction does result in less disturbed hemodynamic conditions within the host artery junction. Abnormal wall shear stress magnitudes and gradients are reduced, and normal fully developed flow occurs sooner in the distal host artery. This suggests that the proposed graft may have design attributes that are relevant in the search for increased prosthetic femoral-popliteal bypass graft patency rates. A drawback of the proposed device is that significant flow recirculation and separation exist within the prosthesis itself.

CLINICAL RELEVANCE

The search for a viable alternative to traditional end-to-side anastomosis for prosthetic femoral-popliteal bypass procedures is ongoing. Prosthetic femoral-popliteal bypass procedures have low long-term patency rates, and there is a need for methods that increase the life span of the procedure. Although research is progressing on a variety of different fronts, this study is significant in that it reports on in vitro tests on a potential device that may increase bypass patency. The device is simple, may be manufactured from clinically proven materials, does not require any additional training in its use, and combines attributes of end-to-side anastomoses with those of end-to-end anastomoses. In addition, the design concept behind the device, the natural bifurcation, may be relevant in other aspects of cardiovascular surgery.