Experimental comparison of four methods of end-to-side anastomosis with expanded polytetrafluoroethylene

BACKGROUND: Four established techniques of distal end-to-side anastomosis (direct anastomosis, Linton patch, Taylor patch and Miller cuff) were compared to investigate the local distribution of anastomotic intimal hyperplasia. The study aimed to elucidate whether mechanical factors or flow alterations are mainly responsible for the improved patency rates reported for vein cuff interposition techniques in infrainguinal arterial reconstructions using prosthetic graft material. METHODS: Thirty-two expanded polytetrafluoroethylene (ePTFE) femoropopliteal bypass grafts were implanted in 16 sheep using the four anastomotic techniques. After 6 months the grafts were explanted and examined histologically. The local distribution of intimal hyperplasia was determined, particularly for areas of material transition and of high and low shear stress. RESULTS: The mean amount and distribution of intimal hyperplasia were similar for all anastomotic types. Intimal hyperplasia was greatest along all transitions between ePTFE and venous patches, and between ePTFE and recipient artery. It was lower along the transitions between venous patches and artery, and was lowest at the host artery floor. CONCLUSION: Vein interposition did not reduce anastomotic intimal hyperplasia and did not change the distribution patterns of hyperplasia, which were influenced mainly by mechanical factors. The effect of vein interposition is to move areas of maximum intimal hyperplasia away from the small recipient artery up to the more capacious graft-patch anastomosis.     

Steady and pulsatile flow fields in an end-to-side arterial anastomosis model

We investigated the flow field within a rigid-walled in vitro model of an end-to-side 45 degree anastomosis in an attempt to identify possible hemodynamic factors that may contribute to the pathogenesis of distal anastomotic intimal hyperplasia. A high-resolution photochromic tracer technique was used to visualize the flow in orthogonal planes and to determine the axial wall shear stress profiles for both steady and pulsatile flows over a range of physiologically relevant conditions. The flow field showed qualitative similarities to those seen in curved vessel: rapidly moving fluid from the graft section affects the bed of the host vessel, that is, the wall opposite the anastomosis, eventually advancing down the host vessel in a spiraling motion. A small mobile separation zone was noted at the toe of the anastomosis. Comparison of wall shear stress profiles with previously reported preferential sites for the development of intimal hyperplasia supported a low wall shear stress and/or flow separation pathogenesis hypothesis. One notable exception was the bed of the host artery that appeared to be subjected to a complex hemodynamic environment.     

Particle hemodynamics analysis of Miller cuff arterial anastomosis

OBJECTIVE: Studies of animal and human below-knee anastomoses with Miller cuffs indicate that improved graft patency results from redistribution of intimal hyperplasia away from areas critical to flow delivery, such as the arterial toe. We hypothesize that particle hemodynamic conditions are a biophysical mechanism potentially responsible for the clinically observed shift in intimal hyperplasia localization associated with better patency of the Miller configuration. METHODS: Computational fluid dynamics analysis of vortical flow patterns, wall shear stress fields, and potential for platelet interaction with the vascular surface was performed for realistic three-dimensional conventional and Miller cuff distal end-to-side anastomoses. Sites of significant platelet-wall interaction, including elevated near-wall particle concentrations and stasis, were identified with a validated near-wall residence time model, which includes shear stress-based factors for particle activation and surface reactivity. RESULTS: Particle hemodynamics largely coincide with the observed redistribution of intimal hyperplasia away from the critical arterial toe region. Detrimental changes in wall shear stress vector magnitude and direction are significantly reduced along the arterial suture line of the Miller cuff, largely as a result of increased anastomotic area available for flow redirection. However, because of strong particle-wall interaction, resulting high near-wall residence time contours indicate significant intimal hyperplasia along the graft-vein suture line and in the vicinity of the arterial heel. CONCLUSIONS: While a number of interacting mechanical, biophysical, and technical factors may be responsible for improved Miller cuff patency, our results imply that particle hemodynamics conditions engendered by Miller cuff geometry provide a mechanism that may account for redistribution of intimal hyperplasia. In particular, it appears that a focal region of significant particle-wall interaction at the arterial toe is substantially reduced with the Miller cuff configuration.     

Distal anastomotic intimal hyperplasia: biogenesis and etiology

Anastomotic intimal hyperplasia occurred exclusively at the heel and the toe plus the floor of the distal end-to-side anastomosis of canine autologous femoro-femoral bypass (n = 14) and not in the end-to-end carotid or femoral interposition graft (n = 14). The occurrence of anastomotic intimal hyperplasia in the absence of compliance mismatch in an autologous bypass suggests that the geometry of the end-to-side anastomosis is primarily responsible for intimal hyperplasia formation. It is believed that because an end-to-side distal anastomosis is not a natural occurrence it is conductive to turbulent flow. The latter causes endothelial injury which in turn allows platelet growth factor to incite subendothelial myoblasts in extracellular matrix synthesis and intimal hyperplasia formation. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) identify myofibroblasts and fibrocollagenous matrix as the dominant cellular and extracellular substances in anastomotic intimal hyperplasia.     

Distal anastomotic intimai hyperplasia: Histopathologic character and biogenesis

Although thrombogenicity of the prosthetic graft, progression of the atherosclerotic disease and distal anastomotic intimal hyperplasia are known etiologic factors of late graft failure, its occurrence is frequently encountered in the late graft occlusion. Forth-two canine PTFE iliofemoral grafts (all with end-to-side distal anastomosis) were studied. Computer digitization revealed that distal anastomotic intimal hyperplasia occurred exclusively at the heel and the toe of the graft and the floor of the host artery. The distal anastomotic intimal hyperplasia was 80-130 cells thick. Light microscopy and transmission electron microscopy revealed a similar architecture of interlamination of cellular elements and extracellular matrix in the hyperplastic cells. Transmission electron microscopy further defined a gradual cell transformation and orientation from the graft to the lumen. The cells near the graft were characterized by a gradual reduction of rough endoplasmic reticulum with a concomitant acquisition of myofilaments, transforming ovoid mesenchymoid cells to slender myofibroblasts. The orientation of cells in distal anastomotic intimal hyperplasia was embodied by random cell distribution at the periphery to a well-organized interlamination of myofibroblasts and extracellular matrix near the lumen. Distal anastomotic intimal hyperplasia is a biologic entity with active cellular and subcellular events. Its biogenesis appears to be influenced by the hemodynamics of blood flow at the distal anastomosis.     

Influence of angle on wall shear stress distribution for an end-to-side anastomosis

Purpose: The purpose of this article was to study the effects of anastomotic angle on the wall shear stress distribution for end-to-side anastomosis models under pulsatile flow conditions.Method: The photochromic tracer technique was used to visualize the flow field and to determine the instantaneous wall shear stress at multiple locations simultaneously. Models with angles of 20, 30, 45, and 60 degrees were examined.Results: For all angles, low shear stress was present at the heel and on the bed opposite the heel of the anastomosis apparently as a result of the complete occlusion of the proximal end of the host vessel. Near the toe, increased flow separation occurred with increasing angle. On the bed across from the toe, increasing the angle led to increased shear stress. In addition, in this region the anastomotic angle significantly altered other properties of the shear stress field such as the mean and peak-to-peak magnitudes and cycle-to-cycle fluctuations.Conclusions: This study provides quantitative data on the wall shear stress distribution within an end-to-side anastomosis and its relation to the anastomotic angle. The results are discussed in terms of possible roles of shear-induced intimal hyperplasia. (J VASC SURG 1994;19:1067–73.)     

Improved patency of prosthetic arteriovenous grafts with an acute anastomotic angle and flow diffuser

OBJECTIVE: Conventional end-to-side anastomosis to establish venous outflow for prosthetic arteriovenous grafts often requires operative patch angioplasty within 1 year because of venous stenosis. Rather than conventional venous anastomosis, a modified end-to-side anastomosis at a 15-degree angle with a flow diffuser was constructed. Such diffusers allow decreased flow velocity and increased pressure, inhibiting boundary layer separation. METHODS: Ten brachial artery to axillary vein 6 mm straight se-polytetrafluoroethylene prosthetic arteriovenous grafts were created with this technique. Patients included 6 men and 4 women (mean age, 66.4 years; range, 54-80 years), all with renal failure and a history of diabetes. The degree of stenosis at the venous anastomosis was determined with duplex scanning at intervals of 6 months. Analysis of survival and cumulative primary patency estimates were determined with the Kaplan-Meier method. RESULTS: Primary cumulative patency estimate of 100% for the modified group at 18 and 24 months was significantly greater than that for age-matched historic control fistulas with the conventional end-to-side anastomosis (n = 20): 18 months, 32%; 24 months, 32% (P <.05). Although venous stenosis could not be quantitated for thrombosed conventional fistulas, modified anastomoses had minimal stenosis at 24 months: mean area reduction, 30% (range, 20%-45%). CONCLUSION: Incorporation of a flow diffuser and a 15-degree anastomotic angle significantly increases patency of prosthetic brachial artery to axillary vein grafts.     

Anastomotic intimal hyperplasia: mechanical injury or flow induced.

All anastomotic intimal thickening may not be the same, and the underlying mechanism(s) regulating the different types may vary. We investigated the localization of experimental anastomotic intimal thickening in relation to known biomechanical and hemodynamic factors. Bilateral iliofemoral saphenous vein and polytetrafluoroethylene grafts were implanted in 13 mongrel dogs. The distal end-to-side anastomotic geometry was standardized, and the flow parameters were measured. After 8 weeks, seven of 10 animals (group I) with patent grafts were killed and the anastomoses fixed by perfusion. Histologic sections from each anastomosis were studied with light microscopy, and regions of intimal thickening were identified and quantitated with use of oculomicrometry. To characterize the anastomotic flow patterns, transparent silicone models were constructed from castings of the distal anastomosis of three animals (group II), and flow was visualized with use of helium-neon laser-illuminated particles under conditions simulating the in vivo pulsatile flow parameters. Histologic sections revealed two separate and distinct regions of anastomotic intimal thickening. The first, suture line intimal thickening, was greater in polytetrafluoroethylene anastomoses (0.35 +/- 0.23 microns) than in vein anastomoses (0.15 +/- 0.03 microns, p less than 0.05). The second distinct type of intimal thickening developed on the arterial floor and was the same in polytetrafluoroethylene (0.11 +/- 0.11 microns) and vein anastomoses (0.12 +/- 0.03 microns). Model flow visualization studies revealed a flow stagnation point along the arterial floor resulting in a region of low and oscillating shear where the second type of intimal thickening developed. High shear and short particle residence time were observed along the hood of the graft, an area devoid of intimal thickening.(ABSTRACT TRUNCATED AT 250 WORDS)     

Blood flow in distal end-to-side anastomoses with PTFE and a venous patch: results of an in vitro flow visualisation study.

OBJECTIVES: non-physiological flow behaviour plays a significant role in the development of distal anastomotic intimal hyperplasia. To investigate flow patterns in four anastomotic types of femoral end-to-side distal bypass graft anastomoses, a flow visualisation study was performed. METHODS: transparent 1:1 casted replicas of distal vascular graft anastomoses created by conventional technique, Miller-cuff, Taylor- and Linton-patch were fabricated. A pulsatile mock circulation with a high-speed video system was constructed. Flow pattern was determined at mean Reynolds numbers 100-500. Migrations of the stagnation points on the bottom of the anastomoses at mean Reynolds numbers 100, 230, and 350 were measured. RESULTS: a vortex forms during early systole and increases to maximum systole in all anastomoses. During the diastolic phase the vortex moves in the Miller-cuff distally to the toe of the anastomosis and remains standing, while in the other anastomotic types the vortex moves proximally to the heal of the junction and breaks down. The shift of the stagnation point in the Miller-cuff was considerably smaller than in the other anastomoses. CONCLUSION: conventional, Linton and Taylor anastomoses show similar flow patterns. The Miller-cuff with its wider cavity shows lower shift of the bottom stagnation point, but a persistent washout of the anastomotic cavity, which may contribute to its reported good clinical performance.     

Ultrastructural features of progressive intimal hyperplasia at the distal end-to-side anastomosis of vein grafts

The features of intimal hyperplasia at the distal end-to-side anastomosis of artertally implanted autovein bypass grafts in dogs were examined using light and transmission electron microscopy. The bypass grafting was done under conditions of reduced blood flow with an abnormal flow wave and high peripheral resistance. Anastomotic intimal hyperplasia was evident 14 to 31 days after implantation, then gradually increased, particularly at the toe portion of the anastomosis. From 6 to 12 months after implantation, the intimal hyperplasia was excessively increased and severe luminal stenosis had developed. The hyperplastic neointima consisted of two layers; a laminated superficial layer and a randomly arranged deeper layer. The superficial layer had three to four layers of smooth muscle cells, while the deeper layer was mostly fibrocollagenous tissues. Thus, the intimal hyperplasia at the distal end-to-side anastomosis of the arterially implanted autovein graft developed as a result of infiltration of fibroblast-like cells, presumably tissue-synthesizing mesenchymal cells. The neointima at the distal anastomosis, under conditions of reduced blood flow with high peripheral resistance, remained in an active phase of intimal hyperplasia even 12 months after bypass grafting.     

Mechanical and histologic changes in canine vein grafts

Mechanical and histological studies were performed on dog femoral veins after their implantation as grafts to bypass the ligated femoral arteries. The vein grafts dilated rapidly after implantation with 90% of maximum dilation occurring at 4 weeks. Both the native veins and the vein grafts were highly compliant up to 35-50 mm Hg, but were virtually nondistensible at higher pressures. When implanted with end-to-side anastomoses (end of vein to side of artery), the compliance of the anastomotic region resembled that of the artery rather than that of the vein. This was due to the distensibility of the artery at arterial pressure, as compared with the almost rigid vein. Histologic examination showed that intimal hyperplasia was greater after end-to-side anastomosis than after end-to-end anastomosis (P less than 0.05) and that this increased hyperplasia was reduced by treatment with aspirin and dipyridamole (P less than 0.05). By contrast, medial thickening was increased in all grafts compared with native veins (P less than 0.05), but was not different in end-to-end, end-to-side, and aspirin/dipyridamole-treated end-to-side grafts. These data suggest that intimal hyperplasia and medial thickening are separate responses to different stimuli.     

Local haemodynamics and shear stress in cuffed and straight PTFE-venous anastomoses: an in-vitro comparison using particle image velocimetry.

OBJECTIVES: To use particle image velocimetry (PIV) to study the haemodynamics and shear stress associated with cuffed and straight PTFE-venous anastomoses. METHODS: Silastic models of a straight and cuffed (Venaflo) PTFE-venous anastomoses were attached to a pulsatile flow 'Berlin Heart' circuit filled with glycerine/water and hollow glass tracer spheres. Instantaneous velocity fields were obtained PIV and shear rates and patterns calculated from frame-by-frame analysis. RESULTS: A high velocity jet struck the anastomotic 'floor' and was deflected toward the venous outflow. Shear stresses near the floor were significantly higher, in the straight anastomosis. Sites of high shear stress correlated well with the known sites of intimal hyperplasia. CONCLUSIONS: A cuffed anastomosis type may be favourable in terms of local haemodynamics so enhancing the long-term patency of PTFE-venous grafts.     

Correlation of intimal hyperplasia development and shear stress distribution at the distal end-side-anastomosis, in vitro study using particle image velocimetry.

Low shear areas at the distal anastomosis of peripheral bypasses are thought to promote neointimal hyperplasia. In this study we evaluated the fluid dynamic environment at the distal anastomosis of peripheral bypasses by means of a new method for in vitro flow visualization and quantitative velocity field measurement. A silastic model of a distal end-side anastomosis was attached to a mock circulation loop driven by an artificial heart. High resolution velocity fields were measured by means of particle image velocimetry (PIV). The velocity vector data were used to calculate vorticity omega, strain rates ex, shear rates h and shear stresses tau. Two separations and a stagnation zone were identified by means of flow visualization. Measured velocities inside the three zones were significantly lower than in the high velocity mainstream. Calculated shear rates and shear stresses inside the zones were significantly lower than human wall shear rates. At the transition between the effective mainstream and the boundary layers high vorticity and compressive strain fields existed, indicating the presence of high shear forces. The locations of these areas corresponded to the well known zones of intimal hyperplasia. The high resolution shear stress analysis supports the low shear theory of intimal hyperplasia development. A wall diversion angle greater than 6 degrees leads to flow separation and presumed IH promotion until high shear transition areas are reached.     

Flow patterns and preferred sites of intimal thickening in diameter-mismatched vein graft interpositions

BACKGROUND: It is suspected that blood flow and flow-induced shear stress play an important role in the pathogenesis and localization of intimal hyperplasia in anastomosed vessels. However, experimental data that demonstrate the correlation between the flow and the sites of intimal thickening obtained in the same vessel are scarce. For this reason, we have studied the relationship between the flow and precise locations of wall thickening specific to the particular vessel by performing diameter-mismatched vein graft interpositions. This method created more flow disturbances than those found in our previous study, which was carried out by dividing an artery and simply suturing its ends back to their original positions. METHODS: In the current study, grafting procedures consisting of 26 saphenous vein interpositions and 10 jugular vein interpositions were carried out on the femoral arteries of 22 adult mongrel dogs. The vessels were harvested at 3 months after operation, perfusion-fixed, and rendered transparent. The precise location and the size of intimal thickening and characteristics of the flow, such as flow patterns, distributions of fluid velocity, and wall shear stress, were studied in detail by means of flow visualization and cinemicrographic techniques. RESULTS: It was found that the diameters of interposed saphenous vein grafts, which were about one-half the diameter of host arteries, increased drastically and became almost the same as those of the host arteries. Intimal thickening was found distal to the distal anastomotic junction in smaller diameter saphenous vein-interposed vessels and distal to the proximal anastomotic junction in larger diameter jugular vein-interposed vessels. In both cases, flow was disturbed with the formation of a slow recirculation flow due to a sudden enlargement of vessel diameter caused by a mismatch of vessel diameters at the anastomotic junction and at the location where the wall shear stress was low. CONCLUSIONS: The results suggest that the key hemodynamic factors involved in the localization of intimal thickening are the low velocity of flowing blood and the resultant low shear stress acting on the vessel wall.     

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.     

Does the end-to-end venous anastomosis offer a functional advantage over the end-to-side venous anastomosis in high-output arteriovenous grafts?

This study explores the hemodynamics, mechanics, and biologic response of end-to-end versus end-to-side venous anastomoses in a canine arteriovenous graft model. Femoral polytetrafluoroethylene grafts were implanted bilaterally in a paired fashion (n = 22). Detailed local hemodynamic measurements were made by use of color Doppler ultrasound imaging at 1, 4, 8, and 12 weeks after implant. Measurements included volumetric flow rate and Doppler-derived spectral window (percent window) as a measure of turbulence. Amplitude and velocity of vessel wall movement were also measured. Volume of perivascular tissue vibration quantitated kinetic energy transfer through the vessel wall. Volumetric flow rate (end to end, 1013 +/- 70 ml/min; end to side, 1015 +/- 72 ml/min), percent window (end to end, 6.6% +/- 0.6%, end to side, 5.6% +/- 0.4%) and volume of perivascular tissue vibration (end to end, 19.6 +/- 1.2 ml, end to side, 16.3 +/- 1.8 ml) were statistically equivalent in the two graft types (end to end vs end to side p greater than 0.05). Both graft types developed venous intimal-medial thickening of a similar magnitude: end to end, 0.35 +/- 0.05 mm, end to side, 0.43 +/- 0.09 mm, normal vein 0.070 +/- 0.004 mm (analysis of variance [ANOVA] p less than 0.001, p less than 0.01 for end to end or end to side vs control, end to end vs end to side p greater than 0.05 by Student-Newman-Keuls test). The best correlations with venous intimal-medial thickening were obtained from inverse percent window (r = 0.84, p less than 0.001) and volume of perivascular tissue vibration (r = 0.68, p less than 0.001). In the end to end configuration the relative amplitude of venous wall movement decreased, and the relative velocity of wall motion increased over time. We conclude that in the circumstances of this high flow arteriovenous graft model the end-to-end venous anastomosis does not significantly differ from the end-to-side venous anastomosis in terms of flow stability, turbulence, or kinetic energy transfer. The magnitude of the hyperplastic response is statistically equivalent for the two anastomotic types, but the pattern is somewhat different, possibly providing evidence for differences in stress distribution. Differences in the relative amplitude and velocity of vessel wall movement suggest that anastomotic geometry may affect the way in which kinetic energy is dissipated at the graft/vessel interface.     

The morphology and patency of arterial and venous microvascular anastomoses throughout the first post-operative year. A histological study

End-to-end microvascular suture anastomoses, 40 arterial and 41 venous, from the rabbits carotid artery and posterior facial vein were harvested at 5 different time intervals (1, 2, 3, 6 and 12 months) post surgery and evaluated with light microscopy. A 100% long-term patency was noted both in arteries and veins. Quantitative measurements of the width of the vessel wall components indicated that a statistically significant temporary hypertrophic response occurred in the arterial intima, culminating in the third month when the width of the vessel wall at the anastomotic level almost doubled the normal. After that the width of the vessel wall again declined but it remained thicker than the adjacent vessel wall at one year post surgery. Among the venous anastomoses, however, the wall thickness at the anastomotic level remained thinner than the adjacent vessel wall throughout the evaluation period. The original vessel wall characteristics are not restored at the anastomotic site with intimal hyperplasia compensating for medial necrosis. Despite these events a technically satisfactory microvascular anastomosis should remain patent for years.     

Unconventional vessel wall apposition in off-pump porcine coronary artery bypass grafting: low versus high graft flow

OBJECTIVE: Facilitated coronary anastomosis techniques may involve unconventional vessel wall apposition in contrast to standard intima-intima apposition. We assessed the patency, anastomotic thrombus formation, and intimal hyperplasia of unconventional intima-adventitia apposition versus conventional suturing techniques in beating heart coronary bypass grafting under low versus high graft flow conditions. METHODS: The intima-adventitia (n = 28) and conventional anastomoses (n = 28) were evaluated intraoperatively (n = 56), at 4 hours (n = 20), and at 5 weeks (n = 36) in a new off-pump low-flow (n = 28) and high-flow (n = 28) porcine bypass model (< or = 15 mL/min and about 60 mL/min, respectively). The anastomoses were assigned to the animals by means of randomized stratification and examined by means of flow measurements, angiography, and histology. RESULTS: Mean graft flows in intima-adventitia and in conventional anastomoses were similar (P =.709). All but 1 of 56 anastomoses (low flow conventional) were fully patent at the time of death. At 4 hours, only small platelet depositions were found at the exposed media and adventitia in the unconventional anastomoses. At 5 weeks, little streamlining intimal hyperplasia was found, which was comparable between the anastomoses (P =.600). CONCLUSIONS: In low-flow conditions (< or = 15 mL/min) unconventional intima-adventitia apposition was not detrimental to the internal thoracic-coronary artery anastomosis in the pig. This finding may expand design strategies of facilitated coronary artery bypass anastomosis techniques.     

Effects of anastomotic angle on vascular tissue responses at end-to-side arterial grafts

OBJECTIVE: Hemodynamics has been implicated in the late failure of arterial bypass grafts, which frequently occurs at the distal anastomosis site. This study was designed to assess the relationship between local hemodynamics and pathologic responses of the distal anastomosis by manipulation of the angle of anastomosis of the graft, a major determinant of local hemodynamics. METHODS: End-to-side anastomoses of the right carotid to the left carotid arteries of rabbits were performed at anastomotic angles of less than 10 degrees (acute), 45 degrees (intermediate), or 90 degrees (right angle), and then the upstream left carotid arteries were ligated to simulate pathologic occlusion. We examined tissue responses on the wall of the recipient vessel opposite the anastomosis site (the bed), where unusual hemodynamic forces are imposed. RESULTS: Three months after surgery, intimal thickening was observed on the upstream portion of the acute, and more rarely, the intermediate anastomoses only. Medial thinning caused by loss of cells and matrix, and an aneurysm-like dilation, was observed in the right angle and some intermediate anastomoses, but not in the acute anastomoses. En face confocal microscopy at 3 weeks after surgery revealed severe disruption of the internal elastic lamina in all anastomotic models. Zymography and Western immunoblotting demonstrated gelatinolytic activity, caused by expression and activation of MMP-2, that was lowest in the acute anastomoses, higher in the intermediate anastomoses, and highest in the right-angle anastomoses. CONCLUSIONS: We infer that very different pathologic changes to the vessel wall are elicited when local hemodynamics is manipulated by altering the anastomotic branch angle.     

Impact of In Vivo Ranges of the Variances in the Flow Velocity Waveforms and Flow Split Ratio on the Hemodynamic Effects of the Anastomotic Cuff at Distal End-to-Side Anastomosis

Purpose The blood flow inside distal end-to-side anastomoses may be affected by inlet flow velocity profiles and outlet blood distribution ratios. This study investigated the in vivo range of these variables and their impact on the hemodynamic effects of an anastomotic cuff using a computational fluid dynamics approach. Materials and Methods Predesigned expanded polytetrafluoroethylene cuffed grafts were used in 22 femoropopliteal bypasses and straight grafts were used for 10 cases. The flow distribution was examined by angiographic techniques and the inlet flow velocity was determined by a spectral Doppler method. Results The caudal outflow distribution ratio was 95.6% ± 7.2% (75%–100%). The positive peak flow velocity was 1.66 ± 0.25 m/s. The ratio of the absolute value of the negative to positive peak velocity was 0.32 ± 0.12. The cuff increased wall shear stress along the artery floor regardless of the flow velocity profiles at 100% of the caudal distribution ratio but not at 75%. Conclusion The hemodynamics inside the anastomosis were thus found to be affected by these flow variables. The proper indications for the cuff should therefore not be decided based simply on the location of the anastomosis without taking the fluid dynamic factors in the vicinity of the anastomosis into full consideration.