The vasa vasorum and associated endothelial nitric oxide synthase is more important for saphenous vein than arterial bypass grafts

An Obligatory Role of Perivascular Adipose Tissue in Improved Saphenous Vein Graft Patency in Coronary Artery Bypass Grafting

The gold standard graft for coronary artery bypass grafting (CABG) is the internal thoracic artery (ITA), and the second recommendation is the radial artery. However, complete revascularization with arterial grafts alone is often difficult, and the saphenous vein (SV) is the most commonly used autologous graft for CABG, because it is easier to use without restriction for the length of the graft. On the other hand, the patency of SV grafts (SVGs) is poor compared with that of arterial grafts. The SVG is conventionally harvested as a distended conduit with surrounding tissue removed, a procedure that may cause vascular damage. A no-touch technique of SVG harvesting has been reported to result in improved long-term patency in CABG comparable to that when using the ITA for grafting. Possible reasons for the excellent long-term patency of no-touch SVGs are the physical support provided by preserved surrounding perivascular adipose tissue, preservation of the vascular wall structure including the vasa vasorum, and production of adipocyte-derived factors. In this review, we discuss recent strategies aimed at improving the performance of SVGs, including no-touch harvesting, minimally invasive harvesting and mechanical support using external stents.

The impact of perivascular tissue preservation on 5-year patency of saphenous vein composite grafts

OBJECTIVES

This retrospective study was conducted to evaluate the impact of saphenous vein (SV) harvesting with versus without perivascular tissue on the 5-year angiographic patency in coronary artery bypass grafting.

METHODS

Among the 944 patients who received coronary artery bypass grafting between 2010 and 2015, 579 patients who received off-pump coronary artery bypass grafting using 1 SV as a Y-composite graft based on the in situ left internal thoracic artery were enrolled. SV harvesting was performed using no-touch technique without perivascular tissue (the NoPVT group) in 342 patients and with perivascular tissue (the PVT group) in 237 patients. Follow-up duration was 84.0 months (interquartile range 66.5-105.4). Propensity score matching was performed, and long-term clinical outcomes and angiographic patency were compared.

RESULTS

The average number of distal anastomoses per patient was comparable between the groups, although more SV grafts were anastomosed to left anterior descending territory in the PVT group than in the NoPVT group. Overall survival and cumulative incidence of cardiac death were comparable between the groups, whereas cumulative incidence of target vessel revascularization (1.3% vs 4.3% at 5 year, P = 0.009) and that of major adverse cardiac events (7.3% vs 9.9% at 5 year, P = 0.035) were lower in the PVT group than in the NoPVT group. One-year and 5-year angiographic patency rates of the SV grafts were higher in the PVT group than in the NoPVT group [97.0% vs 91.7% (P = 0.004) and 96.3% vs 89.9% (P = 0.007), respectively].

CONCLUSIONS

SV grafts harvested using no-touch technique with perivascular tissue further improved the 5-year patency of SV composite grafts compared with those without perivascular tissue.

Impact of Graft Velocity on Saphenous Vein Graft Atherosclerosis after Coronary Artery Bypass Grafting

PURPOSE

Saphenous vein grafts (SVGs) sometimes occur as vein graft stenosis or failure in coronary artery bypass grafting. The purpose of this study was to detect the factors affecting vein graft atherosclerosis.

METHODS

We performed two analysis. In the first analysis, we enrolled 120 grafts using conventionally harvested saphenous vein graft (C-SVG) and followed-up with multiple coronary computed tomography angiography (CCTA). We examined the factors that contribute to the graft atherosclerosis defined by graft failure at subsequent CCTA or substantial progression of graft stenosis (a decrease of ≥0.6 mm in diameter). In the second analysis, 66 grafts using no-touch harvested saphenous vein graft (N-SVG) were compared with those in the first analysis using C-SVG, focusing on the differences in intraoperative factors using propensity score-matched analysis.

RESULTS

In the first analysis, graft atherosclerosis+ group comprised 27 grafts, which had a larger SVG diameter, lower graft velocity, and higher graft/native ratio in diameter than the graft atherosclerosis- group. In the multivariable analysis, slow graft velocity and graft/native ≥2 in diameter were independently associated with the graft atherosclerosis. In the second analysis, the N-SVG group had a much greater graft velocity than the C-SVG group.

CONCLUSION

Lower graft velocity and higher graft/native ratio in diameter were associated with the graft atherosclerosis. The N-SVG group had increased graft velocity, which may contribute to prevent the graft atherosclerosis.(Trial registration: UMIN Clinical Trial Registry no. UMIN000050482. Registered 3 March 2023, retrospectively registered.).

3D Elastomeric Stent Functionalized with Antioxidative and Perivascular Tissue Regenerative Activities Ameliorated PVT Deprivation-Induced Vein Graft Failure

Clinically, arterial injuries are always accompanied with perivascular tissue damage, which may contribute to high failure rate of vein grafts due to intimal hyperplasia and acute thrombosis. In this study, a "perivascular tissue (PVT) deprivation" animal model is constructed to mimic clinical scenarios and identify the contribution of arterial PVT to the success of vein grafts. Proteomics analysis suggests that depriving PVT may exacerbate reactive oxygen species (ROS)-induced endothelial apoptosis by up-regulating inflammation response and oxidative stress. Locally administering metformin on vein grafts through 3D-printed external stent (PGS-PCL) shows antioxidative and anti-inflammatory properties to protect cells from ROS invasion, thereafter decreasing acute thrombosis. Moreover, metformin induce rapid regeneration of perivascular adipose tissue in recipient regions, which improves patency by inhibiting intimal hyperplasia. Proteomics, western blot, and in vitro blocking tests reveal that metformin resists endothelial apoptosis through AMPK/mTOR and NFκB signaling pathways. To conclude, PVT deprivation exacerbates inflammatory response and oxidative stress in vein grafts bridging arterial circulation. Metformin-loaded stent ameliorates "PVT damage" related vein graft failure, and enhances patency of through resisting endothelial apoptosis and regenerating arterial PVAT, offering a promising avenue to improve the success of vein grafts in clinic.

Vasa Vasorum in Saphenous Vein for CABG: A Review of Morphological Characteristics

This short article discusses selected scanning electron microscope and transmission electron microscope features of vasa vasorum including pericytes and basement membrane of the human saphenous vein (SV) harvested with either conventional (CON) or no-touch (NT) technique for coronary artery bypass grafting. Scanning electron microscope data shows the general damage to vasa vasorum of CON-SV, while the transmission electron microscope data presents ultrastructural features of the vasa in more detail. Hence there are some features suggesting pericyte involvement in the contraction of vasa blood vessels, particularly in CON-SV. Other features associated with the vasa vasorum of both CON-SV and NT-SV preparations include thickened and/or multiplied layers of the basement membrane. In some cases, multiple layers of basement membrane embrace both pericyte and vasa microvessel making an impression of a "unit" made by basement membrane-pericyte-endothelium/microvessel. It can be speculated that this structural arrangement has an effect on the contractile and/or relaxing properties of the vessels involved. Endothelial colocalization of immunoreactive inducible nitric oxide synthase and endothelin-1 can be observed (with laser confocal microscope) in some of the vasa microvessels. It can be speculated that this phenomenon, particularly of the expression of inducible nitric oxide synthase, might be related to structurally changed vasa vessels, e.g., with expanded basement membrane. Fine physiological relationships between vasa vasorum endothelium, basement membrane, pericyte, and perivascular nerves have yet to be uncovered in the detail needed for better understanding of the cells'specific effects in SV preparations for coronary artery bypass grafting.

Progression of Arterial Vasa Vasorum from Regulator of Arterial Homeostasis to Promoter of Atherogenesis

The vasa vasorum (vessels of vessels) are a dynamic microvascular system uniquely distributed to maintain physiological homeostasis of the artery wall by supplying nutrients and oxygen to the outer layers of the artery wall, adventitia, and perivascular adipose tissue, and in large arteries, to the outer portion of the medial layer. Vasa vasorum endothelium and contractile mural cells regulate direct access of bioactive cells and factors present in both the systemic circulation and the arterial perivascular adipose tissue and adventitia to the artery wall. Experimental and human data show that proatherogenic factors and cells gain direct access to the artery wall via the vasa vasorum and may initiate, promote, and destabilize the plaque. Activation and growth of vasa vasorum occur in all blood vessel layers primarily by angiogenesis, producing fragile and permeable new microvessels that may cause plaque hemorrhage and fibrous cap rupture. Ironically, invasive therapies, such as angioplasty and coronary artery bypass grafting, injure the vasa vasorum, leading to treatment failures. The vasa vasorum function both as a master integrator of arterial homeostasis and, once perturbed or injured, as a promotor of atherogenesis. Future studies need to be directed at establishing reliable in vivo and in vitro models to investigate the cellular and molecular regulation of the function and dysfunction of the arterial vasa vasorum.

Left Internal Mammary Artery as an Endocrine Organ: Insights Into Graft Biology and Long-term Impact Following Coronary Artery Bypass Grafting

The left internal mammary artery (LIMA) is considered the criterion standard vessel for use in coronary artery bypass grafting. In recent decades, countless studies have documented its superiority over other arterial and venous coronary artery bypass grafting conduits, although the full mechanisms for this superiority remain unknown. A growing body of literature has unveiled the importance of extracellular vesicles known as exosomes in cardiovascular signaling and various pathologic states. In this review, we briefly compare the clinical longevity of the LIMA relative to other conduits, explore the effects of varying grafting techniques on clinical and angiographic outcomes, and provide physiologic insights into graft function on a cellular and molecular level. Finally, we explore exosome signaling as it pertains to atherosclerosis in support of the LIMA as an "endocrine organ."

Excessive Adventitial and Perivascular Vascularisation Correlates with Vascular Inflammation and Intimal Hyperplasia

Albeit multiple studies demonstrated that vasa vasorum (VV) have a crucial importance in vascular pathology, the informative markers and metrics of vascular inflammation defining the development of intimal hyperplasia (IH) have been vaguely studied. Here, we employed two rat models (balloon injury of the abdominal aorta and the same intervention optionally complemented with intravenous injections of calciprotein particles) and a clinical scenario (arterial and venous conduits for coronary artery bypass graft (CABG) surgery) to investigate the pathophysiological interconnections among VV, myeloperoxidase-positive (MPO⁺) clusters, and IH. We found that the amounts of VV and MPO⁺ clusters were strongly correlated; further, MPO⁺ clusters density was significantly associated with balloon-induced IH and increased at calciprotein particle-provoked endothelial dysfunction. Likewise, number and density of VV correlated with IH in bypass grafts for CABG surgery at the pre-intervention stage and were higher in venous conduits which more frequently suffered from IH as compared with arterial grafts. Collectively, our results underline the pathophysiological importance of excessive VV upon the vascular injury or at the exposure to cardiovascular risk factors, highlight MPO⁺ clusters as an informative marker of adventitial and perivascular inflammation, and propose another mechanistic explanation of a higher long-term patency of arterial grafts upon the CABG surgery.

Impact of the no-touch harvesting technique on the vessel diameter of saphenous vein grafts for coronary artery bypass grafting

Objectives

To explore the impact of the no-touch harvesting technique on the vessel diameter of saphenous vein grafts.

Methods

This retrospective, single-center study enrolled 166 patients who underwent isolated coronary artery bypass grafting using saphenous vein grafts. Saphenous vein grafts were harvested conventionally in 83 patients (conventional group) and using the no-touch technique in 83 patients (no-touch group). We analyzed graft patency and the vessel diameters of saphenous vein grafts in the pre- and postoperative states. The diameter mismatch between the saphenous vein grafts and the coronary artery at the anastomotic site was also measured; preoperative diameter was measured using ultrasound imaging, and the postoperative diameter was measured using electrocardiogram-gated enhanced computed tomography.

Results

A total of 135 saphenous vein grafts (66 and 69 grafts in the conventional and no-touch groups, respectively) were evaluated for postoperative patency. Graft patency was equivalent in the 2 groups (conventional, 96.9% vs no-touch, 100%; P = .24). A detailed evaluation was performed in 109 saphenous vein grafts (52 and 57 grafts in the conventional and no-touch groups, respectively). Saphenous vein graft diameter was significantly distended in the conventional group (preoperative, 2.6 ± 0.7 mm vs postoperative, 3.4 ± 0.5 mm; P < .0001). However, saphenous vein graft diameter did not change in the no-touch group (preoperative, 2.9 ± 0.4 mm vs postoperative 2.8 ± 0.4 mm, P = .33). The diameter mismatch was significantly smaller in the no-touch group (conventional 1.4 ± 0.6 mm vs no-touch 1.0 ± 0.4 mm, P < .0001).

Conclusions

The no-touch technique avoids the expansion of graft diameter and diameter mismatch between the saphenous vein grafts and coronary artery.

Short-Term Evaluation of a Novel No-Touch Technique for Harvesting Saphenous Veins With Long-Shafted Ultrasonic Scalpel

OBJECTIVE

Saphenous vein grafts (SVGs) are widely used as bypass conduits in coronary artery bypass grafting. Compared with the conventional technique, the "no-touch" technique, wherein the saphenous veins are harvested with the surrounding tissue, may improve SVG patency; however, there are concerns regarding wound complications. To address this issue, we describe our novel no-touch technique with separate skin incisions using a long-shafted ultrasonic scalpel and report the clinical outcomes.

METHODS

We enrolled 66 male patients who underwent isolated coronary artery bypass grafting between April 2016 and April 2021. There were 30 and 36 patients treated using our no-touch technique and the conventional technique, respectively. The participants underwent coronary angiography before discharge and were followed clinically. SVG samples were taken for pathological examination.

RESULTS

SVGs harvested using our no-touch technique displayed preservation of the vessel wall structure and surrounding tissues. Our no-touch technique demonstrated no inferiority in patency compared with the conventional technique, and there was no SVG occlusion in the no-touch group. The frequency of leg wound complications was higher in the no-touch group than the conventional group, but no surgical site infections and severe complications occurred in the no-touch group.

CONCLUSIONS

SVGs harvested using our novel no-touch technique had similar pathological characteristics to those harvested using the original no-touch technique reported previously. Our no-touch technique maintained SVG patency and caused no severe wound complications. However, a large-scale, longitudinal study is required to accurately assess the clinical outcomes of our no-touch technique.

[Comparative study of vasa vasorum and neointima in conduits for coronary artery bypass grafting]

AIM

This study was undertaken to investigate the preoperative incidence and severity of intimal hypertrophy, as well as the level of blood supply of arterial and venous conduits for coronary artery bypass grafting.

MATERIAL AND METHODS

Segments of the internal thoracic artery and great saphenous vein (n=13) were harvested pairwise during coronary artery bypass grafting and were then visualized by scanning electron microscopy in back-scattered electrons. The analysis of the incidence and thickness of intimal hypertrophy, as well as the calculation of the number and the area of the vasa vasorum were performed using the programme ImageJ.

RESULTS

Intimal hypertrophy was more characteristic for the great saphenous vein as compared with the internal thoracic artery (9/13 (69.2%) and 7/13 (55.8%), respectively), although this difference did not reach statistical significance. The maximal-to-minimal neointimal thickness ratio correlated with the percentage of stenosis (r=0.875, p<0.0001), the area (r=0.45, p=0.023) and the number (r=0.47, p=0.015) of the vasa vasorum in the conduits, thus confirming the hypothesis on possible participation of these vessels in the development of intimal hypertrophy, with the area of the vasa vasorum being greater in the vessels with >10% stenosis (p=0.051). The number of the vasa vasorum in the great saphenous vein exceeded that in the internal thoracic artery (p=0.0005), with this difference remaining significant after adjustment for the area of the adventitia (p=0.027). The number of the vasa vasorum per the percentage of stenosis in the great saphenous vein also exceeded that in the internal thoracic artery (p=0.039) and more strongly correlated with intimal hypertrophy in the great saphenous vein as compared with that in the internal thoracic artery (r=0.53 and r=0.27, respectively).

CONCLUSION

Intimal hypertrophy correlates with the area and number of the vasa vasorum in conduits. The great saphenous vein is characterised by a larger number and higher density of the vasa vasorum as compared with the internal thoracic artery. The number of the vasa vasorum is correlated with stenosis of the great saphenous vein more closely than with stenosis of the internal thoracic artery. This may be suggestive of significant predisposition of the great saphenous vein to the onset of adventitial inflammation followed by the development of intimal hypertrophy.

Antiatherosclerotic Phenotype of Perivascular Adipose Tissue Surrounding the Saphenous Vein in Coronary Artery Bypass Grafting

Background

Perivascular adipose tissue (PVAT) is associated with metabolically driven chronic inflammation called metaflammation, which contributes to vascular function and the pathogenesis of vascular disease. The saphenous vein (SV) is commonly used as an essential conduit in coronary artery bypass grafting, but the long‐term patency of SV grafts is a crucial issue. The use of the novel “no‐touch” technique of SV harvesting together with its surrounding tissue has been reported to result in good long‑term graft patency of SV grafts. Herein, we investigated whether PVAT surrounding the SV (SV‐PVAT) has distinct phenotypes compared with other PVATs of vessels.

Methods and Results

Fat pads were sampled from 48 patients (male/female, 32/16; age, 72±8 years) with coronary artery disease who underwent elective coronary artery bypass grafting. Adipocyte size in SV‐PVAT was significantly larger than the sizes in PVATs surrounding the internal thoracic artery, coronary artery, and aorta. SV‐PVAT and PVAT surrounding the internal thoracic artery had smaller extents of fibrosis, decreased gene expression levels of fibrosis‐related markers, and less metaflammation, as indicated by a significantly smaller extent of cluster of differentiation 11c–positive M1 macrophage infiltration, higher gene expression level of adiponectin, and lower gene expression levels of inflammatory cytokines, than did PVATs surrounding the coronary artery and aorta. Expression patterns of adipocyte developmental and pattern‐forming genes were totally different among the PVATs of the vessels.

Conclusions

The phenotype of SV‐PVAT, which may result from inherent differences in adipocytes, is closer to that of PVAT surrounding the internal thoracic artery than that of PVAT surrounding the coronary artery or that of PVAT surrounding the aorta. SV‐PVAT has less metaflammation and consecutive adipose tissue remodeling, which may contribute to high long‐term patency of grafting when the no‐touch technique of SV harvesting is used.

What is the impact of preserving the endothelium on saphenous vein graft performance? Comments on the 'NO' touch harvesting technique

Saphenous veins used for coronary artery bypass surgery are subjected to considerable vascular trauma when harvested by conventional methods. This vascular damage is responsible, at least in part, for the inferior patency of the saphenous vein when compared with the internal thoracic artery. The performance of saphenous vein grafts is improved when this conduit is harvested atraumatically using the no-touch technique. There is growing evidence that the success of the no-touch technique is due to the preservation of a number of vascular structures including the endothelium, vasa vasorum and perivascular fat. There is conflicting evidence regarding the degree of endothelial damage to the endothelium of conventional versus no-touch saphenous vein grafts. In general, it has been shown that this single layer of cells lining the lumen exhibits considerable damage associated with a combination of vascular trauma and high pressure intraluminal distension. Increased platelet aggregation and thrombus formation at the exposed subendothelial membrane is due to a local reduction of endothelium-derived factors including nitric oxide. In addition, damage to the vasa vasorum of conventionally-harvested veins will reduce transmural blood flow, a condition shown to promote neointimal hyperplasia and atheroma formation. By stripping off the perivascular fat during conventional harvesting, mechanical support of the graft is reduced and the source of adipocyte-derived factors potentially beneficial for graft patency removed. While most agree that endothelial damage to the saphenous vein affects graft patency, the contribution of other tissue-derived factors affected by vascular damage at harvesting need to be considered.

A Brief Comment on Vasa Vasorum of Human Saphenous Vein: relevance for Coronary Artery Bypass Surgery

The importance of the vasa vasorum and blood supply to the wall of human saphenous vein (hSV) used for coronary artery bypass grafting (CABG) is briefly discussed. This is in the context of the possible physical link of the vasa vasorum connecting with the lumen of hSV and the anti-ischaemic impact of this microvessel network in the hSV used for CABG.

Saphenous veins in coronary artery bypass grafting need external support

The saphenous vein is the most commonly used conduit for coronary artery bypass grafting. Arterial grafts are harvested with the outer pedicle intact whereas saphenous veins are harvested with the pedicle removed in the conventional graft harvesting technique. This conventional procedure causes considerable vascular damage. One strategy to improve vein graft patency has been to provide external support. Ongoing studies show that fitting a metal external support improves conventionally harvested saphenous vein graft patency. On the other hand, the no-touch technique of harvesting the saphenous vein provides an improved graft with long-term patency comparable to that of the internal mammary artery. This improvement is suggested to be due to preservation of vessel structures. Interestingly, many of the mechanisms proposed to be associated with the beneficial actions of an artificial external support on saphenous vein graft patency are similar to those underlying the beneficial effect of no-touch saphenous vein grafts where the intact outer layer acts as a natural support. Additional actions of external supports have been advocated, including promotion of angiogenesis, increased production of vascular-protective factors, and protection of endothelial cells. Using no-touch harvesting, normal vascular architecture is maintained, tissue and cell damage is minimized, and factors beneficial for graft patency are preserved. In this review, the significance of external support of saphenous vein grafts in coronary artery bypass grafting is discussed.

Stable Hemodynamics within "No-Touch" Saphenous Vein Graft

PURPOSE

To investigate the hemodynamics characteristics of the "no-touch" saphenous vein graft (SVG) conduits by nicardipine intraluminal administration in vivo experiment.

METHODS

A total of 59 consecutive patients were enrolled and underwent a sequential SVG to three non-left anterior descending (LAD) targets with the average runoff ≤2 mm, 30 with "no-touch" harvest technique (group A) and 29 with conventional preparation (group B). The patients were subject to nicardipine intraluminal injection during off-pump coronary artery bypass grafting (CABG) procedure. The intraoperative flow was measured with the ultrasonic transit time flow meter (TTFM), and the graft patency testified by multi-detector computed tomography (MDCT) angiography, respectively.

RESULTS

The baseline blood flow was higher in group A than that in group B (p <0.05). However, the increases in blood flow of SVG conduits in group A were lower than those in group B with 19.7 ± 5.9 vs. 35.4 ± 9.2 mL/min, 14.8 ± 5.6 vs. 23.1 ± 6.8 mL/min, 6.6 ± 2.1 vs. 11.2 ± 4.3 mL/min before the first, second, and third anastomose after nicardipine intraluminal administration, respectively (all p <0.01).

CONCLUSIONS

No-touch SVGs were associated with higher baseline blood flow and less rises after nicardipine intraluminal administration during off-pump CABG procedure compared with conventional preparation. The no-touch SVGs seemed to be less spastic and well-tolerated on flow dilatation.

Comparison of Different Thawing Protocols in Human Cryopreserved Venous Grafts

BACKGROUND

The aim of our study was to assess the impact of different thawing protocols on morphological changes arising in cryopreserved human saphenous vein grafts.

METHODS

The study was performed in 12 saphenous vein grafts harvested in brain death donors. Storage in the vapor phase of liquid nitrogen for 3 or 5 years followed. Two thawing protocols were tested: slow thawing in a refrigerator at temperature +4°C for 2 hr and rapid thawing-in a water bath at +37°C. Grafts were processed for scanning electron microscopy. Comparisons of continuous parameters under study between experimental groups were performed using the t-test (age, cold ischemia time, exposure to cryoprotectant, time of storage, total thawing time, mean thawing rate, morphology scoring of thawed HSVG) and the median test (HSVG length). Categorical parameters (sex and blood group) were formally tested using the chi-square test.

RESULTS

All samples were evaluated according to morphological changes and scored in terms of morphologically intact endothelium, confluent endothelium with structural inhomogeneity, disruption of the intercellular contacts, separation of the endothelial cells, complete loss of the endothelium, and damage of the subendothelial layers. There is no statistically significant difference between the sample sets at the significance level of 0.05. There was no association with donors' age, sex, and time of storage.

CONCLUSIONS

Human cryopreserved saphenous vein grafts in our experimental work showed no difference in terms of structural deterioration of the endothelial surface and basal membrane depending on different thawing protocols used.

State-of-the-Art Coronary Artery Bypass Grafting: Patient Selection, Graft Selection, and Optimizing Outcomes

Despite the progressive expansion of clinical indications for percutaneous coronary intervention and the increasingly high risk profile of referred patients, coronary artery bypass grafting (CABG) remains the mainstay in multivessel disease, providing good long-term outcomes with low complication rates. Multiple arterial grafting, especially if associated with anaortic techniques, might provide the best longer-term outcomes. A surgical approach individualized to the patients' clinical and anatomic characteristics, and surgeon and team experience, are key to excellent outcomes. Current evidence regarding patient selection, indications, graft selection, and potential strategies to optimize outcomes in patients treated with CABG is summarized.

Preserved Vasoconstriction and Relaxation of Saphenous Vein Grafts Obtained by a No-Touch Technique for Coronary Artery Bypass Grafting

BACKGROUND

To obtain a saphenous vein graft (SVG) for coronary artery bypass grafting (CABG), the benefit of using a no-touch (NT) technique in vascular function has not been fully investigated. Methods and Results: The pathological and physiological functions of human SVGs with a NT technique to preserve the perivascular adipose tissue (PVAT) and ones obtained by using a conventional (CON) technique removing PVAT, were examined. Immunohistochemistry of the section of SVGs showed that the phosphorylation of endothelial nitric oxide synthase in the endothelium of the NT group was more responsive to vascular endothelial growth factor. A myograph of SVGs showed greater contraction with phenylephrine in the NT group. However, the strong contraction was eliminated in SVGs taken by electrocautery. In the 10 patients whose SVGs were taken without electrocautery, endothelial-dependent relaxation with bradykinin was apparently increased in the CON group more than in the NT group. Smooth muscle relaxation with nitroprusside was higher in the CON group at the lower concentrations; however, the relaxation became greater in the NT group at the high concentrations. Therefore, the effect of neutralizing PVAT-released factors in the both groups was further examined. After medium of NT and CON were exchanged in half, relaxation of SVGs was immediately restored in the NT group.

CONCLUSIONS

The results suggest that the NT technique preserves the functions of vasoconstriction and relaxation. Also, the presence of PVAT-released vasoconstrictive factors was suspected.

No-touch vein grafts and the destiny of venous revascularization in coronary artery bypass grafting-a 25th anniversary perspective

Ischemic heart disease is currently the leading cause of death globally, with coronary artery bypass grafting among the most common operations performed worldwide. More extensive use of arterial grafts has been advocated because of their high long-term patency, long-term survival benefit, and freedom from reinterventions. Despite this, the saphenous vein is the most frequently used conduit in patients undergoing coronary artery bypass surgery since its introduction over 50 years ago. Consequently, the saphenous vein remains an indispensable conduit in coronary artery bypass grafting and maintaining its long-term patency is one of the most crucial challenges in cardiovascular surgery. This situation led to the development of the no-touch saphenous vein harvesting technique, where the vein is harvested completely with its pedicle of surrounding tissue. Several studies report a superior long-term patency rate, slower progression of atherosclerosis, and better clinical outcomes whilst employing no-touch harvesting technique. The success of the technique is multifactorial, including the decreased risk for graft spasm-and the need for manual distension-preservation of the vaso vasorum and an intact endothelium, reducing neointimal hyperplasia and subsequent atherosclerosis. Furthermore, the intact perivascular tissue, including the surrounding cushion of fat, may act as a "natural external stent", providing mechanical support preventing the graft from kinking. We are convinced that the use of arterial grafts, in combination with the no-touch saphenous vein graft, will significantly improve the results of coronary artery bypass grafting. This is important for achieving a comprehensive and evidence-based balance between the major treatment strategies of ischemic heart disease, explicitly coronary artery bypass grafting and percutaneous coronary intervention. The no-touch technique is becoming increasingly popular among surgeons, with further studies to be initiated worldwide.

Vasa vasorum inside out/outside in communication: a potential role in the patency of saphenous vein coronary artery bypass grafts

The saphenous vein (SV) is the most commonly used conduit for revascularization in patients undergoing coronary artery bypass surgery (CABG). The patency rate of this vessel is inferior to the internal thoracic artery (ITA). In the majority of CABG procedures the ITA is removed with its outer pedicle intact whereas the (human) SV (hSV) is harvested with pedicle removed. The vasa vasorum, a microvessel network providing the adventitia and media with oxygen and nutrients, is more pronounced and penetrates deeper towards the lumen in veins than in arteries. When prepared in conventional CABG the vascular trauma caused when removing the hSV pedicle damages the vasa vasorum, a situation affecting transmural flow potentially impacting on graft performance. In patients, where the hSV is harvested with pedicle intact, the vasa vasorum is preserved and transmural blood flow restored at graft insertion and completion of CABG. By maintaining blood supply to the hSV wall, apart from oxygen and nutrients, the vasa vasorum may also transport factors potentially beneficial to graft performance. Studies, using either corrosion casts or India ink, have shown the course of vasa vasorum in animal SV as well as in hSV. In addition, there is some evidence that vasa vasorum of hSV terminate in the vessel lumen based on ex vivo perfusion, histological and ultrastructural studies. This review describes the preparation of the hSV as a bypass conduit in CABG and its performance compared with the ITA as well as how and why its patency might be improved by harvesting with minimal trauma in a way that preserves an intact vasa vasorum.

Role of Perivascular Adipose Tissue in Health and Disease

Perivascular adipose tissue (PVAT) is cushion of fat tissue surrounding blood vessels, which is phenotypically different from other adipose tissue depots. PVAT is composed of adipocytes and stromal vascular fraction, constituted by different populations of immune cells, endothelial cells, and adipose-derived stromal cells. It expresses and releases an important number of vasoactive factors with paracrine effects on vascular structure and function. In healthy individuals, these factors elicit a net anticontractile and anti-inflammatory paracrine effect aimed at meeting hemodynamic and metabolic demands of specific organs and regions of the body. Pathophysiological situations, such as obesity, diabetes or hypertension, induce changes in its amount and in the expression pattern of vasoactive factors leading to a PVAT dysfunction in which the beneficial paracrine influence of PVAT is shifted to a pro-oxidant, proinflammatory, contractile, and trophic environment leading to functional and structural cardiovascular alterations and cardiovascular disease. Many different PVATs surrounding a variety of blood vessels have been described and exhibit regional differences. Both protective and deleterious influence of PVAT differs regionally depending on the specific vascular bed contributing to variations in the susceptibility of arteries and veins to vascular disease. PVAT therefore, might represent a novel target for pharmacological intervention in cardiovascular disease. © 2018 American Physiological Society. Compr Physiol 8:23-59, 2018.

Nerve-perivascular fat communication as a potential influence on the performance of blood vessels used as coronary artery bypass grafts

Perivascular fat, the cushion of adipose tissue surrounding blood vessels, possesses dilator, anti-contractile and constrictor actions. The majority of these effects have been demonstrated in vitro and may depend on the vessel and/or the experimental method or species used. In general, the relaxant effect of perivascular adipose tissue is local and may be either endothelium-dependent or endothelium-independent. However, nerve stimulation studies show that, in general, perivascular adipose tissue (PVAT) has an anti-contractile vascular effect likely to involve an action of the autonomic vascular nerves. Apart from a direct effect of perivascular fat-derived factors on bypass conduits, an interaction with a number of neurotransmitters and other agents may play an important role in graft performance. Although the vascular effects of PVAT are now well-established there is a lack of information regarding the role and/or involvement of peripheral nerves including autonomic nerves. For example, are perivascular adipocytes innervated and does PVAT affect neuronal control of vessels used as grafts? To date there is a paucity of electrophysiological studies into nerve-perivascular fat control. This review provides an overview of the vascular actions of PVAT, focussing on its potential relevance on blood vessels used as bypass grafts. In particular, the anatomical relationship between the perivascular nerves and fat are considered and the role of the perivascular-nerve/fat axis in the performance of bypass grafts is also discussed.

Exercise-induced saphenous vein graft spasm prevented by stenting

Recurrence of anginal symptoms following coronary artery bypass surgery is usually secondary to graft closure or progression of native vessel disease. The present case demonstrates severe exercise-induced saphenous vein graft (SVG) spasm associated with transmural ischemia refractory to maximal vasodilator therapy. Symptoms resolved and exercise electrocardiography normalized following stenting of SVG regions demonstrating spasm. © 2017 Wiley Periodicals, Inc.

The role of perivascular adipose tissue in obesity-induced vascular dysfunction

Under physiological conditions, perivascular adipose tissue (PVAT) attenuates agonist‐induced vasoconstriction by releasing vasoactive molecules including hydrogen peroxide, angiotensin 1–7, adiponectin, methyl palmitate, hydrogen sulfide, NO and leptin. This anticontractile effect of PVAT is lost under conditions of obesity. The central mechanism underlying this PVAT dysfunction in obesity is likely to be an ‘obesity triad’ (consisting of PVAT hypoxia, inflammation and oxidative stress) that leads to the impairment of PVAT‐derived vasoregulators. The production of hydrogen sulfide, NO and adiponectin by PVAT is reduced in obesity, whereas the vasodilator response to leptin is impaired (vascular leptin resistance). Strikingly, the vasodilator response to acetylcholine is reduced only in PVAT‐containing, but not in PVAT‐free thoracic aorta isolated from diet‐induced obese mice, indicating a unique role for PVAT in obesity‐induced vascular dysfunction. Furthermore, PVAT dysfunction has also been observed in small arteries isolated from the gluteal/visceral fat biopsy samples of obese individuals. Therefore, PVAT may represent a new therapeutic target for vascular complications in obesity. A number of approaches are currently being tested under experimental conditions. Potential therapeutic strategies improving PVAT function include body weight reduction, enhancing PVAT hydrogen sulfide release (e.g. rosiglitazone, atorvastatin and cannabinoid CB₁ receptor agonists) and NO production (e.g. arginase inhibitors), inhibition of the renin–angiotensin–aldosterone system, inhibition of inflammation with melatonin or cytokine antagonists, activators of AMP‐activated kinase (e.g. metformin, resveratrol and diosgenin) and adiponectin releasers or expression enhancers.

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This article is part of a themed section on Molecular Mechanisms Regulating Perivascular Adipose Tissue – Potential Pharmacological Targets? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.20/issuetoc

Eph-B4 mediates vein graft adaptation by regulation of endothelial nitric oxide synthase

OBJECTIVE

Vein graft adaptation is characterized by loss of expression of the tyrosine kinase receptor Eph-B4, the embryonic determinant of venous identity, without increased expression of its ligand ephrin-B2, the embryonic determinant of arterial identity. Endothelial nitric oxide synthase (eNOS) is an important mediator of vessel remodeling. We hypothesized that the mechanism of action of Eph-B4 during vein graft adaptation might be through regulation of downstream eNOS activity.

METHODS

Mouse lung endothelial cells were stimulated with ephrin-B2/Fc, without and with preclustering, without and with the eNOS inhibitor N_ω-nitro-l-arginine methyl ester hydrochloride or the Eph-B4 inhibitor NVP-BHG712, and assessed by Western blot and immunofluorescence for eNOS and Eph-B4 phosphorylation. Nitric oxide (NO) production was assessed using an NO-specific chemiluminescence analyzer. Cell migration was assessed using a Transwell assay. Human and mouse vein graft specimens were examined for eNOS activity by Western blot, and vessel remodeling was assessed in vein grafts in wild-type or eNOS knockout mice.

RESULTS

Ephrin-B2/Fc stimulated both Eph-B4 and eNOS phosphorylation in a bimodal temporal distribution (n = 4; P < .05), with preclustered ephrin-B2/Fc causing prolonged peak Eph-B4 and eNOS phosphorylation as well as altered subcellular localization (n = 4; P < .05). Ephrin-B2/Fc increased NO release (n = 3; P < .01) as well as increased endothelial cell migration (n = 6; P < .05) in an eNOS-dependent fashion. Both human and mouse vein grafts showed increased eNOS phosphorylation compared with normal veins (n = 3; P < .05). Vein grafts from eNOS knockout mice showed less dilation and less wall thickening compared with wild-type vein grafts (n = 7; P < .05).

CONCLUSIONS

eNOS is a mediator of vein graft adaptation to the arterial environment. Eph-B4 stimulates eNOS phosphorylation in vitro and may mediate vein graft adaptation by regulation of eNOS activity in vivo.

Regional differences in perivascular adipose tissue impacting vascular homeostasis

Perivascular adipose tissue (PVAT) releases several important vasoactive factors with physiological and pathophysiological paracrine effects. A large body of evidence suggests regional phenotypic and functional differences among PVAT depots, depending on the specific vascular bed or different regions in the vascular bed where the PVAT is located. These non-uniform and separate PVATs exert various paracrine effects on vascular structure and function that largely impact disease states, such as endothelial dysfunction, atherosclerosis, or insulin resistance. This emerging view of PVAT function requires considering heterogeneous PVAT as a specialized organ that can differentially regulate vascular function depending on its anatomical location. In this context, the adipose-vascular axis may represent a novel target for pharmacological intervention in vasculopathy in cardiometabolic disorders.

Endoscopic Versus “No-Touch” Saphenous Vein Harvesting for Coronary Artery Bypass Grafting

The advantage in terms of wound infection, wound healing, and scarring has resulted in the recent adoption of endoscopic vein harvesting (EVH) as a standard of care for coronary artery bypass grafting in some centers. However, concerns regarding the quality of these grafts have been raised after recent evidence of decreased graft patency, increased reoperation rate, and myocardial infarct, problems that are associated with vascular trauma caused when using this technique. Simultaneously, an atraumatic, “no-touch” technique for harvesting the saphenous vein was developed producing grafts with improved patency comparable to the internal thoracic artery. However, wound complications remain a problem using this technique. This review outlines the need to consider the poor graft quality that may result from EVH and raises the question what is likely to be the “best practice principle” in saphenous vein harvesting?