Does the method of harvesting the saphenous vein for coronary artery bypass surgery affect venous smooth muscle cells? iNOS immunolabelling and ultrastructural findings

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.

Endothelin-1, endothelin receptor antagonists, and vein graft occlusion in coronary artery bypass surgery: 20 years on and still no journey from bench to bedside

The saphenous vein is the most commonly used bypass graft in patients with coronary artery disease. During routine coronary artery bypass, grafting the vascular damage inflicted on the vein is likely to stimulate the release of endothelin-1, a potent endothelium-derived vasoconstrictor that also possesses cell proliferation and inflammatory properties, conditions associated with vein graft failure. In both in vitro and in vivo studies, endothelin receptor antagonists reduce neointimal thickening. The mechanisms underlying these observations are multifactorial and include an effect on cell proliferation and cell/tissue damage. Much of the data supporting the beneficial action of endothelin-1 receptor antagonism at reducing intimal thickening and occlusion in experimental vein grafts were published over 20 years ago. The theme of the recent ET-16 conference in Kobe was "Visiting Old and Learning New". This short review article provides an overview of studies showing the potential of endothelin receptor antagonists to offer an adjuvant therapeutic approach for reducing saphenous vein graft failure and poses the question why this important area of research has not been translated from bench to bedside given the potential benefit for coronary artery bypass patients.

Vascularization of the arteriovenous fistula wall and association with maturation outcomes

BACKGROUND AND OBJECTIVES

The venous vasa vasorum is the mesh of microvessels that provide oxygen and nutrients to the walls of large veins. Whether changes to the vasa vasorum have any effects on human arteriovenous fistula outcomes remains undetermined. In this study, we challenged the hypothesis that inadequate vascularization of the arteriovenous fistula wall is associated with maturation failure.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

This case-control pilot study includes pre-access veins and arteriovenous fistula venous samples (i.e. tissue pairs) from 30 patients undergoing two-stage arteriovenous fistula creation (15 matured and 15 failed to mature). Using anti-CD31 immunohistochemistry, we quantified vasa vasorum density and luminal area (vasa vasorum area) in the intima, media, and adventitia of pre-access veins and fistulas. We evaluated the association of pre-existing and postoperative arteriovenous fistula vascularization with maturation failure and with postoperative morphometry.

RESULTS

Vascularization of veins and arteriovenous fistulas was predominantly observed in the outer media and adventitia. Only the size of the microvasculature (vasa vasorum area), but not the number of vessels (vasa vasorum density), increased after arteriovenous fistula creation in the adventitia (median vasa vasorum area 1366 µm2/mm2 (interquartile range 495-2582) in veins versus 3077 µm2/mm2 (1812-5323) in arteriovenous fistulas, p < 0.001), while no changes were observed in the intima and media. Postoperative intimal thickness correlated with lower vascularization of the media (r 0.53, p = 0.003 for vasa vasorum density and r 0.37, p = 0.045 for vasa vasorum area). However, there were no significant differences in pre-existing, postoperative, or longitudinal change in vascularization between arteriovenous fistulas with distinct maturation outcomes.

CONCLUSION

The lack of change in intimal and medial vascularization after arteriovenous fistula creation argues against higher oxygen demand in the inner walls of the fistula during the vein to arteriovenous fistula transformation. Postoperative intimal hyperplasia in the arteriovenous fistula wall appears to thrive under hypoxic conditions. Vasa vasorum density and area by themselves are not predictive of maturation outcomes.

Increased Contractile Function of Human Saphenous Vein Grafts Harvested by "No-Touch" Technique

Saphenous vein grafts are the most common conduits used for coronary artery bypass grafting (CABG); however, no more than 60% of vein grafts remain open after 10 years and graft failure is associated with poor clinical outcome. The “no-touch” harvesting technique—where a sheet of perivascular tissue is retained around the vein—improves graft patency to over 80% after 16 years of follow-up, but the mechanism for the improved patency rate is unclear. In this study, we investigated acute functional differences between vein grafts harvested conventionally and by “no-touch” technique and explored the importance of perivascular tissue for reducing surgical trauma, minimizing excessive distension, and releasing vasoactive paracrine factors. Segments of human saphenous veins were obtained from CABG surgery and their functional properties investigated by isometric and isobaric myography. We found a broad diameter-tension relationship for human saphenous veins, with peak capacity for active tension development at diameters corresponding to transmural pressures around 60 mmHg. Across the investigated transmural pressure range between 10 and 120 mmHg, maximal tension development was higher for “no-touch” compared to conventionally harvested saphenous veins. Contractile responses to serotonin, noradrenaline, and depolarization induced with elevated extracellular [K⁺] were significantly larger for saphenous veins harvested by “no-touch” compared to conventional technique. Conventional vein grafts are routinely pressurized manually in order to test for leaks; however, avoiding this distension procedure did not change the acute contractile function of the conventionally excised saphenous veins. In contrast, even though surgical removal of perivascular tissue during conventional harvesting was associated with a substantial decrease in force development, removal of perivascular tissue by careful dissection under a stereomicroscope only marginally affected contractile responses of veins harvested by “no-touch” technique. In conclusion, we show that saphenous veins harvested by “no-touch” technique have greater contractile capacity than veins harvested by conventional technique. The different capacity for smooth muscle contraction is not due to vasoactive substances released by the perivascular tissue. Instead, we propose that the larger tension development of saphenous veins harvested by “no-touch” technique reflects reduced surgical damage, which may have long-term consequences that contribute to the superior graft patency.

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 no-touch technique of harvesting the saphenous vein for coronary artery bypass grafting surgery

A new 'no-touch' (NT) technique of saphenous vein (SV) preparation for coronary artery bypass grafting (CABG) surgery was developed where the vein is harvested with a pedicle of surrounding tissue, which protects the vein from spasm therefore obviating the need for distension. The adventitial layer and the structures contained within the cushion of surrounding tissue possess both mechanical and functional properties that protect the vein from spasm and ischemia. In addition, the surrounding tissue supports excessively long vein grafts and prevents kinking. A detailed description of the technique is presented and this is the first time we publish the technique as a videoclip.

Prostaglandin E1 increases the blood flow rate of saphenous vein grafts in patients undergoing off-pump coronary artery bypass grafting

OBJECTIVE

To compare the effects of prostaglandin E1 (PGEl) versus placebo on blood flow rate in coronary artery bypass grafts.

DESIGN

A prospective, randomized, double-blinded study.

SETTING

A teaching hospital.

PARTICIPANTS

Forty-six patients with stable angina scheduled for isolated elective OPCAB were recruited and randomized into group PGE1 and group placebo.

INTERVENTION

Following randomization, the patients in the PGE1 group (Group PGE1, n = 23) received a continuous intravenous infusion of PGEl (10 ng/kg/min) after endotracheal intubation and the placebo group (Group placebo, n = 23) received the same volume of normal saline. The infusion administration was removed after leaving the intensive care unit.

MEASUREMENTS AND MAIN RESULTS

The grafts' blood flow rate was measured with a transit time flowmeter at 10 minutes and 30 minutes after coronary artery grafting. The hemodynamic parameters, including mean arterial pressure (MAP), heart rate, and SvO2, VO2I, DO2I, ERO2 monitored by a pulmonary artery catheter, were recorded. The blood flow of the saphenous vein grafts was significantly higher in the PGE1 group than the placebo group at both 10 and 30 minutes after coronary artery grafting. At the 10-minute mark, the graft flow was 54.9 ± 31.4 mL/min versus 47.3 ± 24.6 mL/min in venous nonsequential grafts to the left coronary artery for group PGE1 and placebo (p = 0.000). Corresponding values at 30 minutes were 60.1 ± 27.8 mL/min versus 48.4 ± 26.3 mL/min (p = 0.002). In the venous non-sequential grafts to the right coronary artery, a tendency of blood flow also was found to be higher in the PGE1 group than in the placebo group at 10-minutes (52.7 ± 29.4 mL/min versus 49.3 ± 23.8 mL/min, p = 0.048) and the 30-minutes (58.6 ± 26.5 mL/min, 50.9 ± 25.9 mL/min, p = 0.037). The blood flow rate of the left internal mammary artery (LIMA) grafts in group PGE1 was higher than that in the placebo group but did not reach statistical significance. The VO2I, DO2I, and ERO2 in the 2 groups at the 2 time points did not reach statistical significance. The cardiac index (CI) in group PGE1 was higher than that of the placebo group at T3 and T4 (p = 0.035 and p = 0.012, respectively). The lactate (LAC) at the end of the operation (T2), 4 hours after the operation (T3), and 24 hours after operation (T4) in the placebo group were higher than that of group PGE1 (p = 0.023, p = 0.015, and p = 0.043, respectively). The oxygenation saturation of the mixed venous blood (SvO2) in the 2 groups was decreased but without significant difference.

CONCLUSION

PGE1 significantly increased the flow rate in anastomosed saphenous vein grafts, and its beneficial effects on hemodynamics and oxygen metabolism were observed.

Effects of elevated perfusion pressure and pulsatile flow on human saphenous veins isolated from diabetic and non-diabetic patients

OBJECTIVE

This study was carried out to determine high pressure and pulsatile flow perfusion effects on human saphenous vein (HSV) segments obtained from diabetic and non-diabetic patients.

METHODS

The veins were perfused with oxygenated Krebs solution for 3 h, with a pulsatile flow rate of 100 mL/min and pressures of 250 × 200 or 300 × 250 mmHg. After perfusion, veins were studied by light microscopy; nitric oxide synthase (NOS) isoforms, CD34 and nitrotyrosine immunohistochemistry and tissue nitrite/nitrate (NO(x)) and malondialdehyde (MDA) quantification.

RESULTS

Light microscopy revealed endothelial denuding areas in all HSV segments subjected to 300 × 250 mmHg perfusion pressure, but the luminal area was similar. The percentage of luminal perimeter covered by endothelium decreased as perfusion pressures increased, and significant differences were observed between groups. The endothelial nitric oxide synthase (eNOS) isoform immunostaining decreased significantly in diabetic patients' veins independent of the perfusion pressure levels. The inducible NOS (iNOS), neuronal NOS (nNOS) and nitrotyrosine immunostaining were similar. Significant CD34 differences were observed between the diabetic 300 × 250 mmHg perfusion pressure group and the non-diabetic control group. Tissue nitrite/nitrate and MDA were not different among groups.

CONCLUSIONS

Pulsatile flow and elevated pressures for 3 h caused morphological changes and decreased the eNOS expression in the diabetic patients' veins.

[What are the guidelines for using a venous segment for an arterial bypass? General review]

Since the first femoropopliteal bypass, performed by J. Kunlin, in 1950, the saphenous vein has remained the material of choice for arterial bypass in a wide variety of localizations. Harvesting must be adapted to vein quality and the length necessary for the bypass. A thorough knowledge of the histological structure of the graft and the impact of the harvesting process on endothelial cells is needed to understand early and late complications related to saphenous harvesting. Several experimental studies and clinical series, particularly for aortocoronary bypass, have shown the role of atraumatic harvesting, removing the perivenous fat, and/or papaverine infusion in the perivascular tissues. A venous graft can be used in six localizations. For femoropopliteal bypass, the venous graft can be used reversed or in situ, after valvular section. For bypass to tibial vessels and bypass to the ankle and the foot, the graft can be the greater saphenous vein or the lesser saphenous vein, or veins from the arm. These bypasses can be done reversed or in situ or transposed reversed or after valvular disruption. This technique has the advantage of placing the largest portion of the vein at the level of the proximal anastomosis, but with the risk of endothelial cell desquamation during vein harvesting, which can lead to late fibrosis of the graft. For aorto-iliac bypass, new prosthetic grafts and the development of endovascular techniques have overshadowed the former advantages of the saphenous vein grafts. Surgical renal revascularisations have become less frequent since the development of endovascular techniques. Nevertheless, the venous graft remains useful for some revascularisations - hepatic-renal bypass, iliorenal bypass, difficult nephrologic situations (solitary kidney, chronic occlusion). For aortocoronary bypass, long-term outcome has been studied in many studies. It is recommended to use the grafts with a no touch technique, using a portion without valves. The carotid venous graft is a useful technique when endarterectomy is difficult or not satisfactory. The graft must be harvested from the calf, without valves, have a diameter of 5mm and be harvested without injury.

Milrinone increases flow in coronary artery bypass grafts after cardiopulmonary bypass: a prospective, randomized, double-blind, placebo-controlled study

OBJECTIVE

To compare the effects of a bolus of milrinone, 50 microg/kg, versus placebo on flow in coronary artery bypass grafts after cardiopulmonary bypass (CPB).

DESIGN

A prospective, randomized, double-blind study.

SETTING

A university hospital.

PARTICIPANTS

Forty-four patients with stable angina and left ventricular ejection fraction >30% scheduled for elective coronary artery bypass graft (CABG) surgery were included.

INTERVENTION

Patients were randomized to receive 50 microg/kg of milrinone (n = 22) or placebo (n = 22) after aortic declamping.

MEASUREMENTS AND MAIN RESULTS

The flow in coronary artery bypass grafts was measured with a transit time flow meter at 10 minutes and 30 minutes after termination of CPB. The hemodynamic evaluation included transesophageal echocardiography, mean arterial pressure (MAP), heart rate, and intracavitary measurement of left ventricular end-diastolic pressure (LVEDP). The flow in the saphenous vein grafts was significantly higher in the milrinone group when compared with the placebo group both at 10 and 30 minutes after termination of CPB (p < 0.001). At 10 minutes, the flow was 64.5 +/- 37.4 mL/min (mean +/- standard deviation) and 43.6 +/- 25.7 mL/min in nonsequential vein grafts for milrinone and placebo, respectively. Corresponding values at 30 minutes were 54.8 +/- 29.9 mL/min and 35.3 +/- 22.4 mL/min. The left internal thoracic artery (LITA) flow was higher in the milrinone group but did not reach statistical significance. The fractional area change was higher, and the MAP and calculated pressure gradient (MAP-LVEDP) were lower at 10 minutes in the milrinone group.

CONCLUSION

Milrinone significantly increases the flow in anastomosed saphenous vein grafts after CPB, and has beneficial effects on left ventricular function.