Conduits for coronary artery bypass surgery: the quest for second best

Consensus statement-graft treatment in cardiovascular bypass graft surgery

Coronary artery bypass grafting (CABG) is and continues to be the preferred revascularization strategy in patients with multivessel disease. Graft selection has been shown to influence the outcomes following CABG. During the last almost 60 years saphenous vein grafts (SVG) together with the internal mammary artery have become the standard of care for patients undergoing CABG surgery. While there is little doubt about the benefits, the patency rates are constantly under debate. Despite its acknowledged limitations in terms of long-term patency due to intimal hyperplasia, the saphenous vein is still the most often used graft. Although reendothelialization occurs early postoperatively, the process of intimal hyperplasia remains irreversible. This is due in part to the persistence of high shear forces, the chronic localized inflammatory response, and the partial dysfunctionality of the regenerated endothelium. "No-Touch" harvesting techniques, specific storage solutions, pressure controlled graft flushing and external stenting are important and established methods aiming to overcome the process of intimal hyperplasia at different time levels. Still despite the known evidence these methods are not standard everywhere. The use of arterial grafts is another strategy to address the inferior SVG patency rates and to perform CABG with total arterial revascularization. Composite grafting, pharmacological agents as well as latest minimal invasive techniques aim in the same direction. To give guide and set standards all graft related topics for CABG are presented in this expert opinion document on graft treatment.

Techniques and Technologies to Improve Vein Graft Patency in Coronary Surgery

Vein grafts are the most used conduits in coronary artery bypass grafting (CABG), even though many studies have suggested their lower patency compared to arterial alternatives. We have reviewed the techniques and technologies that have been investigated over the years with the aim of improving the quality of these conduits. We found that preoperative and postoperative optimal medical therapy and no-touch harvesting techniques have the strongest evidence for optimizing vein graft patency. On the other hand, the use of venous external support, endoscopic harvesting, vein preservation solution and anastomosis, and graft configuration need further investigation. We have also analyzed strategies to treat vein graft failure: when feasible, re-doing the CABG and native vessel primary coronary intervention (PCI) are the best options, followed by percutaneous procedures targeting the failed grafts.

Ten-year outcomes after percutaneous coronary intervention of in-stent restenosis in saphenous vein grafts

BACKGROUND

Only few data is available for long-term outcomes of patients being treated for in-stent restenosis (ISR) in saphenous vein grafts (SVG).

AIMS

Thus, the aim of this observational, retrospective study was to close this lack of evidence.

METHODS

Between January 2007 and February 2021 a total of 163 patients with 186 ISR lesions located in SVG were treated at two large-volume centers in Munich, Germany. Endpoints of interest were all-cause mortality, target lesion revascularization (TLR) and target vessel myocardial infarction (TVMI). Furthermore, recurrent ISR were assessed. Outcomes are presented as Kaplan-Meier event rates.

RESULTS

Mean age was 72.6 ± 8.6 years, 90.8% were male, 36.8% were diabetics and 42.3% presented an acute coronary syndrome. ISR were treated with DES in 64.0% and with balloon angioplasty (BA) in 36.0%. After 10 years, the rates for all-cause mortality, TVMI and TLR were 58.2%, 15.4%, and 22.6%, respectively. No statistically relevant differences were found between the types of treatment (DES or BA) regarding all-cause mortality (55.7% vs. 63.2%, p = 0.181), TVMI (13.8% vs. 18.6%, p = 0.215) and TLR (21.8% vs. 25.0%, p = 0.764). Median time between first and recurrent ISR was 270.8 days. Recurrent ISR were treated with DES in a comparable proportion as during first ISR (p = 0.075). Independent predictor of TLR is patient age (p = 0.034). The median follow-up duration was 5.1 years (75% CI 2.8; 8.5).

CONCLUSIONS

Clinical event rates after intervention of ISR located in SVG are high without statistically relevant differences regarding the type of treatment. However, further studies are needed.

Supercritical carbon dioxide-decellularized arteries exhibit physiologic-like vessel regeneration following xenotransplantation in rats

Currently, many techniques are used for decellularization of grafts, including physical, enzymatic, and chemical treatments. Indeed, decellularized xenogenic grafts provide superior outcomes than alternative synthetic conduits. However, vascular grafts produced by these methods are not perfect; their defects include defective vessel wall structures, detergent residues, and the development of aneurysms after grafting. Therefore, it is essential to develop a more appropriate process to produce decellularized vascular grafts. Supercritical carbon dioxide (ScCO₂) has been used in decellularization technologies in recent years. It is beneficial for the long-term preservation of tissues and regeneration of new vessels. We have previously reported that ScCO₂-produced acellular porcine corneas show excellent biocompatibility following lamellar corneal transplantation in rabbits. In this study, we wanted to use this method to fabricate vascular grafts (ScCO₂-decellularized rabbit femoral artery (DFA)) and analyze their efficacy, parameters regarding rejection by the recipient's (ACI/NKyo rats) immune system and biocompatibility, structural regeneration, and functionality in vivo. The results indicated that the ScCO₂-DFA showed higher biocompatibility, enhanced chemotactic migration of endothelial progenitor cells, lower risk of vasculopathy, lower inflammatory and splenic immune responses, and better physiological-like tension responses after xenotransplantation (XTP) in ACI/NKyo rats compared with the results obtained after XTP using detergent decellularized vascular grafts (SDS-DFA). In conclusion, ScCO₂ is an excellent decellularization technique in the fabrication of biocompatible vascular grafts and has tremendous application in vascular regenerative medicine.

The Role of Endothelial Cells in the Onset, Development and Modulation of Vein Graft Disease

Endothelial cells comprise the intimal layer of the vasculature, playing a crucial role in facilitating and regulating aspects such nutrient transport, vascular homeostasis, and inflammatory response. Given the importance of these cells in maintaining a healthy haemodynamic environment, dysfunction of the endothelium is central to a host of vascular diseases and is a key predictor of cardiovascular risk. Of note, endothelial dysfunction is believed to be a key driver for vein graft disease-a pathology in which vein grafts utilised in coronary artery bypass graft surgery develop intimal hyperplasia and accelerated atherosclerosis, resulting in poor long-term patency rates. Activation and denudation of the endothelium following surgical trauma and implantation of the graft encourage a host of immune, inflammatory, and cellular differentiation responses that risk driving the graft to failure. This review aims to provide an overview of the current working knowledge regarding the role of endothelial cells in the onset, development, and modulation of vein graft disease, as well as addressing current surgical and medical management approaches which aim to beneficially modulate endothelial function and improve patient outcomes.

Competitive Flow: Closure of Internal Thoracic Artery Graft After Successful Coronary Artery Bypass Graft Surgery

The internal thoracic artery has a patency rate of 85%-95% at 10-15 years post coronary artery bypass graft surgery. Development of total occlusion of the internal thoracic artery within a short period (< 6 months) after the surgery is exceedingly rare. However, competitive flow between the native vessel and the conduit internal thoracic artery, or competitive flow between the 2 conduit internal thoracic arteries in a multiple arterial grafting procedure can jeopardize 1 of the 2 conduit internal thoracic arteries. We report the cases of 2 patients who had bilateral internal thoracic artery grafts, with total occlusion of 1 of the 2 grafts within a short period (6 months) after successful coronary artery bypass graft surgery.

Saphenous vein graft disease, pathophysiology, prevention, and treatment. A review of the literature

BACKGROUND

The saphenous vein remains the most frequently used conduit for coronary artery bypass grafting, despite reported unsatisfactory long-term patency rates. Understanding the pathophysiology of vein graft failure and attempting to improve its longevity has been a significant area of research for more than three decades. This article aims to review the current understanding of the pathophysiology and potential new intervention strategies.

METHODS

A search of three databases: MEDLINE, Web of Science, and Cochrane Library, was undertaken for the terms "pathophysiology," "prevention," and "treatment" plus the term "vein graft failure."

RESULTS

Saphenous graft failure is commonly the consequence of four different pathophysiological mechanisms, early acute thrombosis, vascular inflammation, intimal hyperplasia, and late accelerated atherosclerosis. Different methods have been proposed to inhibit or attenuate these pathological processes including modified surgical technique, topical pretreatment, external graft support, and postoperative pharmacological interventions. Once graft failure occurs, the available treatments are either surgical reintervention, angioplasty, or conservative medical management reserved for patients not eligible for either procedure.

CONCLUSION

Despite the extensive amount of research performed, the pathophysiology of saphenous vein graft is still not completely understood. Surgical and pharmacological interventions have improved early patency and different strategies for prevention seem to offer some hope in improving long-term patency.

Effectiveness of Saphenous Vein Y-Grafts in Patients Undergoing Off-Pump Complete Myocardial Revascularization

Background

To evaluate perioperative and mid-term outcomes of saphenous vein Y-grafts in patients with multi-vessel coronary artery disease.

Material/Methods

Sixty patients who underwent off-pump coronary surgery with Y-graft between 2005 and 2016 were enrolled, including 38 patients with natural Y-graft. Sixty patients with multi-vessel lesions in the same period were randomly selected as a control group.

Results

A total of 484 conduits were employed. The intraoperative variables were insignificantly different between groups, but Y-graft group compared with control group had more grafts (4.2±0.84 vs. 3.87±0.85) and anastomoses (6.30±1.39 vs. 5.62±1.15). No patient died during coronary artery bypass grafting and no episode of perioperative myocardial infarction was found. Follow-up duration lasted from 1 to 137 (40.0±27.7) months. No significant difference between Y-graft group and control group was found in Kaplan-Meier 3-year survival rate (93.4% vs. 88.0%) or 5-year survival rate (81.4% vs. 88.0%).

Conclusions

Saphenous vein Y-graft is a feasible and safe revascularization strategy for multi-vessel coronary artery disease patients and brings about satisfactory outcomes.

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.

The no-touch saphenous vein graft in elderly coronary bypass patients with multiple comorbidities is a promising conduit to substitute the left internal thoracic artery

OBJECTIVES

We investigated the patency rates of no-touch saphenous vein grafts anastomosed to the left anterior descending artery compared with the left internal thoracic artery. Further, we compared the patency of no-touch vein grafts to the left anterior descending artery with the patency of no-touch vein grafts to other coronary arteries.

METHODS

Of 2635 consecutive patients undergoing coronary artery bypass grafting between 2003 and 2008, 168 (6.3%) were given at least a saphenous vein graft to the left anterior descending artery to avoid harvesting complications in high-risk patients or in response to a left internal thoracic artery injury. A total of 97 patients were consecutively included after informed consent. A clinical examination and computed tomography angiography were performed on 91 patients at a mean of 6 (4-9) years.

RESULTS

The mean age of patients was 75.6 ± 8.5 years. Postoperatively, 88.7% of patients (86/97) were free of angina. The 91 examined patients had 163 grafts with 286 distal anastomoses. Crude patency, according to distal anastomoses, was 94.4% (270/286). The patency of single versus sequential no-touch vein grafts to the left anterior descending artery was 98% (50/51) versus 92.5% (37/40). The total patency rate was 95.6% (87/91), similar to the reported patency rate for the left internal thoracic artery. The no-touch grafts to the left anterior descending artery versus other coronaries had a patency of 95.6% (87/91) versus 93.8% (183/195), a high similarity confirmed by an equivalence analysis.

CONCLUSIONS

In elderly coronary bypass patients with multiple comorbidities, a no-touch saphenous vein graft is a promising substitute for the left internal thoracic artery.

Right internal mammary artery versus radial artery as second arterial conduit in coronary artery bypass grafting: a case-control study of 1526 patients

OBJECTIVE

Additional arterial grafts such as the right internal mammary artery (RIMA) or the radial artery (RA) have been proposed to improve long term outcomes in coronary artery bypass grafting (CABG). RA is largely preferred over RIMA as it is less technically demanding and there is a perception that bilateral IMA usage increases the risk of sternal wound complications. However, there is a paucity of direct comparison of the two conduits to guide surgeons to choose the best second arterial conduit for CABG.

METHODS

A propensity score adjusted analysis of patients undergoing multiple arterial grafting with RIMA (n = 747) and RA (n = 779) during the study period (2001-2013) was conducted to investigate the impact of the two strategies on early and late outcomes.

RESULTS

RIMA did not increase the incidence of postoperative complications including deep sternal wound infection (P = 0.8). Compared to the RIMA, the RA was associated with an increased risk for late mortality (Hazard Ratio [HR] 1.9; 95% confidence interval (CI) 1.2-3.1; P = 0.008) and repeat revascularization (HR 1.5; 95% CI 1.0-2.2; P = 0.044). A trend towards an extra risk for late mortality from RA over RIMA was observed among diabetic (HR 3.3; 95% CI 1.1-9.7) and obese patients (HR 2.1; 95% CI 0.8-5.46).

CONCLUSIONS

RIMA as a second conduit did not increase the operative risk including sternal wound complications and improved long term outcomes including overall survival when compared to RA. This advantage was stronger among diabetic and obese patients. These findings strongly support RIMA as the first choice second arterial conduit in CABG. Further randomized studies with angiographic control and long-term follow-up are needed to address this issue.

Coronary artery bypass graft: why is the saphenous vein prone to intimal hyperplasia?

Proliferation and migration of smooth muscle cells and the resultant intimal hyperplasia cause coronary artery bypass graft failure. Both internal mammary artery and saphenous vein are the most commonly used bypass conduits. Although an internal mammary artery graft is immune to restenosis, a saphenous vein graft is prone to develop restenosis. We found significantly higher activity of phosphatase and tensin homolog (PTEN) in the smooth muscle cells of the internal mammary artery than in the saphenous vein. In this article, we critically review the pathophysiology of vein-graft failure with detailed discussion of the involvement of various factors, including PTEN, matrix metalloproteinases, and tissue inhibitor of metalloproteinases, in uncontrolled proliferation and migration of smooth muscle cells towards the lumen, and invasion of the graft conduit. We identified potential target sites that could be useful in preventing and (or) reversing unwanted consequences following coronary artery bypass graft using saphenous vein.

Regenerative implants for cardiovascular tissue engineering

A fundamental problem that affects the field of cardiovascular surgery is the paucity of autologous tissue available for surgical reconstructive procedures. Although the best results are obtained when an individual's own tissues are used for surgical repair, this is often not possible as a result of pathology of autologous tissues or lack of a compatible replacement source from the body. The use of prosthetics is a popular solution to overcome shortage of autologous tissue, but implantation of these devices comes with an array of additional problems and complications related to biocompatibility. Transplantation offers another option that is widely used but complicated by problems related to rejection and donor organ scarcity. The field of tissue engineering represents a promising new option for replacement surgical procedures. Throughout the years, intensive interdisciplinary, translational research into cardiovascular regenerative implants has been undertaken in an effort to improve surgical outcome and better quality of life for patients with cardiovascular defects. Vascular, valvular, and heart tissue repair are the focus of these efforts. Implants for these neotissues can be divided into 2 groups: biologic and synthetic. These materials are used to facilitate the delivery of cells or drugs to diseased, damaged, or absent tissue. Furthermore, they can function as a tissue-forming device used to enhance the body's own repair mechanisms. Various preclinical studies and clinical trials using these advances have shown that tissue-engineered materials are a viable option for surgical repair, but require refinement if they are going to reach their clinical potential. With the growth and accomplishments this field has already achieved, meeting those goals in the future should be attainable.

Development and in vivo evaluation of small-diameter vascular grafts engineered by outgrowth endothelial cells and electrospun chitosan/poly(ε-caprolactone) nanofibrous scaffolds

Successful engineering of a small-diameter vascular graft is still a challenge despite numerous attempts for decades. The present study aimed at developing a tissue-engineered vascular graft (TEVG) using autologous outgrowth endothelial cells (OECs) and a hybrid biodegradable polymer scaffold. OECs were harvested from canine peripheral blood and proliferated in vitro, as well as identified by immunofluorescent staining. Electrospun hybrid chitosan/poly(ε-caprolactone) (CS/PCL) nanofibers were fabricated and served as vascular scaffolds. TEVGs were constructed in vitro by seeding OECs onto CS/PCL scaffolds, and then implanted into carotid arteries of cell-donor dogs (n=6). After 3 months of implantation, 5 out of 6 of TEVGs remained patent as compared with 1 out of 6 of unseeded grafts kept patent. Histological and immunohistochemical analyses of the TEVGs retrieved at 3 months revealed the regeneration of endothelium, and the presence of collagen and elastin. OECs labeled with fluorescent dye before implantation were detected in the retrieved TEVGs, indicating that the OECs participated in the vascular tissue regeneration. Biomechanical testing of TEVGs showed good mechanical properties that were closer to native carotid arteries. RT-PCR and western blot analysis demonstrated that TEVGs had favorable biological functional properties resembling native arteries. Overall, this study provided a new strategy to develop small-diameter TEVGs with excellent biocompatibility and regeneration ability.