Arterial versus venous bypass grafts in patients with in-stent restenosis

Potential of Autologous Progenitor Cells and Decellularized Porcine Artery Matrix in Construction of Tissue-engineered Vascular Grafts

To develop a tissue-engineered vascular graft, we used pericardial effusion-derived progenitor cells (PEPCs) collected from drained fluid after open-heart surgery in children with congenital heart diseases to repopulate a decellularized porcine pulmonary artery. The PEPCs were compared with human fibroblasts (HS68) and human umbilical vein endothelial cells (HUVECs) in cell growth and migration. They were cultured with the matrices via an inner approach (intima), lateral approach (media), and outer approach (adventitia). PEPCs grew and migrated better than the other two cells 14 days after seeding in the decellularized vessel. In immunofluorescence assays, PEPCs expressed CD90 and CD105 indicating a vascular differentiation. PEPCs grew in a decellularized porcine pulmonary artery matrix may have the potential for producing tissue-engineered vascular grafts.

Angiographic Patency of Coronary Artery Bypass Conduits: A Network Meta-Analysis of Randomized Trials

Background Several randomized trials have compared the patency of coronary artery bypass conduits. All of the published studies, however, have performed pairwise comparisons and a comprehensive evaluation of the patency rates of all conduits has yet to be published. We set out to investigate the angiographic patency rates of all conduits used in coronary bypass surgery by performing a network meta-analysis of the current available randomized evidence. Methods and Results A systematic literature search was conducted for randomized controlled trials comparing the angiographic patency rate of the conventionally harvested saphenous vein, the no-touch saphenous vein, the radial artery (RA), the right internal thoracic artery, or the gastroepiploic artery. The primary outcome was graft occlusion. A total of 4160 studies were retrieved of which 14 were included with 3651 grafts analyzed. The weighted mean angiographic follow-up was 5.1 years. Compared with the conventionally harvested saphenous vein, both the RA (incidence rate ratio [IRR] 0.54; 95% CI, 0.35-0.82) and the no-touch saphenous vein (IRR 0.55; 95% CI, 0.39-0.78) were associated with lower graft occlusion. The RA ranked as the best conduit (rank score for RA 0.87 versus 0.85 for no-touch saphenous vein, 0.23 for right internal thoracic artery, 0.29 for gastroepiploic artery, and 0.25 for the conventionally harvested saphenous vein). Conclusions Compared with the conventionally harvested saphenous vein, only the RA and no-touch saphenous vein grafts are associated with significantly lower graft occlusion rates. The RA ranks as the best conduit. Registration URL: https://www.crd.york.ac.uk/prospero; Unique identifier: CRD42020164492.

Graft Patency of a Second Conduit for Coronary Artery Bypass Surgery: A Network Meta-Analysis of Randomized Controlled Trials

It has been well documented that the use of the left internal thoracic artery (LITA) to graft the left anterior descending (LAD) artery has a significant benefit in coronary artery bypass graft (CABG) surgery. However, what graft is the best as a second conduit to complement LITA-LAD anastomosis remains uncertain. We thus conducted a network meta-analysis of RCTs to compare graft patency of the radial artery (RA), the right internal thoracic artery (RITA), the right gastroepiploic artery (RGEA), conventional saphenous vein (C-SVG), and no-touch saphenous vein (NT-SVG) as a second conduit in CABG. MEDLINE and EMBASE were searched through August 31, 2020 to identify randomized controlled trials (RCTs) that investigated graft patency of a second conduit in CABG. From each study, we extracted the incidence rate ratios of the outcome. A total of 13 RCTs were identified, including 3728 patients and 2773 angiographic results. The graft failure rates were significantly lower in NT-SVG and RA compared to C-SVG and RGEA. There was no significant difference among the other comparisons. A sensitivity analysis restricting trials with ≥3 years angiographic follow-up time showed the graft failure rates were significantly lower in NT-SVG and RA compared to C-SVG and RGEA, and a sensitivity analysis restricting trials with ≥5 years angiographic follow-up time showed the graft failure rates were significantly lower in NT-SVG and RA compared to C-SVG. In a network meta-analysis of the updated outcomes from RCTs, NT-SVG and RA have better graft patency compared to C-SVG and RGEA.

Is the Use of BIMA in CABG Sub-Optimal? A Review of the Current Clinical and Economic Evidence Including Innovative Approaches to the Management of Mediastinitis

Bilateral internal mammary artery (BIMA) in coronary artery bypass grafting (CABG) has traditionally been limited. This review looks at the recent outcome data on BIMA in CABG focusing on the management of risk factors for mediastinitis, one of the potential barriers for more extensive BIMA utilization. A combination of pre-, intra- and postoperative strategies are essential to reduce mediastinitis. Limited data indicate that the incidence of mediastinitis can be reduced using closed incision negative-pressure wound therapy as a part of these strategies with the possibility of offering patients best treatment options by extending BIMA to those with a higher risk of mediastinitis. Recent economic data imply that the technology may challenge the current low uptake of BIMA by reducing the short-term cost differentials between single internal mammary artery and BIMA. Given that most published randomized controlled trials and meta-analyses of observational long-term outcome data favor BIMA, if short-term complications of BIMA including mediastinitis can be controlled adequately, there may be opportunities for more extensive use of BIMA leading to improved long-term outcomes. An ongoing study looking at BIMA in high-risk patients may provide evidence to support the hypothesis that mediastinitis should not be a factor in limiting the use of BIMA in CABG.

Robustness of the Comparative Observational Evidence Supporting Class I and II Cardiac Surgery Procedures

Background

Current cardiac surgery guidelines give Class I and II recommendations to valve‐sparing root replacement over the Bentall procedure, mitral valve (MV) repair over replacement, and multiple arterial grafting with bilateral internal thoracic artery based on observational evidence. We evaluated the robustness of the observational studies supporting these recommendations using the E value, an index of unmeasured confounding.

Methods and Results

Observational studies cited in the guidelines and in the 3 largest meta‐analyses comparing the procedures were evaluated for statistically significant effect measures. Two E values were calculated: 1 for the effect‐size estimate and 1 for the lower limit of the 95% CI. Thirty‐one observational studies were identified, and E values were computed for 75 effect estimates. The observed effect estimates for improved clinical outcomes with valve‐sparing root replacement versus the Bentall procedure, MV repair versus replacement, and grafting with bilateral internal thoracic artery versus single internal thoracic artery could be explained by an unmeasured confounder that was associated with both the treatment and outcome by a risk ratio of more than 16.77, 4.32, and 3.14, respectively. For MV repair versus replacement and grafting with bilateral internal thoracic artery versus single internal thoracic artery, the average E values were lower than the effect sizes of the other measured confounders in 33.3% and 60.9% of the studies, respectively. For valve‐sparing root replacement versus the Bentall procedure, no study reported effect sizes for associations of other covariates with outcomes.

Conclusions

The E values for observational evidence supporting the use of valve‐sparing root replacement, MV repair, and grafting with bilateral internal thoracic artery over the Bentall procedure, MV replacement, and grafting with single internal thoracic artery are relatively low. This suggests that small‐to‐moderate unmeasured confounding could explain most of the observed associations for these procedures.

Catalytic Generation of Nitric Oxide from Poly(ε-caprolactone)/Phosphobetainized Keratin Mats for a Vascular Tissue Engineering Scaffold

Tissue-engineered vascular graft (TEVG) is a promising alternative to meet the clinical demand of organ shortages. Herein, human hair keratin was extracted by the reduction method, followed by modification with zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) through thiol-Michael addition to improve blood clotting nature. Then, phosphobetainized keratin (PK) was coelectrospun with poly(ε-caprolactone) (PCL) to afford PCL/PK mats with a ratio of 7:3. The surface morphology, chemical structure, and wettability of these mats were characterized. The biocomposite mats selectively enhanced adhesion, migration, and growth of endothelial cells (ECs) while suppressed proliferation of smooth muscle cells (SMCs) in the presence of glutathione (GSH) and GSNO due to the catalytic generation of NO. In addition, these mats exhibited good blood anticoagulant activity by reducing platelet adhesion, prolonging blood clotting time, and inhibiting hemolysis. Taken together, these NO-generating PCL/PK mats have potential applications as a scaffold for vascular tissue engineering with rapid endothelialization and reduced SMC proliferation.

The ROMA trial: why it is needed

PURPOSE OF REVIEW

We herein summarize the current evidence on the clinical outcome associated with the use of single and multiple arterial grafts for coronary bypass surgery and the role and importance of the Randomized comparison of the clinical Outcome of single versus Multiple Arterial grafts (ROMA) trial.

RECENT FINDINGS

Observational evidence suggests that the use of multiple arterial grafts is associated with better clinical outcomes compared to the use of a single arterial graft. Randomized evidence is inconclusive; the 5-year interim analysis of the largest randomized trial on the topic did not show any clinical benefit associated with the use of bilateral versus single internal thoracic arteries, whereas a pooled analysis of the trials comparing the radial artery and the saphenous vein as a second graft showed a significant reduction in follow-up cardiac events using the radial artery. Hidden confounders and treatment allocation biases as well as methodological flaws are the most likely explanation of this contradiction.

SUMMARY

ROMA was conceived based on the lessons learned from a critical analysis of the existing randomized and observational evidence with the aim to provide a definitive answer to the question of the potential clinical benefit of multiple arterial grafts for coronary bypass.

Arterial Grafts for Coronary Bypass

Observational and randomized evidence shows that arterial grafts have better patency rates than saphenous vein grafts (SVGs) in coronary artery bypass grafting. Observational studies suggest that the use of multiple arterial grafts is associated with longer postoperative survival, but this must be interpreted in the context of treatment allocation bias and hidden confounders intrinsic to the study designs. Recently, a pooled analysis of 6 randomized trials comparing the radial artery with the SVG as the second conduit and the largest randomized trial comparing the use of single and bilateral internal thoracic arteries have provided apparently divergent results about a clinical benefit with the use of >1 arterial conduit. However, both analyses have methodological limitations that may have influenced their results. At present, it is unclear whether the well-documented increased patency rate of arterial grafts translates into clinical benefits in the majority of patients undergoing coronary artery bypass grafting. A large randomized trial testing the arterial grafts hypothesis (ROMA [Randomized Comparison of the Clinical Outcome of Single Versus Multiple Arterial Grafts]) is underway and will report the results in a few years.

Assessing the Long-term Patency and Clinical Outcomes of Venous and Arterial Grafts Used in Coronary Artery Bypass Grafting: A Meta-analysis

Introduction

The long-term patency of the grafts used during the coronary artery bypass grafting (CABG) is one of the most significant predictors of the clinical outcomes. The gold standard graft used during CABG with the best long-term patency rate and the better clinical outcomes is left internal thoracic artery (LITA) grafted to the left coronary artery (LCA). The controversy lies in choosing the second-best conduit for the non-left coronary artery (NLCA) with similar patency rate as LITA. This meta-analysis examines the long-term patency and clinical outcomes of all arterial grafts versus all venous grafts used during the CABG.

Methods

A comprehensive literature search of all published randomized control trials (RCTs) assessing long-term patency and clinical outcomes of grafts used in CABG was conducted using PubMed, Cochrane Central Registry of Controlled Trials, and Google Scholar (1966-2018). Keywords searched included combinations of “CABG”, “venous grafts in CABG”, “arterial grafts in CABG”, “radial artery grafts in CABG”, “gastroepiploic artery grafts in CABG”, “patency and clinical outcomes”. Inclusion criteria included: RCTs comparing the long-term patency, and clinical outcomes of radial artery, right internal thoracic artery, gastroduodenal artery, and saphenous vein grafts used in CABG. Long-term patency of the grafts and clinical outcomes were analyzed.

Results

Eight RCTs involving 2,091 patients with 1,164 patients receiving arterial grafts and 927 patients receiving venous grafts were included. There was no difference between the long-term patency rate (relative risk (RR) = 1.050, 95% confidence interval (CI) = 0.949 to 1.162, and p = 0.344), overall mortality rate (RR = 1.095, 95% CI = 0.561 to 2.136, and p = 0.790), rate of myocardial infarction (MI) (RR = 0.860, 95% CI = 0.409 to 1.812, and P = 0.692), and re-intervention rate (RR = 0.0768, 95% CI = 0.419 to 1.406, and P = 0.392) between arterial and venous grafts.

Conclusion

The use of arterial conduits over the venous conduits has no significant superiority regarding the long-term graft patency, the rate of MI, overall mortality, and the rate of revascularization following CABG. Additional adequately powered studies are needed to further evaluate the long-term outcomes of arterial and venous grafts following the CABG.

Multiarterial coronary artery bypass grafting: is the radial artery fulfilling the unkept promise of the right internal thoracic artery?

PURPOSE OF REVIEW

The debate on the second best conduit for CABG is still intense. In this review, we discuss the role of the radial artery and the right internal thoracic artery (RITA) compared with saphenous vein grafts (SVG).

RECENT FINDINGS

The recent RADIAL STUDY has been the first evidence based on randomized trials of a clinical benefit using a second arterial graft in CABG.On the other hand, the definitive 10-year results of the ART trial failed to show a clinical advantage associated with the use of bilateral internal thoracic artery (BITA). A thorough and contextualized analysis of this and other studies, however, may offer a different perspective.

SUMMARY

Arterial conduits in CABG have shown better patency rates than SVG. Whether this leads to better clinical outcomes is still debated. In this setting, the radial artery and the RITA seem to offer a similar advantage, although with different indications and contraindications.

Right internal thoracic or radial artery as the second arterial conduit for coronary artery bypass surgery

PURPOSE OF REVIEW

To summarize the available evidence on the use of the right internal thoracic artery (RITA) and the radial artery as the second arterial graft in coronary artery bypass surgery.

RECENT FINDINGS

The current data support the equipoise of the two conduits in terms of clinical and angiographic outcomes. Both RITA and radial artery have better patency than saphenous vein grafts. The use of the RITA carries an increased risk of deep sternal wound infection (DSWI) if the artery is harvested as pedicle. Bilateral internal thoracic artery grafting is more technically demanding than radial artery use and there is a volume-outcome relationship in terms of mortality and incidence of DSWI. The radial artery is preferable over RITA in right-sided or distal circumflex artery targets with high-degree stenosis and in patients at higher risk for DSWI, whereas it is not recommended to graft vessels with moderate stenosis and in cases of insufficient collateralization from the ulnar artery or previous transradial procedures.

SUMMARY

The patency rate and clinical outcomes of radial artery and RITA are similar. The use of one or the other should be based on a careful evaluation of the patient's coronary anatomy and comorbidities, the conduit availability and the surgeon's and center's experience.

The radial artery is protective in women and men following coronary artery bypass grafting-a substudy of the radial artery patency study

Background

Studies have demonstrated that female sex is an adverse risk factor in CABG. The primary aim of this study was to determine whether the radial artery (RA) was associated with reduced angiographic occlusion compared to the saphenous vein graft (SVG) stratified by sex in the multi-centered Radial Artery Patency Study (NCT00187356).

Methods

Between 1996-2001, 529 patients less than 80 years, with graftable triple-vessel disease underwent isolated CABG across 11 centers with late angiographic and clinical follow-up. The primary objective was to compare complete occlusion of RA and SVG with respect to sex. The secondary objective was to determine cumulative patency of both grafts along with predictors of late graft occlusion stratified by sex. The additional objective was to compare major adverse cardiac events (MACE, defined as cardiac mortality, myocardial infarction or re-intervention) between women and men.

Results

Of the 529 enrolled patients (13.4% women), 269 (women: n=41, 15.2%) underwent late angiography at a mean of 7.7±1.5 years after CABG. Women were older (64.1±6.7 versus 59.1±8.0 years, P<0.01) with a higher rate of diabetes (43.9% versus 28.5%, P=0.05). Smoking history was less common (48.8% versus 75.4%, P<0.01) while the mean number of grafts per patient were similar (women: 3.8±0.7, men: 3.8±0.6, P=0.65). RA occlusions were lower than SVG in women (RA: 9.8%, SVG: 26.8%, P=0.05) and in men (RA: 8.8%, SVG: 17.1%, P=0.01). The rate of RA and SVG occlusion was not statistically different between women and men, and cumulative patency curves were also similar between sexes for the RA and study SVG. Multivariable modeling showed that having a RA (versus SVG) was protective in women [odds ratio (OR) 0.15, P=0.04] and men: (OR 0.49, P=0.02). MACE (P=0.15) and event-free cardiac survival (log-rank P=0.14) were similar between women and men.

Conclusions

Radial arteries are protective in both women and men with comparable burden of coronary disease and revascularization.

Persistent Inflammatory Activity in Blood Cells and Artery Tissue from Patients with Previous Bare Metal Stent

BACKGROUND

Studies have pointed out a higher mortality after coronary artery bypass surgery (CABG) in patients with stent.

OBJECTIVE

To evaluate inflammatory markers in peripheral blood cells and in coronary artery tissue samples obtained during CABG in patients with stent compared to controls.

METHODS

The case series consisted of two groups, one with previous stent implantation (n = 41) and one control (n = 26). The expression of the LIGHT, IL-6, ICAM, VCAM, CD40, NFKB, TNF, IFNG genes was analyzed in peripheral blood cells collected preoperatively. The coronary artery was evaluated for: interleukin-6, ICAM, VCAM, CD40, NFKB, TNF-alpha and IFN-gamma by immunohistochemistry. A total of 176 tissue samples were grouped for analysis in: A1- arteries with stent (n = 38); A2- native arteries from patients with stent in another artery (n = 68); and A3- arteries without stent from controls undergoing routinely CABG surgery (n = 70). A significance level of 0.05 was adopted.

RESULTS

Patients with stent showed higher TNF (p = 0.03) and lower CD40 gene expression (p = 0.01) in peripheral blood cells than controls without stent. In coronary artery samples, the TNF-alpha protein staining was higher in the group A1, not only in the intima-media layer (5.16 ± 5.05 vs 1.90 ± 2.27; p = 0.02), but also in the adipose tissue (6.69 ± 3.87 vs 2.27 ± 4.00; p < 0.001). Furthermore, group A1 had a higher interleukin-6 protein staining in adipose tissue than group A3 (p = 0.04).

CONCLUSION

We observed a persistently higher systemic TNF expression associated with exacerbated TNF-alpha and interleukin-6 local production in patients with stents. This finding may contribute to a worse clinical outcome.

Systematic review and meta-analysis in cardiac surgery: a primer

PURPOSE OF REVIEW

The purpose of this article is to review the strengths and weaknesses of systematic reviews and meta-analyses to inform our current understanding of cardiac surgery.

RECENT FINDINGS

A systematic review and meta-analysis of a focused topic can provide a quantitative estimate for the effect of a treatment intervention or exposure. In cardiac surgery, observational studies and small, single-center prospective trials provide most of the clinical outcomes that form the evidence base for patient management and guideline recommendations. As such, meta-analyses can be particularly valuable in synthesizing the literature for a particular focused surgical question. Since the year 2000, there are over 800 meta-analysis-related publications in our field. There are some limitations to this technique, including clinical, methodological and statistical heterogeneity, among other challenges. Despite these caveats, results of meta-analyses have been useful in forming treatment recommendations or in providing guidance in the design of future clinical trials.

SUMMARY

There is a growing number of meta-analyses in the field of cardiac surgery. Knowledge translation via meta-analyses will continue to guide and inform cardiac surgical practice and our practice guidelines.

Unmeasured Confounders in Observational Studies Comparing Bilateral Versus Single Internal Thoracic Artery for Coronary Artery Bypass Grafting: A Meta-Analysis

Background

Observational studies suggest a survival advantage with bilateral single internal thoracic artery (BITA) versus single internal thoracic artery grafting for coronary surgery, whereas this conclusion is not supported by randomized trials. We hypothesized that this inconsistency is attributed to unmeasured confounders intrinsic to observational studies. To test our hypothesis, we performed a meta‐analysis of the observational literature comparing BITA and single internal thoracic artery, deriving incident rate ratio for mortality at end of follow‐up and at 1 year. We postulated that BITA would not affect 1‐year survival based on the natural history of coronary artery bypass occlusion, so that a difference between groups at 1 year could not be attributed to the intervention.

Methods and Results

We searched MEDLINE and Pubmed to identify all observational studies comparing the outcome of BITA versus single internal thoracic artery. One‐year and long‐term mortality for BITA and single internal thoracic artery were compared in the propensity‐score–matched (PSM) series, that is, the form of observational evidence less prone to confounders. Thirty‐eight observational studies (174 205 total patients) were selected for final comparison. In the 12 propensity‐score–matched series (34 019 patients), the mortality reduction for BITA was similar at 1 year and at the end of follow‐up (incident rate ratio, 0.70; 95% confidence interval, 0.60–0.82 versus 0.77; 95% confidence interval, 0.70–0.85; P for subgroup difference=0.43).

Conclusions

Unmeasured confounders, rather than biological superiority, may explain the survival advantage of BITA in observational series.

Covalent immobilization of stem cell inducing/recruiting factor and heparin on cell-free small-diameter vascular graft for accelerated in situ tissue regeneration

The development of cell-free vascular grafts has tremendous potential for tissue engineering. However, thrombus formation, less-than-ideal cell infiltration, and a lack of growth potential limit the application of electrospun scaffolds for in situ tissue-engineered vasculature. To overcome these challenges, here we present development of an acellular tissue-engineered vessel based on electrospun poly(L-lactide-co-ɛ-caprolactone) scaffolds. Heparin was conjugated to suppress thrombogenic responses, and substance P (SP) was immobilized to recruit host cells. SP was released in a sustained manner from scaffolds and recruited human bone marrow-derived mesenchymal stem cells. The biocompatibility and biological performance of the grafts were evaluated by in vivo experiments involving subcutaneous scaffold implantation in Sprague-Dawley rats (n = 12) for up to 4 weeks. Histological analysis revealed a higher extent of accumulative host cell infiltration, neotissue formation, collagen deposition, and elastin deposition in scaffolds containing either SP or heparin/SP than in the control groups. We also observed the presence of a large number of laminin-positive blood vessels, von Willebrand factor (vWF(+) ) cells, and alpha smooth muscle actin-positive cells in the explants containing SP and heparin/SP. Additionally, SP and heparin/SP grafts showed the existence of CD90(+) and CD105(+) MSCs and induced a large number of M2 macrophages to infiltrate the graft wall compared with that observed with the control group. Our cell-free grafts could enhance vascular regeneration by endogenous cell recruitment and by mediating macrophage polarization into the M2 phenotype, suggesting that these constructs may be a promising cell-free graft candidate and are worthy of further in vivo evaluation. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1352-1371, 2016.

The Society of Thoracic Surgeons Clinical Practice Guidelines on Arterial Conduits for Coronary Artery Bypass Grafting

Internal thoracic arteries (ITAs) should be used to bypass the left anterior descending (LAD) artery when bypass of the LAD is indicated (class of recommendation [COR] I, level of evidence [LOE] B). As an adjunct to left internal thoracic artery (LITA), a second arterial graft (right ITA or radial artery [RA]) should be considered in appropriate patients (COR IIa, LOE B). Use of bilateral ITAs (BITAs) should be considered in patients who do not have an excessive risk of sternal complications (COR IIa, LOE B). To reduce the risk of sternal infection with BITA, skeletonized grafts should be considered (COR IIa, LOE B), smoking cessation is recommended (COR I, LOE C), glycemic control should be considered (COR IIa, LOE B), and enhanced sternal stabilization may be considered (COR IIb, LOE C). As an adjunct to LITA to LAD (or in patients with inadequate LITA grafts), use of a RA graft is reasonable when grafting coronary targets with severe stenoses (COR IIa, LOE: B). When RA grafts are used, it is reasonable to use pharmacologic agents to reduce acute intraoperative and perioperative spasm (COR IIa, LOE C). The right gastroepiploic artery may be considered in patients with poor conduit options or as an adjunct to more complete arterial revascularization (COR IIb, LOE B). Use of arterial grafts (specific targets, number, and type) should be a part of the discussion of the heart team in determining the optimal approach for each patient (COR I, LOE C).

Successful endothelialization and remodeling of a cell-free small-diameter arterial graft in a large animal model

The large number of coronary artery bypass procedures necessitates development of off-the-shelf vascular grafts that do not require cell or tissue harvest from patients. However, immediate thrombus formation after implantation due to the absence of a healthy endothelium is very likely. Here we present the successful development of an acellular tissue engineered vessel (A-TEV) based on small intestinal submucosa that was functionalized sequentially with heparin and VEGF. A-TEVs were implanted into the carotid artery of an ovine model demonstrating high patency rates and significant host cell infiltration as early as one week post-implantation. At one month, a confluent and functional endothelium was present and the vascular wall showed significant infiltration of host smooth muscle cells exhibiting vascular contractility in response to vaso-agonists. After three months, the endothelium aligned in the direction of flow and the medial layer comprised of circumferentially aligned smooth muscle cells. A-TEVs demonstrated high elastin and collagen content as well as impressive mechanical properties and vascular contractility comparable to native arteries. This is the first demonstration of successful endothelialization, remodeling, and development of vascular function of a cell-free vascular graft that was implanted in the arterial circulation of a pre-clinical animal model.

Native coronary artery patency after coronary artery bypass surgery

OBJECTIVES

The aim of the study was to determine native coronary artery patency 1 year after coronary artery bypass grafting and to identify clinical and angiographic predictors for the development of a chronic total occlusion (CTO).

BACKGROUND

In contrast to the large body of information regarding graft patency, data regarding atherosclerosis progression and vessel patency in surgically bypassed native coronary arteries are less clear.

METHODS

Of the 440 patients who underwent 1-year follow-up angiography as part of the multicenter RAPS (Radial Artery Patency Study), included in our study were 388 patients (88%) for whom angiograms were available for review. Angiograms were reviewed for native coronary artery patency in an independent blinded manner.

RESULTS

On the pre-operative angiogram, CTO of at least 1 native coronary vessel was demonstrated in 240 patients (61.9%) having 305 occluded vessels. At 1 year after coronary artery bypass grafting, at least 1 new native coronary artery CTO occurred in 169 patients (43.6%). In 7.5% of patients, the native artery and the graft supplying that territory were both occluded. A new CTO was almost 5 times more likely to occur in coronary vessels with a pre-operative proximal stenosis >90% compared with vessels with proximal stenosis <90% (45.5% vs. 9.5%, respectively, p < 0.001). Patients with a new CTO had significantly more baseline Canadian Cardiovascular Society class 4 angina compared with patients without a new CTO. A new CTO was less likely to occur in the left anterior descending artery (18.4%), supplied by the left internal thoracic artery. When comparing radial artery and saphenous vein grafts, neither the type of graft nor graft patency had any association with native coronary artery occlusion.

CONCLUSIONS

CTO of surgically bypassed coronary arteries 1 year after coronary artery bypass grafting is extremely common.

Capture of endothelial cells under flow using immobilized vascular endothelial growth factor

We demonstrate the ability of immobilized vascular endothelial growth factor (VEGF) to capture endothelial cells (EC) with high specificity under fluid flow. To this end, we engineered a surface consisting of heparin bound to poly-L-lysine to permit immobilization of VEGF through the C-terminal heparin-binding domain. The immobilized growth factor retained its biological activity as shown by proliferation of EC and prolonged activation of KDR signaling. Using a microfluidic device we assessed the ability to capture EC under a range of shear stresses from low (0.5 dyne/cm²) to physiological (15 dyne/cm²). Capture was significant for all shear stresses tested. Immobilized VEGF was highly selective for EC as evidenced by significant capture of human umbilical vein and ovine pulmonary artery EC but no capture of human dermal fibroblasts, human hair follicle derived mesenchymal stem cells, or mouse fibroblasts. Further, VEGF could capture EC from mixtures with non-EC under low and high shear conditions as well as from complex fluids like whole human blood under high shear. Our findings may have far reaching implications, as they suggest that VEGF could be used to promote endothelialization of vascular grafts or neovascularization of implanted tissues by rare but continuously circulating EC.

A meta-analysis of randomized controlled trials on mid-term angiographic outcomes for radial artery versus saphenous vein in coronary artery bypass graft surgery

BACKGROUND

Currently, saphenous vein (SV) and radial artery (RA) are the most commonly used conduits in combination with the left internal mammary artery for conventional coronary artery bypass graft surgery (CABG). The present meta-analysis aimed to assess the existing evidence from randomized controlled trials (RCTs) to compare the angiographic outcomes of these two conduits at mid-term follow-up.

METHODS

Four relevant and updated RCTs with follow-up beyond 3 years were identified using five electronic databases. Angiographic endpoints included complete occlusion, 'string sign', graft failure and complete patency.

RESULTS

The incidence of complete occlusion was significantly lower after using RA compared to SV [6.7% vs. 17.2%; odd ratio (OR), 0.36; 95% confidence interval (CI), 0.23-0.58; P<0.0001]. The angiographic 'string sign' was significantly more likely to be identified after using RA compared to SV (3.1% vs. 0%; OR, 5.65; 95% CI, 1.21-26.39; P=0.03). Graft failure was significantly lower after RA compared to SV (9.6% vs. 18.8%; OR, 0.47; 95% CI, 0.30-0.72; P=0.0005). Complete graft patency was found to be significantly higher after RA compared to SV (88.6% vs. 75.8%; OR, 3.19; 95% CI, 1.42-7.16; P=0.005).

CONCLUSIONS

Results of the present meta-analysis suggest that selected patients with severe, proximal stenosis may have superior angiographic outcomes at mid-term follow-up after using RA compared to SV for CABG. However, RA is associated with a significantly higher incidence of the 'string sign'. Future studies should aim to collect additional data on symptomatic outcomes.

Animal models for vascular tissue-engineering

Because of rise in cardiovascular disease throughout the world, there is increasing demand for small diameter blood vessels as replacement grafts. The present review focuses on the animal models that have been used to test small-diameter TEVs with emphasis on the attributes of each model. Small animal models are used to test short-term patency and address mechanistic hypotheses; and large, preclinical animal models are employed to test long-term patency, remodeling and function in an environment mimicking human physiology. We also discuss recent clinical trials that employed laboratory fabricated TEVs and showed very promising results. Ultimately, animal models provide a testing platform for optimizing vascular grafts before clinical use in patients without suitable autologous vessels.

Stem cell sources for vascular tissue engineering and regeneration

This review focuses on the stem cell sources with the potential to be used in vascular tissue engineering and to promote vascular regeneration. The first clinical studies using tissue-engineered vascular grafts are already under way, supporting the potential of this technology in the treatment of cardiovascular and other diseases. Despite progress in engineering biomaterials with the appropriate mechanical properties and biological cues as well as bioreactors for generating the correct tissue microenvironment, the source of cells that make up the vascular tissues remains a major challenge for tissue engineers and physicians. Mature cells from the tissue of origin may be difficult to obtain and suffer from limited proliferative capacity, which may further decline as a function of donor age. On the other hand, multipotent and pluripotent stem cells have great potential to provide large numbers of autologous cells with a great differentiation capacity. Here, we discuss the adult multipotent as well as embryonic and induced pluripotent stem cells, their differentiation potential toward vascular lineages, and their use in engineering functional and implantable vascular tissues. We also discuss the associated challenges that need to be addressed in order to facilitate the transition of this technology from the bench to the bedside.

Impact of repeated percutaneous coronary intervention on long-term survival after subsequent coronary artery bypass surgery

(Background)

In the current stent era, aggressive repeated percutaneous coronary intervention (PCI) has become more common. The aim of this study was to investigate the impact of previous repeated PCI on the subsequent coronary artery bypass grafting (CABG).

(Methods)

Between January 1990 and January 2008, a total of 894 patients underwent first-time isolated elective CABG. Among the 894 patients, 515 patients had had no PCI (group A), 179 patients had had single PCI (Group B), and 200 patients had had multiple PCI (2-15 times, mean 3.6 ± 2.3 times) (group C) before CABG. These groups were compared in terms of early and late clinical results.

(Results)

Preoperative left ventricular ejection fraction was significantly higher in group A (group A;58 ± 13%, group B;54 ± 12%, and group C;54 ± 12%). Number of bypass grafts was significantly smaller in group C (A:3.3 ± 1.0, B 3.4 ± 0.9, C 3.1 ± 1.0). Although there was no statistically significant difference among the groups, in-hospital mortality in group C was higher than that in group A and B (A:1.6%, B:1.1%, C:3.5%, p = 0.16). Survival analysis by Kaplan-Meier method (mean follow-up: 58 ± 43 methods) revealed that freedom from all-cause death and cardiac death was significantly lower in group C in comparison with group A. Freedom from cardiac event was significantly higher in group C than that in group A. Multivariate analysis identified a number of previous PCI as an independent risk factor for cardiac death.

(Conclusions)

Repeated PCI increased risk for long-term prognosis of subsequent CABG.

Systematic comparison of the effectiveness of radial artery and saphenous vein or right internal thoracic artery coronary bypass grafts in non-left anterior descending coronary arteries

Coronary artery bypass grafting surgery is increasingly being carried out on patients with multi-vessel coronary artery disease, but the best grafting candidate for non-left anterior descending coronary arteries is unclear. This research sought to systematically compare the efficacies and safeties of coronary bypass with radial artery and other available grafts. A systematic literature retrieval was performed for all clinical trials comparing the outcomes of coronary artery bypass surgery with radial artery and other grafts in PubMed, EMBASE, and the Cochrane Library. Seven eligible clinical studies, comparing radial artery and great saphenous vein grafts, were found between 1966 and 2010: one prospective non-randomized and six prospective randomized trials. The pooling analysis obtained a relative risk of 0.507 (P<0.05) of graft occlusion in radial arteries compared with great saphenous veins. There was a significantly lower infection rate in arms (i.e., harvest sites for radial arteries) relative to legs (harvest sites for veins), with a pooled relative risk of 0.140 (P<0.05). From the reports on mortality after follow-up ranging from one year to six years, there was no significant difference in mortality between the two graft types (P=0.927). In addition, four cohort controlled trials for radial and right internal thoracic artery grafts were included. The radial graft was associated with less cardiac related events relative to the right internal thoracic artery graft (P=0.014), but with comparable mortality and comparable rates of repeat percutaneous transluminal coronary angioplasty. Subjects with radial arteries seemed to have a lower occlusion rate and a lower graft harvest site infection rate than those with great saphenous veins. Moreover there were fewer cardiac related events with radial arteries relative to the right internal thoracic artery grafts. More studies are needed to confirm these findings concerning the favorable outcomes of coronary artery bypass grafting with radial arteries on long-term patency and mortality.

Hair follicle-derived smooth muscle cells and small intestinal submucosa for engineering mechanically robust and vasoreactive vascular media

Our laboratory recently reported a new source of smooth muscle cells (SMCs) derived from hair follicle (HF) mesenchymal stem cells. HF-SMCs demonstrated high proliferation and clonogenic potential as well as contractile function. In this study, we aimed at engineering the vascular media using HF-SMCs and a natural biomaterial, namely small intestinal submucosa (SIS). Engineering functional vascular constructs required application of mechanical force, resulting in actin reorganization and cellular alignment. In turn, cell alignment was necessary for development of receptor- and nonreceptor-mediated contractility as soon as 24 h after cell seeding. Within 2 weeks in culture, the cells migrated into SIS and secreted collagen and elastin, the two major extracellular matrix components of the vessel wall. At 2 weeks, vascular reactivity increased significantly up to three- to fivefold and mechanical properties were similar to those of native ovine arteries. Taken together, our data demonstrate that the combination of HF-SMCs with SIS resulted in mechanically strong, biologically functional vascular media with potential for arterial implantation.

Radial artery versus saphenous vein conduits for coronary artery bypass surgery: forty years of competition--which conduit offers better patency? A systematic review and meta-analysis

The internal thoracic artery is the most effective conduit for coronary artery bypass surgery; however, most patients have multivessel disease and require additional saphenous vein or radial artery grafts. In this systematic review of the literature and meta-analysis, we aim to compare reported patency rates for these conduits and explore if differences are homogeneous across follow-up intervals. A literature search was performed using Embase, Medline, Cochrane Library, Google Scholar and randomised controlled trial databases to identify studies published between 1965 and October 2009. All studies reporting angiographic comparison of saphenous vein and radial artery conduit patency were included, irrespective of language. The end point was angiographic graft patency stratified over different follow-up intervals. Meta-analysis was performed according to recommendations from the Cochrane Collaboration and Meta-analysis Of Observational Studies in Epidemiology guidelines. We used a random-effect model and the odds ratio as the summary statistic. A total of 35 studies were identified. They reported early patency (≤ 1 year, 6795 grafts), medium-term patency (1-5 years, 3232 grafts) and long-term patency (>5 years, 1157 grafts). Significant variation of comparative patency existed across different follow-up intervals. Early saphenous vein patency was similar to radial artery patency with odds ratio of 1.04 (95% confidence interval 0.68-1.61). Medium-term saphenous vein patency, however, deteriorated significantly (odds ratio 2.06, 95% confidence interval 1.29-3.29). Similarly, long-term patency was better for radial artery conduits (odds ratio 2.28, 95% confidence interval 1.32-3.94). Heterogeneity was due to angiographic patency characteristics and related to risk of bias. In conclusion, the findings of this systematic review of the published literature and meta-analysis support the use of radial artery in preference to saphenous vein conduits for coronary artery bypass surgery.

N-acetylcysteine prevents neointima formation in experimental venous bypass grafts

Background

Neointima formation, mainly characterized by smooth muscle cell proliferation, is an important cause of venous bypass graft failure. The therapeutic potential of the antioxidant N-acetylcysteine (NAC) to attenuate smooth muscle cell proliferation and neointima formation was examined in vivo. The effects of NAC on hyperoxia-induced venous smooth muscle cell (VSMC) cytokine production and proliferation were addressed in vitro.

Methods

Rats underwent autologous epigastric vein-to-femoral artery interposition grafting. Fourteen rats received oral NAC, and a similar control group received saline. Histomorphometric analysis was performed after 7 days or 3 weeks. Cytokine analysis and cell proliferation assay were performed in cultured human VSMCs after hyperoxic or normoxic exposure and NAC administration.

Results

NAC-treated rats displayed a threefold reduction in neointimal area, a sixfold reduction in stenosis rate, and a twofold reduction in VSMC proliferation after vein graft surgery. Incubation of VSMCs in 70 per cent oxygen stimulated the release of mitogenic inflammatory cytokines interleukin (IL) 6 and IL-8. Cytokine-rich medium from these VSMCs induced proliferation of normoxic VSMCs. NAC inhibited hyperoxia-induced cytokine release and VSMC proliferation.

Conclusion

NAC attenuated neointima formation and vein graft stenosis by reducing VSMC proliferation in vivo, and prevented hyperoxia-induced cytokine production and VSMC proliferation in vitro.

Outcomes of second revascularization procedures after stent implantation

Drug-eluting stents (DES) reduce subsequent revascularization procedures. Although randomized trials have compared DES to brachytherapy and balloon angioplasty (PTCA) for in-stent restenosis, few long-term comparisons have been made to bare metal stents (BMS) or bypass surgery (CABG), particularly following second procedures. We sought to assess the association between revascularization modality and long-term clinical outcomes of patients receiving a second procedure for coronary artery disease. Between January 2000 and July 2005, 4,666 consecutive patients underwent initial coronary stent implantation (DES or BMS). From this population we identified 569 patients undergoing a second target vessel revascularization (DES, BMS, PTCA or CABG). Outcomes were assessed at 6, 12, and 24 months after the second procedure, with follow-up through September 2006. Adjusted cumulative incidence rates were calculated using inverse probability weighted estimators. We found that at 24 months, there were no significant differences in death or myocardial infarction for PTCA, BMS, DES, and CABG (17.7%, 14.9%, 7.5%, and 10.2%, p = 0.26[3dfl]). DES patients had lower rates of death or myocardial infarction or third target vessel procedures than patients receiving PTCA (14.6% vs. 30.0%, p = 0.01) and BMS (14.6% vs. 42.2%, p < 0.01), but rates similar to CABG patients (14.6% vs. 14.6%, p = 0.99). For patients undergoing a second revascularization procedure, PTCA, BMS, DES, and CABG are associated with a similar risk of death or nonfatal myocardial infarction. DES and CABG are associated with lower rates of third revascularization procedures compared to PTCA and BMS. Further studies are needed to determine the optimum application for CABG vs. DES as a second or third revascularization procedure.

Composite fibrin scaffolds increase mechanical strength and preserve contractility of tissue engineered blood vessels

OBJECTIVES

We recently demonstrated that fibrin-based tissue engineered blood vessels (TEV) exhibited vascular reactivity, matrix remodeling and sufficient strength for implantation into the veins of an ovine animal model, where they remained patent for 15 weeks. Here we present an approach to improve the mechanical properties of fibrin-based TEV and examine the relationship between mechanical strength and smooth muscle cell (SMC) function.

MATERIALS AND METHODS

To this end, we prepared TEV that were composed of two layers: a cellular layer containing SMC embedded in fibrin hydrogel to provide contractility and matrix remodeling; and a second cell-free fibrin layer composed of high concentration fibrinogen to provide mechanical strength.

RESULTS

The ultimate tensile force of double-layered TEV increased with FBG concentration in the cell-free layer in a dose-dependent manner. Double-layered TEV exhibited burst pressure that was ten-fold higher than single-layered tissues but vascular reactivity remained high even though the cells were constricting an additional tissue layer.

CONCLUSION

These results showed that mechanical strength results largely from the biomaterial but contractility requires active cellular machinery. Consequently, they may suggest novel approaches for engineering biomaterials that satisfy the requirement for high mechanical strength while preserving SMC function.