Should Saphenous Vein Grafts be the Conduits of Last Resort for Coronary Artery Bypass Surgery?

Autologous endothelialized vein allografts in coronary artery bypass surgery - Long term results

BACKGROUND

Lack of autologous graft material restricts the ability to treat patients requiring coronary artery bypass surgery (CABG). An off the shelf tissue engineered small diameter vascular graft is the holy grail of cardiovascular surgery.

METHODS

Allograft saphenous veins were harvested from organ donors, cryopreserved, deendothelialized and then seeded with autologous endothelial cells prior to implantation during coronary artery bypass surgery. All patients treated were followed-up until death and angiographic results were collected. Grafts were explanted during autopsy and immunohistochemistry was performed.

RESULTS

Twelve patients received 15 engineered grafts. Mean patient survival was 9.1 ± 1.8 years. Six month graft patency was 80 (95% CI: 59-100) and 9 month graft patency was 50 (95% CI: 27-93) - graft patency detected up to 32 months after surgery. Immunohistochemistry in grafts explanted showed a presence of CD31 and CD68 positive cells in the luminal region of the vessel walls and layers of Collagen Type I in the abluminal vessel walls.

CONCLUSIONS

Our small diameter tissue engineered vascular graft shows openness up to 32 months after implantation. Immunohistochemistry suggests that monocyte activation may lead to vessel remodeling with thickening of the vessel wall. Research should concentrate on a manipulation of remodeling processes.

Neuronal nitric oxide synthase-derived hydrogen peroxide effect in grafts used in human coronary bypass surgery

Recently, H₂O₂ has been identified as the endothelium-dependent hyperpolarizing factor (EDHF), which mediates flow-induced dilation in human coronary arteries. Neuronal nitric oxide synthase (nNOS) is expressed in the cardiovascular system and, besides NO, generates H₂O₂ The role of nNOS-derived H₂O₂ in human vessels is so far unknown. The present study was aimed at investigating the relevance of nNOS/H₂O₂ signaling in the human internal mammary artery (IMA) and saphenous vein (SV), the major conduits used in coronary artery bypass grafting. In the IMA, but not in the SV, ACh (acetylcholine)-induced vasodilatation was decreased by selective nNOS inhibition with TRIM or Inhibitor 1, and by catalase, which specifically decomposes H₂O₂ Superoxide dismutase (SOD), which generates H₂O₂ from superoxide, decreased the vasodilator effect of ACh on SV. In the IMA, SOD diminished phenylephrine-induced contraction in endothelium-containing, but not in endothelium-denuded vessels. Importantly, while exogenous H₂O₂ produced vasodilatation in IMA, it constricted SV. ACh increased H₂O₂ production in both sets of vessels. In the IMA, the increase in H₂O₂ was inhibited by catalase and nNOS blockade. In SV, H₂O₂ production was abolished by catalase and reduced by nNOS inhibition. Immunofluorescence experiments showed the presence of nNOS in the vascular endothelium and smooth muscle cells of both the IMA and SV. Together, our results clearly show that H₂O₂ induced endothelium-dependent vascular relaxation in the IMA, whereas, in the SV, H₂O₂ was a vasoconstrictor. Thus, H₂O₂ produced in the coronary circulation may contribute to the susceptibility to accelerated atherosclerosis and progressive failure of the SV used as autogenous graft in coronary bypass surgery.

Effect of Bilateral Internal Mammary Artery Grafts on Long-Term Survival

Background—

Although the potential survival benefit of bilateral internal mammary artery (BIMA) grafting in comparison with single internal mammary artery (SIMA) grafting has been emphasized by many investigators, the use of BIMA is still low in clinical practice in the absence of randomized trials and long-term results. In the current study, we aimed to assess if there is a long-term survival benefit of BIMA up to 10 years after coronary bypass surgery.

Methods and Results—

We selected published articles comparing survival between SIMA and BIMA patients with follow-up duration of more than a mean of 9 years. We evaluated the log hazard ratio with 95% confidence interval for included studies by using a random-effects meta-analysis. Nine eligible observational studies provided 15 583 patients (8270 SIMA and 7313 BIMA) for meta-analysis. Five studies used propensity score methods for statistical adjustment, 2 with a propensity score–based patient-matching method and 3 with quintile-based stratification. A significant reduction in mortality by using BIMA was observed (hazard ratio, 0.79; 95% confidence interval, 0.75–0.84); no study showed any significantly harmful effect of BIMA on survival. Subgroups of studies using different statistical approaches—unmatched, quintile-based propensity score analysis, and propensity score–based exact patient matching—all showed the survival benefit of BIMA grafting.

Conclusions—

BIMA grafting appears to have better survival with up to 10 years follow-up in comparison with SIMA grafting. Long-term survival benefit of BIMA seems to continue in the second decade after surgery. An ongoing randomized trial comparing SIMA and BIMA groups will add evidence on this issue.

Surgical patch angioplasty of the left main coronary artery

Isolated ostial stenosis of the left main coronary artery (LMCA) is rare, occurring in <1% of the patients undergoing coronary angiography. Surgical patch angioplasty (SPA) offers an alternative to conventional coronary artery bypass grafting (CABG) in such cases and is advantageous in restoring more physiological myocardial perfusion, maintaining ostial patency and preserving conduit material. However, a number of early technical failures and high perioperative mortality have limited the generalized uptake of this procedure, and only recently have advances in myocardial protection and novel surgical approaches to the LMCA resulted in a resurgence of the technique. A systematic literature search identified 45 studies incorporating 478 patients undergoing SPA. A variety of patch materials were used, including the pericardium, saphenous vein and internal mammary and pulmonary arteries. Patients were followed up for a mean of 54.4 months. The 30-day mortality was 1.7% and cardiac specific mortality 3.3% at last follow-up. Encouragingly, 92.4% of reported cases (n = 182) showed complete angiographic patency at last follow-up. Our results indicate that SPA may be a viable alternative to CABG in the surgical management of isolated ostial LMCA stenosis. However, no randomized trials have been performed, and it is clear that careful patient selection is essential in minimizing morbidity and mortality in the short- and long-term. Further research is required to allow a direct comparison of SPA to techniques with a more substantial evidence base such as CABG and percutaneous coronary intervention, and to define the optimal patch graft material, elucidating that any beneficial effects arterial patches may have on long-term patency.

Propensity matched analysis of bilateral internal mammary artery versus single left internal mammary artery grafting at 17-year follow-up: validation of a contemporary surgical experience

OBJECTIVES

Bilateral internal mammary arteries (BIMA) remains widely underutilized in coronary artery bypass grafting (CABG). Although prior research has demonstrated a long-term benefit of the use of BIMA over left internal mammary artery (LIMA)-only, validation of these results is lacking in a contemporary surgical experience. We compared complications and survival at 17-year follow-up in a large series of consecutive CABG patients from a single institution that underwent BIMA grafting with a propensity-matched group where LIMA only was used.

METHODS

Propensity scores representing the estimated probabilities of patients receiving either BIMA or LIMA alone were developed based on 22 observed baseline covariates in a logistic regression model with procedure group as the dependent variable. The nearest-neighbour-matching algorithm with Greedy 5-1 Digit Matching was used to produce two patient cohorts of 928 patients each balanced for baseline factors. We compared 30-day morbidity and mortality, as well as long-term survival at 5-year intervals up to 17-year follow-up.

RESULTS

In-hospital and 30-day mortality was 0.8% for the BIMA group and 1.1% for the LIMA-saphenous vein grafting (SVG). No significant difference was found in complications, mortality and/or length-of-stay between these two groups. Off-pump was done in 48.9% of BIMA cases and 51.3% of LIMA cases. Regardless of the types of grafts used, on-pump patients were more likely to have postoperative permanent strokes and longer postoperative lengths of stay. Use of the BIMA over LIMA-only had a statistically significant impact conferring a 10% survival advantage at 10-year and 18% at 15-year follow-up. The Kaplan-Meier survival curves comparing off-/on-pump BIMA and off-/on-pump LIMA-SVG patients demonstrated a 22% survival advantage for off-pump BIMA patients when compared with on-pump LIMA-SVG patients at 15-year follow-up.

CONCLUSIONS

Perioperative complications do not increase with the use of BIMAs. Long-term survival is optimized with off-pump CABG and BIMA grafting. The low morbidity and mortality rates in this series are likely due to the continuous evolution of technology and the adoption of less invasive options for CABG patients. A more widespread use of BIMAs in CABG patients would continue to improve the overall excellent short- and long-term results of this operation.

Differential reactivity of human mammary artery and saphenous vein to prostaglandin E(2) : implication for cardiovascular grafts

BACKGROUND AND PURPOSE

Human internal mammary arteries (IMA) and saphenous veins (SV) are frequently used for coronary artery bypass graft surgery. Intra- and postoperatively, the bypass grafts are exposed to inflammatory conditions, under which there is a striking increase in the synthesis of prostaglandin E(2) (PGE(2) ). In this context, the physiological response of these vascular grafts to PGE(2) is highly relevant. The aim of this study was thus to characterize the PGE(2) receptor subtypes (EP(1) , EP(2) , EP(3) or EP(4) ) involved in modulation of the vascular tone in these two vessels.

EXPERIMENTAL APPROACH

Rings of IMA and SV were prepared from 48 patients. The rings were mounted in organ baths for isometric recording of tension, and a pharmacological study was performed, together with associated reverse transcriptase PCR and immunohistochemistry experiments.

KEY RESULTS

PGE(2) induced contractions of IMA (E(max) = 1.43 ± 0.20 g; pEC(50) = 7.50 ± 0.10); contractions were also observed with the EP(3) receptor agonists, sulprostone, 17-phenyl-PGE(2) , misoprostol or ONO-AE-248. In contrast, PGE(2) induced relaxation of the precontracted SV (E(max) =-0.22 ± 0.02 g; pEC(50) = 7.14 ± 0.09), as did the EP(4) receptor agonist, ONO-AE1-329. These results were confirmed by the use of selective EP receptor antagonists (GW627368X, L-826266, ONO-8713, SC-51322) and by molecular biology and immunostaining.

CONCLUSIONS AND IMPLICATIONS

PGE(2) induced potent and opposite effects on the human vascular segments used for grafting, namely vasoconstriction of the IMA and vasodilatation of the SV via EP(3) and EP(4) receptors respectively. These observations suggest that EP(3) and EP(4) receptors could constitute therapeutic targets to increase vascular graft patency.