Coronary Artery Bypass Grafting with Arterial Conduits in the Elderly

Are ovine and porcine carotid arteries equivalent animal models for experimental cardiac surgery: A quantitative histological comparison

BACKGROUND

Coronary artery bypass grafting (CABG) is a common cardiac surgery. Manufacturing small-diameter (2-5mm) vascular grafts for CABG is important for patients who lack first-choice autologous arterial, or venous conduits. Ovine and porcine common carotid arteries (CCAs) are used as large animal models for in vivo testing of newly developed tissue-engineered arterial grafts. It is unknown to what extent these models are interchangeable and whether the left and right arteries of the same subjects can be used as experimental controls. Therefore, we compared the microscopic structure of paired left and right ovine and porcine CCAs in the proximodistal direction and compared these animal model samples to samples of human coronary arteries (CAs) and human internal thoracic arteries (ITAs).

METHODS

We compared the histological composition of whole CCAs of sheep (n=22 animals) with whole porcine CCAs (n=21), segments of human CAs (n=21), and human ITAs (n=21). Using unbiased sampling and stereological methods, we quantified the fractions of elastin, total collagen, type I collagen, type III collagen, smooth muscle actin (SMA) and chondroitin sulfate (CS) A, B, and C. We also quantified the densities and distributions of nuclear profiles, nervi vasorum and vasa vasorum as well as the thickness of the intima-media and total wall thickness.

RESULTS

The differences between the paired samples of left and right CCAs in sheep were substantially greater than the differences in laterality in porcine CCAs. The right ovine CCAs had a smaller fraction of elastin (p<0.001), greater fraction of SMA (p<0.01), and greater intima-media thickness (p<0.001) than the paired left side CCAs. In pigs, the right CCAs had a greater fraction of elastin (p<0.05) and a greater density of vasa vasorum in the media (p<0.001) than the left-side CCAs. The fractions of elastin and CS decreased and the fraction of SMA increased in the proximodistal direction in both the ovine (p<0.001) and porcine (p<0.001) CCAs. Ovine CCAs had a muscular phenotype along their entire length, but porcine CCAs were elastic-type arteries in the proximal segments but muscular type arteries in middle and distal segments. The CCAs of both animals differed from the human CAs and ITAs in most parameters, but the ovine CCAs had a comparable fraction of elastin and CS to human ITAs.

CONCLUSIONS

From a histological point of view, ovine and porcine CCAs were not equivalent in most quantitative parameters to human CAs and ITAs. Left and right ovine CCAs did not have the same histological composition, which is limiting for their mutual equivalence as sham-operated controls in experiments. These differences should be taken into account when designing and interpreting experiments using these models in cardiac surgery. The complete morphometric data obtained by quantitative evaluation of arterial segments were provided to facilitate the power analysis necessary for justification of the minimum number of samples when planning further experiments. The middle or distal segments of ovine and porcine CCAs remain the most realistic and the best characterized large animal models for testing artificial arterial CABG conduits.

Does Age Affect the Short- and Long-Term Outcomes of Coronary Bypass Grafting?

The etiology of coronary artery disease (CAD) is multifactorial, stemming from both modifiable and nonmodifiable risk factors such as age. Several studies have reported the effects of age on various outcomes of coronary artery bypass grafting (CABG). This article reviews age-related outcomes of CABG and offers direction for further studies in the field to create comprehensive, evidence-based guidelines for the treatment of CAD. Ninety-two primary sources were analyzed for relevance to the subject matter, of which 17 were selected for further analysis: 14 retrospective cohort studies, 2 randomized clinical trials, and 1 meta-analysis. Our review revealed four broad age ranges into which patients can be grouped: those with CAD (1) below the age of 40 years, (2) between the ages of 40 and 60 years, (3) between the ages of 60 and 80 years, and (4) at or above 80 years. Patients below the age of 40 years fare best overall with total arterial revascularization (TAR). Patients between the ages of 40 and 60 years also fare well with the use of multiarterial grafts (MAGs) whereas either MAGs or single-arterial grafts may be of significant benefit to patients at or above the age of 60 years, with younger and diabetic patients benefitting the most. Arterial grafting is superior to vein grafting until the age of 80 years, at which point there is promising evidence supporting the continued use of the saphenous vein as the favored graft substrate. Age is a factor affecting the outcomes of CABG but should not serve as a barrier to offering patients CABG at any age from either a cost or a health perspective. Operative intervention starts to show significant mortality consequences at the age of 80 years, but the increased risk is countered by maintenance or improvement to patients' quality of life.

Long-Term Patency Rate of Radial Artery Conduits in Chinese Patients Undergoing Off-Pump Coronary Artery Bypass Grafting

Consensus has yet to emerge among experts as to whether the radial artery (RA) conduit was superior to the saphenous vein (SV) graft for coronary artery bypass grafting (CABG) in terms of long-term patency. This study aimed to evaluate long-term patency of the RA conduit compared to the SV conduit for off-pump CABG, and to screen the independent predictors of long-term RA graft failure.Patients < 80 years of age with graftable triple-vessel disease undergoing non-emergent, primary, isolated off-pump CABG, using both the RA and the SV conduits, were reviewed. Graft patency, all-cause mortality and repeat revascularization were followed-up. The independent predictors of long-term RA graft failure were identified.A total of 296 out of 320 eligible patients (42 females, 61.3 ± 9.9 years old) received follow-up with an observed period of 93.4 ± 16.5 months. All-cause mortality was 14.5%, and repeat revascularization was conducted on 6 RA grafts and 9 SV grafts. Superior patency of the RA grafts compared to the SV grafts was observed (84.4% versus 78.5%, P = 0.035). Independent predictors of long-term RA graft failure included proximal stenosis of target right coronaries < 90% (OR = 2.35, 95%CI 1.41-5.82) and diabetes mellitus (OR = 1.66, 95%CI 1.17-4.26).The RA graft had a superior long-term patency than the SV graft. Long-term patency of the RA graft may be poor in diabetics or in the case of proximal stenosis of target right coronary <90%. (Trial registration: ChiCTR-OCH-1200212).

Sequential Saphenous Vein Coronary Bypass Grafting

The enormous majority of previous reports focused on evaluating the safety and efficacy of sequential saphenous vein (SV) coronary bypass grafting; however, no reports to date have revealed concern regarding the impacts of the number of distal anastomoses of sequential SV grafting on graft patency after coronary artery bypass grafting (CABG). This single-center retrospective study aimed to evaluate the impacts of three versus two distal anastomoses per single SV conduit on SV graft patency after off-pump CABG, and to determine the independent risk factors for sequential SV graft failure.From January 2011 to December 2014, 1320 eligible patients were assigned to either a triple group (three distal anastomoses of sequential SV grafting, n = 758) or a double group (two distal anastomoses of sequential SV grafting, n = 562). The primary endpoint was over a 2-year follow-up SV graft failure after off-pump CABG.The triple and double group received a similar total patency rate of sequential SV conduits (86.5% versus 87.1%, P = 0.757). The number of distal anastomoses of sequential SV grafting (three versus two) was not a predictive factor for the follow-up graft failure of sequential SV conduits (HR = 0.91, 95% CI: 0.66-2.29, P = 0.137). Moreover, the two groups received a similar follow-up survival freedom from repeat revascularization (χ² = 1.881, log-rank P = 0.170).Three versus two distal anastomoses per single SV conduit received a similar SV graft patency. The number of distal anastomoses of sequential SV grafting was not an independent risk factor for graft failure.

Sequential Grafting of in Situ Skeletonized Left Internal Mammary Artery to the Left Coronary System

Sequential grafting may be an effective way to maximize the benefits of the left internal mammary artery (LIMA) conduit. Despite increasing clinical application, the strategy of sequential LIMA grafting has not been proven its superiority. This single-center retrospective study aimed to evaluate the in-hospital and mid-term outcomes of sequential grafting of in situ skeletonized LIMA to the left coronary system.According to the use of sequential or separate LIMA grafting, 1505 eligible patients were assigned to a sequential group (n = 230) and a control group (n = 1275). According to sequential LIMA graft configurations, patients with sequential LIMA grafting were divided into a DOM subgroup (n = 113) and a DLAD subgroup (n = 117). The clinical outcomes and LIMA graft patency were investigated and compared.Sequential LIMA grafting compared with separate LIMA grafting was not an independent predictor either of in-hospital adverse events or follow-up survival free from repeat revascularization during the follow-up period of 32.4 ± 8.5 months. Sequential LIMA grafting had similar LIMA graft patency with separate LIMA grafting (99.5% of 1st sequential sites and 97.7% of 2nd sites versus 98.2% of LIMA-LAD grafts) at 32.3 ± 8.5 months after coronary artery bypass grafting (CABG) surgery. Additionally, the two subgroups received similar mid-term clinical outcomes and graft patency of LIMA segments.Sequential grafting of in situ skeletonized LIMA to the left coronary system resulted in excellent clinical outcomes and graft patency. The two sequential LIMA graft configurations received similar clinical outcomes and graft patency.