Biometry and structure of the left internal thoracic and radial coronary arteries

In an attempt to elucidate the causes of occlusion of radial arteries for coronary artery bypass grafts, we studied the biometry and histology of the coronary, radial and left internal thoracic arteries of 20 anatomical subjects (13 males and 7 females). These specimens were calibrated to the various bypass graft sites using coronary calibrators, and were then submitted to histological examination to determine the structure of the vessel wall. Our preliminary results show no correlation between the internal calibres of these various arteries. Like the coronary arteries and their branches, the radial artery is a muscular artery. In contrast, the left internal thoracic artery like the aorta, is an elastic artery.     

Comparative histological and biometric study of the coronary,radial and left internal thoracic arteries

In an attempt to elucidate the causes of occlusion of radial arteries used for coronary artery bypass grafts and to improve the results of these procedures, we studied the biometry and histology of the coronary, radial and left internal thoracic arteries. These arteries were harvested from 20 cadavers (13 males, 7 females). The specimens were calibrated to the various bypass graft sites using coronary calibrators, and were then submitted to histological examination to determine the structure and innervation of the vessel wall. No correlation was observed between the internal calibers of these various arteries, with the exception of the anterior interventricular and right coronary arteries. Intimal changes and the presence of atheromatous plaque were observed in coronary and radial arteries, but never in the internal thoracic artery. Like the coronary arteries and their branches, the radial artery is a muscular artery. Aging of muscular arteries results in thickening of the intima, which becomes fibrotic due to migration of myocytes from the media and duplication of the internal elastic lamina. The media becomes fibrous, hypertrophic or atrophic. The walls of the radial and coronary arteries contain several adventitial nerves (sympathetic and parasympathetic nerve fibers), but these nerve fibers were not observed in the wall of the left internal thoracic artery. In contrast, the internal thoracic artery, like the aorta, is an elastic artery. Aging of elastic arteries is first observed between the ages of 20 and 29 years and is characterized by loss of one or several elastic laminae of the media and more marked intimal thickening, over a variable length. Even if a radial artery's caliber is similar to that of the coronary artery, histological evolution and graft patency depend on its muscular identity.

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Etude comparative et histologique entre les artères coronaires, radiales et thoracique interne gauche

Résumé Pour tenter de comprendre les causes d'occlusion des artères radiales utilisées comme greffons dans les pontages aorto-coronariens et améliorer les résultats, la biométrie et l'histologie des artères coronaires, radiales et thoracique interne gauche ont été étudiées. Nous avons prélevé ces trois types d'artères chez 20 cadavres (13 hommes et 7 femmes). Ces prélèvements ont été calibrés aux différents sites de pontages avec des calibreurs coronaires, puis analysés en histologie afin de déterminer la structure et l'innervation de la paroi. Nous n'avons pas trouvé de corrélation entre les calibres internes de ces différentes artères, à l'exception des artères interventriculaire antérieure et coronaire droite. Le remaniement de l'intima et la présence de plaques d'athéromes ont été observés dans les artères coronaires et radiales, jamais dans l'artère thoracique interne. Comme les artères coronaires et leurs branches, l'artère radiale est de type musculaire. Leur vieillissement se traduit par un épaississement de l'intima qui se fibrose, par une migration myocytaire de la média et par un dédoublement de la limitante élastique interne. La média devient fibreuse, hypertrophique ou atrophique. A l'opposé l'artère thoracique interne est une artère élastique comme l'aorte. Le vieillissement se caractérise par la disparition, sur une étendue variable, d'une ou de plusieurs lames élastiques de la média et un épaississement intimal plus marqué. Même si, anatomiquement, le calibre reste adapté entre artère radiale et artère coronaire, le devenir histologique et donc la perméabilité des artères radiales est en relation avec sa nature musculaire.

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Observations on detailed histology of the internal thoracic artery and their relevance to its comparatively low incidence of atheroma

The internal thoracic artery (ita) is of value as a coronary artery bypass graft. It is much less prone to develop atheroma than coronary arteries and much less prone to develop graft occlusive disease than the alternative saphenous vein graft, but the reasons for its comparative resistance to atheroma are unclear. We have sought to define the detailed structure of the artery along its length and have shown that the media of the artery changes from an elastic structure in its proximal part to a muscular one in its distal part. The internal elastic lamina has a well-defined structure at all levels, in contrast to the external elastic lamina which becomes well defined only in its distal part. The significant difference in the structure of the media of the ita, compared to that described for the coronary arteries, may be relevant to the observed difference in atheroma between this artery and the similarly sized epicardial coronary arteries. © 1994 Wiley-Liss, Inc.     

Assessment of coronary artery bypass graft patency by multislice computed tomography

The recently developed multislice computed tomography (MSCT) is capable of rapid imaging of cardiac structures, including coronary arteries, during a single breath-hold. We evaluated coronary artery bypass graft (CABG) patency by comparing MSCT results to those of contrast angiography. MSCT and contrast angiography were performed in 39 patients (10 women, 29 men and mean age 60.0 +/- 7.8 years) with a total of 115 bypass grafts including 36 left internal mammary arteries, 4 right internal mammary arteries, 19 radial arteries, 2 gastroepiploic arteries and 54 vein grafts. Patients were investigated for an average of 14 +/- 27 months (range 1 - 108 months) after CABG surgery. Contrast angiography showed a patency rate of 87.0% (100/115). Ninety-nine of these 100 patent grafts by contrast angiography and 14 of the remaining 15 occluded grafts were correctly classified by MSCT (93.3% sensitivity and 99.0% specificity for bypass graft occlusion). The positive and negative predictive values for bypass graft occlusion were 93.3% and 99%, respectively, with an overall diagnostic accuracy of 98.3% (97.2% for left internal mammary artery, 100% for radial artery, 98.1% for vein graft and 100% for other grafts). In conclusion, MSCT is a useful and accurate diagnostic tool for the evaluation of bypass graft patency.     

桡动脉的几何性状和显微结构成份的定量研究

目的　通过对桡动脉几何性状及显微结构成份的定量研究 ,为桡动脉应用于冠状动脉搭桥术提供依据。方法　非心脏病死亡的尸体 2 5具 ,平均年龄 37岁 ,观测桡动脉的长度、上端、中点、下端的外径 ,横断取材制作石蜡切片 ,行HE、VanGieson’s法、Weigert’s法三种染色 ,光镜下观察管壁一般结构 ,并用图像分析仪对管径、内膜和中膜厚度、各层面积等显微结构成份进行了定量分析。结果　桡动脉可用于冠脉搭桥术的长度为 19.99cm ,内弹性膜完整 ,管腔狭窄率较低 ,桡动脉的管壁平滑肌含量较多 ,C/E值 (胶原纤维与弹性纤维之比 )较小。桡动脉有用于冠脉搭桥术足够的长度和管径 ,桡动脉下部位置表浅 ,切取较为方便 ,桡动脉的内膜面积和管腔狭窄率较低 ,有利于移植后保持较高的早、晚期通畅率。结论　桡动脉是冠脉搭桥术可供选择的较理想的血管     

Application of actuator-driven pulsed water jet for coronary artery bypass grafting: assessment in a swine model

Actuator-driven pulsed water-jet (ADPJ) dissection is an emerging surgical method for dissecting tissue without heat and mechanical injury to vessels. We elucidated the mechanical properties of the piezo ADPJ and evaluated its usefulness and safety in coronary artery bypass grafting procedures. The relationship between the input voltage (10–100 V) and peak pressure of the pulsed water jet was evaluated. The tissue strengths of swine internal thoracic and coronary arteries and the surrounding tissues were measured to assure tissue-selective dissection. Internal thoracic arteries were harvested by conventional electric cautery and the water jet in four swine, and eight coronary arteries surrounded by myocardium were attempted to be exposed with the water jet. The dissected specimens were histologically evaluated. The peak pressure of the pulsed water jet was positively correlated with the input voltage (R ²?=?0.9984, P?<?0.001). The breaking strengths of the target vessels (internal thoracic and coronary arteries) and the surrounding tissues were significantly different (P?=?0.002 and P?<?0.001, respectively). Histologic examination revealed that internal thoracic arteries were isolated with less heat damage using the pulsed water jet (P?=?0.002) compared with electric cautery, and coronary arteries also were dissected without apparent histologic damage. ADPJ has the possibility of assuring tissue selectivity among the internal thoracic and coronary arteries. The results also indicated that the use of ADPJ may enhance safe procedures to harvest grafts during coronary artery bypass grafting.     

Anatomic feasibility of creating an inferior epigastric arterio-venous fistula to develop the internal thoracic artery with a view to coronary grafting

Arterio-venous fistulae increase the diameter of their feeding artery. It may be advantageous to increase the diameter of the internal thoracic artery before its use for coronary grafting. A fistula applied directly to the internal thoracic artery may compromise its subsequent use as a coronary graft and is technically difficult and invasive. However, in view of the continuity between the internal thoracic artery and the inferior epigastric artery, it is possible to achieve the same effect by constructing a fistula on the latter. The purpose of this work was to determine, in a cadaveric study, the feasibility of carrying out an arterio-venous fistula on the inferior epigastric artery so as to increase the caliber of the internal thoracic artery before coronary grafting. A morphologic study of the inferior epigastric artery and its vein and their relations as well as the feasibility of such a fistula was carried out on 10 cadavers. The epigastric artery measured 12.35+/-1.2 cm in length. Its diameter decreased from its origin towards it termination from 3.16+/-0.26 cm to 1.76+/-0.18 cm. There was a constant connection between the inferior and superior epigastric arteries. This connection was single in 30% of cases, double in 50% and through an anastomotic plexus of more than two vessels in 20%. The mean number of anastomotic connections was 1.8. The epigastric vein was constant with a diameter of 0.75+/-0.06 mm at its origin and only sufficiently large to carry out a fistula at its termination (2.6+/-0.9 mm). In conclusion, this study indicates that it should be relatively simple to create a fistula between the inferior epigastric artery and either the inferior epigastric vein or the external iliac vein.     

桡动脉与冠状动脉几何性状和显微结构成份的比较

目的：通过对桡动脉与冠状动脉几何性状和显微结构成份的比较研究，为桡动脉应用于冠状动脉搭桥术提供依据。方法：非心脏病死亡的尸体，在其桡动脉的上端、中点、下端及冠状动脉主干根部，横断取材制作切片，光镜下观察并用图像分析仪对其显微结构成份进行定量研究。结果：桡动脉的内、外径与冠状动脉的前室间支、旋支、右冠状动脉接近，但它的内膜面积和管腔狭窄率均明显低于冠状动脉。桡动脉与冠状动脉的显微结构成份相似；管壁平滑肌的含量二者无显著差异。结论：桡动脉是冠脉搭桥术可供选择的较理想的移植血管。     

多普勒超声在全动脉化冠状动脉旁路移植术前桥血管筛查中的应用价值

目的:探讨多普勒超声在全动脉化冠状动脉旁路移植(CABG)术前评估桡动脉及左侧乳内动脉的临床应用价值。方法:回顾性研究。纳入2018年1月—2020年1月蚌埠医学院第一附属医院收治的60例冠心病患者,其中男34例、女26例,年龄44～76岁。患者术前均使用多普勒超声检查左侧乳内动脉及双侧桡动脉。(1)分别采用超声和Al...     

冠状动脉旁路移植术所用桡动脉与乳内动脉的超微结构比较

目的 桡动脉与乳内动脉的生物学特性及冠状动脉旁路移植术后的远期通畅率不同,本研究拟了解桡动脉与乳内动脉的超微结构差异及其对移植术后血管重构的可能影响。方法 在冠状动脉旁路移植术中采集桡动脉远端34例及乳内动脉远端11例。用电镜观察、比较两种动脉的内皮细胞及其脱落比例、内膜平滑肌细胞表型、基质分泌量、内中膜脂质和中层亚显微钙化的有无、中层平滑肌细胞的超微形态和排列。结果 桡动脉内膜较厚,内膜平滑肌细胞较多而密集。它在分泌态内皮细胞（47．1％,16／34）、合成型平滑肌细胞比例（14．4％）、内膜脂质（内膜44．1％,15／34;中膜58．8％,20／34）和基质分泌量增加（14．7％,5／34）方面高于乳内动脉（分别为27．2％,3／11;0．9％;内膜18．2％,2／11及中膜54．5％,6／11;9．1％,1／11）。动脉中膜可出现较多基质小泡及其钙化,而光镜水平未发现钙化,姑且称之为亚显微钙化。桡动脉的中层脂质和亚显微钙化与乳内动脉持平,内皮细胞的肿胀脱落却少于乳内动脉。两者的中层平滑肌细胞结构和排列未见显著差异。结论 冠心病患者桡动脉内皮细胞功能状态和内膜平滑肌细胞潜在的增殖能力高于乳内动脉,它可能参与移植术后重构,并与其远期通畅率较低有关。桡动脉获取中内皮保护较乳内动脉好,有利于通畅率的提高。     

Uterine artery as an arterial conduit for coronary artery bypass graft (CABG) surgery in women: A role for estrogen-receptor alpha (ER-α) in the prevention of post-CABG accelerated atherosclerosis and graft disease

Coronary artery bypass graft (CABG) surgery is the standard of care in the treatment of advanced coronary artery disease (CAD). In order to bypass coronary occlusions, CABG surgery traditionally employs grafts from the left internal thoracic/mammary artery (LITA/IMA), radial artery (RA), and greater saphenous vein (SV). The risk of CABG failure is reported to be higher, or at best similar, for women than for men, and it relates primarily to post-operative accelerated atherosclerosis leading to graft stenosis and recurrent angina, a phenomenon known as “coronary artery bypass graft disease”. In this paper, the authors hypothesize that employing an alternative arterial conduit may help reduce the rate of post-CABG accelerated atherosclerosis in women, and propose that a uterine artery specimen be used instead. Given its greater density of estrogen-receptor alpha (ER-α) relative to other mammalian endothelial cells in the vasculature, uterine arteries may exhibit important anti-atherosclerotic properties. Theoretically, this effect may be amplified with the adjuvant administration of low-dose selective ER-α agonist modulator (SERM) therapy.     

The importance of a substantial elastic lamina subjacent to the endothelium in limiting the progression of atherosclerotic changes

This study examines the hypothesis that progressive intimal thickening and atherosclerosis in the larger pulsatile arteries arise from failure to maintain, subjacent to the endothelial cells, a substantial elastin membrane, a component which has been shown to be of special structural significance. The internal thoracic arteries of 293 subjects of all ages up to 60 years were compared histologically with the anterior descending coronary arteries of the same individuals by light- and electronmicroscopy and immunoperoxidase staining for macromolecules. The internal thoracic arteries usually developed a new robust reduplicated internal elastic lamina at an early age, no further intimal thickening, and no significant entry of lipid or cells to the intima. The coronary arteries showed areas of rapid intimal thickening with poor and incomplete reduplicated internal elastic laminae, entry of lipid, macrophages, and other cells to the intima. The reduplicated internal elastic laminae appeared to be formed primarily by the endothelial cells themselves. An elastin membrane subjacent to the endothelial cells appears to be essential. It provides a secure attachment for the cells and a barrier to the entry of macromolecules and cells to the intima. Its absence is associated with progressive intimal thickening and atherosclerosis.     

Ultrastructure of intramural coronary arteries in pigs with hypertrophic cardiomyopathy.

Pigs with hypertrophic cardiomyopathy diagnosed by echocardiographic examination were selected for study from a genetic breeding herd. Under dissecting microscopic examination, intramural coronary arteries in the septum and left ventricular free wall of euthanized pigs were collected for ultrastructural study. The major lesions of wall thickening included degeneration or denudation of endothelium, subendothelial edema, proliferation of collagen fiber, and hyperplasia of smooth muscle cells. Smooth muscle cells proliferated and migrated through the internal elastic lamella into the intima, which caused the early lesion of wall thickening of the intramural coronary arteries. The extent of smooth muscle cell proliferation was related to the severity of endothelial damage. The smooth muscle cells in the intima were identified by immunohistochemical staining (i.e., smooth muscle actin [SMA] stain). Three major types of severe wall thickening with narrow lumen were observed in the intramural coronary arteries. Edema in the intima caused the major lesion of Type I wall thickening. The internal elastic lamella was broken into small interrupted fragments, and fine fragments of elastic fibers surrounded by the cellular processes of smooth muscle were observed in Type I lesions. Many smooth muscle cells proliferated in the intima and media, which constituted the major lesion of Type II wall thickening of the intramural coronary arteries. Many vacuolized, degenerated smooth muscle cells with fewer sarcoplasmic myofilaments could be clearly observed in the Type II lesions. In advanced cases, severe vacuolization and degeneration of smooth muscle cells with the presence of many bizarrely shaped smooth muscle cells in the walls of the intramural coronary arteries could be observed, which caused the major lesion of Type III wall thickening. Pigs with hypertrophic cardiomyopathy, characterized by spontaneously occurring lesions in intramural coronary arteries, may prove a valuable animal model for human disease.     

翻转胸廓内动脉冠状动脉旁路术的实验研究

目的 研究翻转胸廓内动脉用于冠状动脉旁路术的可行性。方法 对１０具成人尸体胸廓内动脉的特性进行观察,并测量左、右各助间点到ＩＴＡ起点、冠状动脉左前降支中点的距离。结果 于近端切断胸廓内动脉可以保证该动脉逆向供血,血供来源于下位肋间动脉、肌隔动脉和腹壁上动脉。左侧第３肋间以下的各肋间中点,到ＩＴＡ起点处的长度明显长于其到冠状动脉左前降支中点的距离;右侧第４肋间以下的各肋间中点,到ＩＴＡ起点处的长距离     

Endothelial hypoxia induction of atherosclerosis: an explanation of patency rates for internal mammary artery and other coronary artery bypass grafts

The major etiological factors of atherosclerosis are reviewed and the case strengthened for endothelial hypoxia being the major initiator. Hypoxia is also shown to be the major cause of coronary artery bypass graft occlusions. The pathophysiological differences between pedicle and free arterial grafts and venous grafts are discussed. Arguments are presented to explain why pedicle internal mammary artery grafts have longer lasting a patency then saphenous vein grafts. It is proposed that free grafts using other systemic arteries should also give very acceptable results and may, in certain circumstances, be desirable over pedicle internal mammary artery grafts. The differences between single, Y and sequential grafts are also discussed to explain differences in patency rates.     

Hydrogel-electrospun mesh composites for coronary artery bypass grafts

The aim of the present study was to investigate the potential of hydrogel-electrospun mesh hybrid scaffolds as coronary artery bypass grafts. The circumferential mechanical properties of blood vessels modulate a broad range of phenomena, including vessel stress and mass transport, which, in turn, have a critical impact on cardiovascular function. Thus, coronary artery bypass grafts should mimic key features of the nonlinear stress-strain behavior characteristic of coronary arteries. In native arteries, this J-shaped circumferential stress-strain curve arises primarily from initial load transfer to low stiffness elastic fibers followed by progressive recruitment and tensing of higher stiffness arterial collagen fibers. This nonlinear mechanical response is difficult to achieve with a single-component scaffold while simultaneously meeting the suture retention strength and tensile strength requirements of an implantable graft. For instance, although electrospun scaffolds have a number of advantages for arterial tissue engineering, including relatively high tensile strengths, tubular mesh constructs formed by conventional electrospinning methods do not generally display biphasic stress-strain curves. In the present work, we demonstrate that a multicomponent scaffold comprised of polyurethane electrospun mesh layers (intended to mimic the role of arterial collagen fibers) bonded together by a fibrin hydrogel matrix (designed to mimic the role of arterial elastic fibers) results in a composite construct which retains the high tensile strength and suture retention strength of electrospun mesh but which displays a J-shaped mechanical response similar to that of native coronary artery. Moreover, we show that these hybrid constructs support cell infiltration and extracellular matrix accumulation following 12-day exposure to continuous cyclic distension.     

The descending branch of the lateral circumflex femoral artery as an alternative conduit for coronary artery bypass grafting: Experience from an anatomical,radiological and histological study

The descending branch of the lateral circumflex femoral artery (DBLCFA) has been suggested as an option for use in coronary artery bypass grafting (CABG). Our aim was to combine radiological examination, surgical and anatomical preparation, and histological assessment of the DBLCFA to map its variability and to assess the benefits of this conduit in cardiac surgery. The pelvic and femoral arteries were examined by CT angiography (CTA) in 100 patients (aged 68.3 ± 9.3 years) to assess the variability of the DBLCFA. Anatomical dissections were performed on 20 cadavers. In 15 patients, an autologous DBLCFA was implanted during CABG. In 35 samples, possible atherosclerotic lesions were examined histologically. The length of the potential DBLCFA conduits measured by CTA was 9.3 ± 2.9 cm, without correlating with the length of the thigh. Anatomical variations that would prevent the DBLCFA from being used in CABG were found in 27 out of 100 patients. Except for focal thickening of the intima, eccentric hypertrophy of the intima was found in three out of 35 samples. No inflammatory infiltration, foam cells, atheroma, or calcifications were found histologically. The DBLCFA is not to be used routinely or in preference to other grafts of choice. However, owing to its moderate variability, sufficient length, caliber, and rare atherosclerosis, it can be used in the absence of other suitable grafts as an alternative conduit implanted as a composite Y‐graft end‐to‐side to the internal thoracic artery in patients without diabetic angiopathy, neuropathy or peripheral artery disease who are undergoing extensive or repeat coronary revascularization. Clin. Anat. 29:779–788, 2016. © 2016 Wiley Periodicals, Inc.     

Comparison of the endothelial surface and subjacent elastic lamina of anterior descending coronary arteries at the location of atheromatous lesions with internal thoracic arteries of the same subjects: a scanning electron microscopic study

AIM: Current theories fail to explain the localisation of atheromatous lesions or their variable incidence in different arteries of the same subject. The objective of this study was to compare by scanning electron microscopy (SEM) the endothelial surface and the subjacent elastic lamina of human coronary arteries at the location of areas showing infiltration by lipid and cells, with the same components of internal thoracic arteries of the same subjects. METHODS: The endothelial surface and the subjacent elastic lamina of localised atheromatous areas of 146 anterior descending coronary arteries were compared with the same structural components of the internal thoracic arteries of the same subjects, using SEM, transverse paraffin sections and freeze-fracture. Some arteries were digested with formic acid to destroy the endothelium and interstitial tissue, and reveal the elastin fibre structure of the elastic laminae. RESULTS: Coronary arteries showed localised defects of the endothelial surface and of the elastin fibre structure of the subjacent elastic membrane, with the presence of lipid and cells in transverse sections of the intima. Internal thoracic arteries showed such changes only rarely, more particularly in older age groups. CONCLUSIONS: In localised areas of the coronary arteries showing infiltration of the wall by lipid and cells, there were imperfections of the endothelial surface and of the elastin fibre structure of the subjacent elastic lamina. These imperfections were not in general present in the endothelial surface, or subendothelial elastic lamina of the internal thoracic arteries in age groups below 50, and only rarely in older subjects.     

Difference between endothelium-dependent relaxation in arterial and in venous coronary bypass grafts

Both the internal mammary artery and the saphenous vein are used to construct coronary-artery bypass grafts. We hypothesized that the release or production of endothelium-derived relaxing factor, which regulates blood flow and inhibits platelet function, may differ in venous and arterial grafts. We therefore studied endothelium-dependent relaxation in internal mammary arteries, internal mammary veins, and saphenous veins obtained from 58 patients undergoing coronary bypass surgery. Vascular rings with and without endothelium were suspended in organ chambers, and isometric tension was recorded. Acetylcholine (10(-8) to 10(-4) M), thrombin (1 U per milliliter), and adenosine diphosphate (10(-7) to 10(-4) M) evoked potent endothelium-dependent relaxation in the mammary artery but weak response in the saphenous vein (P less than 0.005; n = 6 to 27). In the mammary artery, relaxation was greatest in response to acetylcholine (86 +/- 4 percent reduction in norepinephrine-induced tension), followed by thrombin (44 +/- 7 percent) and adenosine diphosphate (39 +/- 8 percent). In the saphenous and mammary veins, relaxation was less than 25 percent. Relaxation was unaffected by indomethacin but was inhibited by methylene blue and hemoglobin (P less than 0.005 and 0.01, respectively), which suggests that endothelium-derived relaxing factor was the mediator. Endothelium-independent relaxation in response to sodium nitroprusside was similar in arteries and veins. We conclude that endothelium-dependent relaxation is greater in the mammary artery than in the saphenous vein. The possibility that this contributes to the higher patency rate among arterial grafts than among venous grafts will require further study.     

Diffuse coronary arteriodysplasia in a Holstein-Friesian cow

The coronary arteries of a 6-year-old Holstein-Friesian cow showed dysplastic lesions characterized by the following vascular changes: irregular, aneurysmal dilation; intimal fibrosis associated with myointimal cells; aberrant internal elastic lamina; oedema and mast cell infiltrates; and variation in the thickness of the media, including tortuosity with irregular dilation of the lumen of the artery and a plexiform structure formed from the right coronary artery.