Blood supply of the heart
The heart is a muscular, four-chambered organ that is responsible for distributing blood throughout the body. The continuous activity of the heart creates a large demand for nutrients to be delivered to cardiac tissue and for waste to be removed. However, because the organ is several layers thick, it is not feasible for the tissue to obtain nutrients from the blood (via any form of cellular transport mechanism) that passes through its chambers. If that were the case, the inner layers of the heart (endocardium and deep myocardium) would receive nutrients, but the outer layers (superficial myocardium, pericardium, and epicardium) would become ischaemic and necrotic (i.e. die).
Therefore, in order to maintain optimum cardiac performance and homeostasis, the heart has a network of blood vessels known as the coronary vessels that take nutrient-rich blood to the heart tissue; as well as coronary veins that removes waste products from the cardiac myocytes. Their role is similar to that of the vasa nervosa (vessels of the nerves) and vasa vasorum (vessels of the vessels) that perfuse the outer layers of the larger blood vessels.
Left coronary artery (left anterior descending, left circumflex arteries), right coronary artery (conus arteriosus, right anterior atrial and ventricular, right marginal, posterior interventricular arteries)
Anterior cardiac veins, Thebesian veins, coronary sinus (great cardiac vein, middle cardiac vein, small cardiac vein, oblique vein of the left atrium, posterior vein of the left ventricle)
|Lymphatic drainage||Tracheobronchial and brachiocephalic lymph nodes|
- Coronary arteries
- Coronary veins
- Lymphatic drainage of the heart
- Summary of coronary vessels
- Disorders of the coronary vessels
The word coronary arises from the Latin word coronarius, which in English means “belonging to a crown or wreath”. When viewed in cross-section from above, the coronary vessels resemble a tilted, inverted crown wrapped around the root of the great vessels. The coronary arteries are responsible for carrying nutrient-rich, oxygenated blood from the left ventricle to the myocardium; while the coronary veins take nutrient – poor deoxygenated blood away from the myocardium and to the right atrium.
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Although the coronary arteries and their branches are considered as end arteries, they participate in various anastomoses (especially during intrauterine life). However, most of these communications are obliterated by the end of the first year of extrauterine life; and those that persist among the smaller branches have questionable clinical significance. In hypoxic events or on the background of coronary artery disease, these communications may become more prominent.
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The coronary arteries arise from the root of the ascending aorta. Recall that the aortic valve has three semilunar cusps, also known as the sinuses of Valsalva. The left and right semilunar cusps give rise to the corresponding left and right coronary arteries (respectively). The third sinus – which is the posterior semilunar cusp – is not associated with a coronary vessel and is also called the non-coronary sinus. The major divisions of the coronary arteries usually travel just below the epicardial layer of the heart. However, their branches may become deeply embedded in the myocardium as they pass through the cardiac grooves. The proximal end of the coronary arteries range between 1.5 – 5.5 mm in diameter; but the left coronary is typically larger than the right in most cases.
Anatomists and clinicians alike refer to ‘right’ or ‘left’ dominance with respect to the blood supply of the heart. If the right coronary artery gives off the posterior interventricular branch (which perfuses the posterior region of the ventricular septum and the posterolateral aspect of the left ventricle), then the heart would be described as being right dominant; the converse is also true. In the majority of cases, the right coronary is the dominant artery; however, both left dominance, and codominance (equal supply from both coronary arteries) have been observed.
The coronary artery segmentation model divides the left and right coronary arteries into 17 segments. Not only does this aid in understanding the vascular territories associated with the arteries and their branches, but it also helps clinicians to localize and treat vascular lesions. However, the details regarding the specific territories that correspond to each segment is beyond the scope of this article. Instead, a simplified segmentation system where the coronary vessels are divided into proximal, mid, and distal thirds will be used.
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Left coronary artery
The left coronary artery arises from the left semilunar cusp (sinus of Valsalva). The initial portion of the vessel ends at the first bifurcation; it is of variable length and is often referred to as the left main coronary artery. It can be found travelling between the left atrial (auricular) appendage and the pulmonary trunk. As it enters the left half of the sternocostal atrioventricular groove, the vessel turns left, toward the obtuse (right) margin of the heart. Prior to the bifurcation, the initial segment of the vessel usually does not produce any branches. It infrequently gives off a small sinuatrial node artery and atrial ramus.
When compared to the right coronary artery, the left coronary artery tends to be larger and is responsible for supplying a larger territory. It supplies the left atrium, majority of the left ventricle, and most of the interventricular septum. The only variation of this supply occurs in right dominant hearts, where the right posterior descending branch of the right coronary supplies a significant portion of the diaphragmatic side of the left ventricle.
Branches of the left coronary artery
As soon as the right coronary artery enters the atrioventricular septum, the left coronary artery then splits to give rise to the anterior interventricular artery (also known as the left anterior descending artery) and the left circumflex artery. The left circumflex artery is further subdivided into proximal and distal parts, while the left anterior descending is divided into proximal, middle, and distal segments.
The anterior interventricular artery is viewed as a caudal, anterior continuation of the left coronary artery. It travels inferolaterally within the anterior interventricular groove towards the cardiac apex. It is more often than not, covered by bridging myocardial fibers, as well as sections of the great cardiac vein. The first branch of this artery is the left conus artery close to the point of origin. It often decussates to anastomose with the contralateral counterpart, as well as the vasa vasora of the aorta and pulmonary artery.
The artery produces anterior ventricular and anterior septal divisions as well; each having left and right components. It also gives rise to posterior branches that correspond to the previously described anterior derivatives. As many as nine left anterior ventricular branches may arise from the left anterior descending artery. These vessels arise acutely, and travel across the sternocostal surface of the left ventricle. The largest of these vessels usually travels all the way to the obtuse cardiac margin. On the other hand, the anterior septal arteries arise at almost 90 degrees before travelling inferoposteriorly to supply the anterior two-thirds of the septum. While it is not uncommon for the left anterior descending artery to terminate at the cardiac apex, it is more likely to continue onto the diaphragmatic surface and abutt the terminal branches of the posterior descending artery arising from the right coronary artery.
The other branch of the left coronary artery is the left circumflex artery. It is overlapped by the left atrial appendage proximally, as it takes a left course in the atrioventricular groove and crosses over the obtuse border. The vessel may give rise to atrial branches (posterior, lateral and anterior divisions) that supply the left atrium. The left circumflex artery also produces the arteria anastomotica auricularis magna, which is also known as Kugel’s anastomotic artery. This vessel was first described back in 1928 as a large calibre vessel that travels in the walls of the atrial appendage and provides indirect and direct anastomotic pathways between the left and right coronary arteries.
Once on the diaphragmatic surface, the left circumflex artery travels along the diaphragmatic atrioventricular groove. As it crosses the obtuse margin, it gives off the left marginal branch, which divides to give several vessels that cross the obtuse border to supply the diaphragmatic part of the left ventricle. In addition to that, it also gives off anterior and posterior ventricular arteries to supply the left ventricle as well. Although the posterior descending artery supplies the left ventricle, if it is deficient or absent, the left circumflex artery can take its place in the interventricular groove and supply the diaphragmatic ventricular structures.
Check out this video to revise an interesting real-life clinical case of long ectopic left main coronary artery:
Right coronary artery
The right coronary artery arises from the right semilunar cusp (sinus of Valsalva). In the majority of cases, the artery arises as a single vessel. However, as many as four branches have been observed arising from the anterior coronary ostium. The artery travels between the right appendage of the right atrium and the pulmonary trunk, in an anterior direction to gain access to the right half of the atrioventricular groove.
Once in the groove, the vessel then moves inferiorly, to cross the acute (right) cardiac margin. It then enters the diaphragmatic atrioventricular groove and travels towards the cardiac crux. It crosses the crux to anastomose with the left circumflex artery (branch of the left coronary artery). Less frequently, the vessel may stop at the right cardiac margin or travel to the halfway point between the crux and the left cardiac margin. However, if the course of the right coronary deviates from the norm, it is more likely to partially replace the left circumflex as it travels to the left cardiac margin.
Branches of the right coronary artery
The conus arteriosus branch of the right coronary artery (otherwise called the right conus artery or the arteria coni arteriosi) is the first branch of the right coronary artery. In some instances, it arises directly from the right coronary sinus; at which point it is referred to as the third coronary artery. It arborizes anteriorly, between the base of the pulmonary conus (infundibulum) and the superior part of the right ventricle. It may give rise to the annulus of Vieussens by anastomosing with its contralateral fellow (left conus artery arising from the left anterior descending artery); the resulting anastomotic ring encircles the right ventricular outflow tract.
The right anterior ventricular and atrial branches originate from the proximal segment of the right coronary artery; which extends from the right coronary ostia and ends at the right cardiac margin. The vessels almost immediately travel approximately perpendicular to each other as they head towards their respective target sites.
The atrial derivatives arising from the right coronary artery are sub-classified into posterior, marginal (lateral or right) and anterior branches. The right marginal and anterior divisions often occur as paired vessels that supply the entire right atrium. On the other hand, the right posterior atrial branch usually exists as a solitary branch that supplies both right and left atria.
The anterior atrial division of the right coronary artery also produces the sinuatrial node artery. It often extends into the muscular layer of both atria but, it primarily travels through right atrial myocardium. Although there is significant interpersonal variability in the origin of this vessel (left circumflex, right marginal atrial, or right diaphragmatic atrioventricular [distal] part), it eventually passes between the aorta and right atrial appendage. At the base of the superior vena cava, the sinuatrial node artery forms an arterial loop, which arborizes to supply the right atrium. The ramus cristae terminalis also arises from these vessels and directly supplies the sinuatrial node.
About two to three right anterior ventricular branches travel toward the apex and arborize gradually. Similarly, the middle segment of the right coronary artery (extending from the end of the proximal segment at the right cardiac border to the cardiac crux) gives off two or three small posterior ventricular branches. The anterior ventricular arteries supply the sternocostal part of the right ventricle, while the posterior ventricular arteries perfuse the diaphragmatic part of the right ventricle.
As the right coronary artery continues toward the right cardiac margin in the sternocostal atrioventricular groove, it produces the right marginal artery. This is a large calibre vessel that travels along the acute (inferior) margin of the heart towards the cardiac apex. Along its course, it supplies both sternocostal and diaphragmatic surfaces of the right ventricle. The size of the right marginal artery is inversely related to the size and number of right ventricular branches that arise from the proximal and middle segments of the right coronary artery.
The distal segment of the right coronary artery continues to curve across the acute cardiac margin in the diaphragmatic atrioventricular groove. At the cardiac crux, the vessel then turns to travel down the interventricular groove and is now referred to as the posterior interventricular or posterior descending artery. It may persist as s solitary vessel, or accompanied unilaterally or bilaterally by one or two parallel derivatives from the right coronary artery. The artery continues along the diaphragmatic surface of the heart towards the cardiac apex, where it meets and anastomoses with the anterior interventricular (descending) branch of the left coronary artery. Along its course, it supplies the posterior third of the interventricular septum through its septal branches.
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Like all arteries in the body, there are veins that accompany them to drain the tissue of deoxygenated blood. Similarly, the veins of the heart often travel alongside the arterial vessels, carrying blood back to the heart. There are numerous venous tributaries traversing the surface of the heart. They eventually coalesce to form the coronary sinus, which drains indirectly into the right atrium. Additionally, the anterior cardiac veins and the Thebesian (small) veins drain directly into the cardiac chambers.
The arrangements of the drainage pathway of the coronary veins are less predictable than that of the arterial supply. Most cases will have the majority of the veins (except the anterior cardiac and Thebesian veins) converging into the coronary sinus; while about one-third of all cases will have all veins except the Thebesian veins draining into the coronary sinus. In other cases, some of the Thebesian veins may receive some of the anterior cardiac veins before draining into the coronary sinus.
Anterior cardiac veins
Up to five vessels traversing the subepicardial space towards the right aspect of the septal atrioventricular groove form the group of anterior cardiac veins. The right coronary artery can be found variably superficial or deep to the vein along its course in the atrioventricular groove.
The anterior cardiac veins may also receive blood from the right marginal vein as it travels along the acute cardiac border. However, this vein has also been found to drain independently into the right atrium as well as to the coronary sinus. The anterior cardiac veins are responsible for draining the sternocostal aspect of the right ventricle.
The smallest cardiac veins (venae cordis minimae) are a collection of small veins of the heart. Otherwise known as Thebesian veins or small cardiac veins, these vessels range from 0.5 – 2 mm in diameter. Although they are difficult to map throughout the heart, they have been shown to drain directly into all cardiac chambers. However, it is far more likely to find the veins draining into the right, rather than in the left, chambers.
The coronary sinus is roughly a 3 cm saccular dilatation between the left cardiac chambers. The sinus commences at the junction of the great cardiac vein and the oblique vein of the left atrium. It is oriented obliquely in the posterior atrioventricular groove; partly overlying the cardiac crux. Its opening into the right atrium (between the inferior vena caval orifice and opening of the tricuspid valve) is protected by the semilunar valve of the coronary sinus (also called the Thebesian valve), in order to prevent reflux into the cardiac venous system. At least five other cardiac veins drain invariably into the coronary sinus.
Great cardiac vein
The great cardiac vein originates at the cardiac apex, travels through the anterior interventricular and then to the atrioventricular groove. It receives blood from the left marginal vein and other tributaries that drain both ventricles and the left atrium, and empties into the coronary sinus at its origin.
Middle cardiac vein
Also arising at the cardiac apex, the middle cardiac vein travels in the posterior interventricular groove to empty into the atrial end of the coronary sinus.
Small cardiac vein
Not to be confused with the Thebesian veins, the small cardiac vein is a singular vessel found in the posterior atrioventricular groove. It is sometimes joined by the right marginal vein (which travels along the acute cardiac border) as they drain the posterior aspect of the right chambers.
Oblique vein of the left atrium
As the name suggests, the oblique vein of left atrium takes an inferior oblique course along the back of the left atrium to insert in the distal end of the coronary sinus. Like the left vena caval ligament (with which it is continuous), the oblique vein of the left atrium is a remnant of the left common cardiac vein.
Posterior vein of the left ventricle
The posterior vein of left ventricle opens centrally in the coronary sinus. However, it may also open into the great cardiac vein. It travels along the diaphragmatic aspect of the left ventricle, alongside the middle cardiac vein.
Solidify your knowledge about the blood vessels of the heart with our quiz:
Lymphatic drainage of the heart
The lymphatic channels of the heart commence in the subendocardial and myocardial spaces. These tributaries then drain into the subepicardial plexus. From here, the efferent subepicardial vessels coalesce to form right and left cardiac collecting trunks. The left trunks travel in the anterior interventricular groove where they are joined by larger tributaries draining the diaphragmatic aspect of the left ventricle. Of note, the diaphragmatic afferent lymphatic vessels move cranially in the posterior interventricular groove before turning in the atrioventricular groove towards the obtuse cardiac margin. The left trunks receive lymph from both ventricles. The channels formed from the union of the left truncal and diaphragmatic lymphatic channels subsequently travel cranially between the left atrium and pulmonary artery towards the tracheobronchial nodes.
Tributaries from the right atrium, diaphragmatic aspect of the right ventricle, and the right cardiac border drain into the right truncal lymph vessels. These vessels also travel cranially in the atrioventricular groove, adjacent to the right coronary artery. Subsequently, it climbs the outer wall of the ascending aorta to access the brachiocephalic nodes.
Learn more about the lymphatics of the heart here:
Summary of coronary vessels
- The heart is a muscular organ that works continuously from the 4th week of intrauterine life until death.
- In the anatomical position, the heart has six surfaces and four borders that are named in relation to adjacent anatomical structures and their geometrical orientation, respectively:
- The surfaces of the heart are:
- The anatomical base is the posterior surface of the heart and is made up mostly by the left, and part of the right, atria.
- The sternocostal surface is the anterior surface of the heart that sits immediately behind the sternum; and is made up mostly by the right atrium and ventricle, and a portion of the auricle of the left atrium.
- The diaphragmatic surface is the inferior surface of the heart and is made up mostly by the left ventricle.
- The anatomical apex of the heart is the pinnacle of the pyramid; normally found in the left fifth intercostal space, in the midclavicular line of the recumbent patient.
- The right cardiac surface is almost vertical and consists of the wall of the right atrium.
- The left cardiac surface is oblique and faces posterosuperiorly to the left hand side.
- The cardiac margins include:
- The obtuse (left) margin
- The acute (inferior) margin
- The right heart margin
- The superior heart margin
- The surfaces of the heart are:
- There are impressions on the surface of the heart that serve as landmarks for the septa that separate the chambers internally. They also provide a course for the coronary vessels to travel in:
- The anterior and posterior interventricular groove corresponds to the interventricular septum
- The coronary sulcus corresponds to the atrioventricular septum
- The interatrial groove matches up to the interatrial septum
- The blood supply to the heart arises from the left and right semilunar cusps of the aortic valve (respectively):
- The left coronary artery gives rise to the anterior interventricular (left anterior descending) and the left circumflex arteries.
- The left circumflex becomes the posterior interventricular artery in a few cases
- The right coronary artery gives rise to the conus arteriosus, right anterior atrial and ventricular, right marginal, and the posterior interventricular (posterior descending) arteries.
- The left coronary artery gives rise to the anterior interventricular (left anterior descending) and the left circumflex arteries.
- The venous drainage of the heart includes:
- The anterior cardiac veins
- Thebesian Veins
- The coronary sinus and its tributaries:
- The great cardiac vein
- The middle cardiac vein
- The small cardiac vein
- The oblique vein of the left atrium
- The posterior vein of the left ventricle
- The lymphatic channels of the heart drain to the tracheobronchial and brachiocephalic lymph nodes.
Disorders of the coronary vessels
Like the rest of the blood vessels throughout the body, the coronary vessels are also susceptible to numerous pathological processes. A wide range of disorders plague the coronary vessels; ranging from congenital abnormal courses to acquired luminal occlusion. Ultimately, these disorders can result in poor flow of oxygenated blood to the myocardium. The resultant sequelae of hypoxia, ischemia, and infarction may lead to the demise of the patient if they don’t get access to urgent medical care. Please see the Disorders of the Coronary Vessels for more details regarding these pathologies.
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