The coronary circulation refers to the vessels that supply and drain the heart with needed nutrients and oxygen. The coronary arteries encircle the heart in the same way a crown does and provide essential nourishment to the entire body. In this article, we will explore the naming, distribution, and clinical relevance of vessels in the coronary circulation.
The coronary arteries have two main branches – the left and right – that provide blood to the entire heart. The left and right coronary arteries arise from the left and right aortic sinuses, which are small openings located within the aorta behind the left and right flaps of the aortic valve. When the heart is relaxed, the back-flow of blood fills these valve pockets and enters the coronary arteries.
The left coronary artery (LCA) initially branches to yield the left anterior descending (LAD), also called the anterior interventricular artery. The LCA also gives off the left marginal artery (LMA) and left circumflex artery (Cx). In approximately 20-25% of individuals, the left circumflex artery contributes to the posterior interventricular artery (PIv).
The right coronary artery (RCA) branches to form the right marginal artery (RMA) anteriorly. In the remaining 80-85% of individuals, it branches into the posterior interventricular artery (PIv) posteriorly.
The venous drainage of the heart is mostly through the coronary sinus – a large venous structure located on the posterior aspect of the heart. The cardiac veins drain into the coronary sinus, which in turn, empties into the right atrium. There are also smaller cardiac veins which pass directly into the right atrium.
The main tributaries of the coronary sinus are:
The coronary arteries generally travel over the area they perfuse. Here is the description of their anatomical course:
The RCA passes to the right of the pulmonary trunk and runs along the coronary sulcus before branching. The right marginal artery arises from the RCA and moves along the right and inferior border of the heart towards the apex. The RCA then continues to the posterior surface of the heart and runs along the coronary sulcus. The posterior interventricular artery branches from the RCA and follows the posterior interventricular groove towards the apex of the heart.
The LCA passes between the left side of the pulmonary trunk and the left auricle. The LCA divides into the anterior interventricular branch and the circumflex branch. The anterior interventricular branch (LAD) follows the anterior interventricular groove towards the apex of the heart and continues on the posterior surface to anastomose with the posterior interventricular branch. The circumflex branch follows the coronary sulcus to the left border and onto the posterior surface of the heart, giving rise to the left marginal branch which follows the left border of the heart.
Coronary artery disease (CHD), also known as coronary heart disease, is a leading cause of death in both the UK and worldwide. CHD occurs when there is reduced blood flow to the myocardium and can have several causes and consequences. Narrowing and blockage of the coronary arteries can cause reduced blood flow to the heart and be due to atherosclerosis, thrombosis, high blood pressure, diabetes, or smoking.
The coronary circulation, therefore, plays an essential role in providing nourishment to the entire body, and any disruption can be devastating. Understanding the anatomical course of coronary arteries and veins, as well as the clinical relevance of coronary artery disease, is essential for the prevention and treatment of this leading cause of death.
The body's circulatory system serves to provide nutrients and oxygen to all parts of the body - including the heart. The coronary circulation refers to the vessels which supply and drain the heart. Due to the encircling nature of the vessels that feed the heart - much like a crown - they are aptly named coronary arteries. This article will further explore the naming, distribution, and clinical relevance of vessels in the coronary circulation.
Coronary Arteries
There are two primary coronary arteries - the left and right coronary arteries - which branch to supply the entire heart. They emerge from the aortic sinuses, which are small openings located in the aorta behind the left and right flaps of the aortic valve. During the diastolic period, the back-flow of blood fills the valve pockets and enters the coronary arteries.
The left coronary artery (LCA) branches to provide the left anterior descending (LAD) artery, also referred to as the anterior interventricular artery. It then gives off the left marginal artery (LMA) and the left circumflex artery (Cx). In 20-25% of individuals, the left circumflex artery also supplies the posterior interventricular artery (PIv).
The right coronary artery (RCA) offers the right marginal artery (RMA) anteriorly. In 80-85% of individuals, it also provides the posterior interventricular artery (PIv) posteriorly.
Cardiac Veins
The venous drainage of the heart primarily occurs through the coronary sinus, a large venous structure found on the posterior aspect of the heart. Directly into the right atrium, other smaller cardiac veins are also present.
The main tributaries of the coronary sinus are the great cardiac vein (anterior interventricular vein), small cardiac vein, and middle cardiac vein (posterior interventricular vein). The great cardiac vein is the largest tributary of the coronary sinus, originating at the apex of the heart and ascending in the anterior interventricular groove. It then curves to the left and continues onto the posterior surface of the heart, gradually enlarging to form the coronary sinus. The small cardiac vein is situated on the anterior surface of the heart, in a groove between the right atrium and right ventricle. It travels within this groove to the posterior surface of the heart, where it empties into the coronary sinus. The middle cardiac vein begins at the apex of the heart, ascending in the posterior interventricular groove and emptying into the coronary sinus.
The coronary circulation is vitally important to the functioning of the heart. A blockage in one of the coronary arteries can lead to decreased oxygen supply to the heart, resulting in reduced blood flow. This can have serious consequences such as angina pectoris - a transient pain felt across the chest due to lack of oxygen on exercise. If left untreated, angina can progress to more severe outcomes such as a myocardial infarction, where a section of the heart is unable to beat due to sudden occlusion.
A blockage in a coronary artery can be quickly and accurately identified by performing a coronary angiogram. This involves the insertion of a catheter into the aorta via the femoral artery, and the injection of a contrast dye into the coronary arteries for imaging purposes. Following identification of the blockage, immediate treatment can be carried out with a coronary angioplasty. This procedures requires the inflation of a balloon within the affected artery, which pushes aside the atherosclerotic plaque and restores the blood flow to the myocardium. The artery may also be supported by the insertion of an intravascular stent.
In summary, the coronary circulation consists of two main coronary arteries and their accompanying veins, which are essential to supplying the heart with oxygen and nutrients. Blockages in the coronary arteries can be identified through a coronary angiogram procedure, and treated with a coronary angioplasty.
The posterior cardiac vein is a vein located on the posterior surface of the left ventricle. This vein lies to the left of the middle cardiac vein and empties into the coronary sinus.
In general, the area of the heart which a particular artery passes over will be the area that it perfuses. The coronary arteries provide the main source of blood supply to the heart, and the following paragraphs describe the route of each coronary artery in more detail.
The right coronary artery (RCA) passes to the right of the pulmonary trunk and runs along the coronary sulcus. At this point it divides to form the right marginal artery which lies along the right and inferior border of the heart and continues to the apex. The RCA continues to the posterior surface and runs along the coronary sulcus, from where the posterior interventricular artery arises and follows the posterior interventricular groove to the apex of the heart.
The left coronary artery (LCA) passes between the left side of the pulmonary trunk and the left auricle. It then divides into the anterior interventricular branch (also known as the left anterior descending, or LAD) which follows the anterior interventricular groove to the apex, and the circumflex branch which follows the coronary sulcus to the left border of the heart. This gives rise to the left marginal branch which proceeds along the left border of the heart.
Coronary artery disease (also known as coronary heart disease, or CHD) describes a reduction in blood flow to the myocardium, and is a leading cause of death both in the UK and internationally. Though there are a number of potential causes, the most common include atherosclerosis, thrombosis, high blood pressure, diabetes, and smoking.
A reduction in blood flow can lead to a range of consequences, the most common of which is angina pectoris. Angina is a transient chest pain that may be felt upon exercise due to a lack of oxygen supplied to the heart. It occurs as the coronary arteries fill during the diastolic period of the cardiac cycle, however exercise can reduce this period, meaning that there is less time for blood to flow and overcome any blockages. Left untreated, angina may lead to a myocardial infarction (MI), which is a sudden occlusion of an artery and resulting necrosis of the myocardium.
The appearance of an MI on the electrocardiogram (ECG) leads can be used to locate the artery that has been occluded. The following table provides a breakdown of the ECG leads on which an MI may change, and the artery in question:
A blockage in a coronary artery can be rapidly identified by performing a coronary angiogram. This imaging modality involves the insertion of a catheter into the aorta via the femoral artery, injecting contrast dye into the coronary arteries, and obtaining an x-ray based image to visualise any blockages. Immediate treatment of a blockage can be performed through a coronary angioplasty, which involves the inflation of a balloon within the affected artery to push aside the atherosclerotic plaque and restore blood flow. The artery may then be supported by the addition of an intravascular stent.
The following table provides an overview of the major arteries and veins associated with the heart. Each artery and it’s corresponding vein drainage region is identified within the table.
Artery Region supplied Vein draining region Right coronary Right atrium, SA and AV nodes, Posterior part of interventricular septum (IVS) Small cardiac vein, Middle cardiac vein Right marginal Right ventricle, Apex Small cardiac vein, Middle cardiac vein Posterior interventricular Right ventricle, Left ventricle, Posterior 1/3 of IVS Left posterior ventricular vein Left coronary Left atrium, Left ventricle, IVS, AV bundles Great cardiac vein Left anterior descending Right ventricle, Left ventricle, Anterior 2/3 IVS Great cardiac vein Left marginal Left ventricle Left marginal vein, Great cardiac vein Circumflex Left atrium, Left ventricle Great cardiac vein
The right coronary artery supplies blood to the right atrium, the sinoatrial and atrioventricular nodes of the heart, and the posterior part of the interventricular septum (IVS). Its corresponding veins that drain the blood from the supplied regions are the small cardiac vein and the middle cardiac vein. The right marginal artery gives blood to the right ventricle and the apex. The same veins mentioned above are responsible for draining blood from the supplied regions.
The posterior interventricular artery supplies blood to the right ventricle, left ventricle, and the posterior one-third of the IVS. The left posterior ventricular vein is the vein responsible for draining the supplied regions. The left coronary artery gives blood to the left atrium, left ventricle, IVS, and AV bundles. The great cardiac vein is responsible for draining the supplied regions from the left coronary artery.
The left anterior descending artery gives blood supply to both the right ventricle and the left ventricle, as well as the anterior two-thirds of the IVS. Once again, the great cardiac vein is the responsible vein for draining the regions supplied by the left anterior descending artery. The left marginal artery provides blood supply to the left ventricle and the veins responsible for draining the regions supplied are the left marginal vein and the great cardiac vein.
Lastly, the circumflex artery supplies blood to the left atrium and left ventricle, and the great cardiac vein is responsible for draining this supplied region. In summary, this table of the major arteries and veins associated with the heart provides an insight into the vasculature of the heart.
