Video: Coronary arteries and cardiac veins

Ahh, the heart. Like a tireless DJ, it pumps the rhythm of life with a lively beat. Now you might be familiar with how the heart delivers blood to the other major organs in the body, but have you ever wondered exactly which vessels are responsible for delivering oxygen and nutrients and disposing of waste products from the heart itself?

Enter the coronary arteries and cardiac veins, collaborating on a behind-the-scenes remix, supplying and draining the heart, ensuring it keeps on spinning the beats of life. So without further ado, let's delve deeper into the vasculature of the heart and investigate the coronary arteries and cardiac veins.

So in this tutorial, we'll first be looking at the coronary arteries and their main branches, which nourish the heart muscle, also known as the myocardium, followed by the main cardiac veins, which drain deoxygenated blood and remove wastes from the myocardium. So let's get into the heart of the matter and begin by looking at the coronary arteries first.

There are two major parent coronary arteries – the left coronary artery and the right coronary artery. These two arteries arise from aortic sinuses of the aortic root, which are dilations of the aortic wall found just above the cusps of the aortic valve and they give off several major branches that supply the myocardium which we will discuss in this tutorial. So let's have a look at the left coronary artery and its branches first.

The left coronary artery arises from the left coronary aortic sinus and runs between the auricle of the left atrium and the root of the pulmonary trunk, which we can just about see the base of here. After about two centimeters, the left coronary artery bifurcates into two main branches. We have the circumflex artery, which we can see a small segment of here, as well as the anterior interventricular artery.

Looking at the circumflex artery first, we can see that it runs on the left side of the heart coursing within the coronary sulcus, also known as the atrioventricular groove. We can get a better appreciation of its course from this superior view, where we can see it curving around the left border of the heart onto its inferior surface.

The circumflex artery itself gives of several branches including the left marginal artery, several atrial branches like this one seen here, and an inferior left ventricular branch as well. Together, these branches supply the inferolateral parts of the left ventricle and the left atrium.

The other main branch of the left coronary artery is the anterior interventricular artery, also commonly referred to by clinicians as the left anterior descending artery, or the LAD. This branch runs along the anterior interventricular sulcus to the apex of the heart, where it often anastomoses with the inferior interventricular artery, situated on the inferior surface of the heart.

The anterior interventricular artery gives off several anterior ventricular branches which are mostly unnamed, except for the largest example which supplies the left ventricle, sometimes called the diagonal branch, whilst there are also septal branches, which are not visible here, and occasionally a small conal branch. Together, the anterior interventricular artery and its branches supply the anterior, lateral, and apical walls of the left ventricle, a small part of the right ventricle adjacent to the anterior interventricular sulcus, as well as the anterior two-thirds of the interventricular septum.

The anterior interventricular artery is the most commonly occluded artery of the heart, and as it supplies such a large part of the myocardium, occlusion of this vessel can lead to severe infarction.

Next we're going to look at the right coronary artery. This artery arises from the right coronary aortic sinus and travels through the coronary sulcus, continuing around to the inferior surface of the heart. During its course, it gives off several branches, including the sinuatrial nodal artery, conal branch, atrial branches, ventricular branches, right marginal artery, and inferior interventricular artery.

Phew, that sounds like a lot! Fortunately, their names give us insight into their location and supply to make it a bit easier to learn. So let's go and take a closer look at each of these branches.

The conal branch is first to arise from the right coronary artery. It runs between the base of the conus arteriosus and the superior part of the right ventricle. This branch, as the name suggests, supplies the region of the conus arteriosus of the right ventricle. Within millimeters after emerging from the aorta, the right coronary artery also gives off the sinuatrial nodal branch which extends to and supplies – yep, you guessed it – the sinuatrial node. However, it should be noted that in about 40 percent of the population, it has been known to arise from the circumflex branch of the left coronary artery instead. Also arising from the right coronary artery are a series of atrial branches which are commonly grouped into anterior, lateral, and inferior branches. These branches supply the right atrium of the heart.

The next prominent branch of the right coronary artery is the right marginal branch which runs close to the inferior border of the heart along the right ventricle. This branch, in addition to several smaller anterior ventricular branches, supply the right ventricle of the heart.

Finally, the inferior interventricular branch, also commonly known as the posterior descending artery, or PDA, runs along the inferior interventricular sulcus and is the terminal branch of the right coronary artery. It supplies blood to the inferior part of the interventricular septum and adjacent surfaces of both ventricles.

Now it should be noted that the inferior interventricular artery arises from the right coronary artery only in individuals considered to be right-heart dominant. But, what does this mean and what is coronary dominance? Well, it definitely does not mean that we have a heart on each side of our body. Instead, anatomists and clinicians alike refer to right or left dominance with respects to which coronary artery gives rise to the inferior interventricular artery.

If it is via the right coronary artery, then the heart would be described as being right dominant, which is actually the case for about 60 to 80 percent of the population. In about 5 to 10 percent of individuals, the opposite is true, where it arises from the circumflex branch of the left coronary artery, therefore resulting in a left-dominant heart. In 10 to 20 percent of cases, both coronary arteries give rise to the inferior interventricular branch which is termed codominance.

And that takes care of the arterial supply of the heart. Now let's move on to the venous drainage of the heart which is performed by the cardiac veins.

The veins of the coronary circulation can be organized into two groups – the greater and smaller cardiac venous systems. The greater cardiac venous system comprises the large veins found in the subepicardiac, or outer, myocardium and their tributaries. The smaller cardiac venous system refers to the small veins in the subendocardiac, or inner, myocardium which empty directly into the atria and ventricles. So let's take a look at the major veins of these systems, starting with the greater cardiac venous system first.

Drainage through the greater cardiac venous system is primarily governed by the coronary sinus. As we can see here, the coronary sinus is located on the inferior aspect of the left atrium, coursing within the left inferior part of the coronary sulcus. Its function is to drain the majority of deoxygenated blood of the heart into the right atrium. It is a particularly wide, channel-like vein that is initially formed by the confluence of two veins. However, it also receives a number of other tributaries, all of which we will discuss in a moment.

The great cardiac vein is the larger of the two major veins that form the coronary sinus. It originates at the apex of the heart and runs through the anterior interventricular sulcus next to the anterior interventricular artery. As it reaches the coronary sulcus, it passes to the left, accompanying the circumflex artery, before eventually draining into the coronary sinus. The great cardiac vein drains the anterior surface of both ventricles and the left atrium.

Now the great cardiac vein itself commonly receives the left marginal vein as a tributary, which courses the left side of the heart, and it also drains part of the left ventricular myocardium.

Now the vein which joins the great cardiac vein in forming the coronary sinus is the oblique vein of the left atrium. As the name suggests, this vein takes an inferior oblique course along the back of the left atrium to join the great cardiac vein in forming the coronary sinus. Unsurprisingly, this vein drains the left atrium.

The next tributary is the inferior vein of the left ventricle, also known as the posterior vein of the left ventricle. This cardiac vein can be found on the inferior surface of the left ventricle. This vein drains the inferior and lateral walls of the left ventricle into the coronary sinus.

One of the large tributaries to the coronary sinus is the middle cardiac vein, also known as the inferior interventricular vein. This vein ascends in the inferior interventricular groove and enters the coronary sinus on the opposite end to the great cardiac vein. It drains the inferior wall of both ventricles and the interventricular septum.

The next tributary to the coronary sinus is the small cardiac vein. It can be found in the coronary sulcus between the right atrium and the right ventricle and it drains the inferior part of the right atrium and right ventricle into the coronary sinus. It should be noted that the small cardiac vein sometimes receives the right marginal vein as a tributary, which we can see here on the inferior margin of the anterior surface of the heart. However, in approximately two-thirds of individuals, the right marginal vein drains deoxygenated blood from the lateral part of the right ventricle directly into the right atrium, rather than via the coronary sinus.

Phew! Well, that takes care of all the tributaries of the coronary sinus. I'm sure all of your time spent there won't be in vain.

Now you might have noticed that we haven't yet mentioned these veins on the anterior view of the heart, which are the anterior cardiac veins, also known as the anterior veins of the right ventricle. That's because these veins do not drain into the coronary sinus. Instead, they collect deoxygenated blood from the anterior part of the right ventricle and drain directly into the right atrium.

And those were the last of the veins of the greater cardiac venous system that we're covering in this tutorial. Now let's move on to discuss the smaller cardiac venous system.

Fortunately, the only veins to discuss within the smaller cardiac venous system are called the smallest cardiac veins or Thebesian veins. They are a complex network of small vascular channels and sinusoids located within the subendocardial part of the myocardium of all four chambers of the heart. They drain the inner third of the myocardium and empty directly into the four cardiac chambers, however, are the most prevalent in the right atrium and right ventricle.

And that concludes our tutorial on the coronary arteries and cardiac veins. To revise this content and ensure your time spent here was not in vain, check out our quiz and other learning materials in our study unit on this topic.