Coronary Circulation Big Picture

Although blood fills the chambers of the heart, the myocardium is so thick that it requires its own artery-capillary-vein system, called the "coronary circulation," to deliver and remove blood to and from the myocardium. The vessels that supply oxygenated blood to the myocardium are known as coronary arteries. The vessels that remove the deoxygenated blood from the heart muscle are known as cardiac veins.

CORONARY ARTERIES AND ASSOCIATED BRANCHES

The coronary arteries and branches course along the epi-cardium in the cardiac sulci and interventricular grooves (Figure 4-2). Each coronary artery sends branches to the heart muscle.

V Myocardial infarction. Coronary vessels are classified as an "end circulation"; that is, they may not anastomose with each other. Therefore, blockage of any of these vessels is detrimental because once a coronary artery is blocked cardiac tissue supplied by that vessel is damaged. Blood flow in the coronary arteries is maximal during diastole (ventricular relaxation) and minimal during systole (ventricular contraction) because of the compression of the blood vessels in the myocardium during systole. All coronary arteries branch from either the left or the right coronary arteries. ▼

LEFT CORONARY ARTERY The left coronary artery arises from the aorta, superior to the left cusp of the aortic valve, and is shorter than the right coronary artery. However, the branches from the left coronary artery distribute blood to a larger area of myocardium. The left coronary artery supplies most of the left ventricle, left atrium, bundle of His, and the anterior aspect of the interventricular septum. The left coronary artery gives rise to the following two sizable branches:

Left anterior descending artery. Also called the anterior interventricular artery and is often referred to by the acronym LAD. It supplies the anterior region of the left ventricle, including the anterolateral myocardium, apex, anterior interventricular septum, and the anterolateral papillary muscle.

Left circumflex artery. Wraps around the left side to the posterior side of the heart. The circumflex artery supplies the posterolateral side of the left ventricle and gives off the left marginal branches which also supply the left ventricle.

RIGHT CORONARY ARTERY The right coronary artery arises from the aorta, superior to the right cusp of the aortic valve.

The right coronary artery travels along the right AV groove, between the root of the pulmonary trunk and the right auricle, and supplies the right atrium, right ventricle, the sinuatrial (SA) node, and the AV node. The right coronary artery gives rise to the following branches:

Posterior descending artery. Supplies the inferior wall, posterior interventricular septum, and the posteromedial papillary muscle. In a few cases, the circumflex artery gives off the posterior descending artery.

Right marginal artery. Supplies the right ventricular wall. SA nodal artery. Passes between the right atrium and the opening of the superior vena cava and supplies the SA node. In a few cases, the circumflex artery supplies the SA nodal artery.

CORONARY DOMINANCE Coronary dominance is determined by which of the left and right coronary arteries gives rise to the posterior interventricular artery, which supplies the posterior interventricular semptum and part of the left ventricle. The dominant artery is usually the right coronary artery.

CARDIAC VEINS

The cardiac veins and associated tributaries are the major veins of the coronary circulation and run parallel to the arteries (Figure 4-2). They drain blood from the heart wall. The cardiac veins are as follows:

The coronary sinus is the largest vein draining the heart muscle and lies in the coronary sulcus. The coronary sinus collects most of the venous return from the great, middle, and small cardiac veins and returns the venous blood to the right atrium. The coronary sinus opening in the right atrium is superior to the septal leaflet of the tricuspid valve.

• Great cardiac vein. Begins at the apex of the heart and ascends in the anterior interventricular groove, parallel to the left anterior descending artery, and drains into the coronary sinus.

• Middle cardiac vein. Begins at the apex of the heart and ascends in the posterior interventricular sulcus, parallel to the posterior interventricular artery, and drains into the coronary sinus.

• Small cardiac vein. Courses along the acute margin of the heart, along with the marginal artery, and then courses posteriorly into the coronary sinus.

The anterior cardiac veins drain the anterior portion of the right ventricle, cross the coronary groove, and empty directly into the right atrium. Anterior cardiac veins do not drain into the coronary sinus.

Superior vena cava

Pulmonary valve

Ascending aorta

Branch to sinuatrial node Right coronary a. Right atrium

Left pulmonary vv.

Circumflex a

Great cardiac v.

Posterior v. of left ventricle

Right posterolateral a

Left ventricle

Superior vena cava

Pulmonary valve

Superior left pulmonary v. Left auricle

Ascending aorta

Branch to sinuatrial node Right coronary a. Right atrium

Anterior interventricular (left anterior descending) a.

Left ventricle

Anterior cardiac a. and v.

Superior vena cava

Right ventricle

Superior left pulmonary v. Left auricle

Left coronary a. -i-Circumflex a.

Left (obtuse) marginal a.

Great cardiac v.

Small cardiac v. Right marginal a

Anterior cardiac a. and v.

Anterior interventricular (left anterior descending) a.

Left ventricle

Left atrium

Superior vena cava

Left pulmonary

Left atrium vv.

Circumflex a

Posterior v. of left ventricle

Left ventricle

Small cardiac v.

Right ventricle

Middle Posterior Left cardiac v. interventricular a. coronary a

Right ventricle

Branch to sinuatrial node Right pulmonary vv.

Right atrium Coronary sinus

Inferior vena cava Right coronary a.

Cardiac apex

Small cardiac v.

Pulmonary valve

Aortic valve

Right ventricle

Middle Posterior Left cardiac v. interventricular a. coronary a

Mitral valve

Aortic valve

Mitral valve

Right coronary a.

Tricuspid valve

Coronary sinus

Posterior interventricular branch of right coronary a.

Right coronary a.

Tricuspid valve

Coronary sinus

Posterior interventricular branch of right coronary a.

Figure 4-2: Anterior (A), posterior (B), and superior (C) views of the coronary arteries and cardiac veins.

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