Coronary circulation

BY DR. TEHMINA NARU

The heart has its own unique blood supply, more commonly known as the coronary circulation, which encircles the entire surface of the heart to supply its different regions. The vessels that deliver oxygen-rich 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

The two coronary arteries originate from the left side of the heart at the beginning (root) of the aorta, just after the aorta exits the left ventricle. The left coronary artery originates from the left aortic sinus, while the right coronary artery originates from the right aortic sinus. No artery arises from the posterior aortic sinus.

The left main coronary artery supplies the left atrium, interventricular septum, left ventricle and the anterior wall of the right ventricle. On the other hand, the right coronary artery supplies the right atrium, the right ventricle as well as the sino-atrial node.

The Coronary ArteriesThere are two major coronary arteries -right and left (Plate 4-22). The right coronary artery arises from the right coronary sinus of Valsava and runs down in the groove between the right atrium and the right ventricle. In Most hearts, its branches supply the sinus node, the atrioventricular node and bundle, the right ventricle and the inferior part of the left ventricle. The left coronary artery, which arises from the left coronary sinus of Valsava, soon divides into two large branches: The anterior descending branch which runs down between the two ventricle anteriorly, and the left circumflex branch which passes around in the groove between the left atrium and the left ventricle. The anterior descending artery supplies the interventricular septum and the anterior wall of the ventricle. The circumflex supplies the lateral and posterior aspect of the left ventricle. The major vessels traverse the external surface of myocardium, sending branches perpendicularly into the muscle mass. There are normally many small anastomoses between the coronary arteries, but these are of no functional importance. When an area of the heart become ischaemic, the anastomoses enlarge and then provide a collateral blood supply to the affected muscle which is often vital for its survival.

The arteries divide to form arterioles and capillaries similiar to those elsewhere in the body, and the venules and veins join to form larger venous channels. Virtually all the blood from the left coronary artery eventually drains into the coronary sinus; that from the right coronary artery drains mainly into the anterior cardiac veins. From these veins the blood passes into the right atrium.

he Coronary VeinsThe coronary veins drain mainly into the coronary sinus, which drains directly into the right atrium (Plate 4-24). There are some small veins that drain directly into the heart chambers. Generally, these drain into the right side of the heart