Coronary Arterial and Venous AnatomyCHAPTER 1

The circulatory system and coronary anatomy were described and illustrated many centuries ago (Figs. 1.1 and 1.2). For centuries though, the course, position and variations of the coronary arterial system were of interest only to anatomists and pathologists and of no interest to clinicians. However, with the development of coronary angiography, coronary bypass surgery, and more recently percutaneous coronary intervention, knowledge of the details of coronary arterial anatomy has become essential.

The left main coronary artery arises from the left sinus of Valsalva (Figs. 1.14 and 1.15) and passes leftward, posterior to the right ventricular outflow tract and anterior to the left atrial appendage, before bifurcating into the left anterior descending (LAD) and left circumflex coronary arteries. The subjacent position of these arteries to the left atrial appendage is important to electrophysiologists when performing ablations for arrhythmias. The length of the the left main coronary artery varies between 0.5–2.5 cm. The location of the ostium of the left coronary artery with respect to the sinotubular junction is: 48% of the time at the same level; 34% above the sinotubular junction; and 18% below the sinotubular junction. The left main coronary artery is absent in 0.5–1.0% of hearts. The left main coronary artery bifurcates into the LAD and left circumflex artery in approximately two-thirds of patients. In approximately one-third of patients the left main trifurcates and there is a third branch, called the ramus intermedius artery (Fig. 1.16), which supplies the anterolateral left ventricular wall.

The left anterior descending (LAD) artery arises from the left main coronary artery as a direct continuation and passes in the anterior descending interventricular groove distally toward the apex (Figs. 1.17 and 1.18). It terminates before or at the apex in 35% of hearts, and continues around the apex to the inferior interventricular groove of the heart (“wrap around LAD”) in 64% of hearts. It has a variable number of secondary branches to the right and left ventricles adjacent to the artery. The right ventricular branches are usually small and not constant in arrangement. Those to the left ventricle are termed diagonal branches. These branches supply the anterolateral wall and the anterior papillary muscle of the left ventricle. Occasionally, shortly after its origin, the LAD divides into two equal parallel vessels that pass in the anterior interventricular groove distally (referred to as a “dual LAD”).

The left circumflex coronary artery arises at right angles from the left main coronary and proceeds in the anterior atrioventricular groove, giving off small obtuse marginal branches to the left ventricular lateral wall and the left atrium (Fig. 1.21). The left circumflex artery terminates between the obtuse margin and the crux of the heart in 85% of cases, and at or beyond the crux in 15% of hearts. It may also continue down the inferior interventricular groove a variable distance as the posterior descending artery (PDA). Occlusion of the left circumflex artery will result in infarction of the lateral wall of the left ventricle.

The ostium of the right coronary artery (RCA) is in the right coronary sinus of the aortic valve. The RCA originates at the same level with respect to the sinotubular junction in 70% of hearts, above the level of the sinotubular junction in 20% of hearts, and below the level of the sinotubular junction in 10% of the hearts. The RCA then passes posterior to the right ventricular infundibulum and into the right anterior atrioventricular groove (Figs. 1.22A to C). In about 10% of the hearts the RCA terminates at or just beyond the acute margin of the heart, but usually it passes around to the inferior atrioventricular groove and then at the crux of the heart, down the inferior interventricular groove as the posterior descending coronary artery (PDA). In this more common situation, the heart is said to have a right dominant coronary system. In cases in which the RCA does not give off the PDA but is only a small artery that supplies the right ventricle, the RCA is referred to as a “non-dominant” RCA.

In the majority of patients the posterior descending artery (PDA) (more anatomically correct termed the inferior descending artery) is given off by the RCA, and the patient is said to have a “right dominant system”. In a minority of patients, the PDA is given off by the left circumflex artery and the patient is said to have a “left dominant system”. In 30% of the hearts there are either two parallel inferior descending arteries from the right coronary or one from the right and one from the circumflex coronary artery (Figs. 1.23A and B).

Arising at right angles from the extramural coronary arteries, the perforating branches in the ventricular walls form a complex network of resistance arteries that form a capillary meshwork around myocardial fibers. The perforating arteries vary in their course through the myocardium, branching off at right angles at all levels of the ventricular wall like the tines of a fork (Fig. 1.24). Some proceed to the subendocardium and then spread out parallel to the endocardium of the cardiac chambers. At the subendocardial level there are anastomosing vessels as well as end-arteries. There are also arterioluminal and venoluminal channels connecting terminal intramural arteries with the ventricular and atrial chambers that have different names depending on the connections and histology of the small vessels. The ostia of these vessels can be seen on examination of the endocardial surface of the ventricles and more prominently of the atria. A general name for these vessels that empty into the cardiac chambers is that of The besian veins or vessels.

The coronary venous system (Fig. 1.26) can be divided into two sections: the extramural veins that drain into the coronary sinus as well as the anterior cardiac veins that drain directly into the right atrial chamber, and the intramural or The besian veins that are at every level within the cardiac walls and are arranged parallel to the myocardial fibers. As with other veins, the cardiac veins have both unifoliate (one leaflet) and bifoliate (two leaflets) valves.

Not a proper vein histologically, the coronary sinus (Figs. 1.27 to 1.29) is a muscular conduit that is formed at the confluence of the oblique vein of the left atrium and the great cardiac vein near the obtuse margin of the heart. The coronary sinus then courses in the inferior left atrioventricular groove toward the right atrium and drains most of the left ventricular wall, as well as parts of the left and right atrium. Joining the coronary sinus is the oblique vein of the left atrium that passes between the left atrial appendage and the left pulmonary veins. The proximal end of the oblique vein is a tendon of Marshall, a vestige of the embryonic left anterior cardinal vein. However, if the embryonic vein remains open, it functions as a persistent left superior vena cava draining into the coronary sinus.

A major vein, the anterior interventricular vein is the most consistent of the coronary venous system. It originates at or near the left ventricular apex and ascends in the anterior interventricular groove, draining the apex and anterior wall of the left ventricle, the anterior two-thirds of the interventricular septum, and the adjacent right ventricular wall. As it reaches the anterior atrioventricular groove the vein passes leftward between the origin of the pulmonary trunk and the tip of the left atrial appendage. It continues as the great cardiac vein, receiving branches that drain the anterior left atrial wall and superior left ventricle, and then becomes the coronary sinus where the oblique vein of the left atrium enters the coronary sinus.

The middle cardiac vein (Fig. 1.30), also known as the inferior interventricular vein, drains the diaphragmatic wall of the left ventricle and the posterior third of the interventricular septum. At the inferior aspect of the left ventricular apex, the middle cardiac vein arises from one or two small superficial veins. Enlarging as it courses in the inferior interventricular groove toward the base of the heart, it usually drains into the coronary sinus near that conduit's entrance to the right atrium, and less often directly into the right atrium. From 2 to 6 veins drain the diaphragmatic and lateral left ventricular wall into the coronary sinus, the most consistent of these being the inferior left ventricular vein draining the diaphragmatic lateral wall of the left ventricle and the obtuse marginal vein draining the lateral wall of the left ventricle.

The small cardiac vein (also known as the right coronary vein) is present in about 70% of hearts. The small cardiac vein, when present, runs in the right inferior atrioventricular groove and terminates at the ostial opening of the coronary sinus or directly into the right atrium. It drains most of the walls of the right atrium, and in the absence of the right cardiac veins, the anterior surface of the right ventricle. In some hearts, the small cardiac vein receives the right marginal vein in which case it drains the anterior wall of the right ventricle.

The anterior cardiac veins, between 3 and 6 in number, drain most of the anterior and lateral wall of the right ventricle directly into the right atrium. Within this group is the right marginal vein, originating at or near the cardiac apex, and ascending along the acute margin of the heart, draining both the adjacent anterior and diaphragmatic surfaces of the right ventricle.

The walls of the right atrium are drained through small, largely intramural, vessels and intramural conduits. They predominantly drain through very small orifices directly into the right atrial cavity and are called The besian veins. The large intramyocardial tunnels, numbering from 1 to 3, are located variably but usually in the posterior and lateral atrial walls, and drain venous blood from the anterior cardiac veins and from the sinoatrial and atrioventricular nodes.

Our understanding of cardiovascular anatomy and physiology continues to advance, even in the current age. A detailed knowledge of normal coronary vascular anatomy is important to understanding the heart's circulation. It is critical to deciphering images of the pathologic anatomy in living patients.