The cells of the developing myocardium initially receive nourishment directly from circulating blood in the ventricular cavity. As the myocardium thickens and develops, the presence of multiple trabeculations allows close proximity of the myocardial cells to the ventricular cavity. These trabeculations then develop into a sinusoidal system that continues to minimize diffusion distance between the myocytes and the circulation. While previously these sinusoids were thought to be the forerunners of the coronary vascular system, but new data have provided evidence for an epicardial origin of the coronary vascular system (7).

The new model of coronary vascular development (7) begins with formation of a proepicardial profusion by cells from the primordial liver. These cells establish the proepicardium and epicardial cells and then migrate over the surface of the heart. The epicardial cells invade the forming subepicardial matrix and form the coronary vascular plexus. The epicardial cells then undergo epithelial mesenchymal transformation by an as yet undefined mechanism that probably involves multiple growth factors. Nascent capillaries then are associated with subepicardial mesenchymal cells to form mature vessels, which fuse and grow inward to penetrate the aorta rather than coronary buds from the aortic sinuses fusing with the coronary vessels (8).

The new experimental data on the development of the coronary system implicate multiple growth factors as well as adhesion molecules and chemotactic factors in this complicated coordinated migration and transformation of cells to form coronary vessels. The presence of congenital anomalies of coronary arteries suggests abnormalities in these signaling pathways or alterations in local factors that direct coronary vessel development.

The right and left coronary arteries arise from the right and left aortic sinuses of Valsalva (see Fig. 32.1). Usually they come from the middle of the sinuses, but they may arise from the sinotubular junction or even above it. The position of the ostium does not appear to affect the flow through it. The ostia may be round, oval, or elliptical. The arteries are usually perpendicular to the aortic wall; that is, they are radially arranged relative to the center of the aorta.

Separate origin of the conus branch of the right coronary artery occurs commonly (11). The corresponding anomaly on the left side—separate origins of the left anterior descending and left circumflex coronary arteries—occurs in about 1% of people and is more frequent with bicuspid aortic valves (11). Neither of these anomalies appears to have any clinical consequences.

In 5% to 20% of major coronary arterial anomalies, a single coronary artery arises from the aorta and then branches (17,24). Sometimes an atretic cord connects part of the artery to a sinus of Valsalva that has no ostium. About 40% of these anomalies are associated with other cardiac malformations, including transposition of the great vessels, tetralogy of Fallot, truncus arteriosus, coronary-cameral fistulas, and bicuspid aortic valves. The single artery can arise from either the right (Fig. 32.5A–C) or the left sinus of Valsalva (Fig. 32.5D–F) with many variations (24). The single coronary artery on either side can follow its usual course and then
continue on to supply the other side of the heart, or separate branches can arise from a main coronary artery and course posteriorly or anteriorly to supply the other side of the heart. Branches also can pass between the great vessels.

For the single coronary arteries arising from the right side, the right coronary can follow the course of the normal right coronary artery and continue as the left circumflex artery, which then gives off the left anterior descending coronary artery (see Fig. 32.5A). Alternatively, after the right coronary artery arises, a separate branch to the left side can arise that passes posterior to the aorta and gives rise to a circumflex vessel and a left anterior descending coronary artery (see Fig. 32.5B), or the separate branch can follow a course anterior to the right ventricular infundibulum, giving rise to the anterior descending coronary artery before continuing on as the circumflex (see Fig. 32.5C).

A single left coronary artery can display branching patterns similar to those on the right. A single left coronary artery can branch into the left anterior descending and left circumflex coronary arteries with the circumflex continuing across the crux to form the right coronary artery (see Fig. 32.5D). A separate right coronary vessel also can arise from the single left coronary artery and pass posterior to the aorta (see Fig. 32.5E) to reach the opposite side of the heart, or the vessel can pass anterior to the right ventricular infundibulum (see Fig. 32.5F). Most single coronary arteries produce no symptoms in the absence of severe atheroma (which is clearly more serious when there is only one main artery supplying the entire myocardium), but a small number of premature deaths have been reported with this anomaly (24). It is usually those variants in which a major branch passes between the aorta and the right ventricular infundibulum that are at greatest risk for sudden death (24), but other patterns can cause myocardial ischemia.

These are very rare (18) and have not been associated with premature or sudden death.

In this anomaly the left coronary artery arises from the pulmonary artery, usually from the left posterior facing sinus (Fig. 32.6) (Video 32.1). This anomaly was first described by pathologists in 1866 (30), and by 1962 Fontana and Edwards (31) had collected descriptions of 58 necropsies with this anomaly; most of these patients died at less than 13 months of age. The first report relating clinical and autopsy findings in a 3-month-old boy was by Bland et al. (32). The anomaly has thus been called the Bland–White–Garland syndrome.

In fetal life, this anomaly probably has no harmful effect: pressures and oxygen saturations are similar in the aorta and pulmonary
artery. Myocardial perfusion is presumably normal, and there is no stimulus to collateral formation (see Fig. 32.6A). After birth, however, the pulmonary artery contains desaturated blood at pressures that rapidly fall below systemic pressures. Therefore, the left ventricle, with its huge demand for oxygen, is perfused with desaturated blood at low pressures. Collateral flow is initially low. The left ventricular myocardial vessels dilate to reduce their resistance and increase flow, but soon coronary vascular reserve becomes exhausted and myocardial ischemia ensues. At first, ischemia is transient and occurs only with exertion such as feeding or crying, but further increases in myocardial oxygen demand lead to infarction of the anterolateral left ventricular free wall (see Fig. 32.6B), with resultant compromise of left ventricular function. This causes congestive heart failure, which is often made worse by mitral regurgitation secondary to a dilated mitral valve annulus or infarction and dysfunction of the anterolateral papillary muscle. Collateral vessels between the normal right and abnormal left coronary artery enlarge, and with the increased flow so does the right coronary artery itself (see Fig. 32.6C; Video 32.1). However, because the left coronary artery is connected to the low-pressure pulmonary artery, the collateral flow tends to pass into the pulmonary artery rather than into the higher resistance myocardial blood vessels; there is a pulmonary–coronary steal with a left-to-right shunt. The shunt is usually relatively small in terms of cardiac output but relatively large in terms of coronary flow. In about 15% of these patients, myocardial blood flow can sustain myocardial function at rest or even during exercise. These are the patients who reach adult life (33).