The Great Arteries

Arterial relationships are independent of both the ventriculoarterial connection and infundibular morphology. There are two principal aspects the description of the great arteries, these being the interrelationships of the aortic and pulmonary valves and those of the ascending portions of the great arteries one to another. The main pulmonary artery usually spirals round the aorta, but, in many hearts, particularly those with abnormal ventriculoarterial connections, the great arteries arise in parallel fashion. Usually, the aorta arches superiorly to the main pulmonary artery, but even this arrangement is not invariable since cases have been seen where the right main pulmonary artery passes above the aortic arch.

The Aorta

The aorta, the major systemic arterial trunk of the normal heart, has an intrinsic structure not markedly different from that of the main pulmonary artery. It is distinguished from the main pulmonary artery by its branching pattern. The origin at the ventriculoarterial junction is characterized by the three sinuses which support the semilunar attachments of the aortic valve. Two of these sinuses usually give rise to the coronary arteries. These sinuses, without exception, have been opposite the main pulmonary artery, irrespective of the origin and relationship of the aorta to the main pulmonary artery. These two sinuses can be termed the facing sinuses. The non-coronary sinus is then termed the non-facing sinus. In the normal heart, the sinus giving rise to the right coronary artery can simply be called the right-facing sinus, while giving rise to the left coronary artery is the left-facing sinus. It helps, however, to use a convention for naming the coronary sinuses which works irrespective of which coronary artery they give origin to and irrespective of the relation of the aorta to the main pulmonary artery. Such a convention is provided by the suggestion of Gittenberger-de-Groot and her colleagues that the observer should consider himself as standing in the non-facing sinus and looking into the two coronary sinuses. The sinus to the right hand is then conventionally described as 'Sinus No. 1' while the other is 'Sinus No. 2'. Since it is still possible to forget the definitions of No. 1 and No. 2, these sinuses are best described in terms of their left and right facing position. This convention is of most value in assessing hearts with abnormal ventriculoarterial connections, such as in complete TGA or double outlet right ventricle.

The ascending portion of the aorta in the normal heart gives rise to the innominate left common carotid, and left Subclavian arteries. The aortic arch then continues at the isthmus, which extends to the junction of the aortic arch with the arterial duct. The duct is a wide channel in the heart of the fetus and the newborn but closes rapidly shortly after birth. It is represented subsequently by the attachment of the arterial ligament to the underside of the arch. The aortic arch itself then continues as the descending thoracic aorta, which gives rise to the bronchial and intercostal arteries before piercing the diaphragm to become the abdominal aorta.

The main pulmonary artery

The main pulmonary artery has a very simple branching pattern, dividing into the right and left pulmonary arteries. The trunk in the fetus continues as the arterial duct into the descending aorta, the right and left pulmonary arteries being side branches from the flow pathway from the duct to the aorta. After birth, with closure of the arterial duct, this arrangement rapidly becomes molded into the bifurcation seen in the normal child and adult.

The coronary arteries

The myocardium is supplied with its own system of arteries, capillaries, veins and lymphatics. The coronary arteries are the first branches of the aorta. There are two major coronary arterial branches from the aorta which arise from two of the three sinuses of Valsalva, permitting the sinuses to be named as right coronary and left coronary, respectively. The coronary arteries usually arise within the expanded portion of the appropriate sinus. Origin of an artery above the commissural ring of the aorta (in other words from the tubular ascending aorta) is considered to be a congenital malformation. The two coronary arteries have major differences in their branching pattern once they have emerged from their sinuses and this establishes their distinction as right or left.

The right coronary artery runs an extensive course around the orifice of the tricuspid valve. It emerges from the right sinus to achieve a position in the transverse sinus above the supraventricular crest of the right ventricle. In this initial part of its course, it usually gives off the sinus nodal artery into the atrial musculature and the infundibular (or conal) artery into the ventricular muscle mass. The artery then runs to the acute margin of the heart where it gives rise to the acute marginal artery of the right ventricle and, usually, a lateral atrial artery. Continuing around the tricuspid orifice, it gives off a varied number of smaller ventricular branches before, in the majority of hearts, it ends in the posterior interventricular groove. The area of junction of the posterior interventricular and the atrioventricular grooves is generally called the crux of the heart. The posterior interventricular artery is given off at this point in most hearts. When supplying the posterior artery, the right coronary artery itself makes a U-turn into the area of the atrioventricular muscular septum and gives off the artery to the atrioventricular node from the apex of the U. It then continues on to the diaphragmatic surface of the left ventricle where it supplies ventricular branches.

The left coronary artery has a shorter course. It emerges into the left margin of the transverse sinus beneath the left atrial appendage and extends for only one or two centimeters before branching into the circumflex and anterior interventricular branches. In a proportion of hearts, the main stem divides into three branches. The third artery has previously been described as the intermediate artery, but is now more customary (following the conventions of the National Heart, Lung and Blood Institute) to describe it as the first diagonal branch of the left anterior descending coronary artery. The anterior artery itself runs down the anterior interventricular groove, often buried, in part, within the musculature, where it is termed bridging. The left anterior descending coronary artery gives off a series of branches which pass perpendicularly into the anterior septum, the septal perforating arteries. The LAD artery supplies infundibular branches to the outflow component of the right ventricle, these often anastomosing with the branches from the right coronary artery. It also gives rise to a varied number of diagonal arteries which supply the anterior free wall of the left ventricle. The circumflex coronary artery gives rise to the sinus nodal artery from its initial course in almost half of all hearts. The rest of its course is variable. In some hearts it terminates almost immediately, under which circumstances it often gives off the atrial circumflex artery which runs in the atrial myocardium around the mitral orifice. More usually the circumflex artery continues to the obtuse margin of the left ventricle and breaks up into the obtuse marginal arteries. These are often embedded within the muscle of the left ventricle. In a small proportion of hearts, the circumflex artery continues all the way round the mitral orifice and hugs closely the annulus of the valve. It then gives rise to both the posterior interventricular artery and the artery to the atrioventricular node. This arrangement is called left dominance, in contrast to the much more common pattern of right dominance. In still other hearts, both the right and circumflex arteries may supply the diaphragmatic surface without there being a prominent posterior interventricular artery. The latter arrangement is termed a balanced circulation.