Intraoperatively, the anatomy of the heart is viewed from the right side of the supine patient via a median sternotomy incision. The structures initially seen from this perspective include the superior vena cava, right atrium, right ventricle, pulmonary artery, and aorta. Medial displacement of the right side of the heart exposes the left atrium and right pulmonary veins. Medial rotation from the left exposes the left ventricle apex, left pulmonary veins, and left atrium. (See the images below.)
The superior vena cava and inferior vena cava drain systemic venous blood into the posterior wall of the right atrium. The internal wall of the right atrium is composed of a smooth posterior portion (into which the vena cavae and coronary sinus drain) and a ridgelike, muscular anterior portion. The coronary sinus drains coronary venous blood into the anteroinferior portion of the right atrium. The thebesian valve is located at the orifice of the coronary sinus. The limbus of the fossa ovalis is located on the medial wall of the right atrium and circumscribes the septum primum of the fossa ovalis anteriorly, posteriorly, and superiorly. (See the image below.)
The aorta begins at the base of the heart and typically branches to form the coronary arteries just distal to the aortic valve. In patients with cardiac malformations, the aorta almost always can be identified by tracing it back from the brachiocephalic arteries, which only very rarely originate from the pulmonary artery.
The main pulmonary artery branches into the pulmonary arterial system. In patients with aberrant cardiac anatomy with a patent ductus arteriosus, accurate identification of the pulmonary artery can be difficult using angiography, because the pulmonary artery becomes opaque during aortic injection. To differentiate the pulmonary artery from the aortic valve, remember that the pulmonary artery almost never gives off brachiocephalic branches.
The ventricular septum is divided into a muscular section (inferior) and a membranous section (superior). The muscular portion makes up the left and right ventricular walls. The membranous septum, also termed the pars membranacea, is a fibrous structure partially separating the left ventricular outflow tract from the right atrium and ventricle.
The atrioventricular (AV) septum, located behind the right atrium and left ventricle, is divided into 2 portions: a superior portion (membranous) and an inferior portion (muscular). Inside the left ventricle, the muscular component makes up part of the outlet septum. The AV node lies in the atrial septum, juxtaposed to the membranous and muscular portions of the AV septum.
The sinoatrial (SA) node occupies a 1-cm2 area on the lateral surface of the junction of the superior vena cava and right atrium near the crista terminalis. The sinus node is found superficially at the anterolateral aspect of the junction between the superior vena cava and the right atrial appendage. In rare cases, the SA node may be found medially along the ridge of the atrial-caval junction. [2, 3, 4]
The spread of electrical activation from the sinus node extends toward the AV node via Purkinjelike pale cells in atrial muscle bundles. Anterior, medial, and posterior interatrial conduction pathways arise from the SA node. The anterior and medial pathways are located anterior and posterior to the foramen ovale; the posterior pathway is situated caudal to the foramen ovale.
The AV node is situated directly on the right atrial side of the central fibrous body in the muscular portion of the AV septum, just superior and anterior to the ostium of the coronary sinus. Measuring approximately 0.1 cm x 0.3 cm x 0.6 cm, the node is flat and oval. The node’s left surface is juxtaposed to the mitral anulus.
Cardiac valves are categorized into 2 groups, based on function and morphology. Mitral and tricuspid valves make up the AV group; aortic and pulmonary valves make up the semilunar group. On cross section, the aortic valve is located in a central location, halfway between the mitral and tricuspid valves. The pulmonary valve is positioned anterior, superior, and slightly to the left of the aortic valve. The tricuspid and mitral anuli merge and fuse with each other and with the membranous septum to form the fibrous skeleton of the heart. (See the image below.)
The 2 main coronary arteries are the right and left. However, from a surgical standpoint, 4 main arteries are named: the left main, the left anterior descending, and the left circumflex (LCX) arteries (which are all branches of the left coronary artery) and the right coronary artery (RCA). The RCA and LCXs form a circle around the AV sulci. The left anterior descending and posterior descending arteries form a loop at right angles to this circle; these arteries feed the ventricular septum. The LCX gives off several parallel, obtuse, marginal arteries that supply the posterior left ventricle. The diagonal branches of the left anterior descending artery supply the anterior portion of the left ventricle.
The term dominance is used to refer to the origin of the posterior descending artery (PDA). When the PDA is formed from the terminal branch of the RCA (>85% of patients), it is termed a right-dominant heart. A left-dominant heart receives its PDA blood supply from a left coronary branch, usually the LCX. This is often referred to as a left posterolateral (LPL) branch.
The coronary sinus is a short (approximately 2 cm) and wide venous channel that runs from left to right in the posterior portion of the coronary groove. The opening of the coronary sinus is located between the right AV orifice and the inferior vena cava orifice. The coronary sinus drains all venous blood from the heart except the blood carried from the anterior cardiac veins. The coronary sinus receives outflow from the great cardiac vein on the left and from the middle and small cardiac veins on the right.
The great cardiac vein is the main tributary of the coronary sinus and drains areas of the heart supplied by the LCA. It begins at the apex of the heart, ascends in the anterior interventricular groove with the LAD artery, and enters the left end of the coronary sinus.
The middle and small cardiac veins drain most of the heart supplied by the RCA. The middle cardiac vein begins at the apex, ascends in the posterior interventricular groove with the posterior interventricular artery, and empties into the right side of the coronary sinus. The small cardiac vein runs in the coronary groove along with the marginal branch of the RCA; this vein usually empties into the coronary sinus but may empty directly into the right atrium.
Coronary veins of the right ventricle drain directly into the right atrium; thebesian veins drain into the right ventricle. The left ventricle venous return drains into the coronary sinus located next to the septal portion of the tricuspid valve annulus.