Joshua Thomas
Jeremy Webb
The coronary arteries provide oxygenated blood to the myocardium and originate from the proximal aorta. There are two main branches: the left coronary artery (LCA) and the right coronary artery (RCA). The LCA branches into the left circumflex, the left marginal, and the left anterior descending arteries. The RCA branches into the right marginal artery and commonly the posterior descending artery (PDA).
Heart “dominance” is determined by which of the initial coronary arteries supplies the PDA which, in turn, supplies the AV node. The heart is right dominant (85%) if the PDA is supplied by the RCA. The heart is left dominant (7.5%) if the PDA is supplied by the circumflex branch of the LCA. If the PDA is supplied by parts of the right and left circulation, then the heart is codominant (7.5%). In a right dominant heart, the right ventricle is supplied by the right marginal branch. In a left dominant heart, the right ventricle is supplied by the circumflex artery. The left ventricle, which contains the majority of the heart’s myocardium, is supplied by both right and left circulation. Coronary arteries are considered end arteries, meaning that there is little collateralization and if blockages develop, ischemia will occur in dependent cardiac tissue.
FIGURE 1.1
Left coronary artery (left main), circumflex artery, left anterior descending artery, and the right coronary artery are detailed in the figure. Reproduced, with permission, from Piktel JS. Cardiac rhythm disturbances. In: Tintinalli JE, Stapczynski J, Ma O, Cline DM, Cydulka RK, Meckler GD. eds. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 7th ed. New York, NY: McGraw-Hill; 2011.
The coronary veins remove deoxygenated blood from the myocardium. The precise venous anatomy varies from patient to patient but commonly mirrors the arterial supply. The coronary veins drain into the coronary sinus, which empties directly into the right atrium. Below figures show the origins of the left and right coronary arteries on cardiac computed tomography (CT) scanning.
FIGURE 1.4
Cardiac CT demonstrating the left coronary artery arising from its source at the ascending aorta. (AAo, ascending aorta; Cx, circumflex artery; DAo, descending aorta; LAD, left anterior descending artery; LAt, left atrium; LCA, left coronary artery; LPa, left pulmonary artery; LPv, left pulmonary vein; MPa, main pulmonary artery; RPa, right pulmonary artery; RPv, right pulmonary vein; SVC, superior vena cava.)
Although coronary structures are rarely imaged directly in the emergency department, it is important for the astute emergency physician to understand the basic coronary anatomy. Knowledge of cardiac structures can be helpful in the emergency department when taking care of patients experiencing myocardial ischemia. Determining the location of ischemia, particularly right versus left ventricular infarction, allows the emergency physician to better manage resuscitation of the patient.
Variations of normal coronary anatomy are very common.
Heart dominance is determined by which coronary artery supplies the AV node via the PDA.
Jeremy Webb
Cedric Lefebvre
The heart is a four-chambered muscular organ, consisting of two atria and two ventricles, with an internal fibrous skeleton. It maintains a right anterior position in the left chest. The atria and ventricles are separated from their contralateral equivalents by septa and from each other by cardiac valves. Deoxygenated blood enters the heart from the superior vena cava, inferior vena cava, and coronary sinus at the right atrium (RA). The RA is composed of a smooth sinus venarum at these connections and a muscular wall consisting of pectinate muscles. The border between these structures is the crista terminalis. The right ventricle (RV) is a trabeculated structure that makes up most of the sternocostal surface of the heart and receives blood from the RA via the tricuspid valve. A distinguishing feature of this chamber is the moderator band, which encases the right bundle of the AV conducting system. The RV propels blood through the pulmonary valve into the pulmonary trunk, which bifurcates into right and left main branches of the pulmonary artery. Blood then continues into the lungs to acquire oxygenation.
Oxygenated blood reenters the heart via pulmonary veins into the posteriorly positioned left atrium (LA). Posterior structures in contact with the LA include the coronary sinus, esophagus, and descending aorta. The LA is connected to the left ventricle (LV) via the mitral valve. The LV has three times the wall diameter of the RV which assists in pumping against systemic pressures. It comprises most of the diaphragmatic surface of the heart.
The heart chambers can be easily viewed with multiple radiologic modalities including chest radiograph, computerized tomography (CT), magnetic resonance imaging (MRI), and bedside cardiac ultrasound. For example, bedside ultrasound can be used to identify an enlarged right ventricle and septal bowing in the setting of massive pulmonary embolism. Understanding the orientation of these chambers and how they are affected by varying disease processes can guide emergency decision making.
FIGURE 1.6
(A) The right atrium receives blood from the superior vena cava, inferior vena cava and coronary sinus. The fossa ovalis, an oval depression in the septal wall of the right atrium, is a remnant relating to the foramen ovale during development. Congenital defects in this area can result in a patent foramen ovale. (B) The right ventricle consists of trabeculae carneae, which are muscular columns originating from the inner surfaces of the ventricle. Papillary muscles (mm) from the ventricular wall connect to the leaflets of the tricuspid valve via chordae tendineae. (C) The left cardiac chambers are characterized by a thin-walled left atrium and a muscular, thick-walled left ventricle. Pulmonary veins (vv) return oxygenated blood from the pulmonary circulation to the left atrium. Chordae tendineae and papillary muscles (mm) attach to the cusps of the mitral valve to prevent prolapse during ventricular systole. Blood is propelled into the aorta and systemic circulation by the left ventricle via the aortic valve. Reproduced, with permission, from Morton DA, Foreman K, Albertine KH. eds. The Big Picture: Gross Anatomy. New York, NY: McGraw-Hill; 2011.
