Great Vessels, Pericardium, Coronary & Venous Anatomy

The Great Vessels

The aorta originates at the aortic annulus and is described in segments: the aortic root (annulus, the three sinuses of Valsalva, and the sinotubular junction), the ascending aorta, the aortic arch (giving off the brachiocephalic/innominate, left common carotid, and left subclavian arteries), and the descending aorta (thoracic, then abdominal). Root and ascending measurements are made from the parasternal long-axis view and are foundational to detecting aneurysmal dilation, discussed with aortic pathology later in this guide.

The main pulmonary artery (MPA) arises from the RV outflow tract, passes posterior and slightly leftward, and bifurcates into right and left pulmonary artery branches. It is the most anterior and superior of the great vessels, lying just anterior and to the left of the ascending aorta — best profiled from the parasternal short-axis/RV outflow view and the suprasternal notch view, where its bifurcation is visualized.

The superior vena cava (SVC) drains venous return from the head, neck, and upper extremities into the posterosuperior right atrium; it is well seen from the suprasternal notch and right parasternal/subcostal windows. The inferior vena cava (IVC) drains the abdomen and lower extremities into the posteroinferior right atrium; the subcostal view is the standard window for IVC diameter and respiratory collapsibility, used later in this guide to estimate right atrial pressure. Four pulmonary veins — right superior, right inferior, left superior, and left inferior — return oxygenated blood to the posterior wall of the left atrium and are best interrogated from the apical and subcostal windows with color and pulsed-wave Doppler.

The Pericardium

The pericardium is a two-part fibroserous sac enclosing the heart and the roots of the great vessels:

• Fibrous pericardium — a tough outer fibrous layer that anchors the heart to the diaphragm, sternum, and great vessel adventitia, and limits acute cardiac distension.
• Serous pericardium — a thin double-layered membrane consisting of a visceral layer (adherent directly to the myocardial surface — histologically identical to the epicardium) and a parietal layer (lining the inner surface of the fibrous pericardium). Between the visceral and parietal layers is the pericardial cavity, which normally contains only a small physiologic volume of serous fluid (typically well under 50 mL) for lubrication during the cardiac cycle.

Two pericardial reflections form recesses that are frequently mistaken for pathology on echo: the transverse sinus, a passage posterior to the aorta and pulmonary artery and anterior to the left atrium, and the oblique sinus, a blind-ending recess posterior to the left atrium bounded by the pulmonary veins and IVC. Recognizing these normal recesses prevents misclassifying a small localized pericardial effusion or mistaking fluid in the oblique sinus for a left atrial mass.

Coronary Arterial Anatomy

The left main coronary artery (LM) arises from the left sinus of Valsalva and typically bifurcates (occasionally trifurcates, with a ramus intermedius branch) into:

• Left anterior descending (LAD) — travels in the anterior interventricular groove, giving off septal perforator branches (supplying the anterior two-thirds of the interventricular septum) and diagonal branches (supplying the anterolateral wall); it supplies the anterior wall, anteroseptal wall, and typically wraps around to supply the true apex.
• Left circumflex (LCx) — travels in the left atrioventricular groove, giving off obtuse marginal branches; it supplies the lateral wall and, in a left-dominant circulation, the inferior wall as well.

The right coronary artery (RCA) arises from the right sinus of Valsalva and travels in the right atrioventricular groove; it typically supplies the RV free wall, and in a right-dominant circulation, gives rise to the posterior descending artery (PDA) supplying the inferior wall and inferoseptum. The RCA is also the origin of the sinoatrial nodal artery in roughly 55–60% of hearts and the atrioventricular nodal artery in most hearts.

Coronary dominance is defined by the vessel that gives rise to the PDA: right-dominant (RCA → PDA) in approximately 80–85% of individuals, left-dominant (LCx → PDA) in roughly 5–10%, and codominant in the remainder. This matters directly for wall-motion-to-vessel correlation, because dominance shifts which artery supplies the inferior and inferoseptal segments.

Mapping Coronary Territory onto the 17-Segment Model

Building on the segment anatomy from earlier in this chapter, the standard AHA/ASE territory assignment (assuming typical right-dominant anatomy) is:

This map is a population-based approximation, not a fixed rule — the inferoseptal segments in particular show real overlap between LAD and RCA territory, and in left-dominant or codominant circulations the inferior and inferolateral segments may actually be supplied by the LCx rather than the RCA. A regional wall-motion abnormality should be correlated with the patient's known coronary anatomy or angiographic findings whenever available, rather than assumed from the territory map alone.

Cardiac Venous Anatomy

Most LV myocardial venous drainage returns via the coronary sinus, which runs in the posterior left atrioventricular groove and empties into the right atrium; a dilated coronary sinus on echo is a clue to either a persistent left SVC draining into it or elevated right atrial pressure. Its major tributaries are the great cardiac vein (parallels the LAD, then curves posteriorly), the middle cardiac vein (parallels the posterior interventricular/RCA territory), and the small cardiac vein. Two additional venous routes bypass the coronary sinus entirely: the anterior cardiac veins, which drain the RV anterior wall directly into the right atrium, and the thebesian veins, tiny vessels draining directly into the cardiac chambers (predominantly the right atrium and right ventricle).