Internal Cardiac Anatomy and Valve Structures

The pulmonary trunk then bifurcates into the Main Pulmonary Artery branches:

• Left Pulmonary Artery (LPA): Arches backward and laterally toward the left lung.
• Right Pulmonary Artery (RPA): Travels posterior to the ascending aorta and the Superior Vena Cava (SVC) toward the right lung.

The Left Heart: Systemic Circulation

The left side of the heart is the high-pressure engine of the cardiovascular system, responsible for delivering oxygenated blood to the entire body.

The Left Atrium (LA) and Left Ventricle (LV)

The Left Atrium receives oxygenated blood from the four pulmonary veins (two from the right and two from the left). A notable feature is the left atrial appendage, which is often described as being shaped like a "piglet ear" or "devil's horn".

The Left Ventricle is the most muscular chamber of the heart. Because it must generate high pressure to drive systemic circulation, its walls are significantly thicker than those of the right ventricle, measuring between 6–10 mm. In a short-axis view, the LV appears circular, and the high pressure often causes the interventricular septum to bulge toward the right ventricle.

The Aorta

Blood is ejected from the left ventricle into the Aorta, which is divided into several segments:

1. Ascending Aorta
2. Aortic Arch (which gives rise to the right innominate, left carotid, and left subclavian arteries)
3. Descending Aorta (further divided into thoracic and abdominal segments).

Cardiac Valve Apparatus and Mechanics

Valves are essential for maintaining unidirectional blood flow. They are located at the base of the heart and consist of an annulus (the outer ring), leaflets (the moving parts), and a coaptation zone where the leaflets meet to create a seal.

The Mitral Valve (Left Atrioventricular Valve)

The mitral valve is a complex apparatus designed to withstand high systemic pressures. Its components include:

• Mitral Leaflets: Divided into the Anterior Mitral Valve Leaflet (AMVL) and the Posterior Mitral Valve Leaflet (PMVL).
• Mitral Valve Scallops: The leaflets are further subdivided into scallops. The anterior leaflet is divided into A1, A2, and A3, while the posterior leaflet is divided into P1, P2, and P3.
• Subvalvular Apparatus: The leaflets are anchored to the ventricular walls by Papillary Muscles (anterolateral and posteromedial), which are connected to the leaflets via the Chordae Tendinae.

The Aortic Valve (Semilunar Valve)

The aortic valve consists of three distinct cusps:

1. Right Coronary Cusp (RCC): Faces the right ventricle and serves as the origin for the right coronary artery.
2. Left Coronary Cusp (LCC): Faces the pulmonary artery and serves as the origin for the left main coronary artery.
3. Non-Coronary Cusp (NCC): Faces the inter-atrial septum and has no associated coronary artery.

[!TIP] Exam Tip: Valve Orientation When studying the aortic valve in a Parasternal Short Axis (PSAX) view, remember the relationship between the cusps and the coronary arteries. The RCC and LCC are the "coronary" cusps because they are the sites where the coronary arteries originate.

The Pulmonary Valve

Structurally similar to the aortic valve, the pulmonary valve also consists of three cusps: the anterior cusp, the left (posterior) cusp, and the right (posterior) cusp. Unlike the aortic valve, abnormalities in the pulmonary valve are frequently congenital in nature.

Summary of Internal Structures