💡 Learning Outcomes:

1. Describe the origin and course of right & left coronary arteries.
2. List the branches of left & right coronary arteries and describe the areas supplied by right & left coronary arteries.
3. Describe the coronary sinus and its tributaries.
4. Describe the great blood vessels of the mediastinum.
5. Explain clinical applications of the blood supply of the heart. 

1. Describe the origin and course of right & left coronary arteries.

Origin of Coronary Arteries:

• Both coronary arteries originate from the ascending aorta:
  • Right Coronary Artery (RCA) from the Anterior/Right Aortic Sinus.
  • Left Coronary Artery (LCA) from the Left Aortic Sinus.
• The myocardium requires extensive arterial supply due to its high oxygen demand.
  • Each square centimeter has an 11-meter-long capillary bed.
  • Blood flow: 225ml per minute (5% of total cardiac output).
  • Blood flow increases during diastole and decreases during systole.

Course of Right Coronary Artery (RCA):

• Runs between the pulmonary trunk and right auricle.
• Follows the anterior atrioventricular groove (accompanied by the anterior cardiac vein).
• Winds around the inferior border of the heart.
• Ascends and moves leftward in the posterior atrioventricular groove (also known as the coronary sulcus).
• Anastomoses with the circumflex branch of the left coronary artery.

Course of Left Coronary Artery (LCA):

• Initially passes behind the pulmonary trunk.
• Courses between the pulmonary trunk and the left auricle.
• Divides into two main branches:
  • Anterior Interventricular Artery (LAD – Left Anterior Descending):
    • Descends in the anterior interventricular groove alongside the great cardiac vein.
    • Winds around the apical incisura and anastomoses with the posterior interventricular branch of the right coronary artery.
  • Circumflex Artery:
    • Winds around the left border of the heart.
    • Travels along the posterior atrioventricular groove (coronary sulcus).
    • Anastomoses with the right coronary artery.

2. List the branches of left & right coronary arteries and describe the areas supplied by right & left coronary arteries.

Branches of Right Coronary Artery (RCA):

1. S-A nodal branch (in 25% of humans, it originates from the left coronary artery).
2. Atrial branches.
3. A-V nodal branch.
4. Conus branch.
5. Right marginal branch.
6. Right anterior ventricular branches.
7. Right posterior ventricular branches.
8. Posterior interventricular branch (supplies the posterior one-third of the interventricular septum).

Areas Supplied by RCA:

• Entire right atrium.
• Most of the right ventricle.
• Posterior one-third of the interventricular septum (part of the major pump).
• S.A node in the majority of individuals.
• A.V node in the majority of individuals.

Branches of Left Anterior Descending Artery (LAD):

1. Conus branch.
2. Septal branches (anterior two-thirds of the interventricular septum).
3. Anterior diagonal branch.
4. Ventricular branches.

Branches of Circumflex Artery:

1. Left marginal branch.
2. Lateral diagonal branch.
3. Posterior artery to the left ventricle.
4. Atrio-ventricular branches (A-V bundle).

Areas Supplied by LCA:

• Most of the left atrium and left ventricle, except along the posterior and inferior surfaces.
• Anterior two-thirds of the interventricular septum.
• Bundle of His, right and left bundle branches.

3. Describe the coronary sinus and its tributaries.

Coronary Sinus:

• Develops from the left horn of the sinus venosus.
• A wide venous channel, 2 to 3 cm long.
• Located in the posterior atrioventricular groove (coronary sulcus).
• Receives 60% of venous blood from the heart.
• Begins at the left end of the coronary sulcus from the great cardiac vein.
• Runs down and to the right, accompanying the anastomosis between the right and left coronary arteries.
• Opens into the right atrium between the right atrioventricular orifice and the opening of the inferior vena cava.

Tributaries of Coronary Sinus:

1. Great cardiac vein.
2. Middle cardiac vein.
3. Small cardiac vein.
4. Oblique vein of the left atrium (remnant of the left common cardinal vein).

Other Veins Opening into the Right Atrium:

• Venae cordis minimi.
• Anterior cardiac veins (three or four variably sized veins arising from the sternocostal surface of the right ventricle).

4. Describe the great blood vessels of the mediastinum.

Great Blood Vessels in the Mediastinum:

Superior Mediastinum:

• Anterior boundary: Manubrium of the sternum.
• Posterior boundary: T1 to T4 vertebrae.
• Superficial Plane:
  • Superior vena cava: Formed by the right and left brachiocephalic veins.
• Intermediate Plane:
  • Arch of the aorta and its three branches: Brachiocephalic trunk, left common carotid, left subclavian.
  • Phrenic nerve, vagus nerve, left recurrent laryngeal nerve.
• Deep Plane:
  • Trachea and esophagus.

Key Blood Vessels:

• Pulmonary trunk.
• Ascending aorta.
• Arch of the aorta.
• Descending aorta.

5. Explain clinical applications of the blood supply of the heart.

Coronary Angiography:

• Radiographic visualization of coronary vessels after injection of radiopaque contrast media.
• Performed with specialized intravascular catheters.
• Purpose: To define coronary anatomy and the degree of luminal obstruction in coronary arteries.
• Commonly used to determine the presence and extent of obstructive coronary artery disease (CAD).

Most Common Arteries Blocked in CAD:

1. LAD (anterior interventricular branch of the left coronary artery).
2. LCX (circumflex branch of the left coronary artery).
3. RCA (right coronary artery).

Angina Pectoris:

• Sympathetic origin: Lateral horn cells of T1 to T4 spinal segments, predominantly T1.
• Referred pain from angina: Inner border of the arm (T1 dermatome).
• Spinal segments (C3, C4) supplying cervical sympathetic nerves to the heart, also supplies skin over left shoulder, neck and jaw (same dermatomes). Hence cardiac pain is referred to tip of left shoulder, neck and jaw.
• Two cardiac plexuses (superficial and deep) supply the heart.

Coronary Dominance:

• Defined by the artery supplying the posterior one-third of the interventricular septum.
• Majority: Right coronary dominance.
• Minority (10% to 20%): Left coronary predominance.
  • Dangerous because both anterior and posterior parts of the interventricular septum are supplied by the left coronary artery.
  • Blockage of the left coronary artery may produce massive output failure.

Collateral Circulation & Anastomoses:

• Inter-arterial anastomosis at the capillary level increases with age.
• Arterio-venous anastomosis.
• Arterio-sinusoidal anastomosis.