MDCT – Coronary Artery Anatomy
Hemant B Telkar MD, DNB
The coronary circulation is divided into two compartments:
(1) The large extramural coronary arteries
(2) Small intramural coronary branches in the capillary bed.

ORIGIN OF CORONARY ARTERIES
Two major arterial vessels, the right and the left coronary arteries, arise from corresponding sinuses, the aortic cusp. The third sinus is the noncoronary cusp.

RIGHT CORONARY ARTERY (RCA)
The right coronary artery departs from the aorta via its mostly anteriorly directed orifice, runs in the right atrioventricular sulcus.
Its course, which begins between the aortic root side and the main trunk of the pulmonary artery, subsequently extends downward along the right side of the heart to the diaphragmatic surface and forms a semicircle.
In the majority, of it reaches the crux of the heart, the latter representing the intersection of the atrioventricular sulcus with the posterior interventricular groove, which indicates the border between the walls of the right and left ventricle.

 
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Branches: -
From the aortic orifice to its division at the crux, the right coronary artery gives off branches in the anterior direction toward the right ventricular wall called right ventricular (RV) branch. Because it is close to the acute margin of the right ventricle, its designation is the acute marginal branch and in the posterior direction toward the right atrium called anterior, posterior and intermediate atrial branches.
At the crux, the right coronary artery divides its arterial distribution in two directions. One branch continues to the left in the area of the posterior atrioventricular sulcus forming poster lateral ventricular (PLV) branch; the other turns toward the apex to supply the area of the posterior interventricular groove forming posterior descending artery (PDA) Very small septal branches usually arise from the posterior descending coronary artery to distribute in the posterior third of the interventricular septum.
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Conus Artery is first branch of RCA and is usually directed anteriorly and passes around the anterior of the outflow tract of the right ventricle close to the level of the pulmonic valve. This pulmonary conus branch is relatively constant in its distribution but frequently has its own orifice closely adjacent but clearly separate from the main right coronary artery ostium in the right coronary sinus. Because of this rather frequent appearance (almost 50 percent); this usually small branch has been denoted as the third coronary artery.


LEFT CORONARY ARTERY (LM): -
Arising from the left sinus of Valsalva, the left coronary artery runs in the groove between the left atrial appendage and the main trunk of the pulmonary artery. Initially it courses backward to the left, but then turns in the ventral direction before bifurcation into the left circumflex artery (Cx) and the left anterior descending artery (LAD).


LEFT ANTERIOR DESCENDING ARTERY (LAD): -

The LAD is a direct continuation of the main trunk of the left coronary artery, whose length between the ostium and bifurcation varies from a few millimeters to a few centimeters.
The anterior descending artery enters the anterior interventricular groove forming the border between the left and right ventricles on the anterior wall of the heart. It runs under the left atrial appendage for the first few centimeters of its course, but it subsequently lies on the cardiac surface directly below the visceral layer of the pericardium.

Branches:-
Diagonal branches (D) arise from LAD extend over surface of heart between interventricular and A-V groove
Septal (S) Branches are small branches coursing perpendicularly and enter into septum.

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CIRCUMFLEX ARTERY (Cx): -
The left circumflex artery, in contrast to the anterior descending artery, rises almost perpendicularly from the main trunk and follows a course in the left atria ventricular sulcus. Its length in this location varies, as do the number and size of its branches to the adjacent areas of the left and posterior walls of the left ventricle. These variations in size and extension are related in a reciprocating fashion to those occurring in the most distal distribution of the right coronary artery.

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Branches:-
Obtuse Marginal branches are the anteriorly directed side branches from the left circumflex artery; a relatively large branch is usually visible and located approximately halfway between the anterior and posterior free walls of the left ventricle along obtuse margin and hence the name

RAMUS INTERMEDIUS: -
In some hearts, an artery running toward the midportion of the lateral wall of the left ventricle arises from the angle between the division of the anterior descending and the circumflex arteries. This creates the appearance of a trifurcation of the main trunk. This branch is sometimes so large that it may even reach the region. Appropriate terms for this vessel are left intermediate artery, ramus medianus, or arteries intermedia.

DOMINANCE OF ARTERY: -
Reciprocity exists between the right and left coronary arteries of the human heart; a large distribution of one takes place at the cost of the other. Variations of this nature have the greatest implication with regard to the blood supply of the crux and the posterior interventricular sulcus. In roughly 90 percent of the cases, the right coronary artery reaches and supplies this area; otherwise, the left circumflex artery provides the supply. Consequently, the supply of the posterior third of the interventricular septum and the atrioventricular node by the posterior septal branches depends on the integrity of the coronary artery that serves this area. The concept of right or left coronary preponderance is based on these variations in contribution.
When right and left coronary artery branches share rather equally in the supply of the crux, the term balanced or codominant coronary distribution has been applied.