Coronary arteries


Blood supply to the heart begins at the aorta, immediately distal to the aortic valve in the sinuses of Valsalva.

Coronary arteries arise from ostia, openings of the aorta at the upper third or middle third of the sinuses of Valsalva.

Coronary arteries originate from the aortic root and lie on the outer or epicardial surface of the heart. 

The coronary arteries are 2-4 mm diameter vessels that are 5-10 cm long that run along the external surface of the heart.

The epicardial coronary arteries penetrate into the myocardium as intramural arteries that yield arterioles and capillaries in which nearly one vessel is adjacent to each cardiac muscle cell.

The walls of coronary arteries consist of three layers: the tunica intima or inner layer, the tunica media and adventitia.

The intima is the possible site of lipid deposits and fibrosis.

The tunica media is a smooth muscle layer whose tone is modulated by the nervous system, influencing vessel diameter and resistance.

The adventitia is where nerve endings are located.

Normally, the initial portion of coronary arteries lies onto the external surface of the heart (epicardium) where fat deposits tend to form during life.

Three major epicardial coronary arteries are the left anterior descending (LAD), and the left circumflex arteries which arise from the bifurcation branches of the left main coronary artery, and the right coronary artery.

Branches of the left anterior descending coronary artery are the diagonal and the septal perforators and those of the left circumflex are the obtuse marginals.

Most blood flow to the myocardium occurs during ventricular diastole, when the coronary circulation is not compressed by the heart muscle.

With normal heart rate diastole contributes about 80% of coronary blood flow and about 20% occurs in systole.

Normal coronary artery blood flows in a laminar orientation and reaches its maximum velocity during diastole.

In the presence of tachycardia systole becomes a greater contributor to coronary artery blood flow.

The LAD artery supplies most of the apex of the heart, the anterior wall of the left ventricle and the anterior two thirds of the ventricular septum.

The artery that provides the posterior descending branch that perfuses the posterior third of the septum is the dominant artery and can arise from the right coronary artery or the left circumflex artery.

The left anterior descending artery and the left circumflex artery perfuse the majority of the left ventricular myocardium, with the LAD accounting for about 50% by itself.

A right dominant vasculature is present in 4/5th of individuals with the right coronary artery supplying the entire right ventricular free wall and the posterior basal wall of the left ventricle and the posterior third of the ventricular septum, while the circumflex branch of the left coronary artery perfuses the lateral wall of the left ventricle.

The posterior descending artery, providing blood flow to the infero-posterior wall of the heart, originates from the RCA in 70-90% of individuals, right coronary dominance,  whereas in 10-15% cases it originates from the LCx, left coronary dominance.

Occlusion of the right or left coronary artery can cause left ventricular damage.

Right and left coronary arteries are end vascular structures, but the heart has numerous intercoronary collaterals.

Arterial stenosis disrupts blood flow as it accelerates through a lesion and as flow velocity exceeds laminar thresholds turbulence occurs and produces an intracoronary murmur.

Intercoronary anastomotic vessels, the collateral circulation, is utilized when coronary artery vessels are narrowed, otherwise little blood flow through these vessels.

When coronary arteries are compromised and collateral circulation is inadequate the subendocardium tissues are the most vulnerable to ischemia.

Coronary vessels diameter progressively decreases proceeding from their origin to the periphery. 

Capillaries represent the smallest peripheral vessels of the coronary tree that lack muscular tissue and are responsible for oxygen and nutrients exchange within the myocardium.

Leave a Reply

Your email address will not be published. Required fields are marked *