Coronary circulation
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Rim Halaby
Overview
- The coronary circulation is the circulation of blood in the blood vessels that supply blood to and from the heart muscle itself.
- Although blood fills the chambers of the heart, the muscle tissue of the heart, or myocardium, is so thick that it requires coronary blood vessels to deliver blood deep into it.
- Coronary arteries are the vessels that deliver oxygen-rich blood to the myocardium.
- Cardiac veins are the vessels that remove the deoxygenated blood from the heart muscle.
- Epicardial coronary arteries are the coronary arteries that run on the surface of the heart.
- These arteries, when healthy, are capable of autoregulation to maintain coronary blood flow at levels appropriate to the needs of the heart muscle.
- These relatively narrow vessels are commonly affected by atherosclerosis and can become blocked, causing angina or a heart attack. (See also: circulatory system.)
- Subendocardial coronary arteries run deep within the myocardium.
- The coronary arteries are classified as "end circulation", since they represent the only source of blood supply to the myocardium: there is very little redundant blood supply, which is why blockage of these vessels can be so critical.
Coronary Arteries
- The exact anatomy of the myocardial blood supply system varies considerably from person to person. A full evaluation of the coronary arteries requires cardiac catheterization or CT coronary angiography.
- In general there are two main coronary arteries:
- Both of these arteries originate from the beginning (root) of the aorta, immediately above the aortic valve:
- The left coronary artery originates from the left aortic sinus
- The right coronary artery originates from the right aortic sinus.
- Below is an image showing the coronary arteries.
Left Coronary Artery
- The left coronary artery arises from the left aortic sinus.
- It is shorter than the right coronary artery; however, it supplies a larger portion of the myocardium.
- The left coronary artery branches into:
- Left anterior ascending LAD (also called anterior interventricular artery)
- It supplies the anterior part of the left ventricle: anterolateral myocardium, apex, anterior interventricular septum, anterolateral papillary muscle.
- Left circumflex LCX
- It supplies the posterolateral side of the left ventricle.[1]
- Left anterior ascending LAD (also called anterior interventricular artery)
Right Coronary Artery
- The right coronary artery branches into:
- SA branch
- It supplies the SA node.
- Acute marginal artery
- It supplies the right ventricular wall.
- Posterior descending artery
- It supplies the inferior wall, posterior interventricular septum and posteromedial papillary muscle.[2]
- SA branch
Variations
- Four percent of people have a third, the posterior coronary artery.
- In rare cases, a person will have one coronary artery that runs around the root of the aorta.
- Occasionally, a coronary artery will exist as a double structure (i. e. there are two arteries, parallel to each other, where ordinarily there would be one).
Coronary Artery Dominance
- The dominance of coronary circulation is determined by the type of arteries that supply the posterior and inferior wall of the left ventricle.
- The artery that supplies the posterior descending artery (PDA) and the posterolateral artery (PLA) determines the coronary dominance.
- Right-dominant circulation: The right coronary artery (RCA) supplies both these arteries.
- Left-dominant circulation: The circumflex artery (CX), a branch of the left artery, supplies both these arteries.
- Co-dominant circulation: The RCA supplies the PDA and the CX supplies the PLA.
- Approximately 60% of the general population are right-dominant, 25% are co-dominant, and 15% are left-dominant.[3]
Coronary Artery Anastomoses
Extracardiac Anastomoses of the Heart
Cardiac Veins
- Cardiac veins] run parallel to coronary arteries.
- The components of the cardiac venous system are the following:
- Coronary sinus
- It is present in the coronary sulcus.
- It receives most venous return of the heart.
- It empties in the right atrium.
- Great cardiac vein
- It runs parallel to the LAD in the anterior interventricular groove.
- It drains in the coronary sinus.
- Middle cardiac vein
- It runs parallel to the PDA in the posterior interventricular groove.
- It drains in the coronary sinus.
- Small cardiac vein
- It runs parallel to the marginal artery.
- It drains in the coronary sinus.
- Anterior Cardiac Veins
- Coronary sinus
Blood supply of the papillary muscles
- The papillary muscles tether the mitral valve (the valve between the left atrium and the left ventricle) and the tricuspid valve (the valve between the right atrium and the right ventricle) to the wall of the heart.
- If the papillary muscles are not functioning properly, the mitral valve leaks during contraction of the left ventricle and causes some of the blood to travel "in reverse", from the left ventricle to the left atrium, instead of forward to the aorta and the rest of the body.
- This leaking of blood to the left atrium is known as mitral regurgitation.
- The anterolateral papillary muscle:
- It receives two blood supplies: the LAD and LCX.
- It is therefore somewhat resistant to coronary ischemia (insufficiency of oxygen-rich blood).
- The posteromedial papillary muscle:
- It is supplied only by the PDA.
- This makes the posteromedial papillary muscle significantly more susceptible to ischemia.
- The clinical significance of the nature of blood supply to the papillary muscles is that a myocardial infarction involving the PDA is more likely to cause mitral regurgitation.
Coronary flow
- During contraction of the ventricular myocardium (systole), the subendocardial coronary vessels (the vessels that enter the myocardium) are compressed due to the high intraventricular pressures. However the epicardial coronary vessels (the vessels that run along the outer surface of the heart) remain patent. Because of this, blood flow in the subendocardium stops.
- As a result most myocardial perfusion occurs during heart relaxation (diastole) when the subendocardial coronary vessels are patent and under low pressure. This contributes to the filling difficulties of the coronary arteries.
- Failure of oxygen delivery via increases in blood flow to meet the increased oxygen demand of the heart results in tissue ischemia, a condition of oxygen debt.
- Brief ischemia is associated with intense chest pain, known as angina.
- Severe ischemia can cause the heart muscle to die of oxygen starvation, called a myocardial infarction.
- Chronic moderate ischemia causes contraction of the heart to weaken, known as myocardial hibernation.
- In addition to metabolism, the coronary circulation possesses unique pharmacologic characteristics. Prominent among these is its reactivity to adrenergic stimulation. The majority of vasculature in the body constricts to norepinephrine, a sympathetic neurotransmitter the body uses to increase blood pressure.
- In the coronary circulation, norepinephrine elicits vasodilation, due to the predominance of beta-adrenergic receptors in the coronary circulation.
- Agonists of alpha-receptors, such as phenylephrine, elicit very little constriction in the coronary circulation.
Coronary Collateral Circulation
Angiography
See also
References
- ↑ Morton DA, Foreman KB, Albertine KH. Chapter 4. Heart. In: Morton DA, Foreman KB, Albertine KH, eds. The Big Picture: Gross Anatomy. New York: McGraw-Hill; 2011.
- ↑ Morton DA, Foreman KB, Albertine KH. Chapter 4. Heart. In: Morton DA, Foreman KB, Albertine KH, eds. The Big Picture: Gross Anatomy. New York: McGraw-Hill; 2011.
- ↑ Kaimkhani ZA, Ali MM, Faruqi AM (2005). "Pattern of coronary arterial distribution and its relation to coronary artery diameter". Journal of Ayub Medical College, Abbottabad : JAMC. 17 (1): 40–3. PMID 15929526.
- ↑ Morton DA, Foreman KB, Albertine KH. Chapter 4. Heart. In: Morton DA, Foreman KB, Albertine KH, eds. The Big Picture: Gross Anatomy. New York: McGraw-Hill; 2011.