The epicardial coronary artery system consists of the left and right coronary arteries, which normally arise from ostia located in the left and right sinuses of Valsalva, respectively. In about 50 per cent of humans a “third coronary artery” (“conus artery”) arises from a separate ostium in the right sinus. The left main (LM) coronary artery ranges in length from 1 to 25mm before bifurcating into the left anterior descending (LAD) and left circumflex (LC) branches. The LAD coronary artery measures from 10 to 13 cm in length, whereas the usual nondominant LC artery measures about 6 to 8 cm in length. The dominant right coronary artery (RCA) is about 12 to 14cm in length before giving rise to the posterior descending artery (PDA). Portions of the epicardial coronary arteries may dip into the myocardial (“mural artery” or “tunneled artery”) and be covered for a variable length (1 to several millimeters) by ventricular muscle (“myocardial bridge”). The branches of the LAD artery, in their usual order of origin, are the first diagonal, the first septal perforator, other septal perforators, and other diagonal branches. Diagonal branches course laterally over the free wall of the left ventricle in the angle between the LAD and the LC.Septal branches, which leave the LAD artery at a right angle plunge deeply into the ventricular septum. The branches of the LC are variable but may include the sinus node artery (40 to 50 per cent), the left atrial circumflex branch, the anterolateral obtuse marginal, the distal circumflex,one or more obtuse marginals, and the PDA (10 to 15 per cent). The branches of the RCA include the conus artery (which may originate from a separate ostia in the right coronary sinus in 40 to 50 per cent of hearts) to the right ventricular outflow area, the artery to the sinus node (50 to 60 per cent), several anterior right ventricular branches, right atrial branches, the acute marginal branch,the artery to the AV node and proximal bundle branches, the PDA, and terminal branches to the left ventricle and left atrium.
Coronary Artery Distribution and Myocardial Supply
There is a well-established relation between a given epicardial coronary artery and its myocardial supply. Generally, the basal half of the ventricular septum and the anterior left ventricular free wall are prefused by the LAD coronary artery. A dominant right coronary artery perfuses anterior,lateral and posterior right ventricular myocardium. The posterior coronary artery (most commonly arising from the RCA) supplies blood to the posterior quarter of the ventricular septum and posterior left ventricular free wall. The LC coronary artery usually perfuses the lateral wall of the left ventricle (defined as that portion of ventricular myocardium located between anterolateral and posteromedial papillary muscles). The basal most portion of the ventricular septum is usually perfused by branches of the PDA. The apical third of the posterior left ventricle may be predominantly perfused by the LAD. LAD artery and its branches supply the right and left bundle branches, and the anterolateral papillary muscle of the left ventricle. When the PDA is provided by the circumflex artery, the entire ventricular septum is vascularized by the left coronary system.
The LAD artery can also provide collateral circulation to the anterior right ventricle via the circle of Vieussens, to the posterior ventricular septum by the septal perforators and to the PDA from the distal LAD artery or a diagonal branch. Kogel’s artery arises from the proximal RCA or LC or, rarely, the LM; it passes posteriorly into the lower portion of the atrial septum and anastomoses with the AV node artery.
Although the large epicardial coronary arteries are capable of constriction and relaxation, in healthy persons they serve as conduits and are referred to as conductance vessels. They can cause severe ischaemia from constriction in Prinzmetal’s angina. The intramyocardial arterioles normally exhibit changes in tone and are therefore referred to as resistance vessels. Abnormal constriction or failure of normal dilation of the coronary resistance vessels can also cause ischaemia. This condition is referred to as microvascular angina.
The normal coronary circulation is dominated and controlled by the heart’s requirements for oxygen. This need is met by the ability of the coronary vascular bed to vary its resistance (and therefore blood flow) considerably while the myocardium extracts a high and relatively fixed percentage of oxygen. Normally, intramyocardial resistance vessels demonstrate an immense capacity for dilation. For example, the changing oxygen needs of the heart with exercise and emotional stress affect coronary vascular resistance and in this manner regulate the supply of oxygen and substrate to the myocardium (metabolic regulation). The coronary resistance vessels also adapt to physiologic alterations in blood pressure in order to maintain coronary blood flow at levels appropriate to myocardial needs (autoregulation).
By reducing the lumen of the coronary arteries, atherosclerosis limits appropriate increases in perfusion when the demand for flow is augmented, as occurs during exertion or excitement.When the luminal reduction is severe, myocardial perfusion in the basal state is reduced.
Coronary Artery Distribution and Myocardial Supply
There is a well-established relation between a given epicardial coronary artery and its myocardial supply. Generally, the basal half of the ventricular septum and the anterior left ventricular free wall are prefused by the LAD coronary artery. A dominant right coronary artery perfuses anterior,lateral and posterior right ventricular myocardium. The posterior coronary artery (most commonly arising from the RCA) supplies blood to the posterior quarter of the ventricular septum and posterior left ventricular free wall. The LC coronary artery usually perfuses the lateral wall of the left ventricle (defined as that portion of ventricular myocardium located between anterolateral and posteromedial papillary muscles). The basal most portion of the ventricular septum is usually perfused by branches of the PDA. The apical third of the posterior left ventricle may be predominantly perfused by the LAD. LAD artery and its branches supply the right and left bundle branches, and the anterolateral papillary muscle of the left ventricle. When the PDA is provided by the circumflex artery, the entire ventricular septum is vascularized by the left coronary system.
The LAD artery can also provide collateral circulation to the anterior right ventricle via the circle of Vieussens, to the posterior ventricular septum by the septal perforators and to the PDA from the distal LAD artery or a diagonal branch. Kogel’s artery arises from the proximal RCA or LC or, rarely, the LM; it passes posteriorly into the lower portion of the atrial septum and anastomoses with the AV node artery.
Although the large epicardial coronary arteries are capable of constriction and relaxation, in healthy persons they serve as conduits and are referred to as conductance vessels. They can cause severe ischaemia from constriction in Prinzmetal’s angina. The intramyocardial arterioles normally exhibit changes in tone and are therefore referred to as resistance vessels. Abnormal constriction or failure of normal dilation of the coronary resistance vessels can also cause ischaemia. This condition is referred to as microvascular angina.
The normal coronary circulation is dominated and controlled by the heart’s requirements for oxygen. This need is met by the ability of the coronary vascular bed to vary its resistance (and therefore blood flow) considerably while the myocardium extracts a high and relatively fixed percentage of oxygen. Normally, intramyocardial resistance vessels demonstrate an immense capacity for dilation. For example, the changing oxygen needs of the heart with exercise and emotional stress affect coronary vascular resistance and in this manner regulate the supply of oxygen and substrate to the myocardium (metabolic regulation). The coronary resistance vessels also adapt to physiologic alterations in blood pressure in order to maintain coronary blood flow at levels appropriate to myocardial needs (autoregulation).
By reducing the lumen of the coronary arteries, atherosclerosis limits appropriate increases in perfusion when the demand for flow is augmented, as occurs during exertion or excitement.When the luminal reduction is severe, myocardial perfusion in the basal state is reduced.
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