Question

Case Study – Thorax Presentation/History A 52-year-old insurance adjuster is brought to the hospital in an ambulance. His wife, who accompanied him, stated that during dinner he started to complain of excruciating chest pain in the region of the sternum. These symptoms were accompanied by nausea, vomiting, and severe shortness of breath. She also pointed out that for several years the patient had been suffering from chest pain that radiated into the left arm, particularly after physical effort or emotional upsets. Examination On admission the patient appears in shock. His skin is ashen gray with some cyanosis (bluish tinge), and is cold and clammy. His blood pressure is low, his pulse is quite weak, and his pulse rate is 110 per minute. His respirations are noisy and gasping. On auscultation of the lungs, abnormal breaths sounds are heard. His heart sounds are feebly and arrhythmic. In spite of oxygen application, intravenous injection of circulatory stimulants, electric defibrillation and terminal cardiac massage, the patient expires within two hours of admission. At autopsy there is found marked narrowing of both coronary arteries and many of their branches, due to atherosclerosis of the vessel wall. There is an old occlusion in the first portion of the right coronary artery and a fresh intimal hemorrhage in the anterior interventricular branch near its origin from the left coronary artery. This, in combination with a fresh blood clot, has completely occluded the anterior interventricular branch. Discussion Ischemic heart disease, i.e., heart disease caused by insufficient blood supply to the heart muscle, is one of the most frequent conditions encountered in patients past 40 years of age. It is the leading cause of death in the United States. It is the function of the coronary arteries to carry blood to the myocardium and thus maintain its nutrition. When the lumen of the coronary artery becomes narrowed or obliterated due to atherosclerosis of the intima, the portion of the myocardium supplied by the affected artery suffers from lack of oxygen (hypoxia) and becomes damaged. This myocardial hypoxia may result in rapid death, as happened in our patient. It is generally due to ventricular fibrillation. The latter condition is a cardiac arrhythmia leading to completely disorganized ventricular excitation and ineffective contraction resulting in circulatory failure and, frequently, death. The decisive factor in the life of individuals with coronary artherosclerosis is the state of the coronary circulation. Identify the arterial supply to the heart and give the origin of these arteries. The right and left coronary arteries are middle-sized muscular arteries that arise from the right and left aortic sinuses of the first part of the aorta just distal to the semilunar valves. The main arteries run in the epicardial fat of the atrioventricular and interventricular grooves and are partly concealed by fact and in some locations also by thin layers of ventricular myocardium, so that dissection becomes necessary for their demonstration. 1) Discuss the exceptions to the statement that the right coronary artery supplies the right heart and the left coronary artery supplies the left heart (10). 2) Define an end-artery (1). From the frequent occurrence of cardiac infarction we can deduce that a collateral circulation is absent or inadequate in these cases. However, the branches of the coronary arteries are not true end-arteries, since numerous anastomoses take place either between the right and left coronary arteries (intercoronary anastomoses) or between branches of the same artery (intracoronary anastomoses). 3) Identify the four most common sites of anastomosis between the two coronary arteries (3). Normally, however, these communications, while anatomically patent, are small and functionally inactive. Thus we can speak of the coronary arteries as physiologic end-arteries. In other words, the collateral circulation is usually ineffective to prevent an infarction in case of sudden interruption of the circulation. Depending on the degree of obstruction and the order and size of the obstructed arterial branch, interference with the coronary circulation may result in functional insufficiency leading to angina pectoris, i.e., cardiac pain, or myocardial necrosis of variable extent. If, however, the occlusion of a coronary branch is slow and gradual, anastomoses have time to enlarge and can carry an adequate circulation to the heart muscle. 4) List the three most common sites of predilection of coronary occlusion (5). Of great practical importance is the variation in the pattern of coronary arterial distribution from individual to individual. There are three types of distribution in terms of the dominance of one or the other of the coronary arteries. In approximately 50 per cent the right coronary artery is the preponderant vessel, which, with its posterior interventricular branch, supplies most of the diaphragmatic surface of both ventricles and part of the interventricular septum. In approximately 20 per cent the left coronary predominates with the posterior interventricular branch essentially being derived from the circumflex branch of the left coronary. In the remaining approximately 30 per cent there exists a balanced circulation. 5) Given an atherosclerotic obstruction of the left circumflex artery, speculate as to which of the three types described would be least desirable and why (3). It is a peculiarity of the cardiac circulation that there are channels that pass from coronary arterioles, from the capillary bed, and from the cardiac veins directly into the lumen of the heart. Irregular thin-walled channels of larger than capillary size, which are called "myocardial sinusoids," also receive blood from the coronary arterioles or the capillary bed and communicate with the smallest cardiac veins that open directly into the chambers of the heart, particularly into the atria. It has been assumed that the stream in these veins can be reversed and thus help in nourishing the ischemic myocardium in case of coronary obstruction. Some of these openings in the cardiac cavity can be seen with naked eye by inspection of the endocardial lining. They vary from pinpoint size to almost 1 mm in diameter. 6) Detail any exceptions to the notion that all cardiac veins drain into the coronary sinus, if there are any such exceptions (4). 7) Detail any and all points where the coronary arterial system enters into communication with other arteries in the neighborhood and how these arteries reach the heart (9). 8) Speculate as to whether or not these vessels are important in overcoming myocardial ischemia and why (1). Within the Discussion Forum, develop a working diagnosis and associated treatment plan for this patient.

Answer 1

Ans.

1 )

The right coronary artery supplies blood mainly to the right side of the heart. The right side of the heart is smaller because it pumps blood only to the lungs. The left coronary artery, which branches into the left anterior descending artery and the circumflex artery, supplies blood to the left side of the heart

The posterior descending artery branch supplies blood to the inferior aspect of the heart. The LMCA supplies blood to the left side of the heart. The LAD provides blood to the anterior ventricular septum and the greater portion of the anterior portion of the left ventricle.

Coronary Arteries

The heart receives its own supply of blood from the coronary arteries. Two major coronary arteries branch off from the aorta near the point where the aorta and the left ventricle meet. These arteries and their branches supply all parts of the heart muscle with blood.

Left Main Coronary Artery (also called the left main trunk)

The left main coronary artery branches into:

• Circumflex artery
• Left Anterior Descending artery (LAD)

The left coronary arteries supply:

• Circumflex artery - supplies blood to the left atrium, side and back of the left ventricle
• Left Anterior Descending artery (LAD) - supplies the front and bottom of the left ventricle and the front of the septseptum.

collateral circulation?

Collateral circulation is a network of tiny blood vessels, and, under normal conditions, not open. When the coronary arteries narrow to the point that blood flow to the heart muscle is limited (coronary artery disease), collateral vessels may enlarge and become active. This allows blood to flow around the blocked artery to another artery nearby or to the same artery past the blockage, protecting the heart tissue from injury.

Coronary arteriesEdit

The vessels that deliver oxygen-rich blood to the myocardium are the coronary arteries. When the arteries are healthy, they are capable of autoregulating themselves to maintain the 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. The coronary arteries that run deep within the myocardium are referred to as subendocardial. 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, that is why blockage of these vessels can be so critical.

2 )

End artery

An end artery is an artery that is the only supply of oxygenated blood to a portion of tissue. Arteries which do not anastomose with their neighbors are called end arteries. There is no collateral circulation present besides the end arteries.

functional end artery. an artery having only ineffectual anastomoses, so that it is unable to maintain viability of the tissue supplied when occlusion of the artery occurs. Synonym(s): functional terminal artery.

The collateral circulation is a network of specialized endogenous bypass vessels that is present in most tissues and provides protection against ischemic injury caused by ischemic stroke, coronary atherosclerosis, peripheral artery disease, and other conditions and diseases.

3 )

T HE question whether the coronary
arteries are end arteries has been
subjected to vigorous discussion for
many decades. Intense interest in this
problem has been provoked not only be-
cause of its scientific importance but also
because of the direct clinical implications
for our understanding of angina pectoris
and acute myocardial infarction. The im-
possibility of measuring coronary flow in
man during life and the manifold variations
in the technics of postmortem studies in
man and in experimental conditions in
animals have led to conflicting and contra-
dictory opinions. Differences between the
architecture of the coronary tree in the dog
and man have not always been appreciated.
The issue also has been confused by
diverse interpretations of the term “end
artery.” To the anatomist an end artery
is an artery which does not communicate
with other arteries through any anastomotic
connection so that its capillary bed receives
blood from no other artery. To the physi-
ologist an end artery is an artery which
alone supplies sufficient blood to an area to
maintain its function and integrity; when
this vessel is occluded, the dependent area
undergoes loss of function or necrosis be-
cause other arteries do not supply the given
area sufficiently. These two definitions
differ widely from each other; anatomic
studies in other parts of the body have
repeatedly demonstrated interarterial com-
munication with vessels which physiologi-
cally are clearly end arteries.

An end artery (or terminal artery) is an artery that is the only supply of oxygenated blood to a portion of tissue.

Arteries which do not anastomose with their neighbors are called end arteries. There is no collateral circulation present besides the end arteries.

Examples of an end artery include the splenic artery that supplies the spleen and the renal artery that supplies the kidneys. End arteries are of particular interest to medicine where they supply the heart or brain because if the arteries are occluded, the tissue is completely cut off, leading to a myocardial infarction or an ischaemic stroke. Other end arteries supply all or parts of the liver, intestines, fingers, toes, ears, nose, retina, penis, and other organs.^[1]

Because vital tissues such as the brain or heart muscle are vulnerable to ischaemia, arteries often form anastomoses to provide alternative supplies of fresh blood. End arteries can exist when no anastomosis exists or when an anastomosis exists but is incapable of providing a sufficient supply of blood, thus the two types of end arteries are:

• Anatomic (true) end artery: No anastomoses.
• Functional end artery: Ineffectual anastomoses.

An example of a true terminal arteries is that which supplies the retina. Functional end arteries supply segments of the brain, liver, kidneys, spleen and intestines; they may also exist in the heart.

IMPORTANCE OF END ARTERIES :- Occlusion of an end-artery causes serious nutritional disturbances resulting in death of the tissue supplied by it. For example, occlusion of central artery of retina results in blindness. The results are severe because the blood flow to that region is completely stopped since there is no collateral circulation.

4 )

Predilection Sites

Sites with low or oscillatory endothelial shear stress, located near branch points and along inner curvatures, are most susceptible,²⁰ and the abdominal aorta, coronary arteries, iliofemoral arteries, and carotid bifurcations are typically the most affected.

three main coronary arteries?

The Coronary Arteries are the blood vessels that supply blood to your heart. They branch off of the aorta at its base. The right coronary artery, the left main coronary, the left anterior descending, and the left circumflex artery, are the four major coronary arteries.

The artery that supplies the posterior third of the interventricular septum – the posterior descending artery (PDA) determines the coronary dominance. If the posterior descending artery is supplied by the right coronary artery (RCA), then the coronary circulation can be classified as "right-dominant".