Case Study – Thorax
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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.
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.
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.
To what extent does the statement that the right coronary artery supplies the right heart, and the left coronary artery the left heart, require qualification?
What is an end-artery and do coronary arteries qualify as such?
What are some vital organs that are supplied by end-arteries?
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).
What are some of the common sites of anastomosis between the two coronary arteries?
Give an example of an intracoronary anastomosis.
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.
How can you explain the fact that a patient who has cardiac ischemia as indicated by angina pectoris, and who survives a cardiac infarction, may be relieved of his pain afterwards?
What are some of the sites of predilection of coronary occlusion?
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.
Given an atherosclerotic obstruction of the left circumflex artery, which of the three types just described would be least desirable and why?
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.
With the exception of the smallest cardiac veins, do all cardiac veins drain into the coronary sinus?
Does the coronary arterial system enter into communications with other arteries in the neighborhood and if so, how do these arteries reach the heart?
How important are they for the supply of the ischemic myocardium?