The heart is a small muscular structure that is about the size of an adult fist. It is found in the thoracic cavity, specifically in the mediastinum, which is the space between the lungs. Its main purpose is to pump blood to all areas of the body using the circulatory system. In order to accomplish this, it depends on four chambers total. The two superior chambers are known as the atria and the two inferior chambers are known as the ventricles. The septum separates the left and right side of the heart. (1)
The hearts (outer wall) consists of three layers. The outermost layer enclosing the heart is known as the pericardium, which is a double-walled sac. Within it lies a hefty exterior layer known as the fibrous pericardium. This layer is composed of fibrous connective tissue and is connected to the diaphragm. The function of the fibrous pericardium is to avoid an over-inflation of the heart as well as ensuring that the heart stays in place. Deeper into the heart lies the serous pericardium. It is made of delicate connective tissue and has two divisions. The first division is known as the parietal pericardium and the second division is known as the visceral pericardium, which envelops the heart. The area amidst the parietal layer and the visceral pericardium is known as the pericardial space. In order to prevent friction during each heartbeat, serous fluid lubricates the layers. (1)
The middle layer is known as the myocardium. It is made up of cardiac muscle, making it very durable. This is important, because it functions to pump blood throughout the human body. Cardiac muscle cells are arranged in a way so that they are bound at each end, increasing the amount of gap junctions that exists. This is advantageous to the heart because when fibers contract around cardiac cavities, this allows for pressure to eject blood in to both pulmonary and systemic circuits.
The deepest later is known as the endocardium. It is made of flat epithelial cells, bordering the heart and blood vessels. This border of epithelial cells aids in blood flow, because it is the endothelial folds that are what make up the valves which direct blood flow.(1)
Coronary circulation is the system which supplies blood to the heart. Two coronary arteries found on the aorta are involved in this system. In the diastole phase, the valves cause pressure to eject blood in to the coronary arteries then in to the heart itself. Blood that is deoxygenated is brought back to the heart chambers through the coronary veins. (2)
Pathophysiology
The main cause of coronary artery disease is linked to atheroma blockage, which is when a buildup of debris remains in an artery wall. This debris consists of fatty material that eventually matures in to plaque. The plaque’s center is made of foam cells, which are a type of macrophage. The tissue portion consists of smooth muscle cells, which have the ability to move and change in to fibrous capsules that surround the center. (5). Atheromatous plaque creates an irregular pressure of coronary vessels, causing lumen to be the lumen blocked off. This also disrupts the balance of oxygen supply and demand. It is not the angiograph-visible atheromatous plaque that causes coronary artery diseases. Rather, it is soft, mobile atheromatous plaque that makes a person more susceptible to coronary artery disease. This soft plaque is more likely to rupture, thus resulting in the obstruction of blood supply. (3,4)
Coronary artery disease is the number one cause of death for both men and women in developed countries. In regards to all spectrums of age, men are generally more susceptible to this disease than woman are. In fact, the disease is approximately three to four times higher for men and even appears ten years earlier for men than women. (3) Many factors both genetic and lifestyle, determine the difference of susceptibility in men and women. For example, hypertension, smoking, abdominal fat distribution, etc. all prove to be more biologically susceptible in men. Smoking in particular causes an increase in systolic blood pressure and has proven to be more common in the male population. This in turn causes men to more frequently experience development of plaque and plaque ruptures within the arteries. They also have more functional and structural irregularities in regards to their blood vessels. On the other hand, women experience more protective factors that prevent them from acquiring the disease. This could include how females posess the protective lipoprotein cholesterol and cadio-protective sex hormones. Even the shape of blood vessels in women give them an advantage. (6)
Diagnostic Tools
Apart from the routine checkup of medical history, blood tests and physical exams, there are several ways to diagnose coronary artery disease. One of the most common ways to diagnose coronary artery disease is an electrocardiogram. One version of this is to place a monitor that is portable on an individual who performs his or her daily activities. This form of diagnosis documents electrical signals passing throughout the heart. It can even show former attacks, find present ones or predict attacks likely to occur in the future. This way, the doctor can tell if there are any irregularities in blood flow.
The next possible form of diagnosis is a stress test. This test involves exercise to induce signs and symptoms of coronary artery disease. For example, a patient may be asked to perform activities such as walking on the treadmill or biking. Doctors can even provide heart-stimulating medicine to test the patient. Other stress tests involve the use of an echocardiogram or nuclear stress test. In the echocardiogram, soundwaves create images of the patient’s heart. More specifically, an ultra sound is taken before and after activity to determine portions of the heart that are weak, not as mobile or are not receiving a sufficient amount of oxygen. The purpose of a nuclear stress test is to determine the amount of blood which flows to cardiac muscles both in phases of stress and rest. In order to do so, a tracer is placed in the blood and cameras can tell places where blood flow is low.
An angiogram or cardiac catheterization can also be used to diagnose coronary artery disease. In an angiogram, a catheter is placed within an artery and dye is injected in to the cardiac arteries. The next form, cardiac catheterization involves dye that highlights blocked or constricted arteries on an x ray picture. In the case that there is a blocked area, a balloon is put through a catheter and then blown up in order to promote blood flow. To ensure that the artery is dilated, a stent can keep the artery wide.
A heart scan is one of the final diagnostic tools. Here, calcium deposits which block the arteries can be seen through computerized technology. A specific type of heart scan known as a computerized technology coronary angiogram exists where a dye is placed through a vein simultaneously with a computer technology scan. This way, a picture of a person’s cardiac arteries can be seen. (7)
Risk factors
Many risk factors exist with coronary artery disease. One of the biggest risk factors is smoking. Smoking can double the risk of acquiring coronary artery disease and cause one to suffer the effects of atherosclerosis, high blood pressure and damage their heart tissues. This hinders the flow oxygen rich blood throughout the body. Another risk factor is low density lipoprotein cholesterol linked with total serum cholesterol. A study published by the Framingham study and the Lipid Research Clinic discovered that there was a 0.8% risk increase in coronary artery disease for approximately every 1% lipoprotein cholesterol found in men and 1.9% found in women. Abdominal fat distribution and obesity also contribute to the list of risk factors. This accumulation of fat has been linked with increased levels of triglyceride, hypertension, cholesterol, high blood pressure and atherosclerosis. Diabetes mellitus is a more powerful risk factor in both men and women. Although diabetes is a risk factor for both sexes, hyperinsulinemia is associated only for men and higher plasma insulin resistance for women. The hemostatic factor of plasma fibrinogen proves to be one of the final risk factors for coronary artery disease in both sexes. This causes blood to be stagnant which ultimately reduces coronary blood flow. (6)
Methods of Treatment
There are a variety of ways to treat coronary artery disease. One of the first important steps is to make lifestyle changes. This includes simple activities such as setting up a weekly exercise schedule to lose excess weight, stopping smoking completely, having a healthy diet, and avoiding any thing that may cause stress.
Different types of drugs are also available as forms of treatment. For instance, aspirin can be used as a blood thinner, decreasing the likelihood of blood clothing and blockage of coronary arteries. Nitroglycerin in the form of tablet, patches or even sprays are used to manage chest pain. In order to accomplish this, nitroglycerin widens the coronary arteries temporarily as well as decrease the hearts blood demand. Cholesterol modifying medications such as fibrates, niacin, bile acid sequestrants and statins are used to lower the level of lipoprotein cholesterol in the blood. These medications also reduce plaque or excess material that make be blocking the coronary arteries. Beta blockers are another type of drug. The purpose of these drugs are to stall one’s heart rate and lower blood pressure, thus lowering the demand of oxygen for the heart. Their effectiveness allows for the reduction events leading to potential future attacks. Angiotensin converting enzyme inhibitors and angiotensin II receptors blockers complete the list of drug treatments. These drugs are similar to beta blockers in the way that they lower blood pressure and prohibit further advancement of coronary artery disease.
The last forms of treatments are the most intrusive. One of the treatments is called coronary artery bypass surgery. In this open heart surgery, a vessel or vein. from an alternative area of the body is connected to the coronary artery and is used as a new path for blood flow. This alternative transplant can be portion of a leg vein or wrist or chest artery. This allows for blood bypass the blocked portion of the artery. Another intrusive form of treatment is known as angioplasty and stent replacement. First, a catheter is placed in to the constricted area of the artery. Then, a balloon is inserted in the catheter and blown up to widen the artery. To ensure that the artery is dilated, a stent which is placed inside, even sometimes discharging dilating medicine. (7)