What factors are most important to know in terms of preventing heart attack - Research Paper Example

Preventing Heart Attack Introduction: All cells in a human body require oxygen and nutritional supply to meet their energy needs. Different organs have variable energy requirements depending upon their work load. Blood is a medium by which all these essentials nutrients and oxygen for respiration are made available to these cells. If blood supply to any organ is impaired, it deprives the cells from oxygen and terminates the aerobic respiration process, such as oxidative phosphorylation, responsible for bulk of the ATP production. This initially, leads to reversible injury that can be restored to normal if hypoxia is lifted off. But if oxygen deprivation is prolonged enough it may result in permanent or irreversible cellular damage leading to an ‘infarct’. Heart is one organ that is particularly prone to hypoxia because of its narrow lumen blood supply and lack of sufficient collateral anastamosis. When myocardial cells are irreversibly damaged due to hypoxia or lack of blood supply, the condition is called myocardial infarct or simply ‘Heart Attack’. Atherosclerosis: To understand how certain risk factors can contribute to heart attack, it is important to understand the pathogenesis of atherosclerosis. This is because most of the major risk factors such as diabetes, hypertension and smoking will lead to a common pathway of narrowing the coronary blood vessels by forming atherosclerotic plaques. Atherosclerosis is a chronic phenomenon that takes years to develop and can affect any blood vessel in the body. It begins with accumulation of lipoproteins in the internal layer of blood vessel, the intimae. This accumulation gives a morphological appearance of a fatty streak and is considered as initial lesion of atherosclerosis. These lipoproteins, retained in the extracellular matrix, undergo oxidative modifications that promote atherogenesis. The second phase in atherosclerosis is the recruitment of leukocytes to the site of lipoprotein deposition. This recruitment is facilitated by expression of adhesion molecules of the surface of endothelial cells. Once at the site, these cells reside in the intima and contribute to inflammation mediated by various inflammatory cytokines and tissue necrotic factors. In the third phase, the mononuclear phagocytes, recruited earlier, matures into macrophages and participate in the clearing on lipoproteins by receptor mediated endocytosis. This induces the conversion of these macrophages into foam cells. Recruitment of smooth muscle cells ultimately leads to the formation of fibrous capsule over the plaque. (Harrison and Kasper 1425-1427). Risk factors: Following are the major risk factors associated with atherosclerosis and heart attack. 1. Smoking 2. Hypertension 3. Diabetes Mellitus Smoking: According to the US statistics, 400,000 individuals die prematurely due to cigarette smoking. Smoking is a risk factor commonly associated with the coronary heart disease. It is a well developed fact that the chances of developing large vessel or small vessel atherosclerotic disease are high in cigarette smokers as compared to non smokers. According to the statistics, about 20-30% coronary artery diseases are caused by cigarette smoking (Harrison and Kasper 2574). One important concept to remember about most of the major risk factors of coronary artery disease is that they tend to increment the risk of this disease to a greater extent if coexisted in the same individual. The major underlying pathogenesis by which cigarette smoking can cause coronary artery disease and contribute as risk factor is by promoting formation of atherosclerosis plaques. Moreover, most constituents of cigarette smoke promote platelet aggregation that increases the risk of thrombus formation after the fibrous cap ruptures into the vessel lumen. Cigarette use cessation after an acute episode of myocardial infarct or heart attack results in reversal of these effects, further highlighting the association. It is estimated that after 15 years of cigarette cessation the risk for the development of coronary occlusion is similar to non smokers. (Harrison and Kasper 2574). Hypertension: Hypertension can be roughly defined as abnormal elevation of blood pressure. The exact or quantitative definition varies according to the blood pressure classification as either pre, stage1, stage 2 or isolated systolic hypertension. Long standing uncontrolled hypertension doubles the risk of coronary artery disease (Harrison and Kasper 1463). There are basically two ways by which hypertension act as a risk factor for myocardial infarct or heart attack. Firstly, like cigarette smoking it promotes atherosclerosis in the coronary arteries. However, the underlying pathogenesis is a bit different in hypertension. The elevated pressure exerted on the vessel walls of the coronary artery increase the risk of endothelial damage that triggers a cascade of event leading to atherosclerotic plaque formation. Endothelial damage results in expression of certain platelet aggregating factors that promotes to thrombus formation. Secondly, long standing hypertension can cause hypertrophy of the heart muscle in response to increased after load or total peripheral resistance. This in turn, increases the risk of myocardial infarct by various mechanisms. Increase bulk of heart muscle and excess work load; elevates the oxygen demand, therefore, inducing hypoxia even at minimal narrowing of coronary vessels. Moreover, hypertrophy of the heart leads to congestive heart failure reducing systemic as well as coronary perfusion. (Harrison and Kasper 1467). Diabetes Mellitus: Diabetes mellitus is an endocrine disorder that impairs glucose metabolism and is associated with other metabolic abnormalities. Both type 1 and type diabetes are associated with increased risk of heart diseases including heart attack. An individual with type 2 diabetes without any previous episode myocardial infarct has the same risk of getting heart attack as non diabetic patient that survived the first myocardial infarct. Diabetes contributes to coronary artery occlusion by promoting atherosclerosis due to dyslipidemia which is a common finding in diabetic patients. Moreover, uncontrolled glucose levels in the blood promote hyalinization of blood vessels leading to arteriosclerosis. All these factors contribute to narrowing of coronary arteries, abnormal platelet aggregation and other macro or microvascular abnormalities. Diabetes is also associated with neuropathy, thereby, increasing the risk of silent myocardial infarct which is associated with high mortality rates. (Harrison and Kasper 2166-2167). Coronary Arteries and Atherosclerotic Complications: Heart has three distinct muscular layers; endocardium, myocardium and epicardium. Only inner part of the innermost layer, endocardium is able to receive oxygen and nutritional supply directly from the blood present in the heart chambers by simple diffusion. The remaining outer layers require proper blood supply like most organs. The arteries supplying the heart are called coronary arteries and they originate as the most proximal branches of aorta just above the aortic valves. Unlike other major organ arteries, coronary arteries have comparatively narrow lumen. Therefore, an atherosclerotic process explained earlier can cause significant blockage to the blood flow. The fibrous capsule formed by the smooth muscle cells can sometimes rupture leading to the thrombus formation within the lumen of coronary arteries. In some cases, this thrombus can dislodge and the resulting embolus can travel more distal, narrowed lumen portion of the vessel resulting in complete blockage (Harrison and Kasper 1428). This can ultimately result in myocardial infarct or heart attack. Conclusion: All the above discussed risk factor either contribute by a common pathway of promoting atherosclerosis or by other specific mechanisms that ultimately reduce the oxygen supply to heart tissue. It is crucial to know these risk factors as avoiding them can significantly prevent episodes of myocardial infarction. Work Cited Harrison, T. R., and Dennis L. Kasper. Harrison's Principles of Internal Medicine. New York: McGraw-Hill, 2005. Print. Read More