Atherosclerosis is characteristic inflammatory disease of the arteries. It is triggered by a process called atherogenesis in which there is an accumulation of low density lipoproteins causing the formation of plaque. The plaque thus formed gets accumulated in the arteries causing blockage in the blood flow. The most prominent arteries prone to these plaque accumulations are the elastic and muscular arteries.
Pathology of atherosclerosis
Atherosclerosis in the initial stages appears as a fatty streak and over time it develops into a more prominent condition causing hardening of the arteries. It results in the reduction of the arterial pathway of carotid, abdominal, cardiac and other arteries of the lower and upper extremities. The etiology associated with this condition is the deposition of cholesterol and lipids in the internal lumen of the artery. These depositions are focal in origin. The disruption caused in the endothelial lining because of cholesterol accumulation leads to the emergence of inflammatory disease and arterial injuries.
Atherosclerosis triggers many conditions such as atherosclerotic heart disease, peripheral vascular disorder, coronary artery disease, and carotid artery disease. In atherosclerotic condition, some diagnostic investigations may be non-specific to the patho-physiology associated with the disease. One such test is analysis of C reactive protein which is a non-specific marker of inflammatory disease. However, the fatty streaks and associated lesions caused are identified by the characteristic smooth muscles containing lipids in it.
A fibrous plaque is formed initiating the changes in the arterial wall. The cholesterol translocation in the arterial intima (inner region) is facilitated by the lipoproteins. The fibrous streak contains collagen which is grayish white or yellow in appearance resulting in the narrowing of the blood vessel. The emergence of a complicated lesion like this can induce the formation of ulcers leading to rupture and dissemination of the accumulated plaque to various regions. This leads to the occurrence of three types of strokes. The Thrombolytic stroke which is a result of a clot or thrombus formation, hemorrhagic stroke because of blood vessel damage and embolic stroke in which the clot does not pass through the narrow artery. This eventually results in the occurrence of ischemic stroke in which there is a lack of blood supply to the brain.
Factors associated with atherosclerosis
Hypercholesterolemia is one of the main causes as it causes the low density lipo-proteins to occupy the inner layer of the artery. Elevated homocysteine levels also play an important role in the occurrence of atherosclerosis. Homocyteine levels are generally high in patients who have a history of high red meat consumption rate. Increased homocysteine levels facilitate the hardening of the arterial wall causing atherosclerotic lesions. Increased angiotensin-II concentration is also an important factor in the initiation of atherosclerotic condition as it causes vasoconstriction and associated hypertension. Other factors include infections caused by Chlamydia and Herpes viruses.
In all these factors causing atherosclerosis, the nature of inflammatory response is associated with interactions related to the monocytes, endothelial cells and T cells. In most cases, plaques or associated clots occur in the region of branching, bifurcation or curvature of the arteries. This is because of the alternating blood flow path occurring in the respective region.
The risk factors associated with atherosclerosis are mainly because of lifestyle and preexisting medical conditions. Smoking, alcoholism, obesity and hereditary factors are the predominant reasons. Other factors include diabetes, hypertension and family history of which is associated with a specific altered gene.
Patients with atherosclerosis are advised to incorporate lifestyle changes with constant watch on their eating habits. Physicians and cardiologists recommend cardiovascular exercises on a regular basis apart from medication. Surgical interventions are required in case of increased coronary artery blockage and dispersed thrombus in the blood circulation.
The plaques formed in the arterial walls of one who suffers from atherosclerosis contain significant levels of cholesterol. The risk factor of Coronary Heart Disease (CHD) rises in direct proportion to the level of LDL - Low density Lipoprotein and comes down with an increase in the HDL cholesterol. The LDL is estimated by the following formula:
LDL Cholesterol = Total Cholesterol (mg/dL) - HDL Cholesterol (mg/dL) - (Triglycerides (mg/dL)/5)
Atherosclerotic Peripheral Vascular Disease occurs owing to Atherosclerosis in Aorta and Iliac Arteries which results in Claudication (pain on exertion) or in some cases lesions in the vessels of legs ( Occlusive Atherosclerotic Lesions). The severity of the symptom can vary from time to time and usually subsides after some rest. For men, bilateral common iliac disease can often start with Erectile Dysfunction (ED).
Framingham Heart Study
As the longest standing heart health study in the world, Framingham Heart Study, at Framingham, Massachusetts, continues to mine vast data for the last sixty years regarding the cause of heart trouble and care. The Framingham heart study has played a major role in identifying key risk factors for cardiovascular disease.
The first round of extensive physical examinations and lifestyle studies was conducted on 5,209 men and women who were healthy and ranging in ages 30 to 62 in the 1948. Since then, every two years, detailed medical history, physical examinations and diagnostic tests are carried out on the identified men and women folks. Participants in the study has been tracked using standardized biennial cardiovascular examination, daily surveillance of hospital admissions, information pertaining to death and information obtained from the physicians and sources outside the clinic.
In 1971, a second generation of 5,124 original participants' adult children and spouses were enrolled for similar examinations. Again in year 2002, enrollment of third generation participants, the grandchildren of the original cohort had begun. This is considered as a vital step to increase the understanding of heart disease and stroke and how these affect families. This third generation study was completed in July 2005 and it involved 4,095 participants.
Recently, the study has integrated new diagnostic technologies such as echocardiography, carotid artery ultrasound, magnetic resonance imaging of heart and brain, CT scans of the heart and bone densitometry into the past and ongoing protocols. Framingham heart study, after decades of careful monitoring of the population has led to identification of major Cardiovascular Disease risk factors namely:
The Framingham heart study risk score was primarily designed to predict a 10-year risk for Coronary Heart Disease but subsequent analysis has revealed that the risk score is very effective in predicting the short term cumulative risk for CHD. This is also applicable in the context of competing risk of death from non coronary causes.
However, there are criticisms that the study's risk model does not perform well in predicting life time risk score in younger subjects. This is attributed to changes in risk factor status that occur over time. Rates of hypertension and diabetes seem to increase sharply with age and this may alter the long time risk of younger patients in an unpredictable manner.
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Bibliography / Reference
Collection of Pages - Last revised Date: April 4, 2020