What Is Atherosclerosis

 Atherosclerosis is the hardening of the large and medium sized arteries due to fat deposition (plaques) on their walls, resulting in reduced flow of blood.

  • Injury to the arterial walls caused by elevated cholesterol levels in the blood, diabetes, high blood pressure and tobacco use result in atherosclerosis.
  • Muscle cramps and pain on exertion, because the blood flow is insufficient to meet the oxygen requirement of the tissues, may be the initial symptoms
  • Regular exercise, avoiding high-fat diet and tobacco use and proper management of diabetes and blood pressure may help prevent atherosclerosis.
  • Stroke or heart attack resulting from atherosclerosis is treated first.

 16 million people in the United States alone were found to be having atherosclerosis according to a study in 2005. In fact, atherosclerotic heart disease is the major cause of death in most of the developed countries including the US.

Cardiovascular disease and cerebrovascular disease, mainly resulting from atherosclerosis that cause thickening, hardening and narrowing of major arteries that supply blood to the heart muscle and the brain, account for more deaths than all the other causes such as cancers and injuries put together. Heart attacks caused by coronary artery disease due to atherosclerosis of the coronary artery and stroke caused by atherosclerosis of the arteries to the brain are the main killers in the developed world in spite of all the advances in the medical field.

Arteriosclerosis is the general term for diseases that cause the arterial walls to thicken and consequently become less elastic. Atherosclerosis which affects the medium to large arteries of important organs such as heart, brain and kidneys as well as those in the legs is the most frequently occurring type of arteriosclerosis.

Atherosclerosis Causes

Atherosclerosis is initiated by the repeated injury to the walls of the arteries by high blood pressure, inflammation, infections and high glucose and cholesterol levels in the blood.

  • Physical stress is caused by turbulence in the flow of blood at the places where arteries branch and it is more when the blood pressure is high.
  • Inflammatory stress may be caused due to infections by bacteria and viruses  such as helicobacter pylori, Chlamydia pneumonia cytomegalovirus etc., or by body’s auto immune responses to abnormal amounts of chemical substances in the blood such as cholesterol and glucose

At the initial stages in the development of atherosclerosis, monocytes and T cells responding to the injury of the walls of the artery, congregate on that location and get transformed into another type called foam cells. These foam cells attract fatty materials like cholesterol and become patches called atheromas on the wall. These atheromas or plaques eventually get calcified hardening the walls on which they grow. They are usually concentrated at the site of branching of the arteries but scattered patches are found all along the major arteries.

Plaques growing into lumen of the artery make it narrow and reduce the blood supply to the tissues. Plaques that grow into the artery walls may not impede the flow of blood but both types of plaques can rupture and cause blood clots to form on their surface, which may further narrow the artery or completely block it resulting in heart attacks and strokes depending on the location of the blockage. Fragments of plaques travelling in the blood vessel may cause blockage in smaller arteries anywhere in the body.

Atherosclerosis Risk Factors

Usually, high blood pressure, high blood cholesterol levels, smoking, obesity and diabetes are considered the main modifiable risk factors. Moderate amounts of alcohol and diet rich in vegetables and fruits are known to lower the risk.

The risk of developing atherosclerosis is higher and earlier for men than for women, and members of some families are predisposed to early onset of this disease. Age also increases the risk. These risk factors cannot be modified.

Smoking: Tobacco use in any form including smoking greatly increases the risk of developing atherosclerosis, and eventually coronary artery disease. With other risk factors being present as well, smoking can be potentially fatal. Men who smoke are three times more prone to heart attack than non-smokers and the risk of women who smoke is six times more than their counterparts who do not smoke. When smokers quit, significantly favorable modification in their risk profile is observed.

Tobacco use changes the chemistry of blood in several ways. It raises the levels of bad cholesterol (LDL), while lowering that of the good cholesterol (HDL). Blood levels of carbon monoxide are also raised, which has the effect of damaging the linings of the arterial walls. Constriction of the arteries which are affected by atherosclerosis worsens the coronary artery disease and significantly reduces the blood flow to the vital organs and other tissues. Tobacco makes the platelets stickier and enhances clot formation in the arteries that supply the heart, brain increasing the risk of heart attack and stroke.

Irrespective of the intensity and duration of the habit of smoking or tobacco chewing, the beneficial effects of quitting becomes apparent immediately. By quitting, people may reduce their risk of developing atherosclerosis by half and their chances of dying following a heart attack or a bypass surgery of the coronary artery are also considerably lowered. Those who have peripheral arterial disease also benefit by their lowered risk for illness and death due to their condition. Being in a place filled with tobacco smoke is as risky as smoking and this kind of secondhand smoke also should be avoided.

Cholesterol Levels: The blood cholesterol levels tend to increase with age, especially in men and post-menopausal women. A diet high in low density lipoproteins and low in high density lipoproteins increase the risk of atherosclerosis, but it can be modified by reversing the lipid profile of the diet. There are some inherited disorders, which cannot be modified that result in higher cholesterol levels and such people usually have early death due to coronary artery disease.

Statins are a group of drugs which reduce the LDL cholesterol levels, thus lowering the risk of death due to heart attack and strokes. High HDL cholesterol levels also lower the risk of atherosclerosis.

The normal level of total cholesterol is between 140 mg/dL to 200 mg/dL, inclusive of the bad cholesterol LDL, the good cholesterol HDL and triglycerides. High levels of cholesterol, usually around 300 mg/dL, double the risk of heart attack. To reduce the risk, the LDL should be limited to 130 mg/dL or less and HDL should be raised to 40 mg/dL or more.

People who have other risk factors for atherosclerosis such as diabetes and high blood pressure, and those who have had stroke, heart attacks and heart surgery, are advised to keep their LDL cholesterol level much lower as an extra precaution. But the HDL cholesterol level is very important and should constitute at least a quarter of the total cholesterol. High triglyceride levels are thought to lower the good cholesterol HDL increasing the risk of atherosclerosis. But new findings point to the direct role of triglycerides in raising the risk of atherosclerosis.

 High Blood Pressure: The risk of atherosclerosis increases incrementally as the blood pressure gets elevated above 110/75 mm Hg. High diastolic as well as systolic pressure being a major risk factor for stroke and heart attack due to atherosclerosis, doctors always strive to achieve a blood pressure level lower than 140/90 mm Hg. In people with diabetes and those having kidney disease, the blood pressure is maintained at still lower levels of 130/80 mm Hg keeping in mind their predisposition to coronary artery disease.

Diabetes Mellitus: Type 2 diabetes or diabetes mellitus make people more prone to atherosclerosis of large arteries while type 1diabetes predisposes people to the disease of the small arteries in the kidneys, nerves and eyes resulting in kidney failure, damage to the nerves and blindness. People with diabetes, especially women, usually develop atherosclerosis much earlier and quite extensively than those without diabetes. Unlike non-diabetic women who are protected from atherosclerosis before menopause, women with diabetes are not afforded any such protection. People with diabetes have an increased risk of death at par with those who have had a heart attack; hence, doctors usually advise regular monitoring and strict control of additional risk factors such as high blood pressure and cholesterol levels.

Obesity: the risk of developing coronary artery disease is considerably increased by obesity, especially abdominal obesity due to disproportionate fat deposition around the midsection. This is also called truncal obesity and it is an added risk to the other risk factors of atherosclerosis such as diabetes mellitus, high blood pressure and elevated cholesterol levels. Weight loss through exercise or diet control may help reduce these risk factors as well.

Physical Inactivity: A sedentary life style with reduced physical activity predisposes a person to coronary heart disease, but even a moderate amount of exercise seems to be beneficial not only in reducing the risk of mortality but also in reducing the other risk factors of atherosclerosis such as insulin resistance, high blood pressure, high cholesterol levels and obesity.  .

Diet: A diet rich in vegetables and fruits is a proven way to reduce the risk of coronary artery disease. The beneficial effect may be due to the phytochemicals present in them. It may also be due to the possibility that those consuming a lot of fruits and vegetables may be consuming less of the fat-rich foods, in addition to the health benefits they derive from the fiber and vitamins contained in them. A group of phytochemicals found in red and purple grapes, black teas and dark beer called flavanoids are considered to protect against coronary artery disease. The comparatively low occurrence of the disease among the French who consume large amounts of red wine, while they generally have high tobacco usage and have a diet rich in fats are attributed to the beneficial action of flavanoids. However, taking flavanoid-rich supplements do not seem to offer the same benefits as eating a diet rich in flavanoids. Though extra fiber content helps lower cholesterol and blood sugar, excess fiber prevents the absorption of essential micronutrients.

Fat is an indispensible part of our diet and while restricting the intake of dietary fat, it is important to know different types of fats.

  • Saturated fats and trans fats are considered bad for health as they contribute to the development of atherosclerosis. Butter and hydrogenated oils like margarine and shortening are high in saturated fats as well as trans fats. They generally have a denser texture. Fats of animal origin, red meat, full fat milk and milk products are rich sources of saturated fats and their usage should be limited to protect against atherosclerosis. Junk foods and many processed foods have high amounts of trans fats which is injurious to health.
  • Unsaturated fats are of two types; polyunsaturated fats and monounsaturated fats. Fats that remain soft or in oil-form at normal room temperature are usually unsaturated fats. Olive oil, canola oil and nuts which are considered heart healthy are monounsaturated fats. Many seeds, vegetable oils and products like mayonnaise have high levels of polyunsaturated fats. Omega-3 is a beneficial polyunsaturated found in oily fish like salmon, walnuts and canola. Omega-6 fats are another polyunsaturated essential fat found in sunflower oil, safflower oil and in some seeds and nuts. People are advised to include foods rich in omega-3 and omega-6 fats in their diets to protect against atherosclerosis.

Alcohol Intake: Drinking alcohol in moderate amounts is found to be reducing the risk of developing coronary artery disease, mainly because alcohol decreases inflammation and blood clot formation and increases the level of HDL, the good cholesterol. It also protects the body from harmful chemicals resulting from cell activity. However, alcohol is counteractive in excess as it increases the risk of other health problems and should be limited to 9 drinks a week for women and 14 drinks for men.

 Hyperhomocysteinemia: People with high levels of the amino acid homocysteine  in the blood due to a hereditary disorder, are predisposed to atherosclerosis of the coronary artery (coronary artery disease) even when they are young.  Higher circulatory levels of this amino acid not only have a direct damaging effect on the artery lining but also encourage blood clot formation but drugs which lower the levels of homocysteine do not seem to help lower mortality.

Atherosclerosis Symptoms

Depending on the location of the artery affected by atherosclerosis, symptoms may vary. When atherosclerosis causes gradual narrowing of the artery, the symptoms may not appear till over 70% of the lumen or the inside space of the artery gets narrowed. The initial symptoms resulting from a narrowed artery may be intermittent cramping or pain on exertion because the reduced blood flow fails to meet the oxygen requirement of the tissues. Chest pain during exercise may result due to inadequate supply of oxygen to the heart muscle. Intermittent claudication is a symptom precipitated by inadequate supply of oxygen to the muscles of the leg, due to which a person experiences leg cramps while walking. Narrowing of renal arteries that supply the kidneys may result in extremely high blood pressure or even kidney failure.  Blocks in the arteries to the legs may also result in the development of gangrene in the foot or toes. If coronary arteries which supply blood to muscles of the heart get blocked, it can precipitate heart attack and stroke can result from a block in the arteries to the brain.

Diagnosis of Atherosclerosis

When a person exhibits symptoms of arterial blockage, doctors use appropriate tests to determine the exact location as well as the extent of the block, based on the indication given by the characteristic symptoms. Since damage to the arteries due to atherosclerosis is not usually limited to one organ, when doctors detect a block in one location; the artery of the leg for example, they always conduct further tests to ascertain the extent of damage to arteries that supply to important organs like the heart and the brain to preempt the incidence of a heart attack or a stroke. They also assess other risk factors such as cholesterol, serum triglycerides and fasting glucose levels through blood tests. These tests are an integral part of routine health check up usually recommended for adults every year.

People who are prone to atherosclerosis are often advised to undergo diagnostic imaging tests such as an MRI scan or CT scan as a preventive measure. Magnetic resonance imaging (MRI scan) of the coronary artery can detect plaques which are hardened by calcification. Electron beam computed tomography (CT scan) also can be employed identify calcified plaques. Thickening of the walls of the carotid arteries in the neck, indicative of atherosclerosis, can be detected by an ultrasound scan. Some doctors are of the opinion that, these tests are unnecessary, as the advice given to a person in the high risk group regarding life style changes, remains the same in spite of the test results.

Prevention and Treatment

People at higher risk of developing atherosclerosis are advised to take antiplatelet drugs such as aspirin, and cholesterol lowering statins, even when they have normal blood levels of cholesterol, as a preventive measure. Avoiding tobacco usage, maintaining low blood cholesterol levels especially of LDL and strict management of diabetes and high blood pressure and maintaining weight through regular exercise go a long way in preventing atherosclerosis.

Leg cramps, kidney failure, stroke, gangrene or heart disorders such as abnormal heart rhythms, angina, heart failure and heart attack are the usual complications precipitated by worsening atherosclerosis and they need to be treated first.

Atherosclerosis Video Summary

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Yasser Elnahas

MD, PHD, Professor Of CardioVascular Surgery
Dr. Yasser Elnahas, Is an associate Professor of Cardiovascular Surgery. Dr. Elnahas was trained as a fellow At Texas Heart Institute And Mayo Clinic Foundation.Dr. Elnahas is dedicated to educating the general public about different disease conditions and simplifying the medical knowledge in an easy to understand terminology.

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2 Responses to What Is Atherosclerosis

  1. Cassie Debruce says:

    In some ways, triglycerides are the easiest to understand. Simply put, triglycerides are fat in the blood and are used to provide energy to the body. If you have extra triglycerides, they are stored in different places in case they are needed later. High triglyceride levels have been linked to a greater chance for heart disease. Just what your triglyceride levels mean and how much lowering triglycerides reduces heart disease risk is sometimes less clear.

  2. yasser says:

    Absolutely true. Thank you for your comment.

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