What is atherosclerotic plaque?
It is a raised focal deposit of fat and other substances that accumulate within the intimal layer of the artery (intimal layer is the inner most layer of artery). The plaque is composed of a covering fibrous cap with a necrotic lipid rich core. The fibrous cap is formed by smooth muscle cells and matrix; and the necrotic core, in which there is a cholesterol, cholesterol ester, lipid-laden foam cells, calcium and cellular debris. Atherosclerotic plaque is the principal cause of narrowing of the artery in adults.
Certain factors increase the risk of developing atherosclerotic plaque within the arterial wall. These are hypercholesterolemia (high cholesterol level in the blood), hypertension (high blood pressure), cigarette smoking, diabetes mellitus, increasing age, male sex, familial predisposition, insufficient regular physical activity, competitive and stressful lifestyle with type A personality, obesity, use of oral contraceptives, excess alcohol consumption and high carbohydrates intake.
Commonly affecting arteries:
Involvement of atherosclerotic plaque in the human body tends to quite constant. In descending order the most heavily affected arteries are –
1) Abdominal aorta – a large artery present in the abdomen.
2) Coronary arteries – supply the oxygen-rich blood to the heart.
3) Popliteal arteries – supply the oxygen-rich blood to the leg.
4) Descending aorta – a large artery present in the chest cavity.
5) Internal carotid arteries – they present on each side of the neck and supply the oxygen-rich blood to the brain.
6) Cerebral arteries – supply the oxygen-rich blood to the brain.
7) Mesenteric arteries – supply the oxygen-rich blood to the intestine.
8) Renal arteries – supply the oxygen-rich blood to the kidneys.
At first, the atherosclerotic plaques sparsely distributed within the arterial wall, but as the process advances they become more and more numerous and sometimes cover the whole intimal layer of severely affected arteries.
As the atherosclerotic plaques increase in size within the arterial wall, they progressively encroach on the lumen of artery as well as on the subjacent middle layer of artery. Consequently, they compromise arterial blood flow and produces symptoms. They cause clinical symptoms by the following:
1) Slow and insidious narrowing of the arterial lumen may cause ischemia of tissues supplied by the involved arteries. For example, narrowing of coronary arteries may cause chest pain, palpitation and shortness of breath after physical exertion; carotid arteries may cause light-headedness, blurring of vision, sudden loss of consciousness; arteries of the leg may cause leg pain after some walking (claudication).
2) Sudden occlusion of the arterial lumen by superimposed thrombosis into a plaque may cause myocardial infarction (if occlude coronary artery) and stroke (if occlude cerebral artery).
Many of atherosclerotic plaques eventually undergo a variety of complications such as –
1) Calcification – Atherosclerotic plaques in advanced case almost always undergo patchy or massive calcification due to accumulation of calcium. Severely calcified arteries may be converted into virtual pipe stems.
2) Ulceration, fissuring or rupture – Ulcerated, fissured or ruptured plaques may discharge debris into the bloodstream that may produce micro-emboli.
3) Thrombus formation – It is the most feared complication. Any ulcerated, fissured or ruptured plaque will expose its contents to the blood and will trigger platelet aggregation and ultimately formed thrombus. Thrombi may either occlude the lumen of artery or become incorporated within the plaque. Occlusion of the coronary artery in the heart may cause myocardial infarction or sudden death; the cerebral artery in the brain may cause stroke or transient ischemic attack; and the artery of the lower limb may cause acute limb ischemia or gangrene.
4) Aneurismal dilation – Basically, atherosclerotic plaques are deposited in the inner layer of the artery. But in severe cases, the plaques may create enough pressure on underlying middle layer to produce pressure atropy (shrinkage in the size) and loss of elastic tissue, causing sufficient weakness to permit aneurismal dilation. It may occur in any artery, but the most common and most significant are in the aorta. Aortic aneurismal dilation may cause death by sudden rupture.
Atherosclerotic plaques can be detected by –
Doppler ultrasound imaging of arteries – A Doppler ultrasound imaging uses reflected sound waves to see how blood flows through an artery.
Traditional angiography – It is an imaging technique used to visualize the lumen of blood vessels by using a fluoroscopy. It is done by injecting a special dye into the blood vessel. Here the dye is injected directly into the target blood vessel via an inserted angiographic catheter thread.
CT (computed tomography) angiography – It is similar to a CT scan, but a special dye is injected into the blood vessel shortly before the scan is performed. CT angiography shows detailed images of the blood vessels in the body.
Magnetic resonance angiography (MRA) – When MRI (magnetic resonance imaging) is applied to the blood vessels, it is referred to as magnetic resonance angiography. A variety of techniques can be used to generate the images. In most cases, a special dye is injected into the blood vessel to make easier to see the lumen of the blood vessels.
People should follow the following tips to prevent atherosclerotic plaque formation within their arterial wall:
1) Do not smoke.
2) Take regular exercise, minimum of 20 minutes 3 times per week.
3) Maintain an ideal body weight. BMI (body mass index) between 18.5 to 24.9 kg/m2 indicates an ideal body weight (BMI is the weight in kilograms divided by the height in meters, squared. For example, a person weighing 60 kilograms with a height of 1.6 meters has a BMI of 60/1.62=23.4 kg/m2).
4) Eat a mixed type diet rich in fresh fruit and vegetables.
5) Avoid fatty foods. Aim to take not more than 10% of energy from saturated fat.
People, who already develop symptoms of atherosclerotic plaques, should be offered treatment. They should strictly avoid the smoking. They should be intake statin therapy (atorvastatin, simvastatin, rosuvastatin) irrespective of their serum cholesterol level. Blood pressure should be treated to a target of 140/85 mm Hg or lower. Aspirin and ACE inhibitors (lisinopril, ramipril, captopril) are of benefit that reduces the risk of myocardial infarction, stroke and death. Sometimes beta-blocker may be beneficial for selected patient.