Simply put, coronary artery disease describes the build up of plaque material in the lumen of the blood vessels that feed or nourish the heart muscle. The Heart, like any other organ in the body, requires a blood supply and that supply does not unfortunately come from any of the blood that fills its chambers. The coronary arteries, the first branch blood vessels of the aorta supply the Heart with almost all of its required blood, which is quite a lot given its high metabolic activity. If these blood vessels become obstructed, then the blood flow can diminish. If this happens slowly, "angina" or chest pain can become a symptom. If this happens suddenly, a "myocardial infarction" or heart attack can occur. Some individuals never develop symptoms that they can feel and the heart muscle can deteriorate slowly and silently until heart failure becomes apparent.
Plaque material consists of fat, cholesterol, calcium and a variety of other cellular components like smooth muscle cells and blood cells. The deposition of this material occurs almost throughout life, starting even during childhood in many people. As this deposition progresses, the lumen gradually narrows and the blood flow is limited. The plaque material can also be somewhat brittle and fragile. Sometimes, the plaque cracks or fractures causing an acute obstruction with a sudden build-up of platelets which completely closes the lumen and flow ceases altogether. Most commonly, a heart attack then ensues.
Coronary artery disease affects over 13 million Americans, but sadly, many people don't know they have it. Annually, over 1 million procedures are performed in the United States to mechanically, clear the obstruction from the coronary arteries, either with a balloon angioplasty and a stent or an operation designed to bypass the blocked areas. Despite all these interventions, more than 500,000 individuals die of complications of coronary artery disease annually, and the vast majority of these people never were aware of their problem. Coronary atherosclerosis, as it is often called, develops slowly and often silently over decades. The first presenting symptom in many people is unfortunately a heart attack that is fatal.
It is important to control as many of the risk factors that lead to coronary artery disease as possible. Though new medicines can help control the progression of the process, the best long-term solution is often life-style choices that are best practiced throughout life.
There are many risk factors for the development of coronary artery disease, or coronary atherosclerosis. Many are controllable, but some are not. Certainly, the greatest risk factor is an inherited predisposition to develop the blockages, either a familial inheritance or one associated with a particular race. African-Americans, Mexican-Americans, Hawaiians and Native Americans are all at increased risk of having this kind of heart disease. Gender is also a risk factor - men are generally at greater risk, though women's risks dramatically increase after menopause. Age is, of course, another risk beyond our control. Most individuals dying of coronary artery disease are over the age of 65, but this does not mean that a heart attack cannot be fatal in younger people. Individuals who inherit a particularly virulent form of atherosclerosis can succumb to this problem even in their twenties and people with a somewhat lesser severe form, who have other so-called controllable risk factors can often develop severe problems much younger than 65.
Amongst risk factors that we can control, smoking and over-eating to the point of obesity are the most important. Smoking, like high blood pressure, damages the lining of the blood vessels and promotes the formation of blockages. Obesity not only raises blood pressure and cholesterol levels but also increases the strain on the heart and the risk of diabetes. Excessive intake of fatty foods, especially those high in saturated fat can dramatically increase the amount of low density lipoprotein (so-called "bad cholesterol") in blood which leads to blockage formation. Diabetes, especially with poorly controlled blood sugar levels, can cause a particularly diffuse type of coronary artery blockage pattern. Physical inactivity tends to elevate levels of low-density lipoprotein and causes hypertension. Stress is also known to increase the risk of coronary artery disease and may also contribute to over-eating, smoking and drinking alcohol. While moderate consumption of alcohol may lower the risk of heart disease, large amounts usually cause high blood pressure and elevate triglyceride levels.
The relationship between cholesterol levels and coronary artery disease is often misinterpreted. In general, a level below 180 is preferred, but many individuals have very low cholesterol levels and still develop atherosclerosis. Others have very high levels of cholesterol and never develop blockages. In brief, it is best to maintain a diet low in saturated fat and exercise regularly. If there is a strong family history for atherosclerosis then one could consider a more strict diet plan even with a low cholesterol and the addition of a lipid lowering drug ("statins"). Consult a physician before starting any medication as some of these drugs can cause serious side-effects.
Signs and Symptoms
The problem with coronary artery disease is that often the symptoms are inconsistent or even non-existent and there is no perfect screening examination. Often the first symptom is a full-blown heart attack. Commonly, however, varying degrees of chest pain occur, either at rest or on exertion. This chest pain represents a relative lack of blood flow to heart muscle and is called "ischemia". It is more commonly known as "angina". This ischemia may present with alternative equivalents: chest pressure or heaviness, left arm discomfort, jaw tightness, back pain, among others. Often, any or all of these symptoms may be associated with shortness of breath. These symptoms may occur at rest or on exertion, either physical or emotional and usually subside rapidly after the stress is over.
If the pain persists for longer period of time and is of a severe nature, a more fixed, acute blockage of blood flow to the heart muscle usually has occurred. This is what causes a heart attack and means that some degree of damage is occurring to the heart muscle.
Whether the pain occurs suddenly and with great severity or is less severe but persists over a long period of time in an intermittent fashion the result may be the same: deterioration of heart muscle function. When the heart muscle loses its ability to contract with vigor, heart failure ensues. The most common manifestation of heart failure is shortness of breath. In contradistinction to the brief episodes of shortness of breath which are associated with cardiac ischemia, this shortness of breath is chronic and persistent. Other symptoms of heart failure include difficulty sleeping flat in bed, a chronic productive cough, and swelling of the feet and ankles.
In many respects, the worst scenario may be "silent ischemia". In this circumstance, the blood supply to the heart is limited by obstructive pathology of the arteries but there are no symptoms - no chest pain at rest or exertion. Although this situation is more common in patients with diabetes, it can also occur in non-diabetics. Over a protracted period of time, the heart muscle slowly deteriorates and loses its ability to contract vigorously and heart failure results. This is called "ischemic cardiomyopathy" and although procedures designed to revascularize the heart may stabilize the condition, the contractile function can usually not be restored to normal. Furthermore, such a situation leads to enlargement of the heart and stretching out of some of the valves leading to valvular leakage, which exacerbates the symptoms of heart failure. In the past, patients with heart failure were largely untreatable except for a transplant, but today newer medications and sophisticated surgical procedures can ameliorate the most severe symptoms and allow an almost normal lifestyle in most instances.
Arteries are blood vessels that carry nutrients and oxygen to all tissues of the body. These blood vessels have the ability to dilate and carry more blood as demand requires and contract when at rest or when damaged and flow needs to be limit leakage. The arterial walls are made up of different layers: an inner layer that is thin and slippery, an elastic layer that protects the inner layer which is quite fragile, a muscular layer that lets the wall dilate and contract and an outer layer that connects the system to nutrients and other factors that help protect the body against infections and damage. The inner layer is fragile and prone to slight breaks when subjected to stress, mostly from high blood pressure. Various components of tobacco smoke can also weaken this inner layer. The body is constantly repairing these small fractures as a normal process of healing, but if the system has a very high fat content or there are too many fractures of the wall, the healing process causes a build up of cellular debris and cholesterol that ultimately causes an obstruction in the lumen. Individuals with a strong family history of atherosclerosis, as the process is called, have inherited a relatively fragile inner layer. The situation is compounded if they are also hypertensive, diabetic or have a high cholesterol level in the blood. Certain arteries have very exuberant elastic layers to reinforce the inner layer and are thereby almost immune to the healing process that causes the obstructive build-up. The Internal Mammary or Internal Thoracic Arteries are such blood vessels and therefore make excellent conduits as replacement arteries during coronary bypass surgery (see Treatment below).
It is reasonable to ask why the obstructive material within the blood vessels cannot simply by removed by grinding the material out. Such technology exists, but is not very successful as a stand alone procedure. The obstructive process replaces the smooth slippery lining of the blood vessel. If the obstruction is ground out (rotoblation), the vessel wall is now more heavily damaged than ever before and the healing process that ensues will create an even more exuberant blockage. There is also a very high likelihood that platelets will aggregate at the site and cause the blood vessel to clot and close down. Rotoblation is, however, combined occasionally with stent placement to manage such situations with some success. The pathological process is analogous to what happens to a galvanized steel pipe with age - as the inner portion of the pipe deteriorates, it obstructs the inner lumen. If one was to grind out the inside of the pipe, there would be no pipe left.
Coronary atherosclerosis, even when quite severe, is often without symptoms. This can make diagnosis difficult. There are, however, some screening tests that are available and based on risk factors and family history, different studies may be appropriate.
Any work-up starts with obtaining a history, including family history, physical exam and routine blood tests. Based on this information, other diagnostic tests may be necessary. A simple office procedure is an electrocardiogram . This analyzes the electrical activity of the heart and is best in identifying an abnormality if there is previous damage or if there is ongoing ischemia. In both of these circumstances the electrical conduction system of the heart is abnormal and there will be an identifiable change in the pattern of the EKG. Unfortunately, this test is not very sensitive and will not diagnose the degree of blockage in the coronary arteries unless blood flow is so severely limited that the heart muscle is being damaged. Sometimes a Holter Monitor EKG is obtained. In essence, this is an EKG that is taken over an entire 24 hour time period and should include periods of ordinary every day stress which might be causing cardiac ischemia.
To simulate the stress of every day life a Stress Test may be obtained. In this circumstance, one is asked to walk on a treadmill or pedal a bicycle to exercise the heart and see if it will show signs of ischemia when placed under the strain of work. It is also possible to give certain medicines to simulate such a work load. A Stress Test is the most common screening examination for coronary arteriosclerosis, usually used in patients without symptoms but at some risk of cardiac ischemia.
An Echocardiogram is a test that obtains a two or even three dimensional picture of the heart and can identify areas that are not contracting normally. This might be due to old damage from a previous heart attack or from on-going ischemia. When coupled with a stress test, this test is much more sensitive than the EKG.
Another type of examination that may show cardiac ischemia is a Nuclear Scan. A very small amount of radioactive material is injected into the bloodstream which is then selectively absorbed by the heart muscle. Areas of heart muscle with limited blood supply will not absorb as much radioactivity and can be identified with special cameras.
Coronary Catheterization or Angiography has long been considered the definitive test to identify coronary artery blockages. A small tube is introduced into the bloodstream either through an artery in the groin or forearm and threaded into the aorta and to the heart. The tube is engaged into the lumen of the coronary arteries, a radio-opaque dye material is injected and a camera records the pictures with X-Ray technology. Blockages of the arteries will be visualized.
MRA (magnetic resonance angiography) and EBCT (electron beam computerized tomography) are two new tests that image the coronary arteries as non-invasive procedures. The first uses magnetic waves to produce a three-dimensional picture of the heart and the latter uses x-ray technology but with advanced computer software to generate an alternative three-dimensional image. Also known as Ultrafast CT this test detects the calcium in plaque material which obstructs the coronary artery lumen. When a substantial amount of calcium is detected it is likely that coronary artery disease is present. Both of these test, however, lack some degree of sensitivity and are considered experimental at this time as more information on their accuracy is obtained.