ECG test to Diagnose Heart Attacks

An electrocardiogram (ECG or EKG) is a routine test that is used to look at the electrical activity of the heartbeat. An electrocardiogram can tell your doctor a lot about your heart and how it is working.

This test can help your doctor learn more about your heart rhythm, the size and function of the chambers of your heart, and your heart muscle. A healthy person's electrocardiogram has a certain pattern. When there are changes in that pattern, your doctor can tell that there is a problem with your heart. For example, during a heart attack, the EKG machine records the changing pattern of the heart's electrical activity.

How does it work?

For your heart to beat, an electrical impulse is sent from the sinoatrial (SA) node, which is located in your heart. The SA node helps your heart keep a steady pace. An electrocardiogram can trace the path of electrical energy that is sent from the SA node and through your heart. This lets your doctor know whether you have a problem that might cause your heart to beat irregularly.

Small metal disks called electrodes are placed on your skin. The electrodes are used to pick up the electrical impulses of the heart. The impulses are recorded, giving doctors a record of your heart's electrical activity.

An electrocardiogram (ECG or EKG) tracing.

What should I expect?

No special preparation is needed before you have an electrocardiogram.

During the test, you will lie on an examination table. A technician will clean the areas on your body where the electrodes will be placed, usually your chest, back, wrists, and ankles. The electrodes have wires called leads, which hook up to the electrocardiogram machine.

Once the electrodes are in place, you will be asked to lie down. The technician will enter some information into the electrocardiogram machine and then tell you to lie still for about a minute while the machine takes its readings. The test is completely safe and painless.

What about heart attacks in women?

Coronary artery disease (CAD) and heart attacks are erroneously believed to occur primarily in men. Although it is true that the prevalence of CAD among women is lower before menopause, the risk of CAD rises in women after menopause. At age 75, a woman's risk for CAD is equal to that of a man's.

CAD is the leading cause of death and disability in women after menopause. In fact, a 50-year-old woman faces a 46% risk of developing CAD and a 31% risk of dying from coronary artery disease. In contrast, her probability of contracting and dying from breast cancer is 10% and 3%, respectively.

The risk factors for developing CAD in women are the same as in men and include:
increased blood cholesterol, high blood pressure, smoking cigarettes, diabetes mellitus, and a family history of coronary heart disease at a young age.
Smoking cigarettes Even "light" smoking raises the risk of CAD. In one study, middle-aged women who smoked one to 14 cigarettes per day had a twofold increase in strokes (caused by atherosclerosis of the arteries to the brain) whereas those who smoked more than 25 cigarettes per day had a risk of stroke 3.7 fold higher than that of nonsmoking women. Furthermore, the combination of smoking and the use of birth control pills increase the risk of heart attacks even further, especially in women over 35.

Quitting smoking immediately begins to reduce the risk of heart attacks. The risk gradually returns to the same risk of nonsmoking women after several years of not smoking.

What is a heart attack?

A heart attack (also known as a myocardial infarction) is the death of heart muscle from the sudden blockage of a coronary artery by a blood clot. Coronary arteries are blood vessels that supply the heart muscle with blood and oxygen. Blockage of a coronary artery deprives the heart muscle of blood and oxygen, causing injury to the heart muscle. Injury to the heart muscle causes chest pain and chest pressure sensation. If blood flow is not restored to the heart muscle within 20 to 40 minutes, irreversible death of the heart muscle will begin to occur. Muscle continues to die for six to eight hours at which time the heart attack usually is "complete." The dead heart muscle is eventually replaced by scar tissue.

Approximately one million Americans suffer a heart attack each year. Four hundred thousand of them die as a result of their heart attack.

What causes a heart attack?

Atherosclerosis

Atherosclerosis is a gradual process by which plaques (collections) of cholesterol are deposited in the walls of arteries. Cholesterol plaques cause hardening of the arterial walls and narrowing of the inner channel (lumen) of the artery.

Arteries that are narrowed by atherosclerosis cannot deliver enough blood to maintain normal function of the parts of the body they supply. For example, atherosclerosis of the arteries in the legs causes reduced blood flow to the legs.

Reduced blood flow to the legs can lead to pain in the legs while walking or exercising, leg ulcers, or a delay in the healing of wounds to the legs. Atherosclerosis of the arteries that furnish blood to the brain can lead to vascular dementia (mental deterioration due to gradual death of brain tissue over many years) or stroke (sudden death of brain tissue).

In many people, atherosclerosis can remain silent (causing no symptoms or health problems) for years or decades. Atherosclerosis can begin as early as the teenage years, but symptoms or health problems usually do not arise until later in adulthood when the arterial narrowing becomes severe.

Smoking cigarettes, high blood pressure, elevated cholesterol, and diabetes mellitus can accelerate atherosclerosis and lead to the earlier onset of symptoms and complications, particularly in those people who have a family history of early atherosclerosis.

Coronary atherosclerosis (or coronary artery disease) refers to the atherosclerosis that causes hardening and narrowing of the coronary arteries. Diseases caused by the reduced blood supply to the heart muscle from coronary atherosclerosis are called coronary heart diseases (CHD). Coronary heart diseases include heart attacks, sudden unexpected death, chest pain (angina), abnormal heart rhythms, and heart failure due to weakening of the heart muscle.

Atherosclerosis and angina pectoris

Angina pectoris (also referred to as angina) is chest pain or pressure that occurs when the blood and oxygen supply to the heart muscle cannot keep up with the needs of the muscle. When coronary arteries are narrowed by more than 50 to 70 percent, the arteries may not be able to increase the supply of blood to the heart muscle during exercise or other periods of high demand for oxygen.

An insufficient supply of oxygen to the heart muscle causes angina. Angina that occurs with exercise or exertion is called exertional angina. In some patients, especially diabetics, the progressive decrease in blood flow to the heart may occur without any pain or with just shortness of breath or unusually early fatigue.

Exertional angina usually feels like a pressure, heaviness, squeezing, or aching across the chest. This pain may travel to the neck, jaw, arms, back, or even the teeth, and may be accompanied by shortness of breath, nausea, or a cold sweat.

Exertional angina typically lasts from one to 15 minutes and is relieved by rest or by taking nitroglycerin by placing a tablet under the tongue. Both resting and nitroglycerin decrease the heart muscle's demand for oxygen, thus relieving angina.

Exertional angina may be the first warning sign of advanced coronary artery disease. Chest pains that just last a few seconds rarely are due to coronary artery disease.

Angina also can occur at rest. Angina at rest more commonly indicates that a coronary artery has narrowed to such a critical degree that the heart is not receiving enough oxygen even at rest. Angina at rest infrequently may be due to spasm of a coronary artery (a condition called Prinzmetal's or variant angina). Unlike a heart attack, there is no permanent muscle damage with either exertional or rest angina.

Atherosclerosis and heart attack

Occasionally the surface of a cholesterol plaque in a coronary artery may rupture, and a blood clot forms on the surface of the plaque. The clot blocks the flow of blood through the artery and results in a heart attack (see picture below). The cause of rupture that leads to the formation of a clot is largely unknown, but contributing factors may include cigarette smoking or other nicotine exposure, elevated LDL cholesterol, elevated levels of blood catecholamines (adrenaline), high blood pressure, and other mechanical and biochemical forces.

Unlike exertional or rest angina, heart muscle dies during a heart attack and loss of the muscle is permanent, unless blood flow can be promptly restored, usually within one to six hours.

While heart attacks can occur at any time, more heart attacks occur between 4:00 A.M. and 10:00 A.M. because of the higher blood levels of adrenaline released from the adrenal glands during the morning hours. Increased adrenaline, as previously discussed, may contribute to rupture of cholesterol plaques.

Approximately 50% of patients who develop heart attacks have warning symptoms such as exertional angina or rest angina prior to their heart attacks, but these symptoms may be mild and discounted.