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 is new in heart attack?

Greater public awareness about heart attacks and changes in lifestyle have contributed to a dramatic reduction in the incidence of heart attacks during the last four decades. Improved anticoagulant drugs such as hirudin and hirulog, are being tested and may complement current therapies. The role of the "super aspirins" [abciximab (Reopro) and eptifibatide (Integrilin)] is currently being investigated as well.

More effective versions of TPA are being developed. Increasingly, paramedics can do ECGs in the field, diagnose a heart attack, and take patients directly to hospitals that have the ability to do PTCA and stenting. This can save time and reduce damage to the heart. At present, the accepted best treatment for a heart attack is identification promptly of the diagnosis, and transport to a hospital that can perform prompt catheterization and PTCA or stenting within the first 90 minutes of the cardiac event.

Recent data has shown that lowering blood LDL levels even further than previously suggested may further decrease the risk of heart attacks.

Research also has shown that inflammation may play a role in the development of atherosclerosis, and this is an active area of current investigation. There also is early evidence that with genetic engineering it may be possible to develop a drug that can be administered to clear plaques from arteries (a "scavenger molecule").


Heart Attack At A Glance
A heart attack results when a blood clot completely obstructs a coronary artery supplying blood to the heart muscle and heart muscle dies.

The blood clot that causes the heart attack usually forms at the site of rupture of an atherosclerotic, cholesterol plaque on the inner wall of a coronary artery.

The most common symptom of heart attack is chest pain.
The most common complications of a heart attack are heart failure, and ventricular fibrillation.

The risk factors for atherosclerosis and heart attack include elevated cholesterol levels, increased blood pressure, tobacco use, diabetes, male gender and a family history of heart attacks at an early age.

Heart attacks are diagnosed with electrocardiograms and measurement of cardiac enzymes in blood.

Early reopening of blocked coronary arteries reduces the amount of damage to the heart and improves the prognosis for a heart attack.

Medical treatment for heart attacks may include anti-platelet, anti-coagulant, and clot dissolving drugs as well as angiotensin converting enzyme (ACE) inhibitors, beta blockers and oxygen.
Interventional treatment for heart attacks may include coronary angiography with percutaneous transluminal coronary angioplasty (PTCA), coronary artery stents, and coronary artery bypass grafting (CABG).

Patients suffering a heart attack are hospitalized for several days to detect heart rhythm disturbances, shortness of breath, and chest pain.

Further heart attacks can be prevented by aspirin, beta blockers, ACE inhibitors, discontinuing smoking, weight reduction, exercise, good control of blood pressure and diabetes, following a low cholesterol and low saturated fat diet that is high in omega-3-fatty acids, taking multivitamins with an increased amount of folic acid, decreasing LDL cholesterol , and increasing HDL cholesterol.

What are the symptoms of heart attack in women and how is heart attack diagnosed?

Women are more likely to encounter delays in establishing the diagnosis of heart attack than men. This is in part because women tend to seek medical care later than men, and in part because diagnosing heart attacks in women can sometimes be more difficult than diagnosing heart attacks in men.

The reasons include:
Women are more likely than men to have atypical heart attack symptoms such as:
neck and shoulder pain,
abdominal pain,
nausea,
vomiting,
fatigue, and
shortness of breath.

Silent heart attacks (heart attacks with little or no symptoms) are more common among women than among men.

Women have a higher occurrence than men of chest pain that is not caused by heart disease, for example chest pain from spasm of the esophagus.

Women are less likely than men to have the typical findings on the ECG that are necessary to diagnose a heart attack quickly.

Women are more likely than men to have angina (chest pain due to lack of blood supply to the heart muscle) that is caused by spasm of the coronary arteries or caused by disease of the smallest blood vessels (microvasculature disease).

Cardiac catheterization with coronary angiograms (x-ray studies of the coronary arteries that are considered the most reliable tests for CAD) will reveal normal coronary arteries and therefore cannot be used to diagnose either of these two conditions.

Women are more likely to have misleading, or "false positive" noninvasive tests for CAD then men.

Because of the atypical nature of symptoms and the occasional difficulties in diagnosing heart attacks in women, women are less likely to receive aggressive thrombolytic therapy or coronary angioplasty, and are more likely to receive it later than men. Women also are less likely to be admitted to a coronary care unit.

How is a heart attack diagnosed?

When there is severe chest pain, suspicion that a heart attack is occurring usually is high, and tests can be performed quickly that will confirm the heart attack. A problem arises, however, when the symptoms of a heart attack do not include chest pain. A heart attack may not be suspected, and the appropriate tests may not be performed. Therefore, the initial step in diagnosing a heart attack is to be suspicious that one has occurred.

Electrocardiogram. An electrocardiogram (ECG) is a recording of the electrical activity of the heart.

Abnormalities in the electrical activity usually occur with heart attacks and can identify the areas of heart muscle that are deprived of oxygen and/or areas of muscle that have died. In a patient with typical symptoms of heart attack (such as crushing chest pain) and characteristic changes of heart attack on the ECG, a secure diagnosis of heart attack can be made quickly in the emergency room and treatment can be started immediately.

If a patient's symptoms are vague or atypical and if there are pre-existing ECG abnormalities, for example, from old heart attacks or abnormal electrical patterns that make interpretation of the ECG difficult, the diagnosis of a heart attack may be less secure. In these patients, the diagnosis can be made only hours later through detection of elevated cardiac enzymes in the blood.

Blood tests. Cardiac enzymes are proteins that are released into the blood by dying heart muscles. These cardiac enzymes are creatine phosphokinase (CPK), special sub-fractions of CPK (specifically, the MB fraction of CPK), and troponin, and their levels can be measured in blood. These cardiac enzymes typically are elevated in the blood several hours after the onset of a heart attack.

A series of blood tests for the enzymes performed over a 24-hour period are useful not only in confirming the diagnosis of heart attack, but the changes in their levels over time also correlates with the amount of heart muscle that has died.

The most important factor in diagnosing and treating a heart attack is prompt medical attention. Rapid evaluation allows early treatment of potentially life-threatening abnormal rhythms such as ventricular fibrillation and allows early reperfusion (return of blood flow to the heart muscle) by procedures that unclog the blocked coronary arteries. The more rapidly blood flow is reestablished, the more heart muscle that is saved.

Large and active medical centers often have a "chest pain unit" where patients suspected of having heart attacks are rapidly evaluated. If a heart attack is diagnosed, prompt therapy is initiated. If the diagnosis of heart attack is initially unclear, the patient is placed under continuous monitoring until the results of further testing are available.

What are the symptoms of a heart attack?

Although chest pain or pressure is the most common symptom of a heart attack, heart attack victims may experience a variety of symptoms including:

• Pain, fullness, and/or squeezing sensation of the chest

• Jaw pain, toothache, headache

• Shortness of breath

• Nausea, vomiting, and/or general epigastric (upper middle abdomen) discomfort

• Sweating

• Heartburn and/or indigestion

• Arm pain (more commonly the left arm, but may be either arm)

• Upper back pain

• General malaise (vague feeling of illness)

• No symptoms (Approximately one quarter of all heart attacks are silent, without chest pain or new symptoms. Silent heart attacks are especially common among patients with diabetes mellitus.)

Even though the symptoms of a heart attack at times can be vague and mild, it is important to remember that heart attacks producing no symptoms or only mild symptoms can be just as serious and life-threatening as heart attacks that cause severe chest pain. Too often patients attribute heart attack symptoms to "indigestion," "fatigue," or "stress," and consequently delay seeking prompt medical attention.

One cannot overemphasize the importance of seeking prompt medical attention in the presence of symptoms that suggest a heart attack. Early diagnosis and treatment saves lives, and delays in reaching medical assistance can be fatal.

A delay in treatment can lead to permanently reduced function of the heart due to more extensive damage to the heart muscle. Death also may occur as a result of the sudden onset of arrhythmias such as ventricular fibrillation.

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.