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A heart attack is when low blood flow causes the heart to starve for oxygen. Heart muscle dies or becomes permanently damaged. Your doctor calls this a myocardial infarction

Causes

Most heart attacks are caused by a blood clot that blocks one of the coronary arteries. The coronary arteries bring blood and oxygen to the heart. If the blood flow is blocked, the heart starves for oxygen and heart cells die.

A clot most often forms in a coronary artery that has become narrow because of the build-up of a substance called plaque along the artery walls. (See: atherosclerosis) Sometimes, the plaque cracks and triggers a blood clot to form.

Occasionally, sudden overwhelming stress can trigger a heart attack.

It is difficult to estimate exactly how common heart attacks are because as many as 200,000 to 300,000 people in the United States die each year before medical help is sought. It is estimated that approximately 1 million patients visit the hospital each year with a heart attack. About 1 out of every 5 deaths are due to a heart attack.

Risk factors for heart attack and coronary artery disease include:

Bad genes (hereditary factors)

Being male

Diabetes

Getting older

High blood pressure

Smoking

Too much fat in your diet

Unhealthy cholesterol levels, especially high LDL ("bad") cholesterol and low HDL ("good") cholesterol

Higher-than-normal levels of homocysteine, C-reactive protein, and fibrinogen may also increase your risk for a heart attack. Homocysteine is an amino acid. C-reactive protein and fibrinogen are linked to inflammation. Fibrinogen is also involved in blood clotting

Angina is the primary symptom of coronary artery disease and, in severe cases, of a heart attack. It is typically experienced as chest pain and occurs when the heart muscle does not get as much blood (hence as much oxygen) as it needs for a given level of work (ischemia). Angina is usually referred to as one of two states:

Stable Angina (which is predictable)

Unstable Angina (which is less predictable and a sign of a more serious situation)

Click the icon to see an image about angina.

The intensity of the pain does not always relate to the severity of the medical problem. Some people may feel a crushing pain from mild ischemia, while others might experience only mild discomfort from severe ischemia.

Angina itself is not a disease. Much evidence indicates that onset of angina less than 48 hours before a heart attack may be protective, possibly by conditioning the heart to resist the damage resulting from the attack. Angina may be experienced in different ways and can be mild, moderate, or severe.

Stable Angina and Chest Pain

Stable Angina. Stable angina is predictable chest pain. Although less serious than unstable angina, it can be extremely painful or uncomfortable. It is usually relieved by rest and responds well to medical treatment (typically nitroglycerin). Any event that increases oxygen demand can cause an angina attack. Some typical triggers include:

Exercise

Cold weather

Emotional tension

Large meals

Angina attacks can occur at any time during the day, but most occur between 6 a.m. and noon.

Specific symptoms that are more likely to indicate angina include:

Angina pain or discomfort is typically described by patients as fullness or tingling, squeezing, pressure, heavy, suffocating, or griplike. It is rarely described as stabbing or burning. Changing one's position or breathing in and out does not affect the pain.

A typical angina attack lasts minutes. If it is more fleeting or lasts for hours, it is probably not angina.

Pain is usually in the chest under the breast bone. It often radiates to the neck, jaw, or left shoulder and arm. Less commonly, patients report symptoms that radiate to the right arm or back, or even to the upper abdomen.

Stable angina is usually relieved by rest or by taking nitroglycerine under the tongue.

Other symptoms that may indicate angina or accompany the pain or pressure in the chest include:

Shortness of breath

Nausea, vomiting, and cold sweats

A feeling of indigestion or heartburn

Unexplained fatigue after activity (more common in women)

Dizziness or lightheadedness

Palpitations

Unstable Angina and Symptoms of Possible Heart Attack

Unstable angina is a much more serious situation and is often an intermediate stage between stable angina and a heart attack, in which an artery leading to the heart (a coronary artery) becomes completely blocked. A patient is usually diagnosed with unstable angina under one or more of the following conditions:

Pain awakens a patient or occurs during rest.

A patient who has never experienced angina has severe or moderate pain during mild exertion (walking two level blocks or climbing one flight of stairs).

Stable angina has progressed in severity and frequency within a 2-month period, and medications are less effective in relieving its pain.

Fainting episode.

Unstable angina is now usually discussed as part of a condition called acute coronary syndrome (ACS). ACS also includes people with a condition called NSTEMI (non ST-segment elevation myocardial infarction) -- also referred to as non-Q wave heart attack. With NSTEMI, blood tests suggest a developing heart attack. These conditions are less severe than heart attacks but may develop into full-blown attacks without aggressive treatment. <!--[For more information, see In-Depth Report #12: Heart attack and acute coronary syndrome.]-->

Doctors use a number of factors to help predict which patients with unstable angina or acute coronary syndrome are most at risk for developing a heart attack.

First, patients are categorized by whether they have a history of heart disease or risk factors for heart disease (such as diabetes, high blood pressure, and peripheral artery disease) or other complicating conditions (such as lung disease and heart failure). The doctor also evaluates the severity of the angina. Other factors that pose a high risk for ACS include:

Age 65 years or older

Evidence of severe heart tissue injury

A history of severe chronic angina

Abnormal lung sounds called rales (a bubbling or crackling sound) on examination

ST-segment deviation on the electrocardiogram

Either very slow or very fast heat beats

Very low blood pressure

Heart Attack. A full-blown heart attack occurs with severe damage to the heart, which blocks oxygen.

People with known heart disease and any unusual chest pain or other symptoms described above that do not clear up with medications should call 911. The degree of pain and the specific symptoms before a heart attack vary greatly among individuals. Symptoms can be abrupt, gradual, or intermittent. Some studies suggest that nearly half of patients with heart attack do not have chest pain as the primary symptom. Patients most likely to have atypical symptoms are women and the very elderly (although they can certainly have classic heart attack symptoms as well).

Symptoms That Are Less Likely to Indicate Angina or a Heart Attack. The following symptoms are less likely to be due to coronary artery disease:

Sharp pain brought on by breathing in and or when coughing

Pain that is mainly or only in the middle or lower abdomen

Pain that can be pinpointed with the top of one finger

Pain that can be reproduced by moving or pressing on the chest wall or arms

Pain that is constant and lasts for hours (although no one should wait hours if they suspect they are having a heart attack)

Pain that is very brief and lasts for a few seconds

Pain that spreads to the legs

However, the presence of these symptoms does not always rule out a serious heart event.

Other Types of Angina

Prinzmetal's Angina. A third type of angina, called variant or Prinzmetal's angina, is caused by a spasm of a coronary artery. It almost always occurs when the patient is at rest. About two-thirds of people with it have severe atherosclerosis in at least one major blood vessel. Irregular heartbeats are common, but the pain is generally relieved immediately with standard treatment.

Silent Ischemia. Some people with severe coronary artery disease do not have angina pain. This condition is known as silent ischemia, which some experts attribute to the brain abnormally processing of heart pain. This is a dangerous condition because patients have no warning signs of heart disease. Some studies suggest that people with silent ischemia experience higher complication and mortality rates than those with angina pain.

Syndrome X. Syndrome X is a condition that occurs when patients have atypical angina chest pain. Their electrocardiograms are abnormal during a stress test, but they have no signs of blocked arteries. It is more likely to occur in women. Although it is unclear what causes this condition, imaging tests suggest that Syndrome X may also be caused by ischemia, as is angina.

Other Causes of Chest Pain or Discomfort

Chest pain is a very common symptom in the emergency room, but heart problems account for only 10 - 33% of all episodes.