A heart attack, or myocardial infarction (MI), occurs when the supply of blood and oxygen to an area of heart muscle is blocked.
A clot (or thrombus) is the final product of the blood coagulation (thickening). Specifically, a thrombus is a blood clot in an intact blood vessel. A thrombus in a large blood vessel will decrease blood flow through that vessel. In a small blood vessel, blood flow may be completely cut-off resulting in the death of tissue supplied by that vessel (as in a heart attack). If a thrombus dislodges and becomes free-floating, it is an embolus.
The clot can partially block the flow of blood in the arteries of the heart, causing a lack of oxygen to the heart muscle tissue (called ischemia). If the clot completely stops the blood flow in an artery in the heart (called coronary artery), then a heart attack develops. If treatment is not started quickly, the affected area of heart muscle begins to die. This injury to the heart muscle can lead to serious complications, and can even be fatal. It is possible to survive a heart attack, but part of the heart muscle may be damaged, causing shortness of breath, chest pain on exertion or at rest, and increases the potential to have another heart attack. It is very important if an individual has had a heart attack in the past to follow doctor's advice in preventing another one.
The survival rate for U.S. patients hospitalized with a heart attack is approximately 90 to 95%. This represents a significant improvement in survival and is related to improvements in emergency medical response and treatment strategies.
In general, a heart attack can occur at any age, but its incidence rises with age and depends on pre-disposing risk factors. Approximately 50% of all heart attacks in the United States occur in people younger than 65 years of age, but as the baby boomers age, this percentage will probably lean toward over 65.
Sudden death from a heart attack can occur due to an arrhythmia (irregular heartbeat or rhythm) called ventricular fibrillation. If an individual survives a heart attack, the injured area of the heart muscle is replaced by scar tissue. This weakens the pumping action of the heart and can lead to heart failure (inability of the heart to pump blood throughout the body) and other complications including fatigue (tiredness), fluid buildup in the feet, ankles, or around the lungs (which makes it hard to breathe).
Heart attack is the leading cause of death in the United States (U.S.) as well as in most industrialized nations throughout the world. Approximately 800,000 people in the U.S. are affected annually, and 250,000 die prior to arrival to a hospital. Approximately every 65 seconds, an American dies of a heart related medical emergency. The World Health Organization (WHO) estimated that in 2002, 12.6% of deaths worldwide were from ischemic heart disease (lack of oxygen to the heart).
There are several types of heart attacks. Acute coronary syndrome is a name given to three types of coronary artery disease that are associated with sudden rupture of plaque inside the coronary artery: unstable angina, non-ST segment elevation myocardial infarction (NSTEMI), or ST segment elevation myocardial infarction (STEMI). The location of the blockage, the length of time that blood flow is blocked, and the amount of damage that occurs determines the type of acute coronary syndrome.
Unstable angina: Unstable angina (chest pain) can occur more frequently, occur more easily at rest, feel more severe, or last longer than stable angina. Although this angina can often be relieved with oral medications, it is unstable and may progress to a heart attack. Usually more intense medical treatment or a procedure is required. Unstable angina is an acute coronary syndrome and should be treated as a medical emergency.
Non-ST segment elevation myocardial infarction (NSTEMI): This heart attack (myocardial infarction) does not cause changes on an electrocardiogram (ECG). However, chemical markers in the blood indicate that damage has occurred to the heart muscle (including c-reactive protein, creatine kinase-MB (CK-MB) and troponin). In NSTEMI, the blockage may be partial or temporary, and so the extent of the damage to the heart is relatively minimal.
ST segment elevation myocardial infarction (STEMI):
This heart attack is caused by a prolonged period of blocked blood supply (ischemia). It affects a large area of the heart muscle, and so causes changes on the ECG as well as in blood levels of the key chemical markers.
Atherosclerosis: Atherosclerosis is the hardening and narrowing of the arteries. It is caused by the slow buildup of plaque on the inside of walls of the arteries. Arteries are blood vessels that carry oxygen-rich blood from the heart to other parts of the body. Plaque is made up of fat, cholesterol, calcium, and other substances found in the blood. As it grows, the buildup of plaque narrows the inside of the artery and, in time, may restrict blood flow.
Coronary artery disease (CAD): Coronary artery disease (CAD), also known as coronary heart disease (CHD), occurs when the coronary arteries gradually become narrowed or blocked by plaque deposits. This can lead to a heart attack.
Unfortunately, sometimes a heart attack is the first sign of coronary artery disease (CAD). According to the Framingham Heart Study, over 50% of men and 63% of women who died suddenly of CAD (mostly from heart attack) had no previous symptoms of this disease.
Some individuals who have CAD and insufficient blood flow to the heart muscle (ischemia) do not have any symptoms. This is called "silent ischemia." In rare instances a patient may have a "silent heart attack," which is a heart attack without symptoms.
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