Depending on which coronary artery is affected, and where it becomes blocked, different parts of the heart are damaged at the time of a heart attack.
The right coronary artery carries blood to
the right side of the heart (the right atrium and right ventricle)
portions of the left side of the heart
parts of the heart that control the heart rhythm
The left coronary artery splits into the left anterior descending artery (LAD) and the left circumflex artery, supplying blood mostly to:
the left side of the heart (left atruim and left ventricle)
the wall of muscle that divides the right and left sides of the heart
Most heart attacks are caused by a plaque rupture and blood clot, or coronary thrombus, in a coronary artery. When a plaque ruptures, it sets off a series of events that can result in clots being formed. This happens when clot-promoting substances contained inside the plaque are exposed to the circulating blood.
Need To Know:
The amount of damage caused by a plaque rupture depends on the size of the rupture. If a plaque rupture is minor, a small blood clot may form but might only partially block a coronary artery. Eventually, the clot may become part of the plaque again or get broken down. A large rupture can lead to the formation of a larger clot that can partially or completely block a coronary artery.
Non-Q-wave heart attack: Sometimes, a coronary artery can become partially blocked and the blockage remains in place for a long time. Over time, a lack of blood (and oxygen) can cause unstable angina, as well as a non-Q wave heart attack. This type of attack shows up differently on a electrocardiogram (ECG), one of the tools used to diagnose a heart attack. This type of heart attack usually involves the innermost layer of heart muscle, which is most susceptible to inadequate blood flow.
A non-Q wave heart attack also may occur if a blood vessel is:
totally blocked for only a short time
totally blocked for a long period of time, but other nearby blood vessels provide some blood flow.
Sometimes, the heart's blood supply can be blocked totally but for just a short time. Usually a spasm or a clot that dissolves is the cause of such an occurrence.
Q-wave heart attack: If a coronary artery is blocked for a long time and blood flow supplied by smaller surrounding blood vessels is poor, the clot will likely cause a Q-wave heart attack. It gets its name because it is general associated with abnormally deep Q waves on the electrocardiogram (ECG). This type of a heart attack generally involves the death of muscle cells throughout the entire thickness of the heart muscle wall.
In rare cases, other factors severely reduce blood flow to heart muscle, causing a heart attack. These causes should be considered in people who are young or who have few or no risk factors for coronary artery disease. These include:
Coronary emboli, in which a piece of a blood clot, a mass of bacteria, or other foreign body in the coronary vessel. These can come from infected or artificial heart valves, blood clots inside the heart's chambers, and even heart tumors.
Blood clots not associated with coronary artery disease, which can be caused by trauma, conditions associated with an increased tendency to form blood clots, or the use of birth control pills in some women.
Congenital (existing at birth) abnormalities of the coronaryarteries
Severe spasm of the coronary artery, which cause a sudden contraction of muscle in the wall of an artery. This can cause a temporary blockage to all layers of heart muscle, resulting in a Q-wave heart attack.
Conditions that increase the "stickiness" or thickness of a person's blood
Marked increase in the oxygen demand of heart muscle, such as aortic stenosis
Most of these "other causes" of a heart attack restrict blood flow to heart muscle by blocking or narrowing a coronary artery. The exception is an increase in the "stickiness" of blood, which causes reduces blood flow to heart muscle because blood cells have difficulty sliding past one another.
Need To Know:
Coronary spasm can cause a heart attack. Spasm of unknown cause are called primary or idiopathic coronary spasm. Causes of secondary coronary spasm include cocaine or amphetamine abuse.
In addition to causing a heart attack, coronary spasm can also cause variant orPrinzmetal's angina. This unusual type of angina occurs at rest or during sleep and is usually associated with coronary artery disease. People with variant angina are at increased risk for serious cardiac arrhythmias and sudden death as well as a heart attack.
Nice To Know:
Syndrome X is a rare cause of a heart attack and refers to angina in people with "normal" coronary arteries. They experience angina symptoms but no signs of blood vessel narrowing shows up during acoronary angiography. (During this test, dye is injected into coronary arteries to look for any narrowing.)
However, some patients do show signs of inadequate blood flow to heart muscle (ischemia) during an exercise tolerance or stress test. This may be due to decreased amount of substances that dilate widen blood vessels from the cells that line blood vessel walls.