What Really Causes a Heart Attack?

Heart Attacks mainly occur as a result of coronary artery disease (CAD). Coronary Artery Disease develops  when plaque buildup on the innter walls of the coronary arteries.  Eventually, a section of plaque can break open, causing a blood clot to form at the site. A heart attack occurs if the clot becomes large enough to cut off most or all of the blood flow through the artery.

The blocked blood flow prevents oxygen-rich blood from reaching the part of the heart muscle fed by the artery. The lack of oxygen damages the heart muscle. If the blockage isn’t treated quickly, the damaged heart muscle begins to die.

Heart attack also can occur due to problems with the very small, microscopic blood vessels of the heart. This condition is called microvascular disease. It’s believed to be more common in women than in men.

Another less common cause of heart attack is a severe spasm (tightening) of a coronary artery that cuts off blood flow through the artery. These spasms can occur in coronary arteries that don’t have CAD. It’s not always clear what causes a coronary artery spasm, but sometimes it can be related to:

• Taking certain drugs, such as cocaine
• Emotional stress or pain
• Exposure to extreme cold
• Cigarette smoking

Source:  http://www.nhlbi.nih.gov/health/dci/Diseases/HeartAttack/HeartAttack_Causes.html

— Almost all cases of Heart Attack occur in someone who has an underlying condition called coronary heart disease (CHD), which is due to narrowings or blockages in the coronary arteries, known as plaques.  Heart Attack occurs when the plaque ruptures and causes a blood clot (thrombus) to form in one of the coronary arteries. CHD and blood clot formation in MI are explained in turn below.

Coronary heart disease — All the organs and tissues in the body need a blood supply in order to function normally; blood carries oxygen and energy sources, especially sugar or glucose, that are required to meet the body’s needs. It is the heart’s job to pump oxygen-rich blood through the huge network of arteries that extend throughout the body, and this includes pumping blood into the vessels that supply the heart muscle itself. These vessels, called coronary arteries, lie on the outside of the heart muscle before entering the heart muscle itself

In coronary heart disease (CHD), the coronary arteries become clogged with fatty deposits. The deposits, called plaques, cause a narrowing of the arteries through which the blood reaches the heart muscle. This can create an imbalance between the supply of blood (or oxygen) available to an area of heart muscle and the demand for blood (or oxygen) that is needed at a given moment. This causes a condition known as ischemia, sometimes felt by the patient as chest discomfort (angina pectoris).

Plaque rupture and clot formation — Sometimes a plaque in a coronary artery bursts or ruptures, leading to the formation of a blood clot that may partially or completely block the artery. A blockage of this type is likely to cause damage to the heart muscle due to a lack of blood and oxygen supply. If there is damage, an Myocardial Infarction , or heart attack, has occurred.

The factors leading to the rupture of a plaque and the formation of a blood clot are not completely understood. There are certain characteristics related to the composition of a plaque that seem to make it vulnerable to rupture. Plaques that have an irregular appearance may contain less calcium and scar tissue and more lipids (fat) within their core, and may be more prone to rupture. Intense physical activity or psychologic stress immediately preceding MI may play a role because these activities affect the heart rate and blood pressure and could cause disruption of a plaque.

Some studies have shown that an emotional or stressful event occurs in a certain percentage of people in the days or hours before an Myocardial Infaction. In addition, an increase in the incidence of Myocardial Infaction has been noted in populations where a disaster has occurred. Because mental stress is known to cause increases in heart rate and blood pressure as well as other changes in the cardiovascular system, it has been suggested that, in some cases, mental stress can affect the stability of a coronary artery plaque and “trigger” an MI.

Source: http://www.uptodate.com/patients/content/topic.do?topicKey=hrt_dis/9329&title=Heart+attack+(Myocardial+infarction)

Heart Disease and C-Reactive Protein

American researchers have found evidence that a blood protein linked to inflammation of the arteries is a cause of heart disease. Two independent studies found that lowering the amount of the protein in the blood is just as important as lowering bad cholesterol to prevent heart attacks.

Until recently, doctors were concerned with lowering the amount of bad cholesterol and raising the amount of good cholesterol in the blood. But new research has shown that levels of C-reactive protein, or C.R.P, also must be reduced in order to prevent heart disease.

Studies during the past ten years have found that a major problem in heart disease is inflammation. Inflammation cannot be easily measured. So doctors use blood tests for C.R.P. to measure it.

C-reactive protein is a substance released by the liver. Some experts say the protein is directly linked to fatty plaque buildup in the arteries leading to the heart. They say the protein causes the plaque to break up and form blood clots in the arteries, which can lead to a heart attack.

Two studies appeared in the New England Journal of Medicine. Paul Ridker of Brigham and Women’s Hospital in Boston led the main study. Patients in the study already had severe heart disease and were taking drugs called statins to reduce bad cholesterol levels. Statin drugs also lower levels of C-reactive protein. The researchers found that patients who already had lowered cholesterol levels could reduce their risk of another heart attack by lowering their C.R.P. levels.

The studies showed that even when bad cholesterol levels were normal, people with lower levels of C.R.P. had slower progression of heart disease and fewer heart attacks and deaths.

Doctors say statins are not the only way to lower C.R.P. They say exercise, a healthy diet and stopping smoking also reduce it.

The new findings are only for people who already have heart disease. A separate study is being done to see if lowering C.R.P can reduce heart attacks in healthy people with normal cholesterol levels, but higher levels of C.R.P. Almost half of all heart attacks happen in people with normal cholesterol levels.

Researchers are hopeful that the new information can lead to new medicines to prevent and treat heart disease.

Source: http://www.voanews.com/specialenglish/archive/2005-01/a-2005-01-18-6-1.cfm?CFID=253725911&CFTOKEN=38237603&jsessionid=8430d7de7f2237f1b61a37384c6162437917

An uncommon cause of a heart attack is a spasm of a coronary artery that shuts down blood flow to part of the heart muscle. Drugs, such as cocaine, can cause such a life-threatening spasm.

Source: http://www.mayoclinic.com/health/heart-attack/DS00094/DSECTION=causes