Attack (Myocardial Infarction)
How Can Plaques Cause Sudden Heart Attacks?
A heart attack occurs suddenly without much warning. But the coronary artery disease, the underlying cause for the heart attack, had been brewing for many years. So, what happened to cause the sudden heart attack?
For many years, researchers thought that the cause of the heart attack was a large plaque that formed on the wall of the coronary artery. This plaque was known to cause an angina because it makes the heart to work too hard. A doctor can observe this blockage with a coronary angiogram. It was suggested that a small blood clot becomes wedged at the site of the plaque. This clot suddenly blocked blood flow completely through the coronary artery resulting in a heart attack. So, according to this theory, both angina and heart attacks originated from the same source - large plaques.
Scientists now agree that this theory is wrong. Research has shown that most heart attacks are caused by rupture of the plaque, and that small plaques are often responsible.
It is not important how big the plaque is. What matters, at least for proneness to precipitate heart attacks, is how the plaque is built.
All plaques have a fatty core covered with a top composed of a meshwork of fibers.
If the top covering on the plaque is thick and the core is small, dry, and hard, the plaque is "stable" and is unlikely to rupture. Big plaques are often stable.
However, if the top covering of the plaque is thin and if the core is filled with soft, fatty material, the plaque is "unstable" and can rupture or break. When the top ruptures, the blood in the artery comes in contact with the fatty material in the core of the plaque. This results in the formation of a big clot at the site of the rupture. This clot, in turn, can suddenly stop blood flow in the artery, resulting in a heart attack.
What is interesting is that the so-called "vulnerable plaques" with thin tops and soft fatty cores may be small. It may not block blood flow or cause any symptoms such as angina. They may even be so small that they cannot be seen on a coronary angiogram. The cause of the "plaque rupture" is largely unknown, but contributing factors may include cigarette smoking, elevated LDL cholesterol, elevated levels of blood catecholamines (adrenaline), high blood pressure, and other mechanical and biochemical forces.