MadSci Network: Medicine
Query:

Re: What are the main reasons why people have heart attacks?

Date: Sat Sep 15 23:20:07 2007
Posted By: Tim Nicholls, M.D., Pediatrics, Children''s Hospital Oakland
Area of science: Medicine
ID: 1189738719.Me
Message:

I'm sorry to hear about your loss, Nicole. If you can, talk with your parents about what they know about heart attacks, and your grandfather's heart attack in particular. You may find they know a lot more about what happened then they told you originally. They may know more about heart health and heart disease than you think, because heart disease is very common, and most adults have taken the time to learn a little about it. I'll say more about heart attacks in general below.

Part of the reason that people generalize about heart attacks is because they are rather common. Most people understand that a heart attack can be fatal (though they are only sometimes fatal) and that the heart can stop or, as you put it, the person suffers heart failure because of the heart attack. The term "heart failure" means something different in medicine, so I won't use the term anymore here.

In general, a heart attack refers to a problem with the function of the heart that happens quickly, different from a problem that builds over time. People in medicine don't use the term "heart attack" to describe these problems, however, because the term is too vague about the cause of the problem. Before I go on, you need to know a few key concepts:

1) blood carries oxygen to the tissues of the body.
2) the tissues of the body almost all need oxygen to function normally. Without it, they can become damaged or die.
3) the heart is the pump that pushes blood to all the tissues of the body.
4) the heart is made almost entirely of muscle that needs oxygen constantly to keep working.

When a medical person hears that someone had a heart attack, the first thing we think of is a problem where a part of the heart suddenly cannnot receive enough oxygen because its blood flow is blocked. When the tissue that needs that blood suffers a lack of oxygen and is either damaged or dies, we call it an infarction. The muscle tissue of the heart is called the "myocardium" of the heart. So when heart muscle can't work because of a lack of oxygen, we call it a myocardial infarction, or for short, an "M.I."

A myocardial infarction is most often caused by the sudden clotting of blood within one of the blood vessels that feeds blood to the heart. These blood vessels are called the coronary vessels, so you may also hear having a heart attack called "having a coronary." The sudden clotting of blood appears to occur at areas where plenty of a fatty build-up accumulates on the inside surface of the vessel. These build up more often in people with age, smoking, obesity, poor diet, poor exercise, and diabetes, among other things. When people say they need to lose weight, exercise more, or stop smoking to improve the health of their heart, they are most often referring to avoiding these fatty build-ups (called plaques). The plaques don't cause the blood to clot at a predictable time, so if we find a plaque in a person, it doesn't mean that we know they will have a myocardial infarction. We understand a lot more now than we did 10 or 25 years ago about why and how the plaques make blood clots, but we still cannot predict when a plaque will cause a blood clot, or in whom.

The heart's main function in the body is to pump blood. If blood flow stops in a certain part of the heart, the tissue in that part of the heart suffers injury because it can't get the oxygen, sometimes enough injury that the tissue dies. If that's the case, the heart may not pump blood well enough to keep someone alive, or it may lead to the heart's electrical rhythm to become irregular, which can also (but not always) prevent the heart's pumping activity from keeping someone alive. There are other ways that infarction can impair the heart's function, as well, such as allowing a blood clot to form within the heart's chambers or weakening the wall of the heart such that it forms a swollen pocket called an aneurysm.

Other than myocardial infarction, there are plenty of other ways that someone can appear to have a fatal heart attack because their heart stops working when they have symptoms that suggest their heart is a problem (chest pain, for example). If someone has a heart rhythm problem without a problem in blood flow, or if air or blood clots from another part of the body get into the coronary vessels, a person can suffer a heart attack that looks just like a myocardial infarction. Of all the events that can be called heart attacks, myocardial infarctions because of the clots formed near plaques are far and away the most common cause of heart attacks.

I should underscore that in children, heart attacks, particularly myocardial infarctions, are *very* rare. Most of the reason for this is that the plaques take decades to build up enough to cause blood flow problems. When we get very old, plaques tend to be very built up, and the heart can become weak because of age. For these reasons, a small myocardial infarction that would only make a middle-aged adult sick for a while can be fatal for an elderly person.

I encourage you again to ask your parents what they know about your grandfather's passing. I can only guess about what may have happened. What they know can shed much more light on it than I can by guessing.

Tim Nicholls, MD
Berkeley, CA


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