I’ll be honest — on my first day of medical school I could not have told you exactly what a heart attack was.  I knew it was due to some kind of blockage, but I didn’t know exactly where, how, or why.  I’m not sure anyone still knows yet exactly why, but research continues to bring us closer to at least some of the answers.  At a certain point though, I did put it together, and that, dear readers, is what I’m going to discuss today.

The heart is a house with four rooms.  Two rooms, the right atrium and left atrium (plural: atria), serve as entryways; and the other two rooms, the right and left ventricles, are the main rooms.  Blood enters the right atrium, moves through the tricuspid valve to the right ventricle, and is then pumped to the lungs, where it receives oxygen.  The blood returns to the heart via the left atrium, passes through the mitral valve to the left ventricle (the largest room), and is then pumped into the aorta (the largest blood vessel in the body), from which it spreads through the entire body, taking oxygenated blood to all the cells.

Think of the heart as having plumbing, electricity, and carpentry.  Diseases of the heart can usually be traced back to some problem in one of these systems.  In other words, some heart problems are due to the plumbing, others to faulty wiring, and still others to either the material itself, or how it is put together.   

Heart attacks happen in the plumbing.  Blood vessels that surround the heart provide it with its very own blood supply.  If blood cannot flow easily through those vessels, the heart muscle will not receive the oxygen it needs to function. 

Just as blood leaves the left ventricle and enters the aorta, some of it is diverted into small arteries that feed the heart itself.   These small arteries are called the coronary arteries.  [“Coronary” means “heart.”]  This efficient system reminds me of an airline’s warning to put on your own oxygen prior to assisting those around you.  The heart makes sure to take blood for itself first.

In most people, the largest of the coronary arteries heads to the front of the left ventricle as the “left main.”  The left main has a large branch, called the “left anterior descending,” that goes straight down to the left ventricle.  A smaller branch, the “circumflex,” wraps leftward around the back.  A second coronary artery is called the “right coronary artery.”  It feeds the right atrium and ventricle, which are smaller because they pump their blood only to the lungs.  The lungs are a lot closer and comparatively easy to reach than the rest of the body, whose blood is pumped by the left ventricle.

What is a heart attack?  A blockage in the coronary arteries.  You could have a heart attack in one of the tiny, last branches of the coronary arteries.  Or you could be extremely unlucky and have a heart attack in the “left main,” or “left anterior descending” arteries.  Cardiologists call these blockages “widow makers.”  Now you know why:  These are likely to be disastrous, because every bit of the heart muscle beyond the blockage suddenly loses its blood supply.  You know how much it hurts to keep your arm up high in the air and compromise its blood supply?  That’s why a heart attack hurts so much. 

The likelihood of developing a blockage rises rapidly if you have diabetes, hypertension, obesity, high insulin levels, low HDL, high triglycerides, or large amounts of small, dense LDL.  Add to these a sedentary lifestyle.  Being physically active markedly decreases your likelihood of developing a blockage.

What else can go wrong?  

Problems in the electrical conduction system affect the timing of heart muscle contractions.  Imagine, just for an instant, how important it is for the atria to contract before the ventricles.  An instant is about how much time your heart has to get this exactly right with each squeeze.

Problems in the “carpentry” affect the valves or muscles of the heart, which is really a specialized pump made mostly from muscle.  The pump has two phases to its function: squeezing and relaxing.  The muscle can become enlarged and floppy.  That makes it hard to squeeze.  Or it can become stiff and shrunken, which makes it hard to relax.  Both affect the heart’s ability to pump efficiently.  We treat these difficulties with different medicines, depending on the exact problem. 

Illnesses of the heart can be congenital, which means you are born with them, or they can be caused by an injury, be it biological (like a virus or bacteria) or chemical (like a vitamin deficiency).  Illnesses can affect a valve, like rheumatic heart disease, which usually damages the mitral valve.  Or, like longstanding alcohol abuse, they can affect the entire heart muscle.
 
Questions?  Ask away!
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