Heart attack versus cardiac arrest

After a long absence from blogging, I return with a long post:

Here’s the thing: these two issues are often confused. They both involve the heart, which probably leads to the primary source of the confusion. In one, the vessels of your heart become so occluded by gunk (yes, that’s a term that we use in the medical field — we are fond of these very technical terms) that it can’t get oxygen to the muscle and it begins to die. In the other, your heart stops beating completely and you are clinically dead. Because I get so many questions about the difference between these two things, I thought I would enlighten our readers.

First, let’s talk about the heart: it is a four-chambered masterpiece. It takes center stage in the cardiovascular system and is surrounded by a supporting cast of the blood vessels to include arteries, veins, arterioles, venules and capillaries…and, of course, blood. (What good are vessels for blood if they don’t have blood in them?) Without this critical organ, your life…well…you wouldn’t have one. It pumps blood throughout your body, taking it to the lungs where it retrieves oxygen to supply the body’s tissues, including the heart muscle, with this necessary nutrient to keep them alive.

Now that we know a little about the heart, we shall explore a heart attack. Known by its medical term as a myocardial infarction, this is often the result of poor lifestyle choices. As demonstrated in this picture (A), the heart muscle (yes, it happens to be quite a strong muscle — one that works 24 hours a day, 7 days a week, 365 days a year…until the day you find yourself in your grave) is fed by coronary arteries. These arteries come directly off of the pulmonary veins which are returning oxygenated blood from the lungs to the heart before it has a chance to be used in any other way by the body. In other words, the heart gets first dibs on the oxygenated blood. However, as the picture (B) shows, when plaque builds up in the coronary artery, it will block blood flow either partially, as demonstrated in the picture, or completely. (Remember, even if the vessel is not 100% blocked, the necessary nutrients cannot always pass through, depending on the percentage of blockage.) As a result of oxygen not being able to reach the portions of the heart muscle beyond the blockage, also called ischemia, that tissue begins to die, what we call to become injured. At least by this point, you as my patient, should be having some pretty significant chest pain and after I put a bunch of stickies on your chest (yes, another super-technical term that we love to use), here’s an example of what you might expect the picture my heart monitor to spit out:

In the event that you are exceedingly interested, this tells me that the inferior (bottom) of your heart is where the tissue injury is. You also have some reciprocal changes on what we call the lateral side (the left ventricle) which simply shows the opposite of what the other side does. And you have some possible posterior involvement. If you were to have the above electrocardiogram, or ECG (also called EKG), we would say that your right coronary artery is what is blocked.

Looking at this picture to the right, you can see the different coronary arteries. The two main ones are the right coronary artery (RCA) and the left main coronary artery (LCA). From these two, the rest of the branches form. The LCA has two specific branches: the left anterior descending, or LAD, which feeds the front of the heart, and the left circumflex, or LCX, which circles around back and helps to supply the posterior of the heart with oxygen. Most people are dominant with their right coronary artery, which is determined based upon what coronary artery (left or right) mainly supplies the posterior, or the back, side of the heart. Based upon each heart attack patient’s EKG, you can often tell which side is their dominant. It’s neat to try to determine the little things like that…after you get them to the hospital, of course. (Not neat that they’re having a heart attack…but neat that…oh…nevermind.)

In the prehospital setting around here, the treatment for a heart attack includes oxygen, an IV, aspirin, nitroglycerin (no, not anything that’s explosive — though it may give you a pretty explosive headache), occasionally morphine depending on your pain level (and depending on your care provider) and rapid transport to one of two facilities that offer heart catheterizations around the clock. Once you get to the hospital, you will likely be whisked away to the cath lab in relatively short order. There, they will insert a catheter into a blood vessel, usually choosing to enter through your groin, and thread it to  your coronary arteries, looking for the blockage and subsequently opening it up. As a result of the vessel being reopened and oxygen returning to your heart muscle, your chest pain should be greatly diminished.

Alright, cardiac arrest. This is also a problem of the heart. It can result from a heart attack that went untreated (that is, unfortunately, relatively common) but it can also result from many other things…and sometimes we have no idea why it happened. If I were to put you on my heart monitor, here’s what I might find:

Asystole. Badness.

Or, I might find this:

Pulseless Electrical Activity, or PEA. Also badness. This has many forms. What I have shown you here is simply one example.

I might also find this:

Ventricular tachycardia, or V-tach. I like this one better. And you would, too.

Here’s the final example of what I might find:

Ventricular fibrillation, or V-fib. I like this one just as much as V-tach. And I’ll explain why…and what these things are.

Asystole is the rhythm that I dislike quite a bit. This rhythm has neither electrical activity or mechanical activity. In terms you may better understand, there is no electricity firing through the heart which is why you don’t see any squiggly lines (another technical term) showing activity. There is also no contraction of the heart muscle, meaning that there is no blood pumping around the body (as with all of these cardiac arrest rhythms). The survival rate is not very good when this is the initial rhythm. There are several ways this can be seen but it often means that the patient has had an extended down time (time since they last had a heart beat).

PEA, pulseless electrical activity, is another rhythm that is greatly disliked. Here, we have electrical activity, which is why we see those squiggly lines. It has the potential to look like a normal rhythm, just like yours or mine right now; however, there is no mechanical activity meaning the heart is not beating and there is no pulse. If this is the initial rhythm, the survival rate is also very poor. This is more commonly seen with traumatic arrests. For example, the heart thinks it is still beating away (thus the electrical activity) but there has been a loss in blood volume such that the heart functions mechanically. This is how I have usually seen it.

Ventricular tachycardia, V-tach, is a more promising rhythm than PEA or asystole. Like the first two rhythms, this one has  electrical activity yet still no mechanical activity present. (You can have mechanical activity, which would yield a pulse. However, that would no longer be a cardiac arrest rhythm. And that is not what we are here to talk about.) Here’s the benefit of this type of V-tach (monomorphic — coming from one place): only one area of the ventricle is firing off these beats. It is relatively easy to break this kind of cardiac arrest. I say it’s relatively easy to break it — not necessarily easy to keep them out of it. It is often because of injury (lack of oxygen) to the heart muscle that causes this. The fix: going to the cath lab at the hospital and opening the vessel that has narrowed too far to allow oxygen to pass.

Ventricular fibrillation, V-fib, is similar to V-tach. Unlike all of the other cardiac arrest rhythms, this has both electrical and mechanical activity present. Unfortunately, the electrical activity is much less organized than V-tach and the mechanical activity does not produce a pulse. The mechanical activity is best described as a quivering (yet another technical term). Even with all of this, there is still a rather promising outcome for the patient. Like V-tach, it is also most likely caused by a lack of oxygen to the heart muscle and it just goes crazy and starts firing off into the pattern you find on the EKG.

And there you go: a long explanation of the difference between a heart attack and cardiac arrest. Hopefully you understand it a little better now and can help others to understand the difference too.

Have a happy heart!

  • Lanie

    Love this explanation, very thorough! You should teach this stuff!!