Dilated Cardiomyopathy: Causes, Symptoms, Treatment, & Prognosis

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  • 0:01 A Dilated Balloon
  • 0:44 Enlargement of the Heart
  • 2:02 Dilated Cardiomyopathy
  • 4:34 The Consequences of DCM
  • 6:26 Diagnosis & Treatment
  • 7:37 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

We will go over an important medical condition known as dilated cardiomyopathy, why it occurs pathologically, what it does to the body physiologically, and how compensatory mechanisms help and hurt the body in this lesson.

A Dilated Balloon

If you have a balloon, take it with you to the nearest sink. Now, turn on the tap and begin filling the balloon up. As you do this, you'll notice that as the volume of water increases inside of the balloon, it begins to dilate. Dilation occurs in order to accommodate increases in volume.

Frankly, you didn't even really have to use water, you could've just increased the volume of air within it by blowing into the balloon. But since we're dealing with blood in this lesson, I thought using a liquid would be a little bit more appropriate. Anyhow, this lesson will head off into the direction of why, just like a balloon, your heart may become dilated and what that alters physiologically.

Enlargement of the Heart

If there's something wrong in your body or directly in your heart, then the heart may enlarge as a result of this. Enlargement of the heart is actually an umbrella term because the heart can enlarge in one of two ways. It can either enlarge by increasing the size of the heart muscle, something termed hypertrophy, or it can enlarge by expanding out just like that balloon I mentioned just a second ago. In this case, we say the heart has dilated.

There's actually another word that's sometimes used instead of dilation. It's called dilatation. Dilatation refers to the abnormal distension or dilation of a structure, sometimes to the point of its dysfunction. Many structures in your body can and must dilate under certain circumstances, but if they do so to an abnormal size that may lead to malfunction, then it's known as dilatation. However, often times the terms dilation and dilatation are used interchangeably in medicine and we'll just stick with the former in this lesson for simplicity's sake. Which end result (hypertrophy or dilation of the heart leading to cardiac enlargement) occurs varies from disease process to disease process.

Dilated Cardiomyopathy

So, for this lesson we'll focus in on a typically irreversible, progressive heart condition that results in ventricular chamber enlargement, potentially diminished ventricular thickness, and subsequent systolic dysfunction. This condition is known as dilated cardiomyopathy (or DCM).

We'll stick to exploring the dilation of the left ventricle of the heart for our purposes, although either or both can be affected in DCM. Anyway, in DCM, something causes the volume of blood to increase within the left ventricle. Before explaining why and how, I encourage you to review the lessons on valvular dysfunction and normal cardiovascular anatomy and physiology in order to understand this lesson a bit better.

There are two important things that can cause DCM: mitral and aortic valve regurgitation. Other causes include drugs, endocrine diseases, alcohol, viral infection, and more. In aortic regurgitation, the left ventricle ejects oxygenated blood into circulation through the aortic valve. But regurgitation implies some of the blood flows back into the left ventricle after ejection. In mitral regurgitation, blood shoots back into the left atrium when the left ventricle contracts. The next time the left atrium pushes blood into the left ventricle, it's going to push in more than normal since it received extra blood from the left ventricle as a result of mitral regurgitation.

In either case, the left ventricle must now accommodate a larger volume of blood than normal. Recall our balloon. How did it accommodate larger amounts of fluid? It dilated; it stretched; it increased in size - all of the above.

So, the left ventricle will enlarge in DCM. As it enlarges, the muscular walls of the chamber stretch. As the muscle stretches, the contractile units of the muscle fail, the muscle becomes weaker, and the heart cannot pump blood out into circulation during systole adequately anymore. In a very basic sense, in dilated cardiomyopathy, the affected heart chamber becomes larger than normal, floppy, weak, and the wall is sometimes thinner than usual as a result of all that stretching out.

The Consequences of DCM

With all those important details in mind, it's equally important to think about the consequences of DCM. If the blood isn't being pumped out into circulation very well, cardiac output decreases. In order to increase the volume of blood being pumped out by the heart, the heart rate increases and the kidneys activate the renin-angiotensin-aldosterone system (or RAAS) in order to preserve sodium and, therefore, fluid volume. What the RAAS system does is it basically turns off the faucet so the water stays in the pipes, our blood vessels, instead of leaking out into the bladder.

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