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Dilated Cardiomyopathy - The fatality of an over-expanded heart

The next series of articles is going to be about “cardiomyopathies"-diseases of the myocardium, or the heart muscle. 

 
heart-chambers
 

These diseases ultimately cause dysfunction during systolic or diastolic. We have to remember that myocardial ischemia, valvular dysfunction and even hypertension can cause dysfunction to the ventricles, we don’t consider these as cardiomyopathies. There are 3 main types of myocardial dysfunction we like to describe:

  1. Dilated cardiomyopathy
  2. Hypertrophic cardiomyopathy
  3. Restrictive cardiomyopathy

The prominent and defining feature of each type of cardiomyopathy is revealed within the name itself. Although cardiomyopathies are often encountered by physicians, the exact mechanism of why they develop still isn’t clear. We do know that genetics plays a vital role in the development of the disease.

The details of each type will be discussed in 3 separate articles starting with Dilated Cardiomyopathy in this article:

DILATED CARDIOMYOPATHY

You guessed it. The first type of cardiomyopathy we’ll be looking at, presents as a dilated heart. Unfortunately, that’s not the end of the story.

Now imagine a normal heart. Zoom into the left ventricle. It’s highly concentrated with myocytes which contributes to its contractility. Contractility is talking about the ability of the heart to eject blood out into the aorta. 

Ejection fraction i.e the fraction of blood leaving the heart must be at least 55%.

So now, if ejection (i.e. contractility), is impaired, EF is impaired, and can be anywhere <40%!

This is an important detail to remember when we compare the different types of cardiomyopathies. 

Pathogenesis

1.    Genetics          

  • DCM is familial in 20%-50% of cases, with an autosomal dominant type of inheritance
  • There is disruption in the structure of the myocyte cytoskeletal proteins
  • The problem may lie within the mitochondria. Do you remember 2 important functions the powerhouse of the cell has? Beta oxidation of fatty acids and yes, oxidative phosphorylation. Without these at optimum levels, it is clear that myocytes are deprived of ATP. 
  • Mutations in the dystrophin gene have also been implicated (dystrophin gene mutations are the cause of Duchenne/Becker muscular dystrophy), and some people with the aforementioned diseases have DCM as a prominent feature

2.    Myocarditis

  • Examination of biopsies of the endomyocardial tissue yielded viral nucleic acids, mainly that of Coxsackie B and enteroviruses

3.    Toxin mediated

  • Alcohol, through its metabolite acetaldehydecauses direct damage to the myocardium. However, alcohol consumption leads to wet beriberi, which is no different from DCM
  • Doxorubicin is an important cause for toxic DCM

4.    Childbirth

  • Prolactin derivatives have been found to be related to peripartum and postpartum cardiomyopathy. Most probably, this is due to an immunologic reaction between prolactin compounds and the myocardium, but the process is poorly understood.

Morphology

All 4 chambers are dilated. The heart is heavy and mural thrombi can be seen. The walls, although increased in size, are flabby. Histology is not very specific either. Myocytes are hypertrophied and can be irregular. Patches of fibrosis are common. Endocardial scars are seen due to ischemic necrosis- a result of the inadequate supply of oxygen to the rapidly expanding myocytes of the heart chambers. 

 
dilated-cardiomyopathy-image
 

How does the patient present?

DCM presents just like congestive heart failure. Exertional dyspnoeais a major symptom. Most patients do not survive DCM due to development of complications. Dilation of the left ventricle often takes the mitral valve along with it, causing increased distance between the leaflets. This causes a functional mitral regurgitation. A similar process results in tricuspid regurgitation. Stretching of the heart also disrupts the conduction system, leading to arrhythmias. Mural thrombi can detach and embolise to far away parts of the body.

How is this condition treated?

The only way to go forward is heart transplantation. So far, we have not found any means to reverse the histological changes found in DCM, and the survival rates without transplantation are only 2-5 years. Maybe in the future, the discovery will be made by one of us aspiring medical students!

Author: Shruthi Sivakumar

Sources and citations

1.Robbins and Coltran Pathologic Basis of Disease, 8th Edition