Cardiomyopathies: Pathology review

Aman is a 60 year old male who came into the clinic with shortness of breath and lower limb edema for the past 3 months. He has a history of hypertension, hyperlipidemia and chronic alcohol use. On auscultation, an additional S3 sound is heard. An echocardiogram is performed, which shows dilated ventricular chambers and a reduced ejection fraction. Alexandra is a 23 year old professional volleyball player who came to the clinic after multiple episodes of “passing out” during her games. At first, she presumed it was due to dehydration, but she is now concerned. She has a family history of sudden cardiac death in multiple relatives. An echocardiogram shows asymmetric hypertrophy of the interventricular septum, and a normal ejection fraction.

Both Aman and Alexandra have cardiomyopathies. From outside to inside, the heart is made of the epicardium, myocardium, and endocardium. Diseases that affect the myocardium are called cardiomyopathies. The three main subtypes are dilated, hypertrophic and restrictive cardiomyopathy.

Let’s start with dilated cardiomyopathy, which is the most common one, accounting for almost 90% of all cases. Now, In dilated cardiomyopathy the ventricular walls become thin and weak. As a consequence, the ventricular chambers dilate. Because the ventricular wall is thinner, muscle contraction is weaker and the heart can’t pump blood efficiently throughout the body. So we have a systolic dysfunction with normal diastole.

Okay, when it comes to the etiology of dilated cardiomyopathy, the large majority of cases are idiopathic, meaning the cause can’t be identified. However, there are many secondary causes that must be excluded first. Examples include toxins like chronic alcohol or cocaine abuse, nutritional deficiencies like thiamine deficiency, also called beri-beri, or selenium deficiency. Another cause is myocarditis, which is inflammation of the heart muscle, usually caused by viruses like Coxsackie B, but can also be related to autoimmune diseases like lupus. Hemochromatosis is a disorder of iron overload in which excessive iron can be deposited in many organ sites, including the cardiac muscle. Too much intracellular iron can act as a toxic free radical, resulting in cellular damage.