AssessmentsCardiomyopathies: Pathology review
USMLE® Step 1 style questions USMLE
A 68-year-old woman comes to the clinic complaining of dyspnea on exertion, fatigue, and chest pain. She also states that she has to use 3 pillows at night when she sleeps. Past medical history includes carcinoma of the breast, for which she received surgery and adjuvant radiation therapy but no chemotherapy. Temperature is 37.2°C (98.9°F), pulse is 80/min, respirations are 20/min, and blood pressure is 100/68. Physical exam shows jugular venous distension and bilateral leg edema. Cardiac auscultation shows S3 and S4 heart sounds. Electrocardiogram (ECG) shows low amplitude signals. Which of the following is the most likely cause of this patient’s disease?
Contributors:Kaia Chessen, MScBMC, Victoria Cumberbatch, Evan Debevec-McKenney, Ahmad El-Gammal, MBBS
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.
Other causes include Chagas disease, a parasitic infection caused by Trypan-o-soma cruzi, which is transmitted by the “kissing bug”. A clue on the exam would be someone who recently travelled to South America, and also has other clinical features like periorbital swelling, megaesophagus and megacolon. Also, during pregnancy, the mother’s body demands more cardiac output. Sometimes, the heart fails to meet this high demand, and we get something called peripartum cardiomyopathy, which commonly occurs in the last trimester of pregnancy and up to 6 months after delivery. Dilated cardiomyopathy can also result as a side effect of some medications like doxorubicin, a chemotherapeutic agent, or trastuzumab, a monoclonal antibody. Even severe emotional stress can cause a form of dilated cardiomyopathy called Takotsubo cardiomyopathy.
This is thought to