USMLE® Step 1 style questions USMLE
A 23-year-old woman comes to the clinic complaining of progressively worsening fatigue, dyspnea, and lightheadedness for the past 6 months and leg swelling for the last month. She has not had any prior episodes of syncope or chest pain with exertion. Past medical history includes anorexia nervosa. Temperature is 37.2°C (98.9°F), pulse is 90/min, respirations are 22/min, and blood pressure is 100/68 mm Hg. Body mass index is 14.5 kg/m2. Physical examination shows a thin woman in respiratory distress and neck examination shows jugular venous distention. Cardiac auscultation shows a holosystolic blowing murmur that radiates to the axilla and an S3 heart sound that is best heard at the apex in early diastole. A chest x-ray is obtained, and the results are shown below. Which of the following is the most likely explanation for this patient’s findings on cardiac auscultation?
Dilated cardiomyopathy exam links
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS, Vincent Waldman, PhD
Cardiomyopathy translates to “heart muscle disease,” so cardiomyopathy is a broad term used to describe a variety of issues that result from disease of the myocardium, or heart muscle.
When cardiomyopathy develops as a way to compensate for some other underlying disease, such as hypertension or valve diseases, it’s called secondary cardiomyopathy. When it develops all by itself, it’s called primary cardiomyopathy.
Now, the most common type is dilated cardiomyopathy, which can cause all four chambers of the heart to dilate, or get bigger. Specifically, new sarcomeres, or muscle units, in the walls are added in series, and the chambers grow larger, which leaves the walls relatively thin compared to the large chamber size, with less muscle to use for contraction.
In other words, they have really weak contractions, which means less blood is pumped out each contraction. This also means that there’s a lower stroke volume, and if the heart’s failing to pump out as much blood to both the body from the left ventricle, and the lungs from the right ventricle, patients develop biventricular congestive heart failure. Since contraction happens during systole, we say this is a type of systolic heart failure.
Also, when the chambers get larger, they tend to stretch out the valves that separate the atria and ventricles. When they are stretched, the valves can’t close all the way, so they start to regurgitate blood back into the atria. This is called mitral valve regurgitation on the left side, and tricuspid valve regurgitation on the right. Mitral valve regurgitation might be heard on auscultation as a holosystolic murmur, meaning that it happens throughout systole.
Additionally, you might also hear an S3 heart sound on auscultation, which is the result of blood rushing and slamming into the dilated ventricular wall during diastole.
Another complication can be arrhythmias, because stretching out the muscle walls can irritate the cells in the conduction system, which are within those walls. Sometimes, an X-ray can be helpful for a diagnosing dilated cardiomyopathy.
As far as causes go, primary dilated cardiomyopathy is most often idiopathic, meaning there isn’t a clearly identifiable cause. Some cases, however, can be traced back to specific genetic mutations or genetic conditions, such as Duchenne Muscular Dystrophy and hemochromatosis. Also, in some cases it can be caused by an infection, like coxsackievirus B, which causes myocarditis — inflammation of the heart muscle — or Chagas disease, a protozoal infection.
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