USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 43-year-old woman who suffers from dilated cardiomyopathy comes to the local university hospital because she has received notification that the emergent transplant team is currently awaiting the arrival of a donor cardiac allograft. She suffered from chronic alcoholism for 10 years after the unexpected death of her parents, but has now been sober for the past 3 years. Meanwhile, at the same institution, a patient with end-stage renal disease has been waiting several months for a compatible kidney allograft. He suffers from lupus nephritis and has attended dialysis sessions three times per week since the diagnosis. Which of the following is the most significant differentiating factor that between these two tissue types with regard to the patient waiting time associated with transplantation?
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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