Welcome to USMLE practice question #139! Today’s topic is cardiology.
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A 28-year-old woman presents to her primary care physician for evaluation of intermittent palpitations and chest discomfort. She denies exertional dyspnea or syncope. Her medical history is unremarkable. Physical examination reveals a late systolic murmur with a mid-systolic click that is accentuated when she stands from a squatting position. Echocardiography confirms excessive leaflet motion with systolic prolapse of the mitral valve into the left atrium. Which of the following best explains the structural abnormality underlying her condition?
A) Commissural fusion and calcification of the mitral valve
B) Weakened connective tissue
C) Fibrotic thickening of the chordae tendineae
D) Myxomatous degeneration of the mitral valve
E) Annular stretching and leaflet malcoaptation
Detailed Breakdown of Answers + Correct Answer Below ⏬
ANSWER + QUESTION BREAKDOWN
It’s important to adopt the correct MENTAL MODEL when answering USMLE questions; it saves time and increases accuracy. The mental model outlined below is a foundational component of our test-taking skills masterclass (check it out if you want to elevate your skills). Here’s how to think through this question:
Step 1. Read the last line to get to the heart of the question: “Which of the following best explains the structural abnormality underlying her condition?”
Step 2: Is this a first-, second-, or third-order question?
Answer: 2nd order. 1st: Diagnose the problem, 2nd: Identify structural abnormality responsible for the diagnosed problem
Step 3: Read the vignette carefully and ask yourself: “The underlying cause of my diagnosis is most likely ______________.”
Step 4. Look at the answer choices and select the option most closely resembling your final thought from “Step 3” above.
GENERAL ANALYSIS
This 28-year-old woman presents with intermittent palpitations, chest discomfort, and a late systolic murmur with a mid-systolic click that is accentuated when standing. Echocardiography confirms systolic prolapse of the mitral valve into the left atrium, consistent with mitral valve prolapse.
ANSWER CHOICES:
CHOICE A: Commissural fusion and calcification of the mitral valve
Explanation: Commissural fusion and calcification are characteristic of rheumatic heart disease, which leads to mitral stenosis. This condition results in restricted leaflet motion rather than excessive leaflet motion or prolapse.
CHOICE B: Weakened connective tissue
Explanation: Weakened connective tissue is seen in systemic connective tissue disorders such as Marfan syndrome or Ehlers-Danlos syndrome, which can be associated with MVP. However, this is not the specific structural abnormality underlying MVP itself.
CHOICE C: Fibrotic thickening of the chordae tendineae
Explanation: Fibrotic thickening of the chordae tendineae can occur in conditions like endocarditis or chronic rheumatic heart disease, leading to restricted leaflet motion or regurgitation. MVP involves elongation and weakening (not fibrotic thickening) of the chordae tendineae due to myxomatous degeneration.
CHOICE D: Myxomatous degeneration of the mitral valve
Explanation: Myxomatous degeneration involves disruption of the extracellular matrix with accumulation of proteoglycans and glycosaminoglycans in the spongiosa layer of the mitral valve leaflets. This weakens the structural integrity of the valve, leading to leaflet elongation, excessive motion, and prolapse into the left atrium during systole.
CHOICE E: Annular stretching and leaflet malcoaptation
Explanation: Annular stretching and leaflet malcoaptation occur in secondary (functional) mitral regurgitation due to left ventricular dilation (e.g., heart failure). These changes are not primary abnormalities of the mitral valve itself.
FINAL VERDICT…
CORRECT ANSWER: D) Myxomatous degeneration of the mitral valve
The hallmark structural abnormality underlying mitral valve prolapse is myxomatous degeneration, which weakens the mitral valve leaflets and chordae tendineae. This leads to excessive leaflet motion and prolapse into the left atrium during systole.
KEY CONCEPTS:
Pathophysiology of Mitral Valve Prolapse (MVP):
Caused by myxomatous degeneration of mitral valve leaflets.
Histologically characterized by accumulation of glycosaminoglycans in the spongiosa layer.
Leads to elongation and redundancy of leaflets and chordae tendineae.
Clinical Features of MVP:
Mid-systolic click followed by a late systolic murmur.
Symptoms include palpitations, chest discomfort, or fatigue.
Murmur accentuates with maneuvers that decrease preload (e.g., standing).
Associated Conditions:
Primary MVP occurs sporadically or in familial clusters.
Secondary MVP may be associated with connective tissue disorders (e.g., Marfan syndrome, Ehlers-Danlos syndrome).
Complications of MVP:
Mitral regurgitation.
Infective endocarditis.
Rarely, arrhythmias or sudden cardiac death.
Diagnosis and Management:
Diagnosed by echocardiography showing leaflet prolapse >2 mm beyond the annular plane.
Most cases are benign; severe cases with significant regurgitation may require surgical repair.