USMLE PRACTICE QUESTION #73
TOPIC: Cardiovascular pathology
Today’s question will test your understanding of a foundational concept in cardiovascular pathology.
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A 6-year-old boy is brought to his pediatrician by his parents due to recurrent headaches and frequent nosebleeds. His medical history is unremarkable. On examination, his vital signs show a temperature of 98.2°F (36.8°C), pulse 85/minute, respirations 20/minute, blood pressure in the right arm 150/90 mmHg, and oxygen saturation 98% on room air. The blood pressure in his lower extremities is measured at 100/60 mmHg. Cardiac examination reveals a continuous murmur heard best at the left interscapular area. Imaging studies confirm the suspected diagnosis. Which of the following collateral circulations will likely develop as a compensatory mechanism?
A. Internal thoracic artery to the lateral thoracic artery
B. Superior epigastric artery to the inferior epigastric artery
C. Subclavian artery to the vertebral artery
D. Axillary artery to the brachial artery
E. Intercostal arteries to the lumbar arteries
F. Subclavian artery to the internal thoracic artery
G. Superior mesenteric artery to the inferior mesenteric artery
Detailed Breakdown of Answers + Correct Answer Below ⏬
ANSWER + QUESTION BREAKDOWN
The mental model used to answer this question comes from our detailed test-taking skills masterclass (check it out if you want to take your USMLE test-taking skills to a whole new level). Here’s how to think through this question:
Step 1. Read the last line to determine the actual question: “Which of the following collateral circulations is most likely to develop as a compensatory mechanism?”
Step 2: Is this a first-, second-, or third-order question?
Answer: 2nd order. 1st: Identify the problem (ie. Correctly diagnose the problem), and 2nd: Know which collateral circulation (of the listed options) is most likely to develop.
Step 3: Read the vignette carefully and ask yourself: “Which collateral pathway is likely to develop due to this patient’s condition?”
Step 4. Look at the answer choices and select the option most closely resembling your final thought from “Step 3” above.
GENERAL ANALYSIS
The clinical presentation and findings, in this case, are consistent with coarctation of the aorta, which often leads to the development of collateral circulation as a compensatory mechanism to bypass the narrowed segment of the aorta. In patients with coarctation of the aorta, collateral circulation typically develops through pathways involving the subclavian and internal thoracic arteries.
ANSWER CHOICES:
CHOICE A: Internal thoracic artery to the lateral thoracic artery
Explanation: This pathway is not typically involved in collateral circulation for coarctation of the aorta as it does not provide significant collateral flow around an aortic coarctation.
CHOICE B: Superior epigastric artery to the inferior epigastric artery
Explanation: This connection is more involved in abdominal wall circulation.
CHOICE C: Subclavian artery to the vertebral artery
Explanation: This pathway supplies blood to the brain but is not involved in bypassing coarctation.
CHOICE D: Axillary artery to the brachial artery
Explanation: This represents normal arm circulation rather than collateral flow; it is unrelated to collateral circulation in coarctation.
CHOICE E: Intercostal arteries to the lumbar arteries
Explanation: Intercostal arteries form collaterals, but typically with other thoracic arteries. While intercostal arteries are involved, they primarily connect with other intercostal or subclavian branches rather than lumbar arteries.
CHOICE F: Subclavian artery to the internal thoracic artery
Explanation: The internal thoracic artery, arising from the subclavian artery, provides collateral circulation by anastomosing with intercostal arteries, allowing blood flow to bypass the coarcted segment and reach the descending aorta. This pathway effectively helps maintain blood flow past an aortic coarctation, making it a key component of compensatory collateral circulation.
CHOICE G: Superior mesenteric artery to the inferior mesenteric artery
Explanation: This involves abdominal organ blood supply and is unrelated to thoracic or intercostal collateral formation.
FINAL VERDICT…
In coarctation of the aorta, one primary collateral pathway involves blood flow from the subclavian artery into the internal thoracic artery. This pathway allows blood to reach intercostal arteries that bypass the narrowed segment of the aorta, ensuring adequate perfusion to areas distal to the obstruction. This mechanism helps compensate for reduced direct aortic flow and supports systemic circulation.
CORRECT ANSWER: F) Subclavian artery to the internal thoracic artery
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That’s it for question 73!
See ya next time 👋