A 16-year-old boy presents with headache, epistaxis, and leg fatigue on exertion. Examination reveals upper-extremity hypertension (BP 180/95 mmHg in arms vs 110/70 mmHg in legs), diminished femoral pulses with radiofemoral delay, and a continuous murmur over the back. CT angiography reveals the structure marked **A** in the diagram—a focal shelf-like narrowing of the proximal descending aorta just distal to the left subclavian artery at the ligamentum arteriosum. Which of the following best explains the pathophysiology of upper-extremity hypertension in this patient?
A. Increased proximal aortic resistance from the discrete juxtaductal narrowing triggers baroreceptor-mediated sympathetic activation and renin-angiotensin system upregulation
B. Bicuspid aortic valve associated with coarctation causes aortic regurgitation leading to systolic hypertension
C. Decreased cardiac output from left ventricular failure reduces renal perfusion pressure, activating the renin-angiotensin-aldosterone system
D. Obstruction of the left subclavian artery prevents normal blood flow to the left upper extremity
Explanation
Why option 1 is right
The discrete juxtaductal narrowing (structure A) creates a focal obstruction to systemic blood flow in the proximal descending aorta. This increases resistance distal to the narrowing, which is sensed by baroreceptors in the aortic arch as a reduction in distal pressure. The baroreceptor reflex responds by increasing sympathetic tone and activating the renin-angiotensin-aldosterone system, leading to elevated blood pressure in the upper extremities (proximal to the coarctation). This is the primary mechanism of hypertension in coarctation of aorta, as documented in the AHA/ACC guidelines—the narrowing itself creates a pressure gradient that the body attempts to overcome through neurohumoral compensation.
Why each distractor is wrong
Option 2: While left ventricular hypertrophy and eventual dysfunction can occur as a late complication of untreated coarctation, the initial and primary mechanism of hypertension is the direct obstruction itself, not cardiac failure. At presentation, the patient's hypertension is driven by the resistance imposed by structure A, not by reduced cardiac output.
Option 3: The narrowing is located just distal to the left subclavian artery, not at the origin of the left subclavian artery. The left subclavian artery arises proximal to the coarctation and therefore receives elevated pressure. Obstruction of the left subclavian itself would not explain bilateral upper-extremity hypertension.
Option 4: Although bicuspid aortic valve is associated with coarctation in 50–80% of cases, aortic regurgitation from BAV causes wide pulse pressure (elevated systolic and low diastolic), not the sustained systolic hypertension seen in coarctation. The hypertension in this case is directly attributable to the aortic narrowing, not valvular disease.
High-YieldNEET PG
Coarctation hypertension = baroreceptor reflex + RAAS activation in response to increased proximal aortic resistance from the discrete narrowing; the gradient across structure A is the hemodynamic driver.
