A 54-year-old woman is brought to the emergency department via ambulance after the sudden … — USMLE Step 3

A 54-year-old woman is brought to the emergency department via ambulance after the sudden onset of severe, tearing chest pain that radiates to her interscapular region. Her medical history is significant for severe persistent asthma, for which she takes an inhaled corticosteroid and long-acting beta-agonist, and hypertension, for which she takes amlodipine. On arrival, she appears in acute distress. Her temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $215/115\text{ mmHg}$ in the right arm and $185/95\text{ mmHg}$ in the left arm, heart rate is $118\text{/min}$ , and respiratory rate is $24\text{/min}$ . Pulse oximetry shows $94\%$ on room air. Physical examination reveals a diaphoretic woman. Pulmonary auscultation reveals diffuse bilateral expiratory wheezing. Cardiovascular examination shows a regular tachycardic rhythm with no murmurs, rubs, or gallops. Radial pulses are symmetric, but the left femoral pulse is diminished. CT angiography of the chest confirms a Stanford type B aortic dissection. Which of the following is the most appropriate initial pharmacologic intervention for this patient?

A
Intravenous esmolol followed by intravenous sodium nitroprusside
B
Intravenous sodium nitroprusside alone
Intravenous diltiazem followed by intravenous sodium nitroprussideAnswer
D
Intravenous labetalol
E
Intravenous nicardipine followed by intravenous diltiazem

Answer

Intravenous diltiazem followed by intravenous sodium nitroprusside

The correct sequence for the medical management of acute aortic dissection is strict heart rate control followed by blood pressure control. The primary goal is to reduce aortic wall shear stress (

dp/dt

). While intravenous beta-blockers (such as esmolol or labetalol) are the standard first-line agents, this patient has severe persistent asthma with active diffuse wheezing. Beta-blockers are contraindicated in active asthma exacerbations as they can precipitate severe bronchospasm. According to major cardiovascular guidelines, in patients with acute aortic dissection who have absolute contraindications to beta-blockers, intravenous non-dihydropyridine calcium channel blockers (e.g., diltiazem or verapamil) should be used as the initial agent for heart rate control. Once the heart rate is controlled, an intravenous vasodilator such as sodium nitroprusside is added to achieve the target systolic blood pressure.

Step-by-Step Solution

Identify the primary diagnosis and its immediate physiologic threat.

The patient has a Stanford type B aortic dissection, which requires immediate reduction of aortic wall shear stress (

dp/dt

High blood pressure and a fast heart rate increase the rate of rise of ventricular pressure, which actively propagates the dissection flap.

Determine the standard pharmacologic protocol for the diagnosis.

The standard sequence is heart rate control (target

< 60\text{/min}

) followed by blood pressure control (target systolic

< 120\text{ mmHg}

) using an intravenous beta-blocker followed by a vasodilator.

Reversing the sequence or using vasodilators alone causes reflex tachycardia, which worsens the dissection.

Evaluate the patient's comorbidities for contraindications to standard therapy.

The patient has severe persistent asthma with active diffuse wheezing, making beta-blockers (like esmolol or labetalol) strongly contraindicated.

Even cardioselective beta-blockers can precipitate life-threatening bronchospasm in active asthma.

Select the appropriate alternative therapy.

Intravenous diltiazem is selected as the initial agent for heart rate control, followed by sodium nitroprusside for blood pressure control.

Non-dihydropyridine calcium channel blockers effectively reduce heart rate and contractility without exacerbating bronchospasm.

Key Concept

In the medical management of acute aortic dissection, beta-blockers are the first-line agents to reduce heart rate and blood pressure. However, in patients with absolute contraindications to beta-blockers, such as active severe asthma, non-dihydropyridine calcium channel blockers (e.g., diltiazem, verapamil) must be used before initiating vasodilator therapy.

Estimated Time:1m 30s

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