An emergency response team evaluates a 68-year-old female who awoke abruptly with severe r… — USMLE Step 2 CK

An emergency response team evaluates a $68$ -year-old female who awoke abruptly with severe respiratory distress. Her medical history is notable for long-standing essential hypertension, obesity, diet-controlled type 2 diabetes mellitus, and a $35$ -pack-year smoking habit.

Upon arrival at the emergency department, she appears highly anxious, diaphoretic, and is utilizing accessory muscles of respiration. Vital signs exhibit a blood pressure of $165/85 \text{ mmHg}$ , a heart rate of $96 \text{ bpm}$ , a respiratory rate of $28 \text{ breaths/min}$ , and an oxygen saturation of $86\%$ on ambient air.

Auscultation of the lungs reveals a prolonged expiratory phase accompanied by high-pitched, diffuse bilateral wheezes. A faint $2/6$ systolic murmur is auscultated at the left lower sternal border.

The evaluating physician suspects an acute exacerbation of chronic obstructive pulmonary disease and immediately orders continuous nebulized albuterol along with intravenous methylprednisolone.

Twenty minutes after initiating therapy, the patient's condition deteriorates precipitously. She reports new-onset severe dizziness and retrosternal chest pressure.
Repeat vital signs indicate a blood pressure of $78/42 \text{ mmHg}$ and a heart rate of $128 \text{ bpm}$ .
Repeat cardiac auscultation demonstrates that the previously faint murmur is now a prominent $4/6$ harsh, crescendo-decrescendo systolic murmur at the left lower sternal border.

A $12$ -lead electrocardiogram demonstrates sinus tachycardia, voltage criteria for left ventricular hypertrophy, and deep, narrow Q waves in leads I, aVL, $V_5$ , and $V_6$ , with no ST-segment elevations.

Which of the following is the most appropriate next step in managing this patient's acute hemodynamic collapse?

Administration of intravenous normal saline and phenylephrineAnswer
B
Administration of intravenous magnesium sulfate and epinephrine
C
Activation of the cardiac catheterization laboratory for coronary angiography
D
Initiation of an intravenous dobutamine infusion
E
Administration of intravenous furosemide and noninvasive positive-pressure ventilation

Answer

The correct management for this patient's hemodynamic collapse is the administration of intravenous normal saline and phenylephrine to increase preload and afterload.

The patient's initial presentation of dyspnea and wheezing ('cardiac asthma') was caused by elevated left-sided filling pressures secondary to undiagnosed Hypertrophic Obstructive Cardiomyopathy (HOCM) or severe hypertensive concentric hypertrophy. The evaluating physician misdiagnosed this presentation as a COPD exacerbation and administered albuterol. Albuterol is a beta-agonist that increases myocardial contractility and heart rate. In patients with HOCM, increased contractility and tachycardia severely worsen the dynamic left ventricular outflow tract (LVOT) obstruction by exacerbating systolic anterior motion (SAM) of the mitral valve. This dynamic obstruction led to a drastic drop in cardiac output (manifesting as hypotension), coronary hypoperfusion (manifesting as chest pressure), and an intensification of the murmur due to the increased pressure gradient. The deep, narrow Q waves on the ECG are classic 'septal Q waves' indicative of massive septal depolarization, not an acute myocardial infarction. The appropriate management for hypotensive dynamic LVOT obstruction is to immediately discontinue the offending inotrope, increase preload with intravenous fluids, and increase afterload with a pure alpha-1 agonist such as phenylephrine. This combination increases the left ventricular cavity volume, which physically separates the anterior mitral leaflet from the hypertrophied septum, thereby reducing the outflow gradient and reversing the shock.

Step-by-Step Solution

Analyze the patient's initial presentation and the physician's intervention.

The patient presented with wheezing and dyspnea ('cardiac asthma') which was misdiagnosed as a COPD exacerbation, leading to the administration of albuterol.

Establishing the iatrogenic trigger is essential to understanding the subsequent deterioration.

Evaluate the clinical deterioration and new physical examination findings.

Following albuterol administration, the patient developed cardiogenic shock, and her faint systolic murmur intensified into a prominent 4/6 crescendo-decrescendo murmur at the left lower sternal border.

A systolic murmur that intensifies after the administration of an inotropic agent (albuterol) strongly suggests a dynamic left ventricular outflow tract (LVOT) obstruction.

Correlate the physical findings with the electrocardiographic evidence.

The ECG reveals left ventricular hypertrophy and deep, narrow 'septal' Q waves in the lateral leads.

These findings confirm the underlying diagnosis of Hypertrophic Cardiomyopathy (HCM) with asymmetric septal hypertrophy, ruling out an acute transmural myocardial infarction.

Determine the pathophysiological mechanism of the shock and select the appropriate pharmacological reversal.

The shock is driven by severe LVOT obstruction exacerbated by increased contractility and tachycardia. The correct intervention is to increase the left ventricular cavity size.

Intravenous normal saline increases preload, and phenylephrine (a pure alpha-1 agonist) increases afterload. Both actions dilate the left ventricle, moving the anterior mitral leaflet away from the septum and reducing the outflow gradient.

Key Concept

Hemodynamic management of dynamic left ventricular outflow tract obstruction (Hypertrophic Cardiomyopathy) exacerbated by beta-agonists.

Estimated Time:2m 30s

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