A 29-year-old G1P0 woman at 32 weeks gestation is brought to the emergency department due … — USMLE Step 2 CK

A $29$ -year-old G1P0 woman at $32$ weeks gestation is brought to the emergency department due to the acute onset of severe shortness of breath and a cough productive of pink, frothy sputum. She recently emigrated from a developing country and had limited prenatal care. She reports a history of frequent, untreated sore throats during childhood. Her temperature is $37.8^\circ\text{C}$ ( $100.0^\circ\text{F}$ ), blood pressure is $110/68\text{ mmHg}$ , pulse is $135/\text{min}$ and irregularly irregular, and respirations are $28/\text{min}$ . Pulse oximetry shows $86\%$ on room air. Physical examination reveals elevated jugular venous pressure. Lung auscultation demonstrates bibasilar crackles and diffuse expiratory wheezes. Cardiac examination reveals a loud S1 and a low-pitched, rumbling, mid-diastolic murmur heard best at the apex.

Laboratory results are as follows:

Test	Value
Hemoglobin	$10.5\ \text{g/dL}$
Leukocyte count	$11,500/\text{mm}^3$
Thyroid-stimulating hormone (TSH)	$2.1\ \mu\text{U/mL}$
Free thyroxine (T4)	$0.6\ \text{ng/dL}$

Continuous fetal heart rate monitoring shows a baseline of $150/\text{min}$ with moderate variability and recurrent late decelerations. Which of the following is the most appropriate next step in management?

Intravenous metoprololAnswer
B
Inhaled albuterol and intravenous methylprednisolone
C
Intravenous packed red blood cell transfusion
D
Immediate cesarean delivery
E
Oral levothyroxine

Answer

Intravenous metoprolol

The correct answer is intravenous metoprolol. This patient presents with acute pulmonary edema (crackles, frothy sputum, hypoxia) in the setting of undiagnosed rheumatic mitral stenosis (low-pitched diastolic rumble, loud S1, immigrant from a developing country) and new-onset atrial fibrillation (irregularly irregular pulse). In normal pregnancy, maternal plasma volume and heart rate increase significantly, peaking around 28-32 weeks. This physiologic change combined with mitral stenosis increases baseline left atrial pressure. The abrupt onset of atrial fibrillation with rapid ventricular response further shortens diastolic filling time, leading to severe left atrial volume overload, rapid pulmonary venous congestion, and acute pulmonary edema. The most appropriate initial step is to decrease the heart rate to prolong diastole, allowing more time for blood to flow across the stenotic mitral valve. Intravenous beta-blockers (e.g., metoprolol) are the medications of choice for acute rate control in pregnant patients.

Step-by-Step Solution

Analyze the physical examination findings to identify the primary maternal pathology.

A low-pitched, rumbling mid-diastolic murmur with a loud S1 indicates mitral stenosis, likely secondary to childhood rheumatic fever.

Accurate diagnosis of the structural heart disease is required to understand the mechanism of acute decompensation.

Evaluate the vital signs and lung auscultation to determine the cause of acute respiratory failure.

The irregularly irregular pulse of 135/min indicates atrial fibrillation. Bibasilar crackles and hypoxia indicate acute pulmonary edema.

In mitral stenosis, tachycardia drastically shortens diastolic filling time, leading to severe left atrial volume overload and pulmonary venous congestion.

Interpret the fetal heart rate tracing in the context of maternal hemodynamics.

Recurrent late decelerations indicate uteroplacental insufficiency driven by the mother's acute hypoxia and decreased forward cardiac output.

Maternal stabilization is the most effective way to restore uterine perfusion and resolve fetal distress.

Select the most appropriate initial management to address the root hemodynamic problem.

Intravenous metoprolol is selected for acute rate control.

Slowing the maternal heart rate prolongs diastole, decreasing left atrial pressure, resolving the pulmonary edema, and improving cardiac output to the fetus.

Key Concept

Management of acute decompensated mitral stenosis with atrial fibrillation in pregnancy requires immediate rate control to prolong diastolic filling time.

Estimated Time:2m 0s

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