An 8-week-old male infant is evaluated in the pediatric clinic for a two-week history of d… — USMLE Step 2 CK

An $8$ -week-old male infant is evaluated in the pediatric clinic for a two-week history of difficulty feeding. His parents report that he takes much longer to finish a bottle, becomes excessively sweaty during feeds, and seems to "breathe fast" constantly. He was born full-term at $39$ weeks gestation weighing $3.2\text{ kg}$ . His current weight is $3.6\text{ kg}$ . His temperature is $37.2^\circ\text{C}$ ( $99.0^\circ\text{F}$ ), heart rate is $165/\text{min}$ , respiratory rate is $68/\text{min}$ , and blood pressure is $85/50\text{ mmHg}$ . Oxygen saturation is $97\%$ on room air. Brachial and femoral pulses are equal and robust. Physical examination reveals a hyperactive precordium. Auscultation demonstrates a grade $4/6$ harsh holosystolic murmur at the left lower sternal border with a palpable thrill, and a faint mid-diastolic rumble at the cardiac apex. Lung examination reveals mild bilateral basilar crackles. The liver edge is palpated $3\text{ cm}$ below the right costal margin. Which of the following is the most appropriate next step in the management of this patient?

Administer furosemide and obtain an echocardiogramAnswer
B
Administer nebulized albuterol and oral dexamethasone
C
Initiate empiric intravenous ceftriaxone and order blood cultures
D
Reassure the parents and schedule a routine follow-up in one month
E
Obtain an arterial blood gas to calculate expected respiratory compensation

Answer

The most appropriate next step is to administer furosemide and obtain an echocardiogram to manage acute heart failure and confirm the diagnosis.

The correct answer identifies that this infant is in acute congestive heart failure due to a large left-to-right shunt, most likely a Ventricular Septal Defect (VSD). The harsh holosystolic murmur at the left lower sternal border with a thrill is classic for a VSD. The mid-diastolic rumble at the apex represents increased blood volume returning from the overcirculated lungs and crossing the mitral valve, creating a relative mitral stenosis. The normal physiological drop in pulmonary vascular resistance at 6-8 weeks of age maximizes this left-to-right shunting, leading to the onset of heart failure symptoms (diaphoresis with feeds, failure to thrive, tachypnea, hepatomegaly, and crackles). The most appropriate next step is administering a diuretic (like furosemide) to reduce volume overload and obtaining an echocardiogram to confirm the anatomical diagnosis.

Step-by-Step Solution

Analyze the growth and vital signs.

The infant exhibits failure to thrive (only 400g weight gain over 8 weeks), tachycardia (

165/\text{min}

), and severe tachypnea (

68/\text{min}

Establishing the severity of the patient's systemic compromise is the first step in differentiating benign murmurs from pathological shunts.

Interpret the physical examination findings.

A harsh holosystolic murmur with a thrill at the left lower sternal border indicates a Ventricular Septal Defect (VSD). The mid-diastolic apical rumble indicates increased flow across the mitral valve (massive left-to-right shunt). Crackles and hepatomegaly indicate bilateral heart failure.

Physical exam findings directly point to a structural cardiac defect complicated by pulmonary overcirculation and systemic venous congestion.

Determine the appropriate management.

The patient requires immediate medical management to reduce preload and pulmonary congestion, followed by definitive diagnostic imaging.

Furosemide provides rapid relief of pulmonary edema, while an echocardiogram is the gold standard to visualize the VSD and measure the shunt fraction.

Key Concept

Management of symptomatic Ventricular Septal Defect (VSD)

Estimated Time:1m 30s

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