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Difficulty: MediumPediatric Cardiovascular Disorders

An 8-week-old infant is evaluated in the pediatric emergency department for poor feeding and excessive sweating during meals. Over the past two weeks, his mother has noticed that he breathes unusually fast and becomes exhausted after consuming only 1 to 2 ounces of formula. A previous evaluation at a local clinic attributed the rapid breathing to a viral respiratory infection, but his symptoms have progressively worsened. Vital signs include a heart rate of 172/min, respiratory rate of 68/min, and blood pressure of 85/45 mmHg. Pulse oximetry is 97% on room air. On physical examination, the infant appears mildly distressed. Auscultation of the lungs reveals bilateral basilar crackles and scattered expiratory wheezes. Cardiovascular examination shows a palpable parasternal heave and a grade 3/6 pansystolic murmur best heard at the left lower sternal border. Abdominal examination demonstrates a firm liver edge palpable 3.5 cm below the right costal margin. Which of the following is the most likely underlying hemodynamic derangement responsible for this patient's presentation?

  1. Excessive pulmonary blood flow from a left-to-right shuntAnswer
  2. B
    Acute inflammation and necrosis of the terminal bronchioles
  3. C
    Hypertrophy of bronchial smooth muscle with airway hyperreactivity
  4. D
    Fixed narrowing of the right ventricular outflow tract
  5. E
    Persistent patency of the vessel connecting the aorta and pulmonary artery

Answer

Excessive pulmonary blood flow from a left-to-right shunt
The correct answer describes the pathophysiology of a Ventricular Septal Defect (VSD). This infant presents with classic signs of congestive heart failure (CHF), including diaphoresis during feeding, tachypnea, poor weight gain, and hepatomegaly. The physical exam confirms the diagnosis of a VSD by the presence of a grade 3/6 pansystolic murmur located at the left lower sternal border. Because pulmonary vascular resistance naturally falls during the first few weeks of life, a large VSD begins to allow a substantial amount of blood to shunt from the left ventricle into the right ventricle and pulmonary circulation. This excessive pulmonary blood flow leads to pulmonary edema, which manifests clinically as crackles and wheezing. This phenomenon is often colloquially called 'cardiac asthma' and is frequently misdiagnosed initially as a viral respiratory infection like bronchiolitis.

Step-by-Step Solution

1
Analyze the physical examination findings.
The patient has a grade 3/6 pansystolic murmur at the left lower sternal border, a parasternal heave, hepatomegaly, and crackles/wheezes.
Identifying the specific characteristics of the murmur and systemic findings is crucial to localizing the cardiac lesion and determining its systemic effects.
2
Correlate the physical findings with a specific diagnosis.
A pansystolic (holosystolic) murmur at the left lower sternal border in an infant strongly suggests a Ventricular Septal Defect (VSD).
VSDs are the most common congenital heart defects and classically present with this specific murmur due to flow from the high-pressure left ventricle to the lower-pressure right ventricle.
3
Determine the pathophysiological consequence of the defect.
A large VSD creates a significant left-to-right shunt, leading to pulmonary overcirculation, pulmonary edema (causing wheezes/crackles), and eventual left-sided and right-sided congestive heart failure (causing poor feeding, diaphoresis, and hepatomegaly).
Understanding the hemodynamic shift explains why the infant is presenting with respiratory distress that was previously misdiagnosed as an infection.

Key Concept

Clinical presentation and pathophysiology of Ventricular Septal Defect (VSD) in infants.
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Topics

Pediatric Cardiovascular Disorders

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