A 2-day-old female neonate is evaluated in the neonatal intensive care unit for persistent… — USMLE Step 2 CK

A $2$ -day-old female neonate is evaluated in the neonatal intensive care unit for persistent cyanosis. She was born at $39$ weeks gestation via normal vaginal delivery to a $28$ -year-old primigravida. The mother has a history of bipolar disorder and was maintained on her prescribed psychiatric medication throughout the pregnancy. On physical examination, the neonate appears comfortably tachypneic but cyanotic. Vital signs show a heart rate of $160$ /min, respiratory rate of $65$ /min, and oxygen saturation of $82\%$ on room air. Cardiac auscultation reveals a widely split $S_1$ , a normal $S_2$ , and a harsh holosystolic murmur heard best at the left lower sternal border. Chest radiography demonstrates massive cardiomegaly spanning nearly the entire thoracic cavity. Electrocardiography reveals right atrial enlargement and a complete right bundle branch block. Which of the following best describes the underlying cardiovascular anomaly in this patient?

Downward displacement of the septal and posterior tricuspid valve leafletsAnswer
B
Anterosuperior deviation of the infundibular septum
C
Complete absence of the right atrioventricular connection
D
Increased pulmonary vascular resistance secondary to maternal medication
E
Failure of the aorticopulmonary septum to undergo a 180-degree spiral

Answer

Downward displacement of the septal and posterior tricuspid valve leaflets

The patient's clinical presentation is classic for Ebstein anomaly, a congenital heart defect strongly associated with maternal lithium use (the primary treatment for bipolar disorder). In Ebstein anomaly, there is a downward (apical) displacement of the septal and posterior leaflets of the tricuspid valve into the right ventricle. This structural change 'atrializes' a portion of the right ventricle, leading to a massive right atrium, severe tricuspid regurgitation (creating the holosystolic murmur), and delayed conduction (right bundle branch block). The extreme right atrial dilation creates a 'wall-to-wall' appearance on chest radiography.

Step-by-Step Solution

Identify the key clinical findings in the neonate.

The patient has neonatal cyanosis, massive cardiomegaly on chest radiography, right atrial enlargement with a right bundle branch block on electrocardiography, and a holosystolic murmur.

Synthesizing the physical exam and diagnostic imaging helps narrow down the specific congenital heart defect.

Correlate the neonate's findings with the maternal history.

The mother took medication for bipolar disorder during pregnancy. The standard mood stabilizer for bipolar disorder is lithium.

Maternal teratogenic exposures strongly predispose neonates to specific cardiac anomalies.

Determine the structural anomaly caused by the suspected teratogen.

Prenatal lithium exposure is classically associated with Ebstein anomaly, characterized by downward displacement of the tricuspid valve leaflets.

This anomaly perfectly explains the massive cardiomegaly (due to severe right atrial enlargement) and the right-sided electrocardiographic conduction delays.

Key Concept

Ebstein anomaly is a congenital heart defect characterized by the apical displacement of the tricuspid valve, leading to severe tricuspid regurgitation and massive right atrial enlargement. It is strongly associated with maternal use of lithium during pregnancy.

Estimated Time:1m 30s

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