A 3-day-old infant with a single second heart sound has had progressively deepening cyanosis since birth but no respiratory distress. Chest radiography demonstrates no cardiomegaly and normal pulmonary vasculature. An electrocardiogram shows an axis of 120° and right ventricular prominence. Which of the following congenital cardiac malformations is most likely responsible for the cyanosis?
a. Tetralogy of Fallot
b. Transposition of the great vessels
c. Tricuspid atresia
d. Pulmonary atresia with intact ventricular septum
e. Total anomalous pulmonary venous return below the diaphragm
the answer is below…
The United States Medical Licensing Examination, or USMLE for short, is a three-part licensing examination that is required in order to receive a license to practice medicine within the United States.
The USMLE assesses a physician’s ability to apply knowledge, concepts, and principles, and to determine fundamental patient-centered skills that are important in health and disease and that constitute the basis of safe and effective patient care.Examination committees composed of medical educators and clinicians from across the United States and its territories prepare the examination materials each year.
This exam is designed by the Federation of State Medical Boards and the National Board of Medical Examiners to determine whether or not an individual understands and can apply the knowledge necessary to practice medicine safely and intelligently.
The USMLE is actually comprised of three different exams that are referred to as steps, which examine the individual’s knowledge of specific topics related to the field of medicine such as basic science, medical knowledge, medical skills, clinical science, and the application of all of these skills and areas of knowledge in the medical field.
All three steps of the USMLE include a series of computerized multiple-choice questions, but the format of the exam and the information covered in each multiple-choice section is different for each step of the USMLE. The USMLE Step II also has a clinical skills portion that examines an individual’s ability to work with real patients and the USMLE Step III has a computerized patient simulation portion in addition to the multiple-choice section of the exam. In order for an individual to receive a license to practice medicine, the individual must pass all three steps of the USMLE.
The correct answer is b; Transposition of the great vessels.
Transposition of the great vessels with an intact ventricular septum presents with early cyanosis, a normal-sized heart (classic “egg on a string” radiographic pattern in one-third of cases), normal or slightly increased pulmonary vascular markings, and an electrocardiogram showing right axis deviation and right ventricular hypertrophy. In tetralogy of Fallot, cyanosis is often not seen in the first few days of life. Tricuspid atresia, a cause of early cyanosis, causes diminished pulmonary arterial blood flow; the pulmonary fields on x-ray demonstrate a diminution of pulmonary vascularity, and left axis and left ventricular hypertrophy are shown by electrocardiogram. Total anomalous pulmonary venous return below the diaphragm is associated with obstruction to pulmonary venous return and a classic radiographic finding of marked, fluffy-appearing venous congestion (“snowman”). In pulmonic atresia with an intact ventricular septum, cyanosis appears early, the lung markings are normal to diminished, and the heart is large.