A 4-year-old girl is brought to the pediatrician’s office. Her father reports that she suddenly became pale and stopped running while he had been playfully chasing her and her pet Chihuahua. After 30 min, she was no longer pale and wanted to resume the game. She has never had a previous episode and has never been cyanotic. Her physical examination was normal, as were her chest x-ray and echocardiogram. The electrocardiographic pattern in the figure shows the configuration of preexcitation, which indicates which of the following?
a. Paroxysmal ventricular tachycardia
b. Paroxysmal supraventricular tachycardia
c. Wolff-Parkinson-White syndrome
d. Stokes-Adams pattern
e. Excessive stress during play
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 c; Wolff-Parkinson-White syndrome.
The child described in the question, who has no cyanosis or murmur, no cardiac or pulmonary vascular abnormalities by chest x-ray, and no evidence of structural anomalies by echocardiogram, is unlikely to have an underlying gross anatomic defect. The electrocardiographic pattern in the figure shows the configuration of preexcitation, the pattern seen in the Wolff-Parkinson-White syndrome (WPW). These patients have an aberrant atrioventricular conduction pathway, which causes the early ventricular depolarization appearing on the electrocardiogram as a shortened PR interval. The initial slow ventricular depolarization wave is referred to as the delta wave. Seventy percent of patients with WPW have single or repeated episodes of paroxysmal supraventricular tachycardia, which can cause the symptoms described in the question. The pre-excitation electrocardiographic pattern and WPW can occur in Ebstein malformation, but this is unlikely in the absence of cyanosis and with a normal echocardiogram. If ventricular tachycardia were present, the symptoms would likely be more profound. Active play and exposure to over-the-counter medications containing sympathomimetics in a healthy 4-year-old child can cause symptoms such as those described in the question in children with WPW by precipitating paroxysmal supraventricular tachycardia.