Each week, Osmosis shares a USMLE® Step 1-style practice question to test your knowledge of medical topics. Today’s case involves a 20-year-old male patient with a seemingly abnormal ECG reading. Can you figure it out?
A 20-year-old male college student comes to the clinic with an ECG obtained at a health fair, where he was told the reading was abnormal. He is a competitive track and field athlete and excels in long-distance running. He denies chest pain, shortness of breath, or loss of consciousness. He has no prior medical history and takes no medications other than a daily multivitamin. He denies family history of sudden unexpected deaths. His temperature is 37.0°C (98.6°F), pulse is 65/min, respirations are 20/min, and blood pressure is 115/75 mmHg. He appears thin and comfortable. Physical exam shows a normal heart rate without murmurs and 2+ regular carotid and radial pulses bilaterally. Lungs are clear. ECG shows the following:
Reproduced from: Wikipedia
Which of the following is the most appropriate management of this patient?
A. Perform invasive electrophysiology study
B. Recommend decreasing physical activity
C. Perform transthoracic echocardiogram
D. Place permanent pacemaker
E. No treatment is required
Scroll down to find the answer!
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The correct answer to today’s USMLE® Step 1 Question is…
E. No treatment is required
Before we get to the Main Explanation, let’s look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!
Incorrect answer explanations
The incorrect answers to today’s USMLE® Step 1 Question are…
A. Perform invasive electrophysiology study
Incorrect: In patients with isolated first degree AV block, an invasive electrophysiology study (EPS) is not needed for diagnosis. If a wide QRS complex is present concurrently with PR prolongation, the conduction delay may be present below the AV node, and EPS may be helpful to determine the precise location.
B. Recommend decreasing physical activity
Incorrect: Highly conditioned endurance athletes may have evidence of first degree AV block because of increased vagal tone with a lower resting heart rate. In the absence of symptoms, reducing physical activity is unnecessary.
C. Perform transthoracic echocardiogram
Incorrect: All patients with suspected first degree AV blocks should be questioned about a history of heart disease. In the absence of risk factors for heart disease, in an otherwise healthy young patient with first degree AV block, an echocardiogram will not provide helpful information and is unnecessary.
D. Place permanent pacemaker
Incorrect: A pacemaker is not recommended in asymptomatic patients with first degree AV block.
Main Explanation
This patient has isolated first degree atrioventricular (AV) block on his ECG. First degree AV block is defined as a PR interval > 200 milliseconds, representing prolonged conduction through the AV node:
First degree AV block may be caused by heightened vagal tone (e.g. highly conditioned endurance athletes), structural abnormalities of the AV node, medications that impair nodal conduction (e.g., digoxin, beta blockers, non-dihydropyridine calcium channel blockers), conduction pathway infiltration (e.g. sarcoidosis), and ischemia (e.g. inferior wall myocardial infarction, because the AV node is supplied by the right coronary artery).
The majority of cases of first degree AV block are found incidentally on ECG, are not dangerous, and do not cause symptoms. History and physical examination should be directed toward identifying any of the pathologies described above. In the absence of concerning cardiac findings on exam, asymptomatic patients like this athlete require no further workup or treatment.
Major Takeaway
First degree AV block is defined on ECG as a PR interval > 200 milliseconds. Most cases are benign and asymptomatic, and therefore, invasive studies and pacemaker placement are not recommended.
References
Viitasalo MT, Kala R, Eisalo A. Ambulatory electrocardiographic recording in endurance athletes. Br Heart J. 1982;47(3):213-220. doi:10.1136/hrt.47.3.213
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The United States Medical Licensing Examination (USMLE®) is a joint program of the Federation of State Medical Boards (FSMB®) and National Board of Medical Examiners (NBME®). Osmosis is not affiliated with NBME nor FSMB.
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