If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 2 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.
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This month’s stumper
A 30-year-old East Asian woman comes to the clinic complaining of chest pain. For the last two years, she has had intermittent nocturnal chest pain that lasts up to 10 minutes. The pain is substernal and is described as a heavy pressure that radiates to her throat. The pain is a six out of 10 on a pain scale and awakens her from sleep. It is associated with mild nausea and a clammy sensation. In the past, she has tried antacids and a proton-pump inhibitor, neither of which seem to help.
Occasionally, significant aerobic exercise induces the pain. Aside from this complaint, she reports being quite healthy; her only medical problem is Raynaud phenomenon, severe during the winter months, and a history of migraine headaches treated with sumatriptan. Social history is remarkable for the occasional use of cocaine. Vital signs and physical examination are unremarkable; the patient appears young and healthy. An electrocardiogram is unremarkable. A Holter monitor study is arranged.
Given this patient's likely diagnosis, which of the following is the most likely finding on Holter monitor during an episode of chest pain?
A. Diffuse ST-segment elevation and PR segment depression.
B. Normal electrocardiographic tracings.
C. Prolonged QT interval with increased duration at night.
D. Transient ST-segment depressions in the lateral leads.
E. Transient ST-segment elevation in the inferior leads.
The correct answer is E.
Kaplan Medical explains why
This patient has a classic presentation for variant (Prinzmetal) angina, which is caused by coronary vasospasm that induces transient ischemia and ST-segment elevations.
Patients with variant angina are younger, typically women, and do not exhibit classic cardiovascular risk factors. It usually occurs at night, though hyperventilation from exercise may induce symptoms (by way of an alkalosis favorable to vasoconstriction) and can be worsened by agents such as cocaine or serotonergic agents such as sumatriptan. Vasospasm can occur in any distribution, though it is seen most commonly in the right coronary artery, which, for most people, provides blood flow to the inferior portion of the heart.
Why the other answers are wrong
Choice A: Diffuse ST-segment elevation and PR segment depression is suggestive of pericarditis. One might expect pain relieved with leaning forward or a pericardial friction rub on physical examination. A recent viral illness and low-grade fevers are clues in the history that would point toward pericarditis. There is no reason to suspect this diagnosis in this woman.
Choice B: Normal electrocardiographic findings are unlikely if this woman has variant angina. The association of other vascular phenomenon, such as Raynaud phenomenon and migraine headaches, makes variant angina the most likely diagnosis. In such cases, the chest pain is associated with ST-segment elevations and occasionally flipped T-waves.
Choice C: There is no reason to suspect a prolonged QT interval and certainly no reason to expect that it would worsen at night. Patients who have syncopal episodes, sometimes associated with abrupt surprises, may have prolonged QT-syndrome, which can predispose to torsade de pointes.
Choice D: Transient ST-segment depressions may be seen in acute coronary syndrome if an unstable plaque is partially or intermittently obstructing blood flow. There is no reason to suspect this finding in this patient.
Tips to remember
- Variant (Prinzmetal) angina classically presents with angina-like symptoms that occur at rest and is caused by focal coronary vasospasm.
- It classically awakens the patient from sleep.
- It is associated with other vasospastic conditions, such as Raynaud disease.
For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series.