USMLE STEP 3 MCQ 42:Most likely diagnosis



Most likely diagnosis :

a) pulmonary embolism
b) early repolarization
c) acute pericarditis
d) acute myocardial infarction
e) Myocarditis

Correct Answer: C


The electrocardiogram (ECG) is a useful, simple tool that may aid in the diagnosis of acute pericarditis. Typical ECG findings include diffuse concave-upward ST-segment elevation and, occasionally, PR-segment depression. ECG changes of both acute myocardial infarction and early repolarization can appear similar to ECG changes of acute pericarditis. However, these conditions can usually be excluded by an accurate history, physical examination and recognition of a few key features on the ECG. In this ECG of a patient with acute pericarditis, note diffuse concave-upward ST-segment elevation, ST-segment depression in aVR, and PR-segment depression which is best demonstrated in leads II and V3. Note lack of reciprocal ST-segment changes, an important feature differentiating acute pericarditis from acute myocardial infarction. Also note that the ST/T ratio is greater than 0.25, a finding frequently indicative of acute pericarditis. 

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