Master the board step 3

Master the Boards: USMLE Step 3
Non-ST Segment Elevation Myocardial Infarction
The predominant differences in the management of non-ST segment elevation
MI (NSTEMI) are as follows:
··
No thrombolytic use
··
Heparin is used routinely. Low molecular weight (LMW) heparin is superior
to IV unfractionated heparin.
··
Glycoprotein IIb/IIIa inhibitors lower mortality, particularly in those undergoing
angioplasty
A 54-year-old man with a history of diabetes and hypertension comes to the
emergency department with crushing, substernal chest pain that radiates to his
left arm. The pain has been on and off for several hours, with this last episode
being 30 minutes in duration. He has had chest pain on exertion before, but this
is the first time it has developed at rest. The EKG is normal. Aspirin, oxygen, and
nitrates have been given. Troponin levels are elevated. Which of the following is
most likely to benefit this patient?
a. Low molecular weight heparin
b. Thrombolytics
c. Diltiazem
d. Morphine
e. CK-MB levels
The single greatest
benefits from GPIIb/
IIIa inhibitors with ACS
come in combination with
angioplasty and stent
placement. Abciximab does
not benefit ST segment
elevation MI.
Answer: A. Heparin is the only one of these choices that has been shown to produce
lower mortality. Thrombolytics do not lower mortality, unless there is ST elevation or
a new LBBB. Positive cardiac enzymes are not an indication for thrombolytics. Other
answers that could be right if they were choices are GPIIb/IIIa inhibitors, such as eptifibatide,
tirofiban, or abciximab, or the use of angioplasty/PCI.
Basic Science Correlate
Mechanism of Heparin
Heparin potentiates the effect of antithrombin. Antithrombin actually inhibits
almost every step of the clotting cascade. This is why it does not work with
antithrombin deficiency. Heparin only prevents new clots from forming.
Chronic Angina
Thrombolytics are only
used if there is ST segment
elevation or a new LBBB
within 12 hours of the
onset of chest pain.
Office-based cases of further management will emphasize the same issues of
mortality benefit.
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