Master the board step 3

Master the Boards: USMLE Step 3
Basic Science Correlate
Mechanism of P2Y 12 Antagonists: Clopidogrel, Prasugrel, Ticagrelor
These agents block aggregation of platelets to each other by inhibiting ADPinduced
activation of the P2Y 12 receptor. Clopidogrel and prasugrel are in
the thienopyridine class.
Thrombolytics and Primary Angioplasty
Step 3 is very big on knowing which treatments will lower mortality.
Thrombolytics and primary angioplasty both lower mortality in ST segment
elevation myocardial infarction (STEMI) and are dependent on time; in other
words, their benefit markedly diminishes with time.
Prasugrel is added only for
angioplasty.
Primary angioplasty means angioplasty during an acute episode of chest pain,
and infarction is the single best evidence for mortality benefit with angioplasty.
Angioplasty is one type of “percutaneous coronary intervention” (PCI). PCI
must be performed within 90 minutes of arrival at the emergency department
for a STEMI. Angioplasty has not been shown to decrease mortality in stable
angina more than medical therapy (aspirin, beta blockers, and statins) alone.
CCS Tip: CCS requires you to know the route of administration of medications.
When is the answer “urgent
angioplasty” or PCI?
• The question asks
“what has the single
greatest efficacy?” in
lowering mortality in
STEMI.
• The question includes a
contraindication to the
use of thrombolytics.
If PCI cannot be performed within 90 minutes of arrival in the emergency
department, the patient should receive thrombolytics. The question will
clearly state that “the patient is at a small rural hospital” or “the nearest
catheterization facility is over an hour away.” The question must be clear on
this point. Thrombolytics are indicated when the patient has chest pain for
< 12 hours and has ST segment elevation in 2 or more leads. A new left
bundle branch block (LBBB) is also an indication for thrombolytic therapy.
Thrombolytics should be given within 30 minutes of a patient’s arrival in the
emergency department with pain.
Basic Science Correlate
Mechanism of Thrombolytics
Thrombolytics activate plasminogen into plasmin. Plasmin chops up fresh or
newly formed fibrin strands into D-dimers. This is why all clots elevate levels
of D-dimers. After several hours, the fibrin clot has been stabilized (made
more permanent) by factor XIII. Plasmin will not cleave fibrin once stabilized
by factor XIII.
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