USMLE Step2 Secrets Cardiology
Terms
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- What is the most important side effect of heparin?
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Heparin can cause thrombocytopenia that in some unlucky patients is associated with arterial thrombosis.
Measure complete blood counts to monitor for this side effect, which usually occurs on day 3-7 of heparin administration. Discontinue heparin immediately if platelet counts begin to fall. - How is the effect of heparin monitored?
- Heparin is monitored with PTT (partial thromboplastin time), a measure of the internal coagulation pathway
- How is the effect of warfarin monitored?
- Warfarin is monitored with the PT (prothrombin time), a measure of the external coagulation pathway
- How do you keep PTT and PT straight?
-
PTT has a "T" inside, intrinsic, internal coagulation pathway.
PT is the other -
Memorize:
Measure heparin with ______
Measure warfarin with ______ -
Measure heparin with PTT
(Hep to the PTT!)
Measure warfarin with PT
(War with the PT) - How is the effect of aspirin monitored?
- Aspirin prolongs bleeding time, a measure of platelet function. Clinically, the effect of aspirin is not monitored with lab testing, but be aware that it prolongs bleeding time test.
- How are the effects of low-molecular-weight heparin monitored?
- LMW Heparin does not affect any of the coagulation parameters (PT or PTT or bleeding time), and its effect is not clinically monitored. Rarely, a special type of factor X assay (anti-Xa) is used to measure the effect.
- In an emergency, how can you reverse the effects of heparin?
- Heparin and LMW heparin can be reversed with protamine.
- In an emergency, how can you reverse the effects of warfarin?
- Warfarin with fresh frozen plasma (contains clotting factors; immediate effect) and or vitamin K (takes a few days to work).
- In an emergency, how can you reverse the effects of aspirin?
- Platelet transfusions
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Condition: Hemophilia A
PT
PTT
Bleeding time
Inheritance -
Condition: Hemophilia A
PT: normal
PTT: prolonged (low levels of factor 8)
Bleeding time: normal
Inheritance: X-linked -
Condition: Hemophilia B
PT
PTT
Bleeding time
Inheritance -
Condition: Hemophilia B
PT: normal
PTT: prolonged (low levels of factor 9)
Bleeding time: normal
Inheritance: X-linked - How do you keep Hemophilia A and B straight?
-
Hemophilia A is 8A (eight = ate = A) missing factor 8), the more common form.
Hemophilia B is 9B -
Condition: vWF deficiency
PT
PTT
Bleeding time
Inheritance -
Condition: vWF deficiency
PT: normal
PTT: prolonged
Bleeding time: prolonged
Inheritance: autosomal dominant
***Normal levels of factor 8 and factor 9 -
Condition: Disseminated intravascular coagulation
PT
PTT
Bleeding time
Inheritance
What else is elevated in terms of labs?
When do you encounter DIC?
What do you see on the blood smear? -
Condition: DIC
PT: prolonged
PTT: prolonged
Bleeding time: prolonged
Inheritance: N/A
Positive D-dimer or FDPs (fibrin degradation products); postpartum, infection, malignancy; schistocytes and fragmented cells on peripheral smear. -
Condition: Liver Disease
PT
PTT
Bleeding time
Inheritance -
Condition: Liver Disease
PT: Prolonged
PTT: normal or prolonged
Bleeding time: normal
Inheritance: N/A
All factors but 8 are low, you see stigmata of liver disease; no correction with vitamin K -
Condition: vitamin K deficiency
PT
PTT
Bleeding time
Inheritance -
Condition: vitamin K deficiency
PT: prolonged
PTT: slightly prolonged
Bleeding time: normal
Inheritance: N/A
** low levels of factors 2,7,9,10, proteins C and S; look for neonate who did not receive prophylactic vitamin K; malabsorption, alcoholism, or prolonged antibiotic use (which kills vitamin K-producing bowel flora) -
MEMORIZE:
PT (extrinsic): 2,5,7,10: increased with warfarin use, vit K deficiency, liver disease
PTT (intrinsic): 8,9,11,12: increased with heparin use, hemophilia A, B, vWF deficiency -
PT (extrinsic): 2,5,7,10: increased with warfarin use, vit K deficiency, liver disease
PTT (intrinsic): 8,9,11,12: increased with heparin use, hemophilia A, B, vWF deficiency - Remember that uremia causes a qualitative platelet defect and that vitamin C deficiency and chronic steroid therapy can cause bleeding tendency with normal coagulation tests.
- Remember that uremia causes a qualitative platelet defect and that vitamin C deficiency and chronic steroid therapy can cause bleeding tendency with normal coagulation tests.