Exam 3- antiplatelets and anti-coagulants Flashcards
What are the functions of von-Willebrand Factor? (2)
Substance releases from damaged endothelium which induces platelet adhesion; also stabilizes Factor VIII
Main factor complexes involved in the
a) extrinsic
b) intrinsic
c) central clotting pathways?
a) Tissue Factor / VIIa complex
b) Factor XIII/VI complex
c) V / Xa
How is thrombin activated from prothrombin?
Cleavage by the factor V/Xa complex
How is fibrin activated from fibrinogen?
Cleavage by thrombin
How does thrombin positively feed back and enhance the clotting response?
Further activates the intrinsic pathway (factor VIII/IX)
Which lab tests assess:
a) the extrinsic pathway
b) the intrinsic pathway?
a) prothrombin time (PT)(and INR)
b) activated partial thromboplastin time (APTT)
Bleeding pattern in a failure of a) primary and b) secondary haemostasis?
a) Mucosal bleeding (e.g. GI, retina, epistaxis)
b) Large haematomas e.g. haemarthroses, intracranial
IgA-mediated vasculitis causing polyarthritis and a palpable purpuric rash over buttocks/extensirs?
Henoch-Schonlein purpura
What is the commonest inherited bleeding disorder and what is its inheritance pattern?
von Willebrand disease; usually autosomal dominant
How does von Willebrand disease presennt?
Presents like a platelet disorder- bruising, mucosal bleeding (e.g. post tooth extraction)
Causes of platelet disorders:
a) decreased production (3)
b) excessive destruction/use (2)
c) poor functioning (2)
a) marrow failure, aplastic anaemia, megaloblastic anaemia
b) immune thrombocytopenic purpura, DIC
c) antiplatelet drugs, uraemia
Causes of multiple clotting factor deficiencies (3)
Liver failure
Vit K deficiency/warfarin
DIC
What does an elevated D-dimer suggest?
Active clotting somewhere in the body; feature of DVT/PE and DIC
X-linked inherited conditions with recurrent haemarthroses and soft tissue bleeds
Haemophilias A (factor XIII deficiency) and B (factor IX deficiency)
Why is APTT deranged in the haemophilias?
APTT measures the intrinsic pathway; which is mediated by factors VIII and IX
What is Virchow’s triad?
Stasis
Hypercoagulability
Endothelial injury/dysfunction
Give examples of hereditary thrombophilias? (5)
Factor V Leiden Antithrombin deficiency Protein C deficiency Protein S deficiency Prothrombin 20210
How should hereditary thrombophilias be managed? (3)
Risk minimization
Short term prophylaxis to cover times of known risk e.g. pregnancy, surgery
Long-term anticoagulation if recurrent thromboses
What is interesting about antiphospholipid syndrome?
Predisposes to both arterial and venous thromboses
Risk factors for venous thrombosis (6)
Surgery Immobility Pregnancy, oral contraceptive pill, HRT Age Obesity Varicose veins/venous insufficiency
Main risk factors for arterial thrombosis (4)
Hypertension
Smoking
High cholesterol
Diabetes
Mechanism of action of asprin?
Inhibits COX-1, thereby inhibiting production of thromboxane 2
Mechanism of action of clopidogrel?
ADP receptor antagonists
How long prior to surgery should antiplatelets be stopped?
7-10 days
