Thrombosis and Hemostasis

Question 1

List the three components of hemostasis

Answer 1

1. Vascular spasm (vasoconstriction).
   2: Formation of platelet Plug.
   3: Blood coagulation.

Question 2

Compare primary and secondary hemostasi

Answer 2

Secondary hemostasis is defined as the formation of insoluble, cross-linked fibrin by thrombin leading to stabilization of the primary platelet plug. This especially important in larger blood vessels where the platelet plug is insufficient alone to stop hemorrhage.

Question 3

List the steps leading to vascular injury repair

Answer 3

Vascular injury with exposure of sub endothelial collagen.

Adherence of platelet to subendothelial collagen: interaction with collagen bound Von Willebrand factor and subsequently directly with collagen (GP receptor complex).

Activation of collagen receptors activates phospholipase C mediated cascades–> increased intercellular calcium.

Activation of kinases leading to secretion of granular content, morphological changes, presentation of procoagulant surface and the activation of phospholipase A2.

The colocalization of numerous coagulation factors on the procoagulant surface of platelets ultimately leads to release of thrombin from prothrombin.
Accumulation of thrombin, TBXA2 and ADP binding to their respective receptors

These cascades results in activation of platelet fibrinogen receptor expressed on platelets with exposure of binding sites for fibrinogen (GPIIb/GPIIIa).

This results in linkage of activated platelets by fibrinogen bridges (aggregation).

Question 4

Normal Hemostasis Sequence

Answer 4

Endothelial injury/dysfunction with reflex vasoconstriction

Clot initiation/formation: primary hemostasis

Clot propagation/stabilization: secondary hemostasis

Clot inhibition/cessation: antithrombotic activity
Clot dissolution: fibrinolysis

Question 5

Identify the function of von Willebrand factor

Answer 5

The VWF gene encodes von Willebrand factor (VWF):

• a large multimeric glycoprotein that plays a central role in the blood coagulation system
• major mediator of platelet-vessel wall interaction and platelet adhesion
• carrier for coagulation factor VIII

Question 6

vWF - more for boards than exam (details)

Answer 6

VWF is synthesized in endothelial cells and megakaryocytes as a 2,813-residue pre-protein. It dimerizes, undergoes extensive posttranslational modification, and is packaged as a mature protein into endothelial cell Weibel-Palade bodies and platelet alpha granules. Endothelial cells secrete VWF constitutively, whereas platelets release VWF when stimulated. Circulating VWF multimers are composed of up to 40 subunits and range in size from 500 to 10,000 kD (review by Goodeve, 2010). VWF is synthesized in megakaryocytes and endothelial cells with a 22-amino acid signal peptide, 741-amino acid propeptide and 2,050-amino acid mature VWF (review by Goodeve, 2010).

Question 7

mechanism of action of heparin

Answer 7

inhibits Gp1b, attachment of platelet to vWF

Question 8

Coagulation cascade: Intrinsic and Extrinsic pathways of coagulation, role of Vitamin K. (details)

Answer 8

2 initial pathways:

contact activation (intrinsic) and

tissue factor (extrinsic)

both –> fibrin

Primary pathway: tissue factor.

These pathways consist of a series of rezctions: zymogen of a serine protease and its glycoprotein co-factor –> activated –> catalyze the next rxn –> cross-linked fibrin.

Coag factors generally indicated by Roman numerals, with a lowercase a to indicate the active form.

Question 9

vitamin K dependent critical factors for coagulation

Answer 9

2, 7, 9, 10

anticoagulant proteins C and S
and protein Z (factor X- targeting)

Question 10

Function of Vitamin K2

Answer 10

add a carboxylic acid to glutamate –> gamma-carboxylglutamate

= posttranslational modification of the protein

Can then chelate calcium –> clotting

Question 11

APTT

Answer 11

Contact activation was provided by the glass tube

activators: ellagic acid, particulate silicates such as celite or kaolin

no significant differences between adult and children 7-10

Longer PTT values is an independent risk factor for death, thrombosis, bleeding and morbidity

Question 12

Activated partial thromboplastin time

Answer 12

intrinsic and common pathway

When a mixture of plasma and phospholipid platelets substitute is re-calcified, fibrin is formed in the presence of ffactors in intrinsic pathway and common pathway

• Platelet substitute- chloroform extract of brain, inosithin- soyabean
• Partial thromboplastin - do not activate the extrinsic pathway which require complete tissue thromboplastin

Question 13

APTT- used for?

Answer 13

PTT is used to detect factor deficiency, screen for lupus anticoagulant

• monitor heparin anti-coagulation

** more sensitive to deficiency of VIII and IX

Yields abnormal results if any factor level is less than 15-30% of normal

PTT may be shortened by a high level of any single factor. m/c is factor VIII

Question 14

Prothrombin time

Answer 14

• extrinsic and common pathway

Tissue factor, factor VII, X, V, prothrombin, fibrinogen

Plasma is recalcified in the presence of tissue factor

Independent of platelet count

** PT is used for controlling anti coagulant therapy

More sensitive to deficiency of VII and X

Question 15

Thrombin time

Answer 15

When thrombin is added to plasma the time required for clot formation is a measure at which fibrin forms

Abnormal value when fibrinogen level is less than 70 to 100 mg/dl

** Prolonged by heparin

Prolonged in qualitatively abnormal fibrinogen, elevated FDP, paraproteinemias, hyper fibrinogenemias

** REPTILASE CLOTTING TIME- unaffected by heparin

Question 16

Fibrinolysis

Answer 16

XIIa, Tissue plasminogen activator (t-PA), and Urokinase

XIIa pathway via coagulation cascade converts plasminogen to plasmin

t-PA- from uninjured endothelial cells binds to fibrin and forms plasmin from plasminogen

Urokinase from endothelial cells, etc., converts plasminogen in circ into plasmin

Question 17

clinically administered plasminogen activators

Answer 17

tPA
urokinase or streptokinase

All produce high plasmin levels to induce rapid clot dissolution

Question 18

Bleeding patterns: Gums, epistaxis, petichiae, ecchymoses

Answer 18

Platelets, vWF, Factor V, blood vessels

Question 19

Bleeding patterns: Joints, muscles, and GI

Answer 19

Factors VIII, IX and severe VII

Question 20

Bleeding patterns: Hematomas, hemarthrosis, **epistaxis, and menorrhagia

Answer 20

Factor II and Factor X

Question 21

platelet disorders that can cause excessive bleeding

Answer 21

inadequate prduction
splenic sequestration
increased platelet destruction/ consumption (ITP, DIC, TTp, HUS, bleeding, sepsis, HIV)
drug-induced destruction

platelet dysfunction- Gp1b-IX deficiency (bernard Soulier
Von Willebrand
Glanzmann Thrombasthenia
Drug-induced dysfunction (aspirin, NSAIDS)

Question 22

Bernard-Soulier syndrome

Answer 22

Step I 
Adhesion - vWF:GpIb adhesion
Defects in adhesion
von Willebrand disease
Bernard-Soulier syndrome
Laboratory test: Ristocetin induced vWF:GpIb agglutination

Question 23

Pancreatic cancer –>

Answer 23

DIC often, because of releasing thromboplastin

Question 24

difference between thrombus and embolus

Answer 24

thrombus stays in place, embolus travels around (often derived from a thrombus)

Question 25

Glanzmann Thrombasthenia

Answer 25

Step II
Aggregation - fibrinogen or vWF binds to GpIIb/IIIa
Defects in aggregation
Glanzmann thrombasthenia
Laboratory test
ADP/collagen/epinephrine/arachidonic acid/thrombin agonist induced aggregation

DECREASED PLATELET FUNCTION

Question 26

Quantitative Platelet Deficiencies

Answer 26

Acute Immune (Idiopathic) Thrombocytopenic Purpura (ITP)
Childhood disease with acute onset (2 weeks post virus)
Self-limited (resolves spontaneously within 6 months)
Autoantibodies against platelet antigens (GpIIb-IIIa or Gp1b-IX)

Chronic ITP of Childhood
20% of Acute Childhood ITP will become chronic (>6 months)
Spontaneous remissions are rare

Chronic Immune (Refractory) Thrombocytopenic Purpura (ITP) of Adults (>6 months)
20 to 40 years; 3F:1M with no history of antecedent infection
Spontaneous remissions are rare
Primary or Secondary (SLE, HIV, B-cell leukemias/lymphomas)
Autoantibodies against platelet antigens (GpIIb-IIIa or Gp1b-IX)
Rx – splenectomy, immune modulators

Question 27

ASA and t-PA

Answer 27

ASA – cyclooxygenase inhibition → ↓thromboxane A2 → ↓platelet aggregation

t-PA - Thrombolysis by generating plasmin which cleaves fibrin

Question 28

Aspirin (ASA) and NSAIDs

Answer 28

potent, irreversible inhibitor of the enzyme cyclooxygenase (Tx A2 and PGs), antiplatelet effects of aspirin used in the prophylaxis and treatment of coronary thrombosis
.

Question 29

von Willebrand Disease

Answer 29

Majority vWD: Mild deficiency - no significant bleeding symptoms
Severe disease with life-threatening bleeding in less than 0.1%
Adhesion - vWF:GpIb adhesion - absent or poor ristocetin induced aggregation
Types 1 and 3 have reduced QUANTITY of circulating vWF
Type 3 also has ↓ factor VIII and severe bleeding resembles hemophilias
Type 2 vWD have QUALITATIVE defects

Testing for vWD – vWF antigen +/- ristocetin cofactor (vWF activity)

Question 30

genetic coag factor deficiencies

Answer 30

Hemophilia A  (x-linked recessive or sporadic Factor VIII deficiency)
	Hemophilia B (x-linked recessive or sporadic Factor IX deficiency “Christmas Disease”) 
	Hemophilia C (autosomal recessive/haploinsufficiency Factor XI deficiency with no bleeding in joints but have prolonged bleeding post trauma and nose bleeds) 
	All other genetic cascade factor deficiencies
		Extremely rare

Question 31

Acquired coag factor deficiencies

Answer 31

Clinical Presentations
Factors VIII and IX
Joints in 80% (ankles in kids, knees and elbows in adults) muscles (quadriceps and iliopsoas), and the gastrointestinal mucosa
Hemarthroses and joint destruction
Factor XI (bleeding tendency does not correlate with factor levels)
Bleeding worse in areas with high fibrinolytic activity - oral cavity or genitourinary tract

Question 32

Factor IX Deficiency

Answer 32

Persons with severe hemophilia have recurrent joint and muscle bleeds, which are spontaneous or follow minor trauma and cause severe acute pain and limitation of movement. The presence of blood in the joint leads to synovial hypertrophy, with a tendency to rebleed, which results in chronic synovitis, with destruction of synovium, cartilage, and bone leading to chronic pain, stiffness of the joints, and limitation of movement because of progressive severe joint damage

Carrier females usually are asymptomatic but can have bleeding (e.g., are easily bruised or have menorrhagia or excess bleeding after trauma)
A prolonged aPTT (corrects with mixed pooled plasma) with a normal PT
Rx- Factor IX concentrate

Question 33

Factor VIII Deficiency

Answer 33

4-6 x more common than IX deficiency

1 per 5,000 male births in US

Persons with severe hemophilia have recurrent joint and muscle bleeds, which are spontaneous or follow minor trauma and cause severe acute pain and limitation of movement. The presence of blood in the joint leads to synovial hypertrophy, with a tendency to rebleed, which results in chronic synovitis, with destruction of synovium, cartilage, and bone leading to chronic pain, stiffness of the joints, and limitation of movement because of progressive severe joint damage

Carrier females usually are asymptomatic but can have bleeding (e.g., are easily bruised or have menorrhagia or excess bleeding after trauma)
A prolonged aPTT (corrects with mixed pooled plasma) with a normal PT

Rx- Factor VIII concentrate

Question 34

Factor V Deficiency

Answer 34

Parahemophilia or Owren disease
Factor V is synthesized in the liver and possibly in megakaryocytes
Affects males and females with equal frequency
Possible symptoms - bleeding into the skin, GI and GU tracts
(but not petechial), excessive bruising, nosebleeds, bleeding gums,
excessive menstrual bleeding and prolonged or excessive loss of blood with surgery or trauma, hemarthrosis, intracerebral hemorrhages, pulmonary hemorrhage

Deficiency may be a congenital or acquired via anti-factor V antibodies
Can use mixing study to distinguish
Genetic deficient plasma + normal plasma – correction of PT and PTT
Only 150 cases of congenital factor V deficiency have been reported worldwide since 1943
Acquired antibody + normal plasma → factor V/Ab complexes with no or only partial correction of PTT and PT

Rx – FFP to increase Factor V levels to 25% of normal if patient is significantly bleeding or for surgery
Contraceptives to control menstrual bleeding

Question 35

Acquired coag factor deficiencies

Answer 35

Vitamin K deficiency -essential factor to a hepatic gamma-glutamyl carboxylase that adds a carboxyl group to glutamic acid residues on factors II, VII, IX and X, as well as Proteins S, C and Z

Anticoagulation

- Unfractionated Heparin: antithrombin III activation
- LMW heparin: antithrombin III activation only against factor Xa
 - Warfarin (Coumadin): Vitamin K dependent factor deficiency

“Washout”: Depletion factors by massive blood loss

Hepatic Failure: ↓synthesis of factors (except VIII and vWF)

Disseminated Intravascular Coagulation (DIC)

Question 36

Specifics of Bleeding Disorders in Liver Failure

Answer 36

Liver synthesis of Factors: I, II, V, VII, VIII, X, IX, XI and XII
Factor VII has the shortest half time
Factor VIII also made by endothelium
vWF is made by the endothelium, platelets and megakaryocytes
With liver disease often have concomitant vitamin K deficiency
Abnormal platelet function due to storage pool (granule) defects, ↓TXA2, ↓ surface receptor function, etc.
Platelets decreased due to bone marrow suppression, hypersplenism and decreased thrombopoetin

Question 37

Disseminated Intravascular Coagulation (DIC)

Answer 37

All the clotting steps are occurring simultaneously continuously EVERYWHERE!

Microthrombi 5-25 micron formed but NOT attached to vessel walls
diffusely narrow or obstruct pre-capillary arterioles and capillaries
Consumptive coagulopathy with bleeding

Question 38

Additional Risk Factors for DVT

Answer 38

Factor V Leiden 
Prothrombin G20210A gene mutation 
Deficiencies in protein S, protein C, and anti-thrombin 
Test those with 
DVT at age less than 50 years 
Thrombosis at unusual sites 
Recurrent thromboses 
Strong family history of thrombotic disease

Question 39

Causes of Arterial Thrombosis

Answer 39

Thromboembolism

• From left heart (vegetations, mural thrombi)
• Paradoxical venous embolism through interventricular heart defect

Vascular defects (e.g. aneurysm, atherosclerotic plaque, anatomic variation)

Vasculitis

Sickle cell anemia

Coagulopathies

• Antiphospholipid antibodies (Lupus anticoagulant, anti-cardiolipin)
• Heparin induced thrombocytosis
• Protein S deficiency
• Hyperhomocysteinemia
• High lipoprotein(a)
• Prothrombin G20210A mutation
• Malignancy associated hypercoagulable state
• Thrombocytosis (polycythemia, etc.)

Question 40

Hypercoagulability Syndromes

Answer 40

Factor V Leiden mutations in Factor V
Prothrombin G20210 A mutation
Heparin-Induced Thrombocytopenia Sindrome (HIT), type 2
Antiphospholipid autoantibodies

Question 41

Factor V Leiden mutations in Factor V

Answer 41

• “Activated Protein C Resistance”
  Mutant V converts to Va and is fully functional in its coagulant role
  Mutant has decreased affinity to Activated Protein C and is not deactivated

The most common genetic cause of primary and recurrent venous thromboembolism in the pregnant and non-pregnant woman
autosomal dominant
50- to 100-fold increased risk of thrombosis in homozygotes

Question 42

Prothrombin G20210 A mutation

Answer 42

Causes increased prothrombin levels which are converted to working thrombin

Question 43

Heparin-Induced Thrombocytopenia Syndrome (HIT), type II

Answer 43

Unfractionated (and occasionally low molecular weight) heparin induces autoantibodies to a molecular complex with Platelet Factor 4
1-5% of patients with repeated use of heparin
Patients have thrombocytopenia and disseminated clots
Autoantibody-heparin-platelet complexes activate platelets and cause endothelial injury, causing a prothrombotic state

Question 44

Antiphospholipid autoantibodies

Answer 44

Affinity for bound phospholipids on the platelet surface that are combined with coagulation factors. Antiphospholipid antibodies detected clinically
Lupus anticoagulant detected during aPTT testing
False positive VDRL (syphillis) test (anticardiolipin autoantibody)
Recurrent venous or arterial thrombosis and/or fetal loss