Haemostasis & Thrombosis

Hemostasis

the process by which blood clots form at the site of vascular injury

4 steps of response to vessel injury

1. Vasoconstriction to reduce blood flow

2. Platelet plug formation (von Willebrand factor binds damaged vessel and platelets)

3. Activation of clotting cascade with generation of fibrin clot formation

4. Fibrinolysis (clot breakdown)

Roel of endothelin at site of injury

Causes Vasoconstriction & stops release of Nitric Oxide and prostacyclin

What triggers primary haemostasis

Disruption of the endothelium exposing collagen and von Willebrand factor (vWF)

How do platelets form a platelet plug

Platelets adhere via vWF

Platelets activate and change shape

Granule release recruits additional platelets

Aggregation forms the platelet plug

What initiates secondary haemostasis in vivo

Exposure of Tissue Factor (TF) from vascular injury

4 steps of secondary haemostasis

Tissue factor exposed → activates Factor VII → thrombin generation → fibrin mesh & platelet plug form

Differentiate between activating the extrinsic & intrinsic pathways of coagulation

Intrinsic - negative charged substance such as glass beads

Extrinsic - source of tissue factor (main one in vivo)

What factors are involved in intrinsic vs extrinsic clotting cascades

Role of t-Pa

tissue plasminogen activator is a counterregulatory mechanism made by endothelial cells that limit clotting to the site of injury and eventually lead to clot resorption & tissue repair

What enzyme is responsible for fibrinolysis

Plasmin

Plasmin is generated by enzymatic catabolism of the inactive circulating precursor …

plasminogen

most important plasminogen activator

t-PA

t-PA; it is synthesized principally by endothelium and is most active when in what state

bound to fibrin

What about the way it works makes t-PA a useful therapeutic agent

its fibrinolytic activity is largely confined to sites of recent thrombosis

What prevents platelet aggregation & coagulation & promotes fibrinolysis in endothelium with no injury

anticoagulant factors

Endothelium is activated by what

trauma, sepsis, bacteria, cancer, cytokines, …

Role of thrombin

Generates cross-linked fibrin (cleaves fibrinogen & activates factor XIII)

Activates several other coagulation factors

Modulates several cellular activities

Directly induces platelet aggregation

Directly induces TxA2 production

Activates endothelial cells

Directly activates leukocytes

Through what receptors does thrombin modulate cellular activities

Through protease-activated receptors (PARs)

When endothelial cells are activated by thrombin, they release what

They respond by expressing adhesion molecules and cytokine mediators (e.g., PDGF ).

True/False platelets are anucleate

True

What type of receptor do platelets have

Glycoprotein receptor

True/False platelet cytoskeleton is rigid

False - it’s contractile

What is contained within platelet α granules

selectin, fibrinogen, vWF, Factor V, PF4, PDGF

What is contained within platelet δ granules

ADP, ATP calcium, serotonin, adrenaline

Main role of platelets

Platelets provide surface that binds and concentrates coagulation factors

What do platelets do when an endothelial injury exposes the underlying basement membrane ECM

platelets adhere to the ECM primarily through the binding of platelet GpIb receptors to VWF

We know that platelets adhere to the ECM in endothelial injury but what could cause them not to do this (2)

Von Willebrand Disease

Bernard Soulier

Adhesion of platelets to the ECM leads to platelet activation → secretion of platelet granule contents. Give 2 examples of what is secreted

Calcium

ADP

What could prevent the release of platelet granule contents such as calcium & ADP

Storage Pool Disorders

Function of calcium in coagulation

cofactor for several coagulation proteins

Function of ADP in coagulation

mediator of further platelet activation

Activation of platelets from adhesion to ECM leads to what structural changes

dramatic changes in shape and membrane composition

Activation of platelets from adhesion to ECM leads to activation of what receptors

activation of GpIIb/IIIa receptors

What happens once GpIIb/IIIa receptors are activated on platelets

They form bridging cross-links with fibrinogen, leading to platelet aggregation

What could interfere with the formation of cross-links with fibrinogen from GpIIb/IIIa receptor activation

Glanzmanns Thrombasthenia

Fibrin deposition cements the platelet plug in place. What promotes fibrin deposition

Activation of thrombin via Protease Activated Receptor (PAR1) promotes fibrin deposition

Name the 3 disorders that can affect platelets in coagulation

Bleeding disorders are generally due to a defect in 3 things. Name the 3 things & their accompanying disorders

Vessel wall: Ruptured aorta/aortic dissection - Ehlers Danlos syndrome

Platelets: Glanzmanns thromasthenia

Coagulation factors: Haemophilia

True/False Bleeding disorders are all inherited

False - inherited/Acquired

Name a Collagen vascular disorder that affects haemostasis

Ehlers Danlos syndrome

Name a disorder that leads to inflammation of blood vessels that affects haemostasis

Vasculitis “palpable purpura”

Name a disorder that can make Blood vessels fragile & affects Haemostasis

Amyloidosis

Primary Haemostasis

How do patients present? (what’s the hallmark sign among the signs)

Hallmark is Mucocutaneous bleeding

– Purpura

– Epistaxis

– Menorrhagia

– Post partum Haemorrage

– GI bleed

– Bleeding post dental extraction

– Post operative bleeding

– Iron deficiency anaemia

Name 3 inherited Disorders of Primary Haemostasis

– Bernard Soulier Gp1b IX

– Glanzmann Thromasthenia GP IIb/IIIa

– Storage pool disorder

Most common inherited bleeding disorder

Deficiency of VWF

Name 3 acquired Disorders of Primary Haemostasis

– Uraemia/renal Failure

– ASPIRIN inhibits cyclooxygenase

– Clopidogrel/Prasugrel/ P2Y12

True/False VWD is a disorder of secondary haemostasis

False - It’s a disorder of Primary Haemostasis

VWF roles (2)

Von Willebrand factor VWF is involved in primary haemostasis and also protects factor VIII from destruction.

True/False Muscle or joint bleeds are rare in VWD

True - only found in severe forms (due to reduction of Factor VIII)

VWD treatment (3 options)

Tranexamic acid

DDAVP

Von Willebrand concentrate

3 steps to a Von Willebrand Disease Diagnosis

1. Personal history of muco-cutaneous bleeding

2. Family history of muco-cutaneous bleeding

3. Laboratory studies consistent with VWD

Differentiate between the 3 different types of VWD

Type 1 VWD: Quantitative Reduction in VWF

Type 2 VWD: Qualitative mutants of VWF

Type 3 VWD: Absence /Severe Reduction in VWF

By what inheritance pattern is VWD inherited

Autosomal Dominant

True/False Defects in platelet function lead to severe bleeding

False - Bleeding usually mild outside of surgery or

dental extractions

How are Platelet function defects diagnosed

– Assess platelet function in Laboratory

– Measure glycoprotein on surface of cells

Platelet function defects treatment options (4)

Tranexamic acid (antifibrinolytic)

DDAVP

Platelet transfusion

Activated Factor VIIa

Name 2 Disorders of secondary haemostasis

B. Coagulation abnormalities

Haemophilia

What causes haemophilia

Factor VIII and IX deficiency.

Disorders of secondary haemostasis also include bleeding disorders from Fibrinogen (Factor I) Factor II, Factor V, Factor VII, Factor X, Factor XI and Factor XIII deficiency. Are these common/rare

Rare

Symptoms of Fibrinogen (Factor I) Factor II, Factor V, Factor VII, Factor X, Factor XI and Factor XIII deficiency

• Muscle bleeding

• Intracerebral Bleeding

• GI Bleeding

• Dental bleeding

• Bleeding at time of surgery

• Joint bleeding

By what pattern are Haemophilia A & B inherited

X linked

Haemophilia A is a deficiency in what factor

Factor VIII

Haemophilia B is a deficiency in what factor

Factor IX

Haemophilia __ is approx. 5x more common than haemophilia _

Haemophilia A is approximately five times more common than haemophilia B

How to differentiate between Haem A/B

Blood test only

Due to its inheritance pattern, severe haemophilia affects only males/females

Males

Method of administration for treatment of bleeds

Treatment given IV through vein or port

Haemophilia treatment (for prevention of bleeds) (& method of administration)

Gene therapy

Mimetic products (Haemlibra, aka Emicizumab)

Subcutaneous administration

Emicizumab brings baseline clotting factors up to what % by mimicking what factor

15%

Mimics Factor VIII

A father has Haemophilia. Will his son/daughter be affected

Daughter will be a carrier

Son will not be affected (as it is X linked and Dad will pass on Y to son)

A mother has Haemophilia. Will her son/daughter be affected

Daughter has 50:50 chance being a carrier

Son has 50:50 chance of having haemophilia

What % of haemophilia patients have no known family history of haemophilia

30%

Explain how the PT Coagulation Screening Test is carried out & what it assesses & what the normal range is

Prothrombin Time (PT)

Process: Tissue Factor TF, calcium & phospholipid added to plasma and measure time to clot

Assesses: Factor VII in Extrinsic Pathway, & I, II, V, X in Common Pathway

Normal Range: 10-13 seconds

What standardised test is the PT value used in

INR - used to monitor anticoagulant effect of Warfarin

Explain how the APTT Coagulation Screening Test is carried out & what it assesses & what the normal range is

Method: Initiated by negatively charged particles (ground glass/silica) to activate Factor XII in presence of Phospholipid and Calcium. Measure time taken for clot to form.

Assess: Intrinsic Pathway Factors XII, XI, IX and VIII & may also be used to assess Common Pathway Factor II, V, X and Fibrinogen (Factor I)

Normal Range: 20-30 seconds

What would cause an Isolated Prolonged PT

Factor VII deficiency

What would cause a prolonged APTT (4)

• Factor VIII deficiency

• Factor IX deficiency

• Factor XI deficiency

• Factor XII deficiency

What would cause a Prolonged PT & APTT (4)

• Factor I (Fibrinogen) deficiency

• Factor II (prothrombin) deficiency

• Factor V deficiency

• Factor X deficiency

True/ False: A Normal Coagulation Screening can bee seen in all 3 of these diseases

• von Willebrand’s Disease

• Platelet Disorders

• Factor XIII deficiency

True

Outcome of severe factor II deficiency

Severe factor II deficiency (prothrombin) is incompatible with life

Treatment required for people with Severe Fibrinogen (Factor I), X, XIII deficiency

It is present as a neonate & replacement is required from diagnosis

Outcome of Severe V and VII deficiency

variable bleeding

Outcome of severe Factor XI deficiency

Severity of deficiency doesn’t matter - level does NOT correlate with bleeding risk

Outcome of Severe XII deficiency

No bleeding & may contribute to thrombosis

Thrombosis

Blood clot that forms within intact blood vessel or in chambers of the heart

Embolism

detached intravascular solid, liquid or gaseous mass that is carried by blood from its point of origin to a distant site where it often causes tissue dysfunction or infarction

What type of embolism is most common

Pulmonary Embolism is most common

Symptoms and signs of a Pulmonary Embolism

Dyspnoea on exertion

Haemoptysis

Chest pain

Tachypnoea

Hypotension

Tachycardia

Leg symptoms or signs

Collapse

Sudden death

What % patients with DVT also have PE

50%

What % of PE originate in leg veins as a Deep Vein Thrombosis (DVT) (hence term Venous Thromboembolism VTE)

95%

Pulmonary Embolism treatment

anticoagulation

Fill in Virchow’s triad for the causes of thrombosis

Give 2 examples of Endothelial Injury

Plaque rupture in atherosclerosis

Endothelial injury post MI

Give 5 possible causes of Endothelial Injury

It doesn’t need to be physically disrupted

– Increased procoagulant factors

– Decreased anticoagulant factors

– Turbulent flow

– Bacterial endotoxin

– Cigarette smoke

Name 3 causes of Alterations to blood flow

– MI stasis due to reduced contractility

– Aneurysm local stasis

– Atrial fibrillation

Hypercoagulability Definition

• Acquired or inherited abnormality of haemostasis predisposing to thrombosis

Or

• Haemostasis in the wrong place at the wrong time

Venous Thromboembolic Disease includes what 2 things

Deep Venous Thrombosis and Pulmonary Embolism