Primary and Secondary haemostasis. Bleeding disorders including haemophilia A&B and VWD

2. • Haemostasis is the normal physiological response to
prevent significant blood loss following vascular injury
• Cellular and molecular mechanisms interact to seal
damaged blood vessels with localized clot formation to
prevent excessive blood loss
• Haemostasis consists of
-Primary haemostasis with vascular contraction and
platelet formation.
-Clotting of the plasma (secondary haemostasis)-
Involving interaction between numerous factors and
inhibitors
-Fibrinolysis- Process for removing the clot once blood
vessel’s integrity has been restored.

3. • Under normal circumstances blood
components pass unhindered through
the circulatory system
• The vascular barrier provides a non-
thrombotic surface due to the
production of platelet inhibitors
• In contrast, the subendothelial layer is
highly thrombogenic- contains collagen,
von Willebrand factor (VWF) and other
proteins that are involved in platelet
adhesion
• When the vascular endothelium is
disrupted, VWF is released, collagen is
exposed and tissue factor (TF) is
expressed on the surface of endothelial
cells.
• The vascular endothelium switches to a
prothrombotic state and 1° and 2°
haemostasis ensues.

4. • Plays a pivotal role in
primary haemostasis
• Alongside the vessel
wall and adhesive
proteins, forms the
initial ‘platelet plug’
• Activated platelets
express phospholipids
which promote localised
coagulation and the
generation of thrombin
and fibrin

5. • Ligand engagement of G1b/V/IX
by VWF/collagen in damaged
blood vessels activate platelets
• Activated plates changes from
discoid (2um) to irregular shape
with pseudopods, releasing its
granular content (FV, FVIII, Ca, 5-
HT, fibrinogen, ADP and
thromboxane).
• Platelet activation triggers
conformational changes in
GPIIb/IIIa from inactive state to
active state
• Fibrinogen and VWF function as
bridges between GPIIb/IIIa on
neighbouring activated platelets
• Activated platelets provide a
phospholipid domain, which
becomes a catalytic centre for
secondary haemostasis.

6. • Platelet’s integrin membrane glycoprotein IIb/IIIa increases its affinity to bind
fibrinogen.
• Fibrinogen crosslinks with glycoprotein IIa/IIIa supporting the aggregation of
adjacent platelets.

8. • Results in the conversion of thrombin to fibrin,
strengthening the aggregated platelets (2°haemostasis)
• Damaged blood vessels expressing Tissue Factor [TF]
activates coagulation
• TF binds to circulating VIIa, forming the ‘Extrinsic tenase’
• In the presence of factor V, converts factor IX IXa and
factor XXa
• FXa then binds to prothrombin and generates a small
amount of fibrin.
• Thrombin generation through this reaction is not robust
and can be effectively terminated by TF pathway inhibitor

9. • Since the amount of
thrombin is insufficient
to convert fibrinogen
to fibrin, numerous
positive feedback
loops exists
• Thrombin generated
in the initiation phase
further activates FV
and VIII, which serves
as cofactors in its
propagation

10. • Continuous thrombin
generation is ensured
by the action of two
complexes: FVIIIa
complexed to FIXa
(intrinsic tenase), and
FVa to Xa
(prothrombinase).
• This occurs on the
surface of platelets and
leads to the appropriate
localization formation of
greater amounts of
thrombin.

11. The thrombin generated results in the formation of fibrin and activation of factor XIII (fibrin stabilizing
factor).
FXIII covalent links soluble fibrin monomers to form a stable polymer and provides strength and
stability to the fibrin incorporated into the platelet plug.

12. • Coagulation is regulated
and localized by several
anticoagulant
mechanisms.
• Most important includes
anti-thrombin, which
inhibits thrombin, and
factors IXa, Xa, XIa and
XIIa.
• Others include TF
Pathway inhibitor which
inhibits the TF-VIIa
complex and thrombin
• Activated Protein C, which
binds to thrombomodulin
and cleaves FVa and
FVIIIa.

13. • Fibrinolysis is activated at
the same time that the
coagulation system but
operates more slowly and is
important for the regulation
of haemostasis.
• In the presence of fibrin,
tissue plasminogen activator
(tPA) cleaves plasminogen,
producing plasmin which
proteolyzes fibrin.
• Result in the protein
fragment D-dimer, a fibrin
degradation product which is
a useful marker of
fibrinolysis.

14. Haemophilia A and B
• Haemphilia A and B and the two most common forms of
severe inherited bleeding disease.
• Both conditions are X-linked recessive
• Majority affected individuals are males
• 20% of female carriers of haemophilia can also express a
mild bleeding tendency (variation pattern of X
inactivation)
• Diagnosis made through a combination of clinical and
laboratory features.
• ~60% of cases will have a family history of the condition

15. Haemophilia A and B
• Clinical manifestations are very similar for factor VIII
deficiency (haemophilia A), and factor IX deficiency
(haemophilia B)
• Severe disease (factor levels <1%) results in frequent
episodes of spontaneous musculoskeletal bleeding
• Moderate severe disease (factor levels 1-5%) usually do
not manifest spontaneous bleeding
• Mild haemophilia (factor levels 5-40%) only bleed on
provocation
• Current treatment involves various forms of protein
replacement therapy

16. Haemophilia A and B
• Schematic showing the intrinsic and extrinsic pathways of the
coagulation cascade leading to fibrin formation. A deficiency or
dysfunction of coagulation factorVIII orfactorIXcompromises the
activation of factorX, the ensuing reactions are inefficient and
haemophilia results.

17. Von Willebrands Disease
• Most common inherited bleeding disorder of humans
• Prevalence symptomatic subjects of ~1 in 1000
• Females outnumber males by 2:1 presumably due to
manifesting excessive mucocutaneous bleeding at the
time on menses and childbirth
• 3 types- Type 1 disease is a quantitative deficiency of
functionally normal VWF (~65% of VWD cases)
Type 2 VWD represents a group of qualitative
VWF variants (types 2A, 2B, 2M and 2N)
comprising approximately 30% of VWD
Type 3 VWD is the virtual absence of VWF
(~1 in 1 million of the population )

18. Von Willebrands Disease

19. Diagnosis of VWD
• Diagnosis requires consideration of 3 components-
personal history of excessive mucocutaneous bleeding,
lab. test consistent with VWD, and a family history of
VWD.
• Many cases of Type 1 and some type 2 cases can be
treated with desmopressin
• Remaining cases require transfusion with plasma
deprived VWF-FVIII concentrates.

20. Treatment of VWDdisease

21. Haemostasis in LiverImpairment
• Liver is involved in the synthesis of most clotting factor proteins
• In liver impairment, clotting factor proteins are reduced with the
exception of FVIII.
• Decreased capacity to clear activated clotting factor-inhibitor
complexes.
• Liver failure also result in reduced platelet count and function.
• These defects are counterbalanced by a concomitant defect in
anticoagulant and pro-fibrinolytic factors.
• Decreased in platelet function is counterbalanced by elevated levels
of Von Willebrand factor.
• This rebalance is represented by limited bleeding during surgery.
• Coagulopathy in patients with critical liver dysfunction is complex
and quickly decompensate to bleeding as well and thrombosis.