Thrombosis, Embolism, and Infarction Flashcards
What is a thrombus ?
A solidification of blood contents that forms within the vascular system during life
Is thrombosis a pathological or physiological process ?
Pathological
What is Virchow’s Triad ?
The three components which contribute to thrombosis.
- Endothelial Injury
- Abnormal blood flow
- Hypercoagulability
Endothelial injury is important in the formation of thrombi where ?
In arteries and the heart
What are examples of endothelial injuries which can lead to thrombosis ?
- Ulcerated plaques in advanced atherosclerosis
- Injured endocardium during cardiac surgery or in myocarditis
- Myocardial infection in left ventricle
- Valves with inflammatory valve disease, and prosthetic valves
What are potential bases for endothelial injury ?
- Radiation injury
- Chemical agents: exogenous (e.g. cigarette smoking) and endogenous (e.g. high cholesterol in blood)
- Bacterial toxins or endotoxins
- Immunologic injuries
- Neoplastic involvement
What is the role of platelets in thrombosis ?
After injury to a vessel, platelets undergo platelet activation, which is the sum of three important reactions:
1) Adhesion
2) Secretion (release reaction)
3) Aggregation
Describe the sequence of events following endothelial injury.
- Vasoconstriction due to release of endothelin
- Primary Hemostasis: Platelets adhere to exposed collagen, platelets change shape (brick-like), platelets release granules, granules recruit more platelets, platelets aggregate (cycle repeats)
- Secondary Hemostasis: Tissue factor released by endothelial cells, phospholipid complex is expressed, thombin is activated, fibrin is polymerised (from fibrinogen, thanks to thrombin)
- Thrombus and Antithrombotic Events: Release of t-PA (for fibrinolysis) and thrombomodulin (blocks coagulation cascade) from endothelial cells.
What are the names of some of the granules released from the platelets ?
ADP
Thomboxane A2 (TXA2)
Platelet Factor 4 (Pf4)
What factors must be present for the platelets to be able to adhere to collagen ?
Von Willebrand’s factor and Gplb (Glycoprotein lb) complex
What are examples of alterations in normal blood flow ?
Turbulence
Stasis
Which kind of thrombi is each of turbulence and stasis responsible for ?
Turbulence- contributes to the development of arterial and cardiac thrombi
Stasis- contributes to the development of venous thrombi
How does alteration of normal blood flow lead to thrombosis ?
Disrupt laminar flow –> Prevent the dilution of coagulation factors –> Retard the inflow of inhibitors of clotting factors –> Promote endothelial cell activation
What are the main features of primary hypercoagulability ?
- Genetic
- Mutation in the factor V gene = Leiden mutation »
- Results in Antithrombin III, Protein C and S deficiency
What are the main features of secondary hypercoagulability ?
- Acquired
- High Risk factors include bed rest (immobilisation). Myocardial Infarction, Tissue damage, CA, prosthetic valves, DIC (Disseminated intravascular coagulation )
- Lower risk factors include Atrial Fibrillation, cardiomyopathy, nephrotic syndrome, oral contraceptive, sickle cell anaemia, smoking
What are the main kinds of thrombi, morphology-wise ?
- Mural thrombi
- Arterial thrombi
- Venous thrombosis (phlebothrombosis)
What is a mural thrombus ? Where does it occur ?
- Thrombus applied to one wall of underlying structure
- Occurs in the capacious lumina of the heart chambers and aorta
What are the main features of arterial thrombi ?
Where do they frequently occur ?
- Usually occlusive
- May be mural
- Grey-white and friable
- By decreasing frequency, Coronary, Cerebral, and Femoral
What are the main histological features of thrombi ?
Lines of Zahn (‘alternating pale pink bands of platelets with fibrin and red bands of RBC’)
What are the main features of arterial thrombi ?
Where do they frequently occur ?
- Invariably occlusive
- Dark red
-Mainly affect the veins of the lower extremities (90%), including deep calf, femoral, popliteal, iliac veins
What is Thrombophlebitis ?
“Inflammatory process that causes a blood clot to form and block one or more veins”
What are the possible fates of the thrombus ?
- Resolution
- Embolisation to lungs
- Organised and incorporated into wall
- Organised and recanalised (channels through thrombus)
What are clinical correlations of arterial thrombi ?
- Loss of Pulses distal to the thrombus
- Area becomes cold, pale, painful, paraesthesia
- Eventually tissue dies + gangrene results
What are clinical correlations of veinous thrombi (superficial and deep) ?
SUPERFICIAL:
• Congestion, swelling, pain, tenderness (
• Rarely embolise
DEEP:
• Foot and ankle oedema
• Homans’ sign (=”discomfort behind the knee on forced dorsiflexion of the foot”)
• Possibly asymptomatic and only recognised when embolised
What is possible treatment for thrombosis ?
- Stockings (prevention)
- Anticoagulant drugs: aim to prevent clot growing larger + prevent or stop an embolism. Two main forms of anticoagulant drugs: heparin and warfarin
How are heparin and warfarin administered respectively ?
Heparin: IV or SC
Warfarin: Orally