S5 Thrombosis and Embolism

Question 1

What is thrombosis?

Answer 1

Formation of a solid mass of blood within the circulatory system. The solid mass is called a thrombus.

Question 2

What is a clot?

Answer 2

A mass of blood outside the vessel wall

Question 3

What is Virchow’s triad?

Answer 3

1. Vessel wall (damage)
2. Blood flow (stasis)
3. Blood components (hypercoagulable)

Explains how a thrombus forms

Question 4

What are some examples of vessel wall/endothelial wall damage?

Answer 4

• atheroma
• direct injury
• inflammation

Question 5

What are some problems with blood flow?

Answer 5

• stasis - slow blood flow (e.g. chronic hypotension)

* turbulent blood flow (e.g. valves or atheroma)

Question 6

Is thrombosis more common in veins or arteries?

Answer 6

Veins as blood flow is slower and veins also have valves that can cause turbulent flow

Question 7

What are some problems with blood components?

Answer 7

• hypercoagulable states (increased levels of fibrinogen and factor VIII)

Question 8

Which groups of people usually have hypercoagulable blood?

Answer 8

• smokers
• pregnant women or post-partum women
• post-operative patients
• cancer patients
• trauma and burns patients

Question 9

What does an arterial thrombus look like?

Answer 9

• pale
• granular
• lines of Zahn
• lower cell content

Question 10

Why do lines of Zahn form?

Answer 10

In high flow areas, RBCs, platelets and fibrin become layered

Question 11

What does a venous thrombus look like?

Answer 11

• soft
• gelatinous
• deep red
• higher cell content

Question 12

How does a thrombus get broken down?

Answer 12

By fibrinolysis

Question 13

When does lysis of a thrombus occur? What does it result in?

Answer 13

• when thrombi are small
• fibrinolytic system is activated
• complete dissolution of thrombus
• blood flow is re-established

Question 14

What is propagation of thrombi?

Answer 14

The progressive spread of thrombosis

Spread distally in arteries and proximally in veins - in respect to heart

Question 15

What is organisation of thrombi?

Answer 15

• a repair process
• leads to growth of fibroblasts and capillaries (like granulation tissue)
• the lumen remains obstructed
• this is not ideal

Question 16

What is recanalisation?

Answer 16

Blood flow is re-established but not completely

One or more channels are formed through an organising thrombus

Question 17

What is an thromboembolism?

Answer 17

When part of a thrombus breaks off, travels through the bloodstream and lodges at a distant site

Question 18

What are the effects of thrombosis on the tissue if it is a venous thrombi?

Answer 18

• oedema
• ischaemia
• infarction

Question 19

What is a common thrombi?

Answer 19

DVT - deep vein thrombosis

Question 20

Where can thrombi form in veins (other than DVT)?

Answer 20

• sinus thrombosis (in brain)
• thrombosis in subclavian vein
• thrombosis in hepatic vein
• uteroplacental thrombosis in pregnancy (can lead to miscarriage)

Question 21

What are the effects of thrombosis on the tissue if it is a arterial thrombi?

Answer 21

• ischaemia

* infarction

Question 22

Where can thrombi form in arterial system?

Answer 22

• cerebral artery - leads to ischaemic stroke
• carotid artery - ischaemic stroke
• coronary artery - MI
• mesenteric artery - bowel ischameia
• renal artery
• femoral/iliac/popliteal arteries - acute ischaemic limb

Question 23

What is an embolism?

Answer 23

An embolism is the blockage of a blood vessel by a solid, liquid or gas at a site distant from it’s origin

Most common is thromboemboli

Question 24

What is a pulmonary thromboemboli?

Answer 24

When an emboli passes from the systemic veins to the lungs

Question 25

Where would a thrombus in the heart pass to via the arteries?

Answer 25

Passes via the aorta and lodges in the renal, mesenteric, etc arteries Results in bowel ischaemia, renal infarction, etc

Question 26

Where would an emboli go from an atheromatous carotid artery to?

Answer 26

To the brain leading to ischaemia stroke

Question 27

Where would an emboli go from an atheromatous abdominal aorta to?

Answer 27

To arteries of the legs leading to acute limb ischaemia

Question 28

What are some predisposing factors for a DVT?

Answer 28

* immobility/bed rest * post-operative * pregnancy/post-partum * oral contraceptives * severe burns * cardiac failure * disseminated cancer

Question 29

Pulmonary thromboembolism of different sizes/locations have different effects. What would be the effect of a massive coiled embolus in the main pulmonary artery? Of a small embolus lodged in a peripheral pulmonary artery? And multiple repeated small emboli?

Answer 29

* sudden death * pulmonary infarct * pulmonary hypertension

Question 30

What does a massive pulmonary embolism cause?

Answer 30

60% reduction of blood flow - rapidly fatal Especially if a saddle emboli

Question 31

What is a saddle emboli?

Answer 31

An embolus that sits either side of the of the pulmonary arteries (at the bifurcation)

Question 32

What does a major pulmonary embolism result in?

Answer 32

Blocks medium sized vessels Patient will have shortness of breath with/without a cough and blood stained sputum

Question 33

What does a minor pulmonary embolism result in?

Answer 33

Small peripheral pulmonary arteries are blocked This is asymptomatic or patient may have minor shortness of breath

Question 34

What do recurrent minor pulmonary embolisms lead to?

Answer 34

Lead to pulmonary hypertension

Question 35

What does a thromboembolism to the foot result in?

Answer 35

Ischaemia - gangrene

Question 36

What does a thromboembolism from the carotid artery result in?

Answer 36

Ischaemic stroke

Question 37

What are other types of embolism?

Answer 37

* air * amniotic fluid * nitrogen * medical equipment (e.g. silicon or drugs (talcum emboli)) * tumour cells * fat, bone marrow (post trauma)

Question 38

What is an iatrogenic emboli?

Answer 38

A emboli caused by medical treatment/examination

Question 39

What are the prophylaxis of DVT/PE?

Answer 39

* identify high risk patients * give low molecular weight heparin subcutaneously (advantage as it is fast acting) * mobilise early * leg compressions during surgery e.g. stockings/flowtron boots

Question 40

How can thrombus (and/or thromboemboli) be treated?

Answer 40

* clot busters - streptokinase, alteplase (recombinant tPA) * IV heparin type drugs * Novak oral anticoagulants (rivaroxaban, apixaban, edoxaban - antifactor Xa and dabigatran) * filters in inferior vena cava/devices in left atria to stop thrombus formation * embolectomy * oral warfarin

Question 41

What does dabigatran inhibit?

Answer 41

Inhibits thrombin

Question 42

What does heparin inhibit?

Answer 42

Inhibits factor V

Question 43

What does warfarin inhibit?

Answer 43

Factors II, VII, IX, X and protein C and S

Question 44

What do natural anticoagulants inhibit?

Answer 44

Thrombin formation

Question 45

What is a paradoxical emboli?

Answer 45

Very rare Thromboemboli that form in systemic veins but embolism in systemic arteries (small emboli pass through arterio-venous anastomoses in pulmonary circulation or larger emboli enter systemic circulation by passing through defects in interventricular septum/patent foramen ovale during coughing, lifting or straining (increase pressure in right side of heart))

Question 46

How can aspirin be used to treat thromboembolic disease?

Answer 46

It is antithrombogenic Irreversibly acetylates cyclooxygenase - means platelets can’t produce thromboxane A2 (platelet aggregator)