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Thrombosis and Embolism Flashcards

1
Q

Define ‘Thombosis’

A

A solid mass formed of the constituents of blood within the heart or blood vessels during life

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2
Q

When would a thrombus be a clot?

A

Outside of life i.e. in a test tube or in death

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3
Q

What three things in Virchow’s triad are said to contribute to thrombus formation?

A
  • Changes in vascular wall (endothelial changes)
  • Changes in blood flow (slow or turbulent flow)
  • Changes in blood (hyper coagulability)
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4
Q

What things may cause abnormalities in the vessel walls?

A
  • atheroma
  • direct injury
  • inflammation
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5
Q

When would someone have increased coagulability of their blood?

A
  • smokers
  • post partum
  • post operatively
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6
Q

When do arterial and cardiac thrombi usually occur?

A

At the site of injury following endothelial injury or where there is turbulent flow

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7
Q

When do venous thrombi often occur?

A

In areas of blood stasis

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8
Q

Describe the appearance of arterial thrombi

A
  • pale
  • granular
  • lines of Zahn
  • lower cell content
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9
Q

Why is blood hyper coagulable in pregnancy?

A
  • There is stasis of blood due to increased pressure on the large veins of the pelvis by the gravid uterus
  • There are also increased circulating levels of fibrinogen and factor VIII
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10
Q

What are lines of Zahn?

A

They are layers of alternating:

  • fibrin and platelets (white layers)
  • red blood cells (dark layers)
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11
Q

Describe the appearance of venous thrombi

A
  • soft
  • gelatinous
  • high cell content
  • deep red (no well marked lines of Zahn)
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12
Q

What situations can cause endothelial damage?

A
  • Myocardial infarction
  • secondary to haemodynamic stress
  • after trauma or surgery
  • inflammation
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13
Q

How does stasis cause thrombosis?

A

Slower blood flow gives platelets a better chance of sticking to endothelium and clotting factors have better chances to accumulate

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14
Q

How can turbulent flow lead to thrombosis?

A

It can cause direct endothelial damage

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15
Q

How does smoking make blood hyper coagulable?

A

Activates Hagemen factor (factor VIII)

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16
Q

Describe the steps of thrombus formation

A

1) Platelets are concentrated along the endothelium and can catch in eddy’s behind valves or settle on the wall of the vessel if there is injury or slow blood flow
2) Platelets aggregate to the area
3) Fibrinogen binds platelets together and fibrin traps red blood cells
4) more platelets stick to exposed fibrin and the process continues

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17
Q

What is thrombophlebitis?

A

Pain from thrombi in superficial veins

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18
Q

What is the difference between parietal and occlusive thrombi?

A

Parietal thrombi- attach to the of the vessel, restricting the lumen

Occlusive thrombi- fill and obstruct the lumen

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19
Q

What is a vegetation?

A

A thrombus that forms in a cardiac valve (usually form on the LHS of the heart due to greater pressures which cause micro thrombi)

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20
Q

State some of the outcomes of thrombosis

A

1) Resolution
2) Propogation
3) Organisation
4) Recanalisation
5) Embolisation

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21
Q

What is complete resolution?

A
  • Lysis of the the thrombus
  • blood flow is re-established
  • more likely when thrombi are small
22
Q

What is thrombus propagation?

A

The progressive growth and spread of thrombosis

  • distally in arteries
  • proximally in veins
23
Q

What is thrombus organisation?

A

A repairing process where fibroblasts and capillaries grow inwards to form a fibrous scar on the wall of the vessel (lumen remains obstructed)

24
Q

What is thrombus recanalisation?

A

If the thrombus occludes a vessel blood flow can be re-established by one or more new channels forming through the thrombus

Blood flow is not fully restored but gives some capacity to the vessel

25
How do thrombi cause MI?
By occluding arteries resulting in ischaemia and infarction of cardiac myoctes
26
How do thrombi cause skin ulceration?
Thrombi in **venous** beds cause **congestion** and **oedema**, resulting in pain and skin ulceration
27
How can thrombi cause repeated miscarriage?
Thrombosis of the **uteroplacental vasculature** leads to **reduced 02 flow to foetus** (seen in inherited thrombophilias)
28
Define 'Embolism'
A blockage of a blood vessel by a solid, liquid or a gas at a site **distant from its site of origin**
29
What are the majority of embolism caused by?
Thrombus that break off and enter circulation (90% of thrombi)
30
Other than thrombi, name some things that can cause embolisms?
* air * amniotic fluid * nitrogen (seen in scuba diving) * medical equipment * tumour cells * body fat
31
Why can't embolisms occur in veins?
As blood flow goes from **smaller to larger vessels,** embolism will not lodge Instead they are carried to the **RHS of the heart** and embolism in the **pulmonary arteries**
32
What is the most common site for emboli from the LHS of the heart and aorta to end up?
**Mainly in the lower limbs** (although can end up anywhere in systemic circulation)
33
Where do 80% of pulmonary emboli arise from?
Thrombi in the **deep veins** of the thigh and popliteal vein
34
How much of a vessel needs to be occluded to cause sudden death from a PE?
Only **60%** of the pulmonary circulation needs to be occluded
35
What are saddle emboli?
Emboli that become lodged straddling a **bifurcation of an artery,** blocking both branches
36
Give some predisposing factors to DVT
* immobility/ bed rest * post op * pregnancy and post partum * oral contraceptives * severe burns (dehydration makes blood thicker) * cardiac failure * disseminated cancer
37
How can DVT be prevented?
High risk patients identified and offered prophylaxis * Heparin prophylactically * Flowtron boots- compress legs during surgery to aid venous return
38
What can be given to treat DVT?
* IV heparin * oral warfarin
39
Why might thrombi occur in the LHS of the heart?
* AF causes **dilation** of the left atrium and **stagnation** of blood * vegetations are more common in the LHS of the heart
40
What are cardiac mural thrombi?
Thrombi that occur on the wall of the heart chambers
41
What are paradoxical emboli?
Emboli that form in **systemic veins** and embolise in **systemic arteries** (bypassing the lungs) They are RARE
42
How might paradoxical emboli bypass the lungs?
1) emboli pass through **arterio-venous anastomoses** in pulmonary circulation 2) Larger emboli pass through **heart defects** in inter ventricular septum or parent foramen oval during **coughing, lifting or straining** (which increases pressure RHS of heart\> LHS, which pushes the thrombus though the defect)
43
What are TIA's and how are they caused?
**Transient Ischemic Attacks** in the brain due to microscopic emboli, usually coming from **carotid arteries** Small emboli break down quickly before causing lasting damage but are a pre-cursor to strokes
44
In what circumstances would you get fat and/or bone marrow emboli?
* bone fracture * marrow releases fat cells * liposuction
45
What is the bends?
* During diving, increased amounts of **nitrogen dissolve in the blood** * if the diver resurfaces **too quickly**, sudden depressurisation causes the dissolved gases to come out of solution and get released into the body as bubbles * Bubbles distort tissue ad embolise in blood * Nitrogen is fat soluble so causes focal ischema in lipid rich tissues e.g CNS, skeletal muscle joints and lungs
46
How is the bends treated?
* prompt recompression in a **special compression chamber** which forces the gas back into solution * patient than then undergo **slow decompression**
47
What are talcum emboli?
Emboli in the lungs **IV drug users** that are using drugs that have been cut with talcum powder The body cannot deal with talcum powder which also causes foreign body reactions
48
How is aspirin anti-thrombogenic?
* Aspirin irreversibly acetylates COX enzymes - * Platelets cannot produce thromboxane A2 ( a powerful platelet aggregator)
49
How is heparin anti-thombogenic?
Heparin **irreversibly complexes** with **antithrombin III** causing its ACTIVATION
50
How is warfarin anti-thombogenic?
Warfarin interferes with vitamin K metabolism (needed for clot formation)
51
How do filters prevent PE?
Umbrella shaped filters can be implanted into inferior vena cava to prevent emboli entering the lungs

Path Processes (12 decks)

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