Session 5 - Thrombosis and Embolism Flashcards
(34 cards)
What is a thrombus?
A thrombus is a solid mass formed from the constituents of the blood within the heart or vessels during life.
When does thrombosis occur?
This is the process by which a thrombus forms. It occurs when normal haemostatic mechanisms are turned on inappropriately.
What is Virchow’s triad?
Virchow was the the first person to name the process of thrombosis and he said that it depended on 3 things.
- change in the vascular wall (endothelial damage)
- change in the blood flow (slow or turbulent)
- Changes in the blood (hypercoagulability)
Where are arterial and cardiac thrombi often seen?
At a site of endothelial injury or turbulence.
Where are venous thrombi often seen?
At a location where there is stasis
How many factors of the Virchows triad usually have to occur for a thrombus to form?
2 out of the 3.
Why do platelets tend to flow nearer to the inner surface of the vessels?
This is because they are smaller and therefore as part of the laminar flow they flow on the outside.
What are lines of Zahn and how do they form?
lines of Zahn is the name of the pattern formed in an arterial thrombus. There are alternating layers of platelets and red blood cells combined with fibrin.
- Initially platelets will bind to the endothelium and aggregate, especially if there is endothelial injury or the blood flow is slow.
- Fibrinogen binds the platelets together and fibrin grows out of the platelet layer. The fibrin traps the red blood cells.
- The surface of the red layer is thrombogenic and platelets stick to the exposed fibrin. A second white layer of platelets forms and the process continues.
What are some of the most common clinical effects of thrombosis?
- Occlusion of an artery at the site of the thrombus resulting in iscahemia and infarction.
- Embolism at a distant artery. eg - pulmonary embolism and cerebrovascular accident.
- Congestion and oedema in venous bed resulting in pain and skin ulceration
- Repeated miscarriages due to thrombosis of uteroplacental vasculature
What is an embolus?
Sudden blocking of an artery by a thrombus or foreigh material that has been brought to its site of lodgement by the blood current - it can be a solid, liquid or gas that is large enough to lodge and impact at a secondary site.
Provide some examples of emboli material (Name at least 5)
- body fat
- bone marrow
- atheromatous plaques
- tumour fragments
- parasites
- bubbles of air or other gases
- debris injected intravenously
- amniotic fluid
- medical equipment
- fragments of brain or liver after trauma.
How do emboli occur in the veins?
Trick question. Veins cannot emobilise. This is because the blood flows from smaller vessels to larger vessels and therefore the blood will go through the heart and usually lodge in the pulmonary arteries.
What happens to emboli originating in the left heart or aorta?
The emboli will end up anywhere in the systemic circulation - especially in the lower limbs.
Where do most pulmonary emboli originate from?
Deep veins of the thigh and the popliteal vein.
What can small pulmonary emboli lead to?
They are quite often clinically silent however can lead to pulmonary hypertension.
How would you define a large pulmonary emboli?
This is an emboli which results in >60% occlusion of the pulmonary circulation causing sudden death, right-sided heart failure or cardiovascular collapse.
What is a saddle embolus?
This is a large emboli that becomes lodged at the site of a bifurcation of an artery thus blocking both branches. This classically occurs at the bifurcation of pulmonary arteries and can result in sudden death.
Why are thrombi often seen on the left hand side of the heart?
- Atrial fibrillaiton resulting in dilatation of the left atrium and stagnation of blood resulting in thrombus formation
- Vegetations are more common on the valves of the left hand side of the heart
- Infarcts commonly affect the left ventricle. Thrombi then form on the affected necrotic endothelium of the ventricular cavity.
What is the name of an embolus that forms in the systemic veins and embolises in the systemic arteries?
A paradoxical embolus.
What can cause a paradoxical embolus?
- Passing through the arterial venous anastamoses in the pulmonary circulation - they are 20-40 times the diameter of a capillary.
- septal defects
- passing through a patent foramen ovale during coughing, lifting or straining.
What location(s) do an emboli derived from an atheroma usually affect?
- usually affects the intestine. Patients present with abdominal pain.
- Can affect the brain resulting in transient ischaemic attacks
What is the most common original location of an emboli resulting in a transient ischaemic attack?
carotid artery atheroemboli
can be a result of a thromboemboli from the left heart.
What differentiates between a transient ischaemic attack and a stroke pathologically?
A stroke is a complete occlusion of brain matter with no resolution.
A transient ischaemic attack is a result of a microemboli and due to its small size it is broken down within a matter of hours and therefore this is why the patient only has temporary loss of neurological function.
Provide two examples of how a gas emboli could occur?
- Divers resurfacing too quickly and the change in pressure causes the nitrogen to become gas in the blood and cause multiple gas emboli.
- Trauma to the neck and chest - air drawn in upon inspiration.
- During childbirth
