Infarction and Embolism Flashcards
What is an infarct?
An area of ischaemic necrosis within a tissue or organ, produced by occlusion of either its arterial supply or its venous drainage
What do infarcts usually results from?
Acute arterial occlusion
Where do the different types of acute arterial occlusion occur?
1) Thrombosis e.g. coronary arteries → MI
2) Embolism e.g. lung, kidney, spleen
3) Either thrombosis or embolism e.g. brain (but also hypotension)
Why is venous infarction less common?
Because arrest of blood flow due to venous obstruction is unusual as most tissues have numerous anastomoses
When can venous infarction occur?
1) Thrombosis of the mesenteric veins → intestinal infarction (usually red)
2) In the brain following thrombosis in the superior sagittal (longitudinal) sinus
3) In the testis or ovary following torsion
What happens in an intestinal infarction?
- Bright, red dilation due to blood in the bowel
- Can be reperfused but mostly has to be removed otherwise it will rupture
How are infarcts divided?
1) Colour → red/haemorrhagic vs white/pale/anaemic)
2) Presence (septic) or absence (bland) of bacterial contamination
When do white infarcts occur?
- With arterial occlusion (bc no blood)
- In solid tissues e.g. heart, spleen, kidneys
What is the most important form of ischaemic heart disease and a leading cause of death?
AMI
What are the two types of myocardial infarction?
1) Transmural
2) Subendocardial
Describe a transmural infarct
- Commonest
- The ischaemic necrosis involves the full or nearly full thickness of the ventricular wall in the distribution of a single coronary artery
- Usually associated with coronary atherosclerosis, plaque rupture and super-imposed thrombosis
Describe a subendocardial infarct
- This constitutes an area of ischaemic necrosis limited to the inner ⅓ or at most inner ½, of the ventricular wall
- There is diffuse stenosing coronary atherosclerosis and global reduction of coronary flow e.g. due to shock but no plaque rupture and no thrombosis
- RV collapsed
- Inner ⅓ of heart (endocardium) supplied by blood in lumen so if blood supply stops, this blood supply will also stop
- Can occur in road traffic accident → not enough blood in heart or in blood supply to heart
- Pallor in area of myocardium with infarct
What can a recent MI cause?
Severe arrhythmia
What happens initially to cells in an AMI?
- Cell shape starts to change and infiltration by other cells
- Lose nuclear definition
What happens after a while to cells in an AMI?
- Nuclei start to fragment → dead cells so can’t bring them back
What happens to the myocardium after infarct?
Fibrous tissue (scar) is laid down bc can’t regenerate myocyte
What can happen if the infarct is transmural?
Can get fibrin deposition
What are complications of an MI from early to late?
Arrhythmias, HF → pericarditis, papillary muscle dysfunction, mural thrombus → ventricular/papillary muscle rupture → aneurysm, post MI syndrome, ischaemia and re-infarction
What are the main morphological complications following MI?
1) Cardiac rupture
2) Pericarditis
3) Mural thrombosis
4) Ventricular aneurysm
How does cardiac rupture as a complication of MI result from?
Results from the mechanical weakening that occurs in necrotic and inflamed myocardium
When does cardiac rupture most commonly occur?
4-7 days post infarct
Which part of the heart does cardiac rupture usually involve and what does this lead to?
Ventricular free wall → haemopericardium and cardiac tamponade
When does pericarditis usually develop?
2-3 days post infarct
Describe the pericarditis resulting as a complication of MI
- Fibrinous or fibrinohaemorrhagic
- Usually localised to the region overlying the necrotic area
What causes mural thrombosis and thromboembolism?
The combination of a local myocardial abnormality in contractility (causing stasis) and endocardial damage (causing a thrombogenic surface)
What is the result of mural thrombosis?
Endothelium gets sticky, clot forms inside ventricle → coronary or cerebral arteries
What is a ventricular aneurysm and how does it form?
A late complication that most commonly results from a large anteroseptal, transmural infarct that heals into a large area of thin scar tissue that paradoxically bulges during systole
What are the consequences of cardiac rupture?
- Rupture of inter-ventricular septum → left-to-right shunt
- Rupture of papillary muscle → severe acute mitral incompetence
What is embolism?
The transfer of abnormal material by the bloodstream and its impaction in a vessel
In what % of cases does cardiac rupture occur?
1-5%
In what % of cases does mural thrombosis occur?
15-40%
What is an embolus?
The impacted material
What are 7 different types of emboli?
1) Fragments of thrombus (commonest)
2) Material from ulcerating atheromatous plaques (common in distal leg arteries)
3) Septic emboli
4) Fragment of tumour growing into a vein
5) Fat globules from bone marrow
6) Air emboli (due to external trauma of vessels)
7) Parenchymal cells
Embolus in what blood vessel would be catastrophic?
Inferior vena cava
What type of emboli might lead to a lung infarct?
Tumour emboli (hepatocellular carcinoma) in pulmonary circulation
What colour is a lung infarct?
Red
What is an example of something that could cause a fat embolism?
A fracture of a long bone
What does PE result from?
Detachment of a thrombus in a systemic vein, usually in the deep venous plexus in the leg (DVT)
When is PE the most common?
Post-operative day 10
What are the consequences of PE?
- Sudden death or death after a short period of respiratory distress
- Large thrombi may be detached en masse → RH
- Can cause sudden blockage of the pulmonary trunk or at a major division
Where are fatal pulmonary emboli usually derived from?
Femoral and iliac veins
What is the morphology of a PE?
- Form a cylinder about 1cm diameter and up to 30cm long
- At autopsy are found coiled like a snake in pulmonary artery and RV
Where do less gross fragments impact in?
Major or minor pulmonary arteries
What may be present if a patient lives after PE?
Varying amounts of haemorrhagic infarction in the territory of the blocked vessels
Why is infarction never co-extensive with the area of distribution?
Because of collateral vessels and the bronchial circulation
What else can PE cause?
Breathlessness and crepitations
How else can PEs occur?
As multiple small emboli, impacting over time
What do multiple small emboli rarely cause?
Chronic pulmonary hypertension
What are some causes of chronic pulmonary hypertension?
Congenital cardiac shunts
Chronic hypoxia
Pulmonary fibrosis
What is in the structure of a thrombus?
RBCs, platelets
