Embolus Definition
A detached intravascular solid, liquid or gaseous mass that is carried by the blood
to a site distant from its origin.
Embolism
Occlusion or obstruction of a vessel by an embolus
Causes and Types of emboli
- Thrombi: Thromboembolism
- Microemboli
- Fragments of atheromatous plaques-Atheroemboli
- Bone marrow and bone fragments
- Fat emboli
- Air/nitrogen emboli
- Aminiotic fluid
- Tumour
- Foreign body emboli: IV catheters
- Parasitic emboli
Where emboli lodge depend on their size, their origin, and
relevant cardiovascular anatomy.
Those arise in the venous system can travel through the
right side of the heart to end up in pulmonary circulation.
Those arise in the left side will block the systemic
arteries, and the clinical effect will depend on the organ involved, be it
brain, kidneys, spleen, or periphery of the limbs.
Categories of Embolism
- Systemic embolism- Arise in arterial system eg: thromboemboli in arterial system and left heart, atheroemboli, fat, tumor
- Pulonary embolism- Arise in venous system thrombi in right heart and deep venous thrombosis, all except atheroemboli.
- Paradoxical- By right to left shunt- ASD and VSD
- Retrograde
Pulmonary embolism
Thrombo-emboli
often originate in the deep veins and pass in the venous circulation through
right side of heart.
The outcome
of pulmonary embolism depends on the size of the blood vessel blocked &
presence of pre-existing lung diseases.
Massive
pulmonary embolism
Massive
coiled pulmonary emboli are impacted in
a main pulmonary artery at bifurcation (Saddle embolus).
This leads
to acute right heart failure and sudden death.
Obstruction
of medium sized artery
Dual blood
supply protects lung from effects of pulmonary arterial embolism.
No
infarctions are seen.
There will
be local haemorhage but no damage to pulmonary frame work.
Patient may
be asymptomatic or breathlessness or
haemoptysis may present
Emboli
in small peripheral arteries
Smaller
emboli in periphery can lead to infarctions of the lung as there are no
collateral supplies to pulmonary arteries in end arteries.
Area
affected is often small but may produce symptoms if multiple
Patient has
dyspnoea if these are multiple.
If the
bronchial blood supply is impaired
Emboli
lodging in medium sized arteries can lead to infarctions.
Since the
blockage is proximal the infarcted area is large extending as a cone with the
base towards the surface and apex at the blocked artery.
Infarcted
area is red due to haemorhage and
congestion.
Infarcts
are common in lower lobes and are often multiple.
Microscopy
Bloked
blood vessel.
Infarcted
area shows haemorhage with loss of
nuclear staining.
But still
the alveoli can be identified.
The main
pulmonary trunk and pulmonary arteries to right and left lungs are seen here
opened to reveal a large "saddle" pulmonary thromboembolus. Such an
embolus will kill your patient.
Here is
another large pulmonary thromboembolus seen in cross section of this lung. The
typical source for such thromboemboli is from large veins in the legs and
pelvis
This
pulmonary thromboembolus is occluding the main pulmonary artery. Persons who
are immobilized for weeks are at greatest risk. The patient can experience
sudden onset of shortness of breath. Death may occur within minutes.
This
pulmonary embolus is adherent to the pulmonary arterial wall. If the patient survives,
the thromboembolus will organize and, for the most part, be removed.
A pulmonary
infarct is hemorrhagic because of the dual blood supply from the non-occluded
bronchial arteries which continue to supply blood, but do not prevent the
infarction.
Systemic embolism
Systemic emboli travel in the internal circulation, commonly
originating in the left side of the heart.
Arterial emboli, unless very small, nearly always cause
infarction. Emboli to the lower limb may produce gangrene of a few toes or of
the entire limb.
Sources of emboli
Heart
- Ischemic heart disease-mural thrombi, aneurisms,, hypokinetic segments
- Arrhythmias
- Valvular- Rheumatic hreart
- Myocardial - Myocarditis
- Intra cardiac lesions-
- Myxomas
- Ulcerated atheromatous plaque
- Aortic aneurisma
- Venous shunts in dialysis patients
- Coronary arteries
- Cerebral Arteries
- Renal Arteries
- Splenic Arteries
- Retinal arteries
- Mesentric Arteries
- Limb arteries
- Embolous at the bifurcation of the aorta
Cerebral emboli cause death or infarction unless the embolus
lodges in an area that receives adequate collateral supply through the circle
of Willis.
A special type of systemic embolus comprises the infected
material from vegetations on the heart valves in infective endocarditis. These
produce septic infarcts and large abscesses in the affected tissues.
Paradoxical embolus: Venous thrombi that pass through a
right–to-left congenital cardiac anomaly
Bone marrow emboli
Common in patients who suffered major trauma eg. RTA
Attempted cardiac resuscitation with rib fractures can lead to this.
Any thing that fractures bones can release bone marrow into
venous circulation, resulting in pulmonary emboli.
Clinical significance unclear
Embolism of fragments of
atheromatous plaques
Ulcerated atheromatous plaques can cause thrombosis on
surface of it or cause embolism of fragments
Cholesterol clefts are seen in the embolus
Fat embolism
Fat from marrow cavities of long bones or from soft tissues
can also enter the circulation as a result of severe trauma.
‘Fat embolism syndrome’ characterized by respiratory
problems, haemorhagic skin rash, and mental deterioration 24-72 hours after the injury.
The syndrome results from mechanical blockage of vessels,
chemical injury to vessels of lung producing pulmonary oedema and activation of
coagulative pathway to cause DIC.
Causes of fat embolism
·
Severe trauma with fractures of long bones
·
Damage to fatty tissues
·
Diabetes mellitus
·
Pancreatitis
·
Hyperlipidaemia
Laboratory investigations
·
Urine deposit: fat globules
·
Sputum: fat globules
·
Blood picture :DIC and thrombocytopenia
Air embolism
Large quantities of air within the circulation can act as
emboli by forming a frothy mass that can block vessels or become trapped in the
right heart chambers to impede pumping.
Over 100 ml of air is needed to produce problems. Lesser
amounts dissolve in plasma.
Air can either enter the circulation from
Atmosphere: cut injuries of neck and thorax allowing air to
be sucked in.
Air forced into the uterine vessels during badly performed
abortions and deliveries,
Produced within circulation: decompression sickness in deep
sea divers
Acute decompression sickness
.jpg)
N2 or He will dissolve in blood and tissues at high
pressures.
As the diver surfaces, the pressure is reduced and gas
begins to come out as minute bubbles.
If rapid this causes air embolism (lodge in brain and
skeletal muscle).
Platelets adhere to nitrogen bubbles causing DIC.
Pain around joints, skeletal muscle, respiratory distress
coma and death.
Treatment of decompression sickness
·
Early stages, by putting the victim in a
decompression chamber pressure will dissolve the bubbles where the high
pressure will redissolve the bubbles and allow a slow, controlled
decompression.
·
The chronic form, Caisson disease, produces
multiple areas of ischaemic necrosis in the long bones
Amniotic fluid embolism
Uncommon but life threatening forms of embolisation.
Amniotic fluid is
forced into the circulation as as a result of traring of the placental
membranes and rupture of uterine wall or cervical veins.
Emboli are a mixture of fat, hair, mucous, meconeum and
squamous cells from the fetus
Commonly lodge in the alveolar capillaries
Clinically, respiratory failure, cerebral convulsions and
coma. Often excessive bleeding due to DIC
Tumour emboli
This is an important mechanism of tumour spread.
Unlikely to have immediate CVS effects
