Embolism

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
  1. Ischemic heart disease-mural thrombi, aneurisms,, hypokinetic segments
  2. Arrhythmias
  3. Valvular- Rheumatic hreart
  4. Myocardial - Myocarditis
  5. Intra cardiac lesions-
  6. Myxomas
Arterial System
  • Ulcerated atheromatous plaque
  • Aortic aneurisma
  • Venous shunts in dialysis patients
Sites of lodgement
  • 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
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

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