Embolism is the partial or complete obstruction of the cardiovascular system by some part of a mass carried through the circulation. This mass is called an embolus. Most of these emboli are some forms of thromboemboli. Some types of emboli are,

Depending upon matter in the emboli:

  • Solid
  • Liquid
  • Gas

Depending upon if it’s infected or not:

  • Bland
  • Septic

Depending upon the source of emboli:

  • Cardiac
  • Arterial
  • Venous
  • Lymphatic

Depending upon flow of blood:

  • Paradoxical
  • Retrograde


This is caused by detached thrombus or part of thrombus. It is the most common type.

Arterial emboli may be due to:

  1. Causes within heart – these are mural thrombi in the left atria or ventricles, vegetations, prosthetic valves and in the mitral and aortic valves.
  2. Causes within arteries – emboli developing with relation to atherosclerotic plaques, aortic aneurysm. If vascular occlusion occurs, it may cause infarction, gangrene, arteritis, mycotic aneurysm, myocardial infarction and sudden death.

Venous thromboembolism may occur due to,

  1. Thrombi in the veins of lower legs
  2. Thrombi in the pelvic veins
  3. Thrombi in the upper limbs
  4. Thrombi in the cavernous sinus of brain
  5. Thrombi in the right side of the heart

Pulmonary thromboembolism:

It is the most fatal type. There is occlusion of pulmonary arterial tree by the embolus. May occur in pulmonary hypertension.


These are more common in bedridden patients but can also occur in ambulatory patients. This arises due to thrombi originating from large veins of lower limbs such as femoral and iliac and thrombi from unsuspecting areas such as varicose veins and and pelvic veins.


Detachment of the thrombus causes embolus to enter into veins and therefore larger veins, entering right side of the heart.

Consequences of pulmonary embolism:

  • Sudden death
  • Acute cor pulmonale
  • Pulmonary infarction
  • Pulmonary haemorrhage
  • Resolution
  • Pulmonary hypertension
Pulmonary thromboembolism

Systemic embolism:

It is an arterial embolism that occurs from the diseased heart. The diseases include myocardial infarction, RHD, cardiomyopathy, congenital heart disease, etc. these emboli cause infarction at the sight of lodgement which are usually lower extremity, brain and internal visceral organs.

Fat embolism:

It is the obstruction of arteries and arterioles by fat globules. Trauma to the bones is the most common cause. Systemic circulation in that some of the fat globules may pass through foramen ovale, arteriovenous shunts in the lungs and vertebral venous plexuses, and get lodged in the capillaries of organs like the brain, kidney, skin etc.

Gas embolism:

Air, nitrogen and other gases may causes bubbles in the circulatory system, causing obstruction in the blood flow and causing damage to the tissue. Two types – air embolism and compression sickness are discussed below.

Air embolism:

It occurs when air is introduced into the arteries or veins.

Venous air embolism:

Air may be sucked into systematic veins due to,

  1. Operations on head and neck and trauma
  2. Obstetrical operations and trauma
  3. Intravenous infusion of blood and fluid
  4. Angiography

The effects of venous air embolism may happen due to’

  1. Amount of air introduced into circulation
  2. Rapidity of entry of air
  3. Position of the patient
  4. General condition of the patient

Arterial air embolism:

It is the entry of air into the pulmonary vein or its tributaries. It may occur due to,

  • Cardiothoracic surgery and trauma
  • Paradoxical thromboembolism
  • Arteriography

Effects of arterial embolism may look like,

  1. Marble skin
  2. Air bubbles in the retinal vessels
  3. Pallor of tongue
  4. Sudden death
Arterial and venous thromboembolism

Decompression sickness:

It is a specialised form of gas embolism also known as Caisson’s disease or diver’s disease.


Divers who descend to low levels containing high atmospheric pressure have gases like oxygen and carbon dioxide dissolved into their blood and tissues. When the diver comes to the surface too rapidly, the gases come out of the solution as bubbles which coalesce together as gas emboli. Individuals who ascend to great heights with low atmospheric pressure and descend quickly, are exposed to sudden decompression just like the divers.


  • The effects depend upon,
  • Depth or altitude reached
  • Duration of exposure to altered pressure
  • Rate of ascent or descent
  • General condition of the patient

Clinical effects of decompression sickness are of two types,

Acute form:

Occurs due to acute obstruction of the small blood vessels in the vicinity of joints and skeletal muscles which are characterized by the bends, chokes and cerebral effects.

Chronic form:

Occurs due to ischaemic necrosis throughout the body but especially the skeletal system. The features are avascular necrosis of bones, neurological symptoms, haemorrhage and skin manifestations.

Amniotic fluid embolism:

This is the most fatal, unexpected and unpreventable form of embolism. During labour and postpartum, the amniotic fluid may enter the uterine veins and reach the right side of the heart, resulting in fatal complications. The mechanism by which these amniotic fluid contents enter the maternal circulation is not clear. Possibly, they gain entry either through tears in the myometrium and endocervix, or the amniotic fluid is forced into uterine sinusoids by vigorous uterine contractions.

The clinical syndrome of amniotic fluid embolism is

  • characterised by the following features:
  • Sudden respiratory distress and dyspnoea
  • Deep cyanosis
  • Cardiovascular shock
  • Convulsions
  • Coma
  • Unexpected death

The sudden death may occur due to the following reasons:

  • Mechanical blockage of the pulmonary circulation in extensive embolism.
  • Anaphylactoid reaction to amniotic fluid components.
  • Disseminated intravascular coagulation (DIC) due to liberation of thromboplastin by amniotic fluid.
  • Haemorrhagic manifestations due to thrombocytopenia and afibrinogenaemia.


Atheromatous plaques, especially from aorta, may get eroded and form atherosclerotic emboli which may get lodged in the smaller arteries. These emboli consist of cholesterol crystals, hyaline debris and calcified material, and may evoke foreign body reaction at the site of lodgement.

Click here to know more about Nambi Narayanan