The fate of an embolism depends on the type of embolism involved, its size, location, and the underlying health of the individual. For example, a pulmonary embolism is a blood clot that blocks and stops blood flow to an artery in the lung. In most cases, the blood clot starts in a deep vein in the leg and travels to the lung. Because one or more clots block blood flow to the lungs, pulmonary embolism can be life-threatening. However, prompt treatment greatly reduces the risk of death.

The impact of a pulmonary embolism on the heart’s right ventricle function is the most common cause of pulmonary embolism death. For people with pulmonary embolism but no associated decrease in right ventricle function, estimates place mortality (death) at around 2%.

An embolism is the obstruction of the flow of blood by an embolus, a particle or aggregate of substance that is abnormally present in the bloodstream. When a thrombus, a blood clot, becomes dislodged and a piece breaks off, it is called an embolus. The embolus can obstruct the pulmonary circulation, and the body sends a signal to release neurohormonal substances and inflammatory mediators, which cause vasoconstriction.

Pulmonary embolism occurs when clots break off and embolize into the pulmonary circulation. Pulmonary emboli are typically multiple, with the lower lobes being involved more frequently than the upper, and bilateral lung involvement being more common. Once deep venous thrombosis develops, clots may dislodge and travel through the venous system and the right side of the heart to lodge in the pulmonary arteries, where they partially or completely occlude one or more vessels.

There are different types of embolism classified based on the embolic material:

1. Thromboembolism – embolism of thrombus or blood clot.

2. Fat embolism – embolism of fat droplets.

3. Air embolism (also known as a gas embolism) – embolism of air bubbles.

4. Septic embolism – embolism of pus containing bacteria.

5. Tissue embolism – embolism of small fragments of tissue.

6. Foreign body embolism – embolism of foreign materials such as talc and other small objects.

7. Amniotic fluid embolism – embolism of amniotic fluid, fetal cells, hair or other debris that enter the mother’s blood stream via the placental bed of the uterus and trigger an allergic reaction.

The pathway of the embolus can have 3 different types:

1. Anterograde.
2. Retrograde.
3. Paradoxical.
In anterograde embolism, we say that the movement of emboli is according to the direction of blood flow. However it is otherwise in retreograde embolism, when the weight of the emboli is high enough to oppose the blood flow direction. This is usually only siginificant in blood vessels with low pressure (veins) or emboli of high weight. In paradoxical embolism or also known as crossed embolism, the embolus from veins are crossed to the arterial blood system. This is usually only found in heart defects such as septal defects between the atria or ventricles.