Pulmonary embolism and infarction
Pulmonary embolism is an obstruction of the pulmonary arterial bed by a dislodged thrombus or foreign substance. Pulmonary infarction, or lung tissue death from a pulmonary embolus, is sometimes mild and may not produce symptoms. However, when a massive embolism occurs involving more than 50% obstruction of pulmonary arterial circulation, it can be rapidly fatal.
What causes it
Pulmonary embolism usually results from dislodged thrombi that originate in the leg veins. Other less common sources of thrombi are the pelvic, renal, hepatic, and arm veins and the right side of the heart.
Trauma, clot dissolution, sudden muscle spasm, intravascular pressure changes, or a change in peripheral blood flow can cause the thrombus to loosen or fragmentize. Then the thrombus — now called an embolus — floats to the heart’s right side and enters the lung through the pulmonary artery. There, the embolus may dissolve, continue to fragmentize, or grow.