Thrombosis and thromboembolism

When there’s a problem in normal blood flow, we call it a hemodynamic disorder. They are caused when there’s an overcoagulation of blood forming a thrombus in side a vessel. The process is called thrombosis, which can also result in embolism or infarction.

When a thrombus forms, it’s made up of platelets, erythrocytes, leukocytes and fibrin. It doesn’t form outside a blood vessel as clots do, but instead forms at a blood vessel wall. The thrombosis begins at a point attached to the vascular wall where platelets group together.

A coagulation cascade is triggered, but there’s no threatened blood loss. How does this happen? Endothelial damage, altered blood flow, or a state of blood hyper coagulation.

Endothelial damage can result from hemodynamic stress as blood flow under pressure causes arteries to expand and elongate. The pressure can be produced due to hypertension, a major cause.

But a second major cause is atherosclerosis.

Abnormal blood flow can cause more platelet contact with endothelium, which reduces rate of flow or stops it completely. The change can produce risk of adherence causing thrombosis.

Blood hypercoagulation is a situation when blood is highly susceptible to coagulation despite whether or not there is endothelial damage. It can occur when malfunction in systems, which may be due to immune system problems or liver overproduction of clotting factors.

Older people may have a deficiency of a coagulation inhibitor. Smokers and obese people may have hypercoagulation problems, but the mechanisms are not well understood.

Thrombosis ultimately results in a sequela of either resolution, organization, propogation, infarction or embolism.

Resolution is when the anticoagulation system is seeking to overcome the problem and is least threatening.

Organization happens when phagocytic digestion of a thrombus occurs about two or three days after the thrombus forms. An endothelium forms over the organizing tissue and the thrombus simply becomes part of the vascular wall. While this happens small channels sometimes are created for blood to pass through the thrombus through a process called recanalization.

Propagation is when a thrombus enlarges going along a vessel (a vein usually) and a red cap is produced along the vein’s lumen.

Infarction is when ischemia (when lumen is completely blocked by the thrombus) produces necrosis of a region. This is the most serious in arteries since they supply oxygen and nutrients.

Embolism is when a blood vessel is occluded by an embolus, when a mass of some sort is going along in the blood stream, which is usually result of a thrombus breaking away (as in thromboembolus).

Anticoagulatns, like heparin, are commonly used as therapy to avoid thromboembolism .

Reference

Nowak TJ, Hanfod AG. Pathophysiology: Concepts and applications for health care professionals, 3rd ed. 2004. New York, McGraw-Hill.