Thrombosis is the underlying cause of heart attack (myocardial infarction), stroke, and a category of disorders known as venous thromboembolic events (VTE), including deep vein thrombosis (DVT) and pulmonary embolism (PE).

The circulatory system

The circulatory system carries blood throughout the body. The circulatory system consists of the heart, the blood and a network of vessels known as arteries and veins, which carry blood throughout the body. Both side of the heart have different functions. The left side of the heart pumps oxygen-rich blood into the arteries. The arteries are consecutively branched, in order to supply this oxygen-rich blood to all the tissues in the body. The smallest branches are called capillaries. Capillaries have two functions: they supply tissue with the oxygen and nutrients it needs to function, and also carry away its metabolic waste. Capillaries containing low-oxygen blood merge into the venous bloodstream, the network of veins that return the blood from throughout the body to the right side of the heart. The right side of the heart then pumps the blood into the lungs where it is re-loaded with oxygen. The oxygen-rich blood then flows into the left side of the heart, starting the cycle once again.

Injured blood vessels are healed through haemostasis

When the inner wall of a blood vessel becomes injured, the body initiates a process known as haemostasis. Haemostasis enables the process of healing (or tissue repair) through activating the formation of a blood clot (known as a thrombus). Beneath the blood clot, healing can take place. In normal circumstances, the thrombus is slowly dissolved by the body following tissue repair to allow normal blood flow to resume.

Blood clotting can occur outside the healing process

The ability to form blood clots (known as coagulation) is vital to the healing process of haemostasis and is essential for maintaining a healthy vascular system. In normal circumstances, the clot (or thrombus) plays a positive role in this process. However, sometimes the coagulation reaction is too strong and forms more clot than is needed for tissue repair. This may be triggered by a number of factors, such as certain heart conditions, pregnancy, prolonged periods of immobility, smoking, certain medications, surgery, and inherited blood clotting disorders.

A thrombosis occurs when clots obstruct normal blood flow

When the coagulation reaction is too strong and forms more clot within the blood vessel that is needed for tissue repair (in other words coagulation overproduces or “overshoots” the amount of clotting required), this causes a condition known as thrombosis, in which the unnecessary clot (or thrombus) causes an obstruction to normal blood flow.  At the site of formation, a thrombus can restrict and obstruct blood flow, hindering transport of oxygen and nutrition to the tissues downstream of the blockage. In addition, a detached piece of thrombus may travel through the circulatory system, get stuck elsewhere in the body and cause an obstruction (known as an embolism) to vital blood vessels.

Thrombosis can lead to life-threatening disease

Depending on the location and extent of the clot, thrombosis can be extremely serious and even life-threatening. There are two distinct types of thrombotic disease: arterial thrombosis and venous thrombosis.

  • Arterial thrombosis is the formation of a thrombus within an artery. Generally, arterial thrombosis can affect any organ of the body. Most commonly, they can cause a stroke (a rapid decline of brain function due to a disturbance in the supply of blood to the brain), a heart attack (the obstruction of a coronary artery or myocardial infarction) or an arterial blockage in the limbs.
  • Venous thrombosis is the formation of a blot clot within a vein. The most common manifestations of venous thrombotic disease are superficial-vein thrombosis (SVT), deep-vein thrombosis (DVT) and pulmonary embolism (PE), collectively known as venous thromboembolic events (VTEs).