A blood clot that forms inside a blood vessel or a chamber of the heart is called a thrombus. When abnormal blood clots form in almost any part of the circulation, they can cause dangerous, sometimes life-threatening complications. One way to treat these clots is to dissolve them, a process called thrombolysis.

Thrombolysis is achieved with devices that mechanically break up the clot or with clot dissolving drugs called thrombolytics, popularly known as “clot-busters.” The latter work either by directly degrading the clot or stimulating the body’s own clot-dissolving mechanism. Commonly used thrombolytic drugs include streptokinase and tissue plasminogen activator, or t-PA.

Ordinarily, the body is able to maintain blood clotting ability at a safe level, so that neither excessive bleeding nor excessive clotting occurs. However, many factors can tilt this balance dangerously in favor of the development of blood clots, including inherited blood abnormalities, certain illnesses, and even certain medical procedures. Another significant risk factor for abnormal clot formation is the process of atherosclerosis, also known as “hardening of the arteries.” In atherosclerosis, a fatty and scar-like substance called plaque builds up inside arteries and if severe enough will result in sluggish flow that promotes clot formation. Also, unlike the normal lining of an artery, plaque has a rough surface that can encourage clots to form.

In the veins or arteries of the arms and legs, a clot can obstruct blood flow and cut off the oxygen supply to these areas, causing pain and even tissue damage. Clots that form in the blood vessels that lead into and out of organs such as the kidneys and liver can cause organ failure if left untreated. Clots that form in one place can also dislodge and cause harm in other parts of the body. A traveling clot, called an embolism, can lead to life-threatening conditions such as stroke, heart attack, and pulmonary embolism (a blockage in one or more blood vessels that supply the lungs).

The goal of thrombolytic therapy is to dissolve blood clots in these areas and restore blood flow. Thrombolytics are used with varying degrees of success for different conditions. They are an important treatment for heart attacks and for ischemic stroke (stroke caused by blood clots), and in this situation they are given in a peripheral vein, with the drug bathing all areas including the target site. Thrombolytics are also used for clots in the peripheral circulation, but in this setting they are delivered directly into the clot with a catheter.