The Patient Was…

The process of blood clotting and the presence of blood clots within the body represent a classic example of something that can be both a blessing and a curse, depending on circumstances. Too much or inappropriate clotting can cause life-threatening problems, while too little or interrupted clotting can lead to other but equally serious consequences.

How can this apparent paradox be explained?

It’s important to recognize that blood clots, called thromboses (a single clot is called a thrombosis), are probably forming within your body most of the time. In response to minor, often microscopic, injuries to blood vessels due to a variety of factors, little clots form at the sites of these injuries. The body, fortunately, has its own clot-dissolving mechanisms (a process called thrombolysis) that prevent the clots from growing beyond what is necessary to heal the minor blood vessel injuries. This normal clot-forming and clot-dissolving process is a dynamic one that goes on pretty much all the time, keeping blood flowing through open and intact blood vessels.

The normal, dynamic, and balanced process of forming and removing clots is disturbed when either the clot-forming process or the clot-dissolving one becomes overactive. When clot-forming is excessive for some reason, blood flow through a blood vessel can be obstructed by the semi-solid or solid clump that is the clot. On the other hand, if clot dissolving is too active, either naturally or due to treatments,  blood vessel injuries cannot heal, and excessive bleeding (hemorrhage) may occur.

Blood normally consists of liquid and solid components. The liquid component, called plasma, represents more than fifty percent of the blood volume. Although plasma is composed of more than 90 percent water, it also carries dissolved proteins, minerals, hormones, and other materials. The dissolved proteins, importantly, include blood clotting proteins. The solid component of blood consists mainly of various blood cells; the three main types are red blood cells, white blood cells, and platelets.

The process of blood clotting is a very complicated one. The initiation of the clotting process can take place in different ways, but there is eventually a common pathway that involves a cascade of biochemical reactions in which the clotting proteins in the plasma are activated. Although there are several steps involved, the chemical reactions occur quickly, and the various blood cell types become enmeshed in the structure of the clot, adding to its size and solidity.

Clots can be classified in several ways, including location in the body, the type of blood vessel involved, the predominant blood cell type in the clot, and the fate of the clot itself. The actual effect of the clot within the body, the damage it causes, and the proper treatment of the clot and its consequences, may depend on all of these factors.

Classification by location in the body means identifying the body organ that is affected. Tnus, a blood clot that forms in a coronary artery, an artery supplying the heart muscle, is called a coronary thrombosis. A clot formed in the brain is defined as a cerebral thrombosis. Identifying the location of the clot often decides the appropriate therapy.

Importantly, some organs in which clots are located are not usually the site of actual clot formation.  Rather, clots form elsewhere and travel through the blood stream to arrive at their destination. A clot that forms somewhere and travels to another location is called an embolus or embolism. A blood clot in the lung, for example, is usually a pulmonary embolism, from a clot that formed in the veins of a leg and traveled through the blood stream to the lung. A blood clot in the brain, as noted earlier, may form there as a cerebral thrombosis, or may travel there as cerebral embolism. The medical implications may be quite different, and treatment may vary significantly.

Classification of clots by the type of blood vessel where the clot formed has important implications, as well. Clots that form in the venous (veins) system are usually structurally different from clots that form in the arterial (arteries) system. Again, treatment may be quite different depending on whether the clot is rich in platelets, such as is common in the arteries, or primarily made of fibrin, a clot-forming protein, as in the veins. Most clots contain some of each, but the initiating factor in the formation of the clot and the predominant structural makeup of the clot will often determine the treatment.

There are different strategies for dealing with blood clots, depending on their nature, their location, the injury they have caused, and the potential for future damage. Some clots require active intervention to remove them, some only need prevention of clot growth or extension, while management of others focuses mainly on prevention of recurrent clot formation or development of embolism.

Active so-called mechanical intervention to remove clots may involve either surgery or nonsurgical interventional techniques using catheters inserted through the skin into blood vessels to remove the clots. Pharmaceutical (drugs) intervention maybe used to dissolve the clots within the blood vessels. Occasionally, both mechanical and pharmaceutical interventions are combined.

If a clot is not causing sufficient problems requiring attempts at removal, then the strategy of limiting further growth of the clot may be employed. Here, administering drugs is the main method. Finally, management of many situations involving clot formation depends primarily on preventing new clots from forming in the future. Once again, this is the province of pharmaceutical solutions to clot formation.

There are two major directions in clot prevention. Most clots in arteries are initiated by activation of cells in the blood called platelets. These cells, when stimulated, tend to clump together forming an initial “plug” that interferes with blood flow in the artery. Then, the rest of the coagulation cascade of biochemical reactions occurs and a full clot is formed. Conversely, most clots in veins do not depend on platelet activation, and prevention of clots in this case depends on blocking key steps in the coagulation cascade itself.

Drugs that block the activation of platelets and thereby prevent initiation of clots in arteries are widely available and used. The most common is aspirin, which is why patients who have had heart attacks and strokes, both of which are usually due to artery clots, are so often prescribed aspirin. Other, more powerful anti-platelet drug, are sometimes used in special circumstances.

One very important and growing problem is a condition called atrial fibrillation or A Fib. Here, the upper chambers of the heart don’t contract regularly, and blood tends to pool in those heart chambers. Blood that pools in one place doesn’t flow and tends to clot. A clot in the left upper heart chamber (left atrium) can travel into the left lower heart chamber (left ventricle), the main pumping chamber, and from there travel anywhere in the body as an embolism. These clots in the heart are most like those in veins, so aspirin doesn’t help too much. Rather, so-called anticoagulant drugs, which work against the clotting proteins, are used to prevent these clots.

Although the term “anticoagulant” is widely used to cover all drugs that work against clots, it really represents incorrect usage. The best overall term would be “antithrombotic,” meaning against clots of any kind. Aspirin and drugs like it should be designated “anti-platelet” drugs, and those that work against the clotting cascade are properly called “anticoagulants.” The uses, side effects, antidotes, and risks of the different drug classes are not the same, and confusion among them can be dangerous. Precision in terminology here can be a safety issue.

Finally, another terminology issue. Anticoagulant drugs are often called “blood thinners.” Simply put, anticoagulants do not thin your blood. They prevent clots by inhibiting clotting proteins. Sometimes, patients attribute various symptoms to the belief that their blood is actually thinner than normal. Your blood when taking an anticoagulant is not abnormally thin, so anything you attribute to that falsehood is wrong and represents a misunderstanding.

Blood clotting conveys benefits and advantages as well as risks and dangers. Clotting may save your life in cases where bleeding threatens it. It may threaten or take your life where it interferes with vital blood flow.

Blood clotting is one of nature’s many double-edged swords.