Anticoagulation is where a substance or medication is used to prevent the coagulation (clotting) of blood. Clotting is a normal physiological function to help prevent excessive life-threatening bleeding after an injury. It is a process that depends on certain proteins that our bodies make that are part of the coagulation cascade. Sometimes the coagulation cascade creates a situation where blood clots can form when or where they normally should not which can lead to health problems. As the cardiovascular system depends on blood always freely flowing, blood clots can impair adequate blood flow or can travel to vital organs cutting off blood flow and thus oxygen delivery to the end organ (such as brain, heart, lung or kidney) or extremity (such as a leg or arm).
Anticoagulants are medications that interfere with some part of the coagulation cascade to reduce the odds of blood clots forming or, in simple terms, “thinning” the blood. This is somewhat of a misnomer as the blood is not truly “thinner” but just not as likely to clot or will take longer to clot. Sometimes a clot (thombus) can form in the deeper veins of the legs (deep vein thrombosis or DVT) which can cause pain, redness and swelling of the leg. If a DVT worsens, it can extend or break off and travel (embolus) through the heart and into the lungs causing life threatening problems (pulmonary embolism). In atrial fibrillation, blood stagnates in the upper chambers (atria) of the heart where it can clot and then break off and travel from the heart to the brain causing a stroke. Sometimes after very large heart attacks, a part of the main pumping chamber of the heart (left ventricle) doesn’t move or contract with each heart beat anymore and a blood clot forms due to stagnation of blood flow in that area. Likewise, these clots can embolize up out of the heart and into the brain causing a stroke. When patients receive surgical mechanical (not tissue) valve replacements, the non biological surface of these artificial valves can cause blood clots which can impair the function of the valve or break off and cause a stroke (click here for more information of valvular heart disease).
Anticoagulants are used to achieve the best and safest balance of preventing blood clots without increasing the risk of bleeding too much. It is important for patients who need blood thinning medications to have a physician who has adequate knowledge and experience in using these medications. Most cardiologists have extensive experience with using blood thinners.
Vitamin K antagonists are oral anticoagulants known as the coumarins of which warfarin (Coumadin) is the most commonly used in the United States. It works by interfering with proteins manufactured by the liver that are dependent on vitamin K. Blood tests that measure a “protime” (which has been standardized as an international normalized ratio or INR) of how long it takes for these proteins to clot helps determine if the dosage is enough to reduce the odds of clots but not too much to increase the risk of bleeding too much.
Heparin is an intravenous biological substance derived usually from pig or cow intestines that activates antithrombin III which blocks thrombin (part of the coagulation cascade) from clotting blood. While in certain circumstances in can be injected under the skin a few times a day, for more dangerous clotting situations, it usually has to be given as a continuous intravenous (IV) drip and also requires blood tests (PTT or partial thromboplastin time) to help determine if it is dosed correctly. Both warfarin and heparin can be challenging to dose just right. Heparin is often used in a hospital setting or when doctors know that the anticoagulant effect has to be “turned off” in a relatively short period of time.
Low-molecular weight heparins such as Lovenox (enoxaparin) or Fragmin (dalteparin) have a more predictable anticoagulant effect (in patients with normal kidney function) that usually does not require any blood test monitoring and can be given just once or twice a day as an injection under the skin.
Newer oral anticoagulants such as direct factor Xa inhibitors and direct thombin inhibitors have recently been developed and are being used more as an alternative to warfarin, heparin and low-molecular weight heparins especially in patients with atrial fibrillation (click here for more on these newer agents for patients with atrial fibrillation). As they do not require ongoing blood test monitoring, they promise to be easier to use and possibly safer if used appropriately in the right patient with the right circumstance. Some of them can be used for DVT and pulmonary embolism but none of them have sufficient evidence as of yet of efficacy or safety in patients with artifical heart valves and, as of 2013, definitely should not be used in patients with mechanical heart valves.
Clots that form from unstable plaque in the coronary arteries which can lead to a heart attack, usually are more dependent on a different clotting mechanism. Rather than blood clotting proteins, this mechanism is more dependent on platelets which are cell fragments produced by bone marrow and are always found in the blood. While anticoagulants can help prevents these clots, anti-platelet medications seems to work more reliably with less bleeding risk. Platelets are an important part of normal healing after injury but often can cause problems when injury occurs inside an important artery such as that occurs when plaque in a coronary artery full of cholesterol becomes unstable and ruptures. In an attempt to “heal” the ruptured plaque, the platelets collect (aggregate) and can end up blocking off the coronary artery which causes a heart attack. Anti-platelet medications are generally categorized as blood “thinners” but are not true anti-coagulants as they do not effect the proteins that are part of the coagulation cascade.
Aspirin is the most commonly used antiplatelet medication to help prevent a heart attack in patients with coronary artery disease or in whom are having a heart attack. Stronger antiplatelet medications that sometimes are used after a heart attack or in patients whom need a coronary stent include Plavix (clopidogrel), Effient (prasugrel) and Brillinta (ticagrelor). Often patients need two anti-platelet medications (dual anti-platelet therapy), usually aspirin and one of the other newer agents, especially after coronary stents.
Natural Blood Thinners
Food and herbal supplements with blood-thinning effects include alfalfa, avocado, fish oil, garlic, ginger, ginkgo, ginseng, grapefruit, green tea, horse chestnut, omega-3 fatty acids, papaya, pomegranate, St. John’s wort, turmeric, wheatgrass and willow bark. If you are on or about to be started on any anticoagulants or anti-platelet medications, it is important to inform your doctor of any herbal supplements that you are taking. Otherwise, the risk of bleeding might be dangerously high.
Written by and/or reviewed by Mark K. Urman, MD and Jeffrey F. Caren, MD
Last updated: 11/29/2013