Basic Facts

• The term thrombosis means the formation of a blood clot.
• Clotting is a normal response to injury.  However, blood clots can cause serious health problems if they occur inside the heart or on the inside of a blood vessel.
• When a blood clot obstructs blood flow to the heart muscle it can cause a heart attack.  When it obstructs blood flow to the brain, it can cause a stroke.
• Antithrombotic therapy refers to the use of medications which interfere with blood clot formation.
• Anticoagulants (such as Coumadin), are strong blood thinners which prevent blood cells from sticking to each other to form a blood clot.
• Antiplatelet agents (such as aspirin), are weaker medications which prevent platelets (the tiny discs that circulate in the blood stream and are also important to clot formation), from sticking to blood vessel walls and to one another.
• The goals of antithrombotic therapy are
  • to block the formation of new clots,
  • prevent the growth of existing clots, and
  • reduce a person's risk of complications from blood clots.

A More Detailed Explanation

Physicians prescribe antithrombotic therapy for people who have developed a thrombus, or blood clot, or who are at risk of developing one. Clotting is a normal response to injury. However, blood clots can cause serious health conditions if they block blood flow to organs such as the heart or brain.

Antithrombotic medications include anticoagulants and antiplatelet agents.  These two types of medicines have different effects and are used under different circumstances:

Anticoagulants

When blood stagnates or circulates poorly, it can coagulate or congeal.  Anticoagulant medications reduce the blood's ability to congeal - even when it is not moving around very quickly or efficiently.  Anticoagulants are often referred to as “blood thinners”, although they do not actually thin the blood. Anticoagulants are used to prevent blood clots from forming and to prevent existing clots from getting larger.  Anticoagulants do not dissolve clots.  Warfarin (Coumadin) is an example of an anticoagulant.

Antiplatelet agents

Antiplatelet medications prevent the clumping of tiny disks called platelets in the blood.  Platelets clump together at the site of tissue injury (like a cut, or on the inside of a damaged blood vessel).   You can think of a platelet clump as the first step in scab formation.  Although a platelet clump sealing off a cut on your hand is very useful, a platelet clump on the inside of a coronary artery can wreak havoc and cause a heart attack.  Aspirin, clopidrogel (Plavix), and ticlopidine (Ticlid) are common examples of antiplatelet agents. 

When are Antiplatelet Medications Indicated?

Antiplatelet therapy is used frequently in the care of patients with atherosclerosis (plaque build up, “hardening of the arteries”) and in those patients at increased risk for atherosclerosis:

• Acute myocardial infarction (heart attack) Heart attacks occur when the innermost lining inside a coronary artery breaks down or is injured.  This injury provides a stimulus for a platelet clump to form in that spot.  If the clump is big enough, it may inadvertently block blood flow beyond it, cutting off vital oxygen and nutrients to heart muscle.  Patients who have suffered a heart attack are routinely placed on antiplatelet medications as soon as possible.
• Unstable angina pectoris: Angina refers to chest pain secondary to an inadequate blood supply to heart muscle.  Usually, this is a consequence of severe blockage(s) being present inside the heart arteries. Because these blockages usually build up slowly over time, angina severity worsens slowly over time as well.  This is called “stable angina pectoris”.  Occasionally, a patient will experience a break down in the innermost lining inside a coronary artery which will result in a platelet plug forming, but the plug will not be big enough to completely block flow beyond it.  It will, however, be big enough to mimic the effects of a severe blockage.  Under these circumstances, the patient will experience a sudden change in their symptoms, including marked limitations with exertion and even chest pain at rest.  This is called “unstable angina pectoris”.  Because a platelet clump is central to the development of unstable symptoms, patients diagnosed with unstable angina will also be placed on antiplatelet medications. 
• Stents:  When a stent is placed inside an artery, some injury at the site of implatantion is inevitable.  Therefore patients who have had a stent placed are at increased risk of a platelet plug forming inside the affected artery.  All stents (regardless of type, size or whether they are “bare metal” or “coated”) have some risk of platelet clumping, particularly in the first days and weeks after they have been placed. For stents without drug coating (bare metal stents), aggressive antiplatelet medication is typically prescribed for 1 month following stent implantation. Recent research has shown that drug-coated stents may be associated with a longer term risk of clotting. Therefore, the latest recommendations call for patients who receive drug-coated stents to continue aggressive antiplatelet medication for at least 1 year if they are not at high risk for bleeding.  “Aggressive antiplatelet medication” means using more than one antiplatelet drug at the same time (ie. not just aspirin but aspirin plus clopidrogel or ticlopidine).
• Coronary artery disease:  Anyone who has been diagnosed with coronary artery disease (CAD) or who is at high risk for CAD is usually placed on lifetime aspirin therapy as a prophylactic measure against the occurrence of a heart attack.
• Diabetes, peripheral vascular disease:  Patients with diabetes or those with blockages in the arm, leg or body arteries are at such an increased risk of developing a heart attack or stroke that antiplatelet agents are frequently prescribed as a purely prophylactic measure.
• Stroke: A stroke occurs if brain tissue is deprived of blood and oxygen for too long. Permanent damage can occur. A stroke might happen because a platelet clump forms inside one of the brain arteries and prevents blood from flowing beyond it (the exact same mechanism as for heart attack).  Antiplatelet medications would be prescribed.

When are Anticoagulants Indicated?

A blood clot that forms inside the heart can lead to devastating consequences.  A blood clot that forms inside the left heart chambers can cause a stroke.  

• Reduced heart function:  When the pumping capacity of the heart is severely reduced, blood does not move through the heart chambers very quickly.  As a result that blood can stagnate and congeal.  When patients have severely reduced heart pumping function, anticoagulants may be prescribed to prevent blood clots from forming inside the heart (to prevent a stroke). 
• After a heart attack:  Sometimes, a section of heart muscle is so damaged by a heart attack that it no longer contracts (squeezes).  This can lead to the formation of an aneurysm (outpouching) of that damaged heart muscle.  In the aneurismal area, blood could also stagnate and result in the formation of a clot.  So even if the overall heart pumping function is not markedly reduced, function in a segment of the heart is reduced enough to potentially cause problems.  Anticoagulants may be prescribed in this circumstance as well, again to prevent a stroke.
• Atrial fibrillation:  Atrial fibrillation is an abnormal heart rhythm which interferes with the ability of the atria (the two top chambers of the heart) from contracting properly.  Even if the ventricles (the main muscular pumping chambers of the heart) are functioning properly, blood can stagnate in the atria and form clots.  This could also put a person at risk for stroke, and many patients with atrial fibrillation are placed on anticoagulants.
• Pulmonary embolism: When blood stagnates in the veins of a leg (due to prolonged immobility for example) or in the veins of the pelvis (after pelvic surgery for instance) clots can form in the areas of stagnation.  If those clots break loose and travel up to the right heart and then to the lungs, they can damage lung tissues.  The blood clot traveling into the lungs is called a “pulmonary embolus”.  This can be a life threatening emergency.  Warfarin is frequently used to prevent blood clots from forming in the legs, especially if immobility is expected (like around the time of knee or hip surgery.
• Stroke: A stroke occurs if brain tissue is deprived of blood and oxygen for too long. Permanent damage can occur. As already mentioned, a stroke might happen because a platelet clump forms inside one of the brain arteries and prevents blood from flowing beyond it (the exact same mechanism as for heart attack).  A stroke might also happen if a blood clot that is present inside the heart chambers breaks off and travels upstream to the brain.  In the first scenario, antiplatelet medications would be prescribed.  With the latter scenario, anticoagulants would be more appropriate.

Who Should Avoid Antithrombotic Medications?

People with a known allergy to a drug should not take it.  Stomach upset from aspirin is NOT an allergy (though may be uncomfortable enough that aspirin be avoided).

Women who are pregnant or are considering becoming pregnant should talk to their physician about the use of anticoagulants and antiplatelet medications because of possible serious effects on the fetus. Anticoagulants and antiplatelet medications can pass into breast milk, although it is unknown if this is harmful to babies. Women who are nursing should discuss this with their physician.

Patients who are prone to bodily injury (those with a history of falls for example) are not good candidates for anticoagulant therapy.  However, this group is usually able to tolerate antiplatelet medications without undue risk.

Risk Factors for Possible Complications

Anticoagulants

The following conditions may complicate the use of anticoagulants. If you have any of the following conditions, you should discuss them with your doctor: 

• Diabetes mellitus
• Severe allergies
• Hypertension (high blood pressure)
• Inherited blood clotting disorders
• Cancer
• A history of internal bleeding
• Liver disease
• Kidney disease

Lifestyle factors can also affect anticoagulant therapy.  Because the effect of warfarin (Coumadin) is blunted by vitamin K, vitamin K consumption may interfere with the potency of a warfarin dose.  Green leafy vegetables such as broccoli, spinach, and lettuce contain vitamin K. Eating relatively consistent amounts of these vegetables is important.  Cranberry juice and grapefruit juice may also interact with warfarin.

For a multitude of reasons, patients should limit alcohol consumption to no more than 1 drink daily when using anticoagulants. 

Antiplatelet Medications

Patients should use antiplatelet medications with caution if they have liver disease, a history of stomach ulcers, or other bleeding disorders.

In addition, because of possible drug interactions, patients should consult with their physician if they are also taking nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, or if they are already taking anticoagulants. 

Pre-Treatment Guidelines

Because of possible interactions with other drugs, you should report any other medications or supplements that you are taking to a physician prior to commencing antithrombotic treatment.

You should bring the following information with you when discussing antithrombotic therapy with your physician: 

• A list of all prescription medications you take, including the name of the drug and the dose
• A list of  of all over-the-counter drugs, vitamins, and herbal supplements that you are taking;
• A list of side effects experienced from any prescription drugs; and
• A list of previous adverse reactions or allergies to any drugs.

What To Expect

Anticoagulants

Anticoagulants may be given in oral form or injected. Warfarin is the most commonly prescribed anticoagulant and is taken by mouth.  Heparin is frequently used in the hospital and is injected.  Because too much or too little clotting can be dangerous, anticoagulants like heparin and warfarin need to be closely monitored to ensure that the patient is receiving the proper dosage. Patients on these medications will undergo regular blood tests, called protime tests, or international normalized ratio tests (INR), which measure the time it takes their blood to clot. Based on the results, the physician can increase or reduce the dosage.

Patients taking anticoagulants should report any of the following to a physician immediately:

• Blood in urine or stools
• Nosebleeds
• Unexplained fever
• Unusual bruising or bleeding from cuts or wounds
• Unusually heavy or unexpected menstrual bleeding
• Abdominal or stomach pain or swelling
• Back pain or backaches
• Coughing up blood

Antiplatelet Medications

Antiplatelet agents are primarily taken in pill form.  Aspirin is the most common antiplatelet medication prescribed.  Clopidrogel (Plavix) and ticlopidine (Ticlid) are other antiplatelet agents that are used alone or in combination with aspirin.

Potential side effects of antiplatelet medications include:

• Stomach pain
• Heartburn or indigestion
• Nausea or vomiting
• Fatigue
• Muscle aches
• Headache
• A change in bowel habits
• A rash

Severe side effects from antiplatelet agents are rare.  Patients taking antiplatelet medications should report any of the following to a physician immediately: 

• Loss of hearing or vision problems
• Red or purple spots on the skin
• Blood in the urine or stools
• Unusual bleeding
• Confusion or convulsions (seizures)
• Severe diarrhea
• Severe nausea or vomiting, or vomiting blood
• Difficulty in swallowing
• Dizziness or lightheadedness
• Unexplained fever

Post-Treatment Guidelines and Care

Antithrombotic drugs require medical supervision. You should not start or stop taking these medications without first consulting a physician. Additionally, you should ask questions or request written instructions if you do not understand how to follow the treatment plan. Not taking or missing doses of a prescribed drug treatment may not relieve or treat the underlying disease, and can result in potentially life-threatening occurrences such as stroke or heart attack.

Antithrombotic medications increase the risk for bleeding, and other healthcare providers may instruct you to stop them before a medical procedure, such as dental or other surgery. You should check with the physician who prescribed the antithrombotic medications regarding when to stop the medications, when to resume them after the procedure, and if any additional monitoring or testing will be required.  If you have been prescribed antiplatelet medications following stent placement, you should contact your cardiologist prior to discontinuing these medications.

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