Blood clots often play a prominent role in cardiovascular disease. In a healthy person, specialized blood cells called platelets have the capacity to form a clot in response to injury, as a way to limit loss of blood. How- ever, in a person with cardiovascular disease, a blood clot that forms abnormally in an artery leading to the heart can cause a heart attack (myocardial infarction), and one that travels to an artery leading to the brain can cause a stroke .
In a person with coronary artery disease, the plaque that builds up in the coronary arteries can be destabilized by factors such as high blood pressure, high blood sugar, or the toxic ingredients in tobacco. A type of plaque called soft plaque (see page 154) can rupture, and the platelets respond as they would to an injury, by forming a clot over the damaged area. A blood clot in an already clogged artery can block the blood ?ow completely, causing a heart attack.

Thrombolytic Agents

Thrombolytic agents (“clot busters”) dissolve clots in the arteries, restoring blood ?ow to heart tissue. Their use has substantially reduced disability and death from heart attacks and strokes. These drugs (including streptokinase, urokinase, and tissue plasminogen activator, or tPA, used for strokes) can be given as soon as you have been diagnosed as having a heart attack or stroke, either because of your symptoms or in response to the results of an electrocardiogram. If you get to a hos- pital immediately and the thrombolytics go to work within 4 to 6 hours of the onset of your symptoms, you are very likely to have only minimal damage to your heart function. If too much time passes before the thrombolytics are given, the damage is already done and restoring blood ?ow will not revive the tissue.
Emergency department personnel administer thrombolytic agents intravenously. The most serious drawback of these drugs is that they do not distinguish an abnormal blood clot from a useful one. You cannot receive them if you have a condition that might cause a bleeding prob- lem, such as a stomach ulcer, a recent injury or surgical procedure, or a recent stroke.

Antiplatelets

Antiplatelet drugs interfere with platelet function and the formation of blood clots. Platelets are the elements within the blood that stick together and form clots. Some drugs (such as aspirin) are used to prevent clot formation in people at high risk of heart attack. Some types are given if you are having uncontrolled chest pain (unstable angina) or during or immediately after a heart attack to reduce recur- rence. Antiplatelets are also given after an angioplasty, insertion of a stent, or bypass surgery to prevent clots from forming inside the vessel.
Clotting is a chemically complex process, and different antiplatelet agents disrupt speci?c stages of clot formation. They are used alone or in combination to treat different types of heart attacks or under various circumstances.
Aspirin is the most familiar antiplatelet drug. Because it is inexpensive, effective, and easy to take by mouth, it is often the first treatment given at the onset of heart attack symptoms, even before you get help from emergency medical services .

Taking aspirin right after a heart attack may improve survival rates by as much as 20 percent. At the hospital, other antiplatelets (such as clopidogrel or glycoprotein inhibitors) may also be given, either orally or intra- venously. Doctors are learning more all the time about how to use these drugs to bene?t more patients.
Because all antiplatelet drugs interfere with normal blood clotting, the main risk of taking them is bleed- ing. The bleeding is usually very minor, such as skin bruising or nosebleed. In people who are being treated in a hospital for heart attacks, the most common sites of bleeding are where catheters have been inserted— for example, in the groin where an access catheter is inserted for angioplasty. This type of bleeding is usu- ally easily controlled by applying pressure to the site. Rarely, bleeding occurs from another source such as a stomach ulcer.

Anticoagulants

Anticoagulants are used to prevent the forming or growth of a blood clot by interfering with the clotting process. But they do not dissolve an existing blood clot, as a thrombolytic agent does. Although they are commonly called blood thinners, they do not really thin your blood; they just reduce the blood’s ability to clot. These agents, such as war- farin, are stronger than the antiplatelet medications. Therefore, your doctor’s of?ce will need to do careful and frequent monitoring—in the form of a blood test—of the clotting factor in your bloodstream. This is vital to prevent bleeding complications and to ensure adequate clot- ting effect.
If you have had a heart attack, you are at greater risk of developing a blood clot near the site of a clot that was dissolved by a thrombolytic agent. If severe damage occurred in your left ventricle, a clot could also form there, where it can cause serious complications, and your doctor may prescribe warfarin. Also, if you are in bed for a long time after a heart attack, blood clots can develop in your legs. Anticoagulants help prevent all these possibilities.
Heparin, which is administered intravenously in the hospital, is a powerful and well-established anticoagulant for heart attack patients. If you undergo a procedure such as angioplasty, heparin will be adminis- tered to prevent clots from developing at the site of the procedure. The dosage must be carefully adjusted and its use must be monitored closely. A new type of heparin, called low-molecular-weight heparin, has been developed that is injected and does not require as much monitoring. Any form of heparin can cause unintended bleeding as a side effect. After an angioplasty, stronger clot-preventing medications such as clopidogrel may be prescribed.

Aspirin for Heart Disease

For some people, taking aspirin regularly is a means of preventing the recurrence of certain types of heart symptoms or events. Your doctor may recommend aspirin if you have had a heart attack, a transient ischemic attack , or an ischemic stroke , or if you have had trouble with recurring angina (chest pain; ). Some studies even suggest that aspirin may help prevent a ?rst occurrence of some of these events. Aspirin helps ensure adequate blood ?ow and may reduce the likelihood of clot formation. Aspirin works by slowing down the work of platelets in your bloodstream; when platelets are less sticky, clots are less likely to form. Aspirin may also help protect against the in?ammation of arteries that occurs with atherosclerosis and may help prevent heart attacks in people with diabetes.
Taking aspirin regularly is different from taking it occasionally for something like a headache, and it poses some risks. You should not start taking aspirin for your heart without talking to your doctor ?rst. In evaluating whether aspirin ther- apy is right for you, your doctor will consider your medical and family history; other drugs you may take, including vitamin or herbal supple- ments; allergies; the likelihood of certain side effects such as stomach bleeding; the relative risk versus bene?t; and what dose is right. If you have some medical conditions such as bleeding disorders, asthma, ulcers, or kidney disease, aspirin may not be a safe choice.
If your doctor recommends aspirin, it’s important to take it exactly as he or she directs so that you get the desired bene?t, and the chance of side effects is minimized. The instructions on the aspirin bottle are intended for general use, not for heart patients, so do not follow them. But read the label on the product you buy to be sure that it contains aspirin in the correct amount recommended by your doctor. Check the drug facts label for “active ingredients: aspirin” or “acetylsalicylic acid.” If you experience any adverse effects after you start taking aspirin—such as stomach pains, indigestion, cramps, or black tarry stools (a sign of internal bleeding)—tell your doctor immediately.

WARNING!

Aspirin during a Heart Attack or a Stroke

If you are having warning signs of a heart attack (such as chest pain), the most important thing to do is to call 911 or the emergency number for your area. Do not take an aspirin to see if it will relieve the pain before calling 911. Although aspirin will not treat a heart attack by itself, many experts recom- mend chewing one adult aspirin if you think you may be having a heart attack. Of course, if you are allergic to aspirin or have a condition that prevents you from taking aspirin, then wait until you get advice from a doctor. The 911 emergency operator may ask you about allergies and then recommend that you take an aspirin, or the emergency medical technicians may give you one in addition to other treatments. A single adult aspirin may reduce the chance of dying from a heart attack by about 20 percent, making it one of the most cost-effective life-saving measures in medicine.
If you or a family member is having a stroke, do not take or administer an aspirin, because not all strokes are caused by blood clots. The emergency department is best qualified to make a judgment about whether aspirin might be effective for the particular type of stroke.