Clinical controversies surrounding thrombolytic therapy in acute myocardial infarction

Article Abstract:

Some of the controversies surrounding thrombolytic (clot-dissolving) treatment for acute myocardial infarction (AMI; heart attack) are: how long after onset of symptoms of a heart attack therapy is still feasible, which drug or drug combination is best, and how the elderly should be treated. However, at this time there seems to be no question that thrombolytic therapy saves lives. Studies indicate that patients who begin therapy six hours or more after the first symptoms of AMI are helped by thrombolytic therapy. Also, drug treatment of inferior myocardial infarction seems to be useful, although the right coronary artery does not seem to respond as well to therapy as the left one. Recent data suggest that the size of the damaged area is more predictive of outcome than the location. As for thrombolytic therapy in elderly patients, who are more likely to have complications and side effects, it is clinically more reasonable to judge a patient's mental and physical condition rather than age when evaluating treatment options. The first generation of thrombolytic agents includes streptokinase and urokinase. The advantage of urokinase is that it is less likely than streptokinase to cause allergic reactions, and the effects appear to be equivalent, although no mortality trials have been done on urokinase. The second generation began in 1984 with tissue plasminogen activator (TPA), and also includes anisoylated plasminogen-streptokinase activator complex (APSAC), and prourokinase or single-chain urokinase plasminogen activator (scu-PA). Its rapid effect seems to give TPA an advantage, but easier administration of APSAC and a longer half-life (the time it takes for half the dosage to be used by the body) make APSAC the better choice in some circumstances. Trials with scu-PA show more rapid reperfusion (restored blood flow) but the difference disappears within 24 hours. Combinations and variants of these drugs make up the third generation, which, it is hoped, will act more specifically on the clot over a longer time, and with greater safety than is now possible. The range of cardiovascular problems treated with thrombolytic therapy is expanding. The implications are that every emergency care unit should be prepared to diagnose and treat heart attack patients with thrombolytic drugs, using a standard protocol designed to ensure proper and rapid assessment and administration of therapy. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Thrombolytic therapy: then and now

Article Abstract:

Thrombolytic agents are drugs that are used to dissolve blood clots. Clotted blood is held together by a protein called fibrin. Thrombolytic agents dissolve blood clots by breaking down or degrading fibrin. These agents were developed over 60 years ago, but have only recently been proven to be effective in opening clogged blood vessels in patients. Acute myocardial infarction (AMI), a heart attack, occurs when blood vessels in the heart suddenly become blocked or clogged with blood clots. Streptokinase (SK), urokinase (UK), recombinant tissue plasminogen activator (t-PA), and anistreplase (APSAC) are the four thrombolytic agents that have been approved for treating patients with AMI. All four agents have been shown to be effective in opening clogged blood vessels and in reducing mortality in patients with AMI. However, it is not clear which agent is the most effective. Recent studies have shown that aspirin, when given in combination with a thrombolytic agent, can reduce mortality by an additional 50 percent. Based on these findings, the combination of aspirin and a thrombolytic agent has become the routine therapy for patients with AMI. In most cases, treatment with aspirin is continued for the rest of the patient's life to protect against a second infarction. In cases where thrombolytic agents are not completely effective in reopening clogged blood vessels, a procedure called percutaneous transluminal coronary angioplasty (PTCA) may be beneficial. This technique uses a balloon-tipped catheter to mechanically open or enlarge a plugged blood vessel. At the present time, thrombolytic therapy is the treatment of choice for patients with AMI. The most serious side effects of thrombolytic agents are bleeding and stroke. However, the incidence of stroke following treatment is very low. Studies are now being performed to determine if lower doses of drug can reduce the incidence of bleeding. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Clinical management of patients receiving thrombolytic therapy

Article Abstract:

During a heart attack, an acute myocardial infarction (AMI), the normal flow of blood and the amount of oxygen delivered to the heart muscle are reduced. This occurs when blood vessels in the heart become blocked or clogged. Since tissues cannot survive without oxygen, portions of the heart muscle may die following AMI if treatment is not started immediately. In many cases, AMI is accompanied by severe chest pain, nausea, vomiting, and anxiety. Thrombolytic agents are drugs that dissolve blood clots and are used to treat AMI. Streptokinase, tissue plasminogen activator, and anistreplase are thrombolytic agents that have proven to be effective in treating patients following AMI. The goals of thrombolytic therapy are to open clogged blood vessels, so that normal blood flow can be restored (reperfusion), and to limit damage to the heart muscle. Reocclusion (the reclosing of a blood vessel that was opened during treatment) occurs in 10 to 20 percent of patients treated with thrombolytic agents. Aspirin is used in addition to thrombolytic agents to help keep the blood vessels open. Treatment with aspirin should be started as soon as AMI is diagnosed and should be continued indefinitely. Nitroglycerin and drugs called beta blockers are used to minimized tissue damage in the heart muscle following AMI. Since thrombolytic agents can cause bleeding, they should not be used to treat patients with internal bleeding, recent head surgery or trauma, uncontrolled high blood pressure, or blood disorders. In spite of the side effects, thrombolytic agents remain the first choice in the treatment for AMI. (Consumer Summary produced by Reliance Medical Information, Inc.)

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