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Reperfusion therapy is medical treatment that restores blood flow through blocked arteries, typically after a heart attack (myocardial infarction). Categories of reperfusion therapy thus include clot-busting (fibrinolytic) drugs and procedures to open arteries with stents, or to graft arteries around blockages. These interventions have become so central to the modern treatment of acute myocardial infarction, that we are said to be in the reperfusion era. Patients who present with suspected acute myocardial infarction and ST segment elevation (STEMI) or new bundle branch block on the 12 lead ECG are presumed to have an occlusive thrombosis in an epicardial coronary artery. They are therefore candidates for immediate reperfusion, either with thrombolytic therapy, percutaneous coronary intervention (PCI) or when these therapies are unsuccessful, bypass surgery. Individuals without a ST segment elevation are presumed to be experiencing either unstable angina (UA) or non-ST segment elevation myocardial infarction (NSTEMI). They receive many of the same initial therapies and are often stabilized with antiplatelet drugs and anticoagulants. If their condition remains (hemodynamically) stable, they can be offered either late coronary angiography with subsequent restoration of blood flow (revascularization), or non-invasive stress testing to determine if there is significant ischemia that would benefit from revascularization. If hemodynamic instability develops in individuals with NSTEMIs, they may undergo urgent coronary angiography and subsequent revascularization. The use of thrombolytic agents is contraindicated in this patient subset, however.〔"Indications for fibrinolytic therapy in suspected acute myocardial infarction: collaborative overview of early mortality and major morbidity results from all randomised trials of more than 1000 patients. Fibrinolytic Therapy Trialists' (FTT) Collaborative Group." ''Lancet'' 1994; 343(8893): 311-22. PMID 7905143〕 The basis for this distinction in treatment regimens is that ST segment elevations on an ECG are typically due to complete occlusion of a coronary artery. On the other hand, in NSTEMIs there is typically a sudden narrowing of a coronary artery with preserved (but diminished) flow to the distal myocardium. Anticoagulation and antiplatelet agents are given to prevent the narrowed artery from occluding. At least 10% of patients with STEMI don't develop myocardial necrosis (as evidenced by a rise in cardiac markers) and subsequent Q waves on EKG after reperfusion therapy. Such a successful restoration of flow to the infarct-related artery during an acute myocardial infarction is known as "aborting" the myocardial infarction. If treated within the hour, about 25% of STEMIs can be aborted. ==Thrombolytic therapy== (詳細はthrombolytic therapy is highest in the first 2 hours. After 12 hours, the risk associated with thrombolytic therapy outweighs any benefit.〔 Because irreversible injury occurs within 2–4 hours of the infarction, there is a limited window of time available for reperfusion to work. Thrombolytic drugs are contraindicated for the treatment of unstable angina and NSTEMI〔〔"Effects of tissue plasminogen activator and a comparison of early invasive and conservative strategies in unstable angina and non-Q-wave myocardial infarction. Results of the TIMI IIIB Trial. Thrombolysis in Myocardial Ischemia." ''Circulation'' 1994; 89 (4): 1545-56. PMID 8149520〕 and for the treatment of individuals with evidence of cardiogenic shock. Although no perfect thrombolytic agent exists, an ideal thrombolytic drug would lead to rapid reperfusion, have a high sustained patency rate, be specific for recent thrombi, be easily and rapidly administered, create a low risk for intra-cerebral and systemic bleeding, have no antigenicity, adverse hemodynamic effects, or clinically significant drug interactions, and be cost effective. Currently available thrombolytic agents include streptokinase, urokinase, and alteplase (recombinant tissue plasminogen activator, rtPA). More recently, thrombolytic agents similar in structure to rtPA such as reteplase and tenecteplase have been used. These newer agents boast efficacy at least as well as rtPA with significantly easier administration. The thrombolytic agent used in a particular individual is based on institution preference and the age of the patient. Depending on the thrombolytic agent being used, adjuvant anticoagulation with heparin or low molecular weight heparin may be of benefit. With TPa and related agents (reteplase and tenecteplase), heparin is needed to maintain coronary artery patency (openness.) Because of the anticoagulant effect of fibrinogen depletion with streptokinase and urokinase treatment, it is less necessary there.〔 Intracranial bleeding (ICB) and subsequent cerebrovascular accident (CVA) is a serious side effect of thrombolytic use. The risk of ICB is dependent on a number of factors, including a previous episode of intracranial bleed, age of the individual, and the thrombolytic regimen that is being used. In general, the risk of ICB due to thrombolytic use for the treatment of an acute myocardial infarction is between 0.5 and 1 percent.〔 Thrombolytic therapy to abort a myocardial infarction is not always effective. The degree of effectiveness of a thrombolytic agent is dependent on the time since the myocardial infarction began, with the best results occurring if the thrombolytic agent is used within two hours of the onset of symptoms. If the individual presents more than 12 hours after symptoms commenced, the risk of intracranial bleed are considered higher than the benefits of the thrombolytic agent. Failure rates of thrombolytics can be as high as 20% or higher. In cases of failure of the thrombolytic agent to open the infarct-related coronary artery, the patient is then either treated conservatively with anticoagulants and allowed to "complete the infarction" or percutaneous coronary intervention (PCI, see below) is then performed. Percutaneous coronary intervention in this setting is known as "rescue PCI" or "salvage PCI". Complications, particularly bleeding, are significantly higher with rescue PCI than with primary PCI due to the action of the thrombolytic agent. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Reperfusion therapy」の詳細全文を読む スポンサード リンク
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