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A heart attack is a medical emergency which demands both immediate attention and activation of the emergency medical services. The ultimate goal of the management in the acute phase of the disease is to salvage as much myocardium as possible and prevent further complications. As time passes, the risk of damage to the heart muscle increases; hence the phrase that in myocardial infarction, "time is muscle", and time wasted is muscle lost.
The treatments itself may have complications. If attempts to restore the blood flow are initiated after a critical period of only a few hours, the result is reperfusion injury instead of amelioration. Other treatment modalities may also cause complications; the use of antithrombotics for example carries an increased risk of bleeding.
First line
Oxygen, aspirin, glyceryl trinitrate (nitroglycerin) and analgesia (usually morphine, hence the popular mnemonic MONA, morphine, oxygen, nitro, aspirin) are administered as soon as possible. In many areas, first responders can be trained to administer these prior to arrival at the hospital.
Of the first line agents, only aspirin has been proven to decrease mortality.
Once the diagnosis of myocardial infarction is confirmed, other pharmacologic agents are often given. These include beta blockers, anticoagulation (typically with heparin), and possibly additional antiplatelet agents such as clopidogrel. These agents are typically not started until the patient is evaluated by an emergency room physician or under the direction of a cardiologist. These agents can be used regardless of the reperfusion strategy that is to be employed. While these agents can decrease mortality in the setting of an acute myocardial infarction, they can lead to complications and potentially death if used in the wrong setting.
Reperfusion
The concept of reperfusion has 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 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 anticoagulated. 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.
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
Main article: Thrombolysis
Thrombolytic therapy is indicated for the treatment of STEMI if the drug can be administered within 12 hours of the onset of symptoms, the patient is eligible based on exclusion criteria, and primary PCI is not immediately available. The effectiveness of thombolytic 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 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 good 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. 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.
Percutaneous coronary intervention
The benefit of prompt, expertly performed primary percutaneous coronary intervention over thrombolytic therapy for acute ST elevation myocardial infarction is now well established. Logistic and economic obstacles seem to hinder a more widespread application of percutaneous coronary intervention (PCI) via cardiac catheterization, although the feasibility of regionalized PCI for STEMI is currently being explored in the United States. The use of percutaneous coronary intervention as a therapy to abort a myocardial infarction is known as primary PCI. The goal of primary PCI is to open the artery as soon as possible, and preferably within 90 minutes of the patient presenting to the emergency room. This time is referred to as the door-to-balloon time. Few hospitals can provide PCI within the 90 minute interval, which prompted the American College of Cardiology (ACC) to launch a national Door to Balloon (D2B) Initiative in November of 2006. Over 800 hospitals have joined the D2B Alliance as of March 16, 2007.
The current guidelines in the United States restrict primary PCI to hospitals with available emergency bypass surgery as a backup, but this is not the case in other parts of the world.
Primary PCI involves performing a coronary angiogram to determine the anatomical location of the infarcting vessel, followed by balloon angioplasty (and frequently deployment of an intracoronary stent) of the thrombosed arterial segment. In some settings, an extraction catheter may be used to attempt to aspirate (remove) the thrombus prior to balloon angioplasty. While the use of intracoronary stents do not improve the short term outcomes in primary PCI, the use of stents is widespread because of the decreased rates of procedures to treat restenosis compared to balloon angioplasty.
Adjuvant therapy during primary PCI include intravenous heparin, aspirin, and clopidogrel. The use of glycoprotein IIb/IIIa inhibitors are often used in the setting of primary PCI to reduce the risk of ischemic complications during the procedure. Due to the number of antiplatelet agents and anticoagulants used during primary PCI, the risk of bleeding associated with the procedure are higher than during an elective PCI.
Coronary artery bypass surgery
Despite the guidelines, emergency bypass surgery for the treatment of an acute myocardial infarction (MI) is less common then PCI or medical management. In an analysis of patients in the U.S. National Registry of Myocardial Infarction (NRMI) from January 1995 to May 2004, the percentage of patients with cardiogenic shock treated with primary PCI rose from 27.4% to 54.4%, while the increase in CABG treatment was only from 2.1% to 3.2%.
Emergency coronary artery bypass graft surgery (CABG) is usually undertaken to simultaneously treat a mechanical complication, such as a ruptured papillary muscle, or a ventricular septal defect, with ensueing cardiogenic shock. In uncomplicated MI, the mortality rate can be high when the surgery is performed immediately following the infarction. If this option is entertained, the patient should be stabilized prior to surgery, with supportive interventions such as the use of an intra-aortic balloon pump. In patients developing cardiogenic shock after a myocardial infarction, both PCI and CABG are satisfactory treatment options, with similar survival rates.
Coronary artery bypass surgery involves an artery or vein from the patient being implanted to bypass narrowings or occlusions on the coronary arteries. Several arteries and veins can be used, however internal mammary artery grafts have demonstrated significantly better long-term patency rates than great saphenous vein grafts. In patients with two or more coronary arteries affected, bypass surgery is associated with higher long-term survival rates compared to percutaneous interventions. In patients with single vessel disease, surgery is comparably safe and effective, and may be a treatment option in selected cases. Bypass surgery has higher costs initially, but becomes cost-effective in the long term. A surgical bypass graft is more invasive initially but bears less risk of recurrent procedures (but these may be again minimally invasive).
Monitoring for arrhythmias
Additional objectives are to prevent life-threatening arrhythmias or conduction disturbances. This requires monitoring in a coronary care unit and protocolised administration of antiarrhythmic agents. Antiarrhythmic agents are typically only given to individuals with life-threatening arrhythmias after a myocardial infarction and not to suppress the ventricular ectopy that is often seen after a myocardial infarction.
Rehabilitation
Cardiac rehabilitation aims to optimize function and quality of life in those afflicted with a heart disease. This can be with the help of a physician, or in the form of a cardiac rehabilitation program.
Physical exercise is an important part of rehabilitation after a myocardial infarction, with beneficial effects on cholesterol levels, blood pressure, weight, stress and mood. Some patients become afraid of exercising because it might trigger another infarct. Patients are stimulated to exercise, and should only avoid certain exerting activities such as shovelling. Local authorities may place limitations on driving motorised vehicles. Some people are afraid to have sex after a heart attack. Most people can resume sexual activities after 3 to 4 weeks. The amount of activity needs to be dosed to the patients possibilities.
Secondary prevention
The risk of a recurrent myocardial infarction decreases with strict blood pressure management and lifestyle changes, chiefly smoking cessation, regular exercise, a sensible diet for patients with heart disease, and limitation of alcohol intake.
Patients are usually commenced on several long-term medications post-MI, with the aim of preventing secondary cardiovascular events such as further myocardial infarctions, congestive heart failure or cerebrovascular accident (CVA). Unless contraindicated, such medications may include:
* Antiplatelet drug therapy such as aspirin and/or clopidogrel should be continued to reduce the risk of plaque rupture and recurrent myocardial infarction. Aspirin is first-line, owing to its low cost and comparable efficacy, with clopidogrel reserved for patients intolerant of aspirin. The combination of clopidogrel and aspirin may further reduce risk of cardiovascular events, however the risk of hemorrhage is increased.
* Beta blocker therapy such as metoprolol or carvedilol should be commenced. These have been particularly beneficial in high-risk patients such as those with left ventricular dysfunction and/or continuing cardiac ischaemia. ?-Blockers decrease mortality and morbidity. They also improve symptoms of cardiac ischemia in NSTEMI.
* ACE inhibitor therapy should be commenced 24–48 hours post-MI in hemodynamically-stable patients, particularly in patients with a history of MI, diabetes mellitus, hypertension, anterior location of infarct (as assessed by ECG), and/or evidence of left ventricular dysfunction. ACE inhibitors reduce mortality, the development of heart failure, and decrease ventricular remodelling post-MI.
* Statin therapy has been shown to reduce mortality and morbidity post-MI. The effects of statins may be more than their LDL lowering effects. The general consensus is that statins have plaque stabilization and multiple other ("pleiotropic") effects that may prevent myocardial infarction in addition to their effects on blood lipids.
* The aldosterone antagonist agent eplerenone has been shown to further reduce risk of cardiovascular death post-MI in patients with heart failure and left ventricular dysfunction, when used in conjunction with standard therapies above.
* Omega-3 fatty acids, commonly found in fish, have been shown to reduce mortality post-MI. While the mechanism by which these fatty acids decrease mortality is unknown, it has been postulated that the survival benefit is due to electrical stabilization and the prevention of ventricular fibrillation. However, further studies in a high-risk subset have not shown a clear-cut decrease in potentially fatal arrhythmias due to omega-3 fatty acids.
[edit] New therapies under investigation
Patients who receive stem cell treatment by coronary artery injections of stem cells derived from their own bone marrow after a myocardial infarction (MI) show improvements in left ventricular ejection fraction and end-diastolic volume not seen with placebo. The larger the initial infarct size, the greater the effect of the infusion. Clinical trials of progenitor cell infusion as a treatment approach to ST elevation MI are proceeding.
There are currently 3 biomaterial and tissue engineering approaches for the treatment of MI, but these are in an even earlier stage of medical research, so many questions and issues need to be addressed before they can be applied to patients. The first involves polymeric left ventricular restraints in the prevention of heart failure. The second utilizes in vitro engineered cardiac tissue, which is subsequently implanted in vivo. The final approach entails injecting cells and/or a scaffold into the myocardium to create in situ engineered cardiac tissue.
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The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other
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