Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, is the interruption of blood supply to part of the heart, causing some heart cells to die. This is most commonly due to occlusion (blockage) of a coronary artery following the rupture of a vulnerable atherosclerotic plaque, which is an unstable collection of lipids and white blood cells (especially macrophages) in the wall of an artery. The resulting ischemia (restriction in blood supply) and oxygen shortage, if left untreated for a sufficient period of time, can cause damage or death of heart muscle tissue.
Heart attacks are the leading cause of death for both men and women all over the world. Important risk factors are previous cardiovascular disease (such as angina, a previous heart attack or stroke), older age (especially men over 40 and women over 50), tobacco smoking, high blood levels of certain lipids and low levels of high density lipoprotein (HDL), diabetes, high blood pressure, obesity, chronic kidney disease, heart failure, excessive alcohol consumption, the abuse of certain drugs (such as cocaine and methamphetamine), and chronic high stress levels.
Immediate treatment for suspected acute myocardial infarction includes oxygen, aspirin, and sublingual glyceryl trinitrate (colloquially referred to as nitroglycerin and abbreviated as NTG or GTN). Pain relief is also often given, classically morphine sulfate.
The phrase "heart attack" is sometimes used incorrectly to describe sudden cardiac death, which may or may not be the result of acute myocardial infarction. A heart attack is different from, but can be the cause of cardiac arrest, which is the stopping of the heartbeat, and cardiac arrhythmia, an abnormal heartbeat. It is also distinct from heart failure, in which the pumping action of the heart is impaired; severe myocardial infarction may lead to heart failure, but not necessarily.
SYMPTOMS
Chest pain is a major symptom of heart attack. You may feel the pain in only one part of your body, or it may move from your chest to your arms, shoulder, neck, teeth, jaw, belly area, or back.
The pain can be severe or mild. It can feel like:
· A tight band around the chest
· Bad indigestion
· Something heavy sitting on your chest
· Squeezing or heavy pressure
The pain usually lasts longer than 20 minutes. Rest and a medicine called nitroglycerin do not completely relieve the pain of a heart attack.
Other symptoms of a heart attack include:
· Anxiety
· Cough
· Fainting
· Light-headedness, dizziness
· Nausea or vomiting
· Palpitations (feeling like your heart is beating too fast)
· Shortness of breath
· Sweating, which may be extreme
Some people (the elderly, people with diabetes, and women) may have little or no chest pain. Or, they may experience unusual symptoms (shortness of breath, fatigue, weakness). Approximately one quarter of all myocardial infarctions are silent, without chest pain or other symptoms.
MANAGEMENT
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.
Oxygen, aspirin, glyceryl trinitrate (nitroglycerin) and analgesia are usually administered as soon as possible. Morphine is classically used if nitroglycerin is not effective due to its ability to dilate blood vessels, which may aid in blood flow to the heart as well as relieve pain. Morphine may also cause hypotension (usually in the setting of hypovolemia), and should be avoided in the case of right ventricular infarction.
Aspirin and streptokinase have been shown to markedly reduce mortality. Streptokinase activates plasminogen, which is fibrinolytic.
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.
Cocaine associated myocardial infarction should be managed in a manner similar to other patients with acute coronary syndrome except beta blockers should not be used and benzodiazepines should be administered early.
The treatment itself may have complications. If attempts to restore the blood flow are initiated after a critical period of only a few hours, the result may be a reperfusion injury instead of amelioration.
PREVENTION
To prevent a heart attack:
· Keep your blood pressure, blood sugar, and cholesterol under control.
· Don't smoke.
· Consider drinking 1 to 2 glasses of alcohol or wine each day. Moderate amounts of alcohol may reduce your risk of cardiovascular problems. However, drinking larger amounts does more harm than good.
· Eat a low-fat diet rich in fruits and vegetables and low in animal fat.
· Eat fish twice a week. Baked or grilled fish is better than fried fish. Frying can destroy some of the health benefits.
· Exercise daily or several times a week. Walking is a good form of exercise. Talk to your doctor before starting an exercise routine.
· Lose weight if you are overweight.
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. β- Blockers decrease mortality and morbidity. They also improve symptoms of cardiac ischemia in NSTEMI.
· ACE inhibitor therapy should be commenced 24-8 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.[84] 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.
