Acute Myocardial Infarction

The location and extent of infarction depend upon the anatomic distribution of the occluded vessel, the presence of additional stenotic lesions, and the adequacy of collateral circulation. Thrombosis in the anterior descending branch of the left coronary artery results in infarction of the anterior left ventricle and interventricular septum. Occlusion of the left circumflex artery produces anterolateral or posterolateral infarction. Right coronary thrombosis leads to infarction of the posteroinferior portion of the left ventricle and generally involves the right ventricular myocardium if the obstruction is proximal. The arteries supplying the atrioventricular node and the sinus node more commonly arise from the right coronary; thus, atrioventricular block at the nodal level and sinus node dysfunction occur more frequently during inferior or right-sided infarctions. Individual variation in coronary anatomy and the presence of collateral vessels can make the prediction of coronary anatomy from infarct location imperfect.

Acute Myocardial Infarction occurs when myocardial ischemia exceeds a critical threshold and overwhelms myocardial cellular repair mechanisms that are designed to maintain normal operating function and hemostasis. Acute Myocardial Infarction commonly known as a heart attack. Acute Myocardial Infarction is a disease that occurs when the blood supply to a part of the heart is interrupted, causing death of heart tissue. The term myocardial infarction is derived from myocardium (the heart muscle) and infarction (tissue death due to oxygen starvation or ischemia ). The phrase "heart attack" sometimes refers to heart problems other than MI, such as unstable angina pectoris and sudden cardiac death .

Myocardial infarction can be subcategorized on the basis of anatomic, morphologic, and diagnostic clinical information. From an anatomic or morphologic standpoint, the two types of Acute Myocardial Infarction are transmural and nontransmural. Critical myocardial ischemia may occur as a result of increased myocardial metabolic demand and/or decreased delivery of oxygen and nutrients to the myocardium via the coronary circulation. A heart attack (myocardial infarction) occurs when an area of heart muscle dies or is permanently damaged because of an inadequate supply of oxygen to that area.

Cause of Acute Myocardial Infarction

Some are common causes of Acute Myocardial Infarction:

• Coronary artery vasospasm
• Ventricular hypertrophy (eg, left ventricular hypertrophy [LVH], idiopathic hypertrophic subaortic stenosis [IHSS], underlying valve disease)
• Hypoxia due to carbon monoxide poisoning or acute pulmonary disorders (Infarcts due to pulmonary disease usually occur when demand on the myocardium dramatically increases relative to the available blood supply.)
• Coronary artery emboli, secondary to cholesterol, air, or the products of sepsis
• Cocaine, amphetamines, and ephedrine
• Arteritis
• Coronary anomalies, including aneurysms of the coronary arteries
• A clot in the coronary artery interrupts the flow of blood and oxygen to the heart muscle, leading to the death of heart cells in that area.
• The damaged heart muscle loses its ability to contract, and the remaining heart muscle needs to compensate for that weakened area.
• Hypercholesterolemia and hypertriglyceridemia, including inherited lipoprotein disorders

Symptoms of Acute Myocardial Infarction

Premonitory pain - Many patients give a history of alteration in the pattern of angina preceding the time of onset of symptoms of myocardial infarction, classically the onset of angina with minimal exertion or at rest.

Pain of infarction - Unlike anginal episodes, most infarctions occur at rest, and more commonly in the early morning. The pain is similar to angina in location and radiation but it may be more severe, and it builds up rapidly or in waves to maximum intensity over a few minutes or longer. Nitroglycerin has little effect; even opioids may not relieve the pain.

Associated symptoms of Acute Myocardial Infarction

Patients may break out in a cold sweat, feel weak and apprehensive, and move about, seeking a position of comfort. They prefer not to lie quietly. Light-headedness, syncope, dyspnea, orthopnea, cough, wheezing, nausea and vomiting, or abdominal bloating may be present singly or in any combination. Some are common symptoms of Acute Myocardial Infarction:

• Chest pain behind the sternum (breastbone) is a major symptom of heart attack, but in many cases the pain may be subtle or even completely absent (called a "silent heart attack"), especially in the elderly and those with diabetes. Often, the pain radiates from your chest to your arms or shoulder; neck, teeth, or jaw; abdomen or back. Sometimes, the pain is only felt in one these other locations.
• Shortness of breath
• Cough
• Lightheadedness - dizziness
• Fainting
• Nausea or vomiting
• Sweating , which may be profuse
• Feeling of "impending doom"
• Anxiety

Treatment of Acute Myocardial Infarction

All patients with definite or suspected myocardial infarction should receive aspirin at a dose of 162 mg or 325 mg at once regardless of whether thrombolytic therapy is being considered or the patient has been taking aspirin. Chewable aspirin provides more rapid blood levels. Patients with a definite aspirin allergy may be treated with clopidogrel 300 mg, though the onset of its effectiveness will be slower. The most common treatment of Acute Myocardial Infarction:

• A heart attack is a medical emergency! Hospitalization is required and possibly intensive care. Continuous ECG monitoring is started immediately, because life-threatening arrhythmias (irregular heart beats) are the leading cause of death in the first few hours of a heart attack.
• The goals of treatment are to stop the progression of the heart attack, to reduce the demands on the heart so that it can heal, and to prevent complications.
• Medications and fluids will be inserted directly into a vein using an intravenous (IV) line. Various monitoring devices may be necessary. A urinary catheter may be inserted to closely monitor fluid status.
• Oxygen is usually given, even if blood oxygen levels are normal. This makes oxygen readily available to the tissues of the body and reduces the workload of the heart.
• A heart attack, especially because of cardiac arrhythmias , is often a life-threatening medical emergency which demands both immediate attention and activation of the emergency medical services .
• Immediate termination of arrhythmias and transport by ambulance to a hospital where advanced cardiac life support (ACLS) is available can greatly improve both chances for survival and recovery.
• The more time that passes, even 1 � 2 minutes, before medical attention is available/sought, the more likely the occurrence of both (a) life threatening arrhythmias/death and (b) more severe and permanent heart damage.

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