Myocardial Infarction (MI) – Signs & symptoms, Diagnosis, Management

Myocardial Infarction (MI):

Myocardial infarction (MI) or acute myocardial infarction (AMI) is the medical term for an event commonly known as a heart attack. An MI occurs when blood stops flowing properly to a part of the heart, and the heart muscle is injured because it is not receiving enough oxygen. Usually this is because one of the coronary arteries that supplies blood to the heart develops a blockage due to an unstable buildup of white blood cells, cholesterol and fat. The event is called “acute” if it is sudden and serious.
Important risks are previous cardiovascular disease, old age, tobacco smoking, abnormal blood levels of certain lipids, diabetes, high blood pressure, lack of physical activity, obesity, chronic kidney disease, excessive alcohol consumption, and the use of cocaine and amphetamines.

This video tutorial on Myocardial Infarction has been provided by: khan Academy Medicine

Pathophysiology of Myocardial Infarction:

Acute myocardial infarction refers to two subtypes of acute coronary syndrome, namely non-ST-elevated and ST-elevated MIs, which are most frequently (but not always) a manifestation of coronary artery disease. The most common triggering event is the disruption of an atherosclerotic plaque in an epicardial coronary artery, which leads to a clotting cascade, sometimes resulting in total occlusion of the artery. Atherosclerosis is the gradual buildup of cholesterol and fibrous tissue in plaques in the wall of arteries (in this case, the coronary arteries), typically over decades. Blood stream column irregularities visible on angiography reflect artery lumen narrowing as a result of decades of advancing atherosclerosis. Plaques can become unstable, rupture, and additionally promote the formation of a blood clot that occludes the artery; this can occur in minutes. When a severe enough plaque rupture occurs in the coronary vasculature, it leads to MI (necrosis of downstream myocardium).

If impaired blood flow to the heart lasts long enough, it triggers a process called the ischemic cascade; the heart cells in the territory of the occluded coronary artery die (chiefly through necrosis) and do not grow back. A collagen scar forms in their place. Recent studies indicate that another form of cell death, apoptosis, also plays a role in the process of tissue damage subsequent to MI. As a result, the patient’s heart will be permanently damaged. This myocardial scarring also puts the patient at risk for potentially life-threatening arrhythmias, and may result in the formation of a ventricular aneurysm that can rupture with catastrophic consequences.

Signs and Symptoms of Myocardial Infarction:

One-third of all myocardial infarctions occur with no prior warning signs. In the remainder, attacks of chest pain (angina) brought about by stress or exertion occur periodically for months or years prior to a heart attack. In some cases, a mild myocardial infarctions produces no symptoms and is often referred to as a “silent myocardial infarctions.”
Here are a few of the warning signs you should know:

  • Chest pain or pressure, tightness, squeezing, burning, aching, or heaviness in the chest lasting longer than 10 minutes. The pain or discomfort is usually located in the center of the chest just under the breastbone and may radiate down the arm (especially the left), up into the neck, or along the jaw line.
  • Shortness of breath.
  • Profuse sweating.
  • Dizziness.
  • Muscle weakness.
  • Nausea and vomiting.
  • A choking sensation.
  • Anxiety or a feeling of impending doom.
  • No symptoms occur with a silent heart attack.
Diagnosis of Myocardial Infarction:
  • The doctor will take a patient history and perform a physical exam. The diagnosis will sometimes be made immediately by a doctor or emergency response technician but frequently requires further blood tests to confirm.
  • An electrocardiogram, also called an ECG or EKG, may be ordered to record the heart’s electrical activity, identifying any abnormal heart rhythms that result from abnormalities in the flow of blood.
  • Blood tests may be ordered to measure the release of certain cardiac enzymes (e.g. Troponin, CK-MB and myoglobin) from damaged heart muscle into the bloodstream.
  • Coronary angiography, may be performed to evaluate possible narrowings of the coronary arteries. In this procedure a tiny catheter is inserted into an artery of a leg or arm and threaded up into the coronary arteries. A contrast material is then injected from the end of the catheter into the coronary arteries, and X-rays are taken.
Treatment for Myocardial Infarction:

Time is critical during treatment of myocardial infarctions. Most heart attack deaths result from an abnormal heart rhythm during delays in reaching the hospital. Call 911 if there is any suspicion of a heart attack. A stopped heartbeat must be restarted immediately by cardiopulmonary resuscitation (CPR) or by a device known as an electrical defibrillator. The longer the time from the onset of a heart attack to re-establishing blood flow to the heart, the more permanent heart damage can occur.

  • Chew on an aspirin at the onset of the symptoms of a myocardial infarctions as it may help break up a blood clot.
  • Thrombolytic, or clot-dissolving, drugs such as tissue plasminogen activator (tPA), streptokinase or urokinase may be injected immediately to dissolve arterial blockage. This technique is most effective within three hours of the onset of a heart attack.
  • Painkillers such as morphine or meperidine may be administered to relieve pain.
  • Nitroglycerin may be given to reduce the heart’s oxygen demands and to lower blood pressure.
  • Antihypertensive drugs such as beta-blockers, ACE inhibitors or calcium channel blockers may also be administered to lower blood pressure and to reduce the heart’s oxygen demand. Diuretics may enhance the effect of these drugs.
  • Oxygen may be administered through nasal tubes.
  • Anticoagulants such as heparin, aspirin or warfarin may be administered to reduce the risk of blood clots.
  • Digitalis glycosides, such as digoxin, may be prescribed in some cases to strengthen heart muscle contraction.
  • Dopamine or dobutamine may be administered to increase blood flow to the heart and strengthen the heartbeat.
  • Angioplasty, a procedure to open up narrowed arteries, may be performed. Using local anesthesia, the doctor will insert a catheter — a long, narrow tube with a deflated balloon at its tip — into the narrowed part of the artery. Then the balloon is inflated, compressing the plaque and enlarging the inner diameter of the blood vessel so blood can flow more easily.
  • Coronary bypass surgery may be performed to go around blocked blood vessels and restore adequate blood flow to the heart.
  • Electronic implants such as a pacemaker or a defibrillator may be attached to the heart to maintain strong, regular contractions of the heart muscle.
  • Severe cases that badly damage heart tissue may require a heart transplant.
  • During recovery, follow prevention tips given by your doctor to reduce the risk of another heart attack.
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