Myocardial infarction; MI; Acute MI
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.
Causes, incidence, and risk factors
Most heart attacks are caused by a clot that blocks one of the coronary arteries (the blood vessels that bring blood and oxygen to the heart muscle). The clot usually forms in a coronary artery that has been previously narrowed from changes related to atherosclerosis. The atherosclerotic plaque (buildup) inside the arterial wall sometimes cracks, and this triggers the formation of a clot, also called a thrombus.
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.
Occasionally, sudden overwhelming stress can trigger a heart attack.
It is difficult to estimate exactly how common heart attacks are because as many as 200,000 to 300,000 people in the United States die each year before medical help is sought. It is estimated that approximately 1 million patients visit the hospital each year with a heart attack.
The risk factors for coronary artery disease and heart attack include:
- High blood pressure
- Too much fat in your diet
- Poor blood cholesterol levels, especially high LDL (“bad”) cholesterol and low HDL (“good”) cholesterol
- Male gender
Many of the risk factors listed are related to being overweight.
Newer risk factors for coronary artery disease have been identified over the past several years, including elevated homocysteine, C-reactive protein, and fibrinogen levels. High homocysteine can be treated with folic acid supplements in the diet. Studies are still ongoing about the practical value of these new factors.
Heart attack accounts for 1 out of every 5 deaths. It is a major cause of sudden death in adults.
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 diabetics. 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.
The pain typically lasts longer than 20 minutes and is generally not fully relieved by rest or nitrioglycerine, both of which can clear pain from angina.
The pain can be intense and severe or quite subtle and confusing. It can feel like:
- squeezing or heavy pressure
- a tight band on the chest
- “an elephant sitting on [your] chest”
- bad indigestion
Other symptoms you may have either alone or along with chest pain include:
- Shortness of breath
- Lightheadedness - dizziness
- Nausea or vomiting
- Sweating, which may be profuse
- Feeling of “impending doom”
Signs and tests
During a physical examination, the doctor will usually note a rapid pulse. Blood pressure may be normal, high, or low. While listening to the chest with a stethoscope, the doctor may hear crackles in the lungs, a heart murmur, or other abnormal sounds.
The following tests may reveal a heart attack and the extent of heart damage:
- Electrocardiogram (ECG) - single or repeated over several hours
- Coronary angiography
- nuclear ventriculography (MUGA or RNV)
The following tests may show the by-products of heart damage and factors indicating you have a high risk for heart attack:
- Troponin I and troponin T
- CK and CK-MB
- Serum myoglobin
A heart attack is a medical emergency! Hospitalization is required and, possibly, intensive care. Continuous ECG monitoring is started immediately, because life-threatening arrhythmias 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.
PAIN CONTROL MEDICATIONS
Intravenous nitroglycerin or other medicines are given for pain and to reduce the oxygen requirements of the heart. Morphine and similar medicines are potent pain killers that may also be given for a heart attack.
BLOOD THINNING MEDICATIONS
If the ECG recorded during chest pain shows a change called “ST-segment elevation,” clot-dissolving (thrombolytic) therapy may be initiated within 6 hours of when chest pain began. This initial therapy will be administered as an IV infusion of streptokinase or tissue plasminogen activator, and will be followed by an IV infusion of heparin. Heparin therapy will last for 48 to 72 hours. Additionally, warfarin,taken orally, may be prescribed to prevent further development of clots.
Thrombolytic therapy is not appropriate for people who have had:
- A major surgery, organ biopsy, or major trauma within the past 6 weeks
- Recent neurosurgery
- Head trauma within the past month
- History of GI (gastrointestinal) bleed
- Brain tumor
- Stroke within the past 6 months
- Current severely elevated high blood pressure
Thrombolytic therapy can be complicated by significant bleeding.
A cornerstone of therapy for a heart attack is antiplatelet medication. Such medication can prevent the collection of platelets at a site of injury in a blood vessel wall - like a crack in an atherosclerotic plaque. Platelets collecting and accumulating is the initial event that leads to clot formation. One antiplatelet agent widely used is aspirin. Two other important antiplatelet medications are ticlopidine (Ticlid) and clopidogrel (Plavix).
- Beta-blockers (like metoprolol, atenolol, and propranolol) are used to reduce the workload of the heart.
- ACE Inhibitors (like ramipril, lisinopril, enalapril, or captopril) to prevent heart failure.
SURGERY AND OTHER PROCEDURES
Emergency coronary angioplasty may be required to open blocked coronary arteries. This procedure may be used instead of thrombolytic therapy, or in cases where thrombolytics should not be used. Often the re-opening of the coronary artery after angioplasty is ensured by implantation of a small device called a stent. Emergency coronary artery bypass surgery (CABG) may be required in some cases.
For additional information and resources, see heart disease support group.
The expected outcome varies with the amount and location of damaged tissue. The outcome is worse if there is damage to the electrical conduction system (the impulses that guide heart contraction).
Approximately one-third of cases are fatal. If the person is alive 2 hours after an attack, the probable outcome for survival is good, but may include complications.
Uncomplicated cases may recover fully; heart attacks are not necessarily disabling. Usually the person can gradually resume normal activity and lifestyle, including sexual activity.
- Arrhythmias such as ventricular tachycardia, ventricular fibrillation, heart blocks
- Congestive heart failure
- Cardiogenic shock
- Infarct extension: extension of the amount of affected heart tissue
- Pericarditis (infection around the lining of the heart)
- Pulmonary embolism (blood clot in the lungs)
- Complications of treatment (For example, thrombolytic agents increases the risk of bleeding.)
Calling your health care provider
Call your local emergency number (such as 911) if crushing chest pain or other symptoms suggestive of heart attack occur.
To prevent a heart attack:
- Control your blood pressure.
- Control total cholesterol levels. To help with cholesterol control, your doctor may prescribe a medication of the statins group (atorvastatin, simvastatin).
- Stop smoking if you smoke.
- Eat a low fat diet rich in fruits and vegetables and low in animal fat.
- Control diabetes.
- Lose weight if you are overweight.
- Exercise daily or several times a week by walking and other exercises to improve heart fitness. (Consult your health care provider first.)
If you have one or more risk factors for heart disease, talk to your doctor about possibly taking aspirin to help prevent a heart attack.
After a heart attack, follow-up care is important to reduce the risk of having a second heart attack. Often, a cardiac rehabilitation program is recommended to help you gradually return to a “normal” lifestyle. Follow the exercise, diet, and medication regimen prescribed by your doctor.
by David A. Scott, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.