Acute MI

Causes and Risks:
Causes include clot formation or spasm in one of the arteries that supply the heart muscle (a coronary artery). These and other similar conditions block the supply of oxygen to an area of the heart, leading to damage or death of the cells in that area. Most often, this occurs in a coronary artery that has been narrowed from changes related to atherosclerosis . The damaged tissue results in a permanent loss of contraction of this portion of the heart muscle.

Risk factors for MI include smoking , hypertension , diabetes mellitus , high fat diet, high blood cholesterol ( LDL ) levels, obesity , male gender, age over 65, and heredity. A personal or family history of coronary artery disease , cerebrovascular disease , peripheral vascular disease , angina (particularly unstable angina ), or kidney failure requiring hemodialysis indicates increased risk for MI. Occasionally, sudden overwhelming stress can trigger an MI, but this is rare. In older persons, straining to have a bowel movement can be a risk factor.

Chest pain is the cardinal symptom of MI, but in many cases the pain may be subtle or even completely absent, especially in the elderly and diabetics. Other symptoms such as weakness , shortness of breath , nausea , or vomiting may predominate.

Acute MI occurs in approximately 2 out of 1,000 people per year. It is a major cause of sudden death in adults.

Prevention:
Control cardiac risk factors whenever possible. Control blood pressure and total cholesterol levels, reduce or avoid smoking , modify diet (increase high density lipoproteins & decrease low density lipoproteins) if necessary, control diabetes , lose weight if obese . Follow an exercise program to improve cardiovascular fitness. (Consult the health care provider first.)

After an MI, followup care is important to reduce the risk of developing a new MI. Often, a cardiac rehabilitation program is recommended to aid in gradual return to a "normal" lifestyle. Follow the exercise, diet, and/or medication regimen prescribed by your doctor.

Symptoms:

Additional symptoms that may be associated with this disease:

Note: The victim commonly denies that he or she may be having a heart attack. The person may have no symptoms ("silent attack").

Signs and Tests:
Examination often reveals a rapid pulse . Blood pressure may be normal, high, or low. Listening to the chest with a stethoscope ( auscultation ) may show crackles in the lungs, heart murmur, or other abnormal sounds.

  • An ECG , single or repeated over 2 to 3 days, often shows MI.

Indications of MI and extent of heart damage may show on the following tests:

Byproducts of heart damage and factors indicating high risk for MI may show on the following tests:

This disease may also alter the results of the following tests:



Treatment:
Acute MI is a medical emergency! Hospitalization is usually required for 1 to 14 days. Treatment may include the need for intensive care and may involve emergency surgery. ECG monitoring is begun immediately because life threatening dysrhythmias are the leading cause of death in the first few hours after an acute myocardial infarction.

The goal of treatment is to decrease the demands on the heart so that it can heal, and to prevent and treat complications. Activity may be restricted initially, then gradually increased.

An intravenous catheter will be inserted to administer emergency medications and fluids. Additional invasive monitoring devices may be used based on overall status. 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.

Diet may or may not be restricted. If diet is restricted, low salt intake, no caffeine and low fat diet are often included in the restrictions.

MEDICATIONS:
Morphine is the analgesic most often given for pain (see morphine - oral). Nitrates such as nitroglycerin are given for pain and to reduce the oxygen requirements of the heart. Beta-blockers (metoprolol and atenolol) reduce the workload of the heart. Digitalis improves the heart's pumping action. Calcium channel blockers reduce oxygen requirements in the heart muscle . Anti-arrhythmics and diuretics may also be prescribed.

Thrombolytic (clot-dissolving) therapy:
Thrombolytic therapy is usually initiated within 6 hours of the onset of chest pain . Initial therapy consists of IV infusion of a thrombolytic medication (streptokinase or tissue plasminogen activator) immediately followed by IV infusion of heparin. Heparin therapy will last for 48 to 72 hours. Additionally, oral aspirin and warfarin 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. The therapy is also not administered if there has been recent neurosurgery, head trauma within the past month, history of GI (gastrointestinal bleed) bleed, intracranial tumor , stroke within the past 6 months, or the person is currently pregnant .

Possible complications of thrombolytic therapy include bleeding and hemorrhage.

SURGERY:
Surgical interventions may be necessary. Emergency angioplasty may be required to open blocked coronary arteries. Emergency coronary artery bypass surgery ( CABG ) may be required in some cases.

Support Groups:
The stress of illness can often be helped by joining a support group where members share common experiences and problems. See heart disease - support group .

Prognosis:
The expected outcome varies with the amount and location of damaged tissue. Damage to the electrical conduction system (the impulses that guide heart contraction) worsens the outcome.

Approximately 1/3 of cases are fatal. If the victim is alive 2 hours after an attack, the probable outcome for survival is good, but may include complications. Uncomplicated cases may recover fully. MI is not necessarily disabling, and the person usually can gradually resume normal activity and lifestyle, including sexual activity.

Complications:



Call Your Healthcare Provider:
Go to the emergency room or call the local emergency number (such as 911) if crushing chest pain or other symptoms suggestive of acute MI occur.


This is a cross-sectional view of the interior of the heart. The valves, chambers, and associated vessels are labeled.



This is an illustration of the exterior of the heart. The arteries are colored blue and represent blood that is flowing into the heart. The veins are red and indicate blood flow out from the heart. The chambers are also labeled.



This picture shows damage to the heart muscle following a heart attack.