Myocardial Infarction

 

Myocardial infarction is the medical term for heart attack.  Heart attack means there has been death of heart cells.  This is the result of a complete blockage of one of the blood vessels that feeds the heart muscle (coronary artery).  Cell death does not occur immediately once the artery is blocked.  It takes several minutes to start the injury process and this continues for several hours unless the artery is opened, restoring blood flow.  The blockage that causes a heart attack is usually a blood clot which forms inside the vesse l in an area where there is hardening of the arteries (atherosclerosis).                                

The basic disease process which leads to myocardial infarction is atherosclerosis or hardening of the arteries.  An atherosclerotic plaque is a complex structure made up of cells, cholesterol, and other fatty substances. The plaque develops in the wall of the coronary artery and over time becomes large enough to start narrowing the blood vessel.   The pool of lipid (fat) within the plaque is covered by a thin fibrous cap.  This cap may split or fracture exposing the blood to elements within the plaque that stimulate blood clot formation.  This clotting process may be controlled by substances in the body that dissolve clots, or may lead to complete blockage of the artery.  When the artery is blocked for more than a few minutes, cell death begins.

Much of what happens depends on the size of the heart attack, where it is located in the heart and if there has been damage previously.  If the area of damage is small, recovery is usually rapid with few or no complications.  If the area of involved heart muscle is large, the loss of normal heart contraction (pumping) may cause low blood pressure, shock, or congestive heart failure.  Recovery may be prolonged and death may occur.  In the early stages of a heart attack, the heart is particularly susceptible to heart rhythm abnormalities.  Such abnormal rhythms can be quite serious and may lead to death if not treated promptly. Until the area of damage heals, the dead heart muscle is soft and weak and rupture of the heart wall can occur.  This usually results in death.  Most potential complications and death from myocardial infarction can be avoided with prompt and effective treatment.

The body heals the heart damage caused by a heart attack by forming scar tissue.  This healing process is usually complete in 4 to 8 weeks.   Hospitalization following a heart attack is usually brief in the absence of complications, or need for surgery. Often patients are home within 4 to 5 days.  Activities will be restricted for a few weeks to allow healing to occur.  Many patients will participate in a formal cardiac rehabilitation program.  Cardiac rehabilitation is a program of progressive exercise and education for people who have heart illnesses. Cardiac rehabilitation helps people to resume normal activity as quickly as possible. 

The best way to limit the size of a heart attack is to restore the flow of blood to the heart muscle as fast as possible.  There are two basic methods to do this.  Because most heart attacks are caused by clots forming within the coronary artery, dissolving the clot quickly will restore blood flow.  Drugs called thrombolytics are quite effective.  The sooner these drugs are given, the quicker the blood flow will be restored.  An alternative method involves the use of balloon angioplasty.  This involves taking the heart attack victim promptly to the cardiac cath lab in the hospital.  An angiogram is performed to show the blocked blood vessel leading to the heart attack.  Then a balloon catheter is placed across the blockage and blood flow is restored to the artery.  Often a stent is placed to create a large channel for the blood to pass through.

Smaller heart attacks, often those not producing significant abnormalities on the ECG are often treated with bed rest and blood thinners such as heparin as well as drugs to reduce the work the heart does.  These heart attacks are called non-transmural myocardial infarctions.  Before discharge, an angiogram or CT angiogram of the coronary arteries is often carried out to see if angioplasty or surgery will be necessary.

In cases when thrombolytic therapy is used, angiograms are often performed to outline the coronary anatomy to help determine if additional therapy such as angioplasty or bypass surgery is indicated.  This may be done during the initial hospitalization or later as an outpatient procedure.

A variety of medications are also used in treating cardiac patients.  Beta blockers reduce the workload of your heart and are usually prescribed.  ACE inhibitors help the heart work better.  Aspirin is usually given as a blood thinner.  Heparin, an intravenous blood thinner, is usually given early.  If you receive a stent, medication is often given to help prevent clotting within the stent.  Before your discharge from the hospital the cardiac rehabilitation program begins with a progressive exercise program and counseling about any lifestyle or diet changes that need to be made.