Myocardial Infarction

What is a myocardial infarction?

In patients who have coronary artery disease, there are cholesterol plaques on the walls of the coronary arteries.  A piece of the plaque may break off and leave a raw area on the surface of the plaque.   A blood clot forms on this raw surface of the cholesterol plaque.  If the blood clot is large enough, blood flow through the artery may be completely blocked.  This deprives the area of heart muscle supplied by that artery of its blood supply.  This is called a “myocardial infarction” (M.I.) or heart attack.  If the blood flow to that region of heart muscle is not promptly restored, that area of heart muscle will slowly die and ultimately form a scar. 

The farther down the coronary artery that the obstruction occurs, the smaller the heart attack will be because less heart muscle will be involved.  On the other hand, a blockage early in the course of a coronary artery will involve all the heart muscle dependent on this blood vessel and may cause a very large myocardial infarction.

A small myocardial infarction may have little impact on the patient’s long-term prognosis, yet a large myocardial infarction may have a significant influence on long-term survival, causing significant weakening of the heart muscle.

What are the symptoms?

The symptoms of a myocardial infarction are identical to those associated with angina, but in the case of an M.I., the symptoms are persistent and unrelenting.  In the setting of an M.I., there may be other accompanying symptoms such as nausea, indigestion, profuse sweating, lightheadedness, palpitations, or feeling faint.  Occasionally patients experiencing an M.I. will simply have severe prolonged indigestion or shortness of breath.  Occasionally myocardial infarctions may have no symptoms at all, referred to as “silent myocardial infarctions”.  

What are the dangers?

Patients who experience a large myocardial infarction, having a large portion of their heart muscle become severely scarred, may develop significant weakness of the heart muscle as a pump.  Over time this may lead to congestive heart failure which is characterized by symptoms related to fluid retention or reduced cardiac output (the amount of blood pumped by the heart).  Patients with small myocardial infarctions generally have a better long-term outlook with some heart attacks small enough to not alter their long-term prognosis at all.  However, whether large or small, any acute myocardial infarction may be life threatening in the first 24 to 48 hours after its onset.  The injured heart muscle may lead to electrical instability within the heart, generating life threatening heart rhythms called ventricular arrhythmias.  Occasionally, a fatal rhythm abnormality will develop within the first seconds or minutes into a heart attack, leading to “sudden cardiac death”.

What are the treatments?

If a person suffering an acute myocardial infarction seeks medical attention promptly, much can be done to limit the amount of injury to the heart muscle.  Deprived of its blood supply, a heart muscle only becomes irreversibly damaged slowly over several hours.  If a patient with an acute myocardial infarction is treated within the first six hours of the onset of symptoms, the heart attack will often be made much smaller than it would otherwise have been.  If the heart attack patient is fortunate enough to present to a hospital that has a cardiac catheterization laboratory, that patient may emergently undergo cardiac catheterization and angioplasty where their occluded vessel is opened by special balloon catheters.  A stent, a metal sleeve that buttresses open the artery in the region of the original plaque, is often placed at the time of the angioplasty.  Angioplasty and stenting are available at MetroWest Medical Center for patients presenting with a heart attack.

If the heart attack patient presents to a hospital that does not have a cardiac catheterization laboratory, the emergency room doctors have the option of transferring them by ambulance to a hospital that does perform angioplasty or may treat the patient with medication to dissolve the blood clot that is obstructing the coronary artery.  This “thrombolytic therapy” has an approximately 70% chance of successfully opening the artery and restoring blood flow as opposed to a greater than 95% chance of doing so with a primary angioplasty.  For patients who present more than six hours into their myocardial infarctions, there is less benefit from angioplasty or thrombolytic therapy.  Generally, medications are used to support the injured heart muscle, and the patient’s heart rhythm and vital signs are closely monitored. 

Overall, in the modern day era, patients having a myocardial infarction who seek medical attention promptly may benefit from medications or procedures that can open an occluded coronary artery and restore blood flow to an area of injured heart muscle, rendering the heart attack smaller than it would have otherwise been, often dramatically improving the long-term prognosis of that patient.