PART I: Acute Myocardial Infarction

Dr. Terry Murphy

ED Medical Director

Samaritan Hospital

A heart attack, also known as an Acute Myocardial Infarction, is the death of heart muscle.  Whenever any tissue (in this case, heart muscle cells) has an inadequate delivery of oxygen to that tissue, its cells begin to lose their ability to function.  Whenever the oxygen delivery shortage is severe enough or sustained long enough, the cells of those tissues begin to die.  In other words, a mismatch of oxygen supply versus the demand, causes heart muscle cell dysfunction and, when severe enough, death of the muscle cells.

Ninety percent of the time heart muscle cell death occurs because of a sudden blockage of an artery to the heart (coronary artery) keeps blood flow (and hence oxygen) from reaching a portion of the heart.  The majority of the time the sudden blockage occurs when an atherosclerotic plaque of the artery lining ruptures (tears away from the lining) and a blood clot forms around the plaque, blocking the artery.  Other, less common, causes of sudden occlusion include a small clot from another site (most commonly a heart valve) floating in the blood stream that floats downstream into a coronary artery, blocking it off; inflammation of a coronary artery (arteritis); and spasm of the artery, causing intense narrowing of the artery diminishing the ability to deliver oxygen - usually from cocaine or amphetamine use.  Other less common causes of inadequate oxygen delivery include a low blood pressure (not enough pressure to reach some areas of the heart), and severe anemia (not enough red blood cells to carry oxygen).

In the case of a Myocardial Infarction (MI), cells begin to die if blood supply is not restored within 20 to 40 minutes, and by six to eight hours, an area of irreversible damage has occurred.

Estimates vary by source, but anywhere from one to one and a half million people in the U.S. suffer a Myocardial Infarction every year.  One quarter to one third die suddenly, before reaching the hospital, another 10% die in the hospital and a final ten percent die during the first year after their Myocardial Infarction.  It is estimated that there are 500,000 to 700,000 deaths per year in the U.S. as a result of Myocardial Infarctions; making Myocardial Infarction related deaths more common than deaths from all cancers and strokes combined.  The good news is that there has been a steady decline in both the number of Myocardial Infarctions and death from Myocardial Infarctions in the U.S. in the past 10 years.

We know that the vast majority of Myocardial Infarctions occur because of atherosclerotic coronary artery disease causing artery narrowing diminishing blood (oxygen) supply, and plaque rupture causing artery occlusion with cessation of blood (oxygen) supply.  Atherosclerosis is the slowly progressive disease of accumulation of cholesterol on the inner layer of the arteries.  This disease is known to start as early as the teens.  We also know that multiple factors influence the predilection for, and the rate of progression of this disease, including:

Family history - genetic predisposition is probably the greatest risk factor and individuals whose fathers or other first degree relative had a Myocardial Infarction or sudden death before age 55, or whose mothers or first degree female relative are at greater risk for an Myocardial Infarction.

High blood pressure - while not the greatest risk factor; controlling elevated blood pressure can mitigate the increased risk.

High blood cholesterol - cholesterol, like all oils, cannot dissolve in blood unless its chemical nature is changed by being attached to a protein molecule called a lipoprotein.  Low density lipoproteins (LDL) increases deposition of cholesterol on artery walls; while high density lipoproteins (HDL) protects against deposition.

Tobacco use - primarily cigarette smoking, but any form of tobacco significantly increases cholesterol deposition in the arteries, even only a couple of cigarettes a day.

Diabetes - both Type I (insulin dependent) and Type II diabetes increase atherosclerotic plaque development, but Type I diabetes have a much higher incidence of sudden death with a Myocardial Infarction, and many diabetics do not have warning symptoms when they have a Myocardial Infarction - they have "silent" Myocardial Infarctions.

Gender - males are much more likely than females to develop atherosclerosis, and have Myocardial Infarctions up until age 75 when the likelihood equalizes.  Post menopausal females begin to catch up with men in the production of atherosclerosis, and often females presenting symptoms of a Myocardial Infarction differs from those of men.

The symptoms of a Myocardial Infarction can be highly variable, everything from the classic "elephant sitting on my chest" to easy fatigue to sudden death without warning.  Typically the symptoms related are:

Aching or squeezing discomfort/pain in the central chest area

Neck, arm, jaw or upper back discomfort

Shortness of breath, especially with exertion

Nausea or upper abdominal discomfort

Heartburn or indigestion

Sweating

Lack of energy, weakness, easy fatigue

Any person with any of the above symptoms, especially when they have any of the previously described risk factors for atherosclerosis or have been diagnosed with heart disease, should call 911. 

JOIN US NEXT WEEK FOR PART II: "What to do."

This article is intended to provide useful information, not medical advice. This information cannot, and is not meant to, replace consultation with your physician regarding your individual circumstances.