By James M. Rippe

A heart attack, known medically as a myocardial infarction (MI), occurs when one of the three coronary arteries that supply oxygen-rich blood to the heart muscle (myocardium) becomes severely or totally blocked, usually by a blood clot. When the heart muscle doesn’t receive enough oxygenated blood, it begins to die.

The severity of the heart attack depends on how much of the heart is injured or dies when the attack occurs.

When you think you’re having a heart attack it’s critical to go immediately to a hospital by ambulance where therapy can be initiated to save your heart muscle from dying. New clot-busting medicines, as well as procedures such as angioplasty, often can dissolve a clot that causes the heart attack, open the blood vessel, and save some or all of the heart muscle at risk.

Although some of the heart muscle usually dies during a heart attack, the remaining heart muscle continues to function and often can compensate, to a very large degree, for the heart muscle that has died.

The causes of a heart attack

Heart attack almost always is caused when a blood clot forms at the site of an existing fatty plaque that has narrowed the coronary artery. Thus, individuals are at much higher risk for heart attack if they

  • Have a history of coronary heart disease

  • Have experienced previous bouts of angina

  • Have suffered a previous heart attack

The blockage that triggers a heart attack usually is caused by an acute blood clot. Most acute blood clots occur when one of the plaques or fatty deposits on the artery walls cracks or ruptures. Other, much more rare causes of acute blockages in arteries, such as a severe coronary artery spasm, can also cause heart attack.

The symptoms of a heart attack

Different people experience the symptoms of a heart attack in different ways. However, typical symptoms include some or all of the following symptoms (as described by the American Heart Association):

  • Uncomfortable pressure, fullness, squeezing, or pain in the center of the chest lasting more than a few minutes

  • Pain spreading to the shoulders, neck, or arms

  • Chest discomfort with lightheadedness, fainting, sweating, nausea, or shortness of breath

In an individual who has angina, symptoms may be particularly difficult to differentiate from the chest discomfort of angina. However, when a heart attack is occurring, chest discomfort usually is more severe and may occur while the individual is at rest or less active than usual.

The signs of a heart attack often are subtle, particularly with individuals who have diabetes. People with diabetes may not have the classic symptoms of chest, shoulder, or arm discomfort. Chest pain experienced by many women likewise may not present the classic symptoms.

Coronary heart disease (CHD) is extremely common in men and women in the United States and particularly in men in their 40s and older and postmenopausal women. Even if you’ve never had a single sign of trouble, you need to call 911 and go straight to the hospital for prompt evaluation whenever you experience any of the preceding warning signs. Do not take a meeting. Do not put it off for an hour . . . just call 911 and go!

About two-thirds of the individuals who experience an acute heart attack also experience some warning symptoms in the weeks or days preceding the acute event. They often don’t realize what the warning signs were until after the event — with keen hindsight. So work on your foresight. That way you’ll know the warning signs of heart attack and take them seriously.

The difference between heart attack and sudden cardiac arrest

Although doctors often call sudden cardiac arrest “a massive heart attack,” the two technically are not the same thing. A massive heart attack (myocardial infarction) results from a blockage of the coronary arteries. Sudden cardiac arrest is caused by ventricular fibrillation, an electrical malfunction in which the heart begins to quiver rapidly, instead of contracting and pumping blood regularly.

Cardiac arrest strikes without warning. Because blood flow essentially stops, victims of cardiac arrest lose consciousness and die within minutes unless emergency help is available.

Many victims of sudden cardiac arrest have underlying CHD. Sudden cardiac arrest often (but not always) occurs in the setting of an acute heart attack. It can also occur from electrical malfunction when a heart attack is not involved.