There is a lot of confusion over the terms heart attack, cardiac arrest, and myocardial infarction. The media often incorrectly reports these events when discussing the deaths of celebrities and other public figures. Even among the medical community, many people are not sure what meets the criteria of a heart attack. I will explain some of these terms here.

“Heart Attack”

What is commonly referred to as a heart attack is what physicians call a “myocardial infarction”, or an MI. An MI occurs when heart muscle (known as myocardium) is damaged. When heart muscle is injured, it releases a protein called troponin into the bloodstream. Blood tests can detect troponin, and, in addition to symptoms and the EKG, this is the usual method by which we diagnose an MI.

The most common cause of an MI is a blockage in an artery that feeds the heart muscle, called a coronary artery. This usually happens because of rupture of a cholesterol-filled plaque in the wall of a coronary artery. The blood in the artery then clots and results in decreased blood flow to the heart muscle. When most people think about a heart attack, this is the type they are thinking of. This kind of event is classified as a Type I myocardial infarction. It is treated by restoring blood flow in the coronary artery, usually through a procedure or surgery.

When you think of a heart attack, you are probably thinking of a Type I myocardial infarction.

Sometimes a plaque ruptures in a coronary artery, causing chest pain and/or EKG changes, but the blockage is not severe enough to cause damage to the heart muscle. Since heart muscle doesn’t die, the troponin level is not elevated. In this case, the event is not called a myocardial infarction, but instead it is called unstable angina.

There is another type of myocardial infarction that many people are not aware of. MIs can also occur because the heart muscle is working too hard and not getting enough oxygen – called a supply/demand mismatch. An example of this would be a really bad pneumonia where there isn’t as much oxygen in the blood and the heart rate is very elevated. Another example would be severe bleeding, which results in less blood to carry oxygen to the heart and also an elevated heart rate. These are Type II myocardial infarctions. As you can imagine, these generally would not benefit from an intervention on a coronary artery.

Nowadays, the troponin tests are so advanced that they can detect even the smallest amount of troponin released into the bloodstream. For example, two-thirds of runners completing the Boston marathon have some elevation of their troponin level, and in 1 in 10 have significant elevations.

Presumably, most of those people are fairly healthy. Physicians often struggle with the significance of such findings, and in the right setting will often describe them as a “small heart attack” or “mini heart attack” or “strain on the heart”. Additionally, if a Type I myocardial infarction is caught and treated quickly enough, the damage to the heart can be minimal.

Often, these events are so small that they will not be detected in imaging of the heart with tests like an echocardiogram or nuclear stress test, and usually will not show up on an electrocardiogram (ECG or EKG).

For medical professionals: Technically, an elevated troponin should be associated with ischemic EKG changes or symptoms to be called an MI. Otherwise, it should be called “myocardial injury”.

Cardiac arrest

A cardiac arrest is different than a heart attack.  A cardiac arrest is when the heart stops. This will result in sudden loss of consciousness. A heart attack can cause a cardiac arrest, but so can a number of other things.  In older patients, especially those with risk factors for coronary disease, a heart attack is the most common cause of cardiac arrest and sudden death.  In younger patients, there are a number of potential causes. Some of those causes might be an abnormal heart rhythm or a massive blood clot that travels to the lungs.  If not treated quickly, a cardiac arrest will usually result in sudden death.

Immediate CPR is crucial for the survival of someone who is suffering a cardiac arrest.

If someone suffers a cardiac arrest, they can sustain damage to the heart, resulting in a Type II myocardial infarction. So… a heart attack can cause a cardiac arrest, but less commonly, a cardiac arrest can also cause a heart attack.

In someone under the age of 50, cardiac arrest is often due to an electrical or structural problem in the heart.  These types of problems are often hereditary, so it is important for family members to know the cause of a cardiac arrest.

If someone is having a cardiac arrest, you need to call 911 and immediately start CPR if you know it. The American Heart Association offers classes on CPR. If there is an Automated External Defibrillator (AED) nearby, you can use that to help restore a normal electrical rhythm.  Use of AEDs is also taught in CPR training classes.

Summary

A heart attack (myocardial infarction) is different than a cardiac arrest. One can cause the other, but it is important to know which came first. That way it can be treated appropriately, and family members can be informed of any potential inherited risks.