Adapted from the Harvard Heart Letter

Six minutes to save a life

Minutes matter when someone collapses from a cardiac arrest.

Every day more than a thousand Americans keel over, felled by a cardiac arrest. Most stricken with this type of attack die. More could be saved with faster emergency care.

There are two kinds of heart attack. One, called a myocardial infarction, happens when a blood clot blocks an artery that nourishes heart muscle. This blockage usually causes chest pain or other warning signs that can last for hours. The second type, called a cardiac arrest, strikes so fast that there's little or no time to call for help. Unless two specific treatments — cardiopulmonary resuscitation (CPR) and an electric shock to the heart — are started within six minutes, the chances of surviving or living without permanent brain damage dwindle to nothing.

Defining cardiac arrest

Most cardiac arrests begin when something pushes the heart into ventricular tachycardia (tack-ee-KAR-dee-uh). In this rhythm, the heart's lower chambers beat very fast. It can give way to ventricular fibrillation (fib-rih-LAY-shun), which is fast and chaotic. In either case the ventricles contract so quickly they don't have time to fill with blood between beats. Circulation ceases. Collapse follows.

The "something" that kicks off ventricular tachycardia differs from person to person. The other kind of heart attack can cause it. So can a structural or electrical problem; dehydration; an imbalance of potassium, magnesium, or other minerals in the blood; stress; some inherited diseases; or a sudden blow to the chest.

Recognizing a cardiac arrest

Unlike a myocardial infarction, a cardiac arrest gives few warning signs. You might feel dizzy, lightheaded, or out of breath, then suddenly collapse.

Recognizing the signs of a cardiac arrest in someone else is probably more important than recognizing them in yourself. Knowing what is happening means you can respond quicker, and maybe save a life.

Someone having a cardiac arrest

• faints or collapses all of a sudden

• stops breathing

• has no pulse

• may have twitching muscles.

Keep in mind that a person who has simply fainted keeps breathing and has a pulse. That's not the case with a sudden cardiac arrest.

What to do

If you see someone go into cardiac arrest, call 911 right away. The sooner professional help arrives, the better.

Once you've made the call, start CPR. Compressing the person's chest keeps blood flowing to the brain and the rest of the body.

If you are in a public place such as an airport, ask a bystander to see if an automated external defibrillator is nearby. If there's one available, use it to shock the heart out of its deadly pace and back into a normal, steady rhythm.

The aftermath

Survivors of a cardiac arrest undergo extensive testing to find what caused the problem. Many get an implantable cardioverter/defibrillator. This machine, the size of a deck of cards, constantly monitors the heart and delivers a jolt of electricity if it senses the start of a potentially deadly rhythm. Some people take drugs that prevent irregular heart rhythms. The small minority with seemingly healthy hearts may end up with no long-term treatment at all.

Prevention and preparation

Researchers have been trying for years to find a way to identify people who are likely to have cardiac arrests. So far, no accurate tests have emerged. Some possibilities include two tests of the heart's electrical properties, T-wave alternans and QT-interval dispersion. Genetic testing and heart rate variability are other possibilities.

Since prediction isn't yet possible, general prevention efforts are in order. All the things you might do to prevent a myocardial infarction — stopping smoking, exercising more, eating healthier, taking medications if needed to lower blood pressure and cholesterol — help stave off cardiac arrests. Seeing your doctor regularly can also help. He or she may spot problems that could nudge you toward a cardiac arrest. These include an enlarged heart, some other structural defect, or an electrical irregularity. For people prone to a cardiac arrest, taking a fish oil supplement or drugs may help.

The best way to prepare for a cardiac arrest is to make sure you and your loved ones know to call 911 right away. Next come taking a course in CPR and learning to use an automated external defibrillator. Some people are even buying these devices for their homes (see the January 2003 Heart Letter).

If you're a bit of a social activist, ask the director of your city or town's emergency services about the average time it takes to respond to a medical emergency. In Seattle and Boston, where more than 40% of people survive cardiac arrests, average response times are under six minutes. They're far longer in most other cities, where only 5%–10% survive.