About Defibrillators

Go to an airport or a sport stadium today and you’ll likely see external defibrillators on the walls, sort of like fire extinguishers. The medical term defibrillation is slipping into the common vocabulary. But what is a defibrillator, really, and why would a person need one?

The popular notion is that a defibrillator is required to help “re-start” a heart that has stopped. Technically, that is not true. Defibrillators deliver electricity to the heart to restore a faulty heart rhythm. The name for this situation is called “sudden cardiac arrest” or even “sudden cardiac death.” That last name is rapidly falling out of favor (and you can no doubt see why), but they are actually two terms that mean the same thing. And, yes, many people (about 20%) who have “sudden cardiac death” survive it.defibrillator

Sudden cardiac arrest typically occurs when the heart starts to beat dangerously fast. A rapid heart rate can be appropriate when the body is exercising or highly stressed. But sometimes the heart tries to beat at rates that are overly fast-200 or even 300 times a minute.

The healthy heart at rest beats about 60 times a minute or once a second. If you make a fist (which is about the size of your heart) and open and close it to simulate pumping action, you can see that the heart is pumping at a pretty good clip to maintain a normal rhythm.

Now imagine the heart trying to beat 120 times a minute-an appropriate rate for mild exercise. To achieve this rate, you now have to open and close your fist two times per second. The heart is still efficient at this rate, but it’s hard work.

But let’s double it-240 times a minute or four times a second. If your heart ever tried to beat 240 times a minute, it would no longer be able to pump efficiently. Try it with your fist and you see that you just can’t keep up. Your movements have to become abbreviated. That’s what happens during sudden cardiac arrest. Your heart is trying to beat so rapidly that it can no longer really pump. The heart muscle just quivers. Blood sloshes around in the heart instead of being pumped out.

In medical terms, your cardiac output drops to zero in a matter of seconds. This heart condition is usually attributable to a rhythm disorder called ventricular fibrillation (VF). But no matter what it is called, it is a sudden and potentially lethal heart rhythm.

Left untreated, a person with VF can die in as few as four minutes.

Sudden cardiac arrest from VF is not the same thing as a heart attack. A heart attack is essentially a “plumbing problem” of the heart, a situation where blockage in the “pipes” or blood vessels prevents blood flow. Other plumbing problems that can occur in the heart relate to the valves or the ability of the heart muscle to pump.

Cardiac rhythm disorders are electrical problems. They occur because of disorders in the heart’s electrical system and they can happen in a person who has an otherwise “healthy heart.”

The heart generates electricity to make it beat. That electricity flows through the heart along established conduction pathways. But sometimes an electrical impulse gets “stuck” on the pathway and makes endless loops, faster and faster, causing the heart to try to contract and relax to keep up with the electrical signals.