What's an AICD, and how could it save your life?

So what happens after the ­heart's natural pacemaker, the SA node, sits at the head of the boat and yells "Row!" to the rest of the heart's crew by transmitting an electrical signal?

The atria, the two chambers in the upper part of the heart, respond first, contracting as the signal travels through. Next, the signal arrives at the atrioventricular (AV) node. The atria contract a split second before the signal reaches the ventricles and causes them to contract. This delay creates a synchronized squeezing action, starting in the upper atria and passing through the lower ventricles. This squeezing motion forces blood into your arteries.

The signal is a stickler for routine. It follows a specific path through all four chambers, and it normally prevents any other heart cells from mutinying and trying to send out their own pulses. Interestingly, all heart cells are able to create an electrical signal. The SA node just does it faster and better. Other cells don't get the chance to fire off their own electrical cues because they're too busy responding to the prompt sent by the SA node.

This normal heartbeat -- and the sequence of electrical events that produce it -- is known as the sinus rhythm. It fluctuates between 60 and 100 beats per minute, depending on if you're daydreaming about butterflies or fielding questions from an Internal Revenue Service auditor [source: A.H.A.]. A heartbeat going faster than this for no good reason is called a tachycardia, and one that lags behind is called a bradycardia.

Both types of arrhythmia occur when your heart's normal electrical sequence gets out of whack. Sometimes the SA node misfires or establishes a bad rhythm. Other times the electrical signal takes a wrong turn and gets to different parts of the heart in the wrong order. Some arrhythmias are caused by thyroid conditions, diabetes or drug abuse. In these cases, treating the underlying cause normally fixes the problem. If you feel like your heartbeat is adding extra beats or beating out an avant-garde rhythm, get it checked out immediately.

Other problems, such as ventricular tachycardia -- an electrical problem in a damaged ventricle, causing rapid-fire contractions -- may result from a previous heart attack and may in turn cause more heart attacks. Ventricular tachycardia varies in intensity. Some episodes may require no action, and others won't stop until a new rhythm is introduced to replace the broken one. For ventricular tachycardia and similar arrhythmias, automatic implantable cardioverter defibrillators can perform cardioversion, or deliver a series of shocks that returns the heart to a normal rhythm.

So that device implanted underneath your collarbone can be pretty handy. Next, we'll learn how the AICD can stop your h­eart and leave you feeling grateful for it the next morning.

Now that we know how heart disease can disrupt the rhythm of life, we'll take a closer look at the AICD technology that can restore that rhythm.

Your doctor may decide that an automatic implantable cardioverter defibrillator is right for you if your heart has been damaged by heart attacks or coronary artery disease, or if you have ventricular tachycardia or ventricular fibrillation. Although they can be implanted into almost anyone, people receiving an AICD average in their 60s [source: Mount Sinai]. The device can cost between $20,000 and $35,000, and Medicare may cover up to $30,000 of the cost [source: Pear].

An AICD has two main parts: the generator and the leads. The generator is a small, flat box that stores data and provides battery power. It's about the size of two saltine crackers stacked together. The leads are thin wires that connect the generator to the heart, monitor how the heart is functioning and, of course, deliver shocks to the heart when needed.

Hav­ing an AICD implanted isn't­ like ­having open-heart surgery. You may not even need general anesthesia, only numbing for the location of the incision. The generator sits beneath the skin between your pectoral tissue and your collarbone.

The two leads are directed through veins into the heart. Once in place, these two small wires actually grow into the heart tissue, and when the sealed battery dies in about seven years, those wires will be left in place, and doctors will simply replace the generator and then reattach the wires. Crazy, huh?

Before you go home after the operation (the next day, likely), your new device will be tested. Doctors will cause your heart to lose control to see if the device can restore order. They'll also hand you a long list of magnetic and electrical devices that can mess up your AICD, such as power plants and even cell phones. Regular appointments allow your doctors to check the battery's strength and download data stored in the generator. That is, the saltine-sized computer underneath your collarbone.

If your heart starts acting up, the AICD will, in a split second, review the data for a period of time preceding the onset of the problem. It then decides if it needs to speed you up, slow you down, or reset your heart. It does everything but broadcast the ballgame for you.

Now, if your heart goes into fibrillation -- remember that crazy boat going nowhere? -- the AICD sees what's happening and transmits a perfectly timed big jolt that stops your heart for about half a second, allowing the SA node to restore order and reestablish the dominance of its electrical pulse.

You might be passed out when you receive this shock. Otherwise, it's going to feel like you've been kicked in the chest. If you weren't already on the ground, you very well may be after your heart has been stopped with a blast of electricity. But it beats flopping around and dying in a state of fibrillation.

After the AICD is implanted, you'll need to tone it down for a while. If you follow your doctor's instructions, you should able to return to your pre-implant activities within a few months. Some people find they have even more energy than before. But even if you don't decide to join a competitive rowing team after your AICD is implanted, take heart: You'll still be doing much better than 100 percent of dead people.

See the next page for lots more information that could keep your heart happy and healthy.