Pacemaker

The heart's electrical system includes a natural pacemaker, a group of special cells that signal the heart when and how strongly to beat.

When the heart's natural pacemaker is not working properly, the signals it sends out may become erratic: either too slow, too fast, or irregular which means it cannot stimulate strong contractions of the heart chambers. When the heartbeat becomes erratic, it is referred to as an arrhythmia.

Arrhythmias can cause problems in two ways:

1. Tachycardia: a condition in which the electrical signal causes the heart to pump too fast, so the chambers don't have time to fill adequately between each beat.
2. Bradycardia: a condition in which the electrical signal causes the heart to pump too slowly.

In both situations, the heart fails to pump enough blood. This leads to a lack of oxygen-rich blood in the lungs, brain, heart, and other body tissues.

What symptoms might indicate that there is a problem with the heart's electrical system?

• weakness
• fatigue
• palpitations
• low blood pressure
• dizziness
• fainting

Arrhythmias can be diagnosed by various kinds of EKG recordings or through electrophysiology testing.

Bradycardia can be treated when necessary by the implanting of a pacemaker. Tachycardia that requires therapy may be treated with medications or with an implantable converter defibrillator.

A pacemaker is a small electronic device (about the size of a teaspoon) that is implanted under the skin (usually in the shoulder area) to regulate the heartbeat. It backs up the heart's natural pacemaker and electrical system. Pacemakers can "sense" when the heart's natural heartbeat becomes too slow. They can send out weak electrical signals to restore the heart rate to normal.

Pacemakers can also relay signals from the natural pacemaker to the heart's pumping chambers when those signals are not getting through over the heart's natural conduction system (a condition known as heart block).

A permanent pacemaker consists of:

• a pulse generator. This is a sealed container made of titanium (the same metal that coats the space shuttle!). In this container are a long-lived battery and a small computer that coordinates the pacemaker's functions with the heart's own signals and monitors the battery energy and other pacemaker information.
• one or two wires, or leads, which conduct electrical signals between the heart and the pulse generator.

Pacemaker insertion is done in the operating room or the electrophysiology laboratory. The patient is asleep during the procedure; sedation is given to help the patient relax, and local anesthesia (novocaine-like drugs) is used to prevent pain.

Insertion of the pacemaker begins with an incision below the collarbone. One or two lead are inserted into a blood vessel which runs under the collarbone and are floated to appropriate areas in the heart chambers. Because there are no nerves inside the heart and blood vessels, the leads cause no pain. Once the lead sytem is in place, it is tested to make sure it is working properly. The lead system is then attached to the generator, which is placed just under the skin through the incision made earlier. The incision is closed with dissolving stitches.

An implantable cardioverter defibrillator (ICD) is a device, similar to a pacemaker, that is implanted in the same way that a pacemaker is implanted. The ICD contains a pacemaker, so it can treat bradycardia, just like a pacemaker. The chief difference is that the ICD can also treat tachycardia. When the heart rate gets too fast because of a fatal, dangerous rhythm called ventricular tachycardia, the ICD senses the abnormallity, It can then stop the ventricular tachycardia by delivering a brief burst of rapid impulses through its pacemaker or by sending a small electrical shock through the lead wire to the heart.

Once the tachycardia is stopped, the normal rhythm returns. It it fails to do so, the ICD's pacemaker can stimulate the heart to provide a normal beat.