A pacemaker is an electronic device that sends small electrical impulses to the heart, to correct certain kinds of irregular heartbeats (arrhythmias). It is typically recommended for patients whose hearts beat too slowly (bradycardia) or do not properly conduct electrical impulses (a blockage in the electrical system, called heart block). A pacemaker may also be helpful for patients suffering from fainting spells (syncope), heart failure and thickening of the heart walls (hypertrophic cardiomyopathy).
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While pacemakers share many similarities with defibrillators (ICDs) — both are battery-powered, implantable devices that regulate abnormal heartbeat by sending electrical signals to the heart — the devices have some important differences.
Pacemakers only send low-energy electrical impulses, typically to speed the heart rate. Defibrillators, by contrast, also can send high-energy "shocks" to the heart, usually to slow the heart rate or regulate it. Likewise, defibrillators are reserved for patients who have experienced sudden cardiac arrest — when the heart stops completely — or are at risk for the condition.
How a Pacemaker Works
A defibrillator is programmed by an electrophysiologist, a cardiac physician who specializes in heart rhythms. A pacemaker can be programmed to regulate the heart's upper chambers (atria), lower chambers (ventricles) or both. It can maintain a suitable heart rate — based on a minimum rate — or prevent irregular heartbeats.
A pacemaker consists of two components:
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- Leads: Long, thin wires that are directly connected to the heart, to monitor heart rhythms. A pacemaker may have one, two or three leads.
- A pulse generator, which consists of a battery and a small computer that receives signals from the lead.
If the computer detects a slow heart rate or an abnormal heart rhythm, the battery will deliver an electrical signal to the lead, which causes the heart muscle to contract.
A pacemaker can be adjusted to maintain normal heart rhythm in two main ways:
- Demand pacing: Electrical signals are transmitted to the heart only when it beats too slowly or skips a beat. Signals are sent "on demand."
- Rate-responsive pacing: Electrical signals adjust to the patient's activity level. They speed up, or slow down, the heart based on breathing, blood temperature and other factors.
Rate-responsive pacing is more popular, simply because the target heart rate can change from moment to moment, based on the patient's body movements and breathing. More activity entails a faster target heart rate.
Types of Pacemakers
Pacemakers have one, two or three wires. These can be placed in different chambers of the heart, depending upon the patient's heart condition.
- Single-chamber pacemakers have one lead. This will carry impulses from the pulse generator to an upper or lower chamber of the heart.
- Dual-chamber pacemakers have two leads. These will carry impulses to an upper chamber and a lower chamber, coordinating the timing of contractions made by these two chambers.
- Biventricular pacemakers — also called cardiac resynchronization therapy (CRT) devices — have three leads. These leads will carry impulses to an upper chamber and both lower chambers (ventricles), ensuring that the ventricles contract at the same time.
Pacemaker Implant Surgery
Pacemakers are most frequently inserted through small incisions in the skin, near the collarbone. The patient is given a mild sedative, but is kept awake; a local anesthetic is used. An electrophysiologist — a physician who specializes in heart rhythm problems — will perform the procedure.
After the incision is made, the pacemaker's leads are guided along a vein until they reach the heart. A large X-ray machine, called a fluoroscopy machine, will help the doctor position the leads into place. Next, the tip of each lead is attached to the heart muscle. Then, the leads are connected to the pacemaker's pulse generator, which is then placed in a pocket created beneath the skin in the upper chest.
With the pacemaker in place, a doctor will perform tests to ensure that the device is working properly. An artificially fast heart rhythm might be programmed, simply to ensure that the leads are properly monitoring the heart and the pulse generator is correctly sending signals to stop the abnormal heart beat. Once testing is complete, the device is programmed to meet the patient's needs.
After Pacemaker Implant Surgery
Following surgery, patients are asked to return to doctor for routine follow-up visits. The first appointment will be scheduled within six weeks of the device implant procedure.
During the first visit, the pacemaker will be checked by a programmer device, which will indicate how the pacemaker is working. Thereafter, the pacemaker should be checked every three months from home, using a telephone transmitter. An annual in-person device check, along with an echocardiogram, may also be scheduled.
A pacemaker's battery typically lasts up to eight years. When the battery's voltage runs low, a new pacemaker will be implanted. However, in most cases, the device's leads will not require replacement.
Pacemaker therapy is part of a larger treatment program, which may include medications, proper nutrition, moderate physical activity and healthy lifestyle choices.