Pacemakers and implantable defibrillators (patient information)
Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
An arrhythmia is any disorder of your heart rate or rhythm. It means that your heart beats too quickly, too slowly or with an irregular pattern. Most arrhythmias result from problems in the electrical system of the heart. If your arrhythmia is serious, you may need one of two devices implanted under your skin: a cardiac pacemaker or an implantable cardioverter defibrillator (ICD).
A pacemaker monitors the electrical impulses in the heart. When needed, it delivers electrical pulses to make the heart beat in a more normal rhythm. A pacemaker may be helpful when the heart beats too slowly or has other abnormal rhythms. An ICD is a device that monitors heart rhythms. If it senses dangerous rhythms, it delivers shocks. Many ICDs record the heart's electrical patterns when there is an abnormal heartbeat. This can help the doctor plan future treatment.
Pacemakers: Generating regular heartbeats
Your doctor has recommended that you get a pacemaker. You're not alone. Pacemakers are common, with more than 3 million of these small devices in use worldwide and about 600,000 implanted each year.
People need pacemakers for a variety of reasons - mostly due to one of a group of conditions called arrhythmias, in which the heart's rhythm is abnormal. One of the most common problems requiring a pacemaker is a heart rate that's too slow, which is known as bradycardia. Almost any heart condition can lead to bradycardia by disrupting the heart's natural electrical system, which controls your heartbeat.
Normal aging of the heart may disrupt your heart rate, making it beat too slow or irregularly. Heart muscle damage resulting from a heart attack is another common cause of abnormalities of the heart rate or rhythm. Some medications can affect the heart rate as well. For some, genetic conditions cause an abnormal heart rate.
Regardless of the underlying cause of a slow heart rate, a pacemaker - a small, battery-powered device implanted in your chest - may correct it, offering substantial relief.
Your natural pacemaker
To appreciate how a pacemaker works, it helps to understand your heart and the electrical system that makes it beat.
The heart is a muscular, fist-sized pump with four chambers, two on the left side and two on the right. The upper chambers are the right and left atria. The lower chambers are the right and left ventricles.
For your heart to function properly, the heart's chambers must operate in a coordinated fashion. In addition, your heart must beat at an appropriate rate - normally from 50 to 100 beats a minute in adults. If your heart beats too slowly or rapidly, not enough blood is pumped to your internal organs, leading to fatigue, fainting, shortness of breath, confusion and other symptoms.
Your heart's electrical system controls the chambers' pumping action. A normal heartbeat begins in your right atrium, in the sinus node. This cluster of cells - your natural pacemaker - acts like a spark plug, generating regular electrical impulses that travel through specialized muscle fibers.
When an electrical impulse reaches the right and left atria, they contract and squeeze blood into the ventricles. After a split-second delay to allow the ventricles to fill, the impulse reaches the ventricles, making them contract and pump blood to the rest of your body.
An implanted electronic pacemaker mimics the action of your natural pacemaker. A pacemaker consists of two parts:
- The pulse generator. This small metal container houses a battery and the electrical circuitry that regulates the rate of electrical pulses sent to your heart.
- Leads. These flexible, insulated wires deliver the electrical pulses to your heart.
Early pacemakers operated at a fixed rate regardless of your activity. The next type developed were "demand" pacemakers, which kicked in only when your heart rate fell below a certain level. Today's "rate responsive" pacemakers monitor several parameters, including blood temperature and breathing rate. By measuring these, the pacemaker will speed up or slow down your heart rate to adjust to the body's needs. For example, it can increase your heart rate during exercise to meet your body's increased need for blood and oxygen.
Pacemakers today are more compact than their predecessors. Some models are as small as a quarter and weigh less than an ounce. Average battery life is five to 10 years. When a battery wears out, the entire pacemaker's pulse generator is replaced.
The latest advance in pacemakers is biventricular pacing, which is particularly valuable for people with heart failure whose hearts' electrical systems have been damaged. Unlike a regular pacemaker, a biventricular pacemaker stimulates both the right and left ventricles to make the heart beat more efficiently.
Pacemaker implantation and maintenance
Surgery to implant the pacemaker is usually performed under local anesthesia and typically takes less than three hours.
During surgery, a flexible, insulated wire (lead) is inserted into a major vein under or near your collarbone and guided to your heart with the help of X-ray images. One end of the lead (the electrode) is secured to your heart's right ventricle while the other end is attached to the pulse generator, which is usually implanted under the skin beneath your collarbone. In most cases another lead is secured to your heart's right atrium as well to maintain coordinated pumping of the heart. This is called a dual chamber pacemaker system because both the right atrium and right ventricle are stimulated.
You may stay in the hospital for one to three days after having a pacemaker implanted. Before you leave, your pacemaker is programmed to fit your particular pacing needs. A return visit is scheduled to refine the settings.
After that, you'll periodically have your pacemaker checked via telephone. You connect to a phone line with either a transmitter attached to wristbands on each of your arms or a wand placed over the pacemaker. These devices send pacemaker information to your doctor's office. A technician on the other end of the line checks your heart rate and rhythm and assesses your pacemaker's function and remaining battery life.
Because modern pacemakers are more sophisticated than their predecessors, pacemaker malfunction due to interference from electronics and security systems is rare. Still, a few precautions are in order:
- Cellular phones. It's safe to talk on a cell phone, but avoid placing your cell phone directly over your pacemaker implantation site when the phone is turned on. Although unlikely, your pacemaker could misinterpret the cell phone signal as a heartbeat and withhold pacing, producing symptoms such as sudden fatigue.
- Security systems. Passing through an airport metal detector won't interfere with your pacemaker, although the metal in it may sound the alarm. But avoid lingering near or leaning against a metal-detection system. If security personnel insist on using a hand-held metal detector, ask them not to hold the device near your pacemaker any longer than necessary or ask for an alternative form of personal search. To avoid potential problems, carry an ID card stating that you have a pacemaker.
- Medical equipment. If a doctor is considering any medical procedure that involves intensive exposure to electromagnetic energy, tell him or her that you have a pacemaker. Such procedures include magnetic resonance imaging, therapeutic radiation for cancer treatment, and shock wave lithotripsy, which uses shock waves to break up large kidney stones or gallstones. If you're having surgery, the electrocautery procedure that controls bleeding also can interfere with pacemaker function.
- Power-generating equipment. Stand at least two feet from welding equipment, high-voltage transformers or motor-generator systems. If you work around such equipment, your doctor can arrange a test in your workplace to determine whether it affects your pacemaker.
Devices that present little or no risk to pacemaker function include microwave ovens, televisions and remote controls, radios, toasters, electric blankets, electric shavers and electric drills.
Once considered a novelty, pacemakers are now a standard treatment for many conditions affecting your heart's electrical system. By restoring your heart's normal rhythm, pacemakers can alleviate symptoms such as fatigue, lightheadedness and fainting. Because most of today's pacemakers automatically adjust your heart rate to match your level of physical activity, they can allow you to resume a more active lifestyle.