What is a natural pacemaker?
The heart's "natural" pacemaker is called the sinoatrial
(SA) node or sinus node. It's a small mass of specialized
cells in the top of the right atrium or chamber of the heart.
It makes the electrical impulses that cause your heart to
beat.
A chamber of the heart contracts when an electrical impulse
moves across it. For the heart to beat properly, the signal
must travel down a specific path to reach the ventricles,
the heart's lower chambers.
The natural pacemaker may be defective, causing the heartbeat
to be too fast, too slow or irregular. The heart's electrical
pathways also may be blocked.
What is an artificial pacemaker?
An "artificial pacemaker" is a small, battery-operated
device that helps the heart beat in a regular rhythm. Some
are permanent (internal) and some are temporary (external).
They can replace a defective natural pacemaker or blocked
pathway.
A pacemaker uses batteries to send electrical impulses to
the heart to help it pump properly. An electrode is placed
next to the heart wall and small electrical charges travel
through the wire to the heart.
Most pacemakers have a sensing device that turns itself
off when the heartbeat is above a certain level. It turns
back on when the heartbeat is too slow. These are called
demand pacemakers.
AHA Recommendation
If you have an artificial pacemaker, be aware of your surroundings
and the devices that may interfere with pulse generators:
Home appliances
CB radios, electric drills, electric blankets,
electric shavers, ham radios, heating pads, metal detectors,
microwave ovens, TV transmitters and remote control TV changers,
in general, have not been shown to damage pacemaker pulse
generators, change pacing rates, or totally inhibit pacemaker
output.
Several of these devices have a remote potential to cause
interference by occasionally inhibiting a single beat. However,
most people can continue to use these devices without significant
worry about damage or interference with their pacemakers.
Power-generating equipment, arc welding equipment and powerful
magnets (as in medical devices, heavy equipment or motors)
can inhibit pulse generators. Patients who work with or
near such equipment should know that their pacemakers may
not work properly in those conditions.
Cellphones
Cellphones available in the United States (less than 3 watts)
don't appear to damage pulse generators or affect how the
pacemaker works.
Technology is rapidly changing as the Federal Communications
Commission (FCC) is making new frequencies available. Newer
cellphones using these new frequencies might make pacemakers
less reliable. A group of cellphone companies is studying
that possibility.
Medical equipment
Carry a wallet I.D. card with you. Equipment used by doctors
and dentists can affect your pacemaker, so tell them you
have one.
Magnetic resonance imaging (MRI) uses a powerful magnet
to produce images of internal organs and functions. Metal
objects are attracted to the magnet and are normally not
allowed near MRI machines. The magnet can interrupt the
pacing and inhibit the output of pacemakers. If MRI must
be done, the pacemaker output in some models can be reprogrammed.
Discuss with your doctor the possible risks and benefits
before you undergo MRI scanning.
Extracorporeal shock-wave lithotripsy (ESWL) is a noninvasive
treatment that uses hydraulic shocks to dissolve kidney
stones. This procedure may be done safely in most pacemaker
patients, with some reprogramming of the pacing. You'll
need careful follow-up after the procedure and for several
months to be sure the unit is working properly. Patients
with certain kinds of pacemakers implanted in the abdomen
should avoid ESWL. Discuss your specific case with your
doctor before and after the treatment.
Radiofrequency (RF) ablation uses radio waves to manage
a wide variety of arrhythmias. Recent studies of patients
with implanted pacing systems measured the units before,
during and after RF catheter ablation. They showed that
most permanent pacemakers aren't adversely affected by radio
frequencies during catheter ablation. A variety of changes
in your pacemaker can occur during and after the treatment.
Your doctor should carefully evaluate your pacing system
after the procedure.
Transcutaneous (tranz"ku-TA'ne-us) electrical nerve
stimulation (TENS) is used to relieve acute or chronic pain.
Several electrodes are placed on the skin and connected
to a pulse generator. Most studies have shown that TENS
rarely inhibits bipolar pacing. It may sometimes briefly
inhibit unipolar pacing. This can be treated by reprogramming
the pulse generator.
Diagnostic radiation (such as screening X-ray) appears to
have no effect on pacemaker pulse generators. However, therapeutic
radiation (such as for treating cancerous tumors) may damage
the circuits of the pacemaker. The degree of damage is unpredictable
and may vary with different systems. But the risk is significant
and builds up as the radiation dose increases. The American
Heart Association recommends that the pacemaker be shielded
as much as possible, and moved if it lies directly in the
radiation field. If you depend on your pacemaker for normal
heart pacing, the electrocardiogram (ECG) should be monitored
during the treatment, and your pulse generator should be
tested often after and between radiation sessions.
Dental equipment doesn't appear to affect pacemakers adversely.
Some patients may feel an increase in pacing rates during
dental drilling.
Electroconvulsive therapy (such as for certain mental disorders)
appears to be safely used in patients with pacemakers.
Short-wave or microwave diathermy uses high-frequency, high-intensity
signals. These may bypass your pacemaker's noise protection
and interfere with or permanently damage the pulse generator.
Related AHA publications
Heart and Stroke Facts
Living With Your Pacemaker
Abnormal Heart Rhythms
Detailed Research
Heart and Stroke Facts
2001 Heart and Stroke Statistical Update
"Interference With Cardiac Pacing," Kenneth A.
Ellenbogen, M.D., Intelligence Reports in Cardiac Pacing
and Electrophysiology, HealthScan Inc., 1995
ACC/AHA Practice Guidelines for Implantation of Cardiac Pacemakers
and Antiarrhythmia Devices (Executive Summary, #71-0136 Circulation.
1998;97;1325-1335; Full Text, #71-0137 JACC. 1998;31:1175-1209)
