Putting a pacemaker in a dog may sound high-tech and far-fetched, but the practice is
neither as uncommon nor as costly as you might think. As pacemakers for human beings
have become fairly routine, lower prices and increased availability have made them an
option that can extend some animal's lives for several years.

"Between 100 and 200 pacemakers are implanted into animals--mostly dogs but some cats
and horses--in the United States each year," notes Dr. David Sisson, a veterinary
cardiologist at the University of Illinois College of Veterinary Medicine Teaching Hospital in
Urbana, where the procedure is done 6 to 20 times a year.

Dr. Sisson knows what he's talking about. For the past 5 years, he has served as the
director of a pacemaker registry started in the late 1980s by the Cardiology Specialty of the
American College of Veterinary Internal Medicine, an organization of veterinary medical
specialists who have completed special training and passed a certifying exam. There are
about 70 veterinary cardiologists in the United States.

"Pacemakers can correct the same abnormalities in dogs that they do in people," he
explains. Normally the body sends an electrical charge to stimulate the chambers of the
heart to contract and pump blood through the body. In a condition known as sinus node
dysfunction, or sick sinus syndrome, an abnormality of this electrical charge causes a very
slow heart rate (bradycardia).

Heart block is another condition that may be treated with a pacemaker. It occurs when the
top chambers of the heart, the atria, receive the electrical charge but the impulse doesn't
make it to the lower half of the heart, or ventricles, because of a blockage.

"The main symptom of these disorders is a slow heart rate that cannot be accounted for by
other reasons, such as hypothyroidism or other underlying metabolic problems," says Dr.
Sisson. "Some dogs with a slow heart rate will also exhibit fainting episodes that last 10 to
15 seconds and may occur as often as ten times a day."

Dogs who need pacemakers--like their human counterparts--are typically older. The
average age is 9 years. "The best candidates have hearts in reasonably good shape and
have no systemic illnesses, such as cancer, that would unnecessarily shorten their life span,"
says Dr. Sisson.

"A pacemaker is made up of a pulse generator and wires," he explains. "The pulse
generator, which is about the size of a silver dollar but thicker, contains an energy supply
and a tiny computer that monitors and controls the rhythm of the heart. Wires called leads
transmit electrical impulses between the pulse generator and the heart. When the
pacemaker detects that the heart's electrical activity has failed, it sends an appropriate
stimulus to get the heart going at the correct rate."

Twenty years ago, pacemakers were always implanted surgically. Surgeons cut through the
chest wall to attach the leads to the heart. The leads were brought through the rib spaces
and connected to the pulse generator, which was implanted on the animal's flank. This is still
the standard procedure used with cats.

A less invasive approach was developed in the early 1980s. In this procedure, a lead is
threaded through a vein in the neck until it reaches the heart. A tiny retractable screw built
into the lead attaches it firmly to the heart muscle and keeps it in place until scarring anchors
it there. The pulse generator is inserted under the skin at the back of the dog's neck. This
technique--which may require only one day in the hospital--is less risky for older dogs who
may not withstand major surgery.

The prognosis for dogs with pacemakers depends largely on how healthy the dog is other
than having an abnormal heart rhythm. A pacemaker often extends the life of the dog 3 to 5
years. Young dogs that receive pacemakers because of congenital heart blockage typically
do very well.

For owners, this treatment is not too taxing. "The dog is essentially cured and there are no
pills or injections to administer," Dr. Sisson points out. "All owners have to do is bring the
dog in for a checkup once or twice a year to make sure the pacemaker is functioning
correctly. The cost of the procedure is about the same as the cost of bone plating--surgical
repair of a fractured leg in a dog."

The pacemakers used for dogs are the ones made for people. Manufacturers often donate
unused pacemakers when several months have expired from the shelf-life of the power
source, making it undesirable for use in human beings. Receiving a pacemaker powered for
5 instead of 7 years in not a problem for dogs, since they have much shorter life spans than
people do. Sometimes dogs receive a secondhand pacemaker from a deceased person.

As director of the pacemaker registry, Dr. Sisson contacts manufacturers to request
donations of pacemakers, matches donated pacemakers with needs nationwide, and
collects data from board-certified veterinary cardiologists about the conditions and
outcomes of all pacemaker surgeries. He's currently working on article that will report on 5
years of data from the registry.

Dr. Sisson advises owners considering this procedure in their dog to seek a board-certified
surgeon or cardiologist who is trained to do appropriate programming of the pulse
generator. These specialists can make sure the computer is sensing and pacing the heart
correctly.

If you would like further information, contact your local veterinarian or contact the
American College of Veterinary Internal Medicine, with headquarters in Lakewood, Colo.,
at 800/245-9081 (email: [email protected]) for a referral.