Webster's New World Medical Dictionary

pacemaker, artificial
An electronic device that
uses electrical impulses to regulate the heart
rhythm. A pacemaker may be external (located out-
side the body) or internal (implanted in the body).
Although there are many different types of pace-
makers, all are designed to treat bradycardia, a too-
slow heart rate. Pacemakers may function
continuously and stimulate the heart at a fixed rate
or at an increased rate during exercise. A pace-
maker can also be programmed to detect too long a
pause between heartbeats and then stimulate the
heart. See also 
pacemaker, implantable.
pacemaker, implantable
A pacemaker in which
the electrodes to the heart, the electronic circuitry,
and the power supply are all implanted internally
within the body. 
pacemaker, internal
See 
pacemaker,
implantable.
pacemaker, natural
See 
sinoatrial node.
pachyonychia congenita
An inherited condition
that is characterized by abnormally thick, curved
nails; thickening of the skin of the palms, soles,
knees, and elbows; and white plaques in the mouth.
Abbreviated PC. There are two distinct syndromes of
PC. The basic abnormality in both is a mutation in
one of the genes for keratin, which is a primary con-
stituent of nails, hair, and skin. 
Paget’s disease
A chronic bone disorder that
typically results in enlarged, deformed bones due to
excessive breakdown and formation of bone tissue
that can cause bones to weaken and may result in
bone pain, arthritis, bony deformities, and frac-
tures. Paget’s disease generally occurs in persons
over the age of 40 years. Men and women are
affected equally. Paget’s disease can be diagnosed by
using one or more of the following tests: X-rays,
because bone in Paget’s disease has a characteristic
appearance; alkaline phosphatase tests, because an
elevated level of alkaline phosphatase in the blood
can be suggestive of Paget’s disease; and bone scans.
The bisphosphonate drugs, which slow the rate of
bone breakdown and turnover, are the first line of
treatment. Treatment can control Paget’s disease and
lessen symptoms, but there is no cure. Also known
as osteitis deformans.