Pacemaker Devices
A pacemaker is
used to treat abnormal rhythms of the heart. These are collectively
known as arrhythmias. In most cases pacemaker therapy is used when the
heart rate is too slow. Patients may feel faint or may actually pass
out due to a very slow heart rate. This is known as bradycardia. The
normal pacemaker of the heart is in the right atrium, and it fires an
electrical signal to make the rest of the heart beat or contract. When
this natural pacemaker malfunctions by not firing or by firing too slowly,
or when the natural pacemaker signal can not get through to the rest
of the heart, a man-made pacemaker can be inserted. This procedure is
usually done under local anesthesia. With the aid of x-ray guidance,
thin wires are positioned into the appropriate chambers of the heart.
The heart chambers are accessed through a vein under the collarbone.
The wires are attached to a battery and sophisticated electronics contained
in a very small metal package. This battery or generator is inserted
under the skin near the collar bone. The pacemaker can sense when a
beat comes and can pace the heart when a heart beat does not come soon
enough. The battery lasts for years, and it is a simple matter to replace
a worn out battery. 
In
recent years, the functions of implantable devices like pacemakers have
been expanded to correct abnormally rapid heart rhythms. Particularly
dangerous forms of rapid heart beats are ventricular tachycardia and
ventricular fibrillation. When the heart is in ventricular tachycardia,
its pump function is poor, resulting in very little ejection of blood
to the brain and rest of the body. This can lead to random heart muscle
contractions and cardiac arrest, called ventricular fibrillation. New
devices that look and function like pacemakers, called implantable cardio-defibrillators,
can recognize these life-threatening heart rhythms. The devices will
deliver a jolt of electricity to shock the heart into a more normal
and safer rhythm.