Cardiac Pacemakers
The heart is bestowed with a specialized system that automatically
generates rhythmic control via the sinus node, located in the superior lateral
wall of the right atrium near the opening of the superior vena cava. The
specialized pacemaker cells dictate control of the rest of the heart through
regular electrical impulses that propagate from the right atria to the lower
ventricles. The rapid conduction of these impulses cause the muscle cells of the
atria to contract and squeeze blood into the ventricles, which contract and
force blood into the aorta and pulmonary arteries. Abnormalities of the heart
rhythm, called arrhythmias, can disrupt this normal cardiac control making it
necessary to use some artificial means to regulate the rhythm of the heart.
Today, some half a million men and women, most of them over the age of sixty,
carry implanted cardiac pacemakers that take over the duties of the natural
conduction system. Tens of thousands of these devices are implanted each year in
this country alone. Over the past thirty years cardiac pacemakers have evolved
from simple devices only capable of fixed-rate stimulation of a single chamber
of the heart to more sophisticated "implanted computers" that medical
personnel can interrogate and reprogram from outside the patient's body. These
refinements have allowed for more physiologic pacing with maintenance of
atrioventricular synchrony and cardiac output. There are various types of
cardiac pacemakers available today that can be surgically implanted to treat
specific arryhythmic disorders in the heart. Abnormal rhythms in the heart are
one of the most frequent causes of heart malfunction, and in most cases
necessitate some type of cardiac pacing unit. Cardiac arrhythmias are common in
the elderly, in whom age-related physiologic changes often alter the conduction
system of the heart. Such changes may remain asymptomatic, or they may progress
to syncope, or possibly...