|
A pacemaker (or "artificial
pacemaker", so as not to be confused with the
heart's natural pacemaker) is a medical device designed
to regulate the beating of the heart. The purpose of an
artificial pacemaker is to stimulate the heart when
either the heart's native pacemaker is not fast enough
or if there are blocks in the heart's electrical
conduction system preventing the propagation of
electrical impulses from the native pacemaker to the
lower chambers of the heart, known as the ventricles.
History of
the implantable pacemaker
The first external pacemaker was
designed and built by the Canadian electrical engineer
John Hopps in 1950. A substantial external device, it
was somewhat crude and painful to the patient in use. A
number of inventors, including Paul Zoll, made smaller
but still bulky external devices in the following years.
The pacemakers built in the late 1950s were bulky,
relied on external electrodes, and had to be plugged
into a wall outlet. External electric shocks were
frequently too traumatic for young heart block patients,
and the AC-operated pacemaker could fail during a power
blackout.
The first implantation into a human
was made in 1958 by a Swedish team using a pacemaker
designed by Rune Elmqvist and Åke Senning. The device
failed after three hours. A second device was then
implanted which lasted for two days. The world's first
implantable pacemaker patient, Arne Larsson, survived
the first tests and died in 2001 after having received
22 different pacemakers during his lifetime. In February
1960, an improved model relying on better materials was
implanted in Montevideo, Uruguay. That device lasted
until the patient died of other ailments, 9 months
later. The early Swedish-designed devices used
rechargeable batteries, which were charged by an
induction coil from the outside.
Devices constructed by the American
Wilson Greatbatch entered use in humans from April 1960
following extensive animal testing. The first patient
lived for a further 18 months. The early devices
suffered from battery problems - every patient required
an additional operation every 24 months to replace the
batteries. Others who contributed significantly to the
technological development of the pacemaker in the
pioneering years were Bob Anderson of Medtronic
Minneapolis, Geoffrey Davies of Devices Ltd in England,
Barouh Berkovits and Sheldon Thaler of American Optical,
Geoffrey Wickham of Telectronics Australia, Walter
Keller of Cordis Corp. of Miami, Hans Thorander who
joined previously mentioned Rune Elmquist of
Elema-Schonander in Sweden, Janwillem van den Berg of
Holland and Manuel A. Villafaña of Cardiac Pacemakers
Inc.
Pacemakers require wires (called
leads) to both send the pacing pulses to the heart and
sense the intrinsic rhythm of the heart. The first
pacemakers required these leads to be placed surgically
on the outer surface of the heart. In the mid 1960s, the
first transvenous leads were placed. This allowed the
placement of pacemakers without opening the thoracic
cavity and therefore without the use of general
anesthesia.
The first American-made
radioisotope-powered pacemaker was developed and
implanted by Victor Parsonnet at Newark Beth Israel
Medical Center in Newark, New Jersey. The first
pacemaker implanted into an infant was July 26, 1974 to
Jason A. Haines when he was 16 hours old.
Applications
Artificial pacemakers can be used in
order to help with and/or treat these conditions:
Methods of pacing
External
pacing
External pacemakers can be used for
initial stabilization of a patient, but implantation of
a permanent internal pacemaker is usually required for
most conditions. External cardiac pacing is typically
performed by placing two pacing pads on the chest wall.
Usually one pad is placed on the upper portion of the
sternum, while the other is placed along the left axilla,
near the bottom of the rib cage. When an electrical
impulse goes from one pad to the other, it will travel
through the tissues between them and stimulate the
muscles between them, including the cardiac muscle and
the muscles of the chest wall. Electrically stimulating
any muscle, including the heart muscle, will make it
contract. The stimulation of the muscles of the chest
wall will frequently make those muscles twitch at the
same rate as the pacemaker is set. It was first invented
by Canadian doctor John Hopps in 1950. He studied as an
electrical engineer at the University of Manitoba.
Pacing the heart via external pacing
pads should not be relied upon for an extended period of
time. If the person is conscious, he or she may feel
discomfort due to the frequent stimulation of the
muscles of the chest wall. Also, stimulation of the
chest wall muscles does not necessarily mean that the
heart is being stimulated as well.
Temporary
internal pacing
An alternative to external pacing is
the temporary internal pacing wire. This is a wire that
is placed under sterile conditions via a central venous
catheter. The distal tip of the wire is placed into
either the right atrium or right ventricle. The proximal
tip of the wire is attached to the pacemaker generator,
outside of the body. Temporary internal pacing is often
used as a bridge to permanent pacemaker placement. Under
certain conditions, a person may require temporary
pacing but would not require permanent pacing. In this
case, a temporary pacing wire may be the optimal
treatment option.
Permanent
pacemaker placement
Placement of a permanent pacemaker
involves placement of one or more pacing wires within
the chambers of the heart. One end of each wire is
attached to the muscle of the heart. The other end is
screwed into the pacemaker generator. The pacemaker
generator is a hermetically sealed device containing a
power source and the computer logic for the pacemaker.
Most commonly, the generator is
placed below the subcutaneous fat of the chest wall,
above the muscles and bones of the chest. However, the
placement may vary on a case by case basis.
The outer casing of pacemakers is so
designed that it will rarely be rejected by the body's
immune system. It is usually made of titanium, which is
very inert in the body.
Basic
pacemaker function
Modern pacemakers all have two
functions. They listen to the heart's native electrical
rhythm, and if the device doesn't sense any electrical
activity within a certain time period, the device will
stimulate the heart with a set amount of energy,
measured in joules.
Pacemaker
naming code
The NASPE/BPEG generic (NPG) code is
a pacemaker naming convention originally developed in
1974 that uses a 3-5 letter code to describe the main
features of an artificial pacemaker. Each of the 5
positions signifies a particular aspect of pacemaker
functionality. Using this scheme, a designation of
VATOO would describe, for example, a pacemaker that
sensed the atria and paced the ventricles in a triggered
mode with no rate response or multisite pacing.
Bi-Ventricular Pacing (BVP)
A bi-ventricular pacemaker, also
known as CRT (Cardiac Resynchronization Therapy) is a
type of pacemaker that can pace both ventricles (right
and left) of the heart. By pacing both sides of the
heart, the pacemaker can resynchronize a heart that does
not beat in synchrony, which is common in heart failure
patients. CRT devices has three leads, one in the
Atrium, one in the right ventricle, and the last one is
inserted through the coronary sinus to pace the left
ventricle. CRT devices are shown to reduce mortality and
improve quality of life in groups of heart failure
patients.
Advancements in pacemaker function
When first invented, pacemakers
controlled only the rate at which the heart's two
largest chambers, the ventricles, beat.
Many advancements have been made to
enhance the control of the pacemaker once implanted.
Many of these enhancements have been made possible by
the transition to microprocessor controlled pacemakers.
Pacemakers that control not only the ventricles but the
atria as well have become common. Pacemakers that
control both the atria and ventricles are called
dual-chamber pacemakers. Although these dual-chamber
models are usually more expensive, timing the
contractions of the atria to precede that of the
ventricles improves the pumping efficiency of the heart
and can be useful in congestive heart failure.
Rate responsive pacing allows the
device to sense the physical activity of the patient and
respond appropriately by increasing or decreasing the
base pacing rate via rate response algorithms.
The DAVID trials have shown that
unnecessary pacing of the right ventricle can lead to
heart failure. New devices can keep the amount of right
ventricle pacing to a minimum and thus prevent worsening
of the heart disease.
Another advancement in pacemaker
technology is left ventricular pacing. A pacemaker wire
is placed on the outer surface of the left ventricle,
with the goal of more physiological pacing than what is
available in standard pacemakers. This extra wire is
implanted to improve symptoms in patients with severe
heart failure.
Devices
with pacemaker function
Sometimes devices
resembling pacemakers, called ICDs (implantable
cardioverter-defibrillators) are implanted. These
devices are often used in the treatment of patients at
risk for sudden cardiac death. An ICD has the ability to
treat many types of heart rhythm disturbances by means
of pacing, cardioversion,or defibrillation.
From Wikipedia, the free
encyclopedia
Cardiothoracic & Vascular Surgeons of Michigan provides this on-line
information for educational and communication purposes
only and it should not be construed as personal medical
advice. Information published on this website is not
intended to replace, supplant, or augment a consultation
with a
Cardiothoracic & Vascular professional regarding the
viewer/user's own medical care.
Cardiothoracic & Vascular
Surgeons of Michigan disclaims any and all
liability for injury or other damages that could result
from use of the information obtained from this site.
|
