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A single-chamber pacemaker paces either the right atrium or the
right ventricle with one lead. Most common is the right ventricle.
A dual-chamber pacemaker paces both the right atrium and right
ventricle of the heart. This often requires two pacing leads.
A dual-chamber pacemaker is the most common type of pacemaker
implanted today.
Single-chamber pacing system in the Atrium
A pacing lead is attached in the right atrium to begin a heartbeat.
This kind of atrial pacing is necessary when the heart's natural
pacemaker (the sinus or SA node) does not begin a heartbeat, which
is a condition known as sick sinus syndrome. A pacing lead attached
in the atrium will ensure that a heartbeat is begun. (The signal
then travels to the ventricles.)
Single-chamber pacing system in the Ventricle
A lead attached in the right ventricle ensures that the ventricles
pump blood. This kind of ventricular pacing may be done when heart
block occurs. Heart block is when the electrical signal begins
in the atrium but the signal is stopped at or just below the atrioventricular
(AV) node and the ventricles cannot pump. A pacing lead attached
in the ventricle will ensure that the heart's ventricles contract
rhythmically and fully.
Dual-chamber pacing system
As mentioned above, your heart has four chambers through which
blood is pumped: the left and right upper chambers (atria), and
the left and right lower chambers (ventricles).
A dual-chamber pacemaker typically requires two pacing leads:
one placed in the right atrium, and the other placed in the right
ventricle.
A dual-chamber pacemaker monitors (senses) electrical activity
in the atrium and the ventricle to see if pacing is needed. When
pacing is needed, the pacing pulses of the atrium and ventricle
are timed so that they mimic the heart's natural way of pumping.
By helping the upper and lower chambers of your heart to beat
in their natural sequence, dual-chamber pacemakers mimic the normal
heart's activity.
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Type of pacing
There are two ways a pacemaker starts a heartbeat:
- Fixed rate pacemakers
- Rate-responsive pacemaker
Fixed rate pacemakers
When a heart can increase its rate according to a person's needs
a fixed rate pacemakers is suitable. The pulse rate is set and
programmed by the physician.
Rate responsive pacemakers
A rate-responsive pacemaker is needed when a heart cannot appropriately
increase its rate according to a person's needs. This type of
pacemaker varies the pacing rate depending upon a person's level
of activity, respiration, or other factors. The pacemaker's circuitry
interprets these changes and increases the pacing rate (the number
of times per minute that a pacing pulse is sent). Rate-responsive
pacing can be part of single-chamber and dual-chamber pacing.
Many pacemakers implanted today are rate-responsive.
A rate-responsive pacemaker uses one or more special sensors
to detect changes in the body that indicate when more oxygen is
needed. A normal heart rhythm slows down or speeds up many times
during the day. The heart beats slower while resting or sleeping.
Exercise or emotional excitement makes a heart beat faster because,
in an excited state, a body requires greater amounts of oxygen.
And, oxygen is brought to all parts of the body through the blood.
When a heart is unable to adjust its pumping rate, a rate-responsive
pacemaker is used.
A rate-responsive pacemaker mimics the heart's natural function
to adjust the heart rate. A rate-responsive pacemaker uses one
or more special sensors to recognize changes in how much blood
and oxygen are needed by the body. Based on this information,
the heart rate is adjusted to meet the body's changing needs for
blood flow.
When a change is detected, the pacing rate is increased according
to how the doctor programmed the pacemaker. You do not need to
engage in very strenuous activity to benefit from a rate-responsive
pacemaker. For example, the simple act of walking may require
a rate of more than 100 beats per minute.
A pacemaker may have one or more sensors . Two common sensors
are an activity sensor and a QT sensor.
An activity sensor is a component of some rate-responsive pacemakers.
This type of rate-responsive pacemaker allows the heat rate to
vary in response to different levels of physical activity. The
sensor, which is bonded to the inside of the pacemaker's metal
case, detects pressure waves caused by muscle movement or body
motion. The pacemaker's circuitry translates these pressure waves
into electrical signals that adjust the pacing rate up and down.
minute ventilation sensor- A component of some rate-responsive
pacemakers that detect changes in the frequency and depth of breathing.
This helps the pacemaker assess if the heart rate is appropriate
for the activity one is engaged and if extra pacing assistance
is needed.
QT sensor- A QT sensor is a physiologic sensor. This sensor detects
required changes in the heart rate based on the variation in the
hearts' own signal. This electrical signal has several components:
Q,R,S and T waves. The variation in the Q wave to T wave is an
indicator for metabolic demand changes. This sensor is an unique,
Vitatron patented, sensor.
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Benefits of Rate-responsive Pacing
Individuals who have rate-responsive pacing report feelings of
well being and the ability to resume more active and satisfying
lifestyles. In diaries kept during clinical studies of rate-responsive
pacemakers, individuals reported feeling better and enjoying a
higher quality of life because they could participate in activities
that previously were not possible
For people whose heart rate does not increase when needed, rate-responsive
pacing:
- Provides people with a more appropriate heartbeat for their
current activity.
- Allows people to perform ordinary, daily activities more effectively.
- Allows people to perform more vigorous exercise.
- Gives people a greater sense of well-being in their day-to-day
lives.
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