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16
Pacemakers and Implantable
Cardioverter-Defibrillators
Fast & Easy ECGs, 2nd E – A SelfPaced Learning Program
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Artificial Pacemakers
• Medical devices used to generate and deliver
electrical impulses to the myocardium to
stimulate a normal heartbeat
• Some are external to the body and provide
temporary treatment, others are permanently
implanted in the chest
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Artificial Pacemakers
• One type of temporary pacemaker is the
transcutaneous pacemaker
– It delivers electrical impulses through lead wires
to electrode pads that are applied to the surface
of the patient’s chest
• Permanent pacemakers are implanted in a
surgically created pocket beneath the skin in
the patient’s chest wall just below the clavicle
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Permanent Pacemakers
• Consist of:
– A generator
– One or more lead
wires
– A power source
(often a lithium
battery)
– Logic circuits that
detect cardiac
electrical activity
and determine the
appropriate
response
I
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Permanent Pacemakers
• May be used to:
– Symptomatic bradycardia
– Sick sinus syndrome
– Atrial fibrillation with bradycardia
– 3rd-degree (complete) AV heart block
– Symptomatic 2nd-degree AV heart block, particularly type II
– The sudden development of various combinations of AV
heart block and bundle branch block in patients experiencing
acute MI
– Recurrent tachycardias that can be overdriven and thereby
terminated by pacemaker activity
– Synchronization of the heart beat in heart failure (cardiac
resynchronization therapy)
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Pacemaker Electrodes
• Are either positioned in the atrium or
ventricle alone (single-chamber pacemakers)
or, more often, in both chambers (dualchamber pacemakers or AV sequential
pacemakers)
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Permanent Pacemakers
• Are programmable
– Receive and transmit data/programming
instructions through the skin using
electromagnetic waves
• Adjustments can be made to:
– Output
– Sensitivity
– Refractory period
– Rate adaption
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Pacing Modes
• Single-chamber
– One pacing lead is inserted into either the right atrium or
right ventricle but not both
• Dual-chamber
– Electrodes are placed into two chambers of the heart
– One lead paces the atrium while the other paces the
ventricle
– By assisting the heart in coordinating the function between
the atria and ventricles, this type of pacemaker acts
similarly to how the heart naturally paces itself
– Also referred to as an AV sequential pacemaker
– Most can be programmed to a single chamber mode,
which can be useful if the atrial lead wire fails
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Pacing Modes
• Fixed-rate
– Paces the heart at a single, preset rate
• Rate-responsive
– Has sensors that identify increases or decreases in the
patient’s physical activity and automatically adjusts
base pacing rate to meet the body’s metabolic needs
– Can boost the heart rate in response to motion or
increased respirations for those patients whose body
cannot appropriately increase the heart rate during
activity
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Pacing Modes
• Demand
– Most common type used
– Fires only when the patient’s intrinsic heart rate
falls below a given threshold level
• i.e., if the pacemaker is set at 60 beats per minute it
remains inactive until there is a pause between beats
that translates into a rate below 60, then the
pacemaker fires
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Coding System
• Pacemaker mode and function described by a
five letter coding system
– in practice, only three to four are commonly used
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Coding System
• First letter represents the heart chamber being paced.
This letter may be
–
–
–
–
O = none
A = atrium
V = ventricle
D = dual (ventricle and atrium)
• Second letter represents the chamber of the heart
being sensed by the pacemaker. This letter may be
–
–
–
–
O = none
A = atrium
V = ventricle
D = dual (ventricle and atrium)
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Coding System
• Third letter indicates how the pacemaker
generator responds to sensing. This letter may be
–
–
–
–
O = none
T = triggers pacing
I = inhibits pacing
D = dual (triggers and inhibits pacing)
• Fourth letter has to do with adjustment of the
pacing rate in response to exercise
– If pacemaker is rate responsive, it is denoted with the
letter “R”
– If there is none, it is denoted as “O”
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Coding System
• The fifth letter indicates multisite pacing. This
letter may be
– O = none
– A = atrium
– V = ventricle
– D = dual (ventricle and atrium)
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Coding System Examples
• VOO
– In this mode, the ventricle is paced and there is no
sensing function
• AAI
– Pacemaker paces and senses in the atrium
– When it senses atrial activity, pacing is inhibited
• VVI
– Ventricle is paced and sensed
– If spontaneous cardiac output is detected, then the
device is inhibited
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Coding System Examples
• VDD
– Here the pacemaker paces the ventricle and
senses both the atrium and ventricle
– On sensing intrinsic atrial activity, the pacemaker
triggers ventricular pacing; on sensing ventricular
activity, the pacemaker inhibits pacing
– It is also known as a P-synchronous pacer
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Coding System Examples
• DVI
– Pacemaker can pace in the atrium, the ventricle, or both
– Sensing takes place only in the ventricle
– When the pacemaker senses intrinsic ventricular activity, it
inhibits pacing
• DDD
– Pacemaker paces and senses in the atrium, the ventricle,
or both
– On sensing activity in either chamber, the pacemaker
inhibits pacing in that chamber
– Or, on sensing atrial activity, the pacemaker may trigger
ventricular pacing
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Cardiac Resynchronization Therapy
(CRT)
• Used to resynchronize a heart that does not beat
in synchrony, a common problem in patients with
heart failure
• Employs three leads:
– one is placed in right atrium
– one is located in right ventricle
– last one is inserted through the coronary sinus to pace
the free wall of the left ventricle
– These three wires are connected to a CRT generator
and programmed so that the two ventricular wires are
activated simultaneously
I
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Unipolar and Bipolar Systems
• Unipolar
– positive electrode is positioned in the heart tissue
and the negative electrode is connected to the
pulse generator
– produces tall pacing spikes on the ECG
• In a bipolar system,
– electrodes are only millimeters apart in the
cardiac tissue
– produces short pacemaker spikes
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
ECG Features of a Pacemaker
• Depending on how many chambers are paced,
the firing of a pacemaker produces one or two
narrow pacemaker spikes on the ECG
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
ECG Features of a Pacemaker
• A paced ECG complex
shows two features:
(a) a narrow “pacing
spike,” which reflects
the impulse
depolarizing the
paced chamber and
(b) a P wave or QRS
complex that
immediately follows
the pacing spike
I
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Pacemaker Failure
• Pacemakers may not work properly for a
number of reasons, including a failure to
capture, a failure to pace, a failure to sense,
oversensing, and pacemaker-mediated
tachycardia
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Pacemaker Failure
• Failure to capture is seen as the presence of
pacemaker spikes that are not followed by a P
wave or broad QRS complex
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Pacemaker Failure
• Failure of the pacemaker to sense is seen as
the presence of ECG pacemaker spikes that fall
where they shouldn’t
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Pacemaker Failure
• Oversensing is seen as an absence of
pacemaker spikes in the presence of a heart
rate that is slower than the rate set for the
pacemaker
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Pacemaker Failure
• Pacemaker-mediated tachycardia is seen as a
fast heart rate with a pacemaker spike
preceding each QRS complex on EGG.
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Implantable Cardioverter-Defibrillator
(ICD)
• Is implanted in patients who are at risk of
sudden cardiac death due to ventricular
fibrillation and ventricular tachycardia
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Implantable Cardioverter-Defibrillator
• Is programmed
to detect
cardiac
dysrhythmias
and correct
them by
delivering
paced beats,
cardioversion,
or
defibrillation
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Therapies Provided by the ICD
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect
• Analyze this ECG tracing
I
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect
• Analyze this ECG tracing
I
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect
• Analyze this ECG tracing
I
Fast & Easy ECGs, 2E
32
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect
• Analyze this ECG tracing
I
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.