beat
The
goes on:
A pacemaker primer
Whether temporary or permanent, single- or
dual-chamber, pacemakers optimize cardiac output
and improve quality of life.
By Nicolette C. Mininni, MEd, RN, CCRN
NEARLY 400,000 cardiac pacemakers and cardioverter-defibrillators
are implanted annually in the United
States. In some cases, pacemakers
are used as a temporary intervention
to support a patient through an
acute episode. In other situations, as
for patients with permanent conditions that require cardiac pacing,
pacemakers are implanted surgically.
Whether temporary or permanent, a pacemaker generates an
electrical impulse that travels via
one or more leadwires, or leads,
which in turn stimulate the myocardium to depolarize and initiate a
contraction. A pacemaker’s primary
function is to keep the ventricles
beating at a rate that maintains sufficient blood pressure and perfuses all
organs adequately.
Pacemaker components
The main parts of a pacemaker are
the pulse generator, which contains
the power source (typically a lithiumiodide battery and a small electronic
circuit), leads, and electrodes at the
terminal ends of the leads. Electrodes
may be unipolar or bipolar.
• Bipolar electrodes are located on
the same lead. Once the electrode is implanted in the myocardium, the impulse travels to
the negative electrode at the tip
of the lead, where it stimulates
the myocardium. Then the current flows back to the positive
electrode to complete the circuit.
Compared to unipolar electrodes,
bipolar electrodes are less easily
affected by outside electrical ac26
American Nurse Today
tivity, including skeletal muscle
contractions and magnetic fields.
• With a unipolar electrode, a negative electrode is located at the
distal tip of the lead and the positive electrode is located at the
pulse generator. Unipolar electrodes are more sensitive to myocardial electrical activity.
CE
1.6 contact
hours
L EARNING O BJECTIVES
1. Differentiate temporary and permanent pacemakers.
2. Describe how to interpret rhythm
strips of a patient with a pacemaker.
3. Identify a system for pacemaker
codes.
The author and planners of this CNE activity have
disclosed no relevant financial relationships with
any commercial companies pertaining to this activity. See the last page of the article to learn how to
earn CE credit.
Volume 7, Number 3
Single-chamber vs. dualchamber pacemakers
Single-chamber pacemakers are
used primarily to pace the ventricle
when the patient’s underlying
rhythm is atrial fibrillation or another atrial arrhythmia. Temporary single-chamber pacemakers most commonly are used in emergencies
when temporary pacing is required.
If the patient has an atrial arrhythmia, the lead for a single-chamber
pacemaker is placed in the right
ventricle. If the patient has intact
atrioventricular (AV) conduction
with a slow heart rate, the lead is
placed in the right atrium.
Dual-chamber pacemakers—the
most commonly implanted pacemaker type—have two leads. The pulse
generator is implanted in the chest
wall; one lead is implanted in the
right atrium and the other in the
right ventricle. The pacemaker then
maintains synchrony between the
atria and ventricles. Dual-chamber
pacemakers are used to treat AV
node dysfunction, acquired AV
blocks, and advanced second- and
third-degree heart blocks in adults, as
well as chronic bifascicular blocks.
Pacemaker codes
Many clinicians use the North American Society for Pacing and Electrophysiology/British Pacing and Electrophysiology Group (NASPE/BPEG)
generic code for Antibradycardia,
Adaptive-Rate Pacing, and Multisite
Pacing. This system describes pacemaker and automatic implantable
cardioverter-defibrillator settings.
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NASPE/BPEG generic code for pacemakers
(See NASPE/BPEG generic code for
pacemakers.)
Temporary pacemakers
Temporary pacing is indicated when
the heart rate must be increased urgently or as a preventive measure—
for instance, in postoperative cardiac
surgery patients. Right coronary artery myocardial infarction (MI) commonly causes bradycardic arrhythmias due to lack of blood flow to
the sinoatrial node. In a large percentage of individuals, the right
coronary artery also perfuses the AV
node. Many drugs, including diltiazem, digitalis, and beta blockers,
slow the heart rate and in toxic doses may cause symptomatic bradycardia. These conditions may call for
temporary pacing.
Normally, all types of temporary
pacing are demand pacing, in which
the pacemaker delivers electrical
current only when the heart’s intrinsic rate falls below the preset rate.
The three types of temporary pacing
are transcutaneous, transvenous, and
epicardial.
Transcutaneous pacing
Transcutaneous pacing is used in the
most urgent situations. The American
Heart Association’s Advanced Cardiac Life Support Guidelines recommend noninvasive transcutaneous
pacing (NTP) for hemodynamically
unstable bradycardia. When used for
symptomatic bradycardia, NTP is a
Class I recommendation—always acceptable, unquestionably safe, and
definitely useful. NTP also is recommended to ready a patient for pacing
if needed. For example, if a patient
has the potential to develop a heart
block (as after an MI), transcutaneous pacing pads are placed on the
patient so pacing can begin if symptomatic bradycardia develops.
Today, most defibrillators have a
temporary pacing function. With NTP,
one large pacing pad is placed on the
patient’s chest wall and another on
the back; both are attached to the defibrillator set in the pacing mode. (See
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The North American Society for Pacing and Electrophysiology/British Pacing and
Electrophysiology Group (NASPE/BPEG) generic code for Antibradycardia, AdaptiveRate Pacing, and Multisite Pacing has five letters (positions), indicated by Roman
numerals in the table below.
• The first letter of the code identifies which heart chamber is being paced.
• The second letter identifies the chamber where intrinsic electrical activity is being sensed.
• The third letter indicates the pacemaker’s response to what it senses. A VVI pacemaker, for instance, paces and senses the ventricle; when it senses ventricular activity, it inhibits firing.
• The fourth letter tells whether the pacemaker’s rate is modulated. A rate-modulated pacemaker increases the pacing rate to ensure the heart rate can meet the
greater cardiac output demanded by increased activity.
• The fifth letter refers to the pacemaker’s multisite pacing settings or biventricular
pacing setting.
I
II
III
IV
V
Chamber(s)
paced
Chamber(s)
sensed
Response
to sensing
Rate
modulation
Multisite
pacing
O = None
O = None
O = None
O = None
O = None
A = Atrium
A = Atrium
T = Triggered
R = Rate
modulation
A = Atrium
V = Ventricle
V = Ventricle
I = Inhibited
V = Ventricle
D = Dual (A+V) D = Dual (A+V) D = Dual (T+I)
D = Dual (A+V)
Bernstein AD, Daubert JC, Fletcher RD et al. The Revised NASPE/BPEG generic code for antibradycardia,
adaptive-rate, and multisite pacing. North American Society of Pacing and Electrophysiology/British Pacing
and Electrophysiology Group. Pacing Clin Electrophysiol. 2002 (Feb);25(2):260-4.
NASPE/BPEG implanted cardioverter-defibrillator code
The short form of the NASPE/BPEG generic pacemaker code describes the response
of an implanted cardioverter-defibrillator (ICD) to sensing.
ICD-S: ICD with shock capability only
ICD-B: ICD with bradycardia pacing as well as shock capability
ICD-T: ICD with tachycardia and bradycardia pacing, plus shock capability
Pad placement for temporary transcutaneous pacing.) When the patient’s
heart rate falls below the programmed
rate, the NTP fires or paces the myocardium through the chest wall. The
amount of milliamperes (mA) required to stimulate the myocardium
through the chest wall is higher than
when an electrode is placed directly
on the myocardium; for NTP, up to
200 mA may be used. Because NTP
may be uncomfortable for patients
who are awake, sedation and analgesia should be used if possible.
With NTP, electrocardiograph
(ECG) leads are attached to the patient to sense a QRS complex, which
represents ventricular depolarization.
Like other ventricular demand pace-
makers (which may be temporary or
permanent), an NTP fires only when
the intrinsic heart rate falls below a
set rate. When it senses a QRS complex, it inhibits firing. (See Evaluating pacemaker rhythm strips.)
Transvenous pacing
Transvenous pacing is used after the
recommended 12 hours of continuous or 24 hours of intermittent transcutaneous pacing have elapsed. It’s
also used as a bridge to permanent
pacemaker implantation. A leadwire
is guided through the vascular system to the myocardium and attached
to a cable that connects to the pulse
generator.
Transvenous pacing is relatively
March 2012
American Nurse Today
27
Pad placement for temporary transcutaneous pacing
Front
Back
around the tips of the pacing wires,
affecting capture and sensing. When
this happens, the mA setting may
have to be raised to achieve capture
and the sensitivity setting may have
to be lowered to achieve sensing.
The patient’s fluid and electrolyte
status also influences the ability to
pace and sense properly. Pacing of
both the atria and ventricles (dualchamber pacing) maintains cardiac
synchrony and optimizes preload
and cardiac output.
Permanent pacemakers
Temporary transcutaneous pacing is used in emergencies. The pads can be placed quickly so pacing can begin immediately. Most defibrillators have a temporary pacing option,
with multifunctional pads that can be used for temporary pacing or defibrillation.
Reprinted with permission from Zoll Medical.
comfortable for the patient. The
pacemaker rate can be set at a low
of 40 to 60 paced beats; the pacemaker fires when the rate drops below the set rate. In some models,
the rate can be set for up to 110
beats/minute. Transvenous pacemakers have built-in sensing to
identify ventricular depolarization.
A temporary transvenous pacemaker may be set between 0 and 20
mA; the average setting is 10 mA. The
pulse generator’s sensitivity settings
allow the generator to “see” intrinsic
myocardial activity more clearly. Sensitivity should be set so the pulse generator can “see” intrinsic P and QRS
waves, which appear on the ECG and
are measured in millivolts (mV). An
initial ventricular sensitivity setting of
2 to 5 mV is the recommended starting point for ventricular pacing. If sensitivity is set too high, electrical activity
won’t be “seen” and the pacemaker
will fire—a phenomenon called undersensing or failure to sense. If sensitivity is set too low, the pacemaker
may recognize electrical artifacts, such
as muscle movements, and will fail to
fire; this is known as oversensing.
In some patients, two pacing leads
may be placed—one in the atrium
and the other in the ventricle. When
programmed for AV sequential pacing,
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American Nurse Today
the pacemaker is used to increase cardiac output by maintaining the heart’s
natural cycle (atrial contraction followed by ventricular contraction). Additional settings for AV sequential pacing include sensitivity for atrial pacing
and the AV interval (the interval between atrial pacing and ventricular
pacing). For atrial pacing, the average
setting is 0.5 mV (which is lower than
ventricular sensitivity because the P
wave is smaller than the QRS complex). In a normal heart, the AV interval is about 200 milliseconds. Pacemaker AV intervals can be set to
mimic the patient’s normal PR interval.
Epicardial pacing
Epicardial pacing is used only with
cardiac surgery patients. Common
postoperative complications of cardiac valve surgery and coronary artery bypass surgery include episodic
sinus bradycardia, second- and thirddegree heart block, and asystole.
During the intraoperative period,
epicardial pacing wires are attached
to the epicardium, passed through
the chest wall, and attached to a
cable connected to the pacemaker’s
pulse generator. Epicardial pacemaker settings are similar to transvenous
pacemaker settings.
An endothelial sheath may form
Volume 7, Number 3
Permanent pacemakers are implanted during a short surgical procedure.
The pulse generator is placed in a
subcutaneous pocket created in the
chest wall—usually on the upper left
part of the chest below the clavicle.
Then the pulse generator is attached
to leads, which are threaded through
the vascular system to the heart and
implanted into the myocardial wall.
The atrial electrode is implanted in
the right atrium near the coronary
sinus; the ventricular electrode, near
the right ventricular apex. Currently,
most implanted pacemakers are
dual-chamber pacemakers; about
one-third have cardioversion-defibrillation settings. Implanted cardioverterdefibrillator (ICD) use is approved as
a first-line treatment for patients at
risk for ventricular tachycardia or
ventricular fibrillation.
Permanent pacemakers are used
to treat various bradycardic arrhythmias. (See Permanent pacemaker
indications.) Usually, patients are
evaluated for bradycardia based on
ECG records from 24-hour or Holter
monitoring.
Biventricular pacing
Also called cardiac resynchronization
therapy, biventricular pacing is indicated for patients with heart failure,
dilated cardiomyopathy, prolonged
ventricular conduction, or a reduced
ejection fraction. Asynchronous activation of the heart chambers (indicated by a QRS duration greater than
0.13 seconds) is linked to worsening
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Evaluating pacemaker rhythm strips
When evaluating a pacemaker rhythm strip, first locate the P wave, QRS complex, and T wave. Then look for atrial and ventricular
pacing spikes. These spikes may appear as a positive or negative deflection; they may be very small (less than 0.2 mV) or very
large (more than 10 mV). Instead of measuring the PR interval as you would with a normal electrocardiographic waveform,
measure the atrioventricular interval. Finally, assess for proper sensing.
Ventricular demand pacing (VVI)
failure to capture. Common causes of failure to capture include
a weak pulse-generator battery, loose connections, a fractured
lead, and an increased pacing threshold. An increased threshold can result from fibrosis or edema at the lead implantation
site, metabolic changes, and electrolyte abnormalities. The patient may experience such signs and symptoms as hypotension, syncope, light-headedness, and confusion.
A VVI pacemaker paces and senses the ventricle. Note the pacing spike preceding the QRS complex; the third QRS complex
isn’t preceded by a pacing spike and looks different from paced
QRS complexes because it’s an intrinsic waveform. When this
pacemaker senses an intrinsic QRS complex, it’s inhibited from
firing (as denoted by the “I” in VVI).
Failure to pace
AV sequential pacing
Atrioventricular (AV) sequential pacing is often called DDD pacing
because it senses and paces both the atria and ventricles. The third
D refers to the response to sensing; in this mode, pacemaker activity may be either inhibited or triggered. Note that the two pacing
spikes are regular and consistently appear the same distance
apart; this is called 100% AV sequential pacing. In this rhythm strip,
you can’t assess sensing because no intrinsic activity is occurring.
Failure to pace is identified by absent pacemaker activity
where it should appear. Causes include a weak battery or a
more serious pacemaker problem. To prepare for this situation,
keep a noninvasive transcutaneous pacemaker ready.
Failure to sense
Failure to capture
In this strip from a patient receiving ventricular pacing, pacing
spikes aren’t always followed by QRS complexes, indicating
heart failure and increased morbidity
and mortality. A biventricular pacemaker has three leads—one for the
atrium and one for each ventricle.
Biventricular pacing causes synchronous contraction of both ventricles
and improves cardiac output.
End-of-life concerns
In terminally ill patients and those
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Failure to sense may result from inappropriately set sensitivity or
mechanical failure, including battery failure, fractured leads, displaced electrodes, or other electrical interference. The rhythm
strip shows pacing spikes after the third and fourth QRS complexes, indicating the pacemaker failed to sense and subsequently
fired inappropriately. If the pacemaker fires during ventricular repolarization, life-threatening ventricular arrhythmias may arise.
who’ve opted to forgo further resuscitative efforts, pacemakers with ICD
functionality may interfere with the
natural process of dying by continuing to function and delivering
shocks. As the end of the patient’s
life approaches, the patient and family should discuss with healthcare
providers whether the ICD function
should be discontinued.
If you’re caring for a monitored
hospital patient with a pacemaker,
remember that the ECG will continue to show pacing spikes and
possible electrical activity without
a pulse. This could cause confusion
in family members at the bedside,
so the healthcare team should
consider monitoring the patient
remotely.
March 2012
American Nurse Today
29
Left subclavian vein
Superior vena cava
pacing. North American Society of Pacing
and Electrophysiology/British Pacing and
Electrophysiology Group. Pacing Clin Electrophysiol. 2002 (Feb);25(2):260-4.
Chow WC, Buxton AE. Implantable Cardiac
Pacemakers and Defibrillators: All You
Wanted to Know. Malden, MA: Blackwell
Publishing, Inc; 2006.
Right atrium
Left ventricle
Permanent pacemaker indications
Patients with the following conditions may be candidates for pacemakers.
• Sinus node dysfunction: persistent sinus bradycardia, atrial fibrillation with sinus
node dysfunction, chronotropic incompetence, sinus arrest, tachy-brady syndrome, sick sinus syndrome
• Atrioventricular (AV) node dysfunction
• Acquired AV blocks in adults: post-myocardial infarction
• Chronic bifascicular block
• Hypersensitive carotid sinus syndrome
• Neurocardiogenic syncope
• Prevention of atrial arrhythmias: atrial tachyarrhythmias, prolonged QT syndrome.
•
•
•
•
Special conditions that may call for pacing include:
heart transplantation
neuromuscular disease
sleep apnea syndrome
cardiac sarcoidosis.
Biventricular pacing and cardiac resynchronization therapy may be indicated for
patients with low ejection fraction or cardiomyopathy.
Pediatric indications
Pacemakers may be indicated for children and adolescents with congenital heart
disease, including advanced heart block, sinus node dysfunction, atrial tachyarrhythmias, and sinus bradycardia.
ECG Interpretation: An Incredibly Visual!
Pocket Guide. Philadelphia, PA: Lippincott
Williams & Wilkins; 2009.
Epstein AE, DiMarco JP, Ellenbogen KA, et al.
ACC/AHA/HRS 2008 Guidelines for DeviceBased Therapy of Cardiac Rhythm Abnormalities: a report of the American College of
Cardiology/American Heart Association Task
Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002
Guidelines Update for Implantation of Cardiac Pacemakers and Antiarrhythmic Devices) developed in collaboration with the
American Association of Thoracic Surgery
and Society of Thoracic Surgeons. J Am Coll
Cardiol. 2008 May 27;51(21);e1-62. Erratum
in: J Am Coll Cardiol. 2009 Apr 21;53(16):1473.
J Am Coll Cardiol. 2009 Jan 6;53(1):147.
Field JM, Hazinski MF, Sayre MR, et al. 2010
American Heart Association Guidelines for
Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science. Circulation. 2010;122(suppl 3):S640-656. http://
circ.ahajournals.org/content/122/18_suppl_3
.toc. Accessed January 30, 2012.
Indications for use of non-invasive transcutaneous pacing. Resuscitation Central. www
.resuscitationcentral.com/pacing/indications.
Accessed January 30, 2012.
Cardioverter-defibrillator indications
Jackson A. An overview of permanent cardiac pacing. Nurs Stand. 2010 Nov 24-30;
25(12):47-57.
A permanent pacemaker with a cardioverter-defibrillator may be used for secondary prevention in sudden cardiac death survivors or for cardiomyopathy, as well as
for patients with genetic arrhythmia syndromes and long QT syndrome.
Runge MS, Stouffer GA, Patterson C. Netter’s
Cardiology (Netter Clinical Science). 2nd ed.
Philadelphia, PA: Saunders; 2010.
What the future may hold
Experts predict that permanent
pacemakers of the future will be
much smaller—about the size of a
large grain of rice—and will be implanted intravascularly, not surgically. What’s more, the pulse generator will be seated directly into the
myocardium without leads. For children, this means fewer surgeries to
replace leads in a growing body.
For adults, benefits include the possibility of fewer lead fractures and
less lead displacement.
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American Nurse Today
Each year, the number of patients
who receive permanent pacemakers
grows. Although pacemaker technology is changing constantly, the goal
of therapy remains the same—to
sustain the heart rate and improve
AV synchrony, thus optimizing cardiac output and improving the patient’s quality of life.
✯
Russo JE. Original research: deactivation of
ICDs at the end of life: a systemic review of
clinical practices and provider and patient attitudes. Am J Nurs. 2011 Oct:111(10):26-35.
Scheibly K. Systematic assessment of basic
pacemaker function. AACN Adv Crit Care.
2010 Jul-Sep:21(3);322-8.
The eleven most implanted medical devices
in America. 24/7 Wall St. Wire. July 18, 2011.
http://247wallst.com/2011/07/18/the-elevenmost-implanted-medical-devices-in-america/2/.
Accessed January 30, 2012.
Visit www.AmericanNurseToday.com/Archives
.aspx for a glossary of pacemaker terms.
Selected references
Bernstein AD, Daubert JC, Fletcher RD, et al.
The Revised NASPE/BPEG generic code for
antibradycardia, adaptive-rate, and multisite
Volume 7, Number 3
Nicolette C. Mininni is an advanced practice nurse
in critical care at UPMC Shadyside in Pittsburgh,
Pennsylvania.
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CE
POST-TEST • The beat goes on: A pacemaker primer
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Commission on Accreditation.
ANA is approved by the California Board of Registered Nursing,
Provider Number 6178.
Contact hours: 1.6.
Expiration: 12/31/14
Post-test passing score is 75%.
Please mark the correct answer online.
1. Which statement about unipolar
pacemaker electrodes is correct?
a. The negative electrode is located at the
distal tip of the lead and the positive
electrode at the pulse generator.
b. The positive electrode is located at the
distal tip of the lead and the negative
electrode at the pulse generator.
c. Unipolar electrodes are less sensitive
than bipolar electrodes to myocardial
electrical activity.
d. Unipolar electrodes are less easily
affected than bipolar electrodes by
skeletal muscle contractions.
2. A single-chamber pacemaker typically is
used for a patient with:
a. chronic bifascicular heart block.
b. acquired atrioventricular heart block.
c. advanced third-degree heart block.
d. an emergency need for pacing.
3. Which type of temporary pacing would
most likely be chosen for a patient with
hemodynamically unstable bradycardia?
a. Epicardial pacing
b. Endocardial pacing
c. Noninvasive transcutaneous pacing (NTP)
d. Biventricular pacing
4. Which type of temporary pacing usually
is used for a patient having major cardiac
surgery?
a. Epicardial pacing
b. Transvenous pacing
c. NTP
d. Biventricular pacing
5. For a patient with dilated
cardiomyopathy, which type of pacing
should you anticipate?
a. Epicardial pacing
b. Transvenous pacing
c. NTP
d. Biventricular pacing
6. The average setting for a temporary
transvenous pacemaker is:
a. 2 mA.
b. 300 mA.
c. 200 mA.
d. 10 mA.
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CE: 1.6 contact hours
ANA Center for Continuing Education and Professional Development’s
accredited provider status refers only to CNE activities and does not imply
that there is real or implied endorsement of any product, service, or company referred to in this activity nor of any company subsidizing costs related to the activity. This CNE activity does not include any unannounced
information about off-label use of a product for a purpose other than
that for which it was approved by the Food and Drug Administration
(FDA). The planners of this CNE activity have disclosed no relevant financial relationships with any commercial companies pertaining to this CNE.
P URPOSE / GOAL
To provide the information nurses need to deliver optimal care for
patients with pacemakers
L EARNING O BJECTIVES
1. Differentiate temporary and permanent pacemakers.
2. Describe how to interpret rhythm strips of a patient with a pacemaker.
3. Identify a system for pacemaker codes.
7. Up to how many milliamperes can be
used with an NTP?
a. 2 mA
b. 300 mA
c. 200 mA
d. 10 mA
8. Your patient’s pacemaker is recognizing
electrical artifacts, such as muscle movements, and isn’t firing. This situation is
called:
a. undersensing.
b. underpacing.
c. oversensing.
d. overpacing.
9. During a short surgical procedure, the
pulse generator of a permanent pacemaker
is placed:
a. in an intermuscular pocket created in the
chest wall—usually on the upper left part
of the chest below the clavicle.
b. in an intermuscular pocket created in the
chest wall—usually on the upper right
part of the chest below the clavicle.
c. in a subcutaneous pocket created in the
chest wall—usually on the upper left part
of the chest below the clavicle.
d. in a subcutaneous pocket created in the
chest wall—usually on the upper right
part of the chest below the clavicle.
10. When examining the rhythm strip of a
patient with a transvenous pacemaker, you
see that the pacing spikes aren’t always
followed by QRS complexes. You identify the
situation as:
a. ventricular demand pacing.
b. failure to pace.
c. atrioventricular sequential pacing.
d. failure to capture.
11. The first letter of the five-letter North
American Society for Pacing and Electrophysiology/British Pacing and Electrophysiology Group (NASPE/BPEG) generic
code for Antibradycardia, Adaptive-Rate
Pacing, and Multisite Pacing indicates:
a. which chamber is being paced.
b. the pacemaker’s response to sensing.
c. rate modulation.
d. multisite pacing.
12. A patient’s implanted cardioverterdefibrillator code is ICD-T, which means:
a. implanted cardioverter-defibrillator (ICD)
with shock capability only.
b. ICD with tachycardia and bradycardia
pacing, plus shock capability.
c. ICD with bradycardia pacing and shock
capability.
d. ICD with tachycardia pacing and shock
capability.
13. What does a DDI pacemaker do?
a. It paces and senses the ventricles and
atria; when it senses intrinsic activity, it
increases firing.
b. It paces and senses the atria; when it
senses intrinsic activity, it inhibits firing.
c. It paces and senses the ventricles and
atria; when it senses intrinsic activity, it
inhibits firing.
d. It paces and senses the ventricles; when
it senses intrinsic activity, it inhibits firing.
14. Which statement about a biventricular
pacemaker is correct?
a. It causes asynchronous contraction of
both ventricles.
b. It causes synchronous contraction of
both atria.
c. It has two leads.
d. It has three leads.
15. If an endothelial sheath forms around
the tips of epicardial pacing wires, which
action may be warranted?
a. The mA setting may need to be
increased and the sensitivity lowered.
b. Both the mA setting and sensitivity may
need to be decreased.
c. The mA setting may need to be
decreased and the sensitivity increased.
d. Both the mA setting and sensitivity may
need to be increased.
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