Pacemaker Basics
Module 5
1
Objectives
• Identify the components of a pacemaker circuit
• Identify how pacemaker leads and systems are
characterized
• Perform basic pacemaker rhythm recognition
2
Intrinsic Pacemaker
• The heart generates electrical impulses that travel along a
specialized conduction pathway
– Typically, the sinus node (SA node) generates the impulses
– Conduction paths include:
• Bachman’s Bundle
• AV node
• Bundle of HIS
• Bundle Branches
• Purkinje Network
• This pattern of conduction makes it possible for the heart to
pump blood efficiently
Cardiac Conduction Review
SA node
Atria
Ventricles
AV node
Bundle
branches
The Diseased Heart May:
• Prevent, or delay, impulse
generation in the SA node
• Prevent, or delay, impulse
conduction via the AV node
SA node
• Inhibit impulse conduction
via the bundle branches
AV node
Implantable Pacemaker System
Lead
wire(s)
Implantable
pulse
generator (IPG)
Myocardial
tissue
Implantable Pacemaker Circuit
• Implantable pulse
generator (IPG):
– Battery
Lead
– Circuitry
– Connector(s)
• Leads or wires
– Cathode (negative electrode)
IPG
– Anode (positive electrode)
• Body tissue
Anode
Cathode
The Pulse Generator
• Contains a battery to
provide energy for sending
electrical impulses to the
heart
• Houses the circuitry that
controls pacemaker
operations
• Includes a connector to join
the pulse generator to the
lead(s)
Connector
Block
Circuitry
Battery
Leads are Insulated Wires
• Deliver electrical impulses
from the pulse generator to
the heart
• Sense cardiac
depolarization
Lead
Lead Characterization
• Position within the heart
• Polarity
– Endocardial or transvenous leads
– Unipolar
– Epicardial leads
– Bipolar
• Fixation mechanism
• Insulator
– Active/Screw-in
– Silicone
– Passive/Tined
– Polyurethane
• Shape
– Straight
– J-shaped used in the atrium
Endocardial Passive Fixation Leads
• The tines become lodged
in the trabeculae,
a fibrous meshwork, of
the heart
• Inserted via a cut-down
or transvenous sheath
Tines
Transvenous Active Fixation Leads
• The helix, or screw,
extends into the
endocardial tissue
– Allows for lead
positioning anywhere in
the heart’s chamber
– The helix is extended
using an included tool
– Inserted via a cut-down or
transvenous sheath
Epicardial Leads
• Leads applied directly to
the surface of the heart
– Fixation mechanisms include:
• Epicardial stab-in
• Myocardial screw-in
• Suture-on
– Applied via sternotomy or
laproscopy
Lead Polarity
• Unipolar leads
– May have a smaller diameter
lead body than bipolar leads
Unipolar lead
– Usually exhibit larger pacing
artifacts on the surface ECG
To tip (cathode)
• Bipolar leads
– Usually less susceptible to
oversensing of non-cardiac
signals (i.e., myopotentials,
EMI, etc.)
Bipolar coaxial lead
Unipolar Pacing System
• The lead has only one
electrode – the cathode –
at the tip
• The pacemaker can is the
anode
Anode
+
• When pacing, the impulse:
– Flows through the tip electrode
(cathode)
– Stimulates the heart
– Returns through body fluid and
tissue to the IPG can (anode)
Cathode
-
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Bipolar Pacing System
• The lead has both an
anode and cathode
• The pacing impulse:
– Flows through the tip
electrode located at the end
of the lead wire
– Stimulates the heart
Anode +
– Returns to the ring electrode,
the anode, above the lead tip
Anode
Cathode -
Cathode
Lead Insulators
Silicone insulated leads
• Inert
• Biocompatible
• Biostable
• Repairable with medical adhesive
Polyurethane
Silicone
• Historically very reliable
Polyurethane insulated leads
• Biocompatible
• High tear strength
• Low friction coefficient
• Smaller lead diameter
Newer bipolar lead insulation
Single Chamber and Dual Chamber Pacing Systems
Single Chamber System
• The pacing lead is
implanted in the atrium
or ventricle, depending
on the chamber to be
paced and sensed
How else can you
describe this system?
Click for answer
Ventricular pacemaker with a bipolar lead
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Paced Rhythm Recognition
Atrial pacing at a rate of 60 ppm
Paced Rhythm Recognition
Ventricular pacing at a rate of 60 ppm
The “spike” is an artifact created by the
pacemaker’s output
Paced Rhythm Recognition
On the ECG, note the difference between the paced and intrinsic
beats. Why do you think this is?
Click for answer
Because the paced beat originates and is conducted
differently than the intrinsic beat.
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Advantages/Disadvantages of
Single Chamber Pacing Systems
• Advantages
– Implant only one lead
– Pacemaker itself usually
smaller
• Disadvantages
– Single ventricular lead does
not provide AV synchrony
• Ventricular based pacing
linked to AF and HF
hospitalizations
– Single atrial lead does not
provide ventricular backup if
A-V conduction is lost
Dual Chamber System
• Two leads
– One lead implanted in the
atrium
– One lead implanted in the
ventricle
• These systems can be
unipolar or bipolar
Are these leads in the picture
active or passive fixation?
Click for answer
Passive fixation. Note, the tines look like small grappling hooks, but are
actually soft silicone.
Paced Rhythm Recognition
Dual chamber pacing at a rate of 60 ppm
The “spike” followed closely by the P- or R-wave is how we tell
if the pacemaker has “captured” the myocardium
Why a Pacemaker is Implanted
• A pacemaker is implanted to:
– Provide a heart rate to meet metabolic needs
• In order to pace the heart, it must capture the myocardium
• In order to pace the heart, it must know when to pace, i.e., it must be
able to sense
– Today’s pacemakers also:
• Provide diagnostic information
– About the pacing system
– About the patient
We’ll discuss how a pacemaker performs these
functions in upcoming CorePace modules.
26
Status Check
• Which beats are paced?
1
2
Click for answer
3
4
5
6
7
Beats 3 and 6 are intrinsic
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Status Check
• Is this a unipolar or bipolar lead?
Click for answer
Bipolar. The tip (screw) is the cathode, the ring is the anode. For
simplicity’s sake we often refer to these as the “tip” and “ring.”
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Status Check
In this unipolar system,
the lead tip is
negatively charged
(cathode). What acts
as the positive
electrode (anode)?
Anode +
Click for answer
Cathode -
The pacemaker case.
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Status Check
Provide an explanation
for why the pacemaker
did not “capture” (think of
the electrical concepts)
?
Click for answer
Lead fracture, failing battery, improper programming, insulation failure
any or all might explain this. We’ll discuss how to determine the cause in
“Evaluation and Troubleshooting.”
30
Status Check
• Identify the most likely pacemaker that resulted in this strip
Click for answer
Atrial pacemaker
Ventricular pacemaker
Dual chamber pacemaker
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Brief Statements
Indications
•
Implantable Pulse Generators (IPGs) are indicated for rate adaptive pacing in patients who ay benefit from increased
pacing rates concurrent with increases in activity and increases in activity and/or minute ventilation. Pacemakers are
also indicated for dual chamber and atrial tracking modes in patients who may benefit from maintenance of AV
synchrony. Dual chamber modes are specifically indicated for treatment of conduction disorders that require restoration
of both rate and AV synchrony, which include various degrees of AV block to maintain the atrial contribution to cardiac
output and VVI intolerance (e.g. pacemaker syndrome) in the presence of persistent sinus rhythm.
•
Implantable cardioverter defibrillators (ICDs) are indicated for ventricular antitachycardia pacing and ventricular
defibrillation for automated treatment of life-threatening ventricular arrhythmias.
•
Cardiac Resynchronization Therapy (CRT) ICDs are indicated for ventricular antitachycardia pacing and ventricular
defibrillation for automated treatment of life-threatening ventricular arrhythmias and for the reduction of the symptoms of
moderate to severe heart failure (NYHA Functional Class III or IV) in those patients who remain symptomatic despite
stable, optimal medical therapy and have a left ventricular ejection fraction less than or equal to 35% and a QRS
duration of ≥130 ms.
•
CRT IPGs are indicated for the reduction of the symptoms of moderate to severe heart failure (NYHA Functional Class
III or IV) in those patients who remain symptomatic despite stable, optimal medical therapy, and have a left ventricular
ejection fraction less than or equal to 35% and a QRS duration of ≥130 ms.
Contraindications
•
IPGs and CRT IPGs are contraindicated for dual chamber atrial pacing in patients with chronic refractory atrial
tachyarrhythmias; asynchronous pacing in the presence (or likelihood) of competitive paced and intrinsic rhythms;
unipolar pacing for patients with an implanted cardioverter defibrillator because it may cause unwanted delivery or
inhibition of ICD therapy; and certain IPGs are contraindicated for use with epicardial leads and with abdominal
implantation.
•
ICDs and CRT ICDs are contraindicated in patients whose ventricular tachyarrhythmias may have transient or
reversible causes, patients with incessant VT or VF, and for patients who have a unipolar pacemaker. ICDs are also
contraindicated for patients whose primary disorder is bradyarrhythmia.
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Brief Statements (continued)
Warnings/Precautions
• Changes in a patient’s disease and/or medications may alter the efficacy of the device’s programmed
parameters. Patients should avoid sources of magnetic and electromagnetic radiation to avoid
possible underdetection, inappropriate sensing and/or therapy delivery, tissue damage, induction of an
arrhythmia, device electrical reset or device damage. Do not place transthoracic defibrillation paddles
directly over the device. Additionally, for CRT ICDs and CRT IPGs, certain programming and device
operations may not provide cardiac resynchronization. Also for CRT IPGs, Elective Replacement
Indicator (ERI) results in the device switching to VVI pacing at 65 ppm. In this mode, patients may
experience loss of cardiac resynchronization therapy and / or loss of AV synchrony. For this reason,
the device should be replaced prior to ERI being set.
Potential complications
• Potential complications include, but are not limited to, rejection phenomena, erosion through the skin,
muscle or nerve stimulation, oversensing, failure to detect and/or terminate arrhythmia episodes, and
surgical complications such as hematoma, infection, inflammation, and thrombosis. An additional
complication for ICDs and CRT ICDs is the acceleration of ventricular tachycardia.
• See the device manual for detailed information regarding the implant procedure, indications,
contraindications, warnings, precautions, and potential complications/adverse events. For further
information, please call Medtronic at 1-800-328-2518 and/or consult Medtronic’s website at
www.medtronic.com.
Caution: Federal law (USA) restricts these devices to sale by or on the order of a physician.
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Brief Statement: Medtronic Leads
Indications
• Medtronic leads are used as part of a cardiac rhythm disease management system. Leads are
intended for pacing and sensing and/or defibrillation. Defibrillation leads have application for patients
for whom implantable cardioverter defibrillation is indicated
Contraindications
• Medtronic leads are contraindicated for the following:
• ventricular use in patients with tricuspid valvular disease or a tricuspid mechanical heart valve.
• patients for whom a single dose of 1.0 mg of dexamethasone sodium phosphate or dexamethasone
acetate may be contraindicated. (includes all leads which contain these steroids)
• Epicardial leads should not be used on patients with a heavily infracted or fibrotic myocardium.
• The SelectSecure Model 3830 Lead is also contraindicated for the following:
• patients for whom a single dose of 40.µg of beclomethasone dipropionate may be contraindicated.
• patients with obstructed or inadequate vasculature for intravenous catheterization.
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Brief Statement: Medtronic Leads (continued)
Warnings/Precautions
• People with metal implants such as pacemakers, implantable cardioverter defibrillators (ICDs), and
accompanying leads should not receive diathermy treatment. The interaction between the implant and
diathermy can cause tissue damage, fibrillation, or damage to the device components, which could
result in serious injury, loss of therapy, or the need to reprogram or replace the device.
• For the SelectSecure Model 3830 lead, total patient exposure to beclomethasone 17,21-dipropionate
should be considered when implanting multiple leads. No drug interactions with inhaled
beclomethasone 17,21-dipropionate have been described. Drug interactions of beclomethasone
17,21-dipropionate with the Model 3830 lead have not been studied.
Potential Complications
• Potential complications include, but are not limited to, valve damage, fibrillation and other arrhythmias,
thrombosis, thrombotic and air embolism, cardiac perforation, heart wall rupture, cardiac tamponade,
muscle or nerve stimulation, pericardial rub, infection, myocardial irritability, and pneumothorax.
Other potential complications related to the lead may include lead dislodgement, lead conductor
fracture, insulation failure, threshold elevation or exit block.
• See specific device manual for detailed information regarding the implant procedure, indications,
contraindications, warnings, precautions, and potential complications/adverse events. For further
information, please call Medtronic at 1-800-328-2518 and/or consult Medtronic’s website at
www.medtronic.com.
Caution: Federal law (USA) restricts this device to sale by or on the order of a physician.
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Disclosure
NOTE:
This presentation is provided for general educational purposes
only and should not be considered the exclusive source for this
type of information. At all times, it is the professional
responsibility of the practitioner to exercise independent
clinical judgment in a particular situation.
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