The Electrical Management of Cardiac Rhythm Disorders
Bradycardia
Device Course
Pacemaker Components
Leads
● Epicardial
● Endocardial
Goals of Cardiac Pacing
● The electrical management of bradyarrhythmias requires
○ Ability to deliver enough energy to consistently
depolarize the heart (capture)
○ Ability to correctly sense intrinsic cardiac activity
● These functions are affected by many factors
○ Settings of output parameters (pulse amplitude, pulse
width)
○ Sensitivity parameter settings
○ Impedance
○ Electrical concepts
Capture
● The capture threshold is defined as the minimum amount
of electrical energy required to consistently depolarize the
myocardium
● When a pacemaker output causes a depolarization, that
is also called “capture”
● The capture threshold is also called the pacing threshold
or the stimulation threshold
● The capture threshold is not constant
○ It can change over time (disease, medications, age)
○ It can even change over the course of the day!
What Affects the Capture Threshold?
• Activity level
• Posture
• Time of day
• Comorbidity
• Heart failure
• Meals
• Drugs
• Disease progression
Capture Threshold Values
Atrial
Ventricular
Acute Threshold
< 1.5 V
< 1.0 V
Chronic Threshold
< 2.5 V
< 2.5 V
Threshold values at implant should be low; expect chronic
thresholds to increase
These are suggested values and may not be possible for
all patients
Sensing
● Sensing refers to how well the pacemaker is able to
“listen to” or perceive intrinsic cardiac events
● Important things to consider when talking about sensing
○ Surface ECG
○ Intracardiac electrogram (EGM)
○ Sensing threshold
○ Sense amplifier
○ Sensitivity setting and sensitivity safety margin
○ Unipolar/bipolar configurations
○ Electromagnet interference
Surface ECG/Intracardiac EGM
● Surface ECG: graphic depiction of heart’s electrical signals
recorded from electrodes on the body’s surface
● Intracardiac EGM: graphic depiction of the heart’s electrical
signals recorded by electrodes from inside the heart (pacing lead)
Sensitivity Safety Margin
● Sensing thresholds are not constant and vary with many
factors
● The sensitivity safety margin allows reliable sensing even
with fluctuations in the sensing threshold
● Using this formula, the safety margin should be at least 2
at implant
Safety margin
=
Sensing Threshold
Sensitivity Setting
Electromagnetic Interference (EMI)
● EMI is defined as electrical signals of nonphysiologic
origin
● May interfere with pacemaker (temporarily or
permanently)
● Common sources of EMI
○ Cardioversion/defibrillation
○ Electrocautery
○ MRIs
○ Extracorporeal shock wave lithotripsy (ESWL)
○ Therapeutic radiation
○ Radiofrequency ablation
What About Cardioversion/Defibrillation?
● May permanently damage the pulse generator
● Can temporarily inhibit or reprogram the pacemaker
○ Backup or noise reversion mode
● Myocardial thermal damage secondary to shock which
may result in ventricular fibrillation, myocardial infarction,
or both
● Guidelines
○ Evaluate potential device interactions
○ Place paddles 4 to 6 inches away from implanted
pacemaker
○ Orient paddles in anterior/posterior position, if possible
What About Electrocautery?
● May reprogram or permanently damage the pacemaker
● May inhibit the pacemaker
● May cause the device to go into backup or noise
reversion mode
● Myocardial thermal damage secondary to the
transmission of the electrical energy may result in VF, MI,
or both
● Guidelines
○ Contraindicated
What About MRI?
● The magnet in the MRI device can cause asynchronous
pacing (pacing without sensing)
● Guidelines
○ Generally contraindicated
● Magna-Safe Study
What About Lithotripsy?
● The vibrations in extracorporeal shock wave lithotripsy
can damage the pacemaker (especially pacemakers with
sensors, i.e. rate-adaptive units)
● Guidelines
○ Program to VVI or VOO mode
○ Keep focal point of lithotripter at least 6 inches away
from the implanted pacemaker
○ Monitor the heart throughout the procedure
What About Therapeutic Radiation?
● Damage depends on dose
● Damage is cumulative; monitor device throughout course
of radiation therapy
● Transistors may fail
● Pacemakers may fail but mode of failure cannot be
predicted
● Guidelines
○ Therapeutic ionizing radiation is contraindicated
○ If therapeutic radiation is used, pacemaker should be
shielded or moved to a less vulnerable location
What About Radiofrequency Ablation?
● RF ablation can temporarily or permanently reprogram
the pulse generator
● Guidelines
○ Interrogate the pacemaker following the procedure to
verify proper function
○ If necessary, reprogram
Myopotentials
● Myopotentials are muscle noises that are sensed by the
pacemaker
● Can inhibit pacing
○ The pacemaker senses the myopotential and inhibits
the output, thinking the heart has beat on its own!
● Can interfere with sensing
● Can cause inappropriate pacing
○ The pacemaker senses myopotential noise and
inappropriately “thinks” it is atrial activity; it then tries to
pace the ventricle to keep up or track that atrial activity
More EMI Sources
● Arc welding
● Automobile alternators
● Cell phones
○ Phone antenna should not overlap area of
implanted pacemaker
○ Talk on other side from implanted device
○ Do not carry an activated cell phone near
the implanted pacemaker
○ May cause inappropriate inhibition,
asynchronous pacing, backup mode,
inappropriate rate adaptation, and mode
switching
○ Cellular Tested only from St. Jude Medical
EMI in the Medical Environment
● Electrocoagulation from
electrocautery
● Defibrillation
● Electroconvulsive therapy
● Diathermy
● MRI
● Stimulators (e.g.
transcutaneous nerve)
● Dental equipment
● Diagnostic ultrasound
● Low-frequency acupuncture
● Lithotripsy
EMI in the Industrial Environment
●
●
●
●
●
●
Arc welding
Power lines
Transformers
Radio and TV transmitters
Static charge
Large metal frames in
magnetic fields
● Induction furnaces and
heaters
● Electrical switches
EMI in the Public Environment
● CB radio
● Radiofrequency transmissions
● Telecommunications
antennas
● Airport metal detectors
● Anti-theft detectors in stores
○ These may not be marked!
● Digital cell phones
Effects of EMI
● Pacemaker protection
○ Hardware backup circuits (to protect against loss of memory or
software errors)
○ Shields
● Effects
○ EMI inhibition: pulse-to-pulse interval extends to the point that the
pacemaker does not pace as often as it should.
○ Noise reversion: change in mode (typically to asynchronous
pacing at the programmed rate) which may require
reprogramming.
○ EMI tracking: acceleration of pacing as the pacemaker tries to
track electromagnetic signals (“thinking” they are atrial signals)
Pacemaker Overview
NASPE / BPEG (NBG) Pacemaker Code
NAPSE/BPEG Generic (NBG) Code
Position
I
II
III
IV
Category
Chamber(s)
Paced
Chamber(s)
Sensed
Response
to Sensing
Rate modulation
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)
Letters
Used
Manufacturer’s
Designation
Only
S- Single
(A or V)
S- Single
(A or V)
V
Multisite Pacing
Magnet Use
● Pacemakers
○ Pace Asynchronously (VOO or DOO) at the given
battery rate (Temporarily)
○ Device will revert back to exactly the same parameters
it was programmed to once the magnet is removed
● ICD
○ Will disable ICD Shock Therapy (Temporarily)
○ Does not affect pacing
○ Device will revert back to exactly the same parameters
it was programmed to once the magnet is removed.
● Magnet must be placed over the device in order for
temporary changes to occur.
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●
●
●
●
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●
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A Systematic Approach to Diagnosing Rhythm
Strips
Measure Base Rate
Measure AV/PV Interval
Verify Atrial capture
Verify Atrial sensing
Verify Ventricular capture
Verify Ventricular sensing
Verify Underlying rhythm
Document
Dual Chamber ECG Analysis
What is the Analysis?
ECG # 1
Base Rate
60 ppm
MTR
120 ppm
AVD
200 ms
PVARP
250 ms
Dual Chamber ECG Analysis
Base Rate
What is the analysis?
ECG # 2
60 ppm
MTR
120 ppm
AVD
200 ms
PVARP
250 ms
Dual Chamber ECG Analysis
● What is the analysis
Base Rate
MTR
AV
PV
PVARP
ECG # 3
60 ppm
120 ppm
200 ms
200 ms
250 ms
Dual Chamber ECG Analysis
● What is the analysis?
Base Rate
MTR
AV
PV
PVARP
ECG # 4
60 ppm
120 ppm
200 ms
200 ms
250 ms
ECG Tracing Results!!!
● #1- Normal ECG –Dual chamber pacing and Atrial pacing
w/ Ventricular (intrinsic) sensing.
● #2- Loss of atrial capture.
● #3- Normal ECG
● #4-No ventricular sensing and loss of ventricular capture.
ECG #5
Answer
● Slide #5
○ Normal Sinus Rhythm
○ Can not determine any pacemaker function
• Pacers are usually set to pace above 50 or 60 bpm
• Single Chamber ICD- Pace above 40bpm
○ Pacemakers only work when?
• Native heart rate goes below the base rate
• An intrinsic beat does not occur before the set Paced and
Sensed AV Delays.
• Set at an Asynchronous Mode (VOO or DOO)
Thank you for your time!!!