The document provides an overview of basic technical concepts in cardiac pacing. It discusses how artificial electrical stimulation works by creating an electrical field that initiates action potentials in cardiac cells. It also covers topics like: - Myocardial stimulation theory - Components of a pacemaker system - Unipolar and bipolar pacing systems - Pacing circuit parameters like voltage, current, impedance, and energy - Factors that determine stimulation threshold - Programming considerations for pacemaker output

1. Basic Technical Concepts inBasic Technical Concepts in
Cardiac PacingCardiac Pacing
Dr D Sunil Reddy
Consultant Cardiologist
KIMS Hospital

2. TopicTopic
 Electrical Stimulation of Cardiac Tissue

3. Myocardial StimulationMyocardial Stimulation
 An artificial electrical stimulus
excites cardiac tissue by the
creation of an electrical field at the
interface of the stimulating
electrode and the myocardium
 The electric field should be strong
enough and should last long
enough to initiate action potentials
in the cells at the electrode-tissue
interface

4. Myocardial StimulationMyocardial Stimulation
 The AP’s at the site of stimulation
result in AP’s in the neighbouring
areas of the myocardium
resulting in a wave of AP’s
(depolarization) propagating
away from the site of stimulation
Time (Milliseconds)
100 200 300 400 500
Phase 2
Phase 1
Phase 3
Phase 4
TransmembranePotential
(Millivolts)
-50
0
50
-100
Phase0
Threshold
 An artificial electrical stimulus excites
cardiac tissue by the creation of an
electrical field at the interface of the
stimulating electrode and the myocardium
 The electric field should be strong enough
and should last long enough to initiate
action potentials in the cells at the
electrode-tissue interface

5. Electric Field – Current DensityElectric Field – Current Density
TheoryTheory
 Electric Field Theory
– A Minimum Voltage/cmis required to trigger a
self-propagating wave of depolarization
 Current Density Theory
– A Minimum Current/cm2
is required to trigger a
self-propagating wave of depolarization
 Stimulation threshold is a function of Voltage/cm or
Current/ cm2
that is induced in the myocardium
beneath the stimulating electrode
 The two theories are related by Ohm’s Law

6. The Implantable Pacemaker SystemThe Implantable Pacemaker System
 The Implantable Pulse Generator (IPG) : metal can
(titanium) containing electronics/battery & an electrode or
lead connector header
 Lead : Electrical connection between the pacemaker & the
heart

7. The Pacemaker CircuitThe Pacemaker Circuit
 Stimulation of cardiac tissue using electric pulses
– IPG
– Lead – insulated current conductor (s) &
electrodes to transmit pulses to heart tissue
and measure or sense electrical activity in the
heart
Heart
Lead
IPG
Completion of circuit
through
Lead or Body tissue

8. A Unipolar Pacing System Contains a Lead withA Unipolar Pacing System Contains a Lead with
Only One Electrode Within the Heart; In ThisOnly One Electrode Within the Heart; In This
System, the Impulse:System, the Impulse:
 Flows through the tip
electrode (cathode)
 Stimulates the heart
 Returns through
body fluid and tissue
to the IPG (anode)
Cathode
Anode
-

9. Anode
 Flows through the
tip electrode located
at the end of the
lead wire
 Stimulates the heart
 Returns to the ring
electrode above the
lead tip
A Bipolar Pacing System Contains a Lead with TwoA Bipolar Pacing System Contains a Lead with Two
Electrodes Within the Heart. In This System, the Impulse:Electrodes Within the Heart. In This System, the Impulse:
Cathode
Tip electrode coil
Indifferent electrode
coil

10. Lead Components
Connector
Lead body
Electrode(s)
Insulation
Conductors
Fixation
Threshold
Sensing
Connector
Standards

11. Electrodes -- Fixation Mechanism
 Passive Fixation Mechanism – Endocardial
– Tined
– Finned
– Canted/curved

12. Electrodes – Fixation Mechanism
 Active Fixation Mechanism – Endocardial
– Fixed screw
– Extendible/retractable

13. Electrodes -- Fixation Mechanism
 Fixation Mechanism – Myocardial/Epicardial
– Stab-in
– Screw-in
– Suture-on

14. Single-Chamber SystemSingle-Chamber System
 The pacing lead is
implanted in the
atrium or ventricle,
depending on the
chamber to be paced
and sensed

15.  One lead implanted
in the atrium and
one in the ventricle
Dual-Chamber Systems Have Two Leads:Dual-Chamber Systems Have Two Leads:

16. A pacing system can be thought of a standard electrical
circuit:
The pacemaker supplies the voltage.
Current (electrons) flow down the
conductor to the lead tip or cathode (-)
Where the lead tip touches the
myocardium, electrical resistance is
produced.
The current then flows through the
body tissues to the anode (+) and back
to the battery.
All of these things are required for
current to flow.

17. Pacing Circuit ParametersPacing Circuit Parameters
 Voltage
 Current
 Impedance (resistance)
 Energy

18. VoltageVoltage
Pushes electrons through an electric circuit resulting in electric
current through the circuit

19. VoltageVoltage
 Voltage is the force or “push” that causes
electrons to move through a circuit
 In a pacing system, voltage is:
– Measured in volts
– Represented by the letter “V”
– Provided by the pacemaker battery
– Often referred to as amplitude

20. CurrentCurrent
Current is the flow of charge or electrons through a circuit

21. CurrentCurrent
 The flow of electrons in a completed circuit
 In a pacing system, current is:
– Measured in mA (milliamps)
– Represented by the letter “I”
– Determined by the amount of electrons that
move through a circuit

22. Resistance or ImpedanceResistance or Impedance
Opposition offered by a circuit to the flow of current

23. ImpedanceImpedance
 The opposition to current flow in a circuit
 In a pacing system, impedance is:
– Measured in ohms
– Represented by the letter “R” (Ω for
numerical values)
– The measurement of the sum of all
resistance to the flow of current

24. Ohm’s LawOhm’s Law
Voltage = Current X Resistance
Current = Voltage ÷Resistance
Resistance = Voltage ÷ Current

25. The Pacemaker StimulusThe Pacemaker Stimulus
Time
5 Volts 5 Volts
0.5 ms
1 sec
Pacing Stimulus Voltage or Amplitude – 5 Volts
Pulse Width – 0.0005 seconds or 0.5 milliseconds
Pacing Rate – One stimulus per second or 60 stimuli (beats)
per minute
Voltage

26. The Pacing PulseThe Pacing Pulse
tt
Pacing Pulse
Pulse Duration (Width)
OutputVoltage
V = Pulse Amplitude in Volts (V) (say 2.5 V)
t = Pulse Duration or Width in milliseconds (ms)
(say 0.5 ms)
R = Impedance of Pacing Circuit (ohms)
(say 500 ohms)
I = V/R = Current through pacing circuit (mA)
= 2.5 V/ 500 ohms = 0.005 A = 5 mA
E = Energy supplied by Pulse to the Pacing Circuit
and Cardiac Tissue = V . I . t = I2
Rt = V2
t/R
= 2.5 V . 5 mA . 0.5 ms = 6.25 micro Joules
V
t

27. Stimulation ThresholdStimulation Threshold
 Pacing Voltage Threshold – The minimum
pacing voltage at any given pulse width
required to consistently achieve myocardial
depolarization outside the heart’s refractory
period

28. Loss of Capture

29. The Strength-Duration RelationThe Strength-Duration Relation
 The intensity of an electrical stimulus (Energy,
Voltage, Current, Charge) required to capture
(non-refractory) cardiac tissue is dependent on
the duration for which the electrical stimulus is
applied (i.e. pulse width)

30. The Voltage-Strength DurationThe Voltage-Strength Duration
CurveCurve
 Stimulus Voltage & Pulse Width
have an exponential relationship
 At short pulse widths (<0.25 ms)the
curve rises sharply (i.e. small
reductions in pulse width result in
large increases in the voltage
threshold)
 At long pulse widths (>1.0 ms)the
curve is flat (i.e. the voltage
threshold does not reduce with
increasing pulse width) Duration
Pulse Width (ms)
.50
1.0
1.5
2.0
.25StimulationThreshold(Volts)
0.25 1.0 1.5
Capture

31. Rheobase & ChronaxieRheobase & Chronaxie
Rheobase Voltage = Voltage
Threshold at infinite Pulse widths
(e.g. 2 ms) – also known as
fundamental threshold
Chronaxie Point = Pulse Width
threshold at twice the rheobase
voltage (i.e. 1 V & 0.3 ms)
Energy of Pacing Pulse
At rheobase = 0.5V. 2ms. 1mA = 1
MicroJoule
At Chronaxie = 1V. 0.3 ms. 2mA
= 0.6 MicroJoules
At PW=0.25 ms, = 1.5V. 0.25ms.
3mA = 1.125 MicroJoules
The chronaxie point approximates the point of minimum threshold energy on the Strength-Duration Curve
Duration
Pulse Width (ms)
StimulationThreshold(Volts)
0.2 0.6 1.0
Energy Strength Duration
Curve
Capture
0.4
0.5
1.0
2.0
0.8 1.2 1.4
Rheobase Voltage
Chronaxie Point

32. Goals of Pacemaker OutputGoals of Pacemaker Output
ProgrammingProgramming
 Consistent capture & Patient Safety is ensured
 Battery drain minimized, Pacemaker longevity
maximized

33. Programming Chronic PacemakerProgramming Chronic Pacemaker
OutputOutput
Duration
Pulse Width (ms)
StimulationThreshold(Volts)
0.2 0.6 1.0
Energy Strength Duration Curve
• Capture
Adequate Safety Margin while minimizing
Pulse Energy
Operate around the chronaxie point
Programming long pulse widths (& low
Voltages) increases Pulse energy but
hardly increases safety margin
Programming high voltages (with short
Pulse widths) increases Pulse energy but
hardly increases safety margin
For a 2 times safety margin :
Output = 2 x chronaxie voltage at
chronaxie pulse width (2V, 0.35 ms)
Output = 3 x pulse duration threshold
at twice chronaxie voltage (2V, 0.51 ms)
0.4
0.5
1.0
2.0
0.8 1.2 1.4
Rheobase
Chronaxie

34. Determination of StimulationDetermination of Stimulation
Threshold during Implant or Follow-upThreshold during Implant or Follow-up
 Pace the heart at
– Rate higher than sinus or intrinsic rate
– Stimulus amplitude and pulse width that ensure
capture (usually 5 V and 0.5 ms)
 Gradually reduce stimulus amplitude while maintaining
pulse width constant till capture is lost
 The Stimulation threshold is specified by the minimum
stimulus amplitude at which capture consistently occurs
at a given stimulus pulse width

35. Programming Pacemaker OutputProgramming Pacemaker Output
 Acute – Immediately post-implant
 Chronic – Approx. 6 to 8 weeks post implant
 Goal : To ensure consistent capture despite potential
changes in the SD curve while minimizing the energy
delivered by the pulse

36. Evolution of Pacing ThresholdEvolution of Pacing ThresholdVoltage
Threshold(V)
Observation Time (weeks)
Acute Phase
Chronic Phase
Safety Margin
6
5
4
3
2
1
0 4 8 12 16

37. Programmable ParametersProgrammable Parameters
 Pacemaker Pulse Output or Amplitude
– 0.5 V, 1.0 V, 1.5 V…., 7.5 V
 Pacemaker Pulse Width
– 0.03, 0.06, …., 0.25, 0.5,…, 1.0 milliseconds

38. Pacing Impedance - ConsiderationsPacing Impedance - Considerations
 Maximize Pacemaker Longevity
– Reduce current drain
– Maintain relatively high impedance
 Ensure consistent capture
– Appropriate voltage & current are available
at the electrode-tissue interface required to
stimulate tissue

39. I pacing
Components of Pacing ImpedanceComponents of Pacing Impedance
Rcoil
Zpolarisation -electrode tissue
interface
Rtissue
Electrode
Tissue
Interface
Pulse
Generator
V pulse
I pacing

40. RRcoil -coil - Lead Conductor ResistanceLead Conductor Resistance
– Lead Conductor
Impedance
• Reduces the voltage &
energy available at the
tissue for pacing
• Generates waste heat
• Designed to be low
conductor
resistance

41. Conductor ResistanceConductor Resistance
Total Coil Voltage Voltage
impedance resistance at tip loss
(Ω)(Ω) (V) %
600 50 2.3 8.3
750 200 1.8 26.7
1200 650 1.1 54.2
1200 50 2.4 4.2
Output Voltage = 2.5 V
Impact of conductor coil resistance upon
available tip electrode voltage

42. Conductor Resistance
V mV
2.5 2500
Total imp 600
Current I =V/R 4.166666667 mAConductor
imp 50
Voltage drop V = IR 208.3333333 mV
0.208333333 V

43. What is the Polarization Effect – PolarizationWhat is the Polarization Effect – Polarization
Impedance ?Impedance ?
As the pacing pulse begins, electrons from the pacemaker battery flow to the lead
tip and positively charged ions from the tissue are attracted to the lead tip.
Initially, the movement of these negatively
charged ions results in the flow of current
from the electrode into the myocardium.
As the pacing pulse continues, positively charged ions surround the electrode tip. This
produces a positively charged layer on the electrode called polarization. Polarization can
impede current flow from the electrode into the tissue.

44. Polarization Impedance &Polarization Impedance &
Electrode Surface AreaElectrode Surface Area
 As electrode surface area goes up
– Polarization impedance decreases
 As electrode surface area goes down
– Polarization impedance increases

45. Polarization ImpedancePolarization Impedance
Pacing Pulse
Polarization

46. Factors affecting PolarizationFactors affecting Polarization
ImpedanceImpedance
 Pulse Width
 Surface area of the electrode tip
– Larger the surface area – Lower the
Polarization

47. Electrode – Tissue InterfaceElectrode – Tissue Interface
ImpedanceImpedance
 Resistance to current flow from body tissue at the
electrode-tissue interface

48. Electrode – Tissue InterfaceElectrode – Tissue Interface
ImpedanceImpedance
 Smaller the surface area of the tip electrode, the higher
the current density (or electric field strength) at the
electrode-tissue interface
 The higher the field strength, the greater the pacing
efficiency & lower the threshold

49. Electrode – Tissue InterfaceElectrode – Tissue Interface
ImpedanceImpedance
 Smaller the geometric size of the tip electrode, the
higher the resistance between electrode and tissue
PacingImpedance(Ohms)
0
500
1000
1500
0 1 2 3 4 5.5 6
Geometric Tip Electrode Surface Area (mm2
)
Size = Impedance

50. The Ideal Stimulating ElectrodeThe Ideal Stimulating Electrode
 Needs large surface area to reduce Polarization
Impedance
 Needs small size to maximize Electric Field
Strength and Stimulation Efficacy
 Needs small size to maximize Electrode-tissue
resistance and minimize pacemaker current
drain

51. Electrodes -- Surface StructureElectrodes -- Surface Structure
 Porous Electrode Surface
CapSure®
8.0 mm2
Porous Electrode
CapSure®
SP Novus
5.8 mm2
Platinized
Porous Electrode
CapSure®
Z Novus
1.2 mm2
Platinized
Porous Electrode
15KV x2500 12.0V MDT

52. Analogy:
Lead with low impedance
and poor efficiency
Lead Impedance I

53. Lead Impedance II
(Conductor-) Resistance
Analogy:
Lead with high impedance in the
conductor and poor efficiency

54. Lead Impedance III
Analogy:
Lead with big tip-tissue impedance
low conductor impedance
and increased efficiency

55. The Chronic Virtual ElectrodeThe Chronic Virtual Electrode
IMPLANT CHRONIC
(8 weeks or longer)
Excitable
Cardiac
Tissue
Non-Excitable
Fibrotic
Tissue
Excitable
Cardiac
Tissue

56. Evolution of Pacing ThresholdEvolution of Pacing ThresholdVoltage
Threshold(V)
Observation Time (weeks)
Acute Phase
Chronic Phase
Safety Margin
6
5
4
3
2
1
0 4 8 12 16

57. Electrodes -- Steroid ElutionElectrodes -- Steroid Elution
Tines for
Stable Fixation
Silicone Rubber Plug
Containing Steroid
Porous,
Platinized Tip
for Steroid
Elution
 Type - Steroid in matrix

58. Electrodes -- Steroid ElutionElectrodes -- Steroid Elution
 Effect of Steroid on Stimulation Thresholds
Pulse Width = 0.5 msec
0
3 6
Implant Time (Weeks)
Textured Metal Electrode
Smooth Metal Electrode
1
2
3
4
5
Steroid-Eluting Electrode
0 1 2 4 5 7 8 9 10 11 12
Volts

59. Factors that affect StimulationFactors that affect Stimulation
ThresholdThreshold
 Eating, Sleeping, Exercise, Medications, Changes in Cardiac condition –
30 to 50 % during the day
 Drugs e.g. Steroids reduce stimulation threshold by reducing
inflammation
 Sympathomimetic drugs decrease threshold
 Amiodarone, Class I A (quinidine, procainamide), Class I B (Mexilitene)
 Hypokalemia increases threshold (diuretics)
 Hypocalcemia increases threshold
 Hypoxia & Hypercapnia – Increase threshold
 Electrolyte imbalance & pH e.g. acidosis and alkalosis increase threshold

60. Typical Pacing CircuitTypical Pacing Circuit
ImpedancesImpedances
 300 to 1200 ohms
 May be measured at implant time with a
Pacing System Analyzer (PSA) at implant time
 May be measured through telemetry with a
pacemaker programmer

61. Pacing Impedance Values Will Change DuePacing Impedance Values Will Change Due
to:to:
 Insulation breaks
 Wire fractures

62. An Insulation Break Around the Lead WireAn Insulation Break Around the Lead Wire
Can Cause Impedance Values to FallCan Cause Impedance Values to Fall
 Insulation breaks expose the
wire to body fluids which
have a low resistance and
cause impedance values to fall
 Current drains through the
insulation break into the body
which depletes the battery
 An insulation break can cause
impedance values to fall
below 300 Ω
Insulation break
Decreased resistance

63. A Wire Fracture Within the Insulating SheathA Wire Fracture Within the Insulating Sheath
May Cause Impedance Values to RiseMay Cause Impedance Values to Rise
 Impedance values
across a break in the
wire will increase
 Current flow may be
too low to be effective
 Impedance values
may exceed 3,000 Ω
Lead wire fracture
Increased resistance

64. Unipolar &Bipolar StimulationUnipolar &Bipolar Stimulation
+
-
+ -
-
+
Anode is IPG
Case
Cathode is lead tip
electrode
-
+
Anode is lead
proximal
electrode
Cathode is lead tip
electrode

65. Unipolar & Bipolar StimulationUnipolar & Bipolar Stimulation
Unipolar Stimulation– Large Stimulus Artifact
Bipolar Stimulation – Small Stimulus Artifact
There is a greater chance of pacemaker pocket
muscle stimulation with Unipolar Stimulation

66. The Pacemaker BatteryThe Pacemaker Battery
 Pacemakers typically use Lithium-Iodide batteries
 Most LiI batteries have a Beginning of Life (BOL) value
of 2.8 volts
 Recommended Replacement Time (ERI/RRT) value of
2.6 V
 End of Service (EOL/EOS) value of 2.5 V
 As battery depletes its internal resistance goes up – (BOL
= 100 ohms , EOL > 5000 ohms )

67. Recommended Replacement Time
RRT (ERI)
2.8V-
2.6V-
2.5V-
BOL
RRT 2.6V
EOS 2.5V
Time
Lithium Iodine Battery depletion
BOL – Beginning of Life
RRT – Recommended Replacement Time
EOS - End of Service

68. Battery LifeBattery Life
 Battery Life
– Battery Life = Battery Capacity/Current Drain
– 2.0 Ah/25microamps = 80,000 hours = 9.3 years
 Battery properties
– Reliability – no premature failure
– High volumetric energy density – Small battery
volume with high storage capacity
– Low self-discharge rate
– High hermiticity – no gas generation during
operation

69. Pacemaker LongevityPacemaker Longevity
 Energy = (V.I.t) = (V2
/R) . t Joules
 Reducing V by a factor of 2 reduces E by a
factor of 4
 Increasing Z by a factor by 2 reduces E by a
factor of 2

70. Pacemaker LongevityPacemaker Longevity
 High Outputs and pulse widths are the primary
cause for reduced pacemaker longevity
• Output Voltages higher than the Battery Voltage (2.8 V)
require the use of voltage doublers that use high battery
energy
• Long Pulse Widths Reduce pacing efficiency due to
increased polarization impedance

71. Sensing Intracardiac ElectricalSensing Intracardiac Electrical
ActivityActivity

72. A Pacemaker Must Be Able to Sense
and Respond to Cardiac Rhythms
 Accurate sensing enables the pacemaker to determine
whether or not the heart has created a beat on its own
 The pacemaker is usually programmed to respond with
a pacing impulse only when the heart fails to produce
an intrinsic beat

73. Intracardiac Electrical SignalsIntracardiac Electrical Signals
 Electrical currents that arise in the myocardium during
depolarization and repolarization
 A myocardial electrode - records voltage difference
wrt reference electrode when the myocardium under
the electrode undergoes depolarization or
repolarization
 The electrical activity measured by such an electrode
(which is in direct contact with cardiac tissue) – local
tissue electrical activity- Intracardiac Electrogram or
EGM

74. Sensing the EGMSensing the EGM

75. Depolarization WaveDepolarization Wave
Processed byProcessed by
DeviceDevice
Processed byProcessed by
DeviceDevice
The EGM Signal
The signal from a depolarization wave passing between two electrodes

76. Intracardiac ElectrogramIntracardiac Electrogram
R wave of the EGM indicating
depolarisation of cardiac
ventricular tissue at lead tip –
Roughly corresponds to R
wave of the ECG that
represents depolarisation of the
ventricles
T wave of the EGM indicating
repolarisation of cardiac
ventricular tissue at lead tip –
Roughly corresponds to T wave
of the ECG that represents
repolarisation of the ventricles

77. Voltage Deflections of the SensedVoltage Deflections of the Sensed
EGM in a PacemakerEGM in a Pacemaker
Pacemaker
Stimulus
Paced R wave
Post-pace T wave
Intrinsic R wave
T wave corresponding to
intrinsic R wave

78. Undersensing . . .
 Pacemaker does not “see” the intrinsic beat, and therefore
does not respond appropriately
Intrinsic beat
not sensed
Scheduled pace
delivered
VVI / 60

79. Oversensing
 An electrical signal other than the intended P or R wave
is detected
Marker channel
shows intrinsic
activity...
...though no
activity is
present
VVI / 60

80.  Measured by:
– Amplitude
• Peak-to-peak measurement (height)
of deflection
• Measured in Millivolts (mV)
– Slew Rate
• Speed of deflection change over time
• Measured in volts per second (V/s)
EGM amplitude

81. EGM Amplitude & Slew RateEGM Amplitude & Slew Rate
Amplitude of the EGM R wave = dV
Slew Rate of the EGM R wave= dV/dt

82. EGM amplitude & slew rate – ideal
values
Atrium Ventricle
Slew Rate 0.5 volts/sec 0.75 volts/sec
Amplitude >1.5 mV >5.0 mV

83. Which of the these complexes shows the
highest slew rate?
a)1
b)2
c)3
d)4

84. Frequency (Hz)
Accurate Sensing Requires That
Extraneous Signals Be Filtered Out

85. Effect of Filtering on EGMEffect of Filtering on EGM
FILTER
•Filters out frequencies below 5 Hz (T waves) and above 50 Hz
(myopotentials)
•Enhances frequencies between 10 Hz and 50 Hz (R waves) with maximum
enhancement at around 30 Hz frequency
• Low Slew Rate implies Low Frequency implies Less enhancement due to
filtering
Level
Detector

86. Level Detector or SensitivityLevel Detector or Sensitivity
SettingSetting
This is a value specified to the pacemaker in millivolts through programming.
All ventricular EGM deflections AFTER FILTERING that exceed the sensitivity
setting will be identified by the pacemaker as intrinsic R waves
The typical sensitivity setting that is programmed for Ventricular sensing is 2.5 mV

87. Sensitivity
The Greater the Number, the Less Sensitive the Device to Intracardiac Events

88. Sensitivity
Amplitude(mV)
Time
5.0
2.5
1.25

89. Sensitivity SettingSensitivity Setting
Sensitivity settings less than 2.5 mv – High sensitivity – can lead
to oversensing
Sensitivity settings greater than 2.5 mV – Low sensitivity – can
lead to undersensing
Amplitude(mV)
Amplitude(mV)
Time Time
5.0
2.5
1.25
5.0
2.5
1.25

90. Factors That May Affect Sensing Are:
 Lead polarity (unipolar vs. bipolar)
 Lead integrity
– Insulation break
– Wire fracture
 EMI – Electromagnetic Interference

91. Unipolar Sensing
 Produces a large
potential difference due
to:
– A cathode and
anode that are
farther apart than
in a bipolar
system
_

92. Bipolar Sensing
 Produces a smaller potential
difference due to the short
interelectrode distance
– Electrical signals from
outside the heart such
as myopotentials are
less likely to be sensed

93. An Insulation Break May Cause Both
Undersensing or Oversensing
 Undersensing occurs when inner and outer conductor coils are in
continuous contact
– Signals from intrinsic beats are reduced at the sense
amplifier and amplitude no longer meets the programmed
sensing value
–
 Oversensing occurs when inner and outer conductor coils make
intermittent contact
– Signals are incorrectly interpreted as P or R waves

94. Wire Fracture Can Cause Both Undersensing and
Oversensing
 Undersensing occurs when the cardiac signal is unable to get back to the
pacemaker – intrinsic signals cannot cross the wire fracture
 Oversensing occurs when the severed ends of the wire intermittently make
contact, which creates potentials interpreted by the pacemaker as P or R waves
Fracture in one filament leads to an
increase in resistance

95. Electromagnetic Interference
 Interference is caused by electromagnetic energy with a source that is
outside the body
 Electromagnetic fields that may affect pacemakers are radio-frequency
waves
– 50-60 Hz are most frequently associated with
pacemaker interference
 Few sources of EMI are found in the home or office but several exist in
hospitals

96. Oversensing May Occur When EMI Signals Are
Incorrectly Interpreted as P Waves or R Waves
 Pacing rates will vary as a result of EMI:
– Rates will accelerate if sensed as P waves in
dual-chamber systems (P waves are “tracked”)
– Rates will be low or inhibited if sensed in single-
chamber systems, or on ventricular lead in
dual-chamber systems

97. Electrocautery is the Most Common Hospital
Source of Pacemaker EMI
 Outcomes
– Oversensing–inhibition
– Undersensing (noise
reversion)
– Power on Reset
– Permanent loss of
pacemaker output
(if battery
voltage is low)
 Precautions
– Reprogram mode to
VOO/DOO, or place a
magnet over device
– Strategically place the
grounding plate
– Limit electrocautery
bursts to 1-second burst
every 10 seconds
– Use bipolar
electrocautery forceps

98. Transthoracic Defibrillation
 Outcome
– Inappropriate reprogramming
of the pulse
generator (POR)
– Damage to
pacemaker circuitry
 Precautions
– Position defibrillation paddles
apex-posterior (AP) and as far
from the pacemaker and leads
as possible

99. Magnetic Resonance Imaging (MRI) is Generally
Contraindicated in Patients with Pacemakers
 Outcomes
– Extremely high
pacing rate
– Reversion to
asynchronous pacing
 Precautions
– Program pacemaker
output low enough to
create persistent
non-capture, ODO
or OVO mode

100. Radiation Energy May Cause Permanent
Damage
 Certain kinds of radiation energy may cause damage to the semi-
conductor circuitry
– Ionizing radiation used for breast or
lung cancer therapy
 Damage can be permanent and requires
replacement of the pacemaker

101. Therapeutic Radiation May Cause Severe
Damage
 Outcomes:
– Pacemaker circuit damage
– Loss of output
– “Runaway”
 Precautions:
– Keep cumulative radiation
absorbed by the pacemaker
to less than 500 rads;
shielding may be required
– Check pacemaker after
radiation sessions for changes
in pacemaker function (can
be done transtelephonically)

102. Refractory & Blanking PeriodsRefractory & Blanking Periods

103. Voltage Deflections of the SensedVoltage Deflections of the Sensed
EGM in a PacemakerEGM in a Pacemaker
Pacemaker
Stimulus
Paced R wave
Post-pace T wave
Intrinsic R wave
T wave corresponding to
intrinsic R wave
2.5 mV

104. Refractory PeriodRefractory Period
Refractory Period Refractory Period Refractory Period
NO SENSING NO SENSING NO SENSING

105. Refractory PeriodRefractory Period
 A programmable period immediately following a
pacemaker stimulus or a sensed intrinsic R wave
during which the pacemaker does not react to sensed
events
 To prevent repeated sensing of the same intrinsic R
wave
 To prevent misidentification of T waves as intrinsic R
waves
 To prevent misidentification of effects of pacemaker
stimulus/evoked R wave
Usually programmed to 325 ms
To Prevent Oversensing

106. Afterpotential due to PolarizationAfterpotential due to Polarization
Afterpotential

107. Blanking PeriodBlanking Period
 The first portion of every refractory period
 Pacemaker is “blind” to any activity and no events can
be sensed
 Designed to prevent oversensing of pacing stimulus &
after-potential
Blanking Period
Refractory Period

108. ConductorTip Electrode Insulation Connector Pin
Pacing Lead ComponentsPacing Lead Components
 Conductor
 Connector Pin
 Insulation
 Electrode

109. ConnectorConnector
 Purpose
– Connects lead to IPG, and provides a conduit to:
• Deliver current from IPG to lead
• Return sensed cardiac signals to IPG
Connector

110. Connector -- IS-1 StandardConnector -- IS-1 Standard
 IS-1 Standard Connectors
 Sizes Prior to IS-1 Standard
– 3.2 mm low-profile connectors
– 5/6 mm connectors

111. Insulation -- TypeInsulation -- Type
 Insulation Types
– Silicone
– Polyurethane
– Fluoropolymers (PTFE, ETFE)

112. Electrodes -- Fixation MechanismElectrodes -- Fixation Mechanism
 Passive Fixation Mechanism – Endocardial
– Tined
– Finned
– Canted/curved

113. Electrodes – Fixation MechanismElectrodes – Fixation Mechanism
 Active Fixation Mechanism – Endocardial
– Fixed screw
– Extendible/retractable

114. Electrodes -- Fixation/VisualizationElectrodes -- Fixation/Visualization
Fluoroscopic Visual Quality of Active Fixation Leads
SureFixCapSureFix®
Extended Retracted Fixed Screw
space

115. Electrodes -- Fixation MechanismElectrodes -- Fixation Mechanism
 Fixation Mechanism – Myocardial/Epicardial
– Stab-in
– Screw-in
– Suture-on

116. Battery CapacityBattery Capacity
 A battery is a reservoir of electrical charge measured in
Coulombs
 Current is the amount of charge delivered per unit time
– 1 Ampere = 1 Coulomb per second
– 1 Coulomb = 1 Ampere x 1 second
 Qc = Battery Capacity is specified as the quantity of
charge it can deliver in AmpereHours (0.5 to 3
Amperehours)

117. Battery LifeBattery Life
 Battery Life
– Battery Life = Battery Capacity/Current Drain
– 2.0 Ah/25microamps = 80,000 hours = 9.3 years
 Battery properties
– Reliability – no premature failure
– High volumetric energy density – Small battery
volume with high storage capacity
– Low self-discharge rate
– High hermiticity – no gas generation during
operation

118. On the figure, the zone of non capture is
indicated by which number?
a)1
b)2
c)3
d)4

119.  Which of the following output settings best
represents the Chronaxie point on the strength-
duration curve when the Rheobase is 0.5V @
1.5ms?
a) 0.5V @ 1.5ms
b) 1.0V @ 0.5ms
c) 1.5V @ 0.1 ms
d) 2.0V @ 0.05ms

120. Sensing
 Sensing is the ability of the pacemaker to “see” when a natural (intrinsic)
depolarization is occurring
– Pacemakers sense cardiac depolarization by measuring
changes in electrical potential of myocardial cells between the
anode and cathode
 Intrinsic deflection on an EGM
occurs when a depolarization wave
passes directly under the
electrodes
 Two characteristics of the EGM
are:
– Signal amplitude
– Slew rate