Pacemaker basics

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1. PACEMAKER BASICSPACEMAKER BASICS
Dr. R. Praveen Babu
Vijaya Hospital
Chennai

2. Implantable pulse
generator (IPG)
Lead wire(s)
Implantable Pacemaker Systems Implantable Pacemaker Systems
Contain the Following Components:Contain the Following Components:

3. Pulse generator: power
source or battery
Leads or wires
Cathode (negative
electrode)
Anode (positive
electrode)
Body tissue
IPG
Lead
Anode
Cathode
Pacemaker Components Combine with Pacemaker Components Combine with
Body Tissue to Form a Complete CircuitBody Tissue to Form a Complete Circuit

4. Contains a battery
that provides the
energy for sending
electrical impulses to
the heart
Houses the circuitry
that controls
pacemaker
operations
Circuitry
Battery
The Pulse Generator:The Pulse Generator:

5. Deliver electrical
impulses from the
pulse generator to
the heart
Sense cardiac
depolarization
Lead
Leads Are Insulated Wires That:Leads Are Insulated Wires That:

6. Begins in the pulse
generator
Flows through the lead
and the cathode (–)
Stimulates the heart
Returns to the anode (+)
During Pacing, the Impulse:During Pacing, the Impulse:
Impulse onset
*

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

8. 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 Two A 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

9. Stimulate cardiac depolarization
Sense intrinsic cardiac function
Respond to increased metabolic demand by
providing rate responsive pacing
Provide diagnostic information stored by the
pacemaker
Most Pacemakers Perform Four Functions:Most Pacemakers Perform Four Functions:

10. 10
Capture
Depolarization of atria and/or ventricles in
response to a pacing stimulus

11. 11
Sensing
Ability of device to detect intrinsic cardiac
activity
Undersensing: failure to sense
Oversensing: too sensitive to activity

12. Rate Responsive PacingRate Responsive Pacing
When the need for oxygenated blood increases, the
pacemaker ensures that the heart rate increases to
provide additional cardiac output
Adjusting Heart Rate to Activity
Normal Heart Rate
Rate Responsive Pacing
Fixed-Rate Pacing
Daily Activities

13. A Variety of Rate Response Sensors ExistA Variety of Rate Response Sensors Exist
Those most accepted in the market place are:
–Activity sensors that detect physical movement
and increase the rate according to the level of
activity
–Minute ventilation sensors that measure the
change in respiration rate and tidal volume via
transthoracic impedance readings

14. 14
Types
1. Asynchronous/Fixed Rate
2. Synchronous/Demand
3. Single/Dual Chamber
Sequential (A & V)
4. Programmable/nonprogrammable

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

16. DisadvantagesDisadvantagesAdvantagesAdvantages
Advantages and Disadvantages of Advantages and Disadvantages of
Single-Chamber Pacing SystemsSingle-Chamber Pacing Systems
Implantation of a
single lead
Single ventricular lead
does not provide AV
synchrony
Single atrial lead does
not provide ventricular
backup if A-to-V
conduction is lost

17. One lead implanted
in the atrium
One lead implanted
in the ventricle
Dual-Chamber Systems Have Two Leads:Dual-Chamber Systems Have Two Leads:

18. Benefits of Dual Chamber PacingBenefits of Dual Chamber Pacing
Provides AV synchrony
Lower incidence of atrial fibrillation
Lower risk of systemic embolism and stroke
Lower incidence of new congestive heart failure
Lower mortality and higher survival rates

19. Benefits of Dual-Chamber PacingBenefits of Dual-Chamber Pacing
Study Results
Higano et al. 1990
Gallik et al. 1994
Santini et al. 1991
Rosenqvist et al. 1991
Sulke et al. 1992
Improved cardiac index during low level
exercise (where most patient activity occurs)
Increase in LV filling
30% increase in resting cardiac output
Decrease in pulmonary wedge pressure
Increase in resting cardiac output
Increase in resting cardiac output, especially
in patients with poor LV function
Decreased incidence of mitral and tricuspid
valve regurgitation

21. 21
Examples
VVI
V: Ventricle is the paced chamber
V: Ventricle is the sensed chamber
I: Inhibited response to a sensed
signal
Thus, a synchronous generator that paces
and senses in the ventricle
Inhibited if a sinus or escape beat occurs
Called a “demand” pacer

22. 22
Examples
DVI
D: Both atrium and ventricle are
paced
V: Ventricle is sensed
I: Response is inhibited to a sensed
ventricular signal

23. Examples
DDDRA
Dual chamber, adaptive-rate pacing with
multisite atrial pacing (i.e., biatrial pacing,
more than one pacing site in one atrium,or
both features)
23

24. Stimulation ProcessStimulation Process
Time (Milliseconds)
100 200 300 400 500
Phase 2
Phase 1
Phase 3
Phase 4
T
r
a
n
s
m
e
m
b
r
a
n
e

P
o
t
e
n
t
i
a
l
(
M
i
l
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i
v
o
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)
-50
0
50
-100
P
h
a
s
e


0
Threshold

25. Stimulation ThresholdStimulation Threshold
The minimum electrical stimulus needed to consistently
capture the heart outside of the heart’s refractory period
VVI / 60
Capture
Non-Capture

26. Amplitude
Pulse width
Two Settings Are Used to Ensure Capture:Two Settings Are Used to Ensure Capture:

27. Amplitude is the Amount of Voltage Amplitude is the Amount of Voltage
Delivered to the Heart By the PacemakerDelivered to the Heart By the Pacemaker
Amplitude reflects the strength or height of the
impulse:
–The amplitude of the impulse must be large
enough to cause depolarization ( i.e., to
“capture” the heart)
–The amplitude of the impulse must be
sufficient to provide an appropriate pacing
safety margin

28. Pulse Width Is the Time (Duration) Pulse Width Is the Time (Duration)
of the Pacing Pulseof the Pacing Pulse
Pulse width is expressed in milliseconds (ms)
The pulse width is just the length of time each pacing pulse is
delivered & must be long enough for depolarization to disperse to
the surrounding tissue
5 V
0.5 ms 0.25 ms 1.0 ms

29. The Strength-Duration CurveThe Strength-Duration Curve
The strength-duration
curve illustrates the
relationship of amplitude
and pulse width
–Values on or above
the curve will result
in capture
Duration
Pulse Width (ms)
.50
1.0
1.5
2.0
.25
S
t
i
m
u
l
a
t
i
o
n

T
h
r
e
s
h
o
l
d

(
V
o
l
t
s
)
0.5 1.0 1.5
Capture

30. Strength-Duration Curve Strength-Duration Curve

31. SDCSDC
Rheobase- (the lowest point on the curve) by definition is the
lowest voltage that results in myocardial depolarization at
infinitely long pulse duration
Chronaxie(pulse duration time ) by definition, the chronaxie is
the threshold pulse duration at twice the rheobase voltage
The ideal pulse duration should be greater than the chronaxie
time
Cannot overcome high threshold exit block by increasing the
pulse duration, If the voltage output remains less than the
rheobase

32. SDCSDC

33. Lead impedance
Amplitude and pulse width setting
Percentage paced vs. intrinsic events
Rate responsive modes programmed “ON”
Factors That Affect Battery Factors That Affect Battery
Longevity Include:Longevity Include:

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

35. Impedance Changes Affect Pacemaker Impedance Changes Affect Pacemaker
Function and Battery LongevityFunction and Battery Longevity
High impedance reading reduces battery
current drain and increases longevity
Low impedance reading increases battery
current drain and decreases longevity
Impedance reading values range from 300 to
1,500 W
–High impedance leads will show impedance
reading values greater than 1,500 ohms

36. ImpedanceImpedance
Factors that can influence impedance
–Resistance of the conductor coils
–Tissue between anode and cathode
–The electrode/myocardial interface
–Size of the electrode’s surface area
–Size and shape of the tip electrode

37. Ohm’s Law is a Fundamental Ohm’s Law is a Fundamental
Principle of Pacing That:Principle of Pacing That:
VV
IIRR
V = I X RV = I X R
I = V / RI = V / R
R = V / IR = V / I
Describes the relationship between voltage,
current, and resistance
xx

38. If you reduce the voltage by half, the current is
also cut in half
If you reduce the impedance by half, the
current doubles
If the impedance increases, the current
decreases
When Using Ohm’s Law When Using Ohm’s Law
You Will Find That:You Will Find That:

39. Voltage, Current, and Impedance Voltage, Current, and Impedance
Are InterdependentAre Interdependent
The interrelationship of the three components can
be likened to the flow of water through a hose
–Voltage represents the force with which . . .
–Current (water) is delivered through . . .
–A hose, or lead, where each component
represents the total impedance:
The nozzle, representing the electrode
The tubing, representing the lead wire

40. Voltage and Current FlowVoltage and Current Flow

Spigot (voltage) turned up
(high current drain)
Spigot (voltage) turned low
(low current drain)

41. Resistance and Current FlowResistance and Current Flow
“Normal” resistance
“Low” resistance
“High” resistance
Low current flow
High current flow

42. Electrode Design May Also Impact Electrode Design May Also Impact
Stimulation ThresholdsStimulation Thresholds
Lead maturation process

43. Lead Maturation ProcessLead Maturation Process
Fibrotic “capsule” develops around the
electrode following lead implantation

44. Lead Maturation Process
3 phases
1.A/c phase, where thresholds immediately following implant are low
2.Peaking phase- thresholds rise and reach their highest point(1wk)
,followed by a ↓ in the threshold over the next 6 to 8 wks as the tissue
reaction subsides
3.C/c phase- thresholds at a level higher than that at implantation but
less than the peak threshold
Trauma to cells surrounding the electrode→ edema and subsequent
development of a fibrotic capsule.
Inexcitable capsule ↓ the current at the electrode interface, requiring more
energy to capture the heart.

45. Steroid Eluting LeadsSteroid Eluting Leads
Steroid eluting
leads reduce the
inflammatory
process and thus
exhibit little to no
acute stimulation
threshold peaking
and low chronic
thresholds
Porous, platinized tip
for steroid elution
Silicone rubber plug
containing steroid
Tines for
stable
fixation

46. Lead Maturation ProcessLead Maturation Process
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
012 45 789101112
V
o
l
t
s

47. A Pacemaker Must Be Able to Sense A Pacemaker Must Be Able to Sense
and Respond to Cardiac Rhythmsand 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

48. Accurate Sensing...Accurate Sensing...
Ensures that undersensing will not occur –
the pacemaker will not miss P or R waves that
should have been sensed
Ensures that oversensing will not occur – the
pacemaker will not mistake extra-cardiac activity
for intrinsic cardiac events
Provides for proper timing of the pacing pulse –
an appropriately sensed event resets the timing
sequence of the pacemaker

49. Sensitivity – The Greater the Number, the Sensitivity – The Greater the Number, the LessLess
Sensitive the Device to Intracardiac EventsSensitive the Device to Intracardiac Events

51. Accurate Sensing Requires That Accurate Sensing Requires That
Extraneous Signals Be Filtered OutExtraneous Signals Be Filtered Out
Sensing amplifiers use filters that allow appropriate
sensing of P waves and R waves and reject
inappropriate signals
Unwanted signals most commonly sensed are:
–T waves
–Far-field events (R waves sensed by the atrial
channel)
–Skeletal myopotentials (e.g., pectoral muscle
myopotentials)

52. Pacemaker TimingPacemaker Timing
Pacing Cycle : Time between two consecutive
events in the ventricles (ventricular only
pacing) or the atria (dual chamber pacing)
Timing Interval : Any portion of the Pacing
Cycle that is significant to pacemaker operation
e.g. AV Interval, Ventricular Refractory period

54. Single-Chamber TimingSingle-Chamber Timing

55. Single Chamber Timing TerminologySingle Chamber Timing Terminology
Lower rate
Refractory period
Blanking period
Upper rate

56. Lower Rate IntervalLower Rate Interval
Lower Rate Interval
VP VP
VVI / 60
Defines the lowest rate the pacemaker will pace

57. Refractory PeriodRefractory Period
Lower Rate Interval
VP VP
VVI / 60
Interval initiated by a paced or sensed event
Designed to prevent inhibition by cardiac or
non-cardiac events
Refractory Period

58. Blanking PeriodBlanking Period
Lower Rate Interval
VP VP
VVI / 60
The first portion of the refractory period
Pacemaker is “blind” to any activity
Designed to prevent oversensing pacing stimulus
Blanking Period
Refractory Period

59. Upper Sensor Rate IntervalUpper Sensor Rate Interval
Lower Rate Interval
VP VP
VVIR / 60 / 120
Defines the shortest interval (highest rate) the pacemaker
can pace as dictated by the sensor (AAIR, VVIR modes)
Blanking Period
Refractory Period
Upper Sensor Rate
Interval

60. Single Chamber Mode ExamplesSingle Chamber Mode Examples

61. VOO ModeVOO Mode
Blanking Period
VP VP
Lower Rate Interval
VOO / 60
Asynchronous pacing delivers output regardless of
intrinsic activity

62. VVI ModeVVI Mode
Lower Rate Interval
VP VS
Blanking/Refractory
VP
{
VVI / 60
Pacing inhibited with intrinsic activity

63. VVIR VVIR
VP VP
Refractory/Blanking
Lower Rate
Upper Rate Interval
(Maximum Sensor Rate)
VVIR / 60/120
Rate Responsive Pacing at the Upper Sensor Rate
Pacing at the sensor-indicated rate

64. Dual-Chamber TimingDual-Chamber Timing

65. Rate = 60 bpm / 1000 ms
A-A = 1000 ms
AP
VP
AP
VP
V-AAV V-AAV
Atrial Pace, Ventricular Pace (AP/VP)
Four “Faces” of Dual Chamber PacingFour “Faces” of Dual Chamber Pacing

66. Rate = 60 ppm / 1000 ms
A-A = 1000 ms
AP
VS
AP
VS
V-AAV V-AAV
Atrial Pace, Ventricular Sense (AP/VS)
Four “Faces” of Dual Chamber PacingFour “Faces” of Dual Chamber Pacing

67. AS
VP
AS
VP
Rate (sinus driven) = 70 bpm / 857 ms
A-A = 857 ms
Atrial Sense, Ventricular Pace (AS/ VP)
V-AAV AV V-A
Four “Faces” of Dual Chamber PacingFour “Faces” of Dual Chamber Pacing

68. Rate (sinus driven) = 70 bpm / 857 ms
Spontaneous conduction at 150 ms
A-A = 857 ms
AS
VS
AS
VS
V-AAV AV V-A
Atrial Sense, Ventricular Sense (AS/VS)
Four “Faces” of Dual Chamber PacingFour “Faces” of Dual Chamber Pacing

69. Dual Chamber Timing ParametersDual Chamber Timing Parameters
Lower rate
AV and VA intervals
Upper rate intervals
Refractory periods
Blanking periods

70. Lower Rate Interval
AP
VP
AP
VP
Lower Rate Lower Rate
The lowest rate the pacemaker will pace the atrium in
the absence of intrinsic atrial events
DDD 60 / 120

71. AP
VP
AS
VP
PAV SAV
200 ms 170 ms
Lower Rate Interval
AV IntervalsAV Intervals
Initiated by a paced or non-refractory sensed atrial event
–Separately programmable AV intervals – SAV /PAV
DDD 60 / 120

72. Lower Rate Interval
AP
VP
AP
VP
AV Interval VA Interval
Atrial Escape Interval (V-A Interval)
The interval initiated by a paced or sensed ventricular event
to the next atrial event
DDD 60 / 120
PAV 200 ms; V-A 800 ms
200 ms 800 ms

73. Atrial Escape Interval (V-A Interval)Atrial Escape Interval (V-A Interval)
Lower rate interval- AV interval
=V-A interval
The V-A interval is the longest period that may elapse after a
ventricular event before the atrium must be paced in the absence of
atrial activity.
The V-A interval is also commonly referred to as the atrial escape
interval

74. DDDR 60 / 120
A-A = 500 ms
AP
VP
AP
VP
Upper Activity Rate Limit
Lower Rate Limit
V-APAV V-APAV
Upper Activity (Sensor) RateUpper Activity (Sensor) Rate
In rate responsive modes, the Upper Activity Rate provides
the limit for sensor-indicated pacing

75. AS
VP
AS
VP
DDDR 60 / 100 (upper tracking rate)
Sinus rate: 100 bpm
Lower Rate Interval{
Upper Tracking Rate Limit
Upper Tracking RateUpper Tracking Rate
SAV SAVVA VA
The maximum rate the ventricle can be paced in response to
sensed atrial events

76. Post Ventricular Atrial
Refractory Period (PVARP)
Refractory PeriodsRefractory Periods
VRP and PVARP are initiated by sensed or paced
ventricular events
–The VRP is intended to prevent self-inhibition such
as sensing of T-waves
–The PVARP is intended primarily to prevent sensing
of retrograde P waves
AP
VPVentricular Refractory Period
(VRP)
A-V Interval
(Atrial Refractory)

77. Post-Ventricular Atrial Refractory PeriodPost-Ventricular Atrial Refractory Period
PVARP is initiated by a ventricular
event(sensed/paced), but it makes the atrial channel
refractory
PVARP is programmable (typical settings around 250-
275 ms)
Benefits of PVARP
–Prevents atrial channel from responding to
premature atrial contractions, retrograde P-waves,
and far-field ventricular signals
–Can be programmed to help minimize risk of
pacemaker-mediated tachycardias

78. Blanking PeriodsBlanking Periods
First portion of the refractory period-sensing is disabled
AP
VP
AP
Post Ventricular Atrial
Blanking (PVAB)
Post Atrial Ventricular
Blanking
Ventricular Blanking
(Nonprogrammable)
Atrial Blanking
(Nonprogrammable)

79. PVARP and PVABPVARP and PVAB
The PVAB is the post-ventricular atrial blanking
period during which time no signals are “seen” by the
pacemaker’s atrial channel
It is followed by the PVARP, during which time the
pacemaker might “see” and even count atrial events
but will not respond to them
PVAB-independently programmable
–Typical value around 100 ms

80. What is happening here?
DDD / 60 / 120 / 310

81. PVARP
Wenckebach Operation
Upper Tracking Rate
Lower Rate Interval{
AS AS
AR AP
VPVP VP
TARP
SAV PAVPVARP SAV PVARP
P Wave Blocked (unsensed or unused)
•Prolongs the SAV until upper rate limit expires
–Produces gradual change in tracking rate ratio
TARP TARP

82. Wenckebach
•Occurs when the intrinsic atrial rate lies
between the UTR and the TARP rate
•Results in gradual prolonging of the AV
interval until one atrial intrinsic event occurs
during the TARP and is not tracked

83. What is happening here?
DDD / 60 / 120 / 310

84. •Every other P wave falls into refractory and does not restart the
timing interval
Upper Tracking Limit
Lower Rate Interval{
{
P Wave Blocked
AS AS
VPVP
ARAR
Sinus rate = 133 bpm (450 ms)
PVARP = 300 ms SAV = 200 ms
TARP=500 ms
AVPVARP AVPVARP
TARP TARP
2:1 Block

85. PVARP
Upper Tracking Rate
Lower Rate Interval
{
No SAV started for events sensed in the TARP
AS AS
VPVP
SAV = 200 ms
PVARP = 300 ms
Thus TARP = 500 ms (120 ppm)
DDD
LR = 60 ppm (1000 ms)
UTR = 100 bpm (600 ms)
SAV
TARP
PVARP
Total Atrial Refractory Period (TARP)
•Sum of the AV Interval and PVARP
•defines the highest rate that the pacemaker will
track atrial events before 2:1 block occurs
SAV

86. Fixed Block or 2:1 Block
•Occurs whenever the intrinsic atrial rate
exceeds the TARP rate
• Every other atrial event falls in the TARP
when the atrial rate exceeds the TARP rate
•Results in block of atrial intrinsic events in
fixed ratios

87. PACEMAKER MODE?PACEMAKER MODE?

88. PACEMAKER MODE?PACEMAKER MODE?

89. PACEMAKER MODE?PACEMAKER MODE?

90. WHAT IS HAPPENING HERE?WHAT IS HAPPENING HERE?

91. WHAT IS HAPPENING HERE?WHAT IS HAPPENING HERE?

92. THANK YOUTHANK YOU