1) Unipolar and bipolar pacing configurations determine the size of the electrical field for sensing and stimulation. Bipolar pacing has a smaller field to reduce muscle stimulation. 2) Pacemaker output is determined by pulse amplitude and width. Increasing either increases energy delivered. Strength-duration curves show relationships between pulse parameters and stimulation threshold. 3) Dual chamber pacing (DDD mode) provides atrioventricular synchrony for better cardiac output than single chamber pacing. It uses refractory periods and programmable delays to control ventricular pacing in response to atrial signals.

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Basic Pacing Concepts
Shibu Chacko

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Basic Electrical Concepts

3. SM
-
Unipolar
Stimulation
& Sensing
Polarity of the Pacemaker System
• Larger “antenna” for sensing
√ bigger signals
√ more interference (myopotentials !)
• Big spike on ECG
• Pectoral (pocket) stimulation possible
+
+

4. SM
CONFIGURATION
UNIPOLAIRE
-
Polarity of the Pacemaker System
Bipolar
Stimulation
& Sensing
+
• Smaller “antenna” for sensing
√ smaller, more specific signals
√ less interference
• Spike difficult to see on ECG
• No pectoral (pocket) stimulation

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Fixation mechanisms of the Electrode
Passive fixation
Wingtips
Active fixation
Screw
Active fixation
Tines

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Stimulation Threshold
The smallest amount of electrical energy that is
required to depolarize the heart adequately
outside the refractory period.

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• Inversely proportional to current density
(amount of current per mm²)
• Electrode surface as small as possible
• Compromise with the sensing of intracardiac
signals, for which a larger surface is required
• Surface of the electrode: around 6 to 8 mm²
Stimulation Threshold

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Output
Pulse
Pulse Amplitude
Pulse Width
Leading Edge
The energy is proportional to the pulse amplitude and the pulse
width (=surface under the curve)
Stimulation Threshold
Trailing Edge

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L’IMPULSION DE STIMULATION
Pulse Width
Stimulation Threshold
0.5 V
to
10 V

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L’IMPULSION DE STIMULATION
Stimulation Threshold
0.5 V
to
10 V
0.1 to 1.5 ms

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L’IMPULSION DE STIMULATION
Energy
Stimulation Threshold
0.5 V
to
10 V
0.1 to 1.5 ms

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Strength - Duration Curve
Pulse Width (ms)
Pulse Amplitude (V)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
2.5
2.25
2
1.75
1.5
1.25
1
0.75
0.5
0.25
0

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Strength - Duration Curve
Pulse Amplitude (V)
Pulse Width (ms)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Capture
Non-Capture
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
2.5
2.25
2
1.75
1.5
1.25
1
0.75
0.5
0.25
0

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Strength - Duration Curve
Pulse Amplitude (V)
Pulse Width (ms)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Threshold at 0.5 ms = 0.7 V
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
2.5
2.25
2
1.75
1.5
1.25
1
0.75
0.5
0.25
0

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Energy and
Longevity
E = x t
V
R
²

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Energy and Longevity
E = x PW
V
R
²
Example : 5 V, 500 Ω , 0.5 ms
E = x 0.5 = 25 µJ
5 ²
500

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Energy and Longevity
E = x PW
V
R
²
Example : 5 V, 500 Ω , 0.5 ms
2.5 V, 500 Ω , 0.5 ms
E = x 0.5 = 25 µJ
5 ²
500

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Energy and Longevity
E = x PW
V
R
²
Example : 5 V, 500 Ω , 0.5 ms
2.5 V, 500 Ω , 0.5 ms
E = x 0.5 = 25 µJ
5 ²
500
E = x 0.5 = 6.25 µJ
2.5
500
²
( Increased longevity! )

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Pacemaker codes and
modes

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NASPE/ BPEG Generic (NBG) Pacemaker Code
I. Chamber II. Chamber III. Response to IV. Programmability V. Antitachy
Paced Sensed Sensing Rate Modulation arrhythmia
funct.
O= none O= none O= none O= none O= none
A=atrium A= atrium T= triggered P= simple P= pacing
V= ventricle V= ventricle I= inhibited M= multi S= shock
D= dual D= dual D= dual C= communication D= dual
(A+V) (A+V) (T+I) R= Rate Modulation
Manufacturers’ Designation only:
S= single S= single
(A or V) (A or V)

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Causes of bradycardia requiring pacing and recommended pacemaker modes
Diagnosis Incidence (%) Recommended Pacemaker Mode
Optimal Alternative Inappropriate
Sinus node disease 25 AAIR AAI VVI; VDD
AV block 42 VDDR DDD AAI; DDI
Sinus node disease
+ AV block 10 DDDR DDD AAI; VVI
Chronic A fib
with AV block 13 VVIR VVI AAI; DDD; VDD
Carotid Sinus S. 10 DDD AAI VVI; VDD
Neurocardiogenic + hysteresis + hysteresis
Syncope

22. SM
Choice of a Stimulation Mode
Bradycardia
Atrial fib Normal P waves
RR  Normal A-V A-V Block
RR 
RR 
RR 
RR 
RR
VVI AAI
DDI
AAIR
DDIR
DDD DDDRVVIR

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Single Chamber Pacing
VVI (R)

24. SM
Single Chamber Pacing
AAI (R)

25. SM
Single Chamber Pacemaker (VVI)
 Easy to implant a ventricular lead
 Easy to program the pacemaker
 Easy follow-up
 Longevity of > 6 years
 Only one pacing rate (except rate responsive
pacemakers)

26. SM
NASPE/ BPEG Generic (NBG) Pacemaker Code
I. Chamber II. Chamber III. Response to IV. Programmability V. Antitachy
Paced Sensed Sensing Rate Modulation arrhythmia
funct.
O= none O= none O= none O= none O= none
A=atrium A= atrium T= triggered P= simple P= pacing
V= ventricle V= ventricle I= inhibited M= multi S= shock
D= dual D= dual D= dual C= communication D= dual
(A+V) (A+V) (T+I) R= Rate Modulation
Manufacturers’ Designation only:
S= single S= single
(A or V) (A or V)

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VVI MODE

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VVI
MODE
Vp Vp Vp Vs Vs Vp Vp Vs Vs

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VVI MODE
Automatic
Interval
• Automatic interval starts
from a paced complex (to
the next paced complex)
• Escape interval starts from
a sensed complex (to the
next paced complex)
Escape Interval
If the intervals are equal:
•No hysteresis
If the escape interval > automatic interval:
•Hysteresis

30. SM
VVI MODE (with
hysteresis)
1000 ms
850 ms
Escape interval = 1000 ms (60 ppm)
Automatic interval = 850 ms (70 ppm)

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NASPE/ BPEG Generic (NBG) Pacemaker Code
I. Chamber II. Chamber III. Response to IV. Programmability V. Antitachy
Paced Sensed Sensing Rate Modulation arrhythmia
funct.
O= none O= none O= none O= none O= none
A=atrium A= atrium T= triggered P= simple P= pacing
V= ventricle V= ventricle I= inhibited M= multi S= shock
D= dual D= dual D= dual C= communication D= dual
(A+V) (A+V) (T+I) R= Rate Modulation
Manufacturers’ Designation only:
S= single S= single
(A or V) (A or V)

32. SM
MODE AAI

33. SM
MODE AAI
Ap Ap Ap As Ap

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Dual Chamber Pacing

35. SM
DUAL CHAMBER
STIMULATION

36. SM
DUAL CHAMBER
STIMULATION

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DDD Pacemaker
A DDD pacemaker puts in the
beat that’s missing in order to
maintain AV synchrony

38. SM
DDD timing
Ap Vp Ap VpAsVs As Vs PVC
AA interval
AV-D
NPAVD
VB
CSW
PVARP ARE
VRP
VTL
VA int.
TARP

39. SM
DDD Pacing
• Indications:
– Sick Sinus Syndrome
– AV block
– Chronic Sinus Bradycardia with AV conduction
problems
– Pacemaker Syndrome (instead of VVI)
– AV synchrony needed (instead of VVI)
• Contraindication:
– Atrial tachyarrhythmias

40. SM
DUAL CHAMBER STIMULATION
Advantages  AV Synchrony
 Variability of the pacing rate
Results  Increase of the cardiac output
 Improved quality of life
 No Pacemaker Syndrome

41. SM
AV Synchrony
• Cardiac Output = Heart Rate X Stroke Volume
= amount of blood expelled from the heart per
minute
• Ventricles contribute 70 % to the C.O.
• Atria contribute 30 % to the C.O.
 If there is AV synchrony: C.O. = 100 %
+ appropriate opening and closing of AV valves!

42. SM
Pacemaker Syndrome
• = the result of a loss of AV synchrony
 atria contract against closed valves
• Symptoms: Cannon A waves
Pulsations in the neck
Fatigue
Diziness
Syncope

43. SM
NASPE/ BPEG Generic (NBG) Pacemaker Code
I. Chamber II. Chamber III. Response to IV. Programmability V. Antitachy
Paced Sensed Sensing Rate Modulation arrhythmia
funct.
O= none O= none O= none O= none O= none
A=atrium A= atrium T= triggered P= simple P= pacing
V= ventricle V= ventricle I= inhibited M= multi S= shock
D= dual D= dual D= dual C= communication D= dual
(A+V) (A+V) (T+I) R= Rate Modulation
Manufacturers’ Designation only:
S= single S= single
(A or V) (A or V)

44. SM
ECG: DDD mode

45. SM
DDD
mode
Vp Vp Vp Vp
As As Ap Ap
Vs Vs Vs Vs
As As Ap Ap

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Differential AV delay
• AV s < AV p
• Provides shorter AV delay following sensed atrial
events than following paced atrial events
• atrial sensing and pacing for optimal ventricular filling
• Equalizes true PR interval after

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Adaptive AV delay
• Adapts AV delay after atrial events to changes in atrial
interval:
if atrial interval shortens  AV delay shortens
• Maintains relatively constant relationship between AV
delay and total cardiac cycle for optimal hemodynamics
(AV delay = 15-20 % of total cardiac cycle)
• Improves upper rate characteristics

48. SM
Adaptive AV delay
• AV delay adapts in an 8:1 ratio
• For every shortening of the AA interval of 8 ms,
the AV delay shortens by 1 ms (but never < 75
ms)
• Enhances ventricular filling and increases cardiac
output
• Improves upper rate behaviour characteristics

49. SM
NASPE/ BPEG Generic (NBG) Pacemaker Code
I. Chamber II. Chamber III. Response to IV. Programmability V. Antitachy
Paced Sensed Sensing Rate Modulation arrhythmia
funct.
O= none O= none O= none O= none O= none
A=atrium A= atrium T= triggered P= simple P= pacing
V= ventricle V= ventricle I= inhibited M= multi S= shock
D= dual D= dual D= dual C= communication D= dual
(A+V) (A+V) (T+I) R= Rate Modulation
Manufacturers’ Designation only:
S= single S= single
(A or V) (A or V)

50. SM
DDI Pacing
• DDI= DVI + Atrial sensing / inhibition
• DDI is NOT a pacemaker type but a MODE
• DDD pacemaker: mode switch to DDI
 Paroxysmal atrial tachycardia’s: no tracking
allowed!
 Switch from DDD to DDI

51. SM
Refractory Periods
• Refractory period =
a programmable interval occurring after the
delivery of a pacing impulse or after a sensed
intrinsic complex, during which the pacemaker
can sense signals but chooses to ignore them

52. SM
Atrial Refractory Period
• AV delay
• PVARP= Post Ventricular Atrial Refractory Period
 TARP = Total Atrial Refractory Period
= AV delay + PVARP

53. SM
Atrial Refractory Period
AV delay PVARP
TARP

54. SM
AVD PVARP
VRP
Atrial Channel
Ventricular Channel
DDD Mode: Refractory Periods

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Clinical Considerations in DDD pacing
• Upper Rate Behaviour
• Control of Pacemaker Mediated Tachycardia
• Crosstalk Inhibition Protection

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Upper Rate Behaviour
• The pacemaker’s response to sensed rapid atrial
rates.
• A rapid atrial rate is a rate > Upper Rate Limit (URL) or
Ventricular Tracking Limit (VTL)
• VTL= a rate beyond which 1:1 tracking will NOT occur
= “the absolute speed limit in the ventricle”
(max. 180 bpm)

57. SM
Upper Rate Behaviour
• Fixed Ratio Block or Multiblock or 2:1 block
• Wenckebach response

58. SM
Wenckebach Response
• Progressive prolongation of the AV delay until a
ventricular output pulse is missed in response
to atrial activity exceeding the ventricular
tracking limit

59. SM
DDD Mode: 1:1 Tracking
40
50
60
70
80
90
100
110
120
30 60 120 180 180 20060 120 180 200
1:1 tracking
Atrial Rate
Ventricular
Rate

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DDD Mode: Wenckebach
40
50
60
70
80
90
100
110
120
30 60 120 180 180 20060 120 180 200
1:1 tracking Wenckebach
Ventricular
Rate
Atrial Rate

61. SM
Wenckebach Response
P wave (falls
outside PVARP)
AV delay PVARP
VTL
AV delay

62. SM
How to recognize Wenckebach?
• Grouped beating
• Progressive prolongation of the AV delay until
the ventricular output is missed
• Ventricular pacing at the VTL

63. SM
Pacemaker Mediated Tachycardia (PMT)
Rapid ventricular pacing due to RETROGRADE
CONDUCTION, most commonly at exactly the
upper rate limit.

64. SM
Retrograde Conduction
• Propagation of an impulse from the ventricle
back to the atrium.
• Also known as VA conduction
• 60 % of the population have the ability to conduct
retrogradely
• 33 % of patients with complete heart block have the
ability to conduct retrogradely
• Average retrograde conduction time= 235ms ± 55 ms

65. SM
AVD PVARP
VRP
Atrial Channel
Ventricular Channel
DDD Mode: Refractory Periods

66. SM
Common Causes of PMT
• Loss of atrial capture
• Premature Ventricular Contractions (PVC’s)
• Myopotential Tracking

67. SM
AVD
PVARP PVARP
Retrograde P waves
PVARP PVARP
PVC
Pacemaker Mediated Tachycardia

68. SM
PMT Prevention
• Program PVARP longer than VA
conduction time
• PVARP + AV delay = TARP  determines 2:1 block
250 ms + 150 ms = 400 ms  2:1 block at 150 bpm
350 ms + 150 ms = 500 ms  2:1 block at 120 bpm

69. SM
AVD
PVARP AREPVARP
AVD
PVARP
Retrograde P wave
The ARE is programmable (off; 50; 100; 150 ms)
PVC
Atrial Refractory Extension after a PVC

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Tachycardia Termination Algorithm (TTA)
• After 15 consecutive paced ventricular events
at EXACTLY the upper rate limit, the 16 th
ventricular output pulse is dropped.
• TTA breaks PMT, but does not prevent it.
• TTA breaks PMT only at the upper rate limit.

71. SM
Retrograde P wavesPVC
1 2 14 15 Inhibition of the 16 th
ventricular output
pulse
Tachycardia Termination Algorithm

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Crosstalk
• Sensing of the atrial output pulse by
the ventricular sense amplifier

73. SM
Crosstalk Inhibition
• Inappropriate inhibition of the
ventricular spike due to sensing of
the atrial output pulse by the
ventricular sense amplifier.

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Factors Affecting Crosstalk
• Atrial pulse amplitude and pulse width
• Ventricular sensitivity
• Anatomical location of atrial and ventricular
electrodes

75. SM
Managing Crosstalk
• Atrial Pulse Energy
• Ventricular Sensitivity
• Ventricular Blanking Period
• Crosstalk Sensing Window
• Safety Pacing (Non Physiologic AV delay)

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Ventricular Blanking Period (VB)
• A short (21-75 ms) period that begins
simultaneously with an atrial output pulse and
during which the ventricular sense amplifier is
totally blind to incoming signals.
AV delay
VB

77. SM
AVD PVARP
VRP
Ventricular Blanking Period
DDD Mode: Crosstalk Inhibition Protection
Atrial Channel
Ventricular Channel

78. SM
Crosstalk Sensing Window
• A short (25-40ms) period of time that starts at
the end of the ventricular blanking period
• If during this time interval the ventricular lead
senses an event (may be crosstalk, may also
be a PVC), a ventricular output pulse is
delivered after 100 ms = SAFETY PACING
• This 100 ms time period = Non Physiologic AV
delay

79. SM
Safety Pacing
Non Physiologic AV delay (100 ms)
Ventricular Blanking
Period
Crosstalk Sensing Window
Atrial Output
Ventricular Output
Ventricular Sense

80. SM
Pacemaker Follow-Up
Dual Chamber Pacemaker