Basic Pacing Concepts

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Basic Pacing Concepts

• Mr Stuart Allen
• Technical Head
• Southampton General Hospital

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Basic Electrical Concepts
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Polarity of the Pacemaker System
Unipolar Stimulation Sensing

• Larger antenna for sensing
• bigger signals
• more interference (myopotentials !)
• Big spike on ECG
• Pectoral (pocket) stimulation possible

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Polarity of the Pacemaker System
CONFIGURATION UNIPOLAIRE
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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Stimulation Threshold

• 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

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Output Pulse
Stimulation Threshold
Leading Edge
Trailing Edge
Pulse Amplitude
Pulse Width

• The energy is proportional to the pulse amplitude
  and the pulse width (surface under the curve)

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Stimulation Threshold
LIMPULSION DE STIMULATION
0.5 V to 10 V
Pulse Width
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Stimulation Threshold
LIMPULSION DE STIMULATION
0.5 V to 10 V
0.1 to 1.5 ms
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Stimulation Threshold
LIMPULSION DE STIMULATION
0.5 V to 10 V
Energy
0.1 to 1.5 ms
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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
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Strength - Duration Curve
Pulse Amplitude (V)
Capture
Non-Capture
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
Pulse Width (ms)
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Strength - Duration Curve
Pulse Amplitude (V)
Threshold at 0.5 ms 0.7 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
Pulse Width (ms)
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Energy and Longevity
²
V
E x t
R
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Energy and Longevity
²
V
E x PW
R
Example F 5 V, 500 W , 0.5 ms
²
5
E x 0.5 25 µJ
500
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Energy and Longevity
²
V
E x PW
R
Example F 5 V, 500 W , 0.5 ms F2.5 V,
500 W , 0.5 ms
²
5
E x 0.5 25 µJ
500
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Energy and Longevity
²
V
E x PW
R
Example F 5 V, 500 W , 0.5 ms F2.5 V,
500 W , 0.5 ms
²
5
E x 0.5 25 µJ
500
²
2.5
E x 0.5 6.25 mJ
( Increased longevity! )
500
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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 Aatrium 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 (AV) (AV)
(TI) R Rate Modulation Manufact
urers 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 Sinu
s 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
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Choice of a Stimulation Mode
Bradycardia
Normal P waves
Atrial fib
Normal A-V
A-V Block
RR é
RR è
RR é
RR è
RR é
RR
DDD
DDDR
AAI DDI
AAIR DDIR
VVI
VVIR
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Single Chamber Pacing
VVI (R)
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Single Chamber Pacing
AAI (R)
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Single Chamber Pacemaker (VVI)

• Easy to implant a ventricular lead
• Easy to program the pacemaker
• Easy follow-up
• Longevity of gt 6 years
• Only one pacing rate (except rate responsive
  pacemakers)

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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 Aatrium 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 (AV) (AV)
(TI) R Rate Modulation Manufact
urers 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 starts from a paced complex
  (to the next paced complex)
• Escape interval starts from a sensed complex (to
  the next paced complex)

Automatic Interval

• If the intervals are equal
• No hysteresis
• If the escape interval gt automatic interval
• Hysteresis

Escape Interval
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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 Aatrium 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 (AV) (AV)
(TI) R Rate Modulation Manufact
urers Designation only S single S
single (A or V) (A or V)
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MODE AAI
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MODE AAI
Ap Ap Ap As Ap
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Dual Chamber Pacing
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DUAL CHAMBER STIMULATION
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DUAL CHAMBER STIMULATION
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DDD Pacemaker

• A DDD pacemaker puts in the beat thats missing
  in order to maintain AV synchrony

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DDD timing

Ap
Vp
Ap
Vp
As
Vs
As
Vs
PVC

AA interval
AV-D
VA int.
NPAVD
VB
CSW
ARE
PVARP
TARP
VRP
VTL
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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

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DUAL CHAMBER STIMULATION

• Advantages l AV Synchrony
• l Variability of the pacing rate
• Results l Increase of the cardiac output
• l Improved quality of life
• l No Pacemaker Syndrome

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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!

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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

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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 Aatrium 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 (AV) (AV)
(TI) R Rate Modulation Manufact
urers Designation only S single S
single (A or V) (A or V)
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ECG DDD mode
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DDD mode
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Differential AV delay

• AV s lt 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

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Adaptive AV delay

• AV delay adapts in an 81 ratio
• For every shortening of the AA interval of 8 ms,
  the AV delay shortens by 1 ms (but never lt 75 ms)
• Enhances ventricular filling and increases
  cardiac output
• Improves upper rate behaviour characteristics

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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 Aatrium 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 (AV) (AV)
(TI) R Rate Modulation Manufact
urers Designation only S single S
single (A or V) (A or V)
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DDI Pacing

• DDI DVI Atrial sensing / inhibition
• DDI is NOT a pacemaker type but a MODE
• DDD pacemaker mode switch to DDI
• ? Paroxysmal atrial tachycardias no tracking
  allowed!
• ? Switch from DDD to DDI

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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

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Atrial Refractory Period

• AV delay
• PVARP Post Ventricular Atrial Refractory Period
• ? TARP Total Atrial Refractory Period
• AV delay PVARP

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Atrial Refractory Period
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DDD Mode Refractory Periods
Atrial Channel
AVD
PVARP
VRP
Ventricular Channel
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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 pacemakers response to sensed rapid atrial
  rates.
• A rapid atrial rate is a rate gt Upper Rate Limit
  (URL) or Ventricular Tracking Limit (VTL)
• VTL a rate beyond which 11 tracking will NOT
  occur
• the absolute speed limit in the ventricle
• (max. 180 bpm)

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Upper Rate Behaviour

• Fixed Ratio Block or Multiblock or 21 block
• Wenckebach response

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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

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DDD Mode 11 Tracking
Ventricular Rate
11 tracking
60 120 180 200
Atrial Rate
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DDD Mode Wenckebach
Ventricular Rate
11 tracking
Wenckebach
60 120 180 200
Atrial Rate
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Wenckebach Response
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How to recognize Wenckebach?

• Grouped beating
• Progressive prolongation of the AV delay until
  the ventricular output is missed
• Ventricular pacing at the VTL

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Pacemaker Mediated Tachycardia (PMT)

• Rapid ventricular pacing due to RETROGRADE
  CONDUCTION, most commonly at exactly the upper
  rate limit.

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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

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DDD Mode Refractory Periods
Atrial Channel
AVD
PVARP
VRP
Ventricular Channel
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Common Causes of PMT

• Loss of atrial capture
• Premature Ventricular Contractions (PVCs)
• Myopotential Tracking

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Pacemaker Mediated Tachycardia
PVC
Retrograde P waves
PVARP
PVARP
PVARP
PVARP
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PMT Prevention

• Program PVARP longer than VA conduction time
• PVARP AV delay TARP ? determines 21 block
• 250 ms 150 ms 400 ms ? 21 block at 150 bpm
• 350 ms 150 ms 500 ms ? 21 block at 120 bpm
  

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

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Tachycardia Termination Algorithm
PVC
Retrograde P waves
Inhibition of the 16 th ventricular output pulse
1
2
14
15
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Crosstalk

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

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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

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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.

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DDD Mode Crosstalk Inhibition Protection
Atrial Channel
AVD
PVARP
Ventricular Blanking Period
VRP
Ventricular Channel
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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

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Safety Pacing
Ventricular Output
Atrial Output
Ventricular Blanking Period
Ventricular Sense
Crosstalk Sensing Window
Non Physiologic AV delay (100 ms)
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Pacemaker Follow-Up

• Dual Chamber Pacemaker