Pacemaker Concepts by gabyion

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									      Basic Pacing Concepts



Mr Stuart Allen
Technical Head
Southampton General Hospital
Basic Electrical Concepts
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
    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
Fixation mechanisms of the Electrode




Active fixation   Passive fixation   Active fixation
Tines             Wingtips           Screw
          Stimulation Threshold




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

                             Leading Edge


                                                 Trailing Edge



Pulse Amplitude




                         Pulse Width


The energy is proportional to the pulse amplitude and the pulse
                 width (=surface under the curve)
        Stimulation Threshold
L’IMPULSION DE STIMULATION




      0.5 V
       to
      10 V

                Pulse Width
       Stimulation Threshold
L’IMPULSION DE STIMULATION




      0.5 V
       to
      10 V



              0.1 to 1.5 ms
       Stimulation Threshold
L’IMPULSION DE STIMULATION




      0.5 V
       to         Energy
      10 V



               0.1 to 1.5 ms
                   Strength - Duration Curve
Pulse Amplitude (V)

       2.5

       2.25

       2

       1.75

       1.5

       1.25

       1

       0.75

       0.5

       0.25

       0

              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)
                    Strength - Duration Curve
Pulse Amplitude (V)

            5
          2.5

            4.5
          2.25

          24

            3.5
          1.75

            3
          1.5

          1.25
            2.5                              Capture
          12

            1.5
          0.75

            1
          0.5

            0.5
          0.25
                       Non-Capture
          00

                  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)
                  Strength - Duration Curve
Pulse Amplitude (V)

          5
        2.5

          4.5
        2.25

        24

          3.5
        1.75

          3
        1.5

          2.5
        1.25

        12

        0.75
          1.5                      Threshold at 0.5 ms = 0.7 V
          1
        0.5

          0.5
        0.25

        00

                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)
              Energy and Longevity


         ²
     V
E=           x t
     R
              Energy and Longevity

         ²
     V
E=           x PW
     R


Example :      F 5 V,   500 W , 0.5 ms

                                 5²
                           E =         x 0.5   = 25 µJ
                                 500
              Energy and Longevity

         ²
     V
E=           x PW
     R


Example :      F 5 V,   500 W , 0.5 ms

                                 5²
                           E =         x 0.5   = 25 µJ
                                 500

               F2.5 V, 500 W , 0.5 ms
              Energy and Longevity

         ²
     V
E=           x PW
     R


Example :      F 5 V,       500 W , 0.5 ms

                                      5²
                               E =           x 0.5   = 25 µJ
                                     500

               F2.5 V, 500 W , 0.5 ms
                                     2.5 ²
 ( Increased longevity! )      E =           x 0.5 = 6.25 mJ
                                     500
Pacemaker codes and
      modes
  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)
  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
Choice of a Stimulation Mode


           Bradycardia

      Atrial fib            Normal P waves


RR                 Normal A-V     A-V Block
          RR 
                   RR    RR    RR    RR


VVI     VVIR       AAI    AAIR   DDD    DDDR
                   DDI    DDIR
Single Chamber Pacing




              VVI (R)
Single Chamber Pacing




              AAI (R)
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)
  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)
VVI MODE
             VVI MODE




Vp   Vp   Vp Vs Vs   Vp   Vp   Vs   Vs
                      VVI MODE

                               • Automatic interval starts
                                 from a paced complex (to
                                 the next paced complex)
 Automatic                     • Escape interval starts from
  Interval                       a sensed complex (to the
                                 next paced complex)

                  If the intervals are equal:
                       •No hysteresis
Escape Interval   If the escape interval > automatic interval:
                       •Hysteresis
VVI MODE (with hysteresis)




                 1000 ms


                           850 ms




Escape interval = 1000 ms (60 ppm)
Automatic interval = 850 ms (70 ppm)
  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)
MODE AAI
          MODE AAI




Ap   Ap    Ap   As   Ap
Dual Chamber Pacing
DUAL CHAMBER STIMULATION
DUAL CHAMBER STIMULATION
      DDD Pacemaker


A DDD pacemaker puts in the
 beat that’s missing in order to
    maintain AV synchrony
                                DDD timing
Ap       Vp           Ap   Vs      As   Vp      As   Vs   PVC




     AA interval

AV-D
                                                           VA int.
      NPAVD

 VB
         CSW                                                 ARE
                                        PVARP
               TARP
       VRP

        VTL
                   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
     DUAL CHAMBER STIMULATION



Advantages      AV Synchrony
                Variability of the pacing rate


Results         Increase of the cardiac output
                Improved quality of life
                No Pacemaker Syndrome
                   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!
         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
  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)
ECG: DDD mode
                  DDD mode



As    As    Ap      Ap    As    As   Ap    Ap
 Vp    Vp    Vp      Vp    Vs   Vs    Vs    Vs
             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
                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
            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
  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)
                    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
          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
          Atrial Refractory Period

• AV delay

• PVARP= Post Ventricular Atrial Refractory Period

            TARP = Total Atrial Refractory Period
                  = AV delay + PVARP
Atrial Refractory Period




AV delay      PVARP


       TARP
 DDD Mode: Refractory Periods




 Atrial Channel       AVD   PVARP




                               VRP

Ventricular Channel
 Clinical Considerations in DDD pacing


• Upper Rate Behaviour



• Control of Pacemaker Mediated Tachycardia


• Crosstalk Inhibition Protection
           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)
         Upper Rate Behaviour


• Fixed Ratio Block or Multiblock or 2:1 block



• Wenckebach response
        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
                   DDD Mode: 1:1 Tracking

Ventricular
Rate
      120
      110
      100
       90
       80
       70
       60
       50             1:1 tracking
       40
              30    60 60     120 120 180   180 180 200 200

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

                                                   Atrial Rate
           Wenckebach Response

                           P wave (falls
                           outside PVARP)




                            AV delay


AV delay     PVARP


                     VTL
  How to recognize Wenckebach?


• Grouped beating

• Progressive prolongation of the AV delay until
  the ventricular output is missed

• Ventricular pacing at the VTL
  Pacemaker Mediated Tachycardia (PMT)




Rapid ventricular pacing due to RETROGRADE
 CONDUCTION, most commonly at exactly the
                 upper rate limit.
          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
 DDD Mode: Refractory Periods




 Atrial Channel       AVD   PVARP




                               VRP

Ventricular Channel
        Common Causes of PMT


• Loss of atrial capture



• Premature Ventricular Contractions (PVC’s)



• Myopotential Tracking
Pacemaker Mediated Tachycardia


                PVC           Retrograde P waves




        AVD

              PVARP   PVARP    PVARP   PVARP
             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
   Atrial Refractory Extension after a PVC


                            PVC         Retrograde P wave




                    AVD                        AVD

                          PVARP   PVARP ARE          PVARP




The ARE is programmable (off; 50; 100; 150 ms)
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.
Tachycardia Termination Algorithm



 PVC    Retrograde P waves




         1       2           14   15 Inhibition of the 16 th
                                     ventricular output
                                     pulse
              Crosstalk



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



• Inappropriate inhibition of the
  ventricular spike due to sensing of
  the atrial output pulse by the
  ventricular sense amplifier.
     Factors Affecting Crosstalk


• Atrial pulse amplitude and pulse width

• Ventricular sensitivity

• Anatomical location of atrial and ventricular
  electrodes
           Managing Crosstalk

• Atrial Pulse Energy


• Ventricular Sensitivity

• Ventricular Blanking Period

• Crosstalk Sensing Window

• Safety Pacing (Non Physiologic AV delay)
  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
  DDD Mode: Crosstalk Inhibition Protection




             Atrial Channel       AVD   PVARP




Ventricular Blanking Period
                                           VRP

            Ventricular Channel
      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
                       Safety Pacing

                                     Ventricular Output
   Atrial Output




Ventricular Blanking
Period
Ventricular Sense
                             Crosstalk Sensing Window


                             Non Physiologic AV delay (100 ms)
 Pacemaker Follow-Up




Dual Chamber Pacemaker

								
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