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Understanding pacemakers

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presented in LPS institute of Cardiology, Kanpur

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Understanding pacemakers

  1. 1. Understanding Permanent Pacemakers Dr. Dibbendhu Khanra 21.9.16
  2. 2. A Brief History of Pacemakers
  3. 3. Today’s agenda Includes • Pacemaker components • Basics physics/ physiology • Timing cycles & algorithms Excludes • Indications • CRT • ICD BASIC TROUBLESHOOTING
  4. 4. PPM Hardwares
  5. 5. Pulse Generator SINGLE CHAMBER PACEMAKER Block Diagram of Basic Components Input Amplifier Output Circuits Noise Detector Run-away Protection Control Unit CPU Analog.ue Circuits Storage ROM / RAM Transmitting and Receiving logic Rate Control Circuit Rate Response Sensor Telemetry Coil ERI Detection Power Source DEVICE ENCLOSURE HEADER BLOCK Set screws LiI <100microA Li Ag Va in ICD in Amp 3V battery 256 KB to 1MB ROM 1-16 MB RAM 20-40 Hz Timing Cycle by Crystal Magnet mode Magnet close reed switch (VOO)
  6. 6. Pacemaker leads ELECTRODES Steroid eluding Low polarity (Titanium Nitride) Elgiloy CONDUCTORS highly conductive Ag core MP35N for mechanical stress INSULATORS Polyurethane> si rubber CONNECTOR PIN IS/ stainless steel lead anchorage sleeve of radio-dense MDX PASSIVE/ TINES ACTIVE/ SCREWS (mannitol/ polyethelene) FIXATION MECHANSIM
  7. 7. Basic physiology
  8. 8. What we see..
  9. 9. Intracardiac electrogram
  10. 10. Capture
  11. 11. Strength duration curve • Rheobase = lowest stimulus voltage that will electrically stimulate the myocardium at any pulse duration. • Chronaxie = threshold pulse duration at a stimulus amplitude that is twice the rheobase voltage
  12. 12. Threshold • Minimum amplitude and duration required to generate the self-propagating wave front that results in cardiac activation atrial pacing threshold of <1.5 V and ventricular threshold of <1 V
  13. 13. Wedensky Effect • Stimulation thresholds that are measured by decrementing the stimulus voltage until loss of capture are usually 0.1–0.2 V lower than when the stimulus intensity is gradually increased from sub-threshold until capture is achieved • The Wedensky effect may be greater at narrow pulse durations
  14. 14. Automated Capture • AutoCapture in SJM (beat to beat with backup pacing) • Capture Control in Biotronik (no backup pacing) • Ventricular Capture Management in Medtronik (once/ day)
  15. 15. Current of injury • Partially confirm acute tissue-electrode contact • (intracardiac EGM)
  16. 16. Impedance • V = I.R • I is inversely proportional to R • R = R1+R2+R3 • R1 across lead conductors • R2 across electrode/ myocardium interface (max) smaller diameter of electrode increases resistance • R3 due to polarization shorter duration of impulse minimizes polarization larger surface area minimizes polarization thus resistance
  17. 17. Unipolar Sensing 30-50 cms Sensing: - Less affected by change of ventricular activation - Easily influenced by electric interferences Pacing - larger spike _
  18. 18. Bipolar Sensing 3-5 cm Sensing: - Easily affected by change of ventricular activation - Less influenced by electric interferences Pacing - smaller spike
  19. 19. 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
  20. 20. Polarization • Proportional to amplitude & duration of pulse • Blanking period • Cross Talk
  21. 21. Automated Sensing • traditionally a fixed sensitivity • Most common prob is with sensing • Better if Regularly determined Medtronic Sensing Assurance: • atrial is maintained within a range that is 4.0–5.6 times ventricular is maintained within a range that is 2.8-4 times OF the programmed sensitivity.
  22. 22. Electromagnetic Interference (EMI) • 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
  23. 23. EMI May Result in the Following Problems: • Oversensing – 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 • Transient mode change (noise reversion)
  24. 24. Signals vs noise
  25. 25. EMI Fear – Electrocautery – Transthoracic defibrillation – Extracorporeal shock- wave lithotripsy – Therapeutic radiation – RF ablation – TENS units – MRI Fear Not • Home, office, and shopping environments • Industrial environments with very high electrical outputs • Transportation systems with high electrical energy exposure or with high-powered radar and radio transmission – Engines or subway braking systems – Airport radar – Airplane engines • TV and radio transmission sites
  26. 26. NOISE REVERSION RESPONSE
  27. 27. Lead Maturation Process • Fibrotic “capsule” develops around the electrode following lead implantation
  28. 28. Time Changeth Everything Impedence • Falls within 1-2 wks • Then rises to 15% more • Low impedence reflects failure of conductor insulation • High impedence suggest conductor fracture or loose set screws Threshold Active fixation after complete deployment threshold is lesser Steroid eluting electrodes threshold almost unchanged Passive fixation: P/R decreases within days Normalizes in 6-8 weeks Less in SEL Active fixation: Attaches to myocardium P/R decreases within mins Normalises in 20-30 mins Sensing
  29. 29. Rate 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
  30. 30. Sensors
  31. 31. • 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
  32. 32. Pacemaker Codes
  33. 33. Timing cycle
  34. 34. So many parameters..
  35. 35. Understanding language
  36. 36. The Alphabets.. A V P R
  37. 37. Making Words.. PR PV PVAV AR TOTAL INHIBITION P SYNCHRONOUS PACING AV SEQUENTIAL PACING T=TRACKING
  38. 38. The grammar... AV+VA = LRI LRL= 60000/ LRI TARP = AV+PVARP MTR = URI URL= 60000/ URI = 60000/ TARP
  39. 39. Making sense.. BP RP ARP RRP NO DETECTION NO RESET DETECTION BUT NO RESET
  40. 40. Perfect Senses A - ABP : V - PVABP PVARP V - VRP : A - VBP CSW alert period
  41. 41. Modes and hysteresis
  42. 42. VVI RESET
  43. 43. Ventricular oversensing Ventricular undersensing VVI RV<VVRV>VV solution: increase RP solution: decrease RP
  44. 44. VVI VENTRICULAR RATE HYSTERESIS Base rate 60 (1000 ms) Hysteris rate 50 (1200 ms) VV<RV
  45. 45. VOO Magnet mode Magnet close reed switch
  46. 46. AAI
  47. 47. AAI Atrial Oversensing Prevent After polarization Prevent far-field sensing Base rate 70 (857 ms) ARP = 250 ms R wave oversensing Solution: ARP increased to 400 ms
  48. 48. AAI ATRIAL RATE HYSTERESIS Base rate 60 (1000 ms) Hysteris rate 50 (1200 ms) AA<PA
  49. 49. DDD vs DDI Tracking
  50. 50. DVI VS VDD Tracking
  51. 51. Cross talk & safety pacing
  52. 52. Ventricular channel
  53. 53. Cross talk window Pacing spike earlier than programmed AVI • Safety pacing is designed to prevent ventricular asystole if cross-talk were to occur in a pacemaker-dependent patient
  54. 54. Far field R wave oversensing Ventricular channel
  55. 55. Safety Pacing Due To Atrial Undersensing Due To Atrial oversensing Unsesed P Uncaptured A R within CSW
  56. 56. AV Delay
  57. 57. Differential AVI SAV<PAV
  58. 58. Differential AVI SAV 160 ms PAV 200 ms
  59. 59. Dynamic AVI AVI = ABP +atrial sensing window TARP shortened to enhance atrial tracking at first rate
  60. 60. AV hysteresis Negative
  61. 61. PVARP & PMT
  62. 62. PVARP PVC Retrograde P wave is sensed but not tracked in PVARP
  63. 63. DYNAMIC PVARP PVARP increased to maintain adequate sensing window PVARP decreased to minimum PVABP
  64. 64. Pacemaker Mediated Tachycardia
  65. 65. Pacemaker Mediated Tachycardia P wave outside PVARP is tracked Solution: increase PVARP
  66. 66. Extended PVARP T oversense PVC P not sensed
  67. 67. Paradoxical PMT repetitive non-reentrant VA synchrony (RNRVAS)
  68. 68. PMT prevention algorithm Atrial sensed ventricular pacing at MTR = PMT vs atrial arrythmia SOLUTION Stop VP Or extend PVARP PMT stops Atrial arrythmia continues
  69. 69. PMT termination Stable Retrograde VAI Changing AVI Decreasing MTR Withhold VP Followed by atrial pacing at 330 ms
  70. 70. Lack of P wave tracking First degree AV block P wave falling within PVARP P wave outside PVARP 1:1 conduction
  71. 71. Base timing
  72. 72. Base timing 800 ms 850 ms AEI prolongation AEI fixed In Bradycardia, atrial based pacing violates the LRL
  73. 73. Base timing PVC – R interval
  74. 74. Lower Rate Behaviour in rate responsive systems Intact AV ocnduction ARI = 120 ms In tachycardia, ventricular based pacing violates the URL
  75. 75. MODE SWITCH AV nodal conduction absent Vs Brady = ventr based Tachy = atrial based
  76. 76. Rate responsiveness & upper rate behaviour
  77. 77. Rate responsiveness Tracked Not Tracked
  78. 78. Rate responsiveness AV sequential pacing P synchronous pacing Heart rate faster than AIR AVI shortens PVARP fixed SIR is LRL during exercise MSR is MTR during exercise
  79. 79. UPPER RATE BEHAVIOUR AVI 125 ms PVARP 225 ms TARP 350 ms MTR 350 ms (170 bpm) URI 400 ms (150 bpm) Wenchebach interval URI-TARP = 50 ms PP>TARP RATE < MTR (157) PP>TARP RATE > MTR (330) wenchebach 2:1
  80. 80. Wenchebaching
  81. 81. Rate responsiveness
  82. 82. Rate elevation response
  83. 83. Rate smoothing Smoothing 9% up to 6% down RR: 800-72=728 ms 800+48=848 ms AA: 728-150 = 578 ms 848 -150 = 698 ms MTR 100 bpm 6% = 36 ms b=a+36 msa b
  84. 84. Rate modulation acting as rate smoothening 480 ms (125bpm) 810 ms (74bpm) SIR 545 ms (110 bpm) URL 480 ms (125bpm) Difference 330 ms Difference 65 ms MAXIMUM LENGHTHEING = MTR - SIR
  85. 85. Ventricular rate stabilization 1 = VPC 2 = AV sequential pacing at the previous V–V interval plus interval increment 3 = gradual prolongation of AV sequential pacing Prevents pause dependent VT
  86. 86. Atrial arrythmia MTR = 500 ms (120 bpm) LRL =1200 ms (50 bpm)
  87. 87. Fall back
  88. 88. Fall back mode MTR Mode switch DDD DDI slowly decrease the VP rate from the MTR to the LRL
  89. 89. Intrinsic Rate Algorithm
  90. 90. RATE HYSTERESIS SCAN HYSTERESIS BTK SINUS PREFERENCE MDT SLEEP RATE MDT NIGHT RATE BTK REST RATE SJM
  91. 91. Cardioinhibitory neurogenic syncope response
  92. 92. Advanced Rate Hysteresis  pacing is suspended for the pacemaker to “search” for the intrinsic lower rate.  If the lower rate is greater than the hysteresis rate, pacing is inhibited until the rate again falls below the hysteresis rate.
  93. 93. Rate Drop response
  94. 94. Sudden Bradycardia Response
  95. 95. Atrial Arrhythmia algorithms
  96. 96. Blanked Flutter Search, MDT
  97. 97. 2:1 lock in protection algorithm, BTK
  98. 98. Atrial Flutter algorithm, BS An atrial pace will only occur if the AFR window expires at least 50 ms before the scheduled VP. This prevents competitive pacing
  99. 99. Non Competitive Atrial Pacing MDT As
  100. 100. ATRIAL ARRYTHMIA RESPONSE
  101. 101. AF SUPRESSION ALGORITHM
  102. 102. AF suppression algorithm
  103. 103. Ventricular response pacing
  104. 104. Minimizing RV pacing
  105. 105. Intrinsic AV conduction AV hysteresis Ventricular Intrinsic preference Programmable delta PAVI = 200+140
  106. 106. Intrinsic AV conduction cont.. Managed Ventricular Pacing RhythmIQ SafeR
  107. 107. MRI compatible PPM
  108. 108. MRI safety Two coils Less heating Hall sense & Less ferromagnetism
  109. 109. TROUBLESHOOTING
  110. 110. Solution: increase VRP/ increase PVARP
  111. 111. Know your car
  112. 112. THANK YOU

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