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Understanding pacemakers
- 2. A Brief History of Pacemakers
- 3. Today’s agenda Includes • Pacemaker components • Basics physics/ physiology • Timing cycles & algorithms Excludes • Indications • CRT • ICD BASIC TROUBLESHOOTING
- 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. 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
- 10. Capture
- 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. 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. 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. 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. Current of injury • Partially confirm acute tissue-electrode contact • (intracardiac EGM)
- 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. Unipolar Sensing 30-50 cms Sensing: - Less affected by change of ventricular activation - Easily influenced by electric interferences Pacing - larger spike _
- 18. Bipolar Sensing 3-5 cm Sensing: - Easily affected by change of ventricular activation - Less influenced by electric interferences Pacing - smaller spike
- 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. Polarization • Proportional to amplitude & duration of pulse • Blanking period • Cross Talk
- 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. 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. 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. Signals vs noise
- 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
- 27. Lead Maturation Process • Fibrotic “capsule” develops around the electrode following lead implantation
- 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. 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. Sensors
- 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. Pacemaker Codes
- 33. Timing cycle
- 36. The Alphabets.. A V P R
- 37. Making Words.. PR PV PVAV AR TOTAL INHIBITION P SYNCHRONOUS PACING AV SEQUENTIAL PACING T=TRACKING
- 38. The grammar... AV+VA = LRI LRL= 60000/ LRI TARP = AV+PVARP MTR = URI URL= 60000/ URI = 60000/ TARP
- 39. Making sense.. BP RP ARP RRP NO DETECTION NO RESET DETECTION BUT NO RESET
- 40. Perfect Senses A - ABP : V - PVABP PVARP V - VRP : A - VBP CSW alert period
- 42. VVI RESET
- 43. Ventricular oversensing Ventricular undersensing VVI RV<VVRV>VV solution: increase RP solution: decrease RP
- 44. VVI VENTRICULAR RATE HYSTERESIS Base rate 60 (1000 ms) Hysteris rate 50 (1200 ms) VV<RV
- 45. VOO Magnet mode Magnet close reed switch
- 46. AAI
- 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. AAI ATRIAL RATE HYSTERESIS Base rate 60 (1000 ms) Hysteris rate 50 (1200 ms) AA<PA
- 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. Far field R wave oversensing Ventricular channel
- 55. Safety Pacing Due To Atrial Undersensing Due To Atrial oversensing Unsesed P Uncaptured A R within CSW
- 56. AV Delay
- 58. Differential AVI SAV 160 ms PAV 200 ms
- 59. Dynamic AVI AVI = ABP +atrial sensing window TARP shortened to enhance atrial tracking at first rate
- 61. PVARP & PMT
- 62. PVARP PVC Retrograde P wave is sensed but not tracked in PVARP
- 63. DYNAMIC PVARP PVARP increased to maintain adequate sensing window PVARP decreased to minimum PVABP
- 65. Pacemaker Mediated Tachycardia P wave outside PVARP is tracked Solution: increase PVARP
- 66. Extended PVARP T oversense PVC P not sensed
- 67. Paradoxical PMT repetitive non-reentrant VA synchrony (RNRVAS)
- 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. PMT termination Stable Retrograde VAI Changing AVI Decreasing MTR Withhold VP Followed by atrial pacing at 330 ms
- 70. Lack of P wave tracking First degree AV block P wave falling within PVARP P wave outside PVARP 1:1 conduction
- 71. Base timing
- 72. Base timing 800 ms 850 ms AEI prolongation AEI fixed In Bradycardia, atrial based pacing violates the LRL
- 73. Base timing PVC – R interval
- 74. Lower Rate Behaviour in rate responsive systems Intact AV ocnduction ARI = 120 ms In tachycardia, ventricular based pacing violates the URL
- 75. MODE SWITCH AV nodal conduction absent Vs Brady = ventr based Tachy = atrial based
- 76. Rate responsiveness & upper rate behaviour
- 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. 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. Wenchebaching
- 84. 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
- 85. 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
- 86. 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
- 87. Atrial arrythmia MTR = 500 ms (120 bpm) LRL =1200 ms (50 bpm)
- 88. Fall back
- 89. Fall back mode MTR Mode switch DDD DDI slowly decrease the VP rate from the MTR to the LRL
- 91. RATE HYSTERESIS SCAN HYSTERESIS BTK SINUS PREFERENCE MDT SLEEP RATE MDT NIGHT RATE BTK REST RATE SJM
- 93. 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.
- 97. Blanked Flutter Search, MDT
- 98. 2:1 lock in protection algorithm, BTK
- 99. 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
- 107. Minimizing RV pacing
- 108. Intrinsic AV conduction AV hysteresis Ventricular Intrinsic preference Programmable delta PAVI = 200+140
- 109. Intrinsic AV conduction cont.. Managed Ventricular Pacing RhythmIQ SafeR
- 110. MRI compatible PPM
- 111. MRI safety Two coils Less heating Hall sense & Less ferromagnetism
- 112. TROUBLESHOOTING
- 119. Know your car
- 120. THANK YOU
Notes de l'éditeur
- UNIPOLAR – TIP CATHODE PG ANODE ONLY ONE CONDUCTOR SURROUNDED BY INSULATION BIPOLAR – TIP CATHODE RING ANODE CO AXIAL – COMMONER, SIZE INCREASES CORADIAL – SIZE DECRASES PASSIVE TINES – NOT SUITABLE FOR PLACING IN NONTRADITIONAL LOCATION, MAY TRAPPED IN TC valve apparatus, FIBROSED EARLY BY 6M MAKING HARD TO EXTRACT IF NEEDED ACTIVE SCREWS – SUITABLE FOR PLACING IN NONTRADITIONAL LOCATION, EASILY RETRACTABLE, current of injury is promonent as it fixes to myocardium DRAWN BRAZED STRAND DRAWN BRAZED TUBE Si rubber – melts in heat/ high friction/ low tensile strength..however biostable and biocompatible Polyurethane – now choice for 10 years Sleeve to be reinforced by nonabsorbable suture like ethilon Electrode: small radius but high surface area . . . Minimizes polarization . . And improves sensing Smalled radius – higher current density – lower pacing threshold – high resistance of electrode/ myocardium interphase – high sensing impedence and polarization artifact
- The strength-duration curve illustrates the tradeoff of amplitude (intensity of stimulation, measured in volts) and duration (the length of time the stimulation is applied, measured in milliseconds). Capture occurs when the stimulus causes the tissue to react. On the graph, capture occurs on or above the curve. Anything below the curve will not capture. The lowest voltage on a stimulation curve which still results in capture at an infinitely long pulse duration is called rheobase. A voltage programmed below is inefficient and will lead to non-capture. The pulse duration at twice the rheobase value is defined as the chronaxie. Chronaxie time is typically considered most efficient in terms of battery consumption. With pulse durations greater than the chronaxie, there is relatively little reduction in the threshold voltage. Rather, the wider pulse duration results in the wasting of stimulation energy without providing a substantial increase in safety margin doubling the pulse duration results in two-fold increase in stimulation energy, whereas doubling the stimulus voltage results in a four-fold increase, which has practical implications for the effect of programming pacing output on battery longevity
- Safety margins have traditionally been selected as follows, when a threshold is determined by decrementing the pulse width at a fixed voltage: At a given voltage where the pulse width value is < .30 ms: Tripling the pulse width will provide a two-time voltage safety margin. Pulse widths at a given voltage value which are >.30 ms are not typically selected, because they are less efficient (expend more energy), while not providing further safety. In this case, the voltage should be doubled to provide a two-time safety margin. Adequate safety margins must be selected due to daily fluctuations in threshold that can occur due to eating, sleeping, exercise, or other factors that affect thresholds. Also, a patient with an acute pacing system will typically be programmed to a setting allowing a higher safety margin, due to the lead maturation process, which can occur within the first 6-8 weeks following implant. increasing the pulse width beyond 0.6 msec usually does not decrease the voltage threshold. At implant, an atrial pacing threshold of <1.5 V and ventricular threshold of <1 V should be obtained set the pulse amplitude at two to three times that of the pacing threshold close to the chronaxie pulse duration. The threshold commonly increases over the next 2 to 4 weeks, reaches a peak, and then decreases to a chronic threshold level after 6 to 8 weeks. With steroid-eluting leads, the acute rise in threshold is ameliorated and the chronic threshold is significantly lower than in nonsteroid-eluting leads. During initial programing, the pacing output is programed at 3 to 5 times the threshold voltage with a pulse width of 0.4 to 0.5 msec. At the 2-to 3-month follow up visit, the output is decreased to no less than twice the threshold to maintain an adequate safety margin and prevent battery drain
- 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 Threshold kept at atleast two-three times Programming stimulus intensity to greater than 2.8 V results in a marked increase in current drain from the battery Generally, a three-fold safety Generally, a three-fold safety margin may be employed at the time of initial implant, followed by reprogramming to a lower value at the 6–8-week follow-up visit
- The AutoCaptureTM algorithm used in St. Jude pacemakers assures capture on a beat-tobeat basis. This algorithm first verifies that the evoked response can be differentiated from the polarization signal by delivering paired pulses, with the second pulse occurring in the absolute refractory period and thus causing only polarization artifact. Via this mechanism, the algorithm is able to set a reliable evoked response sensitivity. If there is insufficient difference between the evoked response signal and the polarization artifact, the algorithm may not function adequately because it runs the risk of oversensing polarization signal and under-estimating the threshold. In these cases, the automatic capture feature has to be turned off. After determination of the threshold, the pacemaker adjusts the output to stimulate at 0.3 V (for single chamber) or 0.25 V (for dual chamber) above the prevailing threshold. The algorithm works by reducing the pacing output in 0.25-V steps over consecutive pairs of beats until loss of capture occurs on two consecutive beats, with a 5-V back-up pulse delivered with each loss of capture event. The output is then increased in 0.125-V steps until two consecutive capture beats are seen, thereby defining capture threshold. The 0.25-V margin is then added to this threshold for subsequent pacing until loss of capture is seen or the next threshold test is performed. It is important to remember that capture confirmation occurs on a beat-to-beat basis. In several multicenter studies, the algorithm was found to be safe and effective and did not result in loss of capture, exit block, or other adverse events.20,21 However, the algorithm requires use of a bipolar pacing lead with low polarization properties. Furthermore, patients with this feature turned “on” may exhibit unusual pacing behavior on telemetry or ECG when the device is performing automatic threshold testing. The Capture ControlTM algorithm used in Biotronik pacemakers similarly depends on the use of a bipolar lead with low polarization characteristics. The differences from the St. Jude Medical algorithm include the absence of a back-up safety pulse during loss of capture and an output increase in 2-V steps if there is persistent loss of capture. Then, after a programmable length of time, the output is decreased to the original value to see if capture can be obtained with a lower output.
- D duration of injury current ST amplitude of injury current
- Impedance reading values range from 300 to 1,000 W High impedance leads will show impedance reading values greater than 1,000 ohms Most companies 600-800 ohms except biotronik which has high impedence 1500-1600 ohm
- Higher the slew rate higher the frequencey content Sense amplifiers most sensitive to signals at a range of 30-40Hz
- Steroid eluding leads
- T wave is sensed; RV>VV…solution: increase RP SECOND R waVE IS NOT SENSED; RV<VV..solution: decrease RP
- atrial pacing artifact inappropriately sensed by the ventricular-sensing amplifier could result in ventricular pacing inhibition, referred to as cross-talk. To prevent cross-talk, atrial pacing also initiates a PAVB to avoid ventricular oversensing of atrial paced events The blanking period is traditionally of short duration because it is important for the ventricular-sensing circuit to be returned to the “alert” state relatively early the trailing edge of the atrial pacing artifact occurring after the PAVB can occasionally be sensed on the ventricular channel. In a pacemaker-dependent patient, inhibition of ventricular output by cross-talk results in ventricular asystole. To prevent such a catastrophic outcome, DDD pacing mode has a safety mechanism called the “ventricular triggering period” or the “cross-talk sensing window”. If activity is sensed on the ventricular-sensing amplifier during the AVI immediately after the PAVB, it is assumed that cross-talk cannot be differentiated from intrinsic ventricular activity. Sensing during this window will result in a triggered rather than an inhibited output. Safety pacing is designed to prevent ventricular asystole if cross-talk were to occur in a pacemaker-dependent patient
- 20-60ms
- (A) Paradoxical mechanism of pacemakermediated tachycardia (PMT) initiation by an inappropriately long post-ventricular atrial refractory period (PVARP). Early premature ventricular contraction (PVC) re-initiates PVARP and VA interval (VAI). A sinus P wave falls within the PVARP (without resetting VAI), followed by ineffective atrial pacing (AP) due to atrial refractoriness. Ventricular pacing (VP) occurs after the atrioventricular interval (AVI) is completed, causing a retrograde P wave (rP) due to unopposed ventriculoatrial (VA) conduction (dashed red arrows) with subsequent initiation of PMT. (B) Repetitive non–re-entrant VA synchrony. To avoid PMT, a long PVARP is programmed. A rP after an early PVC falls within the PVARP, followed by an ineffective AP (after the VAI is completed), initiating an AVI. VP occurs after completion of the AVI, and finds unopposed VA conduction (retrograde P wave), falling again within the PVARP, causing repetitive ineffective AP and VP with VA conduction.
- 1000-150+200 = 1050 800 850
- Atrial based = compensatory pause Atrial based = VPC in AVI wont reset..as AA is fixed
- Atrial indiacted rate Sensor indicated rate
- Dash dot line = intrinsic rate (P synchronous pacing) Dot line = sensor rate Heavy line =paced ventricuar rate P tracking to AV pacing thru a period of wenchebaching Period of wenchebaching is shortened due to ‘sensor driven rate smoothing’
- 6% == 36 ms
- MDT ONLY IN PAC OR PVC NOT OPERATIONAL IN SUSTAINED TACHYARRYTHMIAS Not operational if hysteresis on or mode switch on For that ventricular rate regulatisation is there…but that is only operational during MODE switch
- 60000/172=52 bpm As no fall back enabled
- Fallback for 15 sec
- Once the atrial rate exceeds the mode switch rate (also referred as the fallback onset rate), pacing mode will switch from DDD to a programmable non-tracking pacing mode (DDI, VDI, VVI). The fallback (FB) feature prevents sudden drop on ventricular pacing (VP) from the MTR to the lower rate limit (LRL). When fallback time is enabled, the device will slowly decrease the VP rate from the MTR to the LRL in the timeframe instructed. Once atrial rate decreases below the mode switch rate, the device will return back to DDD pacing mode
- Sleep rate = 30 mins after bedtime Night rate = after 10 pm Rest rate = every 7days
- For one minute
- Trial mode switch rate