Understanding pacemakers
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Transcript of Understanding pacemakers
UnderstandingPermanent Pacemakers
Dr. Dibbendhu Khanra21.9.16
A Brief History of Pacemakers
Today’s agenda
Includes • Pacemaker components• Basics physics/ physiology• Timing cycles & algorithms
Excludes • Indications• CRT• ICD
BASIC TROUBLESHOOTING
PPMHardwares
Pulse GeneratorSINGLE CHAMBER PACEMAKER
Block Diagram of Basic Components
InputAmplifier
OutputCircuits
NoiseDetector
Run-awayProtection
Control Unit
CPU
Analog.ueCircuits
StorageROM / RAM
Transmitting and Receivinglogic
Rate ControlCircuit
Rate ResponseSensor Telemetry Coil
ERIDetection
Power Source
DEVICE ENCLOSURE
HEADER BLOCK
Set screws
LiI <100microALi Ag Va in ICD in Amp
3V battery
256 KB to 1MB ROM1-16 MB RAM
20-40 Hz
Timing Cycle by Crystal
Magnet mode
Magnet close reed switch
(VOO)
Pacemaker leads
ELECTRODESSteroid eluding
Low polarity (Titanium Nitride)Elgiloy
CONDUCTORShighly conductive Ag core
MP35N for mechanical stress
INSULATORSPolyurethane> si rubber
CONNECTOR PINIS/ stainless steel
lead anchorage sleeve of radio-dense MDX
PASSIVE/ TINES
ACTIVE/ SCREWS(mannitol/ polyethelene)
FIXATION MECHANSIM
Basic physiology
What we see..
Intracardiac electrogram
Capture
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
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
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
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)
Current of injury
• Partially confirm acute tissue-electrode contact• (intracardiac EGM)
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
Unipolar Sensing
30-50 cmsSensing:- Less affected by change of
ventricular activation- Easily influenced by
electric interferences Pacing - larger spike _
Bipolar Sensing
3-5 cmSensing:- Easily affected by change
of ventricular activation- Less influenced by electric
interferences Pacing - smaller spike
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
Polarization
• Proportional to amplitude & duration of pulse• Blanking period• Cross Talk
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.
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
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)
Signals vs noise
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
NOISE REVERSION RESPONSE
Lead Maturation Process
• Fibrotic “capsule” develops around the electrode following lead implantation
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 daysNormalizes in 6-8 weeksLess in SEL
Active fixation:Attaches to myocardiumP/R decreases within minsNormalises in 20-30 mins
Sensing
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 PacingFixed-Rate Pacing
Daily Activities
Sensors
• 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
Pacemaker Codes
Timing cycle
So many parameters..
Understanding language
The Alphabets..
A V
P R
Making Words..
PR PV PVAV ARTOTAL
INHIBITIONP
SYNCHRONOUSPACING
AVSEQUENTIAL
PACING T=TRACKING
The grammar...
AV+VA = LRILRL= 60000/ LRI
TARP = AV+PVARPMTR = URI
URL= 60000/ URI = 60000/ TARP
Making sense..
BP RPARP RRP
NO DETECTIONNO RESET
DETECTIONBUT NO RESET
Perfect Senses
A - ABP : V - PVABP PVARP
V - VRP : A - VBP CSW alert period
Modes and hysteresis
VVI
RESET
Ventricular oversensing Ventricular undersensing
VVI
RV<VVRV>VV
solution: increase RP solution: decrease RP
VVI VENTRICULAR RATE HYSTERESIS
Base rate 60 (1000 ms)Hysteris rate 50 (1200 ms)
VV<RV
VOO
Magnet modeMagnet close reed switch
AAI
AAI
Atrial Oversensing Prevent After polarization
Prevent far-field sensing
Base rate 70 (857 ms)ARP = 250 ms
R wave oversensingSolution: ARP increased to 400 ms
AAI ATRIAL RATE HYSTERESIS
Base rate 60 (1000 ms)Hysteris rate 50 (1200 ms)
AA<PA
DDD vs DDI
Tracking
DVI VS VDD
Tracking
Cross talk &
safety pacing
Ventricular channel
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
Far field R wave oversensing
Ventricular channel
Safety Pacing
Due To Atrial Undersensing Due To Atrial oversensing
Unsesed P Uncaptured
A
R within CSW
AV Delay
Differential AVI
SAV<PAV
Differential AVI
SAV 160 msPAV 200 ms
Dynamic AVI
AVI = ABP +atrial sensing window
TARP shortened to enhance atrial tracking at first rate
AV hysteresis
Negative
PVARP & PMT
PVARP
PVC
Retrograde P wave is sensed but not tracked in PVARP
DYNAMIC PVARP
PVARP increased to maintain adequate sensing window
PVARP decreased to minimum PVABP
Pacemaker Mediated Tachycardia
Pacemaker Mediated Tachycardia
P wave outside PVARP is trackedSolution: increase PVARP
Extended PVARP
T oversensePVC
P not sensed
Paradoxical PMT
repetitive non-reentrant VA synchrony (RNRVAS)
PMT prevention algorithm
Atrial sensed ventricular pacing at MTR = PMT vs atrial arrythmia
SOLUTIONStop VPOr extend PVARP
PMT stopsAtrial arrythmia continues
PMT terminationStable Retrograde VAI
Changing AVIDecreasing MTR
Withhold VPFollowed by atrial pacing at 330 ms
Lack of P wave tracking
First degree AV blockP wave falling within PVARP
P wave outside PVARP1:1 conduction
Base timing
Base timing
800 ms 850 ms
AEI prolongation
AEI fixed
In Bradycardia, atrial based
pacing violates the LRL
Base timing
PVC – R interval
Lower Rate Behaviour in rate responsive systems
Intact AV ocnduction
ARI = 120 msIn tachycardia,
ventricular based pacing
violates the URL
MODE SWITCH
AV nodal conduction absent
Vs
Brady = ventr basedTachy = atrial based
Rate responsiveness&
upper rate behaviour
Rate responsiveness
Tracked Not Tracked
Rate responsiveness
AV sequential pacing
P synchronouspacing
Heart rate faster than AIR AVI shortens
PVARP fixed
SIR is LRL during exercise
MSR is MTR during exercise
UPPER RATE BEHAVIOUR
AVI 125 msPVARP 225 msTARP 350 msMTR 350 ms (170 bpm)URI 400 ms (150 bpm)Wenchebach interval URI-TARP = 50 ms
PP>TARPRATE < MTR(157)
PP>TARPRATE > MTR(330)
wenchebach
2:1
Wenchebaching
Rate responsiveness
Rate elevation response
Rate smoothing
Smoothing9% up to 6% down
RR: 800-72=728 ms 800+48=848 msAA: 728-150 = 578 ms 848 -150 = 698 ms
MTR 100 bpm6% = 36 msb=a+36 msa b
Rate modulation acting as rate smoothening
480 ms (125bpm)
810 ms (74bpm)
SIR545 ms
(110 bpm)URL
480 ms (125bpm)
Difference330 ms
Difference65 ms
MAXIMUM LENGHTHEING = MTR - SIR
Ventricular rate stabilization
1 = VPC2 = AV sequential pacing at the previous V–V interval plus interval increment3 = gradual prolongation of AV sequential pacingPrevents pause dependent VT
Atrial arrythmia
MTR = 500 ms(120 bpm)
LRL =1200 ms(50 bpm)
Fall back
Fall back mode
MTRMode switch
DDD DDI
slowly decrease the VP rate from the MTR to the LRL
Intrinsic Rate Algorithm
RATE HYSTERESIS
SCAN HYSTERESISBTK
SINUS PREFERENCEMDT
SLEEP RATEMDT
NIGHT RATEBTK
REST RATESJM
Cardioinhibitory neurogenic syncope
response
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.
Rate Drop response
Sudden Bradycardia Response
Atrial Arrhythmia algorithms
Blanked Flutter Search, MDT
2:1 lock in protection algorithm, BTK
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
Non Competitive Atrial Pacing
MDT
As
ATRIAL ARRYTHMIA
RESPONSE
AF SUPRESSION ALGORITHM
AF suppression algorithm
Ventricular response pacing
Minimizing RV pacing
Intrinsic AV conduction
AV hysteresis
VentricularIntrinsic
preference
Programmable delta
PAVI = 200+140
Intrinsic AV conduction cont..
Managed Ventricular
Pacing
RhythmIQ
SafeR
MRI compatible PPM
MRI safety
Two coils
Less heating
Hall sense&
Less ferromagnetism
TROUBLESHOOTING
Solution: increase VRP/
increase PVARP
Know your car
THANK YOU