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