BASICS OF PACEMAKER

BASICS OF PACEMAKER

DN

HISTORY• 1958 – Senning and Elmqvist

– Asynchronous (VVI) pacemaker implanted by thoracotomy and functioned for 3 hours

– Arne Larsson• First pacemaker patient• Used 23 pulse generators and 5 electrode systems• Died 2001 at age 86 of cancer

• 1960 – First atrial triggered pacemaker• 1964 – First on demand pacemaker (DVI)• 1977 – First atrial and ventricular demand pacing (DDD)• 1981 – Rate responsive pacing by QT interval, respiration,

and movement• 1994 – Cardiac resynchronization pacing

What is a Pacemaker?What is a Pacemaker?

A Pacemaker System consists of a Pulse Generator plus Lead (s)

S

• Pulse generator- power source or battery

• Leads

• Cathode (negative electrode)

• Anode (positive electrode)

• Body tissue

IPG

Lead

Anode

Cathode

Implantable Pacemaker Systems Contain the Following Components:Implantable Pacemaker Systems Contain the Following Components:

• Contains a battery that provides the energy for sending electrical impulses to the heart

• Houses the circuitry that controls pacemaker operations

Circuitry

Battery

The Pulse GeneratorThe Pulse Generator

Battery

Connector

Hybrid

Telemetry antenna

Output capacitors

Reed (Magnet) switch

Clock

Defibrillation protection

Atrial connector

Ventricular connector

Resistors

Anatomy of a PacemakerAnatomy of a Pacemaker

General Characteristics of Pacemaker Batteries

• Hermeticity, as defined by the pacing industry, is an extremely low rate of helium gas leakage from the sealed pacemaker container

• low rate of self-discharge

• lithium iodine -a long shelf life and high energy density

• DDD drains a battery more rapidly

• Longevity in single chamber pacemaker is 7 to 12 years.

• For dual chamber longevity is 6 to 10 years.

• Most pacemakers generate 2.8 v in the beginning of life which becomes 2.1 to 2.4 v towards end of life.

Power source

9

• Deliver electrical impulses from the pulse generator to the heart

• Sense cardiac depolarisationLead

LeadsLeads

Lead Characterization

• Position within the heart– Endocardial or transvenous leads– Epicardial leads

• Fixation mechanism– Active/Screw-in– Passive/Tined

• Shape– Straight– J-shaped used in the atrium

• Polarity– Unipolar– Bipolar

• Insulator– Silicone– Polyurethane

• Conductor • Connector Pin• Insulation• Electrode

Lead components

Transvenous Leads - Fixation Mechanisms

• Passive fixation

– The tines become lodged in the trabeculae

• Active Fixation

– The helix (or screw) extends into the endocardial tissue

– Allows for lead positioning anywhere in the heart’s chamber

Myocardial and Epicardial Leads

• Leads applied directly to the heart– Fixation mechanisms

include:• Epicardial stab-in• Myocardial screw-in• Suture-on

Active Fixation Passive Fixation

Advantages Easy fixationEasy to repositionLower rate of dislodgementRemovability

Less expensive & simpleMinimal trauma to patientLower thresholds

Disadvantages More expensive>Complicated implantation

Higher rate of dislodgement (>a/c)Difficult to remove chronic lead

• Cathode:-An electrode that is in contact with the heart

• Negatively charged

• Anode:-receives the electrical impulse after depolarization of cardiac tissue

• Positively charged when electrical current is flowing Cathode

Anode

• Flows through the tip electrode (cathode)

• Stimulates the heart

• Returns through body fluid and tissue to the PG (anode)

A Unipolar Pacing System

Contains a lead with an electrode in the heart

Cathode

Anode

-

+

Anode

• Flows through the tip electrode located at the end of the lead wire

• Stimulates the heart

• Returns to the ring electrode above the lead tip

A Bipolar Pacing System

Contains a lead with 2 electrodes in the heart

Cathode

Unipolar leads

• Unipolar leads have a smaller diameter than bipolar leads

• Unipolar leads exhibit larger pacing artifacts on the surface ECG

• One electrode on the tip & one conductor coil

• Conductor coil may consist of multiple strands - (multifilar leads)

Bipolar leads

• Bipolar leads are less susceptible to oversensing noncardiac signals (myopotentials and

EMI)

Coaxial Lead Design

• Circuit is tip electrode to ring electrode

• Two conductor coils (one inside the other)

• Inner layer of insulation

• Bipolar leads are typically thicker than unipolar leads

Unipolar Bipolar

Advantages Smaller diameterEasier to implantLarge spike

No pocket stimulationLess susceptible to EMIProgramming flexibility

Disadvantages

Pocket stimulationFar-field oversensingNo programming flexibility

Larger diameterStiffer lead bodySmall spikeHigher impedance Voltage threshold is 30% higher

Electrodes• Leads have 1/> electrically active surfaces

referred to as the electrodes

• Deliver an electrical stimulus, detect intrinsic cardiac electrical activity, or both

• Electrode performance can be affected by– Materials– Polarization– Impedance– Pacing thresholds– Steroids

Electrode Materials• The ideal material for an electrode

– Porous (allows tissue ingrowth)– Should not corrode or degrade– Small in size but have large surface area– Common materials

• Platinum and alloys (titanium-coated platinum iridium)• Vitreous carbon (pyrolytic carbon)• Stainless steel alloys such as Elgiloy

Voltage• Voltage is the force that causes electrons to

move through a circuit• In a pacing system, voltage is:

– Measured in volts– Represented by the letter “V”– Provided by the pacemaker battery– Referred to as amplitude

Current

• The flow of electrons in a completed circuit

• In a pacing system, current is:– Measured in mA (milliamps)– Represented by the letter “I”– Determined by the amount of electrons that move

through a circuit

• Constant-Voltage and Constant-Current Pacing

• Most permanent pacemakers are constant-voltage pacemakers

• Voltage and Current Threshold

• Voltage threshold is the most commonly used measurement of pacing threshold

Pacing Thresholds

• Defined as the minimum amount of electrical energy required to consistently cause a cardiac depolarization

• “Consistently” refers to at least ‘5’ consecutive beats

• Low thresholds require less battery energy

Capture Non-Capture

The Strength-Duration Curve

• The strength-duration curve illustrates the relationship of amplitude and pulse width– Values on or above

the curve will result in capture Duration

Pulse Width (ms)

.50

1.0

1.5

2.0

.25S

tim

ula

tio

n T

hre

sho

ld (

Vo

lts)

0.5 1.0 1.5

Capture

• Rheobase- (the lowest point on the curve) by definition is the lowest voltage that results in myocardial depolarization at infinitely long pulse duration

• Chronaxie(pulse duration time ) by definition, the chronaxie is the threshold pulse duration at twice the rheobase voltage

Lessons from SDC

• The ideal pulse duration should be greater than the chronaxie time

• Cannot overcome high threshold exit block by increasing the pulse duration, If the voltage output remains less than the rheobase

• Energy (μJ) = Voltage (V) × Current (mA) × Pulse Duration (PD in ms).

• Charge (μC) = Current (mA) × Pulse Duration (ms).

• At very low pulse width thresholds, the charge is low, but the energy requirements are high because of elevated current and voltage stimulation thresholds.

• At pulse durations of 0.4–0.6 ms, all threshold parameters - ideal

• At high pulse durations, the voltage and current requirements may be low, but the energy and charge values are unacceptable

-Safety margins -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.

–Daily fluctuations in threshold that can occur due to eating, sleeping, exercise, or other factors

- a/c pacing system - higher safety margin, due to the lead maturation process- occur within the first 6-8 weeks following implant.

Changes in stimulation threshold (voltage or current) following implantationof a standard nonsteroid-eluting electrode

Impedance

• The opposition to current flow

• In a pacing system, impedance is– Measured in ohms– Represented by the letter “R” ( W for numerical values)

• The measurement of the sum of all resistance to the flow of current

Resistance is a term used to refer to simple electric circuits without capacitors and with constant voltage and current

Impedance is a term used to describe more complex circuits with capacitors and with varying voltage and current

Impedance

• Pacing lead impedance typically stated in broad ranges, i.e. 300 to 1500 Ω

• Factors that can influence impedance

– Resistance of the conductor coils– Tissue between anode and cathode– The electrode/myocardial interface– Size of the electrode’s surface area– Size and shape of the tip electrode

Ohm’s Law is a Fundamental Principle of Pacing That:

V

I RV = I X RI = V / RR = V / I

• Describes the relationship between voltage, current, and resistance

x

Impedance and Electrodes

• Large electrode tip– Threshold ↑– Impedance ↓– Polarization ↓

• Small electrode tip– Threshold ↓– Impedance ↑– Polarization ↑

Polarization• After an output pulse, positively charged particles gather near

the electrode.• The amount of positive charge is

– Directly proportional to pulse duration– Inversely proportional to the functional electrode size

(i.e. smaller electrodes offer higher polarization)

Polarization effect can represent 30–40% of the total pacing impedance As high as 70% for smooth surface, small surface area electrodes

Within the electrode, current flow is due to movement of electrons (e−). At the electrode–tissue interface, the current flow becomes ionic & (-) vely charged ions (Cl−, OH−) flow into the tissues toward the anode leaving behind oppositely charged particles attracted by the emerging electrons.

It is this capacitance effect at the electrode tissue interface, that is the basis of polarization

Lead Maturation Process• Fibrotic “capsule” develops around the electrode following lead

implantation

• 3 phases 1. A/c phase, where thresholds immediately following implant are

low 2. Peaking phase- thresholds rise and reach their highest

point(1wk) ,followed by a ↓ in the threshold over the next 6 to 8 wks as the tissue reaction subsides

3. C/c phase- thresholds at a level higher than that at implantation but less than the peak threshold

• Trauma to cells surrounding the electrode→ edema and subsequent development of a fibrotic capsule.

• Inexcitable capsule ↓ the current at the electrode interface, requiring more energy to capture the heart.

Lead Maturation Process• Effect of Steroid on Stimulation Thresholds

Pulse Width = 0.5 msec

03 6

Implant Time (Weeks)

Textured Metal Electrode

Smooth Metal Electrode

1

2

3

4

5

Steroid-Eluting Electrode

0 1 2 4 5 7 8 9 10 11 12

Vol

ts

Sensing

• Sensing is the ability of the pacemaker to detect an intrinsic depolarization

– Pacemakers sense cardiac depolarization by measuring changes in electrical potential of myocardial cells between the anode and cathode

An Electrogram (EGM) is the Recording of Cardiac Waveforms Taken From Within the Heart

• Intrinsic deflection on an EGM occurs when a depolarization wave passes directly under the electrodes

• Two characteristics of the EGM are: – Signal amplitude(mv)– Slew rate(v/sec)

Intrinsic R wave Amplitude

• Typical intrinsic R wave amplitude measured from pacing leads in the Right Ventricle are more than 5 mV in amplitude

Ampl

itude

Intrinsic R wave in EGM

The Intrinsic R wave amplitude is usually much greater than the T wave amplitude

Slew Rate of the EGM Signal Measures the Change in Voltage with Respect to the Change in Time

• The longer the signal takes to move from peak to peak:

– The lower the slew rate– The flatter the signal

• Higher slew rates translate to greater sensing

– Measured in volts per second

Vo

lta

ge

Time

Slope

Slew rate=Change in voltage

Time duration ofvoltage change

Slew rate measurements at implant should exceed .5 volts per second for P waves; .75 volts per second for R wave measurements

Factors That May Affect Sensing Are:• Lead polarity (unipolar vs. bipolar)• Lead integrity

– Insulation break– Wire fracture

• EMI – Electromagnetic Interference

Undersensing . . .

• Pacemaker does not “see” the intrinsic beat, and therefore does not respond appropriately

Intrinsic beat not sensed

Scheduled pace delivered

VVI / 60

Oversensing

• An electrical signal other than the intended P or R wave is detected

Marker channel shows intrinsic

activity...

...though no activity is present

VVI / 60

Signal Amplitude / Slew Rate

Amplitude Range Slew Rate(mV) (v/sec)

Acute Atrial EGM 1.5 - 4.0 0.6 - 1.7

Chronic Atrial EGM 1.0 - 3.0 0.5 - 1.5

Acute Ventricular EGM 7 - 15 0.8 - 2.0

Chronic Ventricular EGM 5 - 12 0.6 - 1.5

Signal

Pacemaker Implantation

NASPE/ BPEG Generic (NBG) Pacemaker Code

IChamber

Paced

IIChamberSensed

IIIResponseto Sensing

IVProgrammableFunctions/Rate

Modulation

VAntitachy

Function(s)

V: Ventricle V: Ventricle T: Triggered P: Simple programmable

P: Pace

A: Atrium A: Atrium I: InhibitedM: Multi- programmable

S: Shock

D: Dual (A+V) D: Dual (A+V) D: Dual (T+I) C: Communicating D: Dual (P+S)

O: None O: None O: None R: Rate modulating O: None

S: Single (A or V)

S: Single (A or V)

O: None

Pacemaker Timing

• Pacing Cycle : Time between two consecutive events in the ventricles (ventricular only pacing) or the atria (dual chamber pacing)

• Timing Interval : Any portion of the Pacing Cycle that is significant to pacemaker operation e.g. AV Interval, Ventricular Refractory period

Single-Chamber Timing

Single Chamber Timing Terminology• Lower rate• Refractory period• Blanking period• Upper rate

Lower Rate Interval

Lower Rate Interval

VP VP VVI / 60

• Defines the lowest rate the pacemaker will pace

Refractory Period

Lower Rate Interval

VP VP VVI / 60

• Interval initiated by a paced or sensed event• Designed to prevent inhibition by cardiac or non-cardiac

events• Events sensed in the refractory period do not affect the

Lower Rate Interval but start their own Refractory Periods

Refractory Period

Blanking Period

Lower Rate Interval

VP VP VVI / 60

• The first portion of the refractory period• Pacemaker is “blind” to any activity• Designed to prevent oversensing of pacing

stimulus/depolarisation

Blanking PeriodRefractory Period

Physiologic Classification of Sensors- rate adaptive

Primary • Physiologic factors that modulate sinus function

Catecholamine level, Autonomic nervous system activity Secondary • Physiologic parameters that are the consequence of exercise QT, respiratory rate

Minute ventilation,temperature pH, stroke volume, Preejection interval, SVO2 Peak endocardial acceleration

Tertiary • External changes that result from exercise Vibration

Acceleration

Upper Sensor Rate Interval

Lower Rate Interval

VP VP VVIR / 60 / 120

• Defines the shortest interval (highest rate) the pacemaker can pace as dictated by the sensor (AAIR, VVIR modes)

• Limit at which sensor-driven pacing can occur

Blanking PeriodRefractory Period

Upper Sensor Rate Interval

VP VP VS VP

Lower Rate Interval-60 ppm

Hysteresis• Allows the rate to fall below the programmed

lower rate following an intrinsic beat• lower rate limit is initiated by a paced event, while

the hysteresis rate is initiated by a non-refractory sensed event.

Hysteresis Rate-50 ppm

Noise Reversion

VPVPSRSR SR SR

Noise Sensed

Lower Rate Interval

VVI/60

• Continuous refractory sensing will cause pacing at the lower rate

Modes-SINGLE CHAMBER

AOO & VOO-asynchronous modes

• By application of magnet

• Useful in diagnosing pacemaker dysfunction

• During surgery to prevent interference from electrocautery

VOO Mode

Blanking Period

VP VP

Lower Rate Interval

VOO / 60

• Asynchronous pacing delivers output regardless of intrinsic activity

V

VP VPVP

VOO TIMING

VP VP

VVI Mode

Lower Rate Interval

VP VSBlanking/Refractory

VP

VVI / 60

• Pacing inhibited with intrinsic activity

V

VP VPVP VPVS

VVI TIMING

VVIR

VP VP

Refractory/Blanking

Lower Rate

Upper Rate Interval(Maximum Sensor Rate)

VVIR / 60/120Rate Responsive Pacing at the Upper Sensor Rate

• Pacing at the sensor-indicated rate

AAI• Useful for SSS with N- AV conduction• Should be capable of 1:1 AV to rates 120-140 b/m • Atrial tachyarrhythmias should not be present• Atria should not be “silent”• If no A activity, atria paced at LOWER RATE limit (LR)• If A activity occurs before LR,- “resetting”• Caution- far-field sensing of V activity

AAIR

Lower Rate Interval

AP APRefractory/Blanking

Upper Rate Interval(maximum sensor rate)

AAIR / 60 / 120(No Activity)

• Atrial-based pacing allows the normal A-V activation sequence to occur

Single-Chamber Triggered-Mode

• Output pulse every time a native event sensed• ↑current drain• Deforms native signal• Prevent inappropriate inhibition from

oversensing when pt does not have a stable native escape rhythm

Benefits of Dual Chamber Pacing

• Provides AV synchrony

• Lower incidence of atrial fibrillation

• Lower risk of systemic embolism and stroke

• Lower incidence of new congestive heart failure

• Lower mortality and higher survival rates

Dual Chamber Timing Parameters

• Lower rate• AV and VA intervals• Upper rate intervals• Refractory periods• Blanking periods

Lower Rate Interval

APVP

APVP

Lower Rate

• The lowest rate the pacemaker will pace the atrium in the absence of intrinsic atrial events

DDD 60 / 120

AV Delay

• The AV delay in the pacemaker timing cycle is designed to simulate that natural pause between the atrial and ventricular events by mimicking the PR interval

• Benefits of a properly timed AV delay– Allows optimal time for ventricular filling, which

may contribute to improved cardiac output– Allows sufficient time for proper mitral valve

closure- minimize MR

APVP

ASVP

PAV SAV

200 ms 170 ms

Lower Rate Interval

AV Intervals

• Initiated by a paced or non-refractory sensed atrial event

– Separately programmable AV intervals – SAV /PAV• Two things can happen with the AV delay

– AV delay times out (and ventricular pacing spike is delivered)– AV delay is interrupted by a sensed ventricular event (and ventricular pacing spike is

inhibited)

DDD 60 / 120

Paced AV Delay

• The time period between the paced atrial event and the next paced ventricular event

• The pacemaker spike initiates the paced AV delay timing cycle

• Programmable value

Sensed AV Delay

• The time period between the sensed atrial event and the next paced ventricular event

• The pacemaker has to sense the atrial event before the timing cycle is initiated—there is usually a slight time lag

• Program the sensed AV delay to a value slightly shorter than the paced AV delay (~ 25 ms)

Atrial Escape Interval (V-A Interval)

Lower rate interval- AV interval=V-A interval

The V-A interval is the longest period that may elapse after a ventricular event before the atrium must be paced in the absence of atrial activity.

The V-A interval is also commonly referred to as the atrial escape interval

Lower Rate Interval

APVP

APVP

AV Interval VA Interval

Atrial Escape Interval (V-A Interval)Atrial Escape Interval (V-A Interval)

• The interval initiated by a paced or sensed ventricular event to the next atrial event

DDD 60 / 120PAV 200 ms; V-A 800 ms

200 ms 800 ms

DDDR 60 / 120A-A = 500 ms

APVP

APVP

Upper Activity Rate Limit

Lower Rate Limit

V-APAV V-APAV

Upper Activity (Sensor) Rate

• In rate responsive modes, the Upper Activity Rate provides the limit for sensor-indicated pacing

ASVP

ASVP

DDDR 60 / 100 (upper tracking rate) Sinus rate: 100 bpm

Lower Rate Interval

Upper Tracking Rate Limit

Upper Tracking Rate

SAV SAVVA VA

• The maximum rate the ventricle can be paced in response to sensed atrial events

• Prevents rapid ventricular pacing rates in response to rapid atrial rates

Post Ventricular Atrial Refractory Period (PVARP)

Refractory Periods• VRP and PVARP are initiated by sensed or paced

ventricular events– The VRP is intended to prevent self-inhibition such as

sensing of T-waves – The PVARP is intended primarily to prevent sensing of

retrograde P waves

AP

VPVentricular Refractory Period (VRP)

A-V Interval(Atrial Refractory)

Post-Ventricular Atrial Refractory Period

• PVARP is initiated by a ventricular event(sensed/paced), but it makes the atrial channel refractory

• PVARP is programmable (typical settings around 250-275 ms)

• Benefits of PVARP– Prevents atrial channel from responding to

premature atrial contractions, retrograde P-waves, and far-field ventricular signals

– Can be programmed to help minimize risk of pacemaker-mediated tachycardias

PVARP and PVAB

• The PVAB is the post-ventricular atrial blanking period during which time no signals are “seen” by the pacemaker’s atrial channel

• It is followed by the PVARP, during which time the pacemaker might “see” and even count atrial events but will not respond to them

• PVAB-independently programmable– Typical value around 100 ms

PVAB and PVARP

Blanking Periods

• First portion of the refractory period-sensing is disabled

AP

VP

AP

Post Ventricular Atrial Blanking (PVAB)

Post Atrial Ventricular Blanking

Ventricular Blanking (Nonprogrammable)

Atrial Blanking (Nonprogrammable)

Total Atrial Refractory Period (TARP)• TARP is the timing cycle on the atrial channel during which the

pacemaker will not respond to incoming signals• TARP consists of the AV delay plus the PVARP

TARP = AV delay + PVARP

• TARP is not programmable directly -can program the AV delay and PVARP and thus indirectly control TARP

• TARP is important for controlling upper-rate behavior of the pacemaker

PVARP

Upper Tracking Rate

Lower Rate Interval

No SAV started for events sensed in the TARP

AS AS

VPVP

SAV = 200 msPVARP = 300 ms

Thus TARP = 500 ms (120 ppm)

DDDLR = 60 ppm (1000 ms)

UTR = 100 bpm (600 ms) SAV

TARP

PVARP

Total Atrial Refractory Period (TARP)• Sum of the AV Interval and PVARP• defines the highest rate that the pacemaker will

track atrial events before 2:1 block occurs

SAV

Wenckebach

• Occurs when the intrinsic atrial rate lies between the UTR and the TARP rate

• Results in gradual prolonging of the AV interval until one atrial intrinsic event occurs during the TARP and is not tracked

PVARP

Wenckebach Operation

Upper Tracking Rate

Lower Rate Interval

AS AS AR APVPVP VP

TARPSAV PAV PVARP SAV PVARP

P Wave Blocked (unsensed or unused)

• Prolongs the SAV until upper rate limit expires– Produces gradual change in tracking rate ratio

TARP TARP

Wenckebach Operation

DDD / 60 / 120 / 310

Fixed Block or 2:1 Block

• Occurs whenever the intrinsic atrial rate exceeds the TARP rate

• Every other atrial event falls in the TARP when the atrial rate exceeds the TARP rate

• Results in block of atrial intrinsic events in fixed ratios

• Every other P wave falls into refractory and does not restart the timing interval

Upper Tracking Limit

Lower Rate Interval

P Wave Blocked

AS AS

VPVPARAR

Sinus rate = 133 bpm (450 ms)PVARP = 300 ms SAV = 200 ms

TARP=500 ms

AV PVARP AV PVARP

TARP TARP

2:1 Block

2:1 Block

DDD / 60 / 120 / 310

Summary-upper rate behaviours

– 1:1 tracking occurs whenever the patient’s atrial rate is below the upper tracking rate limit

– Wenckebach will occur when the atrial rate exceeds the upper tracking rate limit

– Atrial rates greater than TARP cause 2:1 block

Ventricular Safety Pacing• Crosstalk is the sensing of a pacing stimulus delivered in the opposite

chamber, which results in undesirable pacemaker response, e.g., false inhibition

• Following an atrial paced event, a ventricular safety pace interval is initiated

– If a ventricular sense occurs during the safety pace window, a pacing pulse is delivered at an abbreviated interval (110 ms)

Post Atrial Ventricular Blanking

PAV Interval

Ventricular Safety Pace Window

Ventricular Safety Pace

DDD 60 / 120

VDD Mode• Atrial Synchronous pacing or Atrial Tracking Mode• A sensed intrinsic atrial event starts an SAV• The Lower Rate Interval is measured between Vs to Vp or Vp to Vp• If no atrial event occurs at the end of the Lower Rate Interval a Ventricular

pace occurs• Paces in the VVI mode in the absence of atrial sensing• AV block with intact sinus node function (esp useful in congenital AV

block)

VDD

Upper Tracking Limit

VDDLR = 60 ppmUTR = 120 ppmSpontaneous A activity = 700 ms (85 ppm)

Lower Rate Interval

AS AS

VPVP VP

• Provides atrial synchronous pacing – System utilizes a single lead

DDD Mode• Chamber paced: Atrium & ventricle

• Chamber sensed: Atrium & ventricle

• Response to sensing: Triggered & inhibited

– An atrial sense:• Inhibits the next scheduled atrial pace • Re-starts the lower rate timer• Triggers an AV interval (called a Sensed AV Interval or SAV)

– An atrial pace:• Re-starts the lower rate timer• Triggers an AV delay timer (the Paced AV or PAV)

– A ventricular sense:• Inhibits the next scheduled ventricular pace

Rate (sinus driven) = 70 bpm / 857 msSpontaneous conduction at 150 msA-A = 857 ms

ASVS

ASVS

V-AAV AV V-A

• Atrial Sense, Ventricular Sense (AS/VS)

Four “Faces” of Dual Chamber Pacing

Rate = 60 bpm / 1000 msA-A = 1000 ms

APVP

APVP

V-AAV V-AAV

• Atrial Pace, Ventricular Pace (AP/VP)

Four “Faces” of Dual Chamber Pacing

Rate = 60 ppm / 1000 msA-A = 1000 ms

AP VS

AP VS

V-AAV V-AAV

• Atrial Pace, Ventricular Sense (AP/VS)

Four “Faces” of Dual Chamber Pacing

ASVP

ASVP

Rate (sinus driven) = 70 bpm / 857 msA-A = 857 ms

• Atrial Sense, Ventricular Pace (AS/ VP)

V-AAV AV V-A

Four “Faces” of Dual Chamber Pacing

Mode Selection

DDIR DDDR

N

VVIVVIR

Are they chronic?

Y

Y N

DDD, VDDDDDR DDDR

Y N

Is AV conduction intact?

Is SA node functionpresently adequate?

Symptomaticbradycardia

Are atrial tachyarrhythmias

present?

Is SA node functionpresently adequate?

Is AV conduction intact?

Y

Y N

AAIRDDDR

DDDR, DDIR

N N(SSS)

N

Optimal Pacing Mode (BPEG)

• Sinus Node Disease - AAI (R)• AVB - DDD• SND + AVB - DDDR + DDIR• Chronic AF + AVB - VVI

Thank u

Mode Selection Decision TreeDDIR with SV PVARP

DDDR withMS

N

VVIVVIR

Are they chronic?

Y

Y N

DDD, VDDDDDR DDDR

Y N

Is AV conduction intact?

Is SA node functionpresently adequate?

Symptomaticbradycardia

Are atrial tachyarrhythmias

present?

Is SA node functionpresently adequate?

Is AV conduction intact?

Y

Y N

AAIRDDDR

DDD, DDIwith RDR

N N(SSS) (CSS,VVS)

N

Stuart Allen 06

Pacing ModesPacing Modes

Output circuit

VVI

AMP

Ventricular Demand

Programmed lower rate 50 mm/s

VVI

Stuart Allen 06

Output circuit

VVIR

AMP

Sensor

Ventricular DemandPacing Modesp

Programmed lower rate 50 mm/s

Sensor indicatedrate

Stuart Allen 06

Output circuit

AAI

AMP

Atrial Demand

Programmed lower rate 50 mm/s

AAI

Stuart Allen 06

Pacing Modes - Summary

Output circuit

VAT

AMP

Atrial Synchronised

Output circuit

AAI

AMP

Atrial Demand

Output circuit

DVI

AMP

A-V SequentialOutput circuit

Output circuit

VDD

AMP

Atrial synchronisedVentricular Inhibited

AMP

Output circuit

DDD

AMP

A-V UniversalOutput circuit

Timing & Control

AMP

Output circuit

VVI

AMP

Ventricular Demand