1.3_Burri_PM_timing

7/23/2019 1.3_Burri_PM_timing

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Pacemaker Timing in Single

and Dual Chamber Devices

EHRA Cardiac Pacing Course

17thMarch 2014 Vienna

Haran Burri, MD

University Hospital of Geneva


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Agenda

General aspects Single chamber timing cycles

Dual Chamber timing cycles

Hysteresis Refractory periods

Upper rate behavior

Miscelaneous


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The NBG Code

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Position I II III IV V

Category Chamber(s)paced

Chamber(s)

sensed

Response

to sensing

Rate

Modulation

Multisite

Pacing

Letters O= NoneA=Atrium

V=VentricleD=Dual

S=Single*

O= None

A=Atrium

V=VentricleD=Dual

S=Single*

O=None

T=Triggered

I=InhibitedD=Dual

O=None

R=Rate

Modulation

O=None

A=Atrium

V=VentricleD=Dual

* Manufacturers designation only


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Pacing modes

Asynchronous Principle permanent pacing at the programmed rate

AOO, VOO, DOO Advantages ensures a fixed cardiac rhythm

Drawbacks no sensing of the spontaneous cardiac events

On Demand

AAI, VVI, VDDDDI, DDD

Principle - no spontaneous rhythm: permanent pacing at the

programmed rate

- when spontaneous rhythm < programmed rate: permanent

pacing

- when spontaneous rhythm > programmed rate: inhibition of

the PM

Advantages no competition with the spontaneous rhythm

Synchronous Principle spikes triggered by spontaneous events

AAT, VVT Advantages no spontaneous events = cardiac pacing at the prog. rate

interferences or artifacts = no pacing inhibition

Drawbacks early battery depletion


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Markers

To make sure there is perfect understanding of the operation thedevice is performing, every manufacturer has a specific set of

markers that reflect the devices behaviour.

e.g:

ApAtrial Pacing

AsAtrial Sensing

ArAtrial Sensing in the refractory periodVpVentricular Pacing

VsVentricular Sensing

VrVentricular Sensing in the refractory period


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Converting Rates to Intervals

and Vice Versa

Rate (bpm) to interval (ms):

60.000/rate (in bpm) = interval (in milliseconds)

Example: rate 100 bpminterval 600 ms (60.000/100 bpm = 600 ms)

Interval (ms) to rate (bpm):

60.000/interval (in milliseconds) = rate (in bpm)

Example: interval 500 msrate 120 bpm (60.000/500 ms = 120 bpm)


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Agenda



Hysteresis

Refractory periods

Upper rate behavior

Miscelaneous


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Single chamber pacing - VVI

Chamber paced Chamber Sensed Response to sensing Rate modulation

V=Ventricle V=Ventricle I=Inhibit O=None (not active)

escape interval escape interval < escape interval

Inhibit &

reset

counters

< escape interval

Inhibit &

reset

counters

escape interval

Pace &

reset

counters

Pace &

reset

counters

Inhibit &

reset

counters


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A Refr Per

V Refr Per

Sensitivity value: Atrial < Ventricle

Rp {

Refractory period: Atrial > Ventricle

Differences between AAI and VVI


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Agenda



Hysteresis

Refractory periods

Upper rate behavior

Miscelaneous


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Dual chamber timing cycles

Chamber paced Chamber Sensed Response to sensing Rate modulation

D=Dual D=DualD=Dual

(inhibit+trigger)O=None


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AV interval

AVD

The P-wave starts

before the sensing of

the signal

Sensed AV delay

Similar actual AV delay with atrial pacing or atrial sensing!

Paced AV delay

PAVD

Sense Offset

The P-wave starts at

the beginning of the

spike


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DDI pacing mode

Only paced AV delay can be

programmed (not sensed AV delay)

= VA interval

May be used during modeswitching or to avoid ventricular pacing in sinus rhythm

Maintains AV synchrony if atrial pacing

Loss of AV synchrony if atrial sensing and AV block


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Atrial-based timing

V-A interval = 850 ms V-A interval = 800

AVD

150

Ax-Ap interval is constant!

AVD

200

AVD

200

A-A interval = 1000 ms A-A interval = 1000 ms

Ventricular rate = 57 bpmVentricular rate = 60bpm

VV interval = 1050 ms VV interval = 1000ms


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Ventricular-based timing

V-A interval = 800 ms V-A interval = 800

AVD

150

Vx-Vp interval is constant!

AVD

200

AVD

200

A-A interval = 950 ms A-A interval = 1000 ms

Ventricular rate = 60 bpm Ventricular rate = 60 bpm

VV interval = 1000 ms VV interval = 1000ms

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Agenda



Hysteresis

Refractory periods

Upper rate behavior

Miscelaneous

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Hysteresis

Allows the intrinsic rate to go below theprogrammed lower rate interval (hysteresisinterval)

Favours intrinsic activation More physiological as long as the slower rates are

acceptable and not symptomatic for the patient(e.g periods of rest)

May help increase device longevity

Both for single as well as dual chamber devices

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Hysteresis

Pacing

Spontaneous rhythm

Hysteresis Off

Lower rate

Heart Rate

Time

Hysteresis rate

Hysteresis On

Lower rate

Heart Rate

Time

Hysteresis rate

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Agenda



Hysteresis

Refractory periods

Upper rate behavior

Miscelaneous

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T-wave oversensing

LRI

LRI

LRI

LRI

T-wave oversensing

Actual pacing interval >> LRI

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Far Field R-wave (FFRW) oversensing

indicates Far Field R-waves

inappropriate mode switch

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Sensing unwanted signals

Surface ECG

A EGM

V EGM

AV crosstalk is potentialy lethal in a patient with complete AV block !

As AsVs Vs

As As

Far-field oversensing

Ap Vp Ap Vp

Vs As Vs As

Cross-talk

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Refractory periods

Absolute Refractory Period

Also known as BLANKINGperiod

Initial portion of the refractory

period, usually very short Signals will be not be detected

During this period of time, the

sensing channel is not active

Forces the pacemaker to blind (in

one or both chambers) after a

pacing impulse, avoiding cross-talk

and far field oversensing

Relative Refractory Period

Signals will be seen but will not

reset timers

Forces the pacemaker not to reactto unwanted intrinsic signals, e.g.

T waves and retrograde P waves

Refractory Period

Absolute Relative

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PVARP PVARP= Post Ventricular Atrial Refractory Period

Typical value of PVARP = 270-310 ms (275 ms nominal)

PVARP starts in the atrial channel after a paced or sensed ventricular

event

An atrial event in the PVARP will not start the AV delay timer

PVARP helps to prevent retrograde P-waves of being sensed and

tracked, thereby preventing Pacemaker Mediated Tachycardias

Atrial Channel

AS VP

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PVAB

PVAB= Post Ventrcular Atrial Blanking PVAB is the first part of the PVARP

PVAB starts in atrial channel after paced or sensed ventricular event

Typical value of PVAB is e.g. 150 ms

During PVAB atrial events are blanked PVAB helps to prevent Far Field R-wave oversensing

Atrial Channel

AS VP

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Ventricular Refractory Period

A period in the ventricular channel following a paced orsensed ventricular event during which the sense amplifier will

not respond to incoming signals

To prevent T-wave oversensing or double counting of wide

QRS complexes

Typical nominal value of Ventricular Refractory Period is e.g.

250 ms

Atrial Channel

Ventricular Channel

AP VP / VS

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Ventricular Refractory Period

Vref: 320 ms Vref: 350 ms

Avoidance of T-wave oversensing

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Ventricular blanking

Blanking of the ventricular channel in response toatrial or ventricular pacing (not for atrial sensing)

Primarily intended to prevent cross-talk: detection of

the atrial or ventricular output by the ventricular

sense amplifier

Atrial Channel

Ventricular Channel

AP VP / VS

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VVI timing cycles and refractory periods

LRI LRI < LRI

< LRI

LRI

VRPVRP VRP

VRP VRPB

VRP

LRI

URI

Lower Rate Interval defines the minimum heart rate

Upper Rate Interval defines the highest pacing rate

Ventricular Refractory Period prevents from restarting a new LRI when sensing the T wave

B

B Blanking Period forces the device to be blind to the pacing spike

URI URI URI URI

URI

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PAVB Post atrial

ventricular blanking

VB Ventricular

blanking

PVAB Post ventricular

atrial blanking

AB Atrial

blanking


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AS AP VS VP Usual duration (ms)

A Blanking 50-200

A Refractory 120-150 (post AP); 250-400 (post VP)

V Blanking 20-50 (PAVB); 150-250 (post VP)

V Refractory 150-300

Blanking and refractory periods may vary according to :

- manufacturer

- model

- paced or sensed event

- programmed pacing polarity

Aims:

Blanking: avoid crosstalk (=condition when pacing in one channel is sensed as

intrinsic activity in another channel) and oversensing of the afterpotential

PVARP: avoid sensing of FFRW and of retrograde P-waves

VRP: avoid sensing of T-waves

Summary of DDD timing cycles

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Agenda



Hysteresis

Refractory periods

Upper rate behavior

Miscelaneous

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Upper Rate Behavior

Upper rate behavior relates to

Programmed Upper Tracking Rate (UTR)

Total Atrial Refractory Period (TARP)

TARP = AV delay + PVARP Determines the maximum UTR

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2:1 block

Occurs when PP intervals are shorter than TARP

PVARPARP

SAV

V

P

AS AR

PVARPARP

SAV

V

P

AS AR

ARP

SAV

V

P

AS

TARP TARP TARP

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Example

Sensed AV Delay = 150 ms, PVARP = 275 ms, therefore TARP = 425 ms

2:1-blockpoint: 60000 / 425 = 141 bpm

2:1 Block

160

140

120

100

14012010080

Stimulated

ventr icular ra te

Sensed

tr ial Rate

80

60

160

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Upper Rate Behavior

Wenckebachwindow

UTR

Atrial

Rate

VentricularRate

LR

2:1 Response

UTRLR MTR

= Ventricular Pacing

1:1 Response

MTR

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Wenckebach

Wenckebach behaviour Each AS (P-wave) is followed by an increasing SAV, and then the VP

Eventually an atrial beat is not tracked, and a ventricular beat is dropped

Produces gradual change in tracking rate ratio

Occurs if UTR interval > TARP interval

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Wenckebach Behavior - Example

Dual Chamber pacemaker UTR = 100 bpm (600 ms)

Sensed AV delay = 150 ms, PVARP = 250 ms

TARP = 150 + 250 = 400 ms (150 bpm)

As a result atrial rates >100 bpm (600 ms) but < 150 bpm will show

Wenckebach behavior

Max AV delay prolongation is 200 ms (600 400)

Sensed AV delay ranges from 150 - 350 ms

Wenckebach window is UTR interval minus TARP = 200 ms

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Achieving a Higher UTR without Block

Decrease SAV interval

Program rate-adaptive AV intervals

Decrease PVARP

Program PVARP to auto (decreases with increasing HR) Increase upper tracking rate

PVARPAVI

A

S

A

R

TARP

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Agenda



Hysteresis

Refractory periods

Upper rate behavior

Miscelaneous

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Rate adaptative pacing (R)

Algorithm

Mathematical formula that

converts sensor data into heart

rate (pacing rate)

Indicator

Respiration

Activity

Intra-cardiac impedance

Sensor

Impedance

Quartz

Variable capacitance

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The device switches from a tracking mode (DDDR) to a

non-tracking mode (DDIR or VDIR) at the start of an atrial

arrhythmia

Modeswitching

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Ventricular Safety Pacing

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If a VS event follows shortly (e.g. within 110ms) of an AP event, this maypotentially be crosstalk

triggers a VP at the end of the venricular safety pacing window

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Endless loop tachycardia

A

V

Ap Vp Ap Vp Vs As Vp As Vp As Vp As Vp As Vp As Vp As Vp As Vp As Vp As

Atrial - non-capture

- overdetection

- under-detection

VPB

Long AVI

Causes:

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Endless loop tachycardia termination


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Endless loop tachycardia termination

PVARP increase

To prevent conduction of retrograde P waves, the device increases the PVARP. TheP wave, falling inside the PVARP wont be conducted to the ventricle, terminating the

pacemaker-mediated tachycardia

PVARP PVARP PVARP

As Vp As VpAs Vp Ar

VA interval VA interval

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Noise Reversion

VPVPSRSR SR SR

Noise Sensed

Lower Rate Interval

Continuous refractory sensing will cause asynchronous pacing at

the lower or sensor driven rate

SR=sense refractory

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LRI

Intrinsic rate

Tachycardia

starts

Tachycardia

stops

Rate Smoothing

Pacing

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