Pacemaker timing & advanced dual chamber concepts

transcript

Pacemaker Timing & Advanced Dual Chamber Concepts

Dr D Sunil ReddyConsultant Cardiologist

KIMS Hospital

Topics

• Single Chamber Timing• The NBG Code• Dual Chamber Timing• Dual Chamber Pacing Modes• Upper Rate Behaviour• Timings in Rate-responsive Pacemakers

Single Chamber Timing Terminology

• Lower rate & Lower Rate Interval• Refractory period• Blanking period• Upper Sensor Rate & Upper Sensor Rate

Interval

VP VP VS VP

Lower Rate Interval• Interval corresponding to the programmed Lower Rate• Defines the lowest rate the pacemaker will pace• Starts after every paced or sensed event• Ends at the next paced or sensed event• Vp-Vp or Vs-Vp in a VVI pacemaker• Ap-Ap or As-Ap in an AAI pacemaker

LRILRI

Lower Rate = 60, LRI = 1000 ms

Voltage Deflections of the Voltage Deflections of the Sensed EGM in a PacemakerSensed EGM in a Pacemaker

Pacemaker

Stimulus

Paced R wave

Post-pace T wave

Intrinsic R wave

T wave corresponding to intrinsic R wave

2.5 mV

Refractory PeriodRefractory Period

Refractory Period Refractory Period Refractory Period

NO SENSING NO SENSING NO SENSING

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 e.g.

stimulus evoked R wave, repeated sensing of the same intrinsic R wave, T waves, noise

• Events sensed in the refractory period do not affect the Lower Rate Interval but start their own Refractory Periods

Refractory Period

Lower Rate Interval

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

stimulus evoked R wave, repeated sensing of the same intrinsic R wave, T waves, noise

• Events sensed in the refractory period do not affect the Lower Rate Interval but start their own Refractory Periods

VP VP VR VP

LRI LRI

Afterpotential due to Polarization

Afterpotential

Blanking Period

Lower Rate Interval

VP VP VVI / 60

• The first portion of every refractory period• Pacemaker is “blind” to any activity and no events can be sensed• Designed to prevent oversensing of pacing stimulus & after-

potential

Blanking PeriodRefractory Period

Sensor-Indicated Rate

• The basic pacing rate in all rate responsive modes

• Determined by the pacemaker based on the sensor-detected level of patient activity

• Lower Rate <= Sensor Indicated Rate<= Upper Activity Rate

Activity Sensor

• Fixed to the back of the can• Responds to

– Pressure– Vibrations

Accelerometer Based Activity Sensor

• Located on the IC of the pacemaker

• Does not respond to pressure or vibrations

• Responds to motion – Primarily in the anterior-posterior axis

Body Movement

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)

• A paced event can never occur before the UARI expires

Blanking PeriodRefractory Period

Upper Sensor Rate Interval

Sensor Indicated Rate

VOO Mode

Blanking Period

Lower Rate Interval

VOO / 60

• Asynchronous pacing delivers output regardless of intrinsic activity

VPVPVP VP

VOO TIMINGVOO TIMING

VPVPVP VP

VPVPVP VPVP

VP VPVPVP VP

VP VPVPVPVP

VP VP VPVPVP

VP VPVP

VVI Mode

Lower Rate Interval

VP VSBlanking/Refractory

VVI / 60

• Pacing inhibited with intrinsic activity

VPVPVP

VVI TIMINGVVI TIMING

VP VPVS

VP VP VPVS

VP VPVP VP

VP VPVP VPVS

VVI – Refractory Sensing

VPVP VPVP

VPVP VP

VP VPVS

VVI Timing – T wave Oversensing

VPVPVP

VP VPVS

VPVPVS

VPVS VP

VSVPVP

VPVS VP

VSVPVP

VPVS VP

VP VPVS VP

VP VPVS VS VP

VP VPVS

VPVS VP

VP VPVS

VPVS VP

T wave re-cycling

VR VR VRVR VR

VRVR VR VRVR VR

VP VP VP

VRVR VR VRVR VR

VP VP VP

VRVR VR VRVR VR

VP VP VP

VRVR VR VRVR VR

VP VP VP

VRVR VR VRVR VR

VP VPVP

VRVR VR VRVR VR

Interference Operation

Noise Reversion

VPVPSRSR SR SR

Noise Sensed

Lower Rate Interval

VVI/60

• Continuous refractory sensing will cause pacing at the lower or sensor driven rate

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 (= Upper Rate Interval)

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

Sensor Indicated 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

Hysteresis Rate-50 ppm

Dual Chamber Timing (DDD or Universal Mode)

NBG Code ReviewI

ChamberPaced

IIChamber

Sensed

IIIResponseto Sensing

IVProgrammableFunctions/Rate

Modulation

VAntitachy

Function(s)

V: Ventricle V: Ventricle T: Triggered P: Simpleprogrammable

P: Pace

A: Atrium A: Atrium I: Inhibited M: 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)

O: None

NBG Code Revised - 2002I

ChamberPaced

IIChamber

Sensed

IIIResponseto Sensing

IVProgrammableFunctions/Rate

Modulation

VMulti Site

Pacing

V: Ventricle V: Ventricle T: Triggered V: Ventricle

A: Atrium A: Atrium I: Inhibited

D: Dual (A+V) D: Dual (A+V) D: Dual (T+I) D: Dual (A+V)

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

S: Single (A or V)

O: None

A: Atrium

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

V-AAV V-AAV

• Atrial Pace, Ventricular Pace (AP/VP)

Four “Faces” of DDD Pacing

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

V-AAV V-AAV

• Atrial Pace, Ventricular Sense (AP/VS)

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

• Atrial Sense, Ventricular Pace (AS/ VP)

V-AAV AV V-A

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

V-AAV AV V-A

• Atrial Sense, Ventricular Sense (AS/VS)

DDD Timing Parameters

• Lower rate & Lower Rate Interval• AV and VA intervals• Upper Tracking Rate & Interval• Refractory periods• Blanking periods

Lower Rate Interval

Lower Rate • The lowest rate the pacemaker will pace the ATRIUM in

the absence of intrinsic atrial events• Ap-Ap or As-Ap• Starts with every atrial event and ends with the next

atrial event

DDD 60 / 120

AVI AVI

Lower Rate Interval

AV Intervals• Electric analog of the PR Interval – allows for AV Synchrony or

atrial kick

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

• The Atrial Channel is refractory during the AV interval

DDD 60 / 120

Typical Programming for CHBSAV = 120 ms, PAV = 150 ms

Lower Rate Interval

AV Interval VA Interval

Atrial Escape Interval (V-A Interval)• The interval between a paced or sensed ventricular event to the

next atrial event• Starts with a Vs or Vp• Ends with Ap or (prematurely) with As

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

200 ms 800 ms

1000 ms

Atrial Escape Interval (VA Interval)

• Not programmable

• A (non-refractory) ventricular event not preceded by an atrial event (e.g. PVC, lack of atrial sensing, no sinus activity) starts a new VA interval

Lower rate interval – AV interval = VA interval

Lower Rate Interval

VA Interval

Atrial Escape Interval (V-A Interval)

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

200 ms 800 ms

1000 ms

VPDDDR 60 / 100 (upper tracking rate)

Sinus rate: 100 bpm

Lower Rate Interval {

Upper Tracking Rate Limit

Upper Tracking Rate

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

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

• Starts with every ventricular sensed or paced event• No Vp can occur before the UTRI expires

600 ms

Programing Upper Tracking Rate

• Typically programmed to 120 bpm

• Young, active patients – 150 to 180 bpm

• Patients with angina – 100 to 110 bpm

Refractory Periods

• Ventricular Refractory Period (VRP)• Post-ventricular Atrial Refractory Period

(PVARP)• Total Atrial Refractory Period (TARP)

Separate Amplifiers• Atrial Channel• Ventricular Channel

Ventricular Refractory Period• Same as for VVI mode• Starts with every ventricular event, including refractory

sensed events• Events in the VRP do not affect the VA interval

VPVentricular Refractory Period (VRP)

Retrograde P waves

• If the AV node is not refractory during a ventricular event, the ventricular excitation can be conducted back into the atrium – Retrograde P wave

• Possible in both CHB & SSS patients

• Retrograde P waves may be sensed by the pacemaker and result in initiation of an AV interval followed by a Vp

• The Vp can in turn result in another retrograde sensed P wave causing another Vp

• Pacemaker Mediated Endless Loop Tachycardia

Post Ventricular Atrial Refractory Period (PVARP)

Post-Ventricular Atrial Refractory Period

• PVARP starts with every sensed or paced ventricular event, including refractory sensed events

• It renders the ATRIAL CHANNEL refractory and has no effect on ventricular sensing

• The PVARP is intended primarily to prevent sensing of retrograde P waves by the atrial channel

• Atrial events sensed in the PVARP do not start an SAV and are marked Ar

VPVentricular Refractory Period (VRP)

Retrograde P wave

Lower Rate Interval

Upper Tracking Rate

Lower Rate Interval

{No SAV started for events sensed in the TARP

SAV = 200 msPVARP = 300 ms

Thus TARP = 500 ms (120 ppm)

DDDLR = 60 ppm (1000 ms)

UTR = 100 bpm (600 ms)Sinus rate = 66 bpm (900 ms)

SAVTARP

Total Atrial Refractory Period (TARP)

• Sum of the AV Interval and PVARP

What is happening

DDD / 70 / 120

Issue: Crosstalk

• Crosstalk is the sensing of a pacing stimulus delivered in the opposite chamber, which results in undesirable pacemaker response, e.g., false inhibition

DDD / 70 / 120

Blanking Periods• First portion of the refractory period-sensing when sensing is

completely disabled• To prevent sensing of the pacemaker stimulus, after potential,

repeated sensing of the same intrinsic wave and cross-talk

Post Ventricular Atrial Blanking (PVAB) (Programmable)

Post Atrial Ventricular Blanking (Programmable)

Ventricular Blanking (Nonprogrammable)

Atrial Blanking (Nonprogrammable)

Dual Chamber Modes & their Timing

DDD Mode- Universal Mode

• Atrial Tracking – provides AV Synchrony and preserves Heart Rate reserves

• Atrial intrinsic events start an SAV• Sensed Intrinsic events in a given chamber

inhibit pacing in that chamber

DDD Mode

• ApVp – AV Sequential Pacing• Sinus Rate below programmed Lower Rate• AV conduction absent or PAV interval

programmed shorter than intrinsic AV conduction time

DDD TIMINGDDD TIMING

VP VP VP

V-A Interval

VRPVRP

PVARPPVARP

V-A Interval

VRPVRP

PVARPPVARP

VRPVRP

PVARPPVARP

VRPVRP

PVARPPVARP

VRPVRP

PVARPPVARP AV RP

A-V Interval

PVARPPVARP

VRPVRP

PVARPPVARP AV RP

PVARPPVARP

VRPVRP

AV RPAV RPPVARPPVARP

VRPVRP

PVARPPVARP

VRPVRP

AV RPAV RPPVARPPVARP PVARPPVARP

VRPVRP

PVARPPVARPAV RPAV RP PVARPPVARP

VRPVRP

PVARPPVARPAV RPAV RP PVARPPVARP

VRPVRP

AV RPAV RP PVARPPVARP

VRPVRP

DDD Mode

• AsVs – Pacemaker Inhibited• Sinus Rate greater than programmed Lower

Rate• Normal intrinsic AV conduction

AS AS AS

VS VS VS

AS AS AS

VS VS VS

AS AS AS

VS VS VSVS

AS AS ASAS

VS VS VSVS

AS AS ASAS

VS VS VSVS

AS AS ASAS

VS VS VS VSVS

AS AS ASAS

VS VS VS VSVS

ASAS AS ASAS

VS VS VS VS VS

Pacemaker Inhibited

DDD Mode

• ApVs – Atrial Pacing Ventricular Inhibition• Sinus Rate lower than programmed Lower

Rate• Intrinsic AV Conduction

AP AP AP

VS VS VS

AP AP AP

VS VS VS VS

AP AP AP AP

DDD TIMINGDDD TIMINGAtrial Pacing - Ventricular inhibition

DDD Mode

• AsVp – Atrial Tracking• Sinus Rate greater than programmed Lower

Rate• No intrinsic conduction or programmed SAV

is shorter than intrinsic AV conduction time

VP VP VP

AS ASAS

VP VP VP

AS ASAS

VP VP VP

AS ASAS

VP VP VP

AS ASAS

VP VP VP VP

AS AS ASAS

DDD TIMINGDDD TIMINGAtrial Tracking

DDI Mode

• A-V sequential pacing WITHOUT atrial tracking

• Atrial sensed events do not begin an SAV• Atrial Sensed events inhibit atrial pacing• Ventricular pacing rate cannot increase

beyond the programmed lower rate

DDI mode is used during Mode Switch due to atrial tachycardias

PVARPPVARP

VRPVRP

ARP PVARPPVARP ARP PVARPPVARPARP

PVARPPVARP

ARPARPPVARPPVARP

AV RPAV RP

DDI TIMINGDDI TIMING

PVARPPVARP

VRPVRP

PVARPPVARP

ARPARPPVARPPVARPAV RPAV RP

PVARPPVARP

VRPVRP

PVARPPVARP

ARPARPPVARPPVARP

AV RPAV RP

PVARPPVARP

VRPVRP

PVARPPVARP

ARPARPPVARPPVARP

A-VInterval

AV RPAV RP

A-VInterval

VRPVRP

PVARPPVARP

ARPARP

VRPVRP

PVARPPVARPARPARP

A-VInterval

V-A Interval

VRPVRP

PVARPPVARPARPARP

A-VInterval

V-A Interval

PVARPPVARP ARP PVARPPVARPARP

PVARPPVARP

ARPARPAV RPAV RP

A-VInterval

PVARPPVARP ARP PVARPPVARPARP

PVARPPVARP

ARPARPAV RPAV RP

A-VInterval

ARPARP

A-VInterval

AV RPAV RP ARP

V-A Interval

PVARPPVARP

VRPVRP

ARPARP

A-VInterval

AV RPAV RP

V-A Interval

PVARPPVARP ARP

ARPARPARP

A-VInterval

AV RPAV RP

V-A Interval

PVARPPVARP

VP VP VS

ARPARPARP

A-VInterval

AV RPAV RP

VP VP VS

VRPVRP

ARPARPARP

A-VInterval

PVARPPVARPAV RPAV RP

VP VP VS

ARPARPARPARPAV RPAV RP

A-VInterval

PVARPPVARPPVARPPVARP

V-A Interval

PVARPPVARP

V-A Interval

VRPVRP

VP VP VS

Lower Rate Interval

DDI 60PAV = 200 msPVARP = 300 ms

VPVP VP

AS AS APAS

PVARP PVARP

• A non-tracking mode– Provides AV sequential pacing at lower or sensor indicated rate

VA Interval VA Interval

VA Interval

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 or if programmed lower rate > atrial intrinsic rate

VDD Mode

MVP Basic OperationAAI(R) Mode Atrial based pacing allowing intrinsic AV conduction

PR Intervals are only restricted by the underlying atrial rate or sensor rate; VS events simply need to occur prior to the next AS or AP.

MVP Basic OperationVentricular Backup Ventricular pacing only as needed in the presence of

transient loss of conduction

MVP Basic OperationDDD(R) Switch Ventricular support if lossof A-V conduction is persistent

Ventricular Safety Pacing

Issue: Crosstalk

• Crosstalk is the sensing of a pacing stimulus delivered in the opposite chamber, which results in undesirable pacemaker response, e.g., false inhibition

DDD / 70 / 120

Solution: Ventricular Safety Pacing• 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

AV PVARP PVARP AV110 ms

VS VPVP VP

AP APAP

VS VS VS

APAPAP

VS VS VS

APAPAP

VS VS VS

APAPAPAP

VS VS VS

AP APAPAP

VS VS VS

AP APAP

VS VS VS

AP AP APAP

VS VS VS

AP AP APAP

VS VS VS

AP AP AP

VS VS VS

AP AP AP

VS VS VS

AP AP AP AP

Ventricular Safety Pace

DDD 60 / 120

• Often seen during atrial undersensing in patients with intact AV conduction

• Atrial undersensing results in Ap despite intrinsic event and starts an AV interval with a VSP window

• If the intrinsic event is conducted through the AV Node and and the Ventricular intrinsic event occurs during the VSP window, a ventricular pace is delivered at the end of the VSP window

Other Methods for Managing Crosstalk

• Reduce atrial output (amplitude and/or pulse width)• Decrease (increase value) ventricular sensitivity• Program bipolar (if possible)• Increase the post -atrial ventricular blanking period

Upper Rate Behaviour

• Pacemaker operation and timings when the atrial intrinsic rate is at or above the Upper Tracking Rate

• Governed by two rates`– UTR– TARP rate

The Upper Tracking Rate

• Prevents the ventricles from being paced at high rates in response to atrial tachycardias

• The ventricle can never be paced faster than the Upper Tracking Rate in response to sensed atrial activity

• The Upper Rate Interval is given priority over other timing intervals

Upper Tracking Rate

Lower Rate Interval

{P Waves Blocked

VPVPSAV = 200 ms

PVARP = 300 msThus TARP = 500 ms (120 ppm)

DDDLR = 60 ppm (1000 ms)

UTR = 100 bpm (600 ms)Sinus rate = 66 bpm (900 ms)

SAVTARP

Total Atrial Refractory Period (TARP)

• Sum of the AV Interval and PVARP

• The atrial channel is refractory to sensed events that occur during the TARP

• Any atrial intrinsic event occurring in the TARP does not start an AV interval

• Any atrial intrinsic event occurring in the TARP is not tracked by the pacemaker and does not result in ventricular pacing

TARP Rate

• TARP = SAV + PVARP (during atrial sensed rhythms)• If SAV = 150 ms and PVARP = 350 ms,

TARP = 500 msTARP Rate = 120 bpm

• Atrial rates with cycle length’s less than 500 ms (or rates greater than 120 bpm) will result in at least every other intrinsic atrial wave falling in the TARP

• Only intrinsic events falling outside the TARP will generate an SAV and a resultant ventricular pace

Fixed Block or 2:1 Block

• Occurs whenever the intrinsic atrial rate exceeds the TARP rate

• At least 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

{P Wave Blocked

VPVPARAR

Sinus rate = 133 bpm (450 ms)PVARP = 300 ms SAV = 200 msTracked rate = 66 bpm (900 ms)

AV PVARP AV PVARPTARP TARP

2:1 Block

AS ASARARAR

AS AS AS

AS ASARARAR

AS ASAR ARARAR

VP VP VP

AS ASAR ARARAR

VP VP VP

AS ASAR ARARAR

VP VP VP

AS ASAR ARARAR

2:1 Block

Wenckebach Operation

• 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

• Cycle repeats

Wenckebach Operation

Upper Tracking Rate

AS AS AR APVPVP VP

TARPSAV PAV PVARP SAV PVARP

P Wave Blocked (unsensed or unused)

DDD Sinus rate = 109 bpm (550 ms) LR = 60 bpm (1000 ms) UTR = 100 ppm (600 ms)

SAV = 200 ms PAV = 230 ms PVARP = 300 ms

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

TARP TARP

ASAS ASAR

VP VPVP

ASAS AS ASAR

VPVPVP VP

AS ASAS AS ASAR

VPVPVP VP

AS ASAS AS ASAR

VPVP VP

AS ASAS AS ASAR

VP VPVP

AS ASAS AS ASAR

AS ASAS

AS ASAR

VP VP VP

AS ASAS

AS ASAR

VP VP VP

AS ASAS

AS ASAR

Wenckebach Behaviour

Wenckebach or 2:1 block rate during exercise/activity?

• 2:1 block – – Atrial Rates > TARP rate

• Wenckebach – Upper Tracking Rate < Atrial Rate < Tarp Rate

• Wenckebach is preferred – Fewer symptoms– Warning to patient

Wenckebach vs. 2:1 Block – What Will Happen First?

What will the upper rate behavior of this pacemaker be?

Lower rate = 60 ppmUpper tracking rate = 120 ppm

PAV = 230 msSAV = 250 ms

PVARP = 350 ms

Wenckebach vs. 2:1 Block – Solution

Upper tracking rate = 120 ppmPVARP = 350 ms

SAV = 250 ms

• 2:1 block interval = TARP = SAV + PVARP(250 ms + 350 ms = 600 ms)

• TARP Rate = 100 bpm• TARP rate is less than the upper tracking rate

interval Thus, 2:1 block will occur as soon as atrial rate

exceeds 100 bpm

Wenckebach vs. 2:1 Block – What Will Happen First?

What will the upper rate behavior of this pacemaker be?

Lower rate = 60 ppmUpper tracking rate = 100 ppm

PAV = 150 msSAV = 150 ms

PVARP = 350 ms

Wenckebach vs. 2:1 Block – Solution

Upper tracking rate = 100 ppmPVARP = 250 ms

SAV = 150 ms

• 2:1 block interval = TARP = SAV + PVARP(150 ms + 350 ms = 500 ms)

• TARP rate is 120 bpm Thus, Wenckebach will begin as soon as atrial rate

exceeds 100 bpmWenckebach behaviour will persist until atrial rate

exceeds 120 (TARP rate), after which 2:1 block will commence

What Can We Do to Make Wenckebach Occur First?

• Shorten or reduce the TARP by:– Shortening the PVARP– Shortening the SAV– Automatic PVARP

DDDR 60 / 120A-A = 500 ms

Upper Activity Rate Limit

Lower Rate Limit

V-APAV V-APAV

Upper Sensor Rate• In rate responsive modes, the Upper Sensor Rate provides the

limit for sensor-indicated pacing• It can be programmed independently of the UTR• Typically programmed to 120 bpm• For younger, active patients with chronotropic incompetence –

150 bpm

UAR versus UTR

The ventricle can never be paced at a rate higher than the UTR during sensed atrial activity

e.g. 120 bpm

All atrial rates above 120 bpm will not be tracked 1:1 by the ventricles

Maximum Sensor Indicated Rate

The atrium can never be paced at a rate higher than the UARe.g. 140 bpm

Both atrium and subsequently the ventricle may be paced up to 140 bpm

Pacemaker Mediated Tachycardias

• Any tachycardia that occurs due to the presence of a dual chamber pacemaker

– Rapid ventricular pacing during tracking of rapid atrial rates

– Sensing of EMI or EMG on the atrial channel resulting in rapid ventricular pacing

– Tachycardia resulting from stimulation by pacemaker during myocardial vulnerable periods

– Sensing of Retrograde P waves – Endless Loop Tachycardia

Pacemaker Mediated Tachycardia (PMT)

• PMT is a paced rhythm, usually rapid, which is sustained by ventricular events conducted retrogradely (i.e., backwards) to the atria

• Loss of AV synchrony may be caused by:– PVC– Very early PAC– Atrial non-capture– Atrial undersensing– Atrial oversensing

• Long AV intervals can cause the AV node to recover from refractoriness and result in retrograde conduction

PMT Prevention

• Prevent Retrograde conduction– Maintain normal AV intervals at all rates– Good atrial sensing at implant– Good atrial thresholds at implant

• Prevent sensing of retrograde P wave if it occurs

Rate of PMT

• The rate of the PMT can never exceed the UTR

• Depends on the programmed parameters and the Vp to retrograde P wave interval

• Very often exactly equal to the UTR

UTR = 120 bpm, PMT Rate = 120 bpm

Pacemaker timing & advanced dual chamber concepts

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