timing cycles

goal

mimic natural cardiac cycle

most common modes

DDDR, VVIR, AAIR, DOO, VOO, DDIR

VOO/AOO/DOO

asynchronous pacing

No sensing or refractory period

used TEMPORARILY for outpatient surgery or MRI

90 BPM

magnet application and MRI mode pace asynchronously

open reed switch

normal function

closed reed switch

asynchronous pacing; AOO, VOO, DOO

reed switch in ICD

magnet will turn off shocking mechanism (ATP or tachy)

magnet will ___ reed switch

close

VVI

paces and senses; single chamber ICD

VVI 40

single chamber ICD with NO pacing indication and NO afib

VVIR 60

single chamber pacemaker for AFib with 1 lead in RV; indication for ICD and pacing (VT/VF and AFib)

rate response

synthetic SA node

AAI

uncommon in US but done for young people to minimize hardware

AAIR 60; R beacause something wrong with SA node

alert period

see everything, do/don’t something

blanking period

see nothing, do nothing

prevent: oversensing, double counting, crosstalk

cross talk

a-channel talking to v-channel

refractory period

see something, do nothing

does not reset lower rate

allows detection of rapid events (Afib or flutter) (PVARP)

sensed events utilize other functions: detection for mode switch or response to noise

prevent pace maker mediated tachycardia (PMT)

absolute refractory

phase 1-2; blanking period, no amount of power will make impulse

relative refractory

phase 3; refractory strong impulse could cause depolarization

phase 4

alert period

double counting

counting pacing impulse as “second” signal (“M” shaped P-wave)

VOO timing cycle

1 timing cycle, lower rate interval only

VVI timing cycle

3 timing cycle; lower rate limit, ventricular blanking period, ventricular refractory period

ventricular blanking period VBP

mimic absolute refractory period of action potential; begin with paced or sensed event

Ventricular refractory period VRP

mimic relative refractory period of action potential, begin at same time of blanking period

AAI timing cycles

3 timing cycles; lower rate limit, atrial blanking period, atrial refractory period

AV delay

mimic PR interval to allow ventricle to fill from atrial kick

AV delay is ___ channel parameter but results in ___ pacing

atrial; ventricular

post ventricular atrial refractory period

far-field r-wave solution

post-atrial ventricular blanking

far-field p-wave solution

ventricular channel parameter

post-atrial ventricular blanking and crosstalk detection window

crosstalk detection window

shorten AV delay and force V pace; A activity forces V pace

protects patient from unintended pacing inhibition so patient does not skip beat

ventricular safety pacing (V lead only)

occur with atrial pacing

why CDW is necessary

calling AP R-wave inhibits pacing (oversensing), shorten AVD

why use CDW and not lengthen PAVB

PVC or PJC followed by V-pace from AV delay could pace on T-wave (R on T = torsades)

post ventricular atrial blanking (PVAB)

avoid v-a cross-talk and cover farfield v signals

post ventricular atrial refractory period

avoid PMT and V-pace after PAC

LRL

lower rate limit

ventriculoatrial interval

lower rate limit - AV dela; ventricular based timing to protect V

When does LRL time out

when intrinsic R-wave comes through

paced av delay

LONGER to allow for interatrial conduction time between artifical pacing and natural depolarization

conduct slower cell to cell

sensed av delay

shorter

conducts faster when SA node and bachmann’s bundle propogate signal from LA to RA

positive AV hysteresis

extend av delay to allow/search for intrinsic conduction

avoid Unnecessary RV pacing

negative AV hysteresis

shortens AV delay and forces v-pace

common in BiV devices

occurs during CDW safety pacing

DAVID trail

DDDR70 vs VVI40

DDDR70 resulted in higher mortality and HF complications

want positive AV hysteresis and DO NOT RV pace unnecessarily

MOST trial

SSS patient with dual chamber PPM in DDDR or VVIR

unnecessary V-pace associated with increased risk of AFib and HF

want positive AV hysteresis

medtronic and boston V-pace avoidance

MVP & RhythmIQ

change mode between AAIR and DDDR

Abbott V-pace avoidance

VIP

extend paced av delay for up tp 3 cycles to search for intrinsic conduction

biotronik v-pace avoidance

I-Opt

extend paced AV delay to 400ms

can you use V-pace avoidant algorithm on dependant patient

no

AP to AS

lower LRL

VP to VS

extend AV delay

2 ventricular events in a row will be labeled as

PVC

DDIR to DDDR

A fib/flutter ends

DDDR to DDIR

enter afib/flutter

why would someone be programed to DDIR

someone with frequent atrial tach (not afib)

DDIR

no av delay, pacing both chambers looks like DOO with intrinsic atrial beat looks like VVI

why would V see A

high A threshold or sensitive V