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IBHRE® > Timing cycles > Flashcards

Timing cycles Flashcards

Outlines the constituent cycles that provide appropriately timed pacing therapy for optimal haemodynamics. Currently weighted 6% in the CCDS exam.

1
Q

What does the 1st column in the NGB code dictate?

A

Chamber Paced.

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2
Q

What does the 2nd column in the NGB code dictate?

A

Chamber Sensed.

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3
Q

What does the 3rd column in the NGB code dictate?

A

Action (Inhibit or trigger).

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4
Q

When do we use asynchronous pacing?

A

Used only transiently for pacing-dependent patients.

This avoids inappropriate pacing inhibition during interventions or surgeries associated with noise.

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5
Q

Why use a triggered mode?

A

Excellent marker for the site and time of sensing within a complex in an ECG tracing.

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6
Q

What are the 4 modes of DDD pacing?

A
  1. As Vs
  2. As Vp
  3. Ap Vs
  4. Ap Vp
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7
Q

What are the 4 States of DDD pacing?

A
  1. AV
  2. PV
  3. PR
  4. AR
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8
Q

AV delay + PVARP =

A

TARP - Total Atrial Refractory Period.

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9
Q

True / False

‘In DDD pacing generally a V output can be delivered in absence of an Atrial event’.

A

False

An atrial event is required in order to start the AV delay interval.

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10
Q

When Rate Response is programmed off, what will the atrial pacing rate be?

A

Pacing rate will always be at base rate.

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11
Q

True / False

PV delay = SAV (Sensed AV delay).

A

True.

Also known as the P-wave Tracking Interval, PV Interval.

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12
Q

The following statement best describes what phenomena?

‘Occurs when the sensed atrial rate is faster than the maximum tracking rate’.

A

Pacemaker wenckebach.

This can lead to 2:1 block if the atrial rates are fast enough.

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13
Q

True / False

Ventricular pacing below the base rate is normal in VDD pacing.

A

True.

In VDD mode, if the atrial rate drops below the LRL, the mode will appear VVI.There is no atrial LRL as it is a sensed channel only.

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14
Q

The following statement best describes what type of timing?

‘The sensed R wave causes the AEI/VAI timer to start’.

A

Ventricular Based Timing.

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15
Q

True / False

Ventricular based timing can cause the atrial rate to be above the base rate.

A

True.

The next atrial output will occur at a rate that is faster than the programmed base rate.

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16
Q

The following statement best describes what type of timing?

‘The AEI timer begins with the P-wave’.

A

Atrial Based Timing.

AEI = Atrial Escape Interval

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17
Q

True / False

PR state can be defined as an inhibited pacing state.

A

True.

No outputs are delivered in this state of DDD pacing as intrinsic events are ‘inhibiting’ output.

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18
Q

What mode is use to prevent tracking of Atrial Arrhythmias?

A

DDI / DDIR.

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19
Q

True / False

In DDI the ventricular paced rate will never be greater than the programmed LRL regardless of the atrial rate.

A

True.

In DDIR it may be higher but only if sensor driven.

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20
Q

Which two pacing states cant be provided by VDI when compared to the four pacing states possible in DDD.

A
  1. AS-VP (inhibition mode)
  2. AP-VP (no A pace function)
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21
Q

What is the major difference between DDI and DVI modes?

A

DVI senses only in the ventricle and ignores atrial events.

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22
Q

When would one programme DVI in preference to DDI?

A

Patients with SSS and atrial sensing malfunction (oversensing) in which AV synchrony is desired.

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23
Q

The following statement best describes a lead most commonly associated with what pacing mode?

‘Single-pass lead which integrates an atrial-sensing electrode with a ventricular-pace/sense electrode’

A

VDD.

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24
Q

If DDD device senses well however has an abnormally high atrial threshold, what mode can be used?

A

VDD.

Maximise battery life + Maintains atrial diagnostics. Only for patients who require no atrial pacing!

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25
Q

In VDD mode, if the atrial rate drops below the LRL - what mode will it resemble?

A

VVI.

Atrial is sensed only, thus there is no atrial LRL. If the atrial rate drops below the ventricular LRL, the ventricular clock will time out and will VP at the base rate, asynchronous with the slower atrial intrinsic rate.

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26
Q

What are the 6 types of VDD floating leads?

A
  1. Unipolar
  2. Bipolar (Narrow spacing)
  3. Bipolar (Wide spacing)
  4. Orthogonal
  5. Diagonal
  6. Bipolar half ring
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27
Q

What is the single main purpose of blanking periods?

A

To prevent crosstalk.

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28
Q

What two refractory cycles are present in AAI?

A
  1. ABP - Atrial Blanking Period
  2. ARP - Atrial Refractory Period
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29
Q

True / False

Far Field R-Wave Sensing can reset an AAI timing cycle, giving a longer R-R interval than expected

A

True.

A sensed far field signal can prolong duration between outputs.

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30
Q

What two refractory cycles are present in VVI?

A
  1. VBP - Ventricular Blanking Period
  2. VRP - Ventricular Refractory Period
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31
Q

With respect to Dual Chamber timing, what is the main purpose of the PVARP?

A

Prevent tracking of retrograde P-waves.

Retrograde P-waves (alongside other things) can initiate a PMT.

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32
Q

PVARP is present in which 3 Device Modes?

A
  1. DDD
  2. VDD
  3. DDI
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33
Q

Generally what is the programmable range of PVAB?

A

12-125ms.

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34
Q

The following statement best describes what?

‘Ventricular-sensing amplifier during the AVI immediately after the PAVB’.

A

The crosstalk window.

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35
Q

Inhibit / Triggered

Impulses sensed within the crosstalk window will cause what output response?

A

Device will Trigger pace.

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36
Q

Generally what is the range of ventricular safety pacing?

A

AVI of 100-120ms.

Programmable 50-150ms in some devices.

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37
Q

What should one suspect if the observed AVI is shorter than what is programmed?

A

Suspect crosstalk.

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38
Q

List 4 programmable ways to eliminate crosstalk.

A
  1. Turn on any anti-cross talk algorithms
  2. Increase/extend the PAVB (best answer)
  3. Decrease the atrial output (unlikely answer)
  4. Reduce the ventricular sensitivity (also unlikely answer)
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39
Q

The following statement best describes what?

‘Triggering of an A-Tach by an atrial pacing stimulus that falls within the atrium’s vulnerable period’

A

Competitive Atrial Pacing.

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40
Q

The following statement best describes what window?

‘Portion of the RR cycle that is not part of the PVARP or AVI’.

A

The ASW - Atrial Sensing Window.

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41
Q

True / False

LRL is never violated in V-based timing.

A

True.

With V-based timing its impossible to violate LRL.

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42
Q

True / False

LRL is never violated in A-based timing.

A

False.

A-A LRL will be reset by a sensed ventricular event within the VAI. This function mimics the compensatory pause commonly seen in normal sinus rhythm with ventricular ectopy.

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43
Q

True / False

Max Sensor Rate is never violated in V-based timing.

A

False.

Effective atrial-paced rate may theoretically be considerably higher than the programmed max sensor rate if AV conduction is present.

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44
Q

Hybrid based timing is a combination of what?

A

Atrial and Ventricular based timing.

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45
Q

Hybrid based timing uses predominantly what style of timing?

A

Atrial based timing.

Once a loss of AV conduction occurs it then switches to ventricular based timing.

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46
Q

Yes / No

If the MTR interval has not yet been completed at the end of the AVI will an output be delivered?

A

No.

Ventricular pacing is withheld until the Max Track Rate interval completes.

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47
Q

The following statement best describes what?

‘A PV interval greater than the programmed sensed AV delay’.

A

Pseudo 1st degree AVB.

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48
Q

How does one calculate the Atrial Escape Interval?

A

LRL minus AV interval.

60bpm = 1000ms / PAV = 150ms

1000 - 150 = AEI of 850ms = 70bpm

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49
Q

What does the 4th column in the NGB code dictate?

A

Whether rate responsive pacing is on/off.

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50
Q

What does the 5th column in the NBG code dictate?

A

Whether there is multisite pacing in one anatomical location.

IS4 lead with multiple active pacing electrodes stimulating the LV.

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51
Q

To determine the exact moment a device senses an impulse, what action (NGB 3) can I employ?

A

Triggered pacing will show exact moment of impulse detection.

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52
Q

A V event without a preceding sensed/paced A event will be labeled as a ______.

A

PVC.

This rule is always true. If a device is incorrectly labeling PVCs, look to see if it undersensed the previous atrial event.

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53
Q

List the major difference between device blanking and refractory periods.

A
  • Blanking = Device will see nothing
  • Refractory = Device will see event & log in counters, however won’t necessarly act upon it
54
Q

True / False

The Atrial Escape Interval can be violated in Atrial Based timing.

A

False.

Its impossible to violate the AEI in Atrial Based Timing.

55
Q

True / False

The Atrial Escape Interval can be violated in Ventricular Based timing.

A

True.

LRL will be reset by a sensed ventricular event within the AEI.

56
Q

True / False

Shortening the PVAB will increase sensitivity to atrial arrhythmias.

A

True.

Shorter blanking periods decrease the time the device is ‘blind’. Thus quicker atrial rates will be seen.

57
Q

True / False

Lengthening the PVAB will increase specificity to atrial arrhythmias.

A

True.

Reducing sensitivity increases specificity. Thus a longer PVAB will reduce risk of inappropriate mode switch.

58
Q

List the only 2 P-synchronous ventricular modes in which a PMT can occur.

A
  1. DDD
  2. VDD
59
Q

List 5 ways a PMT can be initiated.

A
  1. Ventricular extrasystole
  2. Loss of Atrial Capture
  3. Atrial Oversensing
  4. Atrial extrasystole
  5. Intermittent loss of Atrial Sensing
60
Q

During PMT is a higher programmed Max Track Rate more or less likely to induce symptoms?

A

More likely.

PMTs typically run at the MTR - Thus higher MTR = Faster PMT which is more likely to induce symptoms.

61
Q

True / False

Most contemporary CRT devices use LV sensing.

A

False.

Most devices sense of the RV only.

62
Q

Which two PVAB cycles exist in CRT?

A
  1. PAVBRV = similar purpose to dual chamber devices
  2. PAVBLV = To prevent inappropriate inhibition of LV pacing due to far-field atrial pace oversensing
63
Q

The following statement best describes what CRT timing cycle?

‘LV-sensed event post an LV event (paced or sensed) that won’t reset timing cycles’.

A

LVRP.

64
Q

What is the purpose of LVRP?

A

Prevents oversensing of QRS or T waves following a ventricular event (paced or sensed).

This prevents inappropriate loss of CRT (seen more commonly with unipolar LV leads).

65
Q

The following statement best describes what CRT timing cycle?

‘Prevents device from inadvertently delivering an LV output during the LV vulnerable period after an LV-sensed event, such as when an LV PVC occurs’.

A

LVPP.

RV pacing is not inhibited however.

66
Q

True / False

LVPP maximises CRT delivery while reducing the risk of inducing a ventricular tachyarrhythmia.

A

True.

67
Q

True / False

Extending the LVPP interval will reduce the MTR and inhibit biventricular pacing at higher rates.

A

True.

68
Q

Which CRT timing cycle is best described below?

‘Timing between the RV and LV-paced events’.

A

VV delay / LV Offset.

69
Q

List the 3 possible programming options of VV delay / LV Offset.

A
  1. Positive (RV first)
  2. Negative (LV first)
  3. Zero (simultaneous RV/LV)
70
Q

List 5 events that inhibit BiV pacing.

A
  1. Rapid atrial or sinus rates above MTR
  2. Short and dynamic PR intervals
  3. PACs
  4. Frequent PVCs
  5. AF with ventricular response > LRL +/- SIR
71
Q

Define negative hysteresis.

A

Shortens AV delay to promote pacing.

72
Q

Define positive hysteresis.

A

Extends AV delay to promote intrinsic conduction.

73
Q

With respect to CRT, the statement below best describes what timing cycle?

‘LV pacing immediately after intrinsic conduction / sensed event’.

A

Ventricular Sensed Response / BiV trigger.

74
Q

True / False

Ventricular Sensed Response / BiV trigger must function between the LRL and MTR.

A

True.

75
Q

True / False

BiV pacing will cease above MTR (TARP).

A

True.

The vast majority of CRT timing problems can be erased by programming higher MTR, irrespective of whether you believe the patient will achieve those rates.

76
Q

With respect to CRT, what timing cycle could further reduce BiV pacing due to PVC’s?

A

PVC response.

Remember PVC response will cause an abnormally long PVARP extension.

77
Q

List 5 things that can be done to improve BiV pacing in AF patients.

A
  1. Increase LRL
  2. Enable ventricular sense response
  3. Aggressive Medical therapy
  4. AF Ablation
  5. AVN Ablation
78
Q

List 4 signals that the Ventricular Refractory Period (VRP) is designed to blank.

A
  1. Its own output stimulus
  2. T-wave
  3. Excessive Afterpotential
  4. Paced QRS complex
79
Q

True / False

All refractory periods start with a blanking period.

A

True.

Blanking periods can be standalone and don’t necessarily need refractory periods following them.

80
Q

What are the 4 fundamental timing cycles associated with the ventricular channel in DDD mode?

A
  1. Lower rate interval (LRI)
  2. Ventricular refractory period (VRP)
  3. Atrioventricular interval (AVI)
  4. Post Atrial Ventricular Blanking (PAVB)
81
Q

What are the 3 fundamental timing cycles associated with the atrial channel in DDD mode?

A
  1. Atrial escape interval (AEI)
  2. Postventricular atrial refractory period (PVARP)
  3. Total atrial refractory period (TARP)
82
Q

The following statement best describes what timing cycle?

‘The longest interval possible following a sensed or paced ventricular event and the following ventricular paced event without and intervening sensed events’.

A

Lower rate interval.

83
Q

The following statement best describes what timing cycle?

‘Initiated by a ventricular event during which a new LRI cannot be initiated’.

A

Ventricular Refractory Period (VRP).

84
Q

The following statement best describes what timing cycle?

‘Interval between an atrial event and a scheduled V paced event’.

A

Atrioventricular interval (AVI).

85
Q

The following statement best describes what timing cycle?

‘Interval between a ventricular event and the following atrial paced event’.

A

Atrial escape interval (AEI).

Most manufacturers use V-Based timing, which ensures the AEI is always a constant interval.

86
Q

The following statement best describes what timing cycle?

‘Interval following a ventricular event during which an atrial event cannot initiate the Atrioventricular interval (AVI)’

A

Postventricular atrial refractory period (PVARP).

Avoids inappropriate atrial sensing of ventricular events and also retrograde P-waves.

87
Q

The following statement best describes what timing cycle.

‘Is a derived value from AVI + PVARP’.

A

Total atrial refractory period (TARP).

A p-wave which falls within the TARP will not be tracked, thus functional 2:1 block can occur.

88
Q

The following statement best describes what timing cycle?

‘Interval is initiated by an Atrial Paced event and disables all sensing of the ventricular channel’

A

Post Atrial Ventricular Blanking (PAVB).

Prevents crosstalk of ventricular channel sensing atrial events and respondent pacing inhibition. Programmable, short duration ~10-50ms.

89
Q

What is the purpose of ventricular safety pacing?

A

To prevent ventricular pacing inhibition respondent to crosstalk.

While also ensuring pacing in a non-vulnerable section of the cardiac cycle.

90
Q

Yes / No

Does VSP prevent crosstalk?

A

No.

It only prevents the deleterious consequences of crosstalk. E.g. V-pacing inhibition.

91
Q

What is the typical AV delay seen during VSP?

A

100-110ms.

Far shorter than a normal AV delay!

92
Q

Why is the VSP stimulus delivered in a far shorter time than a normal physiologic AV delay?

A

To pace within a refractory period of the cardiac cycle.

This prevents pacing on the vulnerable T-wave if there’s a competitive instrinsic impulse present.

93
Q

True / False

The VSP window is initiated by a Ventricular event.

A

False.

The VSP window is typically started by an atrial event.

94
Q

Yes / No

If an atrial event falls within the PVAB, will it be detected and a VSP delivered?

A

No.

Although both are started at the same time, the PVAB must expire before detection in the VSP window can occur and a respondent VSP be delivered.

95
Q

Yes / No

PAVB programmed to 60ms / VSP programmed to 100ms

Would a ventricular detection and subsequent VSP occur 70ms after the initial atrial event?

A

Yes.

The PAVB window has expired and the VSP window is still active, thus ventricular events will be detected and a VSP delivered.

96
Q

Yes / No

PAVB programmed to 60ms / VSP programmed to 100ms

Would a ventricular detection and subsequent VSP occur 110ms after the initial atrial event?

A

No.

Although the ventricular even will be counted, the VSP window expired 10ms prior - thus no VSP delivered.

97
Q

True / False

PVARP should never be programmed shorter than VRP.

A

True.

Short PVARP programming increases risk of far field atrial sensing of the terminal portion of the QRS complex.

98
Q

Give the equation to calculate 2:1 block rate.

A

60,000 / TARP (Total Atrial Refractory Period)

99
Q

True / False

Wenckebach upper rate response will only occur if the URI is longer than the TARP.

A

True.

If the Upper Rate Interval is equal to the Total Atrial Refractory Period the upper rate response will instantly be 2:1 block.

100
Q

If the URI is equal to the TARP, what will my upper rate behaviour be?

A

2:1 block.

No upper rate wenckebach behaviour will occur.

101
Q

True / False

A shorter TARP will equate to a lower 2:1 block rate.

A

False.

A shorter TARP interval will result in a higher 2:1 block rate.

102
Q

Yes / No

If a patients spontaneous atrial interval exceeds the TARP but is shorter than the URI, will Wenckebach behaviour be permitted?

A

Yes.

103
Q

True / False

Sensed AVI is typically longer than Paced AVI.

A

False.

sAVI is shorter than the pAVI as it is assumed the device only detects the p-wave after a portion of the p-wave is already completed. Typically sAVI is shorter by 30-50msec.

104
Q

True / False

Rate adaptive AVI aims to mimic the physiological lengthening of the AVI during exercise.

A

False.

Rate adaptive AVI will shorten, not lengthen, the AVI in response to exercise. Shorter intervals = Faster rates.

105
Q

True / False

Pacemaker mediated tachycardia or Endless loop tachycardia typically occurs at the URI.

A

True.

106
Q

Which 3 programmable parameters can be changed to test for likelihood of PMT?

A
  1. Program lowest possible Atrial Output
  2. Program shortest possible PVARP
  3. Program highest possible Atrial Sensitivity
107
Q

What are the 4 predisposing factors for RNRVAS?

A
  1. Long VA conduction time
  2. Long PVARP
  3. Short LRI
  4. Long AVI
108
Q

True / False

DVI results in competitive atrial pacing, shown to lower risk of Atrial Fibrillation.

A

False.

Competitive Atrial pacing has been shown to increase risk of Atrial Fibrillation.

109
Q

True / False

DDI = Non Triggered / Tracking mode.

A

True.

Both chambers are sensed, however an Atrial sensed event will not start an AVI and a respondent V-pace. This prevents tracking of Atrial Arrhythmia.

110
Q

What dual chamber mode does not have timing cycles of PAVBP or VSP?

A

VDD.

As there is no risk of AV crosstalk due to lack of Atrial output.

111
Q

True / False

A VDD system is suitable for patients with SND, SSS or Chronotropic incompetence.

A

False.

Dedicated atrial lead is required. These patients will require atrial stimulus which a single pass lead does not provide.

112
Q

True / False

With Atrial Based timing, the A-A is constant and equal to the LRI.

A

True.

A-A = As-Ap & Ap-Ap

113
Q

True / False

With Atrial Based timing, the AEI is constant in order to maintain a constant A-A interval.

A

False.

The AEI varies to maintain a constant A-A interval. AEI = Vp-Ap & Vs-AP

114
Q

Which type of lower rate timing is best described by the following statement?

‘The AEI remains constant at all times’.

A

Ventricular based timing.

AEI = Vp-Ap & Vs-AP.

115
Q

Which type of lower rate timing is best described by the following statement?

‘Can cause AV delays longer than the programmed value’.

A

Ventricular based timing.

116
Q

Yes / No

If a signal falls within the Blanking or Refractory period, will it initiate an LRI or AVI?

A

No.

Blanking is blind to all signals. Refractory counts signals but still won’t initiate LRI or AVI.

117
Q

In lieu of an atrial flutter algorithm, what programming changes can be made to prevent 2:1 lock-in.

A

Program AVI + PVAB shorter than Atrial Cycle length.

118
Q

During Automatic Mode Switch - in what mode does a DR device typically function?

A

DDI or DDIR.

This prevents tracking of the arrhythmia, which would lead to overpacing the ventricle.

119
Q

Which timing cycle is best described below?

‘Longer at lower rates to protect against PMT. Shortens at higher rates to elevate the 2:1 block point’

A

Rate Adaptive PVARP.

120
Q

Which timing cycle is best described below?

‘Prevents atrial stimulus when atrial sensed event is detected within the PVARP’.

A

NCAP - Non Competitive Atrial Pacing.

NCAP overrides the AV delay, which may shorten in response.

121
Q

What is the purpose of NCAP?

A

To prevent an Atrial Stimulus being delivered in the vulnerable period of the atrium.

Such a stimulus at this time may invoke an atrial arrhythmia.

122
Q

What is the purpose of AMS (Automatic Mode Switch).

A

To prevent ventricular tracking of rapid atrial rates.

Most Dual Chamber systems will switch to DDI or DDIR mode.

123
Q

True / False

The mode VOO is now obsolete and should never be programmed for fear of R on T pacing into VF.

A

False.

VOO is useful during testing, MRI and Electrocautery surgical procedures as a way to inhibit response to external noise. Outside of MI, Ischemia or electrolyte imbalances it is extremely rare for VOO pacing to induce VF.

124
Q

VVT is a rarely used timing cycle - list 1 instance where its useful today.

A

To determine the exact moment when a device senses an event.

VVT is a triggered mode - thus the exact moment a device senses an event can be determined by observing when the respondent output is delivered.

125
Q

True / False

AAI is functionally the same as VVI except it paces and senses in the Atrium.

A

True.

126
Q

DDD pacemaker programmed as follows will exhbit what when the atrial rate = 128bpm?

‘LRL 50ppm, MTR 125ppm, AVD 175ms (reduced by 25ms above 100bpm), A refractory of 300ms’

  1. 1:1 conduction
  2. 2:1 conduction
  3. 3:1 conduction
  4. Mobitz II
  5. Pseudo Wenckebach
A

5 - Pseudo Wenckeback.

TARP = AVD (175-25 = 150ms) + PVARP (300ms) / 60,000 = 133ppm.

Atrial rates between 125 and 133 will show pseudo wenckebach behaviour. Above 133ppm device will exhibit 2:1 block.

127
Q

DDD pacemaker programmed as follows will exhbit what when the atrial rate = 128bpm?

‘LRL 50ppm, MTR 125ppm, AVD 175ms (reduced by 25ms above 100bpm), A refractory of 300ms’

  1. CHB
  2. Mobitz II
  3. 3:1 block
  4. 4:3 block
A

4 - 4:3 block.

As the atrial rate is just above the MTR most beats will be conducted, only the odd few will be dropped by falling within the TARP. Thus 4:3 is most likely - all other forms of block are too agressive.

128
Q

At sensor indicated rates higher than the max track rate, which is most likely in a CHB patient?

  1. 1:1
  2. Mobitz I
  3. Mobitz II
  4. 2:1
  5. 3:1
A

1 - 1:1.

The following describes normal function. The device effectively has complete control of the heartbeat in both chambers thus will sequentially pace A and V. Upper rate behaviour may arise when the intrinsic rhythm exceeds the programmed sensor / max track rate.

129
Q

Which of the following is not a programmable timing cycle in both VVI and DDD pacemakers?

  1. Output
  2. AV Delay
  3. Refractory periods
  4. Sensitivity
A

2 - AV Delay.

*VVI generators sense/pace the ventricle only, thus cannot initiate AV intervals.8

130
Q

Yes / No

Device is programmed VVI 60 - however you observe a rate of 50ppm. Is this an example of ventricular based timing?

A

No

Venticular based timing allows rates above the LRL but never below

IBHRE® (24 decks)

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