Timing Cycles - SQRLsqrl.mcmaster.ca/_SQRLDocuments/Timing_Cycles.pdf · Timing cycles Objectives...
Transcript of Timing Cycles - SQRLsqrl.mcmaster.ca/_SQRLDocuments/Timing_Cycles.pdf · Timing cycles Objectives...
![Page 1: Timing Cycles - SQRLsqrl.mcmaster.ca/_SQRLDocuments/Timing_Cycles.pdf · Timing cycles Objectives Upon completion of this program the participant will be able to: • Identify the](https://reader035.fdocuments.in/reader035/viewer/2022070713/5ed30270f83e157da72a02e1/html5/thumbnails/1.jpg)
Timing Cycles
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Timing cycles
Objectives
Upon completion of this program the participant will be able to:
• Identify the basic timing cycles of a single and dual chamber pacemaker.
• Describe the characteristics of upper rate pacing in the DDD pacing mode.
• Describe how timing cycles are affected by rate adaptive pacing.
• Explain PMT and name one treatment option.
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Outline
• Single- and Dual-Chamber Timing• Describe the 4 scenarios of dual chamber pacing
• Upper Rate Pacing Characteristics
• Timing & Rate-Adaptive Pacing
• Pacemaker Mediated Tachycardia (PMT)
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Pacemakers have two basic functions
• Pace
• Sense intrinsic rhythm and Inhibit
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Timing cycles
• Single Chamber
• Dual Chamber
• Adaptive Rate
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Single Chamber Timing
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Single chamber
Timing Intervals 60 ppm
V-V Interval
Interval (ms) = 60,000 / rate (ppm)
60,000 / 60 ppm = 1000 ms
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Single chamber
VVI
Vp Vp VpVs
V Ref
V-V
AutomaticInterval
Escape Interval
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Terminology
Refractory Period:In pacing, a programmable parameter that controls the length of time following a paced or sensed beat, during which the pacemaker’s sensing circuit does not respond to sensed events.
• PVARP=Post Ventricular Atrial Refractory Period=atrial refractory period
• VRP=Ventricular Refractory Period
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Single chamber
AAI
AsAp PVC Ap Ap
A RefA-A
AutomaticInterval
Escape Interval
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Dual-Chamber Timing
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Timing intervals
Dual-Chamber (DDD)
Ap Vp Ap Vp Ap Vp
AVVA
V-V
V-V = Lower Rate Limit
VA = Atrial Escape Interval
AV = AV DelayV-V = VA + AV
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Timing intervals
Example
VA = V-V - AV
V-V = VA + AV
Lower Rate = 60 ppm V-V = 1000 msAV Delay = 200 ms
VA = 1000 ms - 200 ms = 800 ms
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AV sequential pacing
A-Pace / V-Pace
Ap Vp Ap Vp Ap Vp
AV Delay
VA Interval
LRL
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Complete inhibition
A-Sense / V-Sense
As VsAs VsAs Vs
AV Delay
VA Interval
LRL
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Atrial pacing with conduction
A-Pace / V-Sense
Ap Vs Ap Vs Ap Vs
AV Delay
VA Interval
LRL
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P-synchronous pacing
A-Sense / V-Pace
As Vp As Vp As Vp
AV Delay
VA Interval
MTR
LRL
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Timing intervals
Dual Chamber (DDD)
Ap Vp Ap VpAp Vp
AV DelayV-Blanking
VA Interval
LRL
A-BlankingPVARP
V RefURL
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Terminology
Blanking Period• The interval of time following a paced output
during which the pacemaker’s sense amplifiers are disabled
• This timing parameter prevents cross chamber sensing
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Upper rate operation
PVARP AND TARP • TARP = AV + PVARP
• 2:1 Rate = 60,000 / TARP
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Upper rate operation
Pacemaker Wenckebach
As Vp
PVARP
TARP
AV
PVARP
TARP
Maximum Tracking Rate
As Vp
WAV
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Upper rate operation
Wenckebach (4:3 Block)
As Vp As Vp AR As Vp As Vp As VpAs Vp
TARP
AV Delay
VA Interval
MTR
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Upper rate operation
2:1 Block
AVPVARP
TARP
AV
TARP
Maximum Tracking Rate
PVARP
As Vp As VpAR
2:1 Rate = 60,000 / TARP
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Upper rate operation
2:1 Block
ARAs Vp AR As Vp As Vp As VpARAR
TARP
AV Delay
VA Interval
MTR
LRL
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Upper rate operation
Upper rate behavior is determined by TARP and MTR
2:1 BlockTARP
WenckebachSinusRate
MTR1:1
LRL
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Upper rate operation
2:1 Block > URL
MTR = 140 ppmAV = 100 msPVARP = 300 msTARP = 400 ms
1:1
Wenckebach
2:1
Sinus Rate
TARP
MTR2:1 Block Point
= 60,000/TARP
= 60,000/400=150 bpm
LRL
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Upper rate operation
2:1 Block < URL
TARP
1:1
2:1
MTR
Sinus Rate
LRL
MTR = 140 ppmAV = 200 msPVARP = 300 msTARP = 500 ms
2:1 Block Point= 60,000/TARP= 60,000/500= 120 bpm
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Adaptive Rate
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Rate responsiveness/adaptive-rate pacing
In Rate Responsive pacing (modes ending with “R”), sensor(s) in pacemaker are used to detect changes in physiologic needs and increase the pacing rate accordingly.
• The sensor
• Sensors are used to detect changes in metabolic demand
• “Sensors” sense motion (piezoelectrode crystal or accelerometer) or use a physiologic indicator, i.e., minute ventilation
• The algorithm
• With-in the software of the pacemaker
• Uses the input from the sensor to determine the appropriate paced heart rate for the activity.
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VVIR timing
Sensor-Determined Rate Controls V-V Interval
LRL
VRef
MSR
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VVIR timing
Shortened Sensing Windows at High Rates
SensingWindow
VRef
Sensing WindowVRef
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DDDR timing
Sensor Rate Controls VA Interval
VA Interval
Sensor Pacing110 ppm
VA Interval
Lower Rate60 ppm
AV PVARP AV PVARPAV PVARP
AV PVARP AV PVARP AV PVARPAV PVARP
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DDDR timing
Sensor-Controlled Pacing Not Limited By PVARP
Sensor Pacing 150 ppm
AV PVARP AV PVARP
AV PVARP AV PVARP
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DDDR: Sinus or sensor?
Follow the Faster Input
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Pacemaker mediated tachycardia
Rapid ventricular pacing secondary to retrograde conduction
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Retrograde conduction
Conduction of an electricalimpulse from the ventriclesto the atria through the heart’s conduction system
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Conditions required for PMT
• Loss of A-V Synchrony
• Intact V-A Conduction
• V-A Conduction Time > programmed PVARP
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Initiators of retrograde conduction
Retrograde conduction is caused by any loss of AV synchrony, such as the following:
• PVC (Retrograde conduction)
• Oversensed P wave
• Undersensed P wave
• Loss of Atrial Capture
• EMI
• Magnet Application or Removal
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PMT prevention
• Program longer PVARP• PVARP after PVC
• Use PMT prevention scheme
• Need to make a programming change, or PMT will recur
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Summary
• List and explain the four different scenarios that may be observed with dual-chamber pacing.
• Explain upper rate pacing characteristics of Wenckebach and 2:1 Block.
• Describe the mechanism and corrective actions for Pacemaker Mediated Tachycardia (PMT).
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Timing Cycles