CRM 6 - TARP and PVARP and Functions Flashcards
What does PVARP stand for?
Post Ventricular Atrial Refractory Period
What does TARP stand for?
Total Atrial Refractory Period
What is the VA interval?
LRL - AV delay
VA interval is not programmable
Goes from beginning of V to beginning of following P
What 2 things are generated after paced V?
-Lower rate limit
-Maximum tracking rate
What is decrement?
-As rate gets faster, PR interval gets longer, then blocks (Wenckebach)
-Protective mechanism so beats don’t get through to ventricles
What 2 things can normal conduction system modulate?
-Sinus rate
-PR interval (AV node - decremental and refractory properties)
AV node decrement with block
-Pacing the atrium
-Completely normal at faster rates
-Seen at slower rates in diseased AV nodes
What happens during PVARP?
-Refractory period where p waves are sensed but not acted on
What are the 3 types of tracking of atrial sensed beats (p waves)?
1:1 tracking
-A sense followed by sensed AV delay and pacing of RV
-Occurs up to MTR
Pacemaker Wenckebach
-A sense followed by extended AV delay until there is a dropped beat
-Occurs between MTR and PVARP
2:1 block
-Every other intrinsic P wave not tracked with a V pace as they fall into refractory blanking period (PVARP)
What happens to p waves that fall into PVARP?
No AV delay
Why was PVARP invented?
-To stop pacemaker mediated tachycardia
-Avoid retrograde P waves, farfield R waves, atrial ectopics starting an AV interval
What is the TARP?
-The whole atrial refractory period
-AV delay + PVARP
How does pacemaker mediated tachycardia occur?
-Ventricle is paced
-Atrium is not refractory and AV node conducts retrograde
-Atrium contracts, generates AV delay, V paces
-PVARP covers retrograde p wave
How can you prevent PMTs?
-Extend the PVARP so retrograde P wave is blanked
What happens to P wave that falls into MTR?
-Wait until after MTR and extend AV delay
What happens to P wave that falls into TARP
-Does not generate AV delay
What rhythm does P wave falling in TARP create?
-2:1 block
What rhythm does P wave falling into MTR create?
-Wenckebach
How to calculate atrial rate behaviour?
60000/interval
-2:1 block rate for TARP interval
-Wenckeback block rate for MTR interval
-1:1, 2:1, Wenckebach
What is chronotropic incompetence?
-the inability to increase the heart rate adequately during exercise to match CO to metabolic demands
What are the types of sensors in rate response?
Non metabolic:
-accelerometer - postural changes and body movements
-piezoelectric crystals - muscular pressure waves converted to electrical signal
Metabolic:
-QT intrval
-Minute ventilation
-Peak endocardial acceleration
How are sensors used?
Dual sensor
-one metabolic, one non
-sensor ‘blending’ and ‘cross-checking’
Considerations when optimising
-IHD?
-Inactive patients
-Lung disease
-Cello players
What happens when magnet is put over pacemaker?
-Asynchronous pacing
-Paces at a faster magnet rate
-Shortens A-V interval
-Confirm battery status
-Identify mode
-Terminate PMT
DDD -> DDO
What will magnet do in ICD?
-Temporarily stop therapy
What is ERI battery status?
ERI - Elective Replacement Indicator
Rhythms after magnet held to pacemaker. What are they?
AAI
VVI
DDO
-1 or 2 leads. Single or dual programmed to VVI/AAI?
Pacemaker and ICD response to noise
Pacemaker:
-Switch to asyncronous pacing AOO, VOO, DOO
ICD:
-Categorise as VF
-Noise discrimination algorithm differentiates RV lead noise from VF
-Compares farfield EGM signal to near-field sensing
What is sleep function?
-Most common in VVI modes
-Reduce pacing rate during sleep for comfort/battery life
-Suspends LRL and paces at programmed rate during programmed hours
What is hysteresis?
-Allows more intrinsic rhythm before intervention
-Saves battery life
-Extend interval, inhibit pacing, no activity, pace at end of hysteresis interval
What is rate adaptive AV delay?
-Mimics PR shortening on exercise
-Helps to prevent 2:1 block on exertion by having a longer atrial sensing window
-Automatic/programmable
What is automatic PVARP?
-Protects against PMT by increasing PVARP at lower tracking rates
Provides higher 2:1 block rate by shortening PVARP and AV delay at higher tracking rates
What is automatic sensing?
-Varies sensing
-Safety margin so that there is not under sensing
-Auto adjusts to 50% of measured wave
What is automatic capture?
-Maintains safe pacing during acute, sub-acute and chronic phase by varying threshold
-Reduces hospital visits
-Adjusts to 2x pulse amplitude or 3x pulse width after taking a threshold
How how lead technology tried to reduce a high threshold during the acute stage?
-Steroid-tipped lead
What causes varying thresholds?
-Activity
-Posture
-Time of day
-Co-morbidities
-Drugs - flecainide
-Disease progression
-Lead position
How does autocapture work?
-Decreases AV delay to force pacing
-Monitors each beat for evoked response
-Back-up safety pulse if there is no capture
