Flashcards in CRT Timing cycles Deck (16):
What two conditions show good CRT response
Wide QRS (>150ms QRSd)
Left Bundle Branch Block
Do most contemporary CRT devices use RV or LV sensing
RV sensing normally
Which two PVAB cycles exist in CRT
PAVBRV = similar to dual chamber devices)
PAVBLV = To prevent inappropriate inhibition of LV pacing due to far-field atrial pace oversensing.
LV-sensed event following an LV event (paced or sensed) will not affect or reset timing cycles
Why is LVRP important
Prevents oversensing of QRS or T waves following a ventricular event (paced or sensed), preventing inappropriate loss of CRT (seen more commonly with unipolar LV leads)
Long LVRP shortens the LV-sensing window that could affect timing cycles
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.
the device will still deliver RB pacing.
Why is LVPP important
Maximise CRT delivery while reducing the risk of inducing a ventricular tachyarrhythmia.
Programming a long LVPP will reduce the MTR and inhibit biventricular pacing at higher rates.
Define VV delay / LV Offset
Programming of different timing between the RV- and LV-paced events
Positive (RV first)
Negative (LV first)
Zero (simultaneous RV/LV)
5 occasions which cause loss of BiV
1. Rapid atrial or sinus rates above MTR
2. Short and dynamic PR intervals
4. Frequent PVCs
5. AF with ventricular response > LRL +/- SIR
Define negative hysteresis
Shortens AV delay to promote pacing
Define positive hysteresis
Extends AV delay to promote intrinsic
Define ventricular sensed response // BiV trigger
LV pacing immediately after intrinsic conduction / sensed event.
MUST OCCUR BETWEEN LRL AND MTR
BiV pacing will cease above MTR (TARP) TRUE/FALSE
Once inhibited through tarp - what two components dictate when BiV pacing will return
PVARP + PR interval
In CRT systems what algorithm could further reduce BiV pacing due to PVC's
PVC response (as there is PVARP extension)