User Manual Part 2

PACING THERAPIES
REFRACTORY
5-53
For heart failure patients with intact AV conduction, a long intrinsic intracardiac
AV interval and a long programmed PVARP can cause the loss of atrial tracking
below the MTR, resulting in the loss of biventricular stimulation (CRT). If an
atrial event, such as a PAC or a P-wave that immediately follows a PVC, falls
into PVARP, it will not b e tracked. This allows for AV cond uc tio n of a n intrinsic
ventricular event, which restarts PVARP. Unless the next atrial event occurs
outside of PVARP, it too will not be tracked, and another intrinsic AV-conducted
ventricular event will occur, again restarting PVARP. This pattern can continue
until an atrial event is finally sensed outside of PVARP (Figure 5-21 on page
5-53).
AV PVARP AV PVARP PR PVARP PR PVARP
PVARP PR PVARP
As Vp As Vp (As)PVC Vs (As) Vs (As) Vs
Figure 5-21. Atrial sensed event in PVA RP
If you believe a loss of atrial tracking below the MTR is occurring, program
Tracking Preference to On. If the loss of CRT below MTR continues to be
a problem or if Tracking Preference is not used, consider reprogramming a
shorter PVARP.
For heart failure patients with second- and third-degree AV block, programming
long a tria l refractory periods in combination with certain AV Delay periods can
cause 2:1 block to occur abruptly at the programmed MTR.
In DDD(R) and VDD(R) pacing modes, the pulse generator may detect
retrograde conduction in the atrium, causing triggered ventricular pacing rates
as high as the MTR (i.e., PMT). Retrograde conduction times may vary over
a patient’s lifetime as a function of changing autonomic tone. If testing does
not reveal retrograde conduction at implantation, it may still occur at a later
time. This problem can usually be avoided by increasing the atria l refra ctory
period to a value that exceeds the retrogra de con duction time. In controlling
the pulse generator ’s response to retrograde conduction, it may also be useful
to program the following:
•PVARPafterPVC
• PMT Termination
• Rate Smo othing
- DRAFT -