User Manual Part 2

PACING THERAPIES
VENTRICULAR TACHY SENSING INTERACTIONS
5-63
• LRL = 75 ppm (800 ms)
•VRP=500ms
• VT Zone = 150 bpm (400 ms)
In this scenario, the pulse generator is VVI pacing at LRL (800 ms). A 500 ms
VRP follows each ventricular pace. VT beats that occur during VRP are ignored
for purposes of pac emaker timing and ven tricular tachy detectio n/ th erapy. If
a stable VT of 400 ms starts simultaneously with a ventricular pace, the VT
will not be detected because every beat will occur during the 500 ms VRP,
either concurrent with a ventricular pace or 400 ms after a pace (Figure 5-29 on
page 5-63).
NOTE: It is not required for the VT to start concurrently with a pace for
undersensing to occ ur. In this example, all pacin g will be inhibite d and tac hy
detection will subsequently occur, as soon as a single VT beat is detected.
VP VP VP VP
(VT) (VT) (VT) (VT) (VT) (VT) (VT)
VRP = 500 ms
400 ms
LRL = 800 ms
Figure 5-29. Ventricular undersensing due to VRP
When the programming interaction described in this scenario is present, a
message will describe the interaction of VRP with LRL. In rate-respon sive or
tracking modes (e.g., DDDR), similar messages may describe the interaction
of VRP with MTR, MSR, or MPR. Along with each message, the pertinent
programmable parameters are displayed to a ssist you in resolving the
interaction. Programming Dynamic V RP can be useful in resolving these
types of interactions.
Example 2: Ventricular Undersensing Due To V-Blank After A-Pace
Certain programmed combinations of dual-chamber pacing parameters may
also interfere with ventricular tachy detection. When dual-chamber pacing
occurs, pulse generator refractory periods are initiated by both atrial and
ventricular paces. Th e ventricula r refractory period followin g a ventricular pace
is controlled by the VRP parameter; the ventricular refractory period following
an atrial pace is controlled by the V-Blank After A-Pace parameter.
- DRAFT -