Medtronic PROTECTA XT DR D314DRG, Clinician Manual

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7.2.7 Evaluation of pacing therapies
To verify that the device is pacing appropriately, review the Percentage of Time (% of Time)
data on the Quick Look II screen.
Select Data icon
⇒ Quick Look II
Percentage of Time (% of Time) – For single chamber modes, the % of Time section
reports the patient’s pacing and sensing as the percentage of the total time during the
reporting period. For dual chamber modes, the % of Time section reports the percentage
for each of the possible AV sequence combinations (AS-VS, AS-VP, AP-VS, AP-VP).
For detailed information about viewing and interpreting all of the information available from
the Quick Look II screen, see Section 6.2, “Viewing a summary of recently stored data”,
page 129.
7.2.8 Tracking rapid atrial rates
When the device is operating in the DDDR or DDD mode, the device can track atrial rhythms
only up to a certain rate. Limitations on atrial tracking include the 2:1 block rate and the
programmed Upper Tracking Rate as described in Section 7.2.8.1.
7.2.8.1 2:1 block
2:1 block occurs when the intrinsic atrial interval is so short that every other atrial sensed
event occurs during PVARP (see Figure 74). These atrial events do not start an SAV interval
and therefore do not result in ventricular paced events. Because only every other atrial
sensed event is tracked, the ventricular pacing rate becomes one-half of the atrial rate. 2:1
block can be a desirable means to prevent rapid ventricular pacing rates at the onset of
AT/AF. However, 2:1 block during exertion or exercise is normally undesirable because the
ventricular pacing rate can suddenly drop to one-half of the atrial rate. The sudden reduction
in cardiac output can result in patient symptoms.
Medtronic PROTECTA™ XT DR D314DRG
220 Clinician Manual