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7 Configuring pacing therapies
7.1 Sensing intrinsic cardiac activity
The device must sense the occurrence of intrinsic cardiac events while avoiding
oversensing so that it can deliver therapies appropriately. Effective sensing can reduce the
effects of long depolarizations after paced events, oversensing the same event,
cross-chamber sensing, sensing far-field R-waves, sensing T-waves, noise, and
interference.
7.1.1 System solution: sensing
Effective sensing is essential for the safe and effective use of the device. The device senses
in both the atrium and right ventricle using the sensing electrodes of the leads implanted in
those chambers. You can adjust the sensitivity to intracardiac signals. Each sensitivity
setting represents a threshold value that defines the minimum electrical amplitude
recognized by the device as a sensed event in the atrium or right ventricle.
Note: Selecting a higher value for the sensing threshold reduces the sensitivity to lower
amplitude signals.
Programmable blanking periods and refractory periods help to screen out extraneous
sensing or to prevent the device from responding to it. Blanking periods follow pacing
pulses, sensed events, and shocks. Sensing is inhibited during blanking periods. Refractory
periods follow pacing pulses and sensed events. The device is able to sense events that
occur during refractory periods, but it marks them as refractory events. Refractory events
generally have no effect on the timing of subsequent pacing events, but they are used by
the tachyarrhythmia detection features.
The sensing polarity is bipolar in the atrium and either bipolar or tip-to-coil in the right
ventricle. The device can use either a true bipolar lead or an integrated bipolar lead for right
ventricular sensing. With a true bipolar lead, right ventricular sensing can occur between
the RV tip and RV ring electrodes (bipolar), or between the RV tip and RV coil electrodes
(see Figure 63). The sensing vector is programmable via the RV Sense Polarity parameter.
With an integrated bipolar lead, right ventricular sensing occurs between the RV tip and RV
coil electrodes. In this case, the RV Sense Polarity parameter has no effect on the sensing
vector. The sensing and blanking functions are identical in these lead configurations.
Medtronic
PROTECTA™ XT DR D314DRG
Clinician Manual
201
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