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At the beginning of a pacing threshold search, the device selects a method for evaluating
atrial capture, based on the patient’s current sinus rhythm. The Atrial Chamber Reset (ACR)
method is used when the patient has a stable sinus rhythm (a sensed atrial rate that is not
faster than 87 bpm). The AV Conduction (AVC) method is used when stable 1:1 AV
conduction is observed with atrial pacing. These methods evaluate capture differently, but
threshold determination is the same.
Atrial Chamber Reset (ACR) method – In the ACR method, each test pace is preceded
by 3 support cycles and followed by 2 extra support cycles. The 3 support cycles monitor
AS-AS intervals to ensure that the patient’s rhythm is stable before the test pace is delivered.
The 2 extra support cycles provide time after the test pace for the atrial rhythm to stabilize.
ACR evaluates capture based on the response of the intrinsic rhythm to the atrial test pace.
“Loss of capture” is characterized by an atrial event that follows the test pace but occurs
within the atrial refractory period. As shown in Figure 92, this event is indicated by an AR
marker.
Figure 92. Atrial Chamber Reset test method
AS
AS
AS
AS
AS
AS
AS
AS
AS
Test
AP
AS
VS
or
VP
Test
AP
Capture
Loss of Capture
VS
or
VP
VS
or
VP
VS
or
VP
VS
or
VP
VS
or
VP
VS
or
VP
VS
or
VP
VS
or
VP
VS
or
VP
VS
or
VP
VS
or
VP
AR
AV Conduction (AVC) method – In the AVC method, each test pace is preceded by
3 support cycles and followed by a backup pace. During this pacing sequence, overdrive
pacing is accomplished with a faster atrial pacing rate and a lengthened AV interval. These
changes result in a stable AP-VS rhythm with a shorter AP-AP interval. The AP-AP interval
before the test pace is even shorter than the intervals that precede it. The backup pace has
the programmed amplitude and a 1.0 ms pulse width.
The AVC method evaluates capture by observing the conducted ventricular response to an
atrial test pace. The intervals containing the test pace and the support cycle preceding it
are shown in Figure 93. If the test pace captures the atrium, the next VS event results from
AV conduction of the test pace. If no capture occurs, the next VS event results from AV
conduction of the backup pace, which is delivered 70 ms after the test pace.
Medtronic
PROTECTA™ XT DR D314DRG
242
Clinician Manual
Содержание PROTECTA XT DR D314DRG
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