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7.5.4.1 Preparing for an RV pacing threshold search
Every day at 1:00 AM, the device prepares to schedule Capture Management operations
in the available chambers. RVCM is scheduled when no other pending features have a
higher priority. RVCM starts with a device check to determine if any parameter settings
would prevent a search. For example, the permanent programmed values of RV Amplitude
or RV Pulse Width cannot exceed limits of 5 V or 1 ms. If the device check is unsuccessful,
no RV pacing threshold searches are scheduled until the following day.
The device also evaluates whether the patient’s current rhythm is stable enough to support
a pacing threshold search. If the stability check is successful, the pacing threshold search
is initiated. If stability checks are unsuccessful, the device automatically continues to
schedule searches at 30 min intervals until the end of the day. If the device is unable to
complete a stability check successfully during one day, the process is repeated on the
following day.
If the programmed pacing mode is an MVP mode and the stability check is successful, the
device switches to a temporary mode for the duration of the pacing threshold search. It
switches from AAIR<=>DDDR mode to DDDR mode or from AAI<=>DDD mode to DDD
mode.
7.5.4.2 Searching for and determining the RV pacing threshold
The device conducts a pacing threshold search to determine the RV pacing amplitude
threshold at a fixed pulse width of 0.4 ms. RVCM varies the amplitude of test paces to find
the lowest amplitude that consistently captures the right ventricular myocardium. The device
evaluates capture by detecting the evoked response signal following each test pace.
If the right ventricle responds to a test pace, the result is “Capture”. If no response is
detected, the result is “Loss of capture”. The result of a test pace is ignored if the device
cannot determine whether the test pace captures the myocardium. In this case, testing may
continue with additional test paces at the same test amplitude. If there are too many
inconclusive results, the device stops the pacing threshold search and retries it at the next
scheduled period (see Section 7.5.4.4).
A pacing threshold search begins at a test amplitude that is 0.125 V lower than the last
measured threshold. If there was no previous search, a new search begins at 0.75 V. The
device continues to decrease the test amplitude in steps of 0.125 V until a test amplitude is
classified as being below the pacing threshold. The device then increases the test amplitude
in steps of 0.125 V until the same test amplitude is classified as being above the pacing
threshold 3 times in succession. This test amplitude is the RV pacing threshold.
Medtronic
PROTECTA™ XT DR D314DRG
Clinician Manual
245
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