Pacing |
Capture Management Operation
Automatic Capture Management will periodically test ventricular thresholds, and reprogram ventricular outputs based on a programmable amplitude safety margin and minimum voltage. The pacemaker will automatically perform a pacing threshold search at a programmable interval (15 min – 42 days, once /day at rest is nominal.)
Pacing Threshold Search
The search begins by decrementing the amplitude at a 0.4 ms pulse width (test pace) while monitoring for an evoked response to pacing (indicating capture). Once the evoked response is no longer detected, the amplitude is increased and evoked response sensing is confirmed. This voltage value, rheobase, is doubled and the threshold search continues by decrementing pulse width in a similar fashion, while monitoring for the evoked response. When the evoked response is again not detected, the pulse width is increased and evoked response sensing is confirmed. This value is chronaxie.
Strength-Duration Curve and Adapting Outputs
A threshold (strength-duration) curve is drawn between chronaxie and rheobase, and an amplitude safety margin curve (typically 2X) is drawn at 0.4 ms pulse width. The ventricular outputs are adapted based on this safety margin curve and a clinician selected minimum amplitude.
Safety
During the pacing threshold search, each test pace is followed by a backup bipolar safety pace (110 ms interval) to prevent the patient from actual loss of capture. Each test pace is delivered at a short AV interval (to minimize fusion) and separated by at least three support events (pacing or sensing) at programmed outputs. Kappa 900 tests the ventricular amplitude threshold at 0.4 ms pulse width to minimize evoked response undersensing (false detection of loss of capture.)
Adaptive Ventricular Sensing during the search
If the amplitude search results in a rheobase > 2.5 V, Kappa 900 is able to automatically retest in unipolar sensing, also designed to minimize evoked response undersensing.
Additional Information |
©Medtronic, Inc. 2008 • Contact Medtronic • Privacy Statement • Terms of Use • Site Map