This attachment accompanies Medtronic’s physician letter dated October 15, 2007 and provides greater detail on our recommendations for the ongoing management of patients with Sprint Fidelis leads.
Based on our review of the available data, there does not appear to be a significant benefit to more frequent follow-up.
The effectiveness of routine monitoring or lead impedance alerts for identifying a lead integrity problem before an inappropriate shock occurs may be enhanced when VF initial Number of Intervals to Detect (NID) are set to nominal values of 18/24 or longer (since longer NIDs reduce the risk of inappropriate detection of short bursts of oversensing). Redetect NID should be set to 12/16. The use of Medtronic CareLink® to facilitate remote access to the device information is suggested.
In the event of a suspected lead fracture, a complete clinical evaluation should be performed. In addition, we recommend the following:
Viewing the Sensing Integrity Counter Data
On the Model 2090 Programmer:
Note: If the Sensing Integrity Counter > 300, the programmer displays a Quick Look observation.
Properly setting the thresholds for Lead Impedance alerts is critical to triggering the Patient Alert™. If the Patient Alert feature is enabled and the impedance is out of range, a device tone alert will sound. For Concerto®/Virtuoso® patients enrolled on the Medtronic CareLink® Network, a Medtronic CareAlert® notification will also be transmitted if Medtronic CareAlert notification for lead impedance is programmed ON. During the early stages of a conductor fracture, the impedance may significantly increase (e.g., two-fold increase) compared to the typical chronic impedance for a patient.
Medtronic recommends enabling the following Lead Impedance Out of Range Patient Alerts and Medtronic CareAlert notifications and establishing the associated maximum impedance threshold value as shown in the following table:
|Lead Impedance Alert||Recommended Maximum Impedance Threshold Value|
To reduce the risk of inappropriate shocks due to lead noise oversensing, Medtronic recommends programming parameters for VF detection duration to the nominal values as follows:
Clinicians should consider programming VF initial NID to 24/32 in Marquis® and later devices (i.e., Marquis, Maximo®, Intrinsic®, InSync MarquisTM family, EnTrust®, Virtuoso®, Concerto®) to further reduce the risk of inappropriate shocks due to lead noise oversensing. Programming VF initial NID to 24/32 in Marquis and later devices is estimated to have minimal impact on the total time to VF shock (compared to GEM III and earlier devices with NID = 18/24), thus minimizing the risk of delayed therapy or syncope.
|Estimated Values||GEM III and Earlier Initial NID = 18/24||Marquis and Later Initial NID = 18/24||Marquis and Later Initial NID = 24/32|
A retrospective review of Fidelis lead fracture data indicated:
Gunderson BD, Patel AS, Bounds CA, et al. An algorithm to predict implantable cardioverter-defibrillator lead failure. J Am Coll Cardiol. November 2, 2004;44(9):1898-1902.
If you have questions or concerns, please contact your Medtronic Representative or Medtronic Technical Services at 1-800-723-4636 (US).