Monday, November 03, 2008

Software Said To Reduce Inappropriate ICD Shocks

In October, 2007, Medtronic issued one of the largest defibrillator lead advisory alerts for their popular and thin Model 6949 Sprint Fidelis lead due to the lead's higher-than-expected fracture rate. More recently, a software patch called a Lead Integrity Alert has been developed that can be uploaded into affected patients' defibrillators in hopes of improving the detection of lead fracture conditions. The software also automatically readjusts the settings of the defibrillator to make it less prone to deliver inappropriate shocks caused by lead failure.

Today in Circulation, the efficacy of this algorithm to avoid shocks was published from in vitro testing on leads returned to the manufacturer.* Real life effectivness of the algorithm has not been tested to date. So far, the algorithm theoretically shows improvement in avoiding unnecessary shocks:
To reduce inappropriate shocks, the lead-integrity algorithm increases the number of intervals to detect (NID) ventricular fibrillation when triggered. The lead-integrity algorithm was tested on data from 15,970 patients with Fidelis leads (including 121 with clinically diagnosed fractures) and 95 other fractured leads confirmed by analysis of returned product. The effect of the NID on inappropriate shocks was tested in 92 patients with 927 shocks caused by lead fracture. Increasing the NID reduced inappropriate shocks (P<0.0001). The lead-integrity algorithm provided at least a 3-day warning of inappropriate shocks in 76% (95% CI, 66 to 84) of patients versus 55% (95% CI, 43 to 64) for optimal impedance monitoring (P=0.007). Its positive predictive value was 72% for lead fractures and 81% for lead fractures or header-connector problems requiring surgical intervention. The false-positive rate was 1 per 372 patient-years of monitoring.
The distribution of the fractures reported was also interesting:
Of the 95 patients in the RPA (returned product analysis) group, 41 (43%) had fractures of the coil conductor to the tip electrode and 54 (57%) had fractures of the cable conductor to the ring electrode. Figure 5 shows that all coil fractures occurred at the anchor sleeve, whereas 52 of the cable fractures (96%) occurred distally or at the bifurcation/trifurcation.
We are about to see a rising number of patients with these leads enter the clinical arena as their ICD batteries reach their elective replacement indicators warning us of battery depletion. Recommendations from the company have so far been few, but most suggest a relatively conservative watch and wait approach. But when the patient's ICD pocket is opened for a battery change, the opportunity to place a new, non-recalled lead presents itself and should be considered (provided of course venous access still exists in which to place the new lead).

The difficult decision will come when there is no venous access in which to place a new lead from the same side as the existing defibrillator. Should we abandon the existing side and place an entirely new system on the opposite side with new, non-recalled leads? Should we send the patient for lead extraction and replacement? Or should we re-connect the old lead and hope for the best if no other option presents itself?

These are not easy decisions.

Patients with Sprint Fidelis leads should discuss what's involved with each of these scenarios with their doctors when the time comes to replace their defibrillator battery. Hopefully, we'll have additional trend data regarding lead survival on which to base future management recommendations. But until we do, battery changes in these patient's with Sprint Fidelis leads will be anything but routine.


*The study was funded by Medtronic.

Other information:
Medtronic's Official Sprint Fidelis Information WebSite Updated Lead Failure Rate Information
Medtronic to Pull Its Most Popular Defibrillator Lead
More on the Medtronic's Sprint Fidelis Advisory
Medtronic's Sprint Fidelis Perfomance Lead Update

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