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ICD algorithm detects lead fracture, prevents inappropriate shocks
20 November 2008
MedWire News: Researchers have developed a downloadable algorithm to reduce inappropriate shocks in patients with implantable cardioverter-defibrillators (ICDs).
The algorithm can be downloaded into presently implanted, nominally functioning ICDs to detect pace-sense lead fractures, which are the commonest cause of inappropriate shocks and can have adverse physical and psychologic consequences for the patient.
The Medtronic Sprint Fidelis ICD lead was withdrawn from the market in 2007 because of a higher-than-expected fracture rate. The clinical sequelae of lead fracture are inappropriate shocks, which may be pro-arrhythmic and lethal.
To preempt such complications in existing devices, Charles Swerdlow (Cedars–Sinai Medical Center, Los Angeles, California, USA) and colleagues developed a Lead Integrity Algorithm to detect abnormal changes in lead impedance or evidence of lead noise. Uniquely, the algorithm calculates a patient-specific impedance threshold that is continuously updated.
Once triggered, the algorithm initiates a sequence of actions by the ICD: it increases the number of intervals to detect (NID) ventricular fibrillation to 30 of 40; activates an audible patient alert that repeats every 4 hours; and sends a wireless internet-based message to a monitoring center.
As reported in the journal Circulation, Swerdlow and team applied the new algorithm to a company dataset of 15,970 patients with Fidelis leads, some of whom had confirmed lead fractures and inappropriate shocks.
The algorithm provided at least a 3-day warning of inappropriate shocks in 76% of cases, they report, while increasing the NID significantly reduced inappropriate shocks (p<0.0001). The algorithm had a positive predictive value of 72% for lead fractures and a false–positive rate of one per 372 patient-years.
Swerdlow and colleagues say their algorithm outperforms optimal impedance monitoring but admit its clinical value depends on a rapid response to alerts by patients and clinicians.
In an accompanying editorial, Robert Hauser, from Minneapolis Heart Institute Foundation in Minnesota, USA, called the algorithm “an important advance” but warns that it is “not a victory” and says that the ultimate goal is “to provide patients with leads that that are so reliable, well tested, and durable that the algorithm and similar fail-safe techniques are rarely needed.”
