Abstract
The pace-sense element of Medtronic ICD leads comprises a 4-filar helical conductor (helix) to the tip and a 49-filar cable to the ring electrode surrounded by inner insulation. Previously, we studied the development of oversensing (OS) and pacing impedance (Z) with helix fracture (Fx): Partial (P) Fx corresponds to onset of OS and abrupt increase in standard deviation (σ) of helix Z ≥ 0.5Ω. Z > 3000Ω (open circuit) indicates complete (C) Fx. To characterize this relationship for ring-cable fractures. We performed bending tests on 16 Quattro™ leads connected to ICD generators. Leads were oriented with the cable on the inner radius for maximum stress and placed in an electrolyte bath with simulated ECG input. Sensing (Tip-ring) and cable (Ring-can) electrograms (EGMs) were telemetered; Z was measured for both cable and helix. Fx was confirmed by x-ray and microscopy. Unlike helix Fx, cable Z and σZ increased gradually through CFx (Figure). An increase in cable σZ ≥ 0.0015Ω corresponded to PFx. CFx corresponded to σZ ≥ 0.5Ω and only minimal Z increase (< 2Ω). Cable-Fx OS on the Ring-can channel did not occur with PFx but occurred consistently with CFx (Figure). At CFx, both Z and OS varied with cyclic bending due to make-break connections. In contrast to helix Fx, early cable PFx does not cause OS. Cable CFx results in consistent OS but minimal Z increase, too small for clinical detection. Different presentations of helix vs. cable Fx may be due to many more filars in cables and constraint of fractured cables by inner insulation, which does not surround the helix.
Published Version
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