Assessment of cardiac cead insulation based on in vivo microenvironment following extended implant durations

Abstract Background The long-term performance of a cardiac lead is largely dictated by the mechanical durability and biochemical stability of the outer insulation material. It is not established whether the different in vivo microenvironments that a lead is subjected to, particularly the subcutaneous space and within the cardiac chambers, have a differential influence on the long-term performance of the insulation material. Purpose Transvenous cardiac leads traverse multiple in vivo microenvironments that have different mechanical and biochemical stressors. For example, whereas insulation from the proximal end resides in the subcutaneous space near the pulse generator with minimal dynamic flexing, the distal region resides within a much different biochemical microenvironment (the blood pool) and undergoes continuous flexing throughout the implant lifetime. In this study, we sought to comparatively assess the effect of the two primary microenvironments on the long-term biostability of the insulation material. Methods Extracted ICD leads with a siloxane-based polyurethane insulation were obtained following implant durations ranging from <24 hrs (non-implant or aborted implant) up to 13.36 yrs. Leads with implant durations <24 hrs served as baseline controls. From each lead, sections of the insulation from the proximal and distal zones were removed and subjected to visual and scanning electron microscopy (SEM) inspection, tensile testing (tensile strength & elongation), and molar mass measurements. Measurements from explanted lead proximal & distal segments were compared against the baseline controls. Results A minimum of 10 leads from short (<5 yrs), intermediate (5-10 yrs), and extended (>10 yrs) implant durations were included in this analysis. Despite exposure to different microenvironments, the molecular weight and tensile properties between proximal and distal lead segments were comparable across the full range of implant durations. Overall, the insulation material exhibited only minor changes in tensile strength compared to controls; from an initial 14.4 ± 1.1 MPa (8.8 ± 0.6 lbf load) to 12.2 ± 0.8 MPa (7.4 ± 0.7 lbf load) for insulation with an implant duration >10 years. Moreover, there was a reduction in molecular weight of 28% over the first 5 years of implant which stabilized thereafter. This reduction-stabilization molecular weight trend is consistent with prior studies of this insulation material which utilized significantly shorter implant durations and only proximal portions of the lead. Conclusion The intracardiac blood pool and chest pocket area were not observed to have a differential influence on the long-term biochemical stability and mechanical durability of this insulation material. Overall, the totality of visual/SEM inspection and tensile properties support the suitability of this material for long-term in vivo applications, even when exposure to multiple in vivo microenvironments is expected.