Evaluation of cardiac lead insulation following implant durations exceeding 10 years

The long-term performance of a cardiac lead is largely dictated by the mechanical durability and biochemical stability of the outer insulation material. While there are numerous in vitro methodologies to gauge the in vivo reliability of these materials, they do not fully recapitulate the mechanical and biochemical nuance of the in vivo environment. Therefore, evaluating the insulation of extracted cardiac leads, particularly after prolonged implant durations, provides valuable insight into the in vivo performance of these materials.

Cardiac leads have an outer insulation that is typically silicone, polyurethane, or a siloxane-based polyurethane (Si-TPU). In the context of Si-TPU, multiple studies have evaluated this material from extracted leads [1-2]; however, the maximum implant duration for those leads was 8 years. Since the service life of a cardiac lead is expected to exceed this duration, the purpose of this study was to evaluate this insulation material from leads with an implant duration exceeding 10 years.

Extracted Si-TPU insulated leads, with a particular emphasis on implant durations beyond 10 years, were analyzed for this study. Leads with an implant duration <24 hrs (non-implant or aborted implant) served as baseline controls. From each lead, the outer insulation was carefully removed and subjected to tensile testing (tensile strength & elongation), scanning electron microscopy inspection, and molar mass measurements. Data obtained from all explanted leads were compared against the baseline controls.

A total of 40 leads were included in this analysis, including 20 extracted leads with a mean implant duration of 14.8 ± 1.2 yrs (max 16.4 yrs). When compared against non-implanted controls, tensile and molar mass measurements confirmed the long-term in vivo stability of the Si-TPU material. For instance, extracted leads exhibited minor changes in tensile strength compared to non-implanted controls: 17.1 ± 1.3 MPa (11.4 ± 0.9 lbf load) vs. 20.5 ± 1.0 MPa (14.3 ± 0.7 lbf load), respectively. Moreover, a 14.8 ± 1.2 yr implant duration produced a 24% reduction in molar mass relative to controls. Interestingly, this reduction is practically unchanged from shorter implant durations: -22% after 2-3 yrs and -23% after 7-8 yrs of implant [1-2]. In other words, almost the entire molar mass change occurs within the first few years of implant with no further changes as implant duration increased up to 16.4 yrs. This trend indicates that the Si-TPU resisted degradation of its backbone polymer chains.

Following prolonged implant durations, the Si-TPU insulation exhibited robust retention of mechanical strength and the lack of progressive molar mass changes with increasing implant duration, up to 16.4 yrs of implant, highlights the biochemical stability of this material. Altogether, these findings support the suitability of this material for long-term in vivo applications.