A fatigue-resistant microcable for small diameter leads of active implantable medical devices.

Reliability is a key-but-challenging requirement of active implantable medical devices. Implanted medical devices, such as leads, are exposed to tough environments in terms of corrosion and movement. Alongside good reliability, there is also a need for the size of medical implants to be reduced, both to minimize trauma and to enable sites that have hitherto been inaccessible to be reached, such as the tortuous venous collateral network of the left ventricle. Finally, specific electrical properties are required to adequately stimulate or sense specific regions within the human body. In this work, we present a composite microcable that combines small size with high electrical performance and long-term lead robustness. Combining multiple individually insulated electrical conductors in a microcable structure is perfectly suited for leads with multiple selectively contacted electrodes. The use of fine wires of 19 µm diameter enables the manufacture of a 7 × 7 microcable with an extremely small total diameter of less than 0.3 mm. In addition, the fine wires are composed of a core-shell metal-to-metal composite, which allows multiple advantages in one microcable: good X-ray visibility, high electrical conductivity, and very high fatigue resistance. The new MP35N®-Pt composite wire exhibits very strong lead robustness with good electrical conductivity. The fatigue test results presented were obtained by applying 90° bending under tensile load and show that the microcable has a 35-fold increase in high cycle fatigue robustness compared to standard PtIr20 leads. The resulting fracture surfaces were analyzed with scanning electron microscopy. Complementary results from conductivity measurements, X-ray visibility tests and mechanical testing have also been presented to illustrate the benefits of this newly developed composite microcable compared to state-of-the-art electrical conductors for medical implant applications.

Exploring a New Systematic Route for Left Ventricular Pacing in Cardiac Resynchronization Therapy.

BACKGROUND: Frequency and distribution of left ventricular (LV) venous collaterals were studied in vivo to evaluate the ease and feasibility of implanting a new ultra-thin LV quadripolar microlead for cardiac resynchronization therapy (CRT).Methods and Results:Evaluable venograms were analyzed to define the prevalence of venous collaterals (>0.5 mm diameter) between: (1) different LV segments; and (2) different major LV veins in: unselected patients who underwent CRT from 2008 to 2012 at Rouen Hospital, France (retrospective); and CRT patients from the Axone Acute pilot study in 2018 (prospective). In prospective patients with evaluable venograms, LV microlead implantation was attempted. Thirty-six (21/65 retrospective, 15/20 prospective) patients had evaluable venograms with ≥1 visible venous collaterals. Collaterals were found between LV veins in all CRT patients with evaluable venograms. Regionally, prevalence was highest between: the apical inferior and apical lateral (42%); and mid inferior and mid inferolateral (42%) segments. Collateral connections were most prevalent between: the inferior interventricular vein (IIV) and lateral vein (64% [23/36]); and IIV and infero-lateral vein (36% [13/36]). Cross-vein microlead implantation was possible in 18 patients (90%), and single-vein implantation was conducted in the other 2 patients (10%). CONCLUSIONS: Venous collaterals were found in vivo between LV veins in all CRT patients with evaluable venograms, making this network an option for accessing multiple LV sites using a single LV microlead.

Evaluating multisite pacing strategies in cardiac resynchronization therapy in the preclinical setting.

BACKGROUND: Multisite pacing strategies that improve response to cardiac resynchronization therapy (CRT) have been proposed. Current available options are pacing 2 electrodes in a multipolar lead in a single vein (multipoint pacing [MPP]) and pacing using 2 leads in separate veins (multizone pacing [MZP]). OBJECTIVE: The purpose of this study was to compare in a systematic manner the acute hemodynamic response (AHR) and electrophysiological effects of MPP and MZP and compare them with conventional biventricular pacing (BiVP). METHODS: Hemodynamic and electrophysiological effects were evaluated in a porcine model of acute left bundle branch block (LBBB) (n = 8). AHR was assessed as LVdP/dtmax. Activation times were measured using >100 electrodes around the epicardium, measuring total activation time (TAT) and left ventricular activation time (LVAT). RESULTS: Compared to LBBB, BiVP, MZP, and MPP reduced TAT by 26% ± 10%, 32% ± 13%, and 32% ± 14%, respectively (P = NS between modes) and LVAT by 4% ± 5%, 11% ± 5%, and 12% ± 5%, respectively (P <.05 BiVP vs MPP and MZP). On average, BiVP increased LVdP/dtmax by 8% ± 4%, and optimal BiVP increased LVdP/dtmax by 13% ± 4%. The additional improvement in LVdP/dtmax by MZP and MPP was significant only when its increase during BiVP and decrease in TAT were poor (lower 25% of all sites in 1 subject). The increase in LVdP/dtmax was larger when large interelectrode distances (>5 cm vs <2.2 cm) were used. CONCLUSION: In this animal model of acute LBBB, MPP and MZP create similar degrees of electrical resynchronization and hemodynamic effect, which are larger if interelectrode distance is large. MPP and MZP increase the benefit of CRT only if the left ventricular lead used for BiVP provides poor response.