Implantation Site Does Matter for Defibrillation Threshold

In Vivo Partial Oxygen Pressure Assessment in Subcutaneous and Intraperitoneal Sites Using Imaging of Solid Oxygen Probe

The purpose of this study was to assess the natural partial oxygen pressure (pO₂) of subcutaneous (SC) and intraperitoneal (IP) sites in mice to determine their relative suitability as sites for placement of implants. The pO₂ measurements were performed using oxygen imaging of solid probes using lithium phthalocyanine (LiPc) as the oxygen sensitive material. LiPc is a water-insoluble crystalline probe whose spin-lattice and spin-spin relaxation rates (R₁ and R₂) are sensitive to the local oxygen concentration. To facilitate direct in vivo oxygen imaging, we prepared a solid probe containing encapsulated LiPc crystals in polydimethylsiloxane (PDMS), an oxygen-permeable and bioinert polymer. Although LiPc-PDMS or similar probes have been used in repeated spectroscopic or average oxygen measurements using continuous wave electron paramagnetic resonance (EPR) since the late 1990s and now have advanced to clinical applications, they have not been used for pulse EPR oxygen imaging. One LiPc-PDMS probe of 2 mm diameter and 10 mm length was implanted in SC or IP sites (left or right side) in each animal. The pO₂ imaging of implanted LiPc-PDMS probes was performed weekly for 6 weeks using O2M preclinical 25 mT oxygen imager, JIVA-25™, using the pulse inversion recovery electron spin echo method. At week 6, the probes were recovered, and histological examinations were performed. We report in this study, first-ever solid probe oxygen imaging of implanted devices and pO₂ assessment of SC and IP sites.

A Numerical Evaluation of Multi-Lead Subcutaneous Implantable Cardioverter Defibrillator for Low Energy and Less Damage in Swine

In the rescue of patients with sudden cardiac death, cardiac electric defibrillation is usually implemented, but the myocardial damage caused by exceeding defibrillation shock is irreversible. The aim of this study is to provide a numerically implanted optimization of a subcutaneous implantable cardioverter defibrillator (S-ICD) for low shock energy and less myocardial damage. In this paper, three anatomically realistic finite element models of swine were constructed for the evaluation study of six Can-Lead configurations with various number of leads at different placements. For each Can-Lead configuration, corresponding numerical modeling and simulation with the finite element method (FEM) were performed to pre-surgically assess quantitatively the efficiency of a certain defibrillation shock, besed on our previously reported multi-criteria evaluation of cardiac defibrillation. The results show that the outcome of an S-ICD shock depends on numbers of the implanted leads as well as the location of Can-Lead, and suggest that an S-ICD implantation with a left pectoral Can and two leads (located at the midline and at the left last ribs oblique upward) would possess the best efficiency of defibrillation, which could offer another option in clinical practice. In conclusion, on basis of the pre-surgical simulation of an S-ICD configuration, an individual optimization of cardiac defibrillation would be potentially useful for a lower energy and a less myocardial damage compared with current implantations with only the knowledge of clinical practices.