Michael Passeri, MD1, William B Lyman, MD1, Timothy J O’Brien, BS2, Melvin F Lorenzo, BS2, Jacob H Swet, MS1, Dionisios Vrochides, MD, PhD, FACS1, Erin H Baker, MD1, John B Martinie, MD, FACS1, Rafael V Davalos, PhD2, David A Iannitti, MD, FACS1, Iain H McKillop, PhD1. 1Carolinas Medical Center, 2Virginia Polytechnic Institute and State University
OBJECTIVES. Irreversible electroporation (IRE) is an alternative to thermal ablation for in situ soft-tissue ablation. Existing IRE passes high voltages (1-3kV) across multiple electrodes placed in/around the tumor. Doing so creates irreversible nanopore formation in cell membranes leading to apoptotic induction while preserving the underlying vascular-biliary architecture. However, the need for precise, multiple electrode placements, coupled with a requirement for intraoperative paralytics and cardiac synchronization, increases surgical time and case complexity, meaning IRE has been slow to be adopted clinically. This study sought to fabricate, model, and test an innovative single needle-dual electrode (SNDE) array coupled with next-generation high frequency IRE (HFIRE) pulse delivery.
DESCRIPTION. A custom-built generator, capable of delivering bipolar HFIRE pulses of an order magnitude shorter than employed with monopolar IRE (0.5ms-2ms vs. 50-100ms), was used. To address the need for multi-electrode placement, we fabricated and modeled a SNDE probe to test with HFIRE pulse delivery. In vitro modeling (COSMOL Multiphysics), employing coupled finite element analysis, was used to solve electric field distribution within a simulated H-FIRE of liver tissue. Using modeling data, we next analyzed the ablative capabilities of SNDE-HFIRE in a swine liver model in vivo. Animals were anesthetized, and a SNDE-HFIRE probe positioned within the parenchyma under US guidance. Ablations (2250V with a total energized time of 100μs, 25 cycles, 2-5-2 configuration (on-off-on time [μs]), delivered at 1-burst/s) were performed without paralytics or cardiac synchronization, and animals survived for 6Hrs. The liver was recovered and analyzed for ablation size/shape, architectural integrity, and apoptotic cell death (TTC and anti-caspase-3 staining).
RESULTS. SNDE-HFIRE probes were fabricated with 8mm electrodes incorporated onto a 1.8mm (25cm-long) needle array, with an 8mm inert-spacing between electrodes. Finite element modeling was plotted and represented as a function of exposed electrical field. Baseline liver conductivity to H-FIRE was 0.24S/m, increasing sigmoidally to 0.36S/m around an inflection electric field value of 750V/cm, the median for IRE threshold delivered with HFIRE. Predicted ablations were ellipsoidal (8-15mm x 10-30mm). In vivo ablations, (including needle placement) were completed in <15 mins, with total HFIRE delivery times of <8mins. No muscle twitch or EKG abnormalities were detected, and all animals survived without complication. Reproducible ellipsoidal ablations were achieved with the pulse settings described (2.84±0.28cm3, range=2.28-3.56cm3 n=4 independent ablations). Histological analysis revealed clear demarcation between ablated and normal tissue, with preservation of underlying architecture within the ablation zone (no coagulative necrosis/thermal damage). The ablated area stained extensively for caspase-3 activity, caspase-3 staining matching that observed with TTC staining.
CONCLUSIONS. A DNSE approach overcame many of the technical challenges associated with multiple electrode insertions. The use of bipolar HFIRE delivery further simplified and shortened the operative procedure by obviating the need for paralytics and cardiac synchronization. Development, optimization, and testing of different pulse parameters for SNDE-HFIRE may overcome current limitations and reservations associated with established IRE technology, including a greater potential for use with minimally invasive approaches, to create a viable alternative to thermal ablation of hepatic tumors.
Presented at the SAGES 2017 Annual Meeting in Houston, TX.
Abstract ID: 91231
Program Number: ETP862
Presentation Session: Emerging Technology iPoster Session (Non CME)
Presentation Type: Poster