Acoustic effects during pulsed field ablation: measurement and control of bubble and void formation

Pulsed field ablation (PFA) is an emerging treatment option for arrhythmogenic myocardial tissue and solid tumors. PFA uses high voltage pulses to alter the electric potential across cell membranes, creating pores and eventual cell death. Bubble nucleation due to gas evolution at the electrode/electrolyte interface follows the delivery of current from the power generator to the body. Here, we investigate the acoustic effects induced by PFA to maximize the electroporation effect without pressure-driven damage.

Acoustic signals created by a PFA probe in saline were measured with a hydrophone. The lethality of PFA was tested in vitro in a 3D tissue mimic to resolve a ratio of cell death area to pressure. Mechanical damage created by PFA was then evaluated by gross measurements in agarose tissue mimics of different stiffness. Electrical resistance was tested with a plant-tissue model.

Monophasic pulses create smaller pressure waves (p < 0.05) and decrease the lethal threshold (p < 0.05) compared to biphasic pulses. The length of the delay within a PFA pulse train has a significant effect on pressure (p < 0.05) and insignificant effect on ablation areas (p = 0.9995 between 5 and 100 μs and p = 0.9997 between 50 and 100 μs). The cathode electrode creates more mechanical damage than the anode electrode (p < 0.05). Conductivity as a function of electric field is more accurately described with a double sigmoid compared to a single sigmoid model (R² = 0.9898 vs 0.8772).

Bubble formation and void formation are generally undesirable when using PFA. This paper presents the first characterization of the pressure waves created by PFA and provides strategies for improving an electrical waveform to maximize the electroporation effect without violent acoustic waves.