Biophysical principles of pulsed field ablation

Figures

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  Figure 1. Relationship between electric field strength and pulse width showing transitions from reversible electroporation (RE) to irreversible electroporation (IRE) and, at higher energy delivery, thermal injury.

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  Figure 2. Normalized temporal evolution of the induced transmembrane potential (TMP), ΔVm, at the pole of an intact spherical cell (θ=0) during rectangular electric pulses of different durations. Here, θ is the polar angle relative to the direction of the applied electric field, t is time, Tp is the pulse duration, and τcharge is the characteristic membrane charging time constant. Time is normalized to τcharge, and the induced TMP is normalized to its passive steady-state value at the cell pole, (ΔV(m,ss)pole=3RE0/2). The curves illustrate incomplete membrane charging when (TP≤τcharge) and quasi-steady-state charging when (Tp≫τcharge). The dashed blue line indicates the normalized passive steady-state TMP, whereas the dashed red line denotes an illustrative normalized electroporation threshold and should not be interpreted as a universal or cell-specific threshold.

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  Figure 3. Multiscale framework of electroporation in pulsed field ablation. Schematic representation of the hierarchical organization of electroporation phenomena across spatial scales. At the molecular level, electric fields stabilize transient aqueous pores in lipid bilayers in a stochastic manner. At higher levels of organization, cellular recovery mechanisms, tissue architecture, and electric field distribution modulate the transition from reversible to irreversible electroporation. Clinical lesion formation in pulsed field ablation emerges from the integration of these multiscale processes rather than from a single deterministic membrane threshold.

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  Figure 4. Sequence of molecular events leading from aqueous defect initiation to pore formation in lipid bilayers under high TMPs. The schematic illustrates the progression from an intact membrane (S1), through intermediate states characterized by field-driven water penetration and aqueous finger formation (S2 and S3), to the formation of a continuous hydrophilic pore across the membrane (S4). Adapted from Marracino et al.21.

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  Figure 5. Modulatory role of lipid peroxidation in membrane susceptibility to electroporation. (A) Schematic representation of membrane lipid peroxidation. Oxidative modification of unsaturated phospholipid acyl chains introduces polar hydroperoxide groups (−OOH), locally disrupting bilayer packing, increasing membrane polarity, and facilitating water penetration into the lipid core. These changes alter membrane material properties without directly inducing pore formation (Páez-Pérez et al.27). (B) Experimental evidence of increased intracellular oxidative stress following pulsed electric field exposure, shown as the mean fluorescence intensity (MFI) ratio of the ROS-sensitive probe H2DCFDA measured 6 h after stimulation at increasing electric field strengths adapted from.70

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  Figure 6. Conceptual and molecular dynamics representation of protein-associated modulation of electroporation. (A) Conceptual schematic linking a simplified representation of a transmembrane protein embedded in a lipid bilayer with its atomistic molecular dynamics model. (B) Atomistic view showing the corresponding simulation box used to investigate protein–membrane assemblies under electric field exposure with a magnified side view of the transmembrane protein spanning the lipid bilayer. (C) Top-down (xy-plane) view of the same protein–membrane assembly in its pre-pore, intact state, showing no aqueous pore formation, provided as a reference baseline for comparison with the field-induced pore formation sequence illustrated in Figure 4.

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  Figure 7. Transition from reversible to irreversible electroporation as a function of applied electric field intensity and cumulative electrical dose. Cellular responses progress from sub-threshold conditions (Zone A), through reversible electroporation with transient membrane permeabilization and recovery (Zone B), to irreversible electroporation associated with loss of cellular recovery capacity and progression towards cell death (Zone C). The boundary between reversible and irreversible effects is stochastic, reflecting biological variability. Higher doses may induce side effects such as Joule heating, gas evolution, and neuromuscular stimulation.88–90 Protocols in PFA are intentionally designed to exceed cellular recovery capacity to induce controlled, non-thermal tissue ablation. This energy modality enables spatially confined lesion formation while preserving extracellular matrix architecture and minimizing collateral damage to adjacent structures.90

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  Figure 8. Cellular responses after irreversible electroporation. Following application of a pulsed electric field, a cell undergoes sustained membrane permeabilization, initiating a cyclic injury cascade. This includes (1) primary membrane failure, (2) ionic and osmotic collapse driven by ion flux and water influx, (3) metabolic and mitochondrial dysfunction with ATP depletion and oxidative stress, and (4) energy-dependent cell death, progressing to apoptosis or necrosis depending on injury severity. Tissue-level factors modulate the extent and evolution of injury during PFA.