Fundamentals of pulsed field ablation at the individual cardiomyocyte level

Pulsed field ablation (PFA) is a rapidly adopted catheter ablation method that employs high-voltage pulses to treat cardiac arrhythmias by cardiomyocyte electroporation.

We systematically characterized cardiomyocyte responses in vitro to different PFA waveforms to better understand the transient electrophysiological effects observed in clinical PFA.

Isolated adult rat ventricular cardiomyocytes were exposed to clinically relevant waveforms: monophasic 100 μs, biphasic 2 μs, and monophasic 200 ns pulses. Transmembrane voltage, intracellular Ca²⁺, and sarcomere shortening were monitored simultaneously. Computational modeling and machine learning were used to characterize the responses.

We observed 6 distinct response types ranging from no response to a complete loss of excitability. All 3 waveforms induced the same spectrum of responses, albeit at different electric field strengths. Cell orientation influenced thresholds in a pulse-duration-dependent manner. Modeling demonstrated that an electroporation-induced increase in membrane conductance explains the observed responses. Machine learning revealed that cells retain signatures of electroporation in their action potentials and Ca²⁺ transients, which differ between microsecond and submicrosecond waveforms. On a longer timescale, 12%-36% of cells that initially lost excitability recovered within ∼10 minutes.

All PFA waveforms produce similar cardiomyocyte responses through an electroporation-induced increase in membrane conductance. A substantial fraction of cells recover excitability within minutes, providing a plausible cellular explanation for the clinically observed transient loss of intracardiac electrograms following PFA and a rationale for pulsed field mapping based on reversible electroporation. Although the fundamental effects are waveform-independent, signatures in recovered cells show waveform-dependent features. These findings advance the mechanistic understanding of PFA at the cellular level.