Po-04-073 electron microscopic insights from an acute pulsed field myocardial lesion

Pulsed field ablation (PFA) is a nonthermal ablative energy modality that increases membrane permeability by creating pores and causing chemical changes to the lipids and proteins on the cell membrane. However, little is known about its effect on cell membrane, organelle structure and time course of lesion formation. To evaluate cell membrane and organelle structure after PFA and assess lesion differences between 1- and 4-hour after PFA. Healthy swine underwent endocardial PFA using an 11 Fr circular, multielectrode catheter (CellFX, Pulse Biosciences) in nanosecond pulsing mode. Pulses were delivered to the left ventricle under general anesthesia with fluoroscopic and intracardiac echocardiography guidance. Two discrete PFA lesions were sampled 1 and 4 hours after PFA. Transmission electron microscopy assessment was performed after fixation using paraformaldehyde and glutaraldehyde. At 1-hour post-PFA, healthy myocytes with normal sarcomeric structure, clear Z band, and A band were noted adjacent to ablated myocytes (Figure). Mitochondria inside the healthy myocyte were aligned in parallel with sarcomere filaments. Ablated myocytes on the other hand demonstrated disrupted sarcomeric structures and were randomly clustered and misaligned. Cell membranes of the ablated myocyte at the lesion border were relatively preserved compared to ablated myocytes from within the core of the PFA lesion. At 4-hour post-PFA, the PF lesion was noticeably more edematous and areas of coagulum could be seen adjacent to the capillaries. Alignment of cell membranes at the 4-hour timepoint was further disorganized. Fewer mitochondria per section were observed at 4-hour post-PFA, and noted to be randomly scattered amongst damaged myocytes. There were no normal sarcomeres noted anywhere within the lesion at 4 hours. This electron microscopy study demonstrates significant rapid disappearance of myocytes after PFA (∼ 1 hour). The cell membrane structure and organelle structure progressively deteriorate by 4 hours post ablation.