Characteristics and time course of acute and chronic myocardial lesion formation after electroporation ablation in the porcine model

Ultrastructural insights from myocardial ablation lesions from microsecond pulsed field vs radiofrequency energy

BACKGROUND

Ultrastructural findings immediately after pulsed field ablation (PFA) of the myocardium have not been described.

OBJECTIVES

The purpose of this study was to elucidate ultrastructural characteristics and differences between microsecond PFA at the 1- and 4-hour timepoints after pulse delivery and to compare them to irrigated radiofrequency ablation (RFA) lesions.

METHODS

Healthy swine underwent endocardial PFA or RFA followed by necropsy. Discrete microsecond PFA and irrigated RFA lesions were created in the ventricles with a lattice tip ablation catheter. Lesions were delivered in a manner so as to allow sampling to occur 1 and 4 hours after ablation. All lesions were located at necropsy, and samples were carefully obtained from within the lesion core, lesion periphery, and adjacent healthy myocardium. Transmission electron microscopic assessment was performed after fixation using paraformaldehyde and glutaraldehyde.

RESULTS

One hour after microsecond PFA delivery, myocytes were noted to be significantly and uniformly disrupted. Clustered, misaligned, swollen mitochondria coupled with degenerating nuclei and condensed chromatin were visualized. These findings progressed over the subsequent few hours with worsening edema. Similar changes were seen with RFA but reduced in severity. However, there was prominent extravasation of red blood cells with occlusion of capillaries that was not seen in PFA. At the lesion periphery, an abrupt change in the degree of myocyte damage was observed with PFA but not RFA.

CONCLUSION

Transmission electron microscopy demonstrates evidence of widespread destruction of myocytes as early as an hour after PFA and corroborates known histologic features such as sparing of vessels and sharp lesion margins.

Pulsed field ablation for atrial fibrillation - Lessons from magnetic resonance imaging

Pulsed field ablation (PFA) is a promising technology for the treatment of atrial fibrillation (AF). Due to its unique tissue selectivity, PFA potentially bears superior characteristics as compared to established thermal energy sources in AF ablation procedures. Cardiovascular magnetic resonance imaging (CMR) using late gadolinium enhancement (LGE) is an established tool in the analysis of myocardial fibrosis representing atrial cardiomyopathy as well as ablation-induced atrial scar formation following catheter ablation with thermal energy. Mechanisms of atrial lesion formation differ between thermal ablation and electroporation and its impact on results of CMR imaging are not fully understood until now. In this review article, the potential of CMR imaging for PFA lesion assessment and available data are discussed. Further, additional needs to adopt imaging approaches to the cellular mechanisms of electroporation are considered.

What is Different About Pulsed Field Ablation … Everything?

From the time of early preclinical reports of the efficacy, speed and safety of pulsed field ablation (PFA), the interventional electrophysiology community has been waiting in anxious anticipation for its clinical approval and release. As most people actively engaged in interventional electrophysiology know, PFA is the technology that creates myocardial lesions with trains of very high voltage pulses that are nanoseconds or microseconds in duration¹ . This form of ablation is nonthermal, and cell injury/death is created by electroporation of the organelles and sarcolemmal membrane, with cell death occurring via apoptosis as well as other mechanisms² .