Zdeněk Stárek

Irreversible electroporation ablation for atrial fibrillation

Atrial fibrillation (AF) is one of the most important problems in modern cardiology. Thermal ablation therapies, especially radiofrequency ablation (RF), are currently “gold standard” to treat symptomatic AF by localized tissue necrosis. Despite the improvements in reestablishing sinus rhythm using available methods, both success rate and safety are limited by the thermal nature of procedures. Thus, while keeping the technique in clinical practice, safer and more versatile methods of removing abnormal tissue are being investigated. This review focuses on irreversible electroporation (IRE), a nonthermal ablation method, which is based on the unrecoverable permeabilization of cell membranes caused by short pulses of high voltage/current. While still in its preclinical steps for what concerns interventional cardiac electrophysiology, multiple studies have shown the efficacy of this method on animal models. The observed remodeling process shows this technique as tissue specific, triggering apoptosis rather than necrosis, and safer for the structures adjacent the myocardium. So far, proposed IRE methodologies are heterogeneous. The number of devices (both generators and applicators), techniques, and therapeutic goals impair the comparability of performed studies. More questions regarding systemic safety and optimal processes for AF treatment remain to be answered. This work provides an overview of the electroporation process, and presents different results obtained by cardiology‐oriented research groups that employ IRE ablation, with focus of AF‐related targets. This contribution on the topic aspires to be a practical guide to approach IRE ablation for cardiac arrhythmias, and to highlight controversial features and existing knowledge, to provide background for future improved experimentation with IRE in arrhythmology.

Phenotypic assays for analyses of pluripotent stem cell-derived cardiomyocytes

Stem cell–derived cardiomyocytes (CMs) hold great hopes for myocardium regeneration because of their ability to produce functional cardiac cells in large quantities. They also hold promise in dissecting the molecular principles involved in heart diseases and also in drug development, owing to their ability to model the diseases using patient‐specific human pluripotent stem cell (hPSC)–derived CMs. The CM properties essential for the desired applications are frequently evaluated through morphologic and genotypic screenings. Even though these characterizations are necessary, they cannot in principle guarantee the CM functionality and their drug response. The CM functional characteristics can be quantified by phenotype assays, including electrophysiological, optical, and/or mechanical approaches implemented in the past decades, especially when used to investigate responses of the CMs to known stimuli (eg, adrenergic stimulation). Such methods can be used to indirectly determine the electrochemomechanics of the cardiac excitation‐contraction coupling, which determines important functional properties of the hPSC‐derived CMs, such as their differentiation efficacy, their maturation level, and their functionality. In this work, we aim to systematically review the techniques and methodologies implemented in the phenotype characterization of hPSC‐derived CMs. Further, we introduce a novel approach combining atomic force microscopy, fluorescent microscopy, and external electrophysiology through microelectrode arrays. We demonstrate that this novel method can be used to gain unique information on the complex excitation‐contraction coupling dynamics of the hPSC‐derived CMs.

A Novel Defibrillation Tool: Percutaneously Delivered, Partially Insulated Epicardial Defibrillation

INTRODUCTION Epicardial defibrillation systems currently require surgical access. We aimed to develop a percutaneous defibrillation system with partially-insulated epicardial coils to focus electrical energy on the myocardium and prevent or minimize extra-cardiac stimulation. METHODS We tested 2 prototypes created for percutaneous introduction into the pericardial space via a steerable sheath. This included a partially-insulated defibrillation coil and a defibrillation mesh with a urethane balloon acting as an insulator to the face of the mesh not in contact with the epicardium. The average energy associated with a chance of successful defibrillation 75% of the time (ED75) was calculated for each experiment. RESULTS Of 16 animal experiments, 3 pig experiments had malfunctioning mesh prototypes such that results were unreliable; these were excluded. Therefore, 13 animal experiments were analyzed - 6 canines (29.8±4.0kg); 7 pigs (41.1±4.4kg). The overall ED75 was 12.8±6.7J (10.9±9.1J for canines; 14.4±3.9J in pigs [P=0.37]). The lowest ED75 obtained in canines was 2.5J while in pigs it was 9.5J. The lowest energy resulting in successful defibrillation was 2J in canines and 5J in pigs. There was no evidence of coronary vessel injury or trauma to extra-pericardial structures. CONCLUSION Percutaneous, epicardial defibrillation using a partially insulated coil is feasible and appears to be associated with low defibrillation thresholds. Focusing insulation may limit extra-cardiac stimulation and potentially lower energy requirements for efficient defibrillation.

Irreversible electroporation-Let's keep it cool: CALUORI et al.

We thank Dr. Futyma for his attention to our manuscript 1 and the interesting discussion he provides in his letter 2 . This gives us the opportunity to further highlight the proposed non-thermal character of irreversible electroporation (IRE). Displacement of ohmic currents inside a tissue, a medium with an intrinsic impedance, will anytime, to some extent, produce a local temperature increase by Joule heating. This issue exists whether IRE is elicited by DC pulses or AC bursts. IRE ablation is considered non-thermal only when finely tuned to induce non- necrotic selective cellular death. As we highlighted in our review, the border is not clearly defined, but sparing adjacent heat-sensitive structures or tissues (especially extracellular matrix and blood vessels) is a relevant aim. Thermal damage will occur in muscle immediately, at temperatures above 50C 3 . This value is considered a maximal threshold to avoid thermal damage in tumor IRE ablation, as reported in in vitro 4 and in vivo 5 studies. Discussing the detailed work by Faroja et al 6 , this shows that elevated temperature levels can be generated due to IRE energy application on liver. Nevertheless, even in this study there is an identified non-thermal working range (measured temperature between 34-42C), detected by peaking of caspase 3, a known apoptotic marker. The study of Meyer et al. 7 is mentioned, as this shows that the use of defibrillating shocks produces skin erythema, with 5 applications at 360J. The application of defibrillating shocks is heavily dependent on skin electrode contact and energy delivered can be over two orders of magnitude stronger than a single IRE pulse. Considering, simplistically, an initial tissue-electrode resistive impedance of 100 Ohm 8 , a 3000 V DC application for 100 µs will cause an energy delivery of 9 J, requiring 200 applications to deliver the same amount of energy delivered in the mentioned study. In a recent work by Neven et al., a 200J single defibrillating shock was delivered from a decapolar circular catheter, using an external reference patch to ablate pulmonary veins sleeves. In this scenario, only mild intimal hyperplasia was reported, together with successful isolation 9 . Whether this proliferation is induced by hybrid thermo-electric effect is not clear, yet it does not hamper the therapeutic effects. It must be taken into consideration that IRE energy delivery, given the same electrical parameter, is also affected by the active electrode area and the proximity between active and reference electrode, as these parameters affect the tissue- electrode impedance. Therefore, it is clear how fundamental is to tune the IRE application parameters (e.g., voltage, pulse width and inter-pulse distance) and physical specifications (e.g., electrode area, reference proximity) to achieve the optimal efficacy and benefits of this approach, among the others providing a “cool” non-thermal method to overcome the limits of purely thermal-based ablation methods.