Background: Pulsed field ablation is a novel nonthermal cardiac ablation modality using ultra-rapid electrical pulses to cause cell death by a mechanism of irreversible electroporation. Unlike the traditional ablation energy sources, pulsed field ablation has demonstrated significant preferentiality to myocardial tissue ablation, and thus avoids certain thermally mediated complications. However, its safety and effectiveness remain unknown in usual clinical care. Methods: MANIFEST-PF (Multi-National Survey on the Methods, Efficacy, and Safety on the Post-Approval Clinical Use of Pulsed Field Ablation) is a retrospective, multinational, patient-level registry wherein patients at each center were prospectively included in their respective center registries. The registry included all patients undergoing postapproval treatment with a multielectrode 5-spline pulsed field ablation catheter to treat atrial fibrillation (AF) between March 1, 2021, and May 30, 2022. The primary effectiveness outcome was freedom from clinical documented atrial arrhythmia (AF/atrial flutter/atrial tachycardia) of ≥30 seconds on the basis of electrocardiographic data after a 3-month blanking period (on or off antiarrhythmic drugs). Safety outcomes included the composite of acute (7 days) major adverse events. Results: At 24 European centers (77 operators) pulsed field ablation was performed in 1568 patients with AF: age 64.5±11.5 years, female 35%, paroxysmal/persistent AF 65%/32%, CHA ₂ DS ₂ -VASc 2.2±1.6, median left ventricular ejection fraction 60%, and left atrial diameter 42 mm. Pulmonary vein isolation was achieved in 99.2% of patients. After a median (interquartile range) follow-up of 367 (289–421) days, the 1-year Kaplan-Meier estimate for freedom from atrial arrhythmia was 78.1% (95% CI, 76.0%–80.0%); clinical effectiveness was more common in patients with paroxysmal AF versus persistent AF (81.6% versus 71.5%; P =0.001). Acute major adverse events occurred in 1.9% of patients. Conclusions: In this large observational registry of the postapproval clinical use of pulsed field technology to treat AF, catheter ablation using pulsed field energy was clinically effective in 78% of patients with AF.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) are a promising tool for drug testing and modelling genetic disorders. Abnormally low upstroke velocity is a current limitation. Here we investigated the use of 3D engineered heart tissue (EHT) as a culture method with greater resemblance to human heart tissue in comparison to standard technique of 2D monolayer (ML) format. I_Na was measured in ML or EHT using the standard patch-clamp technique. I_Na density was ~1.8 fold larger in EHT (−18.5 ± 1.9 pA/pF; n = 17) than in ML (−10.3 ± 1.2 pA/pF; n = 23; p < 0.001), approaching densities reported for human CM. Inactivation kinetics, voltage dependency of steady-state inactivation and activation of I_Na did not differ between EHT and ML and were similar to previously reported values for human CM. Action potential recordings with sharp microelectrodes showed similar upstroke velocities in EHT (219 ± 15 V/s, n = 13) and human left ventricle tissue (LV, 253 ± 7 V/s, n = 25). EHT showed a greater resemblance to LV in CM morphology and subcellular Na_V1.5 distribution. I_Na in hiPSC-CM showed similar biophysical properties as in human CM. The EHT format promotes I_Na density and action potential upstroke velocity of hiPSC-CM towards adult values, indicating its usefulness as a model for excitability of human cardiac tissue.

Background: Human engineered heart tissue (EHT) transplantation represents a potential regenerative strategy for patients with heart failure and has been successful in preclinical models. Clinical application requires upscaling, adaptation to good manufacturing practices, and determination of the effective dose. Methods: Cardiomyocytes were differentiated from 3 different human induced pluripotent stem cell lines including one reprogrammed under good manufacturing practice conditions. Protocols for human induced pluripotent stem cell expansion, cardiomyocyte differentiation, and EHT generation were adapted to substances available in good manufacturing practice quality. EHT geometry was modified to generate patches suitable for transplantation in a small-animal model and perspectively humans. Repair efficacy was evaluated at 3 doses in a cryo-injury guinea pig model. Human-scale patches were epicardially transplanted onto healthy hearts in pigs to assess technical feasibility. Results: We created mesh-structured tissue patches for transplantation in guinea pigs (1.5×2.5 cm, 9–15×10 ⁶ cardiomyocytes) and pigs (5×7 cm, 450×10 ⁶ cardiomyocytes). EHT patches coherently beat in culture and developed high force (mean 4.6 mN). Cardiomyocytes matured, aligned along the force lines, and demonstrated advanced sarcomeric structure and action potential characteristics closely resembling human ventricular tissue. EHT patches containing ≈4.5, 8.5, 12×10 ⁶ , or no cells were transplanted 7 days after cryo-injury (n=18–19 per group). EHT transplantation resulted in a dose-dependent remuscularization (graft size: 0%–12% of the scar). Only high-dose patches improved left ventricular function (+8% absolute, +24% relative increase). The grafts showed time-dependent cardiomyocyte proliferation. Although standard EHT patches did not withstand transplantation in pigs, the human-scale patch enabled successful patch transplantation. Conclusions: EHT patch transplantation resulted in a partial remuscularization of the injured heart and improved left ventricular function in a dose-dependent manner in a guinea pig injury model. Human-scale patches were successfully transplanted in pigs in a proof-of-principle study.

Background: Cardiac repolarization abnormalities in drug-induced and genetic long-QT syndrome may lead to afterdepolarizations and life-threatening ventricular arrhythmias. Human induced pluripotent stem cell–derived cardiomyocytes (hiPSC-CMs) should help to overcome the limitations of animal models based on species differences in repolarization reserve. Here, we compared head-to-head the contribution ofI_Ks(long QT1) andI_Kr(long QT2) on action potentials (APs) in human left ventricular (LV) tissue and hiPSC-CM–derived engineered heart tissue (EHT).Methods: APs were measured with sharp microelectrodes in EHT from 3 different control hiPSC-CM lines and in tissue preparations from failing LV.Results: EHT from hiPSC-CMs showed spontaneous diastolic depolarization and AP generation that were sensitive to low concentrations of ivabradine.I_Krblock by E-4031 prolonged AP duration at 90% repolarization with similar half-effective concentration in EHT and LV but larger effect size in EHT (+281 versus +110 ms in LV). AlthoughI_Krblock alone evoked early afterdepolarizations and triggered activity in 50% of EHTs, slow pacing, reduced extracellular K⁺, and blocking ofI_Kr,I_Ks, andI_K1were necessary to induce early afterdepolarizations in LV. In accordance with their clinical safety, moxifloxacin and verapamil did not induce early afterdepolarizations in EHT. In both EHT and LV,I_Ksblock by HMR-1556 prolonged AP duration at 90% repolarization slightly in the combined presence of E-4031 and isoprenaline.Conclusions: EHT from hiPSC-CMs shows a lower repolarization reserve than human LV working myocardium and could thereby serve as a sensitive and specific human-based model for repolarization studies and arrhythmia, similar to Purkinje fibers. In both human LV and EHT,I_Ksonly contributed to repolarization under adrenergic stimulation.

Catheter ablation for atrial fibrillation induces intracardiac neural damage characterized by glial S100B release, which promotes nerve sprouting.

Aims: Initial clinical studies of pulsed field ablation (PFA) to treat atrial fibrillation (AF) indicated a >90% durability rate of pulmonary vein isolation (PVI). However, these studies were largely conducted in single centres and involved a limited number of operators. We aimed to describe the electrophysiological findings and outcomes in patients undergoing repeat ablation after an initial PF ablation for AF. Methods and results: In the MANIFEST-REDO study, we investigated patients who underwent repeat ablation due to clinical recurrence—AF or atrial tachycardia (AT)—following first-ever PVI with a pentaspline PFA catheter (Farawave, Boston Scientific Inc.). At 22 centres, 427 patients (age 64 ± 11 years; 37% female) were included. Of note, the recurrent arrhythmia leading to the repeat ablation was paroxysmal AF (51%), persistent AF (30%), or AT (19%). At the repeat procedure, the PV reconnection rates were 30% (left superior pulmonary vein), 28% (left inferior pulmonary vein), 33% (right superior pulmonary vein), and 32% (right inferior pulmonary vein). In 45% of patients, all PVs were durably isolated at the beginning of the repeat procedure, with the previous use of any imaging or mapping modality being univariately associated with durable PVI. After a post-redo follow-up period of 284 (90–366) days, the primary effectiveness endpoint (freedom from documented AF/AT lasting ≥30 s after 3-month blanking without class I/III antiarrhythmic drugs or symptoms) was achieved in 65% of patients, with significant differences between groups (PAF 65% vs. PersAF 56% vs. AT 76%; P = 0.04). Persistent AF as recurrent arrhythmia after the initial PFA ablation predicted AT/AF recurrence after repeat ablation [hazard ratio 1.241 (95% confidence interval 1.534–1.005); P = 0.045]. The procedural complication rate was 2.8%. Conclusion: In repeat procedures for AF/AT performed after an index procedure with PFA for AF, PV reconnections are not uncommon. Repeat procedures can be performed safely and with an acceptable subsequent success rate.