Virtual blebbistatin: A robust and rapid software approach to motion artifact removal in optical mapping of cardiomyocytes

Heart-on-a-Miniscope: A Miniaturized Solution for Electrophysiological Drug Screening in Cardiac Organoids

Cardiovascular toxicity remains a primary concern in drug development, accounting for a significant portion of post-market drug withdrawals due to adverse reactions such as arrhythmias. Traditional preclinical models, predominantly based on animal cells, often fail to replicate human cardiac physiology accurately, complicating the prediction of drug-induced effects. Although human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) provide a more genetically relevant system, their use in 2D, static cultures does not sufficiently mimic the dynamic, 3D environment of the human heart. 3D cardiac organoids made from human iPSC-CMs can potentially bridge this gap. However, most traditional electrophysiology assays, developed for single cells or 2D monolayers, are not readily adaptable to 3D organoids. This study uses optical calcium analysis of human organoids combined with miniaturized fluorescence microscopy (miniscope) and heart-on-a-chip technology. This simple, inexpensive, and efficient platform provides robust on-chip calcium imaging of human cardiac organoids. The versatility of the system is demonstrated through cardiotoxicity assay of drugs known to impact cardiac electrophysiology, including dofetilide, quinidine, and thapsigargin. The platform promises to advance drug testing by providing a more reliable and physiologically relevant assessment of cardiovascular toxicity, potentially reducing drug-related adverse effects in clinical settings.

Evaluation of novel open-source software for cardiac optical mapping

KairoSight-3.0 is a recently released Python-based, open-source software for cardiac optical mapping analysis. Addressing challenges in high-resolution electrophysiological data analysis, KairoSight-3.0 facilitates comprehensive studies of cardiac conduction and excitation-contraction coupling. We compared its performance with ElectroMap, focusing on action potential duration and conduction velocity measurements in mouse heart models subjected to ischaemia and flecainide treatment. Our findings reveal that while both software are effective, inherent methodological differences impact measurement outcomes. KairoSight-3.0's robust analysis capabilities make it a valuable tool in cardiac research. Additionally, future directions for KairoSight-3.0 and other mapping analysis tools are explored.

Statement of importance

Open-source methods for analysis of cardiac optical mapping are vital tools in electrophysiological research. Our work directly evaluates the latest version of KarioSight, recently published in JMCC plus, with ElectroMap, an established and widely used tool. Our results show both software are effective in analysis of changes in both conduction and repolarisation. Considering the new features of KairoSight-3.0 and python implementation, our study importantly demonstrates the effectiveness of the software, highlights potential discrepancies between it and ElectroMap, and provides a perspective on future directions for KairoSight-3.0 and other software.

Dynamic control of contractile resistance to iPSC-derived micro-heart muscle arrays

Many types of cardiovascular disease are linked to the mechanical forces placed on the heart. However, our understanding of how mechanical forces exactly affect the cellular biology of the heart remains incomplete. In vitro models based on cardiomyocytes derived from human induced pluripotent stem cells (iPSC-CM) enable researchers to develop medium to high-throughput systems to study cardiac mechanobiology at the cellular level. Previous models have been developed to enable the study of mechanical forces, such as cardiac afterload. However, most of these models require exogenous extracellular matrix (ECM) to form cardiac tissues. Recently, a system was developed to simulate changes in afterload by grafting ECM-free micro-heart muscle arrays to elastomeric substrates of discrete stiffnesses. In the present study, we extended this system by combining the elastomer-grafted tissue arrays with a magnetorheological elastomeric substrate. This system allows iPSC-CM based micro-heart muscle arrays to experience dynamic changes in contractile resistance to mimic dynamically altered afterload. Acute changes in substrate stiffness led to acute changes in the calcium dynamics and contractile forces, illustrating the system's ability to dynamically elicit changes in tissue mechanics by dynamically changing contractile resistance.

Synchronous force and Ca2+ measurements for repeated characterization of excitation-contraction coupling in human myocardium

Dysfunctional Ca2+ signaling affects the myocardial systole and diastole, may trigger arrhythmia and cause transcriptomic and proteomic modifications in heart failure. Thus, synchronous real-time measurement of Ca2+ and force is essential to investigate the relationship between contractility and Ca2+ signaling and the alteration of excitation-contraction coupling (ECC) in human failing myocardium. Here, we present a method for synchronized acquisition of intracellular Ca2+ and contraction force in long-term cultivated slices of human failing myocardium. Synchronous time series of contraction force and intracellular Ca2+ were used to calculate force-calcium loops and to analyze the dynamic alterations of ECC in response to various pacing frequencies, post-pause potentiation, high mechanical preload and pharmacological interventions in human failing myocardium. We provide an approach to simultaneously and repeatedly investigate alterations of contractility and Ca2+ signals in long-term cultured myocardium, which will allow detecting the effects of electrophysiological or pharmacological interventions on human myocardial ECC.

Optical mapping and optogenetics in cardiac electrophysiology research and therapy: a state-of-the-art review

State-of-the-art innovations in optical cardiac electrophysiology are significantly enhancing cardiac research. A potential leap into patient care is now on the horizon. Optical mapping, using fluorescent probes and high-speed cameras, offers detailed insights into cardiac activity and arrhythmias by analysing electrical signals, calcium dynamics, and metabolism. Optogenetics utilizes light-sensitive ion channels and pumps to realize contactless, cell-selective cardiac actuation for modelling arrhythmia, restoring sinus rhythm, and probing complex cell-cell interactions. The merging of optogenetics and optical mapping techniques for 'all-optical' electrophysiology marks a significant step forward. This combination allows for the contactless actuation and sensing of cardiac electrophysiology, offering unprecedented spatial-temporal resolution and control. Recent studies have performed all-optical imaging ex vivo and achieved reliable optogenetic pacing in vivo, narrowing the gap for clinical use. Progress in optical electrophysiology continues at pace. Advances in motion tracking methods are removing the necessity of motion uncoupling, a key limitation of optical mapping. Innovations in optoelectronics, including miniaturized, biocompatible illumination and circuitry, are enabling the creation of implantable cardiac pacemakers and defibrillators with optoelectrical closed-loop systems. Computational modelling and machine learning are emerging as pivotal tools in enhancing optical techniques, offering new avenues for analysing complex data and optimizing therapeutic strategies. However, key challenges remain including opsin delivery, real-time data processing, longevity, and chronic effects of optoelectronic devices. This review provides a comprehensive overview of recent advances in optical mapping and optogenetics and outlines the promising future of optics in reshaping cardiac electrophysiology and therapeutic strategies.