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Atomic force microscopy (AFM) is widely used for the imaging and characterization of biological cells because of its nanoscale spatial resolution and force resolution. However, in the previous studies, the inability to effectively detect the contractile work of cardiomyocytes and the 3D dynamic expressions of their contraction and relaxation behaviors posed significant challenges. Therefore, this work presents a method for the analysis of the contractile work of a single cardiomyocyte by AFM. Two different contractile work measurement modes of cardiomyocytes are proposed, which are the constant height contact mode and the constant force contact mode. The differences in the contractile work were analyzed in two measurement modes. The changes in the contractile work of a single cardiomyocyte in the two measurement modes were studied, and the accuracies of the two measuring models were verified using ginseng extract. After the action of drugs, the contraction force of cardiomyocytes and the work done by contraction force increased. The experimental results indicated that the detection results of the ginseng water extract acting on the same cardiomyocyte by nanomanipulation technology were consistent with its pharmacological effects. Thus, it is reliable to detect the mechanical properties of cardiomyocytes using the nanomanipulation system. This study provides a new method for measuring the contraction force and contractile work of a single cardiomyocyte.

The functional restoration of a damaged cardiac tissue relies on a synchronized contractile capacity of exogenous and/or endogenous cardiomyocytes, which is challenging to achieve. Here, we explored the potential of the short glycopeptide diphenylalanine glucosamine-6-sulfate (FFGlcN6S) conjugated with an aromatic moiety, namely fluorenylmethoxycarbonyl (Fmoc), to enhance cardiac tissue regeneration. At physiological conditions, Fmoc-FFGlcN6S assembles into nanofibrous hydrated meshes, i.e., matrix mimicking hydrogels. These hydrogels can be further micropatterned allowing co-existence of hierarchical structures at different lenght. The patterned hydrogels support the culture of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) and promote their alignment. The cultured iPSC-CMs exhibit anisotropic synchronized contractions, indicating maturation and electrical interconnectivity. Moreover, the cultures express specific cardiac markers including, connexin-43 and sarcomeric-α-actinin, confirming enhanced cell-cell crosstalk, spontaneous contractility, and efficient transmission of electrical signals. Our results showcase the potential of short amphiphilic glycopeptides to mimic physical and biochemical cues that are essential for cardiomyocytes functionality and thus, these conjugates can be used in cardiac tissue engineering and regeneration., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: The contraction behaviors of cardiomyocytes (CMs), especially contraction synchrony, are crucial factors reflecting their maturity and response to drugs. A wider field of view helps to observe more pronounced synchrony differences, but the accompanied greater computational load, requiring more computing power or longer computational time., Methods: We proposed a method that directly correlates variations in optical field brightness with cardiac tissue contraction status (CVB method), based on principles from physics and photometry, for rapid video analysis in wide field of view to obtain contraction parameters, such as period and contraction propagation direction and speed., Results: Through video analysis of human induced pluripotent stem cell (hiPSC)-derived CMs labeled with green fluorescent protein (GFP) cultured on aligned and random nanofiber scaffolds, the CVB method was demonstrated to obtain contraction parameters and quantify the direction and speed of contraction within regions of interest (ROIs) in wide field of view. The CVB method required less computation time compared to one of the contour tracking methods, the Lucas-Kanade (LK) optical flow method, and provided better stability and accuracy in the results., Conclusion: This method has a smaller computational load, is less affected by motion blur and out-of-focus conditions, and provides a potential tool for accurate and rapid analysis of cardiac tissue contraction synchrony in wide field of view without the need for more powerful hardware., Competing Interests: Declarations. Conflict of interest: The authors have no financial conflicts of interest. Ethical Approval: Not applicable as there is no use of animal models for the experiments. All authors approve the submission., (© 2025. Korean Tissue Engineering and Regenerative Medicine Society.)

The Frank-Starling law and Anrep effect describe two intrinsic mechanisms that regulate contraction force in the heart. Based on recent advancements and the historical literature, we propose new perspectives and address several critical issues in this review. ( a ) The Frank-Starling mechanism and Anrep effect are dynamically linked and act synergistically. ( b ) An open question is how cardiomyocytes sense mechanical load and transduce to biochemical signals (called mechano-chemo-transduction or MCT) to regulate contraction in response to load changes. ( c ) One research focus is to identify various mechanosensors and decipher their downstream MCT pathways. ( d ) Innovative experimental techniques engage different mechanosensors that detect different local strain and stress in the cell architecture. ( e ) Closed-loop MCT feedback in the dynamic excitation-Ca2+ signaling-contraction system enables autoregulation of contraction in response to physiological load changes. ( f ) However, pathological overload such as volume and pressure overload lead to excessive MCT-Ca2+ gain, cardiac remodeling, and heart diseases.

Aims: Cardiac implantable electrical devices such as cardiac resynchronization therapy with defibrillator (CRT-Ds) or cardiac contractility modulation (CCMs) are therapy options for patients with symptomatic heart failure (HF) and reduced left ventricular ejection fraction (LVEF) despite optimal medical treatment. As yet, a comparison between both devices has not been performed., Methods and Results: The Mannheim Cardiac Resynchronization Therapy Registry (MARACANA) and the Mannheim Cardiac Contractility Modulation Observational Study (MAINTAINED) included all patients who received CRTs or CCMs in our medical centre between 2012 and 2021. For the present analysis, we retrospectively compared patients provided with either CRT-Ds (n = 220) or CCMs with additional defibrillators (n = 105) regarding New York Heart Association classification (NYHA), LVEF, tricuspid annular plane systolic excursion (TAPSE), QRS-width and other HF modification aspects after 12 months. Before implantation, CCM patients presented with lower LVEF (23.6 ± 6.2 vs. 26.3 ± 6.5%) and worse NYHA (3.03 ± 0.47 vs. 2.81 ± 0.48, both P < 0.05), compared with CRT-D patients. Follow-up improvements in NYHA (2.43 ± 0.67 vs. 2.28 ± 0.72), LVEF (30.5 ± 10.7 vs. 35.2 ± 10.5%) and TAPSE (17.2 ± 5.2 vs. 17.1 ± 4.8 to 18.9 ± 3.4 vs. 17.3 ± 3.6 mm, each P < 0.05) were comparable. The intrinsic QRS-width was stable with CCM (109.1 ± 18 vs. 111.7 ± 19.7 ms, P > 0.05), while the paced QRS-width with CRT-D after 12 months was lower than intrinsic values at baseline (157.5 ± 16.5 vs. 139.2 ± 16 ms, P < 0.05). HF hospitalizations occurred more often for CCM than CRT-D patients (45.7 vs. 16.8%/patient years, odds ratio 4.2, P < 0.001)., Conclusions: Chronic heart failure patients could experience comparable 12-month improvements in functional status and ventricular reverse remodelling, with appropriately implanted CCMs and CRT-Ds. Differences in HF hospitalization rates may be due to the more advanced HF of CCM patients at implantation., (© 2024 The Author(s). ESC Heart Failure published by John Wiley & Sons Ltd on behalf of European Society of Cardiology.)

In maximally Ca 2+ -activated demembranated fibres from the mammalian skeletal muscle, the depression of the force by lowering the temperature below the physiological level (~35 °C) is explained by the reduction of force in the myosin motor. Instead, cooling is reported to not affect the force per motor in Ca 2+ -activated cardiac trabeculae from the rat ventricle. Here, the mechanism of the cardiac performance depression by cooling is reinvestigated with fast sarcomere-level mechanics. We determine the changes in the half-sarcomere compliance of maximally Ca 2+ -activated demembranated rat trabeculae in the range of temperatures of 10-30 °C and analyse the data in terms of a simplified mechanical model of the half-sarcomere to extract the contribution of myofilaments and myosin motors. We find that the changes in the ensemble force are due to changes in the force per motor, while the fraction of actin-attached motors remains constant independent of temperature. The results demonstrate that in the cardiac myosin, as in the skeletal muscle myosin, the force-generating transition is endothermic. The underlying large heat absorption indicates the interaction of extended hydrophobic surfaces within the myosin motor, like those suggested by the crystallographic model of the working stroke.

The use of a video method based on the Digital Image Correlation (DIC) algorithm from experimental mechanics to estimate the displacements, strain field, and sarcolemma length in a beating single-cell cardiomyocyte is proposed in this work. The obtained deformation is then correlated with the calcium signal, from calcium imaging where fluorescent dyes sensitive to calcium Ca 2+ are used. Our proposed video-based method for simultaneous contraction and intracellular calcium analysis results in a low-cost, non-invasive, and label-free method. This technique has shown great advantages in long-term observations because this type of intervention-free measurement neutralizes the possible alteration in the beating cardiomyocyte introduced by other techniques for measuring cell contractility (e.g., Traction Force Microscopy, Atomic Force Microscopy, Microfabrication or Optical tweezers). Three tests were performed with synthetically augmented data from cardiomyocyte images to validate the robustness of the algorithm. First, a simulated rigid translation of a referenced image is applied, then a rotation, and finally a controlled longitudinal deformation of the referenced image, thus simulating a native realistic deformation. Finally, the proposed framework is evaluated with real experimental data. To validate contraction induced by intracellular calcium concentration, this signal is correlated with a new deformation measure proposed in this article, which is independent of cell orientation in the imaging setup. Finally, based on the displacements obtained by the DIC algorithm, the change in sarcolemma length in a contracting cardiomyocyte is calculated and its temporal correlation with the calcium signal is obtained., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Adequate assessment of the contribution of the different phases of atrial mechanical activity to the value of ejection volume and pressure developed by the ventricle is a complex and important experimental and clinical problem. A new method and an effective algorithm for controlling the interaction of isolated rat right atrial and right ventricular strips during the cardiac cycle were developed and tested in a physiological experiment. The presented functional model is flexible and has the ability to change many parameters (temperature, pacing rate, excitation delay, pre- and afterload levels, transfer length, and force scaling coefficients) to simulate different types of cardiac pathologies. For the first time, the contribution of the duration of the excitation delay of the right ventricular strips to the amount of work performed by the muscles during the cardiac cycle was evaluated. Changes in the onset of atrial systole and the delay in activation of ventricular contraction may lead to a reduction in cardiac stroke volume, which should be considered in the diagnosis and treatment of cardiovascular disease and in resynchronization therapy., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Human myocardial function can be investigated in the laboratory using human atrial trabeculae. These multicellular preparations provide a translatable model for assessing the ex vivo contractility, electrophysiology, and ionic and metabolic underpinnings of human cardiac muscle. Here, we detail the materials and methods required to determine the baseline function of a human atrial trabecula, from dissection to stimulation. This method is also adaptable for additional non-human myocardial applications., (© 2025. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Objective: To evaluate the influence of pre-existing maternal diabetes mellitus on fetal myocardial performance index and systolic-to-diastolic duration ratio., Methods: Prospective cohort study included 179 pregnant women between 20 and 36w6d, divided into 3 groups: Group 1 (120, normal), Group 2 (31, type 1 diabetes mellitus), and Group 3 (28, type 2 diabetes mellitus). Systolic-to-diastolic duration ratio was calculated as the sum of isovolumic contraction time and ejection time divided by the sum of isovolumic relaxation time and ventricular filling time. Spectral Doppler was used to assess left ventricle systolic-to-diastolic duration ratio. Tissue Doppler was used to assess right ventricular filling time. Using spectral Doppler, left ventricle myocardial performance index was calculated as the sum of isovolumic contraction time and isovolumic relaxation time divided by ejection time., Results: Pre-existing maternal diabetes mellitus had a significant influence on fasting glucose levels ( p < 0.001), left ventricle isovolumic contraction time ( p < 0.001), left ventricle ejection time ( p = 0.025), and left ventricle myocardial performance index ( p < 0.001). Group 2 had higher left ventricle isovolumic contraction time (0.036 vs. 0.031 sec, p = 0.001) and left ventricle myocardial performance index (0.487 vs. 0.453, p = 0.003) compared with Group 1. Group 3 showed higher left ventricle myocardial performance index (0.492 vs. 0.449, p = 0.006) and lower left ventricle ejection time (0.161 vs. 0.169 sec, p = 0.038) than Group 1. Left ventricle systolic-to-diastolic duration ( p = 0.704), right ventricle systolic-to-diastolic duration ratio' ( p = 0.757), left ventricle isovolumic contraction time ( p = 0.163), left ventricle ejection time ( p = 0.093), and left ventricle myocardial performance index ( p = 0.087) were not useful parameters in predicting composite neonatal outcomes., Conclusion: Pre-existing maternal diabetes mellitus had significant influence on fetal left ventricle myocardial performance index, but no effect on systolic-to-diastolic duration ratio. Systolic-to-diastolic duration ratio was not useful in predicting adverse perinatal outcomes.

Cardiac sex-difference functional studies have centred on measurements of twitch force and Ca 2+ dynamics. The energy expenditures from these two cellular processes: activation (Ca 2+ handling) and contraction (cross-bridge cycling), have not been assessed, and compared, between sexes. Whole-heart studies measuring oxygen consumption do not directly measure the energy expenditure of these activation-contraction processes. In this study, we directly quantified these energy expenditures in terms of heat production. Left-ventricular trabeculae were dissected from rats aged 9-13 weeks. Mechano-energetics of trabeculae were characterized using our work-loop calorimeter under various conditions including varying muscle lengths, stimulus frequencies, and afterloads. Each trabecula was subjected to protocols that allowed it to contract either isometrically or shorten to perform work-loops. Force production, length change, and heat output were simultaneously measured. We extracted various metrics: twitch kinetics, shortening kinetics, mechanical work, and heat associated with cross-bridge cycling and Ca 2+ cycling, and quantified mechanical efficiency. Results show no sex differences in any of the metrics. Peak mechanical efficiency was not affected by sex (10.25 ± 0.57% in female trabeculae; 10.93 ± 0.87% in male trabeculae). We conclude that cardiac mechanics and energetics are not affected by sex at the muscle level, within the rat age range studied., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

The regulation of heart function is attributed to a dual filament mechanism: i) the Ca 2+ -dependent structural changes in the regulatory proteins of the thin, actin-containing filament making actin available for myosin motor attachment, and ii) the release of motors from their folded (OFF) state on the surface of the thick filament allowing them to attach and pull the actin filament. Thick filament mechanosensing is thought to control the number of motors switching ON in relation to the systolic performance, but its molecular basis is still controversial. Here, we use high spatial resolution X-ray diffraction data from electrically paced rat trabeculae and papillary muscles to provide a molecular explanation of the modulation of heart performance that calls for a revision of the mechanosensing hypothesis. We find that upon stimulation, titin-mediated structural changes in the thick filament switch motors ON throughout the filament within ~½ the maximum systolic force. These structural changes also drive Myosin Binding Protein-C (MyBP-C) to promote first motor attachments to actin from the central 1/3 of the half-thick filament. Progression of attachments toward the periphery of half-thick filament with increase in systolic force is carried on by near-neighbor cooperative thin filament activation by attached motors. The identification of the roles of MyBP-C, titin, thin and thick filaments in heart regulation enables their targeting for potential therapeutic interventions., Competing Interests: Competing interests statement:The authors declare no competing interest.

Background: Donation after circulatory death (DCD) hearts have to withstand ischemia/reperfusion injury that is partially driven by proinflammatory cytokines and decreases ventricular contractility. We hypothesize that cytokine adsorption during normothermic ex vivo blood perfusion of DCD hearts reduces the cytokine levels and improves ventricular contractility., Methods and Results: Porcine DCD hearts were maintained 4 hours by ex vivo blood perfusion with (DCD-BP CytoS , all groups: N=8) or without (DCD-BP) CytoSorb, followed by 2 hours reperfusion with fresh blood, including left ventricular functional analysis using a balloon catheter. In a control and a DCD group, hearts were evaluated after procurement. We determined lactate and cytokines after ex vivo blood perfusion and the myocardial and left anterior descending artery transcriptome using microarrays after reperfusion. In DCD-BP CytoS , the developed pressure (control: 124±7 mm Hg/s, DCD: 86±4 mm Hg/s, DCD-BP: 69±11 mm Hg/s, DCD-BP CytoS : 112±9 mm Hg/s; P <0.05) and maximal slope of pressure increment (control: 2010±39 mm Hg/s, DCD: 1219±164 mm Hg/s, DCD-BP: 964±163 mm Hg/s, DCD-BP CytoS : 1794±205 mm Hg/s; P <0.05) were higher compared with DCD-BP and DCD hearts. However, contractility decreased later during reperfusion without CytoSorb. After 4 hours, troponin, lactate (45±5% versus 69±9%, P <0.05), IL (interleukin)-1β, -1ra, and -8 were lower in DCD-BP CytoS hearts. In the myocardium of DCD-BP CytoS compared with DCD-BP hearts, inflammatory mediator receptor activity/binding pathways were enriched, and pathways for collagen-containing extracellular matrix and contractile fiber were underrepresented. In the left anterior descending artery of DCD-BP CytoS hearts, serine/threonine/tyrosine kinase activity and wound-healing pathways were enriched, and mitochondrial protein-containing complex and respiratome-associated pathways were underrepresented., Conclusions: CytoSorb during ex vivo blood perfusion enhances the maintenance of DCD hearts and is likely to improve graft function after transplantation.

Measurements of fetal atrial size, shape, and contractility have been previously reported using the TomTec fetal heart speckle tracking analysis software, which currently is no longer available in the marketplace. At the present time, the only software available for speckle-tracking analysis of the fetal heart is fetalHQ, which analyzes the fetal heart ventricles using the same algorithms as the TomTec software used for speckle-tracking analysis. This communication will review how to use the fetalHQ software to measure the size, shape, and contractility of the atrial chambers., (© 2024 American Institute of Ultrasound in Medicine.)

Cardiac trabeculae form a network of muscular strands that line the inner surfaces of the heart. Their development depends on multiscale morphogenetic processes and, while highly conserved across vertebrate evolution, their role in the pathophysiology of the mature heart is not fully understood. Here we report variant associations across the allele frequency spectrum for trabecular morphology in 47,803 participants of the UK Biobank using fractal dimension analysis of cardiac imaging. We identified an association between trabeculation and rare variants in 56 genes that regulate myocardial contractility and ventricular development. Genome-wide association studies identified 68 loci in pathways that regulate sarcomeric function, differentiation of the conduction system and cell fate determination. We found that trabeculation-associated variants were modifiers of cardiomyopathy phenotypes with opposing effects in hypertrophic and dilated cardiomyopathy. Together, these data provide insights into mechanisms that regulate trabecular development and plasticity, and identify a potential role in modifying monogenic disease expression., Competing Interests: Competing interests: D.P.O. has consulted for Bayer AG and Bristol-Myers Squibb. J.S.W. has consulted for MyoKardia, Inc., Pfizer, Foresite Labs, Health Lumen and Tenaya Therapeutics and has received research support from Bristol-Myers Squibb. R.T.L. has consulted for Health Lumen and FITFILE. None of these activities are directly related to the work presented here. The other authors declare no competing interests., (© 2024. The Author(s).)

Biofabricating 3D cardiac tissues that mimic the native myocardial tissue is a pivotal challenge in tissue engineering. In this study, we fabricate 3D cardiac tissues with controlled, multidirectional cellular alignment and directed or twisting contractility. We show that multidirectional filamented light can be used to biofabricate high-density (up to 60 × 10 6 cells mL -1 ) tissues, with directed uniaxial contractility (3.8x) and improved cell-to-cell connectivity (1.6x gap junction expression). Furthermore, by using multidirectional light projection, we can partially overcome cell-induced light attenuation, and fabricate larger tissues with multidirectional cellular alignment. For example, we fabricate a tri-layered myocardium-like tissue and a bi-layered tissue with torsional contractility. The approach provides a new strategy to rapidly fabricate aligned cardiac tissues relevant to regenerative medicine and biohybrid robotics., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Contraction of heart muscle requires activation of both the actin and myosin filaments. The mechanism of myosin filament activation is unknown, but the leading candidate hypothesis is direct mechano-sensing by the filaments. Here, we tested this hypothesis by activating intact trabeculae from rat heart by electrical stimulation under different loads and measuring myosin filament activation by X-ray diffraction. Unexpectedly, we found that the distinct structural changes in the myosin filament associated with activation had different dependences on the load. In early activation, all the structural changes indicated faster activation at higher load, as expected from the mechano-sensing hypothesis, but, at later times, the helical order of the myosin motors characteristic of the inactivated state was lost even at very low load. We conclude that mechano-sensing does operate in heart muscle, but it is supplemented by a previously undescribed mechanism that links myosin filament activation to actin filament activation. KEY POINTS: Myosin filament activation controls the strength and speed of contraction in heart muscle. Early activation of the myosin filament is determined by the filament load. At later times, myosin filament activation is controlled by a load independent pathway. This load independent pathway provides new targets and assays for drug development., (© 2024 The Author(s). The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)

Background: Efficient excitation-contraction coupling of mammalian ventricular cardiomyocytes depends on the transverse-axial tubular system (TATS), a network of surface membrane invaginations. TATS enables tight coupling of sarcolemmal and sarcoplasmic reticulum membranes, which is essential for rapid Ca 2+ -induced Ca 2+ release, and uniform contraction upon electrical stimulation. The majority of TATS in healthy ventricular cardiomyocytes is composed of transverse tubules (TT, ∼90 % of TATS in rabbit). The remainder consists of mostly axial tubules (AT), which are less abundant and less well studied. In disease, however, the relative abundance of TT and AT changes. The mechanisms and relevance of this change are not known, and understanding them requires a more targeted effort to study the dynamics of AT structure and function. While TATS content is continuous with the interstitial space, it is contained within a domain of restricted diffusion. We have previously shown that TT are cyclically squeezed during stretch and contraction. This can contribute to TT content mixing and accelerates luminal content exchange with the environment. Here, we explore the effects of cardiomyocyte stretch and contraction on AT., Methods: TATS structure and diffusion dynamics were studied using 3D electron tomography of rabbit left ventricular cardiomyocytes, preserved at rest or during contraction, and ventricular tissue preserved at rest or during stretch, as well as live-cell TATS content exchange measurements., Results: We show (i) that cardiomyocyte contraction is associated with an increase in the apparent speed of diffusion of TT content that scales with beating rate and degree of cell shortening. In contrast, (ii) AT develop membrane folds and constrictions during contraction, (iii) with no effect of contraction on luminal exchange dynamics, while (iv) cardiomyocyte stretch is associated with AT straightening and AT and TT 'squeezing' that (v) supports an acceleration of the apparent speed of diffusion in AT and TT. Finally, (vi) we present a simple computational model outlining the potential relevance of AT in healthy and diseased cells., Conclusions: Our results indicate that TT and AT are differently affected by the cardiac contractile cycle, and suggest that AT may play a role in ensuring TATS network content homogeneity in diseased cardiomyocytes. Further research is needed to explore the interplay of structural and functional remodelling of different TATS components in failing myocardium., Competing Interests: Declaration of competing interest The authors declare no competing interests., (Copyright © 2024. Published by Elsevier Ltd.)

The mechanical function of the myocardium is defined by cardiomyocyte contractility and the biomechanics of the extracellular matrix (ECM). Understanding this relationship remains an important unmet challenge due to limitations in existing approaches for engineering myocardial tissue. Here, they established arrays of cardiac microtissues with tunable mechanics and architecture by integrating ECM-mimetic synthetic, fiber matrices, and induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs), enabling real-time contractility readouts, in-depth structural assessment, and tissue-specific computational modeling. They found that the stiffness and alignment of matrix fibers distinctly affect the structural development and contractile function of pure iPSC-CM tissues. Further examination into the impact of fibrous matrix stiffness enabled by computational models and quantitative immunofluorescence implicates cell-ECM interactions in myofibril assembly, myofibril maturation, and notably costamere assembly, which correlates with improved contractile function of tissues. These results highlight how iPSC-CM tissue models with controllable architecture and mechanics can elucidate mechanisms of tissue maturation and disease., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

The mechanisms underlying cooperative activation and inactivation of myocardial force extend from local, near-neighbor interactions involving troponin-tropomyosin regulatory units (RU) and crossbridges (XB) to more global interactions across the sarcomere. To better understand these mechanisms in the hearts of small and large mammals, we undertook a simplified mathematical approach to assess the contribution of three types of near-neighbor cooperative interactions, i.e., RU-induced, RU-activation (RU-RU), crossbridge-induced, crossbridge-binding (XB-XB), and XB-induced, RU-activation (XB-RU). We measured the Ca2+ and activation dependence of the rate constant of force redevelopment in murine- and porcine-permeabilized ventricular myocardium. Mathematical modeling of these three near-neighbor interactions yielded nonlinear expressions for the RU-RU and XB-RU rate coefficients (kon and koff) and XB-XB rate coefficients describing the attachment of force-generating crossbridges (f and f'). The derivation of single cooperative coefficient parameters (u = RU-RU, w = XB-RU, and v = XB-XB) permitted an initial assessment of the strength of each near-neighbor interaction. The parameter sets describing the effects of discrete XB-XB or XB-RU interactions failed to adequately fit the in vitro contractility data in either murine or porcine myocardium. However, the Ca2+ dependence of ktr in murine and porcine ventricular myocardium was well fit by parameter sets incorporating the RU-RU cooperative interaction. Our results indicate that a significantly stronger RU-RU interaction is present in porcine ventricular myocardium compared with murine ventricular myocardium and that the relative strength of the near-neighbor RU-RU interaction contributes to species-specific myocardial contractile dynamics in small and large mammals., (© 2025 Phan and Fitzsimons.)

Phan and Fitzsimons (https://doi.org/10.1085/jgp.202413582) develop a new mathematical model of muscle contraction that explores cooperative mechanisms in small (murine) and large (porcine) myocardium., (© 2025 Childers.)

Mimicking the curved collagenous fibers in the cardiac extracellular matrix to fabricate elastic scaffolds in vitro is important for cardiac tissue engineering. Here, we developed sinusoidal polycaprolactone (PCL) fibrous scaffolds with commendable flexibility and elasticity to enhance the contractility of primary cardiomyocytes by employing melt-based electrohydrodynamic (EHD) printing. Microscale sinusoidal PCL fibers with an average diameter of ∼10 μm were printed to mimic the collagenous fibers in the cardiac ECM. The sinusoidal PCL fibrous scaffolds were EHD-printed in a layer-by-layer manner and exhibited outstanding flexibility and elasticity compared with the straight ones. The sinusoidal PCL scaffolds provided an elastic microenvironment for the attaching and spreading of primary cardiomyocytes, which facilitated their synchronous contractive activities. Primary cardiomyocytes also showed improved gene expression and maturation on the sinusoidal PCL scaffolds under electrical stimulation for 5 days. It is envisioned that the proposed flexible fibrous scaffold with biomimetic architecture may serve as a suitable patch for tissue regeneration and repair of damaged hearts after myocardial infarction.

Non-invasive diagnostic modalities are integral to cardiovascular care; however, current systems primarily measure peripheral pressure, limiting the breadth of cardiovascular prognostication. We report a novel approach for extracting left side heart sounds using a brachial cuff device. The technique leverages brachial cuff device enhanced signal resolution to capture pressure fluctuations generated by cardiohemic system vibrations, the sound pressure waveform. We analyze left heart catheterization data alongside simultaneous brachial cuff device measurements to correlate sound pressure waveform features with left ventricle (LV) contractility. The extracted sound pressure waveform reveals two prominent oscillatory wave packets, termed WP1 and WP2, originating from cardiac structure vibrations associated with LV contractions and relaxation. We demonstrate that WP1 originates from LV contraction during systolic blood ejection through the aortic valve (AV) and is correlated with LV isovolumetric contraction, clinically measured by LV dPdt-max (Pearson-R = 0.65, p < 0.001). Additionally, we show that WP2 comes from LV elongation required for blood flow deceleration at the end of systole, causing AV closure, and is correlated with LV isovolumetric relaxation, measured by LV ndPdt-max (Pearson-R = 0.55, p < 0.001). These findings highlight the value of cuff sound pressure waveforms in providing insights about dynamic coupling of the LV-Aorta complex for non-invasive assessment of LV contractility., (© 2024. The Author(s).)

Sarcomere activation in striated muscle requires both thin filament-based and thick filament-based activation mechanisms. Recent studies have shown that myosin heads on the thick filaments undergo OFF to ON structural transitions in response to calcium (Ca2+) in permeabilized porcine myocardium in the presence of a small molecule inhibitor that eliminated active force. The changes in X-ray diffraction signatures of OFF to ON transitions were interpreted as Ca2+ acting to activate the thick filaments. Alternatively, Ca2+ binding to troponin could initiate a Ca2+-dependent crosstalk from the thin filament to the thick filament via interfilament connections such as the myosin binding protein-C. Here, we exchanged native troponin in permeabilized porcine myocardium for troponin containing the cTnC D65A mutation, which disallows the activation of troponin through Ca2+ binding to determine if Ca2+-dependent thick filament activation persists in the absence of thin filament activation. After the exchange protocol, over 95% of the Ca2+-activated force was eliminated. Equatorial intensity ratio increased significantly in both WT and D65A exchanged myocardium with increasing Ca2+ concentration. The degree of helical ordering of the myosin heads decreased by the same amount in WT and D65A myocardium when Ca2+ concentration increased. These results are consistent with a direct effect of Ca2+ in activating the thick filament rather than an indirect effect due to Ca2+-mediated crosstalk between the thick and thin filaments., (© 2024 Mohran et al.)

Objectives: The impact of residual pulmonary stenosis (rPS) or right ventricular (RV) outflow tract obstruction on prognosis after surgical pulmonary valve insertion) in repaired tetralogy of Fallot patients with pulmonary regurgitation (PR) remains controversial. rPS assessment is partially dependent on RV contractility. We investigated the impact of rPS according to RV ejection fraction (RVEF)., Methods: In this multicentre, retrospective study, 117 repaired tetralogy of Fallot patients who underwent surgical pulmonary valve insertion for more than moderate PR between 2003 and 2021 were examined. Regarding rPS, the threshold for PR with rPS (PSR) and PR was 25 mmHg. For RVEF, the threshold for preserved RVEF (pEF) and reduced RVEF (rEF) was 40%. The patients were divided into 4 groups: patients with PR and pEF (PR-pEF) (n = 48), those with PR and rEF (PR-rEF) (n = 44), those with PSR and pEF (PSR-pEF) (n = 16), and those with PSR and rEF (PSR-rEF) (n = 9). Clinical parameters, postoperative adverse event rates and their associations were studied., Results: The 5-year freedom from adverse cardiovascular events was the highest in the PSR-pEF and the lowest in the PSR-rEF groups. The PSR-rEF group had the highest RV end-diastolic pressure (RVEDP) (12 ± 2.2 mmHg) (P = 0.006). From multivariable analysis, RVEDP was associated with postoperative adverse events (P = 0.016). RVEDP > 8 mmHg was associated with a lower freedom from adverse events., Conclusions: The freedom from adverse events was the lowest in the PSR-rEF group, with the highest RVEDP, suggesting RV systolic and diastolic dysfunction. Reduced RVEF may mask the intrinsic degree of residual stenosis, delay surgical pulmonary valve insertion timing and increase adverse events., (© The Author(s) 2024. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.)

Ca 2+ -mediated activation of thin filaments is a crucial step in initiating striated muscle contraction. To gain mechanistic insight into this regulatory process, thin filament (TF) components and myosin motors from diverse species and tissue sources are often combined in minimal in vitro systems. The contribution of tissue-specific TF composition with native myosin motors in generating contraction speed remains unclear. To examine TF-mediated regulation, we established a procedure to purify native TFs (nTF) and myosin motors (M-II) from the same cardiac tissue samples as low as 10 mg and investigated their influence on gliding speeds and Ca 2+ sensitivity. The rabbit atrial and ventricular nTFs and M-II were assessed in in vitro nTF motility experiments under varying Ca 2+ concentrations. The speed-pCa relationship yielded a maximum TF speed of 2.58 μm/s for atrial (aM-II) and 1.51 μm/s for ventricular myosin (vM-II), both higher than the respective unregulated actin filament gliding speeds. The Ca 2+ sensitivity was different for both protein sources. After swapping the nTFs, the ventricular TFs increased their gliding speed on atrial myosin, while the atrial nTFs reduced their gliding speed on ventricular myosin. Swapping of the nTFs decreased the calcium sensitivity for both vM-II and aM-II, indicating a strong influence of the thin filament source. These studies suggest that the nTF-myosin combination is critical to understanding the Ca 2+ sensitivity of the shortening speed. Our approach is highly relevant to studying precious human cardiac samples, that is, small myectomy samples, to address the alteration of contraction speed and Ca 2+ sensitivity in cardiomyopathies., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interests with the contents of this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Objectives: In a cohort of patients with estimated fetal weights (EFWs) <10th centile, we aimed 1) to compare the prevalence of abnormalities of fetal 4-chamber view (4CV) cardiac size, shape, and ventricular contractility in fetal growth restricted (FGR) and small-for-gestational-age (SGA) fetuses and 2) to compare umbilical vein flow (UVF) measurements to standard Doppler surveillance in predicting abnormalities of cardiac function., Methods: Prospective observational cohort study of fetuses with EFW <10th percentile. Measurements of size and shape used were 4CV transverse width, 4CV cardiac area, 4CV global sphericity index, and right-to-left ventricular mid-chamber width ratio. Variables of contractility used were fractional shortening change at the mid-ventricle chamber, global longitudinal strain, fractional area change, and left ventricular cardiac output. The UVF and standard Doppler surveillance including umbilical artery (UA), middle cerebral artery, and cerebroplacental ratio (CPR) were collected. Control data were from previously published studies., Results: A total of 95 fetuses with EFWs <10th centile were included in the study. The rates of abnormalities of cardiac size and shape and ventricular contractility were all significantly elevated compared with normally grown control fetuses but similar between FGR and SGA fetuses. In a subset of 76 patients with UVF data, evaluation UVF identified more patients with any abnormality of contractility compared with UA (37.9 vs 17.2%, P = .02)., Conclusions: The addition of UVF doubled the detection rate of ventricular contractility abnormalities. The addition of UVF should be considered in the surveillance of FGR and SGA fetuses to further stratify the severity of hypoxemia and to identify those at greater risk for future cardiovascular dysfunction., (© 2024 American Institute of Ultrasound in Medicine.)

Hypertrophic cardiomyopathy (HCM) patients with sarcomere mutations have an increased risk of heart failure and left ventricular (LV) systolic dysfunction. We hypothesize that sarcomere mutation carriers have abnormal myocardial contractility before LV dysfunction. Therefore, we aimed to associate myocardial contractility with identified sarcomere mutations and predict genotyped HCM patients with sarcomere mutation by three-dimensional speckle tracking imaging (3D-STI). A retrospective analysis of 117 HCM patients identified 32 genotype-positive (G +) and 85 genotype-negative (G-) patients. Genotype-positive patients had higher globe circumferential strain (GCS), globe longitudinal strain (GLS), and globe radial strain (GRS) (p < 0.05), and multivariate logistic regression revealed that these variables were associated with a positive genetic status (p < 0.05). After the propensity matches other possible influencing factors, we developed three models, named Model GCS, Model GLS, and Model GRS, which could identified genotype-positive HCM patients with excellent performance (AUC of 0.855, 0.833, and 0.870 respectively, all p < 0.001). Genotype-positive HCM patients show a higher myocardial hyper-contractility status than patients without sarcomere mutations. When combined with clinical and echocardiographic markers, the 3D-STI parameters can effectively identify the likelihood of genotype-positive HCM., (© 2024. Springer Nature Japan KK, part of Springer Nature.)

Background: Cardiovascular magnetic resonance (CMR) derived global function index (GFI) and myocardial contraction fraction (MCF) were identified as useful imaging markers to assess left ventricular (LV) cardiac performance and can provide prognostic information for several cardiac diseases. As pediatric reference values are lacking, the aim of this retrospective study was to establish these values., Methods: 154 CMR examinations of healthy children and adolescents (4-18 years) were included. LV end-diastolic, end-systolic and stroke volumes, ejection fraction (LVEF) and myocardial mass were measured using short axis stacks. Results were used to calculate LVGFI and LVMCF. Statistically, the Lambda-Mu-Sigma (LMS)-method was applied to create percentile curves and tables., Results: The mean age (standard deviation) of the subjects was 13.8 (2.8) years, 102 were male (66%). Mean LVGFI was 46.3 (6.0)% and mean LVMCF was 110.6 (19.9) %. Both, LVGFI and LVMCF decreased significantly with age (LVGFI: r = -0.30, p < 0.001; LVMCF: -0.30, p < 0.001). There was no statistical difference between girls and boys (p all >0.05). Strong correlations between LVGFI and LVMCF (r = 0.78, p < 0.001) as well as between LVGFI and LVEF (r = 0.80, p < 0.001) were documented whereas the correlation of LVMCF and LVEF was weaker (r = 0.32, p < 0.001). Univariable and multivariable regression analysis demonstrated that LVGFI was strongly associated with age whereas LVMCF was associated with weight. Percentile curves and tables were created accordingly., Conclusion: We provide pediatric CMR reference values for the new cardiac functional markers LVGFI and LVMCF. These may improve the interpretation of clinical CMR studies and can be used for future research studies., (Copyright © 2024. Published by Elsevier B.V.)

Physics-based computer models based on numerical solutions of the governing equations generally cannot make rapid predictions, which in turn limits their applications in the clinic. To address this issue, we developed a physics-informed neural network (PINN) model that encodes the physics of a closed-loop blood circulation system embedding a left ventricle (LV). The PINN model is trained to satisfy a system of ordinary differential equations (ODEs) associated with a lumped parameter description of the circulatory system. The model predictions have a maximum error of less than 5% when compared to those obtained by solving the ODEs numerically. An inverse modeling approach using the PINN model is also developed to rapidly estimate model parameters (in ∼ 3 min) from single-beat LV pressure and volume waveforms. Using synthetic LV pressure and volume waveforms generated by the PINN model with different model parameter values, we show that the inverse modeling approach can recover the corresponding ground truth values for LV contractility indexed by the end-systolic elastance E es with a 1% error, which suggests that this parameter is unique. The estimated E es is about 58% to 284% higher for the data associated with dobutamine compared to those without, which implies that this approach can be used to estimate LV contractility using single-beat measurements. The PINN inverse modeling can potentially be used in the clinic to simultaneously estimate LV contractility and other physiological parameters from single-beat measurements., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The co-ordinated electrical activity of ∼2 billion cardiac cells ensures stability of the heartbeat. Indeed, the remarkably low incidence (<1%) of ventricular arrhythmias in the healthy heart is only possible when the electrical event across this syncytium is closely controlled. In contrast, the diseased myocardium is associated with increased electrophysiological heterogeneity, unstable rhythm, and increased incidence of lethal arrhythmias. But what is the link between cellular and tissue level heterogeneity? Recent research has shown the existence of considerable cellular heterogeneity even in the healthy heart, suggesting that cell-to-cell variability in electrical (e.g. action potential duration) and mechanical performance (e.g. twitch amplitude) is a normal property. This observation has been previously unappreciated because the aggregated function in the form of QT-interval and cardiac output varies <1% on a beat-to-beat basis. This article describes the underlying cellular variability that is tolerated-and perhaps needed-by different regions of the heart for normal function and indicates why this variability is not apparent in function at the chamber and organ level. Thus, in contrast to the current dominant view, this article postulates that heterogeneity is normal and potentially endows various functional benefits. This new view of how the component parts of the heart come together to function also suggests novel mechanisms for cardiac pathologies, namely that dysfunction may emerge from changes in the extent and/or nature of heterogeneity. Once understood, restoring normal forms of heterogeneity could be a novel approach to treatment., Competing Interests: Conflict of interest: none declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Background: The role of epigenetics in cardiovascular diseases has paved the way for innovative therapeutic approaches. Investigating epigenetic changes using cell-free DNA (cfDNA) holds substantial promise beyond mere diagnostics, especially for heart-related conditions like acute myocardial infarction (AMI), where obtaining tissue samples is a challenge. This study explores the methylation patterns of cfDNA in AMI patients and compares them with genomic DNA (gDNA) from the same individuals, aiming to evaluate the effectiveness of cfDNA as a valuable resource for studying heart-related diseases., Methodology: We generated global methylome profiles of cfDNA and gDNA from 25 AMI patients using EM-Seq. Tissue deconvolution analysis was performed to estimate tissue specificity based on the methylation patterns. Differentially methylated loci were identified and explored to understand AMI pathophysiology., Results: Comparative analysis of cfDNA and gDNA methylation patterns in AMI patients reveals cfDNA holds more significance than gDNA. Principal component analysis revealed distinct clusters for cfDNA and gDNA, indicating distinct methylome profiles. cfDNA originated from multiple sources, predominantly from neutrophils (~ 75%) and about 10% from the left atrium, highlighting cardiac-specific changes. In contrast, immune cells are the major source of gDNA, indicative of inflammatory responses. Gene set enrichment analysis (GSEA) associates cfDNA methylation patterns with pathways related to cardiac muscle contraction, inflammation, hypoxia, and lipid metabolism. The affected genes include G protein-coupled receptors (GHSR, FFAR2, HTR1A, and VIPR2) that are part of the cAMP signaling pathway., Conclusion: Epigenetic changes in cfDNA are more specific to cardiac tissue compared to those in gDNA, providing better insights into the molecular mechanisms involved in AMI. Genes that are differentially methylated in cfDNA and regulate core pathways, such as cAMP signaling, could be targeted for clinical applications, including the development of effective biomarkers and therapeutic targets., (© 2024. The Author(s).)

Introduction: Neonatologist-performed echocardiography (NPE) is increasingly used in the neonatal intensive care unit, aiding clinicians in enhancing diagnostic precision and guiding treatment decisions based on underlying pathophysiology. Experienced NPE operators typically use visual estimation of the cardiac contractility and if required confirm findings using quantitative echocardiographic markers.While various quantitative echocardiographic markers are available to assess left and right ventricular contractility, this study aims to compare the proficiency of NPE-experienced and non-experienced providers in accurately assessing cardiac contractility using a combination of commonly used qualitative and quantitative echocardiographic markers., Methods and Analysis: Newborn infants, both inborn and outborn, undergoing routine NPE by the authors at Homerton University Hospital and Aberdeen Maternity Hospital from 1 April 2024 to 1 October 2024 will be studied. Indications for NPE include murmur evaluation, infants receiving intensive care and the need to assess underlying cardiovascular physiology.Blinded experienced and non-experienced NPE operators will independently assess left and right ventricular contractility using qualitative echocardiographic markers. The results will be compared with standard quantitative echocardiographic markers for cardiac contractility, and reliability studies will also be conducted for quantitative makers.Clinical data will be sourced from electronic patient records and national neonatal database. Sensitivity, specificity, positive predictive and negative predictive values, and positive and negative likelihood ratios will be calculated., Ethics and Dissemination: The study is approved by the Health and Care Research Wales Research Ethics Committee and the Health Research Authority (HRA) (reference 23/HRA/3066). The study findings will be presented at national/international conferences and published in peer-reviewed scientific journals., Competing Interests: Competing interests: No, there are no competing interests., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

A computational model enables the extraction of two critical myocardial tissue properties: activation time (AT) and contractility (Con) from recorded cardiac strains. However, interference between these parameters reduces the precision and accuracy of the extraction process. This study investigates whether leveraging features in the parameter space can enhance parameter extraction. We utilized a computational model to simulate sarcomere mechanics, creating a parameter space grid of 41 × 41 AT and Con pairs. Each pair generated a simulated strain pattern, and by scanning the grid, we identified cohorts of similar strain patterns for each simulation. These cohorts were represented as binary images-synthetic fingerprints-where the position and shape of each blob indicated extraction uniqueness. We also generated a measurement fingerprint for a strain pattern from a patient with left bundle branch block and compared it to the synthetic fingerprints to calculate a proximity map based on their similarity. This approach allowed us to extract AT and Con using both the measurement fingerprint and the proximity map, corresponding to simple optimization and enhanced parameter extraction methods, respectively. Each synthetic fingerprint consisted of a single connected blob whose size and shape varied characteristically within the parameter space. The AT values extracted from the measurement fingerprint and the proximity map ranged from -59 to 19 ms and from -16 to 14 ms, respectively, while Con values ranged from 48% to 110% and from 85% to 110%, respectively. This study demonstrates that similarity in simulations leads to an asymmetric distribution of parameter values in the parameter space. By using a proximity map, this distortion is considered, significantly improving the accuracy of parameter extraction., Competing Interests: The author declares no conflicts of interest., (Copyright © 2024 Borut Kirn.)

As evidence mounts that the cardiac-sympathetic nervous system reacts to challenging cognitive settings, we ask if these responses are epiphenomenal companions or if there is evidence suggesting a more intertwined role of this system with cognitive function. Healthy male and female human participants performed an approach-avoidance paradigm, trading off monetary reward for painful electric shock, while we recorded simultaneous electroencephalographic and cardiac-sympathetic signals. Participants were reward sensitive but also experienced approach-avoidance "conflict" when the subjective appeal of the reward was near equivalent to the revulsion of the cost. Drift-diffusion model parameters suggested that participants managed conflict in part by integrating larger volumes of evidence into choices (wider decision boundaries). Late alpha-band (neural) dynamics were consistent with widening decision boundaries serving to combat reward sensitivity and spread attention more fairly to all dimensions of available information. Independently, wider boundaries were also associated with cardiac "contractility" (an index of sympathetically mediated positive inotropy). We also saw evidence of conflict-specific "collaboration" between the neural and cardiac-sympathetic signals. In states of high conflict, the alignment (i.e., product) of alpha dynamics and contractility were associated with a further widening of the boundary, independent of either signal's singular association. Cross-trial coherence analyses provided additional evidence that the autonomic systems controlling cardiac-sympathetics might influence the assessment of information streams during conflict by disrupting or overriding reward processing. We conclude that cardiac-sympathetic control might play a critical role, in collaboration with cognitive processes, during the approach-avoidance conflict in humans., Competing Interests: The authors declare no competing financial interests., (Copyright © 2024 the authors.)

Hypertrophic cardiomyopathy (HCM) is a genetic disease of the heart characterized by thickening of the left ventricle (LV), hypercontractility, and impaired relaxation. HCM is caused primarily by heritable mutations in sarcomeric proteins, such as β myosin heavy chain. Until recently, medications in clinical use for HCM did not directly target the underlying contractile changes in the sarcomere. Here, we investigate a novel small molecule, RLC-1, identified in a bovine cardiac myofibril high-throughput screen. RLC-1 is highly dependent on the presence of a regulatory light chain to bind to cardiac myosin and modulate its ATPase activity. In demembranated rat LV trabeculae, RLC-1 decreased maximal Ca2+-activated force and Ca2+ sensitivity of force, while it increased the submaximal rate constant for tension redevelopment. In myofibrils isolated from rat LV, both maximal and submaximal Ca2+-activated force are reduced by nearly 50%. Additionally, the fast and slow phases of relaxation were approximately twice as fast as DMSO controls, and the duration of the slow phase was shorter. Structurally, x-ray diffraction studies showed that RLC-1 moved myosin heads away from the thick filament backbone and decreased the order of myosin heads, which is different from other myosin inhibitors. In intact trabeculae and isolated cardiomyocytes, RLC-1 treatment resulted in decreased peak twitch magnitude and faster activation and relaxation kinetics. In conclusion, RLC-1 accelerated kinetics and decreased force production in the demembranated tissue, intact tissue, and intact whole cells, resulting in a smaller cardiac twitch, which could improve the underlying contractile changes associated with HCM., (© 2024 Kooiker et al.)

Cytochromes P450 can metabolize endogenous fatty acids, such as arachidonic acid, to bioactive lipids such as epoxyeicosatrienoic acids (EETs) that have beneficial effects. EETs protect hearts against ischemic damage, heart failure or fibrosis; however, their effects are limited by hydrolysis to less active dihydroxy oxylipins by soluble epoxide hydrolase (sEH), encoded by the epoxide hydrolase 2 gene (EPHX2, EC 3.3.2.10). Pharmacological inhibition or genetic disruption of sEH/EPHX2 have been widely studied for their impact on cardiovascular diseases. Less well studied is the role of increased EPHX2 expression, which occurs in a substantial human population that carries the EPHX2 K55R polymorphism or after induction by inflammatory stimuli. Herein, we developed a mouse model with cardiomyocyte-selective expression of human EPHX2 (Myh6-EPHX2) that has significantly increased total EPHX2 expression and activity. Myh6-EPHX2 hearts exhibit strong, cardiomyocyte-selective expression of EPHX2. EPHX2 mRNA, protein, and epoxide hydrolysis measurements suggest that Myh6-EPHX2 hearts have 12-fold increase in epoxide hydrolase activity relative to wild type (WT) hearts. This increased activity significantly decreased epoxide:diol ratios in vivo. Isolated, perfused Myh6-EPHX2 hearts were not significantly different from WT hearts in basal parameters of cardiac function; however, compared to WT hearts, Myh6-EPHX2 hearts demonstrated reduced recovery of heart contractile function after ischemia and reperfusion (I/R). This impaired recovery after I/R correlated with reduced activation of PI3K/AKT and GSK3β signaling pathways in Myh6-EPHX2 hearts compared to WT hearts. In summary, the Myh6-EPHX2 mouse line represents a novel model of cardiomyocyte-selective overexpression of EPHX2 that has detrimental effects on cardiac function., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier Inc.)

Precise regulation of sarcomeric contraction is essential for normal cardiac function. The heart must generate sufficient force to pump blood throughout the body, but either inadequate or excessive force can lead to dysregulation and disease. Myosin regulatory light chain (RLC) is a thick-filament protein that binds to the neck of the myosin heavy chain. Post-translational phosphorylation of RLC (RLC-P) by myosin light chain kinase is known to influence acto-myosin interactions, thereby increasing force production and Ca 2+ -sensitivity of contraction. Here, we investigated the role of RLC-P on cardiac structure and function as sarcomere length and [Ca 2+ ] were altered. We found that at low, non-activating levels of Ca 2+ , RLC-P contributed to myosin head disorder, though there were no effects on isometric stress production and viscoelastic stiffness. With increases in sarcomere length and Ca 2+ -activation, the structural changes due to RLC-P become greater, which translates into greater force production, greater viscoelastic stiffness, slowed myosin detachment rates and altered nucleotide handling. Altogether, these data suggest that RLC-P may alter thick-filament structure by releasing ordered, off-state myosin. These more disordered myosin heads are available to bind actin, which could result in greater force production as Ca 2+ levels increase. However, prolonged cross-bridge attachment duration due to slower ADP release could delay relaxation long enough to enable cross-bridge rebinding. Together, this work further elucidates the effects of RLC-P in regulating muscle function, thereby promoting a better understanding of thick-filament regulatory contributions to cardiac function in health and disease. KEY POINTS: Myosin regulatory light chain (RLC) is a thick-filament protein in the cardiac sarcomere that can be phosphorylated (RLC-P), and changes in RLC-P are associated with cardiac dysfunction and disease. This study assesses how RLC-P alters cardiac muscle structure and function at different sarcomere lengths and calcium concentrations. At low, non-activating levels of Ca 2+ , RLC-P contributed to myofilament disorder, though there were no effects on isometric stress production and viscoelastic stiffness. With increases in sarcomere length and Ca 2+ -activation, the structural changes due to RLC-P become greater, which translates into greater force production, greater viscoelastic stiffness, slower myosin detachment rate and altered cross-bridge nucleotide handling rates. This work elucidates the role of RLC-P in regulating muscle function and facilitates understanding of thick-filament regulatory protein contributions to cardiac function in health and disease., (© 2024 The Authors. The Journal of Physiology © 2024 The Physiological Society.)

Cardiovascular disease is a leading cause of morbidity and mortality, and exercise-training (TRN) is known to reduce risk factors and protect the heart from ischemia and reperfusion injury. Though the cardioprotective effects of exercise are well-documented, underlying mechanisms are not well understood. This review highlights recent findings and focuses on cardiac factors with emphasis on K + channel control of the action potential duration (APD), β-adrenergic and adenosine regulation of cardiomyocyte function, and mitochondrial Ca 2+ regulation. TRN-induced prolongation and shortening of the APD at low and high activation rates, respectively, is discussed in the context of a reduced response of the sarcolemma delayed rectifier potassium channel (IK) and increased content and activation of the sarcolemma K ATP channel. A proposed mechanism underlying the latter is presented, including the phosphatidylinositol-3kinase/protein kinase B pathway. TRN induced increases in cardiomyocyte contractility and the response to adrenergic agonists are discussed. The TRN-induced protection from reperfusion injury is highlighted by the increased content and activation of the sarcolemma K ATP channel and the increased phosphorylated glycogen synthase kinase-3β, which aid in preventing mitochondrial Ca 2+ overload and mitochondria-triggered apoptosis. Finally, a brief section is presented on the increased incidences of atrial fibrillation associated with age and in life-long exercisers., Competing Interests: The authors declare that they have no conflict of interest., (Thieme. All rights reserved.)

Competing Interests: Disclosures The authors have no conflicts of interest to disclose.

Purpose of Review: Speckle tracking echocardiography (STE)-derived measures of myocardial mechanics, referred to herewithin as strain measurements, directly assess myocardial contractility and provide a nuanced assessment of ventricular function. This review provides an overview of strain measurements and their current clinical value and utility in decision making in pediatric cardiology., Recent Findings: Strain measurements are advancing understanding of how cardiac dysfunction occurs in children with acquired and congenital heart disease (CHD). Global strain measurements can detect early changes in cardiac function and are reliable methods of serially monitoring systolic function in children. Global strain measurements are increasingly reported in echocardiographic assessment of ventricular function alongside ejection fraction. Research is increasingly focused on how strain measurements can help improve clinical management, risk stratification, and prognostic insight. Although more research is needed, preliminary studies provide hope that there will be clinical benefit for strain in pediatric cardiology management., Summary: Strain measurements provide a more detailed assessment of ventricular function than conventional measures of echocardiographic functional assessment. Strain measurements are increasingly being used to advance understanding of normal and abnormal myocardial contractility, to increase sensitivity to detect early cardiac dysfunction, and to improve prognostic management in children with acquired and CHD., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

With current plans for manned missions to Mars and beyond, the need to better understand, prevent, and counteract the harmful effects of long-duration spaceflight on the body is becoming increasingly important. In this study, an automated heart-on-a-chip platform was flown to the International Space Station on a 1-mo mission during which contractile cardiac function was monitored in real-time. Upon return to Earth, engineered human heart tissues (EHTs) were further analyzed with ultrastructural imaging and RNA sequencing to investigate the impact of prolonged microgravity on cardiomyocyte function and health. Spaceflight EHTs exhibited significantly reduced twitch forces, increased incidences of arrhythmias, and increased signs of sarcomere disruption and mitochondrial damage. Transcriptomic analyses showed an up-regulation of genes and pathways associated with metabolic disorders, heart failure, oxidative stress, and inflammation, while genes related to contractility and calcium signaling showed significant down-regulation. Finally, in silico modeling revealed a potential link between oxidative stress and mitochondrial dysfunction that corresponded with RNA sequencing results. This represents an in vitro model to faithfully reproduce the adverse effects of spaceflight on three-dimensional (3D)-engineered heart tissue., Competing Interests: Competing interests statement:D.-H.K. is a co-founder, scientific advisory board member, and equity holder of Curi Bio, Inc. N.J.S. is a co-founder with equity of Stasys Medical Corporation and is a scientific advisory board member and equity holder of Curi Bio, Inc. J.H.T. is an employee and equity holder of Tenaya Therapeutics, Inc. The other authors declare no competing interest.

The renin-angiotensin system (RAS) is composed of a series of peptides, receptors, and enzymes that play a pivotal role in maintaining cardiovascular homeostasis. Among the most important players in this system are the angiotensin-II and angiotensin-(1-7) peptides. Our group has recently demonstrated that alamandine (ALA), a peptide with structural and functional similarities to angiotensin-(1-7), interacts with cardiomyocytes, enhancing contractility via the Mas-related G protein-coupled receptor member D (MrgD). It is currently unknown whether this modulation varies along the distinct phases of the day. To address this issue, we assessed the ALA-induced contractility response of cardiomyocytes from mice at four Zeitgeber times (ZTs). At ZT2 (light phase), ALA enhanced cardiomyocyte shortening in an MrgD receptor-dependent manner, which was associated with nitric oxide (NO) production. At ZT14 (dark phase), ALA induced a negative modulation on the cardiomyocyte contraction. β-Alanine, an MrgD agonist, reproduced the time-of-day effects of ALA on myocyte shortening. N G -nitro-l-arginine methyl ester, an NO synthase inhibitor, blocked the increase in fractional shortening induced by ALA at ZT2. No effect of ALA on myocyte shortening was observed at ZT8 and ZT20. Our results show that ALA/MrgD signaling in cardiomyocytes is subject to temporal modulation. This finding has significant implications for pharmacological approaches that combine chronotherapy for cardiac conditions triggered by disruption of circadian rhythms and hormonal signaling. NEW & NOTEWORTHY Alamandine, a member of the renin-angiotensin system, serves critical roles in cardioprotection, including the modulation of cardiomyocyte contractility. Whether this effect varies along the day is unknown. Our results provide evidence that alamandine via receptor MrgD exerts opposing actions on cardiomyocyte shortening, enhancing, or reducing contraction depending on the time of day. These findings may have significant implications for the development and effectiveness of future cardiac therapies.

Background and Objective . This study addresses the Force-Frequency relationship, a fundamental characteristic of cardiac muscle influenced by β 1 -adrenergic stimulation. This relationship reveals that heart rate (HR) changes at the sinoatrial node lead to alterations in ventricular cell contractility, increasing the force and decreasing relaxation time for higher beat rates. Traditional models lacking this relationship offer an incomplete physiological depiction, impacting the interpretation of in silico experiment results. To improve this, we propose a new mathematical model for ventricular myocytes, named 'Feed Forward Modeling' (FFM). Methods . FFM adjusts model parameters like channel conductance and Ca 2+ pump affinity according to stimulation frequency, in contrast to fixed parameter values. An empirical sigmoid curve guided the adaptation of each parameter, integrated into a rabbit ventricular cell electromechanical model. Model validation was achieved by comparing simulated data with experimental current-voltage (I-V) curves for L-type Calcium and slow Potassium currents. Results . FFM-enhanced simulations align more closely with physiological behaviors, accurately reflecting inotropic and lusitropic responses. For instance, action potential duration at 90% repolarization (APD90) decreased from 206 ms at 1 Hz to 173 ms at 4 Hz using FFM, contrary to the conventional model, where APD90 increased, limiting high-frequency heartbeats. Peak force also showed an increase with FFM, from 8.5 mN mm -2 at 1 Hz to 11.9 mN mm -2 at 4 Hz, while it barely changed without FFM. Relaxation time at 50% of maximum force (t 50 ) similarly improved, dropping from 114 ms at 1 Hz to 75.9 ms at 4 Hz with FFM, a change not observed without the model. Conclusion . The FFM approach offers computational efficiency, bypassing the need to model all beta-adrenergic pathways, thus facilitating large-scale simulations. The study recommends that frequency change experiments include fractional dosing of isoproterenol to better replicate heart conditions in vivo ., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

The length-dependent activation (LDA) of maximum force and calcium sensitivity are established features of cardiac muscle contraction but the dominant underlying mechanisms remain to be fully clarified. Alongside the well-documented regulation of contraction via the thin filaments, experiments have identified an additional force-dependent thick-filament activation, whereby myosin heads parked in a so-called off state become available to generate force. This process produces a feedback effect that may potentially drive LDA. Using biomechanical modeling of a human left-ventricular myocyte, this study investigates the extent to which the off-state dynamics could, by itself, plausibly account for LDA, depending on the specific mathematical formulation of the feedback. We hypothesized four different models of the off-state regulatory feedback based on (A) total force, (B) active force, (C) sarcomere strain, and (D) passive force. We tested if these models could reproduce the isometric steady-state and dynamic LDA features predicted by an earlier published model of a human left-ventricle myocyte featuring purely phenomenological length dependences. The results suggest that only total-force feedback (A) is capable of reproducing the expected behaviors, but that passive tension could provide a length-dependent signal on which to initiate the feedback. Furthermore, by attributing LDA to off-state dynamics, our proposed model also qualitatively reproduces experimentally observed effects of the off-state-stabilizing drug mavacamten. Taken together, these results support off-state dynamics as a plausible primary mechanism underlying LDA., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Biophysical Society. Published by Elsevier Inc. All rights reserved.)

In vitro cardiomyocyte mechano-sensing platform is crucial for evaluating the mechanical performance of cardiac tissues and will be an indispensable tool for application in drug discovery and disease mechanism study. Magnetic sensing offers significant advantages in real-time, in situ wireless monitoring and resistance to ion interference. However, due to the mismatch between the stiffness of traditional rigid magnetic material and myocardial tissue, sensitivity is insufficient and it is difficult to achieve cell structure induction and three-dimensional cultivation. Herein, a magnetic sensing platform that integrates a neodymium-iron-boron/polydimethylsiloxane (NdFeB/PDMS) flexible microbeam with suspended and ordered polycaprolactone (PCL) nanofiber membranes was developed, providing a three-dimensional anisotropic culture environment for cardiomyocyte growth and simultaneously realizing in situ wireless contractility monitoring. The as-prepared sensor presented an ultrahigh sensitivity of 442.2 μV/μm and a deflection resolution of 2 μm. By continuously monitoring the cardiomyocyte growth status and drug stimulation feedback, we verified the capability of the platform to capture dynamic changes in cardiomyocyte contractility. This platform provides a perspective tool for evaluating cardiomyocyte maturity and drug performance.

Previously, we found analytic solutions for single ventricular system based on the lumped parameter model (LPM). In this study, we generalized the method to biventricular system and derived its analytic solutions. LPM is just a set of differential equations, but it is difficult to solve due to time-varying ventricular elastance and high order. Mathematically, there exist no elementary solutions for time-varying equations. It turns out that instead of differential equations, according to volume conservation, a set of algebraic equations can be carried out. The solutions of the set of equations are just physiological states at end of systolic and diastolic phases such as end systolic/diastolic pressure/volume of left ventricle. As a preliminary application, the method is utilized to deduce the hemodynamic effects of VA ECMO. Left ventricular (LV) distension, a serious complication of VA ECMO, is usually attributed to factors such as increased afterload, inadequate LV unloading, reduced myocardial contractility or aortic valve regurgitation (AR), bronchial and Thebesian return in the absence of aortic valve (AoV) opening. Among these, reduced contractility and AR are strongly associated with LV distension. However, in the absence of reduced contractility or AR, it is less clear whether increased afterload or inadequate LV unloading alone can cause LV distension. This leads to the critical question: under what conditions does LV distension occur in the absence of reduced contractility or AR? The analytic formulas derived in this study give conditions for LV distension. Furthermore, the results show that the analytic hemodynamics are coincident with simulated results., Competing Interests: Declaration of conflicting interestsThe author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Polin Hsu is the founder and CEO of magAssist, Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Contraction of cardiomyocytes is initiated at subcellular elements called dyads, where L-type Ca 2+ channels in t-tubules are located within close proximity to ryanodine receptors in the sarcoplasmic reticulum. While evidence from small rodents indicates that dyads are assembled gradually in the developing heart, it is unclear how this process occurs in large mammals. We presently examined dyadic formation in fetal and newborn sheep (Ovis aries), and the regulation of this process by fetal cardiac workload. By employing advanced imaging methods, we demonstrated that t-tubule growth and dyadic assembly proceed gradually during fetal sheep development, from 93 days of gestational age until birth (147 days). This process parallels progressive increases in fetal systolic blood pressure, and includes step-wise colocalization of L-type Ca 2+ channels and the Na + /Ca 2+ exchanger with ryanodine receptors. These proteins are upregulated together with the dyadic anchor junctophilin-2 during development, alongside changes in the expression of amphiphysin-2 (BIN1) and its partner proteins myotubularin and dynamin-2. Increasing fetal systolic load by infusing plasma or occluding the post-ductal aorta accelerated t-tubule growth. Conversely, reducing fetal systolic load with infusion of enalaprilat, an angiotensin converting enzyme inhibitor, blunted t-tubule formation. Interestingly, altered t-tubule densities did not relate to changes in dyadic junctions, or marked changes in the expression of dyadic regulatory proteins, indicating that distinct signals are responsible for maturation of the sarcoplasmic reticulum. In conclusion, augmenting blood pressure and workload during normal fetal development critically promotes t-tubule growth, while additional signals contribute to dyadic assembly. KEY POINTS: T-tubule growth and dyadic assembly proceed gradually in cardiomyocytes during fetal sheep development, from 93 days of gestational age until the post-natal stage. Increasing fetal systolic load by infusing plasma or occluding the post-ductal aorta accelerated t-tubule growth and hypertrophy. In contrast, reducing fetal systolic load by enalaprilat infusion slowed t-tubule development and decreased cardiomyocyte size. Load-dependent modulation of t-tubule maturation was linked to altered expression patterns of the t-tubule regulatory proteins junctophilin-2 and amphiphysin-2 (BIN1) and its protein partners. Altered t-tubule densities did not influence dyadic formation, indicating that distinct signals are responsible for maturation of the sarcoplasmic reticulum., (© 2023 The Authors. The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)