Bifurcation Analysis on a Generation of Early Afterdepolarization in a Mathematical Cardiac Model

Electrical activity occurs in the cell membrane of cardiomyocytes. This electrical activity forms the action potential that generates pumping of the heart. An abnormality in the action potential turns into arrhythmia, which may cause sudden death. Studies of arrhythmias using mathematical models are important to reduce the risk of sudden death. In this study, we investigate bifurcations related to the generation of early afterdepolarizations (EADs) in a mathematical model. We clarify the transition process from a normal state to a persistent EAD through a transient EAD while changing only one parameter (multiple of conductance of L-type calcium channel current) value. The dependence of the transient EAD generation on parameters is shown through bifurcation analysis in a [Na]i-parameterized system.

An Immuno-Cardiac Model for Macrophage-Mediated Inflammation in COVID-19 Hearts

Rationale: While respiratory failure is a frequent and clinically significant outcome of COVID-19, cardiac complications are a common feature in hospitalized COVID-19 patients and are associated with worse patient outcomes. The cause of cardiac injury in COVID-19 patients is not yet known. Case reports of COVID-19 autopsy heart samples have demonstrated abnormal inflammatory infiltration of macrophages in heart tissues. Objective: Generate an immuno-cardiac co-culture platform to model macrophage-mediated hyper-inflammation in COVID-19 hearts and screen for drugs that can block the macrophage-mediated inflammation. Methods and Results: We systematically compared autopsy samples from non-COVID-19 donors and COVID-19 patients using RNA-seq and immunohistochemistry. We observed strikingly increased expression levels of CCL2 as well as macrophage infiltration in heart tissues of COVID-19 patients. We generated an immuno-cardiac co-culture platform containing human pluripotent stem cell (hPSC)-derived cardiomyocytes (CMs) and macrophages. We found that macrophages induce increased reactive oxygen species (ROS) and apoptosis in CMs by secreting IL-6 and TNF-α after SARS-CoV-2 exposure. Using this immuno-cardiac co-culture platform, we performed a high content screen and identified ranolazine and tofacitinib as compounds that protect CMs from macrophage-induced cardiotoxicity. Conclusions: We established an immuno-host co-culture system to study macrophage-induced host cell damage following SARS-CoV-2 infection and identified FDA-approved drug candidates that alleviate the macrophage-mediated hyper-inflammation and cellular injury.

Feasibility and safety of left atrial appendage closure in a patient with previous foramen ovale occlusion: a case report

Background Left atrial appendage (LAA) closure is an alternative to chronic oral anticoagulation for stroke prevention in patients with atrial fibrillation (AF) at high bleeding risk. Patients with a previous percutaneous closure of a patent foramen ovale (PFO) present an increased risk for developing AF during their life, and the presence of an atrial septal device renders future percutaneous left atrial access more challenging. Very few cases of LAA occlusion in patients with a preexisting PFO closure device have been previously reported. Case summary A 74-years old woman was admitted to our hospital for symptomatic severe anaemia during direct oral anticoagulant treatment. Her past medical history reported an ischaemic stroke at the age of 55, at that time a PFO was diagnosed and a STARFlex™ PFO occluder (NMT Medical, Boston, MA, USA) was implanted. During the current hospitalization, the patient underwent a colonoscopy that showed colonic angiodysplasias unsuitable for endoscopic treatment and LAA closure was indicated for stroke prevention. After a multimodality pre-procedural planning that included a transoesophageal echocardiogram, a cardiac computed tomography scan and a three-dimensional cardiac model printing, the procedure was planned and the LAA successfully occluded. Discussion LAA closure can be performed safely and effectively in patients carrying a previously implanted PFO occlusion device. In complex settings, a pre-procedural multimodality imaging is critical for improving the procedural safety and success rate. We describe the first case of percutaneous LAA closure in a patient with a prior PFO occlusion with the implantation of a STARflex™ septal occlusion device.

HUMAN iPSC ENGINEERED CARDIAC TISSUE PLATFORM FAITHFULLY MODELS IMPORTANT CARDIAC PHYSIOLOGY

Cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CM) may provide an important bridge between animal models and intact human myocardium. Fulfilling this potential is hampered by their relative immaturity. hiPSC-CMs grown in monolayer culture lack a t-tubular system, have rudimentary intracellular calcium-handling systems, express predominantly embryonic sarcomeric protein isoforms, and preferentially use glucose as energy substrate. Culturing hiPSC-CM in a 3D environment and the addition of nutritional, pharmacologic and electromechanical stimuli have proven to be beneficial for maturation. We present an assessment of a model in which hiPSC-CMs and hiPSC-derived cardiac fibroblasts are co-cultured in a 3D fibrin matrix to form human engineered cardiac tissue constructs (hECT).The hECT respond to physiological stimuli, including stretch, frequency and β-adrenergic stimulation, develop a t-tubular system, and demonstrate calcium-handling and contractile kinetics that compare favorably with ventricular human myocardium. Transcript levels of genes involved in calcium-handling and contraction are increased. These markers of maturation become more robust over a short period of time in culture (6 weeks vs. 2 weeks in hECT). A comparison of the hECT molecular and performance variables with those of human cardiac tissue and other available engineered tissue platforms is provided to highlight strengths and weaknesses of these preparations. Important and noteworthy aspects of this human cardiac model system are its reliance on 'off-the-shelf' equipment, ability to provide detailed physiological performance data, and the ability to achieve a relatively mature cardiac physiology without additional nutritional, pharmacological and electromechanical stimuli that may elicit unintended effects on function.

In vivo application and validation of a novel non-invasive method to estimate the end-systolic elastance

Accurate assessment of the left ventricular (LV) systolic function is indispensable in the clinic. However, estimation of a precise index of cardiac contractility, i.e., the end-systolic elastance (Ees), is invasive and cannot be established as clinical routine. The aim of this work was to present and validate a methodology that allows for the estimation of Ees from simple and readily available non-invasive measurements. The method is based on a validated model of the cardiovascular system and non-invasive data from arm-cuff pressure and routine echocardiography to render the model patient-specific. Briefly, the algorithm first uses the measured aortic flow as model input and optimizes the properties of the arterial system model in order to achieve correct prediction of the patient's peripheral pressure. In a second step, the personalized arterial system is coupled with the cardiac model (time-varying elastance model) and the LV systolic properties, including Ees, are tuned to predict accurately the aortic flow waveform. The algorithm was validated against invasive measurements of Ees (multiple pressure-volume loop analysis) taken from n=10 heart failure patients with preserved ejection fraction and n=9 patients without heart failure. Invasive measurements of Ees (median 2.4 mmHg/mL, range [1.0, 5.0] mmHg/mL) agreed well with method predictions (nRMSE=9%, ρ=0.89, bias=-0.1 mmHg/mL and limits of agreement [-0.9, 0.6] mmHg/mL). This is a promising first step towards the development of a valuable tool that can be used by clinicians to assess systolic performance of the LV in the critically ill.

Suppression-Replacement KCNQ1 Gene Therapy for Type 1 Long QT Syndrome

Background: Type 1 long QT syndrome (LQT1) is caused by loss-of-function variants in the KCNQ1 -encoded K v 7.1 potassium channel α-subunit which is essential for cardiac repolarization, providing the slow delayed rectifier current (IKs). No current therapies target the molecular cause of LQT1. Methods: A dual-component "suppression-and-replacement" (SupRep) KCNQ1 gene therapy was created by cloning a KCNQ1 shRNA and a "shRNA-immune" (shIMM) KCNQ1 cDNA modified with silent variants in the shRNA target site, into a single construct. The ability of KCNQ1-SupRep gene therapy to suppress and replace LQT1-causative variants in KCNQ1 was evaluated via heterologous expression in TSA201 cells. For a human in vitro cardiac model, induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) were generated from four patients with LQT1 (KCNQ1-Y171X, -V254M, -I567S, and -A344A/spl) and an unrelated healthy control. CRISPR-Cas9 corrected isogenic control iPSC-CMs were made for two LQT1 lines (correction of KCNQ1-V254M and KCNQ1-A344A/spl). FluoVolt voltage dye was used to measure the cardiac action potential duration (APD) in iPSC-CMs treated with KCNQ1-SupRep. Results: In TSA201 cells, KCNQ1-SupRep achieved mutation-independent suppression of wild-type KCNQ1 and three LQT1-causative variants (KCNQ1-Y171X, -V254M, and -I567S) with simultaneous replacement of KCNQ1-shIMM as measured by allele-specific qRT-PCR and western blot. Using FluoVolt voltage dye to measure the cardiac APD in the four LQT1 patient-derived iPSC-CMs, treatment with KCNQ1-SupRep resulted in shortening of the pathologically prolonged APD at both 90% (APD 90 ) and 50% (APD 50 ) repolarization resulting in APD values similar to those of the two isogenic controls. Conclusions: This study provides the first proof-of-principle gene therapy for complete correction of LQTS. As a dual-component gene therapy vector, KCNQ1-SupRep successfully suppressed and replaced KCNQ1 to normal wild-type levels. In TSA201 cells, co-transfection of LQT1-causative variants and KCNQ1-SupRep caused mutation-independent suppression-and-replacement of KCNQ1 . In LQT1 iPSC-CMs, KCNQ1-SupRep gene therapy shortened the APD, thereby eliminating the pathognomonic feature of LQT1.