Drug Screening Platform Using Human Induced Pluripotent Stem Cell-Derived Atrial Cardiomyocytes and Optical Mapping

Current drug development efforts for the treatment of atrial fibrillation are hampered by the fact that many preclinical models have been unsuccessful in reproducing human cardiac physiology and its response to medications. In this study, we demonstrated an approach using human induced pluripotent stem cell‐derived atrial and ventricular cardiomyocytes (hiPSC‐aCMs and hiPSC‐vCMs, respectively) coupled with a sophisticated optical mapping system for drug screening of atrial‐selective compounds in vitro. We optimized differentiation of hiPSC‐aCMs by modulating the WNT and retinoid signaling pathways. Characterization of the transcriptome and proteome revealed that retinoic acid pushes the differentiation process into the atrial lineage and generated hiPSC‐aCMs. Functional characterization using optical mapping showed that hiPSC‐aCMs have shorter action potential durations and faster Ca2+ handling dynamics compared with hiPSC‐vCMs. Furthermore, pharmacological investigation of hiPSC‐aCMs captured atrial‐selective effects by displaying greater sensitivity to atrial‐selective compounds 4‐aminopyridine, AVE0118, UCL1684, and vernakalant when compared with hiPSC‐vCMs. These results established that a model system incorporating hiPSC‐aCMs combined with optical mapping is well‐suited for preclinical drug screening of novel and targeted atrial selective compounds

Modeling Atrial Fibrillation using Human Embryonic Stem Cells

Background: Atrial fibrillation (AF) is the most common clinical arrhythmia and is associated with significant morbidity and mortality. Hypothesis: “Atrial” cardiomyocytes generated from hESCs will recapitulate the key hallmarks of human AF in a 2 dimensional tissue model, as well as demonstrate the expected electrophysiologic changes in response to drugs. Methods and Results: Our “atrial” cardiomyocytes were 80-90% positive for cardiac troponin, were enriched for the atrial markers ANF and KCNJ3, and lacked ventricular markers (MYL2 and IRX4). The “atrial” cells mimicked the human electrophysiologic phenotype with the majority (90%) demonstrating atrial like action potentials. Optical mapping of multicellular cell sheets was performed on rotors at baseline, after induction of rotor formation and with the addition of commonly employed antiarrhythmic drugs. Conclusions: We have successfully generated a human model of AF in vitro and demonstrated its utility in screening for known, and unpredicted effects of commonly employed anti-arrhythmics.M.Sc.2017-11-26 00:00:0

Modeling Atrial Fibrillation using Human Embryonic Stem Cells

Background: Atrial fibrillation (AF) is the most common clinical arrhythmia and is associated with significant morbidity and mortality. Hypothesis: “Atrial” cardiomyocytes generated from hESCs will recapitulate the key hallmarks of human AF in a 2 dimensional tissue model, as well as demonstrate the expected electrophysiologic changes in response to drugs. Methods and Results: Our “atrial” cardiomyocytes were 80-90% positive for cardiac troponin, were enriched for the atrial markers ANF and KCNJ3, and lacked ventricular markers (MYL2 and IRX4). The “atrial” cells mimicked the human electrophysiologic phenotype with the majority (90%) demonstrating atrial like action potentials. Optical mapping of multicellular cell sheets was performed on rotors at baseline, after induction of rotor formation and with the addition of commonly employed antiarrhythmic drugs. Conclusions: We have successfully generated a human model of AF in vitro and demonstrated its utility in screening for known, and unpredicted effects of commonly employed anti-arrhythmics.M.Sc.2017-11-26 00:00:0

The Inclusion of Underrepresented Populations in Cardiovascular Genetics and Epidemiology

Novel genetic risk markers have helped us to advance the field of cardiovascular epidemiology and refine our current understanding and risk stratification paradigms. The discovery and analysis of variants can help us to tailor prognostication and management. However, populations underrepresented in cardiovascular epidemiology and cardiogenetics research may experience inequities in care if prediction tools are not applicable to them clinically. Therefore, the purpose of this article is to outline the barriers that underrepresented populations can face in participating in genetics research, to describe the current efforts to diversify cardiogenetics research, and to outline strategies that researchers in cardiovascular epidemiology can implement to include underrepresented populations. Mistrust, a lack of diverse research teams, the improper use of sensitive biodata, and the constraints of genetic analyses are all barriers for including diverse populations in genetics studies. The current work is beginning to address the paucity of ethnically diverse genetics research and has already begun to shed light on the potential benefits of including underrepresented and diverse populations. Reducing barriers for individuals, utilizing community-driven research processes, adopting novel recruitment strategies, and pushing for organizational support for diverse genetics research are key steps that clinicians and researchers can take to develop equitable risk stratification tools and improve patient care

Trigger and Substrate Mapping and Ablation for Ventricular Fibrillation in the Structurally Normal Heart

Sudden cardiac death (SCD) represents approximately 50% of all cardiovascular mortality in the United States. The majority of SCD occurs in individuals with structural heart disease; however, around 5% of individuals have no identifiable cause on autopsy. This proportion is even higher in those <40 years old, where SCD is particularly devastating. Ventricular fibrillation (VF) is often the terminal rhythm leading to SCD. Catheter ablation for VF has emerged as an effective tool to alter the natural history of this disease among high-risk individuals. Important advances have been made in the identification of several mechanisms involved in the initiation and maintenance of VF. Targeting the triggers of VF as well as the underlying substrate that perpetuates these lethal arrhythmias has the potential to eliminate further episodes. Although important gaps remain in our understanding of VF, catheter ablation has become an important option for individuals with refractory arrhythmias. This review outlines a contemporary approach to the mapping and ablation of VF in the structurally normal heart, specifically focusing on the following major conditions: idiopathic ventricular fibrillation, short-coupled ventricular fibrillation, and the J-wave syndromes—Brugada syndrome and early-repolarization syndrome.Medicine, Faculty ofReviewedFacultyResearcherOthe

Beyond the Electrocardiogram: Mutations in Cardiac Ion Channel Genes Underlie Nonarrhythmic Phenotypes

Cardiac ion channelopathies are an important cause of sudden death in the young and include long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, idiopathic ventricular fibrillation, and short QT syndrome. Genes that encode ion channels have been implicated in all of these conditions, leading to the widespread implementation of genetic testing for suspected channelopathies. Over the past half-century, researchers have also identified systemic pathologies that extend beyond the arrhythmic phenotype in patients with ion channel gene mutations, including deafness, epilepsy, cardiomyopathy, periodic paralysis, and congenital heart disease. A coexisting phenotype, such as cardiomyopathy, can influence evaluation and management. However, prior to recent molecular advances, our understanding and recognition of these overlapping phenotypes were poor. This review highlights the systemic and structural heart manifestations of the cardiac ion channelopathies, including their phenotypic spectrum and molecular basis

Atrial-specific hiPSC-derived cardiomyocytes in drug discovery and disease modeling

The discovery and application of human-induced pluripotent stem cells (hiPSCs) have been instrumental in the investigation of the pathophysiology of cardiovascular diseases. Patient-specific hiPSCs can now be generated, genome-edited, and subsequently differentiated into various cell types and used for regenerative medicine, disease modeling, drug testing, toxicity screening, and 3D tissue generation. Modulation of the retinoic acid signaling pathway has been shown to direct cardiomyocyte differentiation towards an atrial lineage. A variety of studies have successfully differentiated patient-specific atrial cardiac myocytes (hiPSC-aCM) and atrial engineered heart tissue (aEHT) that express atrial specific genes (e.g., sarcolipin and ANP) and exhibit atrial electrophysiological and contractility profiles. Identification of protocols to differentiate atrial cells from patients with atrial fibrillation and other inherited diseases or creating disease models using genetic mutation studies has shed light on the mechanisms of atrial-specific diseases and identified the efficacy of atrial-selective pharmacological compounds. hiPSC-aCMs and aEHTs can be used in drug discovery and drug screening studies to investigate the efficacy of atrial selective drugs on atrial fibrillation models. Furthermore, hiPSC-aCMs can be effective tools in studying the mechanism, pathophysiology and treatment options of atrial fibrillation and its genetic underpinnings. The main limitation of using hiPSC-CMs is their immature phenotype compared to adult CMs. A wide range of approaches and protocols are used by various laboratories to optimize and enhance CM maturation, including electrical stimulation, culture time, biophysical cues and changes in metabolic factors

Use of 3D mapping system for ablating an accessory pathway associated with coronary sinus diverticulum

Background This is a rare and challenging case of Wolff–Parkinson–White syndrome due to a posteroseptal accessory pathway located in the coronary sinus diverticulum. It is often difficult to precisely locate this type of accessory pathway, and the ablation procedure could be associated with collateral damage to the neighbouring coronary arteries. Case Presentation The patient was a 49-year-old female with Wolff–Parkinson–White syndrome who was referred for catheter ablation. She had had a previous unsuccessful attempt at ablation and had remained symptomatic despite drug therapy. The pre-procedural cardiac computed tomography scan revealed the presence of a diverticulum in the proximal coronary sinus. Using an advanced three-dimensional cardiac mapping system, the electroanatomic map of the diverticulum was created. The accessory pathway potential was identified within the diverticulum preceding the ventricular insertion. The accessory pathway was then successfully ablated using radiofrequency energy. Conclusion We have demonstrated that the advanced three-dimensional cardiac mapping system plays a very important role in guiding clinicians in order to precisely locate and safely ablate this type of challenging accessory pathway.Medicine, Faculty ofCardiology, Division ofReviewedFacult