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Aims Out-of-hospital cardiac arrest (OHCA) mostly results from ventricular tachycardia/ventricular fibrillation (VT/VF), often triggered by acute myocardial infarction (AMI). Sulfonylurea (SU) antidiabetics can block myocardial ATP-regulated K+ channels (KATP channels), activated during AMI, thereby modulating action potential duration (APD). We studied whether SU drugs impact on OHCA risk, and whether these effects are related to APD changes. Methods We conducted a population-based case–control study in 219 VT/VF-documented OHCA cases with diabetes and 697 non-OHCA controls with diabetes. We studied the association of SU drugs (alone or in combination with metformin) with OHCA risk compared to metformin monotherapy, and of individual SU drugs compared to glimepiride, using multivariable logistic regression analysis. We studied the effects of these drugs on APD during simulated ischaemia using patch-clamp studies in human induced pluripotent stem cell-derived cardiomyocytes. Results Compared to metformin, use of SU drugs alone or in combination with metformin was associated with reduced OHCA risk (ORSUdrugs-alone 0.6 [95% CI 0.4–0.9], ORSUdrugs + metformin 0.6 [95% CI 0.4–0.9]). We found no differences in OHCA risk between SU drug users who suffered OHCA inside or outside the context of AMI. Reduction of OHCA risk compared to glimepiride was found with gliclazide (ORadj 0.5 [95% CI 0.3–0.9]), but not glibenclamide (ORadj 1.3 [95% CI 0.6–2.7]); for tolbutamide, the association with reduced OHCA risk just failed to reach statistical significance (ORadj 0.6 [95% CI 0.3–1.002]). Glibenclamide attenuated simulated ischaemia-induced APD shortening, while the other SU drugs had no effect. Conclusions SU drugs were associated with reduced OHCA risk compared to metformin monotherapy, with gliclazide having a lower risk than glimepiride. The differential effects of SU drugs are not explained by differential effects on APD.

Summary Reporter cell lines have already proven valuable in identifying, tracking, and purifying cardiac subtypes and progenitors during differentiation of human pluripotent stem cells (hPSCs). We previously showed that chick ovalbumin upstream promoter transcription factor II (COUP-TFII) is highly enriched in human atrial cardiomyocytes (CMs), but not ventricular. Here, we targeted mCherry to the COUP-TFII genomic locus in hPSCs expressing GFP from the NKX2.5 locus. This dual atrial NKX2.5EGFP/+-COUP-TFIImCherry/+ reporter line allowed identification and selection of GFP+ (G+)/mCherry+ (M+) CMs following cardiac differentiation. These cells exhibited transcriptional and functional properties of atrial CMs, whereas G+/M− CMs displayed ventricular characteristics. Via CRISPR/Cas9-mediated knockout, we demonstrated that COUP-TFII is not required for atrial specification in hPSCs. This new tool allowed selection of human atrial and ventricular CMs from mixed populations, of relevance for studying cardiac specification, developing human atrial disease models, and examining distinct effects of drugs on the atrium versus ventricle., Graphical Abstract, Highlights • Dual NKX2.5EGFP/+-COUP-TFIImCherry/+ hPSCs to identify atrial cardiomyocytes • COUP-TFII is not required for atrial specification of hPSCs in vitro, In this article, Passier and colleagues developed an atrial fluorescent stem cell reporter by CRISPR/Cas9-mediated knockin of mCherry at the genomic locus of COUP-TFII in a cardiac NKX2.5EGFP/w reporter line. As validated at the transcriptional and functional level, the nuclear receptor COUP-TFII successfully marks atrial cardiomyocytes but is not required for atrial specification during in vitro differentiation of hPSCs.

The rate and rhythm of heart muscle contractions are coordinated by the cardiac conduction system (CCS), a generic term for a collection of different specialized muscular tissues within the heart. The CCS components initiate the electrical impulse at the sinoatrial node, propagate it from atria to ventricles via the atrioventricular node and bundle branches, and distribute it to the ventricular muscle mass via the Purkinje fibre network. The CCS thereby controls the rate and rhythm of alternating contractions of the atria and ventricles. CCS function is well conserved across vertebrates from fish to mammals, although particular specialized aspects of CCS function are found only in endotherms (mammals and birds). The development and homeostasis of the CCS involves transcriptional and regulatory networks that act in an embryonic-stage-dependent, tissue-dependent, and dose-dependent manner. This Review describes emerging data from animal studies, stem cell models, and genome-wide association studies that have provided novel insights into the transcriptional networks underlying CCS formation and function. How these insights can be applied to develop disease models and therapies is also discussed.

Genetic causes of many familial arrhythmia syndromes remain elusive. In this study, whole‐exome sequencing (WES) was carried out on patients from three different families that presented with life‐threatening arrhythmias and high risk of sudden cardiac death (SCD). Two French Canadian probands carried identical homozygous rare variant in TECRL gene (p.Arg196Gln), which encodes the trans‐2,3‐enoyl‐CoA reductase‐like protein. Both patients had cardiac arrest, stress‐induced atrial and ventricular tachycardia, and QT prolongation on adrenergic stimulation. A third patient from a consanguineous Sudanese family diagnosed with catecholaminergic polymorphic ventricular tachycardia (CPVT) had a homozygous splice site mutation (c.331+1G>A) in TECRL. Analysis of intracellular calcium ([Ca2+]i) dynamics in human induced pluripotent stem cell‐derived cardiomyocytes (hiPSC‐CMs) generated from this individual (TECRLHom‐hiPSCs), his heterozygous but clinically asymptomatic father (TECRLHet‐hiPSCs), and a healthy individual (CTRL‐hiPSCs) from the same Sudanese family, revealed smaller [Ca2+]i transient amplitudes as well as elevated diastolic [Ca2+]i in TECRLHom‐hiPSC‐CMs compared with CTRL‐hiPSC‐CMs. The [Ca2+]i transient also rose markedly slower and contained lower sarcoplasmic reticulum (SR) calcium stores, evidenced by the decreased magnitude of caffeine‐induced [Ca2+]i transients. In addition, the decay phase of the [Ca2+]i transient was slower in TECRLHom‐hiPSC‐CMs due to decreased SERCA and NCX activities. Furthermore, TECRLHom‐hiPSC‐CMs showed prolonged action potentials (APs) compared with CTRL‐hiPSC‐CMs. TECRL knockdown in control human embryonic stem cell‐derived CMs (hESC‐CMs) also resulted in significantly longer APs. Moreover, stimulation by noradrenaline (NA) significantly increased the propensity for triggered activity based on delayed afterdepolarizations (DADs) in TECRLHom‐hiPSC‐CMs and treatment with flecainide, a class Ic antiarrhythmic drug, significantly reduced the triggered activity in these cells. In summary, we report that mutations in TECRL are associated with inherited arrhythmias characterized by clinical features of both LQTS and CPVT. Patient‐specific hiPSC‐CMs recapitulated salient features of the clinical phenotype and provide a platform for drug screening evidenced by initial identification of flecainide as a potential therapeutic. These findings have implications for diagnosis and treatment of inherited cardiac arrhythmias.

Drugs targeting atrial-specific ion channels, K(v)1.5 or K(ir)3.1/3.4, are being developed as new therapeutic strategies for atrial fibrillation. However, current preclinical studies carried out in non-cardiac cell lines or animal models may not accurately represent the physiology of a human cardiomyocyte (CM). In the current study, we tested whether human embryonic stem cell (hESC)-derived atrial CMs could predict atrial selectivity of pharmacological compounds. By modulating retinoic acid signaling during hESC differentiation, we generated atrial-like (hESC-atrial) and ventricular-like (hESC-ventricular) CMs. We found the expression of atrial-specific ion channel genes, KCNA5 (encoding Kv1.5) and KCNJ3 (encoding K-ir 3.1), in hESC-atrial CMs and further demonstrated that these ion channel genes are regulated by COUP-TF transcription factors. Moreover, in response to multiple ion channel blocker, vernakalant, and K(v)1.5 blocker, XEN-D0101, hESC-atrial but not hESC-ventricular CMs showed action potential (AP) prolongation due to a reduction in early repolarization. In hESC-atrial CMs, XEN-R0703, a novel K(ir)3.1/3.4 blocker restored the AP shortening caused by CCh. Neither CCh nor XEN-R0703 had an effect on hESC-ventricular CMs. In summary, we demonstrate that hESC-atrial CMs are a robust model for pre-clinical testing to assess atrial selectivity of novel antiarrhythmic drugs.

Summary Maximizing baseline function of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) is essential for their effective application in models of cardiac toxicity and disease. Here, we aimed to identify factors that would promote an adequate level of function to permit robust single-cell contractility measurements in a human induced pluripotent stem cell (hiPSC) model of hypertrophic cardiomyopathy (HCM). A simple screen revealed the collaborative effects of thyroid hormone, IGF-1 and the glucocorticoid analog dexamethasone on the electrophysiology, bioenergetics, and contractile force generation of hPSC-CMs. In this optimized condition, hiPSC-CMs with mutations in MYBPC3, a gene encoding myosin-binding protein C, which, when mutated, causes HCM, showed significantly lower contractile force generation than controls. This was recapitulated by direct knockdown of MYBPC3 in control hPSC-CMs, supporting a mechanism of haploinsufficiency. Modeling this disease in vitro using human cells is an important step toward identifying therapeutic interventions for HCM., Graphical Abstract, Highlights • T3+IGF-1+ dexamethasone improves the electrophysiology of hPSC cardiomyocytes • These factors synergistically enhance bioenergetics and contractile force generation • Cardiomyocytes with HCM-causing mutations have a contractile defect, Birket et al. identify a combination of factors that cooperatively improve the function of human pluripotent stem cell (hiPSC)-derived cardiomyocytes. Optimizing the system facilitated the identification of a contraction force defect in a model of hypertrophic cardiomyopathy (HCM), a disease affecting ∼1:500 of the population.