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Dilated cardiomyopathy with ataxia (DCMA) is an autosomal recessive disorder arising from mutations in DNAJC19. Two patient-derived dermal fibroblast cell lines of siblings with the same homozygous splice acceptor site mutation in DNAJC19 (NM_145261.4):c.130-1G>C were reprogrammed into induced pluripotent stem cell (iPSC) lines (LIBUCi001-A and LIBUCi002-A) using non-integrative Sendai virus. Additionally, a third DNAJC19tv (truncation variant) iPSC line (JMUi001-A-1) was generated by CRISPR/Cas9 in healthy control iPSCs (JMUi001-A). All three DCMA iPSC lines present normal karyotypes, high expression of pluripotency markers and the capacity to differentiate into cells of all three germ layers., (Copyright © 2020 The Author(s). Published by Elsevier B.V. All rights reserved.)

Background: Empagliflozin, an SGLT2 inhibitor, has shown remarkable reductions in cardiovascular mortality and heart failure admissions (EMPA-REG OUTCOME). However, the mechanism underlying the heart failure protective effects of empagliflozin remains largely unknown. Cardiac fibroblasts play an integral role in the progression of structural cardiac remodelling and heart failure, in part, by regulating extracellular matrix (ECM) homeostasis. The objective of this study was to determine if empagliflozin has a direct effect on human cardiac myofibroblast-mediated ECM remodelling., Methods: Cardiac fibroblasts were isolated via explant culture from human atrial tissue obtained at open heart surgery. Collagen gel contraction assay was used to assess myofibroblast activity. Cell morphology and cell-mediated ECM remodelling was examined with the use of confocal microscopy. Gene expression of profibrotic markers was assessed with the use of reverse-transcription quantitative polymerase chain reaction., Results: Empagliflozin significantly attenuated transforming growth factor β1-induced fibroblast activation via collagen gel contraction after 72-hour exposure, with escalating concentrations (0.5 μmol/L, 1 μmol/L, and 5 μmol/L) resulting in greater attenuation. Morphologic assessment showed that myofibroblasts exposed to empagliflozin were smaller in size with shorter and fewer number of extensions, indicative of a more quiescent phenotype. Moreover, empagliflozin significantly attenuated cell-mediated ECM remodelling as measured by collagen fibre alignment index. Gene expression profiling revealed significant suppression of critical profibrotic markers by empagliflozin, including COL1A1, ACTA2, CTGF, FN1, and MMP-2., Conclusions: We provide novel data showing a direct effect of empagliflozin on human cardiac myofibroblast phenotype and function by attenuation of myofibroblast activity and cell-mediated collagen remodelling. These data provide critical insights into the profound effects of empagliflozin as noted in the EMPA-REG OUTCOME study., (Copyright © 2019 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved.)

Arrhythmogenic cardiomyopathy is a genetic heart muscle disorder characterized by fibro-fatty replacement of cardiomyocytes leading to life-threatening ventricular arrhythmias, heart failure, and sudden cardiac death. Mutations in genes encoding cardiac junctional proteins are known to cause about half of cases, while remaining genetic causes are unknown. Using exome sequencing, we identified 2 missense variants (p.H33N and p.H77Y) that were predicted to be damaging in the integrin-linked kinase (ILK) gene in 2 unrelated families. The p.H33N variant was found to be de novo. ILK links integrins and the actin cytoskeleton, and is essential for the maintenance of normal cardiac function. Both of the new variants are located in the ILK ankyrin repeat domain, which binds to the first LIM domain of the adaptor proteins PINCH1 and PINCH2. In silico binding studies proposed that the human variants disrupt the ILK-PINCH complex. Recombinant mutant ILK expressed in H9c2 rat myoblast cells shows aberrant prominent cytoplasmic localization compared to the wild-type. Expression of human wild-type and mutant ILK under the control of the cardiac-specific cmlc2 promotor in zebrafish shows that p.H77Y and p.P70L, a variant previously reported in a dilated cardiomyopathy family, cause cardiac dysfunction and death by about 2-3 weeks of age. Our findings provide genetic and functional evidence that ILK is a cardiomyopathy disease gene and highlight its relevance for diagnosis and genetic counseling of inherited cardiomyopathies., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Bradyarrhythmia is a common clinical presentation. Although the majority of cases are acquired, genetic screening of families with bradyarrhythmia has led to the discovery of a growing number of causative hereditary mutations. These mutations can interfere with any of the steps required for the occurrence of each cardiac cycle, including generation of an action potential in the sinoatrial node, successful exit of the action potential from the node, propagation of the action potential throughout the atria until the depolarization waves reach the atrioventricular node, and finally transmission of the action potential to the ventricles through the His-Purkinje system. As expected, channelopathies are the predominant culprit for hereditary bradyarrhythmias, because they play a crucial role in action potential generation and propagation. Interestingly, there are an increasing number of genes that encode for various regulatory or structural cellular components that have been linked to hereditary bradyarrhythmias. Furthermore, population-based genetic screening has revealed that age-related conduction defects may in fact be caused by genetic predispositions rather than the simple process of aging. With recent advances in genetic testing and the creation of animal models, not only have we discovered new culprit genes but it has also has become evident that there are still significant gaps in our knowledge of cardiac pathophysiology. In this review, we discuss the clinical presentations of known hereditary bradyarrhythmias and their associated conditions in addition to detailing our current molecular understanding of the mechanisms by which they are manifested., (Copyright © 2017 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved.)

Andersen-Tawil syndrome (ATS) is caused by mutations in KCNJ2 (Kir2.1). It remains unclear whether dilated cardiomyopathy (DCM) is a primary feature of ATS. We studied a proband with typical physical features of ATS plus DCM and moderate to severe left ventricular dysfunction (left ventricular ejection fraction = 30.5%). Genetic screening revealed a novel mutation in Kir2.1 (c.665T>C, p.L222S). Functional studies showed that this mutation reduced ionic currents in a dominant-negative manner. Suppression of ventricular arrhythmias with bisoprolol led to normalization of left ventricular size and function. We conclude that DCM is likely a secondary phenotype in ATS and is caused by high ventricular arrhythmia burden., (Copyright © 2016 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved.)

Objective: The purpose of this study was to use a candidate gene approach to identify common polymorphisms that are associated with resting sinus heart rate in a population without overt cardiovascular disease., Background: Increased resting heart rate is significantly associated with susceptibility to development of myocardial infarction, sudden cardiac death, and overall cardiac mortality., Methods: A longitudinal cohort of 1468 individuals (active and retired middle-aged Canadian firefighters) who were enrolled in the Firefighters and Their Endothelium (FATE) study was evaluated. Resting heart rate was recorded from the electrocardiogram (ECG) obtained at enrollment. Candidate genes were selected for their known roles in sinus node automaticity and/or its regulation, and single nucleotide polymorphisms (SNPs) with a minor allele frequency of > or =0.20 were targeted. A total of 53 SNPs in 46 genes were selected and analyzed in a screening sample, and 33 SNPs in 29 genes were evaluated in the full population., Results: Univariate analysis detected five putative associations between HR and SNPs. As expected, environmental covariates were identified. Three polymorphisms, ADRB1 G389R, SCN5a H558R, and CASQ1 intron 2, remained statistically significant and independent of covariates. Some alleles were associated with higher and some with lower heart rates. A stepwise increase in heart rate was observed that was dependent on the number of tachycardia-associated alleles with progressive increases in mean heart rate from 51 to 66 bpm., Conclusions: Common polymorphisms are associated with heart rate in a stepwise allele-dependent manner.

Background: Transient bradycardic hypotensive events occur in resting rabbits. If the hypotension is due to vasodepression, these events may be a model for vasovagal syncope., Objectives: To determine whether these events are responses to brief stimuli and whether the hypotensive episodes are solely due to rapid-onset bradycardia., Methods: Rabbits were instrumented with subcutaneous electrocardiogram leads, and cannulae were acutely inserted into an ear artery to obtain continuous arterial pressure measurements. Exposure to brief, low-level auditory stimuli at 5 kHz transiently increased the RR interval by approximately 70 ms and decreased mean arterial pressure by approximately 5 mmHg., Results: These evoked bradycardic hypotensive events were almost identical to previously reported spontaneous bradycardic hypotensive events. Intra-aortic telemetric blood pressure monitoring was used to demonstrate that the evoked hypotension reflected prolonged diastole, rather than local ear arterial vasoconstriction. Furthermore, administration of the muscarinic blocker glycopyrrolate abolished not only bradycardia (RR interval 64+/-14 ms to 1+/-1 ms; P<0.0001), but also hypotension (--4.1+/-0.8 mmHg to --0.4+/-0.3 mmHg; P=0.0055). Finally, cardiac pacing abolished the inducible bradycardia (RR interval 51+/-10 ms to 2+/-1 ms; P=0.0006) and its associated hypotension (--4.1+/-0.7 mmHg to --1.2+/-0.3 mmHg; P=0.003)., Conclusions: Brief auditory stimuli evoked a transient bradycardia mediated by cardiac muscarinic receptors and consequent hypotension. This is not a model for vasovagal syncope.

Background: Environmental and genetic factors interact to define susceptibility to drug-induced long QT syndrome. Although erythromycin induces long QT syndrome, substantial variability exists with regard to its incidence., Objectives: Because fever frequently results in empiric antibiotic usage, we assessed whether temperatures over the range from 36 degrees to 42 degrees C determined responsiveness to erythromycin (100 micromol/L)., Methods: I(hERG) was recorded in mammalian cells, and action potentials were recorded in neonatal ventricular mouse myocytes., Results: Erythromycin (100 micromol/L) produced no block of I(hERG) at 22 degrees C but produced significant block at 37 degrees C. Extent of block of I(hERG) increased linearly (r = 0.46, P < .01) as temperature increased between 36 degrees C and 42 degrees C. To assess physiologic relevance, action potential duration (APD) was recorded at temperatures between 36 degrees C and 42 degrees C in neonatal ventricular myocytes. Significantly greater prolongation of APD by erythromycin was observed at 42 degrees C compared with 37 degrees C. To assess whether transmembrane diffusion of erythromycin was the rate-limiting step for block of I(hERG) at 22 degrees C, erythromycin was applied within the patch pipette. Under these conditions, erythromycin rapidly blocked I(hERG) even at 22 degrees C. The F656C mutation in the distal S6 of KCNH2 completely abrogated block of I(hERG) measured at 37 degrees C., Conclusion: Progressively greater block of hERG and prolongation of APD by erythromycin was observed at temperatures between 36 and 42 degrees C. Temperature-dependent block of I(hERG) is explained by temperature-dependent access of erythromycin to the intracellular binding site at F656.

Objective: Economic evaluation of noninvasive (suppression of ventricular arrhythmias detected by ambulatory monitoring) and invasive (suppression of arrhythmias induced by programmed stimulation) approaches to antiarrhythmic drug selection for ventricular tachyarrhythmias., Design/setting: Randomized clinical trial/tertiary-care hospital., Patients: Of 124 consecutive patients referred for treatment of symptomatic ventricular tachyarrhythmias, 57 consenting patients were eligible to have drug therapy selected by either noninvasive or invasive approaches., Measurements: Costs of initial and follow-up (26 +/- 15 months) admissions for the two groups were compared. This economic evaluation also considered relative efficacies of the approaches using the primary outcome variable of symptomatic, sustained ventricular tachyarrhythmia recurrence (including sudden death)., Results: Initial hospitalization for therapy selection was less costly by the noninvasive approach ($6,869 +/- 4,019) than by the invasive approach ($13,164 +/- 6,740) (P less than 0.001). However, the noninvasive approach generated higher follow-up hospital costs ($9,204 +/- 9,217) than the invasive approach ($3,784 +/- 4,944) (P = 0.01). Thus, total hospital costs of the noninvasive ($16,073 +/- 9,423) and invasive approaches ($16,949 +/- 7,174) were equivalent. The two-year actuarial probability of a recurrent, sustained, symptomatic ventricular tachyarrhythmia was greater in noninvasive (0.50 +/- 0.10) than in invasive (0.20 +/- 0.08) approach patients (P = 0.02)., Conclusions: The lower initial hospital costs of the noninvasive approach are offset by greater follow-up costs. Within two years the costs of the two approaches are equivalent. Thus, greater antiarrhythmic efficacy can be achieved by the invasive approach to drug selection without increasing total hospital costs.