Pathogenesis Of Arrhythmias Research Articles

Abstract 111: Cdk5 is Associated in Cardiac Calcium Channelopathy

Cardiac calcium channels play important roles in hearts. Mutations in Ca V 1.2 channels are associated with cardiac arrhythmias including long QT syndrome type 8 (LQTS8). Using human induced pluripotent stem cells (iPSCs) to generate human cardiomyocytes from LQTS8 patients, we reported that the G406R mutation (LQTS8, Timothy syndrome) affected channel inactivation, action potentials and calcium handling in human cardiomyocytes. We found that roscovitine, a cyclin-dependent kinase (CDK) inhibitor, rescued the phenotypes in LQTS8 cardiomyocytes. However, how roscovitine restores the physiological functions in the patient cardiomyocytes remains unclear. Our recent results using roscovitine analogs and CDK inhibitors suggested that CDK5 is involved in the molecular bases of LQTS8. We found that dominant negative forms and shRNA of CDK5 alleviated the phenotypes of the LQTS8 cardiomyocytes and that the expressions of phosphorylated ERK, EGR1 and CDK5R1, a CDK5 activator, significantly increased in the patient cardiomyocytes. The results reveal that calcium overload due to affected Ca V 1.2 inactivation activates ERK/EGR1 pathway, resulting in increased expression of CDK5R1. Biochemical assays supported a direct binding and phosphorylation of Ca V 1.2 channels by CDK5. Overall, the results demonstrated that CDK5 regulates Ca V 1.2 channels and that CDK5 inhibition could be a new therapeutic for LQTS8. This study demonstrates the role of ERK/EGR1/CDK5 in pathogenesis of cardiac arrhythmia. The outcomes of this study provide new insights into Ca V 1.2 channel regulation.

Abstract 16005: Highly Efficient Derivation of Human Pacemaker Cells From Pluripotent Stem Cells in Chemically Defined Conditions

The cardiac conduction system is a complex network of cells that together orchestrate the rhythmic and coordinated depolarization of the heart. Dysfunction of the cardiac conduction system plays a central role in the pathogenesis of arrhythmia. While much progress has been made understanding cardiomyocyte differentiation, the molecular mechanisms regulating the specification and patterning of cells that form this conductive network is largely unknown. The LIM-homeodomain transcription factor ISL1 is highly expressed in the secondary heart field (SHF) progenitor population that makes a substantial contribution to the developing heart, comprising most cells in the right ventricle, both atria and pacemaker cells. Pacemaker cells comprise the most proximal component of the cardiac conduction system, which have been proposed as the source of most arrhythmogenic events. Their dominance on other spontaneous beating cell types makes them a suitable target for pharmacologic compounds, making access to this cell lineage necessary for the study of new therapeutic agents. To identify the signaling pathways that control the differentiation of human embryonic stem cell (hESC)-derived SHF cells into pacemaker cells, we performed RNA sequencing to compare the hESC-derived ISL1 + population, non-enriched population and undifferentiated hESCs. Furthermore, using a small molecule screen we identified compounds that can improve differentiation of hESCs toward pacemaker cells. Pathway analysis identified the Wnt pathway as the most significant regulator of SHF specification. Further differentiation of human pluripotent stem cells by stage-specific activation of BMP and WNT signaling pathways resulted in phenotypic pacemaker cells, which display morphological characteristics. More than 80% of these cells stained positively for HCN4, Contactin2(CNTN2) and GATA6, key markers of pacemaker cells. The differentiated cells express pacemaker markers, including CNTN2, TBX2, TBX3, HCN4, TBX18, GATA6 indicated by qRT-PCR. They show inward potassium currents through HCN channels in patch clamp experiments. Our data provides a new strategy to obtain human cardiac conduction cells in large scale for disease modeling, drug screening and cell therapy.

Role of adipose tissue in the pathogenesis of cardiac arrhythmias

Epicardial adipose tissue is present in normal healthy individuals. It is a unique fat depot that, under physiologic conditions, plays a cardioprotective role. However, excess epicardial adipose tissue has been shown to be associated with prevalence and severity of atrial fibrillation. In arrhythmogenic right ventricular cardiomyopathy and myotonic dystrophy, fibrofatty infiltration of the myocardium is associated with ventricular arrhythmias. In the ovine model of ischemic cardiomyopathy, the presence of intramyocardial adipose or lipomatous metaplasia has been associated with increased propensity to ventricular tachycardia. These observations suggest a role of adipose tissue in the pathogenesis of cardiac arrhythmias. In this article, we review the role of cardiac adipose tissue in various cardiac arrhythmias and discuss the possible pathophysiologic mechanisms.

Abstract 266: Screening and Validation of Small Molecule Inhibitors of Serum and Glucocorticoid Regulated Kinase-1 as Novel Therapy for Cardiac Arrhythmia Disorders

Alterations in sodium flux (INa) play an important role in the pathogenesis of cardiac arrhythmias and may also contribute to the development of cardiomyopathies. Recent data demonstrates a critical role for the serum and glucocorticoid regulated kinase-1 (SGK1) by modulation of INa in the heart, by regulating the voltage-gated sodium channel NaV1.5. To better understand and pharmacologically probe the significance of SGK1 in cardiac dysrhythmias, we have used computer aided drug discovery (CADD) to identify small molecule inhibitors of SGK1. Expression of a constitutively active form of SGK1 (SGK1-CA) increased INa (1.7 fold, p <0.005) in a stable line of HEK cells expressing NaV1.5. Conversely, expression of a dominant negative form (SGK-DN) decreased NaV1.5 channel activity (2.8 fold, p <0.005). We examined the effects of SGK1 inhibition in a LQT model, by quantifying the ability of SGK1 inhibition to rescue the 2:1 AV block phenotype of the potassium channel zebrafish mutant, breakdance (bkd). Morpholino injection or expression of SGK1-DN significantly rescued the 2:1 AV block phenotype as compared to controls (p < 0.05). Using CADD partnered with iterative empirical screens we identified several hit chemical scaffolds. Our lead compound inhibits the phosphorylation of the SGK1 target gene, GSK3-β in a dose dependent manner in cardiomyocytes (CMs) expressing SGK1-CA at the lowest effective concentration of 0.5μM. There was no significant inhibition of AKT dependent phosphorylation of GSK3-β up to a concentration of 50μM, demonstrating specificity of the inhibitor for SGK1. Incubation of bkd zebrafish mutants with the inhibitor rescued the 2:1 AV block in a dose dependent manner (60% rescue with 45μM, p < 0.05). Acute application of the inhibitor dramatically inhibited INa with either expression of SGK1-CA (90.8% reduction, p <0.05 ) or with RFP only (77.5% reduction p < 0.005). The half-time of inhibition was 200s with resulting current densities that were not statistically different than those observed with genetic inhibition by expression of SGK1-DN. We conclude SGK1 activity regulates INa and speculate that structure activity relationship (SAR) derivatives of our lead compound might have a role in treatment of human cardiac arrhythmias.

Abstract 304: Efficient Generation of Cardiac Purkinje Fiber-like Cells From ESCs by Activating cAMP Signaling

Dysfunction of the cardiac conduction system (CCS) significantly impacts pathogenesis of arrhythmia, a major cause of morbidity and mortality. Strategies to derive cardiac conduction cells including Purkinje fiber cells (PC) would facilitate models for mechanistic studies and drug discovery, and also provide new cellular materials for regenerative therapies. A high-throughput chemical screen using CCS:lacZ and Contactin2:eGFP (Cntn2:eGFP) reporter embryonic stem cell (ESC) lines was used to discover a small molecule, sodium nitroprusside (SN), that efficiently promotes the generation of cardiac cells that express gene profiles and generate action potentials of PC-like cells. Imaging and mechanistic studies suggest that SN promotes the generation of PC from cardiac progenitors initially expressing cardiac myosin heavy chain, and that it does so by activating cAMP signaling. These findings provide a novel strategy to derive scalable PC, along with insight into the ontogeny of CCS development.

Deletion of PDK1 causes cardiac sodium current reduction in mice.

BackgroundThe AGC protein kinase family regulates multiple cellular functions. 3-phosphoinositide-dependent protein kinase-1 (PDK1) is involved in the pathogenesis of arrhythmia, and its downstream factor, Forkhead box O1 (Foxo1), negatively regulates the expression of the cardiac sodium channel, Nav1.5. Mice are known to die suddenly after PDK1 deletion within 11 weeks, but the underlying electrophysiological bases are unclear. Thus, the aim of this study was to investigate the potential mechanisms between PDK1 signaling pathway and cardiac sodium current.Methods and ResultsUsing patch clamp and western blotting techniques, we investigated the role of the PDK1-Foxo1 pathway in PDK1 knockout mice and cultured cardiomyocytes. We found that PDK1 knockout mice undergo slower heart rate, prolonged QRS and QTc intervals and abnormal conduction within the first few weeks of birth. Furthermore, the peak sodium current is decreased by 33% in cells lacking PDK1. The phosphorylation of Akt (308T) and Foxo1 (24T) and the expression of Nav1.5 in the myocardium of PDK1-knockout mice are decreased, while the nuclear localization of Foxo1 is increased. The role of the PDK1-Foxo1 pathway in regulating Nav1.5 levels and sodium current density was verified using selective PDK1, Akt and Foxo1 inhibitors and isolated neonatal rat cardiomyocytes.ConclusionThese results indicate that PDK1 participates in the dysregulation of electrophysiological basis by regulating the PDK1-Foxo1 pathway, which in turn regulates the expression of Nav1.5 and cardiac sodium channel function.

Short-coupled polymorphic ventricular tachycardia at rest linked to a novel ryanodine receptor (RyR2) mutation: Leaky RyR2 channels under non-stress conditions

BackgroundRyanodine receptor (RyR2) mutations have largely been associated with catecholaminergic polymorphic ventricular tachycardia (PMVT). The role of RyR2 mutations in the pathogenesis of arrhythmias and syncope at rest is unknown. We sought to characterize the clinical and functional characteristics associated with a novel RyR2 mutation found in a mother and daughter with PMVT at rest. Methods and resultsA 31-year-old female with syncope at rest and recurrent short-coupled premature ventricular contractions (PVCs) initiating PMVT was found to be heterozygous for a novel RyR2-H29D mutation. Her mother, who also had syncope at rest and short-coupled PMVT, was found to harbor the same mutation. Human RyR2-H29D mutant channels were generated using site-directed mutagenesis and heterologously expressed in HEK293 cells together with the stabilizing protein calstabin2 (FKPB12.6). Single channel measurements of RyR2-H29D mutant channels and wild type (WT) RyR2 channels were compared at varying concentrations of cytosolic Ca2+. Binding affinities of the RyR2-H29D channels and RyR2-WT channels to calstabin2 were compared. Functional characterization of the RyR2-H29D mutant channel revealed significantly higher open probability and opening frequency at diastolic levels of cytosolic Ca2+ under non-stress conditions without protein kinase A treatment. This was associated with a modest depletion of calstabin2 binding under resting conditions. ConclusionsThe RyR2-H29D mutation is associated with a clinical phenotype of short-coupled PMVT at rest. In contrast to catecholaminergic PMVT-associated RyR2 mutations, RyR2-H29D causes a leaky channel at diastolic levels of Ca2+ under non-stress conditions. Leaky RyR2 may be an under-recognized mechanism for idiopathic PMVT at rest.

Arrhythmias in the developing heart.

Prevalence of cardiac arrhythmias increases gradually with age; however, specific rhythm disturbances can appear even prior to birth and markedly affect foetal development. Relatively little is known about these disorders, chiefly because of their relative rarity and difficulty in diagnosis. In this review, we cover the most common forms found in human pathology, specifically congenital heart block, pre-excitation, extrasystoles and long QT syndrome. In addition, we cover pertinent literature data from prenatal animal models, providing a glimpse into pathogenesis of arrhythmias and possible strategies for treatment.

69 * The relationship between the 174G>C IL-6 gene polymorphism and ventricular arrhythmias in patients with ICD

Introduction: There is an evidence indicating that inflammation may play a role in ventricular arrhythmia pathogenesis. IL-6 is a pleiotropic, proinflammatory cytokine which plays a role in the immune, the endocrine and the nervous system. We hypothesized that the polymorphism of the gene coding for IL-6 may be associated with the occurrence of ventricular arrhythmias. Methods: The study group consisted of 136 consecutive patients (pts) -117 males, mean age 59 y (21-88) in whom ICD was implanted as a primary (106 pts) or secondary (30 pts) prophylaxis of sudden cardiac death The pts were followed-up at 6 months intervals after implantation .Genotyping of the polymorphic locus 174 G>C in the promoter of the IL-6 gene was made by the polymerase chain reaction (PCR) with analysis of single nucleotide polymorphism (SNP). Serum levels of inflammatory markers including hsCRP, fibrinogen, IL-6, IL-18, IL-10, TNF-alpha, cd40L were obtained the day before implantation. Results: During the 24 months follow-up ventricular fibrillation (VF) occurred in 25 pts and ventricular tachycardia (VT) in 83 pts (sustained VT-25 pts, non-sustained VT-58 pts) In the study group 3 types of genotypes were detected in the polymorphic locus: GG, GC and CC. GC genotype was associated with higher incidence of VT and VF as compared to GG and CC genotypes (p=0.02). There was also a discordance of the genotype's distribution and the Hardy-Weinberg equilibrium. In pts without VT or VF GG and CC genotypes were more frequent than expected and GC genotype was less frequent than expected (p<0.05). There was no association between levels of inflammatory markers and the occurrence of VT or VF. Conclusions: The 174 G>C polymorphism in the IL-6 gene may contribute to pathogenesis of ventricular arrhythmias.

Oxydative status and atrial fibrillations

According to the recent epidemiological reports atrial fibrillation (AF) affects about 6 million people in Europe and the number is expected to double in the next 50 years (1). Because of the growing incidence, AF is considered as “the new epidemic” (2). Despite being recognized as far back as ancient Greece and China, nowadays AF is a real challenge for cardiologists. The numerous antiarrhythmic drugs, namely blockers of !-adrenergic receptors and cardiac ion channels, as well as catheter ablation have inadequate efficacy on AF recurrences and progressive clinical course. Main limitation for these results is the poor understanding of arrhythmia pathogenesis (3). Thus, in the last years, the efforts of scientists are increasingly focused on the underlying mechanisms concerning AF initiation and recurrences.

Pathogenesis of arrhythmias in a model of CKD.

Patients with CKD have an increased risk of cardiovascular mortality from arrhythmias and sudden cardiac death. We used a rat model of CKD (Cy/+) to study potential mechanisms of increased ventricular arrhythmias. Rats with CKD showed normal ejection fraction but hypertrophic myocardium. Premature ventricular complexes occurred more frequently in CKD rats than normal rats (42% versus 11%, P=0.18). By optical mapping techniques, action potential duration (APD) at 80% of repolarization was longer in CKD rats (78±4ms) than normal rats (63±3 ms, P<0.05) at a 200-ms pacing cycle length. Calcium transient (CaT) duration was comparable. Pacing cycle length thresholds to induce CaT alternans or APD alternans were longer in CKD rats than normal rats (100±7 versus 80±3 ms and 93±6 versus 76±4 ms for CaT and APD alternans, respectively, P<0.05), suggesting increased vulnerability to ventricular arrhythmia. Ventricular fibrillation was induced in 9 of 12 CKD rats and 2 of 9 normal rats (P<0.05); early afterdepolarization occurred in two CKD rats but not normal rats. The mRNA levels of TGF-β, microRNA-21, and sodium calcium-exchanger type 1 were upregulated, whereas the levels of microRNA-29, L-type calcium channel, sarco/endoplasmic reticulum calcium-ATPase type 2a, Kv1.4, and Kv4.3 were downregulated in CKD rats. Cardiac fibrosis was mild and not different between groups. We conclude that cardiac ion channel and calcium handling are abnormal in CKD rats, leading to increased vulnerability to early afterdepolarization, triggered activity, and ventricular arrhythmias.

ASSOCIATION BETWEEN HEART RATE VARIABILITY AND COMPONENTS OF THE METABOLIC SYNDROME IN WOMEN WITH RHEUMATOID ARTHRITIS

Aim. To study the relationship between heart rate variability (HRV) and components of the metabolic syndrome (MS) in women with rheumatoid arthritis (RA). Material and methods. Female patients (n=291) with a firm RA diagnosis under 60 years of age were examined. Evaluation of traditional cardiovascular risk factors, MS components (International Diabetes Federation criteria), 24-hour ECG monitoring were performed along with the assessment of clinical symptoms, the degree of activity and severity of RA. Results. Weak associations of HRV with waist circumference, blood pressure level, hypertriglyceridemia, hypoalphalipoproteinemia and smoking were found in the correlation analysis. Patients with RA were divided into three groups depending on the number of existing MS components. Group 1 (0-1 component) included 113 women (39%), group 2 (2-3 components) – 109 women (37%) and group 3 (4-5 components) – included 69 women with RA (24%). Progressive decrease in the absolute values and the increase in the percentage of the low values of all the studied time and frequency HRV indices, adjusted by age and heart rate, from the 1st to the 3rd group of women with RA were determined. Significant increase in sympathovagal index from the 1st to the 3rd group was also shown. Conclusion. A combination of several components of the MS in RA plays a greater role in the development of disorders of neurovegetative autonomic control of heart activity (increased influence of the sympathetic and/or reduced influence of the parasympathetic nervous system on cardiac function) than each traditional cardiovascular risk factor taken separately. Abnormality in autonomic regulation of cardiac activity may be an important link in the pathogenesis of cardiac arrhythmias, sudden cardiac death and overall cardiovascular mortality in women with RA.

The role of Interleukin-6, its −174 G>C polymorphism and C-reactive protein in idiopathic cardiac arrhythmias in children

ABSTRACT Purpose: Knowledge about the role of inflammation in the pathogenesis of arrhythmias in children is limited. Several studies have suggested a relationship between plasma IL-6 levels and/or the -174G>C IL-6 gene polymorphism and atrial fibrillation in adults. Our present study was performed to investigate whether serum IL-6, -174G>C IL-6 polymorphism and C-reactive protein (CRP) are associated with arrhythmias of unknown origin in children. The study included 126 children diagnosed with supraventricular or ventricular arrhythmia. Patients with congenital heart defects as well as arrhythmias of known origin were excluded from the study. The control group comprised 37 healthy children. The 24 hour Holter electrocardiography monitoring was performed. Serum IL-6, -174 GC IL-6 polymorphism and CRP concentrations were measured on admission. There were no differences in IL-6, CRP and -174 G>C IL-6 genotype distribution between the control and patient groups. No significant differences in IL-6, CRP and -174 G>C IL-6 genotypes were observed between children with supraventricular or ventricular arrhythmias. The severity of arrhythmias showed also no associations with IL-6, CRP or -174 G>C IL-6 genotypes. The results suggest that idiopathic cardiac arrhythmias of unknown origin in children are not associated with selected pro-inflammatory markers of infections i.e. elevated IL-6, CRP or -174 G>C IL-6 polymorphism. This new information can effectively reduce the total financial cost of unnecessary diagnosis and treatment of children affected by cardiac arrhythmias.

Essential Role of the m2R-RGS6-IKACh Pathway in Controlling Intrinsic Heart Rate Variability

Normal heart function requires generation of a regular rhythm by sinoatrial pacemaker cells and the alteration of this spontaneous heart rate by the autonomic input to match physiological demand. However, the molecular mechanisms that ensure consistent periodicity of cardiac contractions and fine tuning of this process by autonomic system are not completely understood.Here we examined the contribution of the m2R-IKACh intracellular signaling pathway, which mediates the negative chronotropic effect of parasympathetic stimulation, to the regulation of the cardiac pacemaking rhythm. Using isolated heart preparations and single-cell recordings we show that the m2R-IKACh signaling pathway controls the excitability and firing pattern of the sinoatrial cardiomyocytes and determines variability of cardiac rhythm in a manner independent from the autonomic input. Ablation of the major regulator of this pathway, Rgs6, in mice results in irregular cardiac rhythmicity and increases susceptibility to atrial fibrillation. We further identify several human subjects with variants in the RGS6 gene and show that the loss of function in RGS6 correlates with increased heart rate variability. These findings identify the essential role of the m2R-IKACh signaling pathway in the regulation of cardiac sinus rhythm and implicate RGS6 in arrhythmia pathogenesis.

Abstract 351: Downregulation of Connexin43 by MicroRNA-130a Results in Cardiac Arrhythmias

MicroRNAs (miRs) are endogenous ~22 nucleotide RNA molecules that are now recognized as critical regulators of diverse physiological and pathological processes; however, studies of miRs and arrhythmogenesis remain sparse. Connexin43 (Cx43), a major cardiac gap junction protein, is critical for maintaining normal cardiac electrical conduction. One aspect of arrhythmia pathogenesis that has elicited great interest has been changes in Cx43 expression. Computational analysis of messenger RNAs predicted Cx43 to be a target for miR-130a. We hypothesized that overexpression of miR-130a in adult cardiomyocytes would result in cardiac arrhythmias. To study this, we used an inducible (tetracycline-off) bigenic system to study miR-130a overexpression in the adult mouse heart. 12 weeks after induction of miR-130a, 100% (16/16) of transgenic mice demonstrated a loss of sinus rhythm and irregular ventricular activity suggestive of atrial fibrillation on surface electrocardiograms (ECG). Nonsustained ventricular tachycardia was also observed during ECG recordings. Atrial contractions could not be detected by pulse wave Doppler. Intracardiac electrocardiography confirmed the presence of atrial arrhythmias. Western blot analysis demonstrated a 90% reduction in Cx43 levels and immunofluorescent staining confirmed a near complete loss of Cx43 in transgenic compared to littermate control hearts (n=12). Morphology of the intercalated disc was evaluated by electron microscopy and showed a loss of gap junctions in transgenic hearts. To validate Cx43 as a direct target of miR-130a, we performed in vitro target assays in 3T3 fibroblasts, known to express miR-130a. Using a luciferase reporter fused to the 3’UTR of Cx43 compared to a control (SV40) 3’UTR, we found a 55% ± 6% reduction in luciferase activity with the Cx43 3’UTR (p&lt;0.01, n=9). Addition of an antisense miR-130a inhibitor resulted in a dose dependent loss of inhibitory activity of the Cx43 3’UTR reporter, with no changes seen in the control vector. In conclusion, we have identified an unappreciated role of miR-130a as a direct regulator of Cx43. Overexpression of miR-130a results in the development of a variety of important cardiac arrhythmias including atrial fibrillation and ventricular tachycardia.

Selectively silencing Nitric Oxide Synthase 1 Adaptor Protein in the Nucleus Tractus Solitarius leads to QT Interval Prolongation via Glutamate‐mediated neurotoxicity

Variants of the nitric oxide synthase 1 adaptor protein (NOS1AP) locus are strongly related to QT interval prolongation and sudden cardiac death (SCD) in human. Our aim was to study the action of NOS1AP in the NTS by knockdown of NOS1AP using lentiviral vector‐mediated shRNA (Lv‐NOS1AP‐shRNA). qPCR data showed NOS1AP mRNA levels were expressed in NTS 3‐fold higher than organs such as kidney and heart in SD rats. Microinjection of Lv‐NOS1AP‐shRNA in NTS caused significant reduction in NOS1AP expression in SD rats. NOS1AP knockdown in NTS did not alter blood pressure (BP), heart rate (HR) recorded by radiotelemetry. ECG analysis revealed heart rate variability (HRV) was significantly reduced (SDNN, 51.2±5.6 vs 5.0±1.3 ms, P&lt; .001) and QTc interval was markedly prolonged (72.4±4 vs 105±11 ms, P&lt; .05) in NOS1AP knockdown rats. To study the cellular mechanism underlying NOS1AP action, we studied the effect of NOS1AP knockdown on glutamate‐induced neurotoxicity in Cath‐a cells. Treatment of cells with Lv‐NOS1AP‐shRNA significantly reduced NOS1AP expression, and was associated with increased glutamate‐induced neurotoxicity, suggesting a protective effect of NOS1AP. In summary, all results indicate that NOS1AP dysfunction in NTS might play an important role in the pathogenesis of cardiac arrhythmia which, in part, could be due to increased sensitivity to glutamate induced neurotoxicity.Research Support: NDSU‐COBRE

Effects of Social Isolation on Connexin 43 Expression in the Left Ventricle of Female Prairie Voles

Social stress plays a key role in the relationship between cardiovascular disease (CVD) and depression. Previous studies in animals have shown that social isolation leads to depressive like behaviors and increased incidence of arrhythmias. Alterations in the expression of left ventricular (LV) connexin43 (Cx43) has been identified in the pathogenesis of cardiac arrhythmias in some forms of CVD. Prairie voles, which are socially monogamous rodents, were used to investigate the hypothesis that social isolation leads to increased depressive like behaviors and decreased LV Cx43 expression. Adult prairie voles were paired with or isolated from a sibling for 4 weeks. Then, half of the paired and isolated animals were exposed to 7 days of chronic mild stressors (CMS) while the other half remained undisturbed. The animals were subjected to the forced swim test (FST) as an index of depressive behavior. Following the FST, hearts were collected and LV Cx43 expression was determined by Western blotting. Data indicate a significant increase in depressive behavior during the FST exhibited by the paired+CMS, isolated, and isolated+CMS groups compared to the paired group. The expression of LV Cx43 was significantly lower in all groups as compared to the paired group. We conclude that a reduction in the expression of LV Cx43 may be a mechanism for the increased arrhythmogenesis in animals that exhibit depressive like behaviors. MH77581, HL112350, IOER 3726

Cardiac Arrhythmias in Adult Patients with Asthma

Objective. The pathogenesis of cardiac arrhythmias in asthma patients has not been fully elucidated. Adverse drug effects, particularly those of β2-mimetics, may play a role. The aim of this study was to determine whether asthma is associated with the risk of cardiac arrhythmias and electrocardiographic characteristics of arrhythmogenicity (ECG) and to explore the role of β2-mimetics. Methods. A cross-sectional study was conducted among 158 adult patients with a diagnosis of asthma and 6303 participants without asthma from the cohort of the Utrecht Health Project—an ongoing, longitudinal, primary care-based study. All patients underwent extensive examinations, including resting 12-lead electrocardiogram (ECG) and pulmonary function tests. The primary outcome was “any arrhythmia on the ECG” (including tachycardia, bradycardia, premature ventricular contraction (PVC), and atrial fibrillation or flutter). Secondary outcomes were tachycardia, bradycardia, PVC, atrial fibrillation or flutter, mean heart rate, mean corrected QT (QTc) interval length, and prolonged QTc interval. Results. Tachycardia and PVCs were more prevalent in patients with asthma (3% and 4%, respectively) than those without asthma (0.6%, p < .001; 2%, p = .03, respectively). The prevalence of QTc interval prolongation was similar in participants with (2%) and without asthma (3%, odds ratio [OR]: 0.6 and 95% confidence interval [95% CI]: 0.2–2.0). In 74 asthma patients, who received β2-mimetics, tachycardia and PVCs were more common (OR: 12.4 [95% CI: 4.7–32.8] and 3.7 [95% CI: 1.3–10.5], respectively). Conclusions. The adult patients with asthma more commonly show tachycardia and PVCs on the ECG than those without asthma. The patients with asthma received β2-mimetics; the risk of tachycardia and PVCs is even more pronounced.

Managing Arrhythmias before and after Aortic Valve Surgery in Children

The proximity of the coronary arteries and the bundle of His to the aortic valve may contribute to the pathogenesis of arrhythmias in patients with aortic valve disease. Severe aortic valve disease may also adversely alter left ventricular hemodynamics (end-diastolic dimensions and wall stress) and thus create a substrate for ventricular arrhythmias before any intervention is performed. The severity of these arrhythmias depends on the severity of the underlying substrate (or the specific problem, such as aortic stenosis or aortic regurgitation), the age at which the aortic valve intervention was performed, the type of intervention (i.e. transcatheter aortic valve interventions or open aortic valve replacement or repair), and the reversibility of the altered hemodynamics after surgery. Both bradyarrhythmias and tachyarrhythmias are known complications of aortic valve interventions. Although data are scant, this review summarizes the incidence of arrhythmias before and after aortic valve interventions from a pediatric perspective.

Mitochondrial Oxidative Stress Mediates the Effect of Angiotensin II on Gap Junctional Remodeling and Sudden Arrhythmic Death

Introduction: Angiotensin II activation and associated elevation in ROS have been implicated in pathogenesis of arrhythmia. We created a transgenic mouse model of cardiac restricted overexpression of ACE (ACE8/8). These mice show spontaneous VT/ VF, SCD, and a reduction in Cx43 level, which impairs conduction and predisposes to arrhythmia. We sought to determine the role and the major source of ROS by angiotensin II in VT/ VF and Cx43 remodeling. Method: Wild type and ACE8/8 mice with and without 2 weeks of treatment with LNIO (NOS inhibitor), Sepiapterin (precursor of BH4), Mito-TEMPO (mitochondria-targeted antioxidant), Apocynin (NADPH oxidase inhibitor), Allopurinol (Xanthine oxidase inhibitor), and ACE8/8 crossed with P67DN were studied. Western blotting, detection of mitochondrial ROS by MitoSOX red, electron microscopy, immunohistochemistry staining, and a fluorescent dye diffusion technique for functional assessment of Cx43 were performed. EP study was performed by a 1.1F catheter through pacing the right ventricle. Results: Treatment with Mito-TEMPO prevented SCD in ACE8/8 mice (p=0.0005, 95% CI of 1.96 to 11.53). Treatment with Mito-TEMPO was also associated with reduction in VT inducibility (from 87% to 50%), correction of gap junction dye conduction (from 75% of control to normal, P<0.05), reduction of mitochondrial ROS (from 6 to 1.8 fold of the control), improvement of structure of mitochondria (detected by electron microscopy), increase in Cx43 level at the gap junctions (from 33% to 70% of control level detected by western blot and immunohistochemistry). Treatments with L-NIO, Sepiapterin, Allopurinol, Apocynin and crossing with P67DN mice did not prevent VT/VF and SCD in ACE8/8 mice. Conclusion: Mitochondrial oxidative stress plays a central role in ROS-induced arrhythmia and mitochondria-targeted antioxidants may be effective antiarrhythmic drugs.