Electrophysiological Remodeling Research Articles

Uremic toxins in chronic kidney disease highlight a fundamental gap in understanding their detrimental effects on cardiac electrophysiology and arrhythmogenesis.

Chronic kidney disease (CKD) and cardiovascular disease (CVD) have an estimated 700-800 and 523 million cases worldwide, respectively, with CVD being the leading cause of death in CKD patients. The pathophysiological interplay between the heart and kidneys is defined as the cardiorenal syndrome (CRS), in which worsening of kidney function is represented by increased plasma concentrations of uremic toxins (UTs), culminating in dialysis patients. As there is a high incidence of CVD in CKD patients, accompanied by arrhythmias and sudden cardiac death, knowledge on electrophysiological remodeling would be instrumental for understanding the CRS. While the interplay between both organs is clearly of importance in CRS, the involvement of UTs in pro-arrhythmic remodeling is only poorly investigated, especially regarding the mechanistic background. Currently, the clinical approach against potential arrhythmic events is mainly restricted to symptom treatment, stressing the need for fundamental research on UT in relation to electrophysiology. This review addresses the existing knowledge of UTs and cardiac electrophysiology, and the experimental research gap between fundamental research and clinical research of the CRS. Clinically, mainly absorbents like ibuprofen and AST-120 are studied, which show limited safe and efficient usability. Experimental research shows disturbances in cardiac electrical activation and conduction after inducing CKD or exposure to UTs, but are scarcely present or focus solely on already well-investigated UTs. Based on UTs data derived from CKD patient cohort studies, a clinically relevant overview of physiological and pathological UTs concentrations is created. Using this, future experimental research is stimulated to involve electrophysiologically translatable animals, such as rabbits, or in vitro engineered heart tissues.

Electrophysiological remodeling in primary versus secondary cardiac hypertrophy: A study in human cardiomyocytes

Electrophysiological remodeling in primary versus secondary cardiac hypertrophy: A study in human cardiomyocytes

Protein Kinase D1 Regulates Cardiac Hypertrophy, Potassium Channel Remodeling, and Arrhythmias in Heart Failure.

Background Structural and electrophysiological remodeling characterize heart failure (HF) enhancing arrhythmias. PKD1 (protein kinase D1) is upregulated in HF and mediates pathological hypertrophic signaling, but its role in K+ channel remodeling and arrhythmogenesis in HF is unknown. Methods and Results We performed echocardiography, electrophysiology, and expression analysis in wild-type and PKD1 cardiomyocyte-specific knockout (cKO) mice following transverse aortic constriction (TAC). PKD1-cKO mice exhibited significantly less cardiac hypertrophy post-TAC and were protected from early decline in cardiac contractile function (3 weeks post-TAC) but not the progression to HF at 7 weeks post-TAC. Wild-type mice exhibited ventricular action potential duration prolongation at 8 weeks post-TAC, which was attenuated in PKD1-cKO, consistent with larger K+ currents via the transient outward current, sustained current, inward rectifier K+ current, and rapid delayed rectifier K+ current and increased expression of corresponding K+ channels. Conversely, reduction of slowly inactivating K+ current was independent of PKD1 in HF. Acute PKD inhibition slightly increased transient outward current in TAC and sham wild-type myocytes but did not alter other K+ currents. Sham PKD1-cKO versus wild-type also exhibited larger transient outward current and faster early action potential repolarization. Tachypacing-induced action potential duration alternans in TAC animals was increased and independent of PKD1, but diastolic arrhythmogenic activities were reduced in PKD1-cKO. Conclusions Our data indicate an important role for PKD1 in the HF-related hypertrophic response and K+ channel downregulation. Therefore, PKD1 inhibition may represent a therapeutic strategy to reduce hypertrophy and arrhythmias; however, PKD1 inhibition may not prevent disease progression and reduced contractility in HF.

Electrophysiological effects of adipose graft transposition procedure (AGTP) on the post-myocardial infarction scar: A multimodal characterization of arrhythmogenic substrate.

ObjectiveTo assess the arrhythmic safety profile of the adipose graft transposition procedure (AGTP) and its electrophysiological effects on post-myocardial infarction (MI) scar.BackgroundMyocardial repair is a promising treatment for patients with MI. The AGTP is a cardiac reparative therapy that reduces infarct size and improves cardiac function. The impact of AGTP on arrhythmogenesis has not been addressed.MethodsMI was induced in 20 swine. Contrast-enhanced magnetic resonance (ce-MRI), electrophysiological study (EPS), and left-ventricular endocardial high-density mapping were performed 15 days post-MI. Animals were randomized 1:1 to AGTP or sham-surgery group and monitored with ECG-Holter. Repeat EPS, endocardial mapping, and ce-MRI were performed 30 days post-intervention. Myocardial SERCA2, Connexin-43 (Cx43), Ryanodine receptor-2 (RyR2), and cardiac troponin-I (cTnI) gene and protein expression were evaluated.ResultsThe AGTP group showed a significant reduction of the total infarct scar, border zone and dense scar mass by ce-MRI (p = 0.04), and a decreased total scar and border zone area in bipolar voltage mapping (p < 0.001). AGTP treatment significantly reduced the area of very-slow conduction velocity (<0.2 m/s) (p = 0.002), the number of deceleration zones (p = 0.029), and the area of fractionated electrograms (p = 0.005). No differences were detected in number of induced or spontaneous ventricular arrhythmias at EPS and Holter-monitoring. SERCA2, Cx43, and RyR2 gene expression were decreased in the infarct core of AGTP-treated animals (p = 0.021, p = 0.018, p = 0.051, respectively).ConclusionAGTP is a safe reparative therapy in terms of arrhythmic risk and provides additional protective effect against adverse electrophysiological remodeling in ischemic heart disease.

Multimodal imaging shows fibrosis architecture and action potential dispersion are predictors of arrhythmic risk in spontaneous hypertensive rats.

Hypertensive heart disease (HHD) increases risk of ventricular tachycardia (VT) and ventricular fibrillation (VF). The roles of structural vs. electrophysiological remodelling and age vs. disease progression are not fully understood. This cross‐sectional study of cardiac alterations through HHD investigates mechanistic contributions to VT/VF risk. Risk was electrically assessed in Langendorff‐perfused, spontaneously hypertensive rat hearts at 6, 12 and 18 months, and paced optical membrane voltage maps were acquired from the left ventricular (LV) free wall epicardium. Distributions of LV patchy fibrosis and 3D cellular architecture in representative anterior LV mid‐wall regions were quantified from macroscopic and microscopic fluorescence images of optically cleared tissue. Imaging showed increased fibrosis from 6 months, particularly in the inner LV free wall. Myocyte cross‐section increased at 12 months, while inter‐myocyte connections reduced markedly with fibrosis. Conduction velocity decreased from 12 months, especially transverse to the myofibre direction, with rate‐dependent anisotropy at 12 and 18 months, but not earlier. Action potential duration (APD) increased when clustered by age, as did APD dispersion at 12 and 18 months. Among 10 structural, functional and age variables, the most reliably linked were VT/VF risk, general LV fibrosis, a measure quantifying patchy fibrosis, and non‐age clustered APD dispersion. VT/VF risk related to a quantified measure of patchy fibrosis, but age did not factor strongly. The findings are consistent with the notion that VT/VF risk is associated with rate‐dependent repolarization heterogeneity caused by structural remodelling and reduced lateral electrical coupling between LV myocytes, providing a substrate for heterogeneous intramural activation as HHD progresses. Key points There is heightened arrhythmic risk with progression of hypertensive heart disease.Risk is related to increasing left ventricular fibrosis, but the nature of this relationship has not been quantified.This study is a novel systematic characterization of changes in active electrical properties and fibrotic remodelling during progression of hypertensive heart disease in a well‐established animal disease model.Arrhythmic risk is predicted by several left ventricular measures, in particular fibrosis quantity and structure, and epicardial action potential duration dispersion.Age alone is not a good predictor of risk.An improved understanding of links between arrhythmic risk and fibrotic architectures in progressive hypertensive heart disease aids better interpretation of late gadolinium‐enhanced cardiac magnetic resonance imaging and electrical mapping signals.

Abstract P1105: Inflammatory Bowel Disease Induced Autonomic Dysregulation Increases The Risk For Atrial Fibrillation

Introduction: Ulcerative colitis causes inflammation of the innermost lining of the colon and rectum. The disease has a relapsing and remitting course and is accompanied by extraintestinal manifestations such as an increased risk for atrial fibrillation (AF). Here we will test the hypothesis that during active colitis, dysregulation of parasympathetic signaling increases the propensity for atrial arrhythmic events. Methods: Dextran Sulfate Sodium (DSS: 3%, 7days) treated mice (C57BL/6) exhibit disrupted intestinal barrier function that mimics the disease phenotype of active colitis. Changes in atrial electrophysiology was quantified in-vivo (EKG) and in the Langendorff (LD)-perfused heart (atrial electrograms) during peak inflammation (DSS A ) and remission (DSS R ). Results: During peak inflammation, structural remodeling was reflected in a decreased heart weight to tibia length ratio (Control (CTL A ): 9.9±0.4 mg/mm, n=10; DSS A : 8.8±0.3 mg/mm, n=12; p&lt;0.05) whereas electrophysiological atrial remodeling was supported by a prolonged P-wave duration (CTL A : 25.5±0.6 ms, n=10; DSS A : 31.2±0.6 ms, n=24; p&lt;0.0001) and shortened atrial effective refractory period (CTL A : 27.3±1.7 ms, n=4; DSS A : 19.3±0.6 ms, n=4; p&lt;0.01). In comparison to CTL A , DSS A mice exhibited autonomic dysregulation reflected in an attenuated heart rate (HR) variability and a decreased change in HR in response to the muscarinic receptor blocker atropine (CTL A : 7.6±1.8 %, n=5; DSS A : 2.2±0.7 %, n=7; p&lt;0.01). The decreased vagal tone in DSS A coincided with an exaggerated response to the parasympathomimetic carbachol (CCh, 150ng/g) that resulted in a larger decrease in HR (in vivo: CTL A : -12.3±3.1 %, n=10; DSS A : -46.0±5.6 %, n=10; p&lt;0.0001) and increased number of spontaneous arrhythmic events (CTL A : 1.7±0.6 events/min, n=10; DSS A : 9.8±3.8 events/min, n=10; p&lt;0.05) in vivo and in the LD-configuration. The susceptibility for pacing induced AF trended to be increased in DSS A animals. Structural and electrophysiological changes were reversible upon remission. Conclusion: Active colitis induces transient structural and electrophysiological remodeling. We propose that dysregulation of cholinergic signaling drives the increased propensity for atrial arrhythmia.

Abstract P1102: Rna-seq Analyses Reveal Roles Of The Hvcn1 Proton Channel In Cardiac Ph Homeostasis

Introduction: The voltage-gated proton channel Hv1 is a member of the voltage-gated ion channel family. Hv1 channel controls acid extrusion and regulates pH homeostasis in various cell types. Recent evidence showed that the Hv1 were expressed in the heart. Hypothesis: We propose the Hv1 channel is associated with cardiac function. Methods: To investigate the role of Hv1 in cardiac myocytes, we performed a transcriptomic analysis of wild-type (WT) and Hv1-/- mouse hearts. Results: Hv1 null hearts exhibited a differential transcriptome profile compared with wild-type hearts. The RNA-seq data indicating impaired pH homeostasis in Hv1 null hearts were the downregulated NADPH oxidoreductases (NOXs) and decreased expression of Cl-/HCO3- exchanger. Additionally, Hv1 null hearts exhibited differential expression of cardiac ion channels, suggesting a potential role of Hv1 in cardiac electrophysiological remodeling. Conclusions: The data indicated that Hv1 was involved in cardiac pH homeostasis and showed that Hv1 was a regulator of gene transcriptional networks controlling NOX signaling and CO2 homeostasis in the heart. The study highlights the importance of Hv1 in cardiac function and may present a new target associated with heart diseases.

Toward ECG-based analysis of hypertrophic cardiomyopathy: a novel ECG segmentation method for handling abnormalities.

Abnormalities in impulse propagation and cardiac repolarization are frequent in hypertrophic cardiomyopathy (HCM), leading to abnormalities in 12-lead electrocardiograms (ECGs). Computational ECG analysis can identify electrophysiological and structural remodeling and predict arrhythmias. This requires accurate ECG segmentation. It is unknown whether current segmentation methods developed using datasets containing annotations for mostly normal heartbeats perform well in HCM. Here, we present a segmentation method to effectively identify ECG waves across 12-lead HCM ECGs. We develop (1) a web-based tool that permits manual annotations of P, P', QRS, R', S', T, T', U, J, epsilon waves, QRS complex slurring, and atrial fibrillation by 3 experts and (2) an easy-to-implement segmentation method that effectively identifies ECG waves in normal and abnormal heartbeats. Our method was tested on 131 12-lead HCM ECGs and 2 public ECG sets to evaluate its performance in non-HCM ECGs. Over the HCM dataset, our method obtained a sensitivity of 99.2% and 98.1% and a positive predictive value of 92% and 95.3% when detecting QRS complex and T-offset, respectively, significantly outperforming a state-of-the-art segmentation method previously employed for HCM analysis. Over public ECG sets, it significantly outperformed 3 state-of-the-art methods when detecting P-onset and peak, T-offset, and QRS-onset and peak regarding the positive predictive value and segmentation error. It performed at a level similar to other methods in other tasks. Our method accurately identified ECG waves in the HCM dataset, outperforming a state-of-the-art method, and demonstrated similar good performance as other methods in normal/non-HCM ECG sets.

Prevention of heart failure, tachyarrhythmias and sudden cardiac death in HIV.

To summarize the state-of-the-art literature on the epidemiology, disease progression, and mediators of heart failure, tachyarrhythmias, and sudden cardiac death in people living with HIV (PLWH) to inform prevention strategies. Recent studies corroborate the role of HIV as a risk enhancer for heart failure and arrhythmias, which persists despite adjustment for cardiovascular risk factors and unhealthy behaviors. Immune activation and inflammation contribute to the risk. Heart failure occurs more frequently at younger ages, and among women and ethnic minorities living with HIV, highlighting disparities. Prospective outcome studies remain sparse in PLWH limiting prevention approaches. However, subclinical cardiac and electrophysiologic remodeling and dysfunction detected by noninvasive testing are powerful disease surrogates that inform our mechanistic understanding of HIV-associated cardiovascular disease and offer opportunities for early diagnosis. Aggressive control of HIV viremia and cardiac risk factors and abstinence from unhealthy behaviors remain treatment pillars to prevent heart failure and arrhythmic complications. The excess risk among PLWH warrants heightened vigilance for heart failure and arrhythmic symptomatology and earlier testing as subclinical abnormalities are common. Future research needs include identifying novel therapeutic targets to prevent heart failure and arrhythmias and testing of interventions in diverse groups of PLWH.

Effect of percutaneous pulmonary valve replacement on ventricular electrophysiological remodeling in a porcine model of repaired tetralogy of Fallot

Tetralogy of Fallot is the most common cyanotic congenital heart disease. Late after corrective surgery, patients are at risk of developing right ventricular (RV) failure due to pulmonary valve regurgitation and arrhythmias related to surgical scars and ventricular electrophysiological remodeling. Pulmonary valve replacement has been identified as an interesting strategy to reduce RV dilatation but its impact on the arrhythmic risk remains uncertain. We sought to determine whether percutaneous pulmonary valve implantation (PPVI) at an early pathological stage leads to benefical effects on right and left ventricular electrophysiological remodeling in a porcine model of repaired tetralogy of Fallot (rTOF). Piglets (<10 kg) underwent pulmonary artery banding, pulmonary valve disruption to induce RV hypertrophy and dilatation and a PTFE patch was sewn across the pulmonary annulus. Two-months later, PPVI was performed in a sub-group of rTOF pigs. At 3 months post-surgery, cardiac function was assessed by MRI in rTOF, rTOF-PPVI and Sham-operated pigs. Animals were euthanized and optical mapping of isolated left and right ventricles electrical activity was performed using the voltage-sensitive dye Di-4-ANEPPS. Expression of selected genes was assessed by quantitative RT-PCR. At 3 months post-surgery, pulmonary artery regurgitation, RV end-diastolic and end-systolic volumes normalized to body surface area were significantly increased in rTOF pigs compared to Sham animals. In rTOF-PPVI animals these parameters were partially reversed and not statistically different from Sham pigs. An action potential prolongation was observed in both the left ventricle and the RV epicardium but not in the endocardium of rTOF pigs. Within the RV epicardium, this prolongation was mainly confined to the anterior side. Interestingly, rTOF-PPVI pigs action potential durations were similar to Sham animals. In line with functional investigations, a large increase in BNP expression was found in rTOF RV compared to Sham pigs (fold change = 34) which was not as pronounced in rTOF-PPVi pigs (fold change = 3) while a lower expression of KCND3 and KCNJ2 was found in rTOF pigs. In our rTOF porcine model, PPVI at an early pathological stage reversed RV dilatation. It also successfully reversed action potential prolongation in the left ventricle and the anterior RV epicardium, and may thus have beneficial effects on the arrhythmic risk.

Cardiac Fibroblasts Promote Ferroptosis in Atrial Fibrillation by Secreting Exo-miR-23a-3p Targeting SLC7A11.

The exact mechanism of atrial fibrillation (AF) has been not well elucidated. Ferroptosis is an iron-dependent cell death due to excessive accumulation of peroxidized polyunsaturated fatty acids. However, the molecular mechanism underlying AF and ferroptosis has never been reported. Here, we established the rapid pacing model in vivo and vitro to investigate the relationship between AF and ferroptosis. In canine model of rapid atrial pacing, the content of malondialdehyde and total ions in the atrial tissue of the Pacing group was significantly increased and the exosome inhibitor GW4869 reduced ferroptosis, fibrosis, and inflammation and improved histological and electrophysiological remodeling. In rapid pacing h9c2 cells, the expression of antioxidative stress genes associated with ferroptosis presented sequential changes and proteins involved in ferroptosis such as FTH1, SLC7A11, and GPX4 were gradually depleted. Furthermore, pacing cardiac fibroblast-derived exosomes (CF-exos) exacerbated ferroptosis in h9c2 cells and pretreated pacing-CF-exos with GW4869 alleviated injury to h9c2 cells. In mechanism, our results demonstrated that pacing-CF-exos highly expressed miR-23a-3p by informatics analysis and experimental verification. Inhibitor-miR-23a-3p protected h9c2 cells from ferroptosis accompanying with upregulation of SLC7A11. In addition, SLC7A11 was shown to be the target gene of miR-23a-3p. In conclusion, our results suggest that CF-exos-miR-23a-3p may promote ferroptosis. The development of AF in a persistent direction could be prevented by intervening with exosomal miRNAs to reduce oxidative stress injury and ferroptosis.

Endurance training induced cellular electrophysiological remodeling in a small and a large animal athlete’s heart model

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Funding: It was supported by NKFIH grants (K-19992, K- 135464, GINOP-2.3.2-15-2016-00047). Background The positive impact of regular exercise on a healthy and fulfilling lifestyle. Therefore, active athletes are considered the healthiest members of our society. However, there is an increasing amount of evidence that long-term high-intensity sporting activity could also have adverse effects on the heart, such as impaired electrophysiological properties. Heavy long-term training can lead to structural and functional remodelling of the heart, which in turn, can evoke malignant cardiac arrhythmias. Purpose To develop animal models with a significant translational value of the human athlete’s heart and to investigate underlying malignant drivers of cardiac arrhythmias due to the long-term endurance training in in vitro studies. Methods 24 dogs from both sexes and 26 male guinea pigs were randomly assigned to sedentary (’Sed’) and trained (’Tr’) groups (n = 12-12; n=13-13). The latter group underwent a long-term endurance interval-training program on the treadmill 5 days a week for 4 months. ECG recordings and echocardiography validated the characteristic of athlete’s heart. After heart removal, the degree of interstitial fibrosis was quantified and ventricular myocytes were enzymatically dissociated via retrograde perfusion. The transmembrane ionic currents were recorded using the whole-cell configuration of the patch-clamp technique. The action potentials were measured by the perforated patch-clamp technique. Immunocytochemistry measurements were performed to determine the density of transmembrane ion channels. Results Based on the ECG and ECHO results, the vigorous training program resulted in significant cardiac adaptation in both species. In addition, it caused mild ventricular fibrosis. The repolarization is reflected as the 90 percent of action potential duration (APD90). It was significantly lengthened in the left ventricular myocytes of ‘Tr’ dogs. (‘Tr’ vs. ‘Sed’ 472.8±29.6 ms; =29 vs. 369.3±31.4 ms; n=24, p=0.023) and there was no difference in the case of guinea pigs. The amplitude of the transient outward current (Ito), which is not expressed in the guinea pig heart, was significantly smaller in the ‘Tr’ dogs (‘Tr’ vs. ‘Sed’ 7.6±0.6 pA/pF, n=54 vs. 10.2±1.0 pA/pF, n=42, p&amp;lt;0.05). Under the currently used protocols, no differences were detected in the magnitude of other ionic currents. The HCN4 gene expression was significantly higher in isolated myocytes in ’Tr’ dogs. Conclusion Increased ectopic activity is not rare among top athletes. Our results suggest an association between increased arrhythmia susceptibility and impaired repolarisation reserve related to down-regulation of Ito and prolonged APD90 and enhanced fibrotic changes. The overexpression of HCN4 gene in hypertrophic hearts, similar to heart failure, may evoke malignant ventricular arrhythmias. Further studies are warranted to clarify this hypothesis in more detail.

Bariatric surgery reduces ventricular repolarisation gradients in obese patients - results from an electrocardiographic imaging study

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): National Institute for Health Research (NIHR) British Heart Foundation Background Obesity confers higher risks of atrial arrhythmias and is associated with abnormal ventricular repolarisation. Despite this, the proarrhythmic substrate in obesity and its reversibility with weight loss has not been studied in-depth. Purpose To characterise the proarrhythmic substrate in obese patients, and its reversibility with bariatric surgery, using electrocardiographic imaging (ECGi). Methods ECGi was performed in 8 obese patients before (PreOb) and after (PostOb) bariatric surgery (mean age 39+/-11years, 7 female), and in 8 age- and sex-matched non-obese controls (NOb) (40+/-11 years). ECGi recordings were made at rest, on exercise, and during recovery from exercise. For ECGi analysis, &amp;gt;2000 atrial and ventricular epicardial electrograms were calculated from body surface potential recordings from 256 sites and information from cardiac magnetic resonance imaging, by solving the inverse problem. Local atrial and ventricular epicardial activation times (AT) were calculated as the steepest downslope of their respective activation complexes, and local ventricular repolarisation times (RT) as the steepest upslope of the T-wave. Atrial activation gradients (ATG) and ventricular repolarisation gradients (RTG) were calculated as the maximum difference within 10mm radius divided by the corresponding Euclidean distance. Results BMI was greater in PreOb vs NOb (46.6+/-4.8 vs 23.8+/-2.6kg/m2, p&amp;lt;0.0001) and decreased with surgery (PostOb 35.3+/-4.2kg/m2, p&amp;lt;0.0001). Total atrial AT was prolonged in PreOb vs NOb (68+/-12 vs 45+/-10ms, p=0.016) and did not change post-surgery (PreOb vs PostOb: 68+/-12 vs 67+/-16ms, p=0.81). Atrial ATG were also greater in PreOb vs NOb: max 254+/-111 vs 106+/-58ms, p=0.035; mean 24+/-6 vs 12+/-6ms, p=0.0087) and did not change with weight loss (PreOb vs PostOb: max 254+/-111 vs 222+/-69ms/mm, p=0.61; mean 24+/-6 vs 21+/-7ms/mm, p=0.52). Ventricular RTG were greater in PreOb vs NOb (max: 287+/-73 vs 131+/-89ms/mm, p=0.012; mean: 33+/-10 vs 17+/-9ms/mm, p=0.0052). Ventricular RTG decreased with weight loss (PreOb vs PostOb: max 287+/-73 vs 151+/-54ms/mm, p=0.0070; mean: 33+/-10 vs 21+/-8ms/mm, p=0.018), and were similar between PostOb and NOb (max, p=0.81; mean p=0.58). Ventricular AT and RT were non-different in NOb, PreOb and PostOb. Conclusion Obesity is associated with pro-arrhythmic electrophysiological remodelling, including steeper ventricular repolarisation gradients and slower atrial activation. At 6 months post-bariatric surgery, there was a reduction in ventricular repolarisation gradients though atrial conduction abnormalities persisted. These findings provide a mechanistic insight into obesity-related arrhythmic risks and its potential reversibility with weight loss surgery.

PO-615-03 MUTANT ATRIAL NATRIURETIC PEPTIDE INDUCES MITOCHONDRIAL DEFECTS AND ION CHANNEL REMODELING IN A HUMAN INDUCED PLURIPOTENT STEM CELL-DERIVED ATRIAL FIBRILLATION MODEL

We identified a mutation in NPPA, encoding atrial natriuretic peptide (ANP), as the first non-ion channel gene causing familial atrial fibrillation (AF). However, lack of a mature and comprehensive model prevents a deeper understanding of the underlying cellular mechanisms. Induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs) are ideally suited for modeling heritable AF and personalized pharmacological therapy, but there is limited data on the maturation of iPSC-atrial (a) CMs. We hypothesized that an electro-metabolic maturation (EMM) approach using biochemical cues (T3, IGF-1, dexamethasone), bioenergetic supplement (fatty acids), and electrical stimulation, synergistically promotes metabolic, structural, and electrophysiological maturity of iPSC-aCMs to a level comparable to human atrial cardiomyocytes (haCMs) and will reveal the novel underlying cellular mechanisms of the NPPA mutation. We applied our EMM approach to iPSC-aCMs and compared the metabolic (Seahorse Analyzer, western blots [WB], RT-PCR), structural (immunofluorescence, WB), electrophysiological (patch clamping, optical voltage mapping), and transcriptomic (RNA-seq) maturity with immature iPSC-aCMs and adult haCMs from the same patient. EMM matured iPSC-aCMs from a family carrying the NPPA-S64R mutation, and an isogenic control using CRISPR-Cas9, elucidated the novel underlying mechanism by which the mutation causes AF. EMM iPSC-aCMs displayed improved sarcomeric organization (Fig. 1a) and oxidative capacity (Fig. 1b), as well as more hyperpolarized RMP and increased APA (Fig. 1c,d). Only mature NPPA-S64R iPSC-aCMs demonstrated that the NPPA mutation caused mitochondrial defects resulting in reduced oxidative capacity and electron transport chain dysfunction (Fig. 2a), as well as electrophysiological remodeling causing prolonged APD (Fig. 2b,c) via increased IKs density (Fig. 2d-g). We established a combinatorial EMM approach that promoted comprehensive maturation of iPSC-aCMs. Using this maturation approach, we unmasked the novel electrophysiological remodeling and mitochondrial dysfunction underlying an AF-causing NPPA mutation.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Mechanisms of ventricular arrhythmias elicited by coexistence of multiple electrophysiological remodeling in ischemia: A simulation study.

Myocardial ischemia, injury and infarction (MI) are the three stages of acute coronary syndrome (ACS). In the past two decades, a great number of studies focused on myocardial ischemia and MI individually, and showed that the occurrence of reentrant arrhythmias is often associated with myocardial ischemia or MI. However, arrhythmogenic mechanisms in the tissue with various degrees of remodeling in the ischemic heart have not been fully understood. In this study, biophysical detailed single-cell models of ischemia 1a, 1b, and MI were developed to mimic the electrophysiological remodeling at different stages of ACS. 2D tissue models with different distributions of ischemia and MI areas were constructed to investigate the mechanisms of the initiation of reentrant waves during the progression of ischemia. Simulation results in 2D tissues showed that the vulnerable windows (VWs) in simultaneous presence of multiple ischemic conditions were associated with the dynamics of wave propagation in the tissues with each single pathological condition. In the tissue with multiple pathological conditions, reentrant waves were mainly induced by two different mechanisms: one is the heterogeneity along the excitation wavefront, especially the abrupt variation in conduction velocity (CV) across the border of ischemia 1b and MI, and the other is the decreased safe factor (SF) for conduction at the edge of the tissue in MI region which is attributed to the increased excitation threshold of MI region. Finally, the reentrant wave was observed in a 3D model with a scar reconstructed from MRI images of a MI patient. These comprehensive findings provide novel insights for understanding the arrhythmic risk during the progression of myocardial ischemia and highlight the importance of the multiple pathological stages in designing medical therapies for arrhythmias in ischemia.

Atrial AMP-activated protein kinase is critical for prevention of dysregulation of electrical excitability and atrial fibrillation.

Metabolic stress is an important cause of pathological atrial remodeling and atrial fibrillation. AMPK is a ubiquitous master metabolic regulator, yet its biological function in the atria is poorly understood in both health and disease. We investigated the impact of atrium-selective cardiac AMPK deletion on electrophysiological and structural remodeling in mice. Loss of atrial AMPK expression caused atrial changes in electrophysiological properties and atrial ectopic activity prior to the onset of spontaneous atrial fibrillation. Concomitant transcriptional downregulation of connexins and atrial ion channel subunits manifested with delayed left atrial activation and repolarization. The early molecular and electrophysiological abnormalities preceded left atrial structural remodeling and interstitial fibrosis. AMPK inactivation induced downregulation of transcription factors (Mef2c and Pitx2c) linked to connexin and ion channel transcriptional reprogramming. Thus, AMPK plays an essential homeostatic role in atria, protecting against adverse remodeling potentially by regulating key transcription factors that control the expression of atrial ion channels and gap junction proteins.

RNA-Seq Analyses Reveal Roles of the HVCN1 Proton Channel in Cardiac pH Homeostasis.

The voltage-gated proton channel HVCN1 is a member of the voltage-gated ion channel family. HVCN1 channel controls acid extrusion and regulates pH homeostasis in various cell types. Recent evidence indicated that the HVCN1 channel was associated with cardiac function. To investigate the role of HVCN1 in cardiac myocytes, we performed an RNA sequencing analysis of murine hearts and showed that HVCN1 null hearts exhibited a differential transcriptome profile compared with wild-type hearts. The RNA-seq data indicating impaired pH homeostasis in HVCN1 null hearts were the downregulated NADPH oxidoreductases (NOXs) and decreased expression of Cl−/HCO3 − exchanger, indicating HVCN1 is a regulator of gene transcriptional networks controlling NOX signaling and CO2 homeostasis in the heart. Additionally, HVCN1 null hearts exhibited differential expression of cardiac ion channels, suggesting a potential role of HVCN1 in cardiac electrophysiological remodeling. The study highlights the importance of HVCN1 in cardiac function and may present a novel target associated with heart diseases.

Epicardial fat and atrial fibrillation: the perils of atrial failure.

Obesity is a heterogeneous condition, characterized by different phenotypes and for which the classical assessment with body mass index may underestimate the real impact on cardiovascular (CV) disease burden. An epidemiological link between obesity and atrial fibrillation (AF) has been clearly demonstrated and becomes even more tight when ectopic (i.e. epicardial) fat deposition is considered. Due to anatomical and functional features, a tight paracrine cross-talk exists between epicardial adipose tissue (EAT) and myocardium, including the left atrium (LA). Alongside-and even without-mechanical atrial stretch, the dysfunctional EAT may determine a pro-inflammatory environment in the surrounding myocardial tissue. This evidence has provided a new intriguing pathophysiological link with AF, which in turn is no longer considered a single entity but rather the final stage of atrial remodelling. This maladaptive process would indeed include structural, electric, and autonomic derangement that ultimately leads to overt disease. Here, we update how dysfunctional EAT would orchestrate LA remodelling. Maladaptive changes sustained by dysfunctional EAT are driven by a pro-inflammatory and pro-fibrotic secretome that alters the sinoatrial microenvironment. Structural (e.g. fibro-fatty infiltration) and cellular (e.g. mitochondrial uncoupling, sarcoplasmic reticulum fragmentation, and cellular protein quantity/localization) changes then determine an electrophysiological remodelling that also involves the autonomic nervous system. Finally, we summarize how EAT dysfunction may fit with the standard guidelines for AF. Lastly, we focus on the potential benefit of weight loss and different classes of CV drugs on EAT dysfunction, LA remodelling, and ultimately AF onset and recurrence.

Effects of Sodium-Glucose Cotransporter-2 Inhibitors on Cardiac Structural and Electrical Remodeling: From Myocardial Cytology to Cardiodiabetology.

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) have changed the clinical landscape of diabetes mellitus (DM) therapy through their favourable effects on cardiovascular outcomes. Notably, the use of SGLT2i has been linked to cardiovascular benefits regardless of DM status, while their pleiotropic actions remain to be fully elucidated. What we do know is that SGLT2i exert beneficial effects even at the level of the myocardial cell and that these are linked to an improvement in the energy substrate, resulting in less inflammation and fibrosis. SGLT2i ameliorates myocardial extracellular matrix remodeling, cardiomyocyte stiffness and concentric hypertrophy, achieving beneficial remodeling of the left ventricle with significant implications for the pathogenesis and outcome of heart failure. Most studies show a significant improvement in markers of diastolic dysfunction along with a reduction in left ventricular hypertrophy. In addition to these effects, there is electrophysiological remodeling, which explains initial data suggesting that SGLT2i have an antiarrhythmic action against both atrial and ventricular arrhythmias. However, future studies need to clarify not only the exact mechanisms of this beneficial functional, structural, and electrophysiological cardiac remodeling but also its magnitude to determine whether this is a class or a drug effect.

Renal Denervation Prevents Atrial Arrhythmogenic Substrate Development in CKD.

In patients with chronic kidney disease (CKD), atrial fibrillation (AF) is highly prevalent and represents a major risk factor for stroke and death. CKD is associated with atrial proarrhythmic remodeling and activation of the sympathetic nervous system. Whether reduction of the sympathetic nerve activity by renal denervation (RDN) inhibits AF vulnerability in CKD is unknown. Left atrial (LA) fibrosis was analyzed in samples from patients with AF and concomitant CKD (estimated glomerular filtration rate [eGFR], <60 mL/min per 1.73 m2) using picrosirius red and compared with AF patients without CKD and patients with sinus rhythm with and without CKD. In a translational approach, male Sprague Dawley rats were fed with 0.25% adenine (AD)-containing chow for 16 weeks to induce CKD. At week 5, AD-fed rats underwent RDN or sham operation (AD). Rats on normal chow served as control. After 16 weeks, cardiac function and AF susceptibility were assessed by echocardiography, radiotelemetry, electrophysiological mapping, and burst stimulation, respectively. LA tissue was histologically analyzed for sympathetic innervation using tyrosine hydroxylase staining, and LA fibrosis was determined using picrosirius red. Sirius red staining demonstrated significantly increased LA fibrosis in patients with AF+CKD compared with AF without CKD or sinus rhythm. In rats, AD demonstrated LA structural changes with enhanced sympathetic innervation compared with control. In AD, LA enlargement was associated with prolonged duration of induced AF episodes, impaired LA conduction latency, and increased absolute conduction inhomogeneity. RDN treatment improved LA remodeling and reduced LA diameter compared with sham-operated AD. Furthermore, RDN decreased AF susceptibility and ameliorated LA conduction latency and absolute conduction inhomogeneity, independent of blood pressure reduction and renal function. In an experimental rat model of CKD, RDN inhibited progression of atrial structural and electrophysiological remodeling. Therefore, RDN represents a potential therapeutic tool to reduce the risk of AF in CKD, independent of changes in renal function and blood pressure.