Atrial Tissue Research Articles

Anesthetic Management of Cesarean Delivery for a Parturient With Dextro-Transposition of the Great Arteries Post-Senning Procedure: A Case Report

The Senning procedure is a palliation technique for addressing dextro-transposition of the great arteries; deoxygenated blood is redirected to the left ventricle, making the right ventricle the systemic ventricle. The physiologic increase in cardiac output during pregnancy may place additional stress on the right ventricle and given the existence of atrial scar tissue, trigger arrythmias. Because the technique was gradually abandoned starting in the 1970s, few remaining patients of child-bearing age remain. We emphasize here the importance of interdisciplinary team planning for delivery. Preparation for possible arrhythmia and potential decompensation in right ventricular function are essential.

Abstract 4147644: Regional Distribution and Overlap of Left Atrial Epicardial Adipose Tissue and Fibrosis

Background: Left atrial epicardial adipose tissue (LA-EAT) and fibrosis are implicated in the pathophysiology of the atrial fibrillation (AF) substrate. Hypothesis: The distribution of fibrosis and LA-EAT differs across various regions of the LA. Aims: Ascertain whether high fibrosis regions coincide with high EAT regions. Identify specific anatomical regions in which LA-EAT and fibrosis tend to co-localize. Methods: LA-EAT was imaged using MRI Dixon sequences and images were segmented axially using the software contouring tools. LGE-MRI was used for LA fibrosis quantification and segmentation. The regions of fibrosis and fat were then co-registered with the atrial geometry and projected onto the left atrial shell. A universal atrial coordinates (UAC) approach was then used to systematically delineate anatomical LA regions in a manner independent of inter-individual variabilities in scale and shape. Specifically, the LA was divided into 10 regions (left and right versions of: posterior-inferior, posterior-superior, roof, anterior-superior, and anterior-inferior). Levene’s test and ANOVA were used to check for any statistically significant variability. Results: Nineteen patients were recruited (94% male; median age 72[62-74]; BMI 32.1±6.3; LA volume index 71.0±21.5mL/m 2 ).LA fibrosis was highest in the left posterior superior segment, right anterior inferior, and left posterior inferior (39.3±16.2%,34.7±26.8%, and 25.7±20.9% respectively;F=1.9,p=0.15). LA-EAT was most prominent in the right anterior superior, left posterior inferior, and left anterior inferior segments (38.1±25.3%,35.6±18.4%,and 33.1±18.9% respectively; F=0.94, p= 0.39). Spatial co-localization of fat and fibrosis was highest in the left posterior inferior region (8.95±2.1%), followed by the left posterior superior, right anterior superior, and left anterior inferior region (7.9±2.1%,7.2±1.7%,and 6.3±1.6% respectively; F= 0.29, p=0.83 ). Conclusion: LA fibrosis and EAT have differing regional preponderances, impacting the AF substrate through infiltrative and paracrine effects. This fibro-fatty remodeling creates structural and conduction abnormalities, forming stable reentrant circuits and perpetuating AF by providing varied pathways and refractory periods.

Abstract 4123639: Tumor Endothelial Marker 1 is Upregulated in Atrial Cardiac Fibroblasts in Atrial Fibrillation and Correlates With Atrial Fibrosis

Background: Tumor endothelial marker 1 (TEM1 or CD248) is a transmembrane protein found in activated mesenchymal cells during embryo development. Its expression level becomes very low or undetectable in adult tissue. Re-expression of TEM1 in fibroblasts has been reported in hepatic, renal, and pulmonary fibrosis. We evaluated atrial TEM1 expression in atrial fibrillation (AF) and its relation with atrial fibrosis. Methods and Results: All data were presented as mean±standard error. Left atrial (LA) tissues were collected from 30 patients (pts) (mean age 64.0±1.6 yrs, male 76.7%) with AF underwent cardiac surgery (mitral and/or tricuspid valve surgery 96.7%) and maze procedure with LA appendage excision. Immunofluorescence (IF) staining showed TEM1 expressed in atrial cardiac fibroblasts (CFs) in the LA tissue of AF pts, but not in normal LA tissue (US Biomax). Primary human CFs were directly isolated from the LA tissue. IF staining showed TEM1 expression in the isolated CFs from AF pts but not in normal human CFs (ScienCell). Western blot could detect TEM1 expression in the LA tissues of all 30 AF pts. Sirius Red staining was used to visualize collagen and atrial fibrosis was quantified using a pixel-based method (Adobe Photoshop) by calculating the total numbers of red pixels and the percentage (%) of red pixels to total pixels. Atrial fibrosis was increased in AF pts compared with normal control (total number of red pixels: 160740±13066 vs. 50863±6357, % of red pixels to total pixels: 11.4±0.8 vs. 3.8±0.2%, all p<0.001). There was a positive correlation between the expression level of TEM1 (ratio of TEM1/actin band density in western blot) with the severity of atrial fibrosis, including the total numbers of red pixels (r = 0.47, p = 0.01) and the % of red pixels to total pixels (r = 0.48, p = 0.01). TEM1 and galectin expression levels had positive correlation (r = 0.60, p < 0.01). There were no correlations of atrial TEM1 expression with the LA diameter and CHA2DS2-VASc score. In vitro study showed TEM1 knockdown in cultured CFs with siRNA reduced cell proliferation (scrambled- vs TEM1-siRNA, BrdU absorbance: 1.84±0.05 vs 1.50±0.07, p<0.05), increased starvation-induced cell apoptosis (cell death ELISA absorbance: 0.69±0.11 vs 2.88±0.05, p<0.05) and decreased cell migration. Conclusions: There is increased TEM1 expression in atrial CFs in AF and its expression level is associated with atrial fibrosis. TEM1 expression changes the cell behaviors of CFs.

Abstract 4123653: Association of Inflammatory Bowel Disease with the Risk of Atrial Fibrillation: A Meta-Analysis

Background: Inflammatory bowel disease (IBD), including Crohn’s disease (CD) and ulcerative colitis (UC), is a prevalent condition associated with chronic noninfectious inflammation of the gastrointestinal tract. It has been hypothesized that chronic inflammation can predispose patients to atrial fibrillation (AF), with proposed mechanisms being structural remodeling of atrial tissue, autonomic dysfunction, and oxidative stress; however, no clear evidence exists to support this. Aims: Our meta-analysis aims to pool all existing data to determine if there is an increased risk of AF in patients with IBD, providing more robust evidence on the matter. Methods: A systematic literature search was conducted using major databases (PubMed, EMBASE, and SCOPUS) aimed at studies focusing on AF development in patients with IBD. Further subgroup analyses were performed for ulcerative colitis (UC) and crohn’s disease (CD). Risk ratios (RR) with their corresponding 95% confidence intervals (CI) were pooled using a random-effects model in the Review Manager Software. Statistical significance was set at p < 0.05. Results: Seven studies with 88,893,407 patients were included (1,002,719 and 87, 890, 688 patients in the IBD and non-IBD groups, respectively). IBD patients were at an increased risk of developing AF [RR: 1.52; 95% CI: 1.19-1.95; p=0.0009] compared to the non-IBD group. In subgroup analyses, patients with UC were at an increased risk of developing AF [RR: 1.29; 95% CI: 1.08-1.53; p=0.004], as were CD patients [RR: 1.30; 95% CI: 1.07-1.58; p=0.008] compared to the non-UC and non-CD groups, respectively (Figure 1). Conclusion: Patients with IBD are at nearly 1.5 times the risk of developing AF compared to the non-IBD population. Our meta-analysis was limited by heterogeneity among the studies, highlighting the importance of further large-scale prospective studies to establish more robust evidence and determine the real-world clinical significance of our findings. Furthermore, future research should explore the impact of confounding variables such as disease severity, medication usage, and lifestyle factors on the observed association between IBD and AF.

Multiphysics simulations reveal haemodynamic impacts of patient-derived fibrosis-related changes in left atrial tissue mechanics.

Stroke is a leading cause of death and disability worldwide. Atrial myopathy, including fibrosis, is associated with an increased risk of ischaemic stroke, but the mechanisms underlying this association are poorly understood. Fibrosis modifies myocardial structure, impairing electrical propagation and tissue biomechanics, and creating stagnant flow regions where clots could form. Fibrosis can be mapped non-invasively using late gadolinium enhancement magnetic resonance imaging (LGE-MRI). However, fibrosis maps are not currently incorporated into stroke risk calculations or computational electro-mechano-fluidic models. We present multiphysics simulations of left atrial (LA) myocardial motion and haemodynamics using patient-specific anatomies and fibrotic maps from LGE-MRI. We modify tissue stiffness and active tension generation in fibrotic regions and investigate how these changes affect LA flow for different fibrotic burdens. We find that fibrotic regions and, to a lesser extent, non-fibrotic regions experience reduced myocardial strain, resulting in decreased LA emptying fraction consistent with clinical observations. Both fibrotic tissue stiffening and hypocontractility independently reduce LA function, but, together, these two alterations cause more pronounced effects than either one alone. Fibrosis significantly alters flow patterns throughout the atrial chamber, and particularly, the filling and emptying jets of the left atrial appendage (LAA). The effects of fibrosis in LA flow are largely captured by the concomitant changes in LA emptying fraction except inside the LAA, where a multifactorial behaviour is observed. This work illustrates how high-fidelity, multiphysics models can be used to study thrombogenesis mechanisms in patient-specific anatomies, shedding light onto the links between atrial fibrosis and ischaemic stroke. KEY POINTS: Left atrial (LA) fibrosis is associated with arrhythmogenesis and increased risk of ischaemic stroke; its extent and pattern can be quantified on a patient-specific basis using late gadolinium enhancement magnetic resonance imaging. Current stroke risk prediction tools have limited personalization, and their accuracy could be improved by incorporating patient-specific information such as fibrotic maps and haemodynamic patterns. We present the first electro-mechano-fluidic multiphysics computational simulations of LA flow, including fibrosis and anatomies from medical imaging. Mechanical changes in fibrotic tissue impair global LA motion, decreasing LA and left atrial appendage (LAA) emptying fractions, especially in subjects with higher fibrosis burdens. Fibrotic-mediated LA motion impairment alters LA and LAA flow near the endocardium and the whole cavity, ultimately leading to more stagnant blood regions in the LAA.

β-Hydroxybutyrate and Citrate Synthase as Potential Diagnostic Biomarkers in Aging-Related Atrial Fibrillation.

The incidence of atrial fibrillation (AF) increases with age; however, the precise mechanisms by which aging elevates AF risk and the effective biomarkers for managing AF in elderly patients remain unclear. We analyzed plasma samples from 100 elderly AF patients, 100 young and 100 elderly patients without atrial fibrillation (NAF), along with left atrial tissues obtained from both AF and NAF patients following valve replacement. Our findings indicate reduced levels of β-OHB and citrate synthase (CS) activity in elderly AF patients compared to their NAF counterparts. Statistical analysis revealed a protective association between β-OHB and CS activity concerning the occurrence of elderly AF. Furthermore, atrial tissues from elderly AF patients exhibited mitochondrial dysfunction, structural remodeling, and low-voltage areas. These results suggest that dysregulation of β-OHB levels and CS activity may contribute to aging-related AF by affecting mitochondrial function and atrial remodeling, highlighting their potential as diagnostic biomarkers for this condition.

ARRHYTHMOGENIC ATRIAL REMODELING DURING PREGNANCY IN MICE

Pregnancy is associated with greater vulnerability to supraventricular tachyarrhythmias (SVT). As the underlying mechanisms remain to be elucidated, we investigated whether pregnancy induces atrial remodeling that might contribute to this. Atrial electrophysiological and contractile properties were examined in non-pregnant (NP) and pregnant (P) mice. Cell shortening and Ca2+ imaging were measured on atrial myocytes. Atrial action potential and ionic currents were recorded using patch-clamp technique. Atrial mRNA and protein expression were analyzed using qPCR and Western blot. The P-wave area on the ECG increased by 50% during pregnancy, suggesting atrial enlargement, confirmed by echocardiography. The atrial myocytes were longer in P mice, adding further evidence to the physiological hypertrophy associated with pregnancy. Echocardiography showed a 50% increase in atrial fractional area change during pregnancy, indicating much stronger contraction. A similar increase in cell shortening was observed in P mice and was associated with a decrease in sarcomere length and changes in myofilament protein phosphorylation. However, pregnancy did not affect L-type Ca2+ current, Ca2+ transients, and SR Ca2+ load. Myocytes from P mice showed twice as many spontaneous contractions and spontaneous diastolic Ca2+ releases. Moreover, pregnancy was associated with a 50% increase in action potential duration, linked to a reduction in the density of the transient outward K+ current Ito and the underlying KV4.3 channel. During pregnancy, atrial tissues undergo substantial remodeling, potentially contributing to the development of SVT.

Atrial hiPSC-CM as a Pharmacologic Model to Evaluate Anti-AF Drugs: Some Lessons From I Kur.

Human induced pluripotent stem cells (hiPSC) and atrial hiPSC-derived cardiomyocytes (hiPSC-CM) have entered the arena of preclinical atrial fibrillation research. A central question is whether they reproduce the physiologic contribution of atrial selective potassium currents (such as the ultrarapid potassium current, I Kur ) to repolarization. Of note, 2 studies in single atrial hiPSC-CM reported prolongation of action potential duration by I Kur block indicating that I Kur might in fact represent a valuable target for the treatment of human atrial fibrillation. However, the results and interpretation are at odds with the literature on I Kur block in human atria and the results of clinical studies. We believe that the discrepancies indicate that experiments in single atrial CM (both adult atrial CM and atrial hiPSC-CM) might be misleading. Under particular experimental conditions, atrial hiPSC-CMs may not closely resemble the electrophysiology of the human atrium. Therefore, we recapitulate here methodological issues evaluating potential value of the I Kur as an antiarrhythmic target when investigated in animal models, in human atrial tissues, and finally in atrial hiPSC-CM.

SP1-mediated transcriptional repression of SFRP5 is correlated with cardiac fibroblast activation and atrial myocyte apoptosis in the development of atrial fibrillation

Secreted frizzled related protein 5 (SFRP5) is a recognized cardioprotective protein with diminished expression in atrial fibrillation (AF). This study investigates SFRP5's function in AF-related cardiac fibrosis and cardiomyocyte apoptosis, exploring the underlying dysregulation causes. Utilizing C57BL/6 mice, mouse cardiac fibroblasts (CFs), and HC-1 mouse atrial myocyte cell line, AF models were induced by angiotensin Ⅱ (Ang Ⅱ). SFRP5 levels were consistently decreased in plasma samples from clinical patients, modeled mice, and CF culture supernatants. Treatment with recombinant SFRP5 restored its levels, mitigating Ang Ⅱ-induced AF in mice and ameliorating atrial tissue fibrosis and oxidative stress. In vitro, SFRP5 recombinant protein suppressed CF activation and fibrosis-related markers. The study identified Sp1 transcription factor (SP1) binding to the SFRP5 promoter, causing transcriptional repression. SP1 knockdown reinstated SFRP5 levels in mice and CFs, thus suppressing fibrosis. Additionally, SP1 knockdown attenuated Ang Ⅱ-induced apoptosis in HC-1 cells, but this effect was counteracted by concurrent SFRP5 knockdown. In conclusion, this investigation underscores that SP1 mediates SFRP5 loss during AF by transcriptional repression, contributing to fibrosis and myocyte apoptosis. These findings illuminate potential therapeutic interventions targeting the SFRP5-SP1 axis in AF-related cardiac complications.

Association between atrial fibrillation and periodontal disease: A bioinformatics analysis

IntroductionAtrial fibrillation (AF), which is an aging disease, and periodontal disease (PD) are prevalent, and AF and PD may be associated with each other. Inflammation plays a role in the two pathologies. However, there is a need for a deeper understanding of the mechanisms associated with these conditions. MethodsA bioinformatics analysis was performed to compare gene expression profiles in the blood and left atrial tissue samples of patients with AF and in the blood samples of patients with PD. Our analysis involved comparing gene expression profiles between patients with AF, those with sinus rhythm, and individuals with and without PD. This comparative approach enabled us to identify upregulated genes in both the AF and PD cohorts. ResultsThe expression of 40 genes was upregulated in patients with AF and PD, with a significant enrichment for genes associated with inflammation. Notably, a network analysis revealed distinct functional associations among these genes. Interestingly, the expressions of three lysosome-related genes in all analyzed tissues (AF blood, PD blood, and AF left atrium) were upregulated. ConclusionInflammation played a role in AF and PD. Further, based on the upregulated expression of lysosome-related genes across all samples that were evaluated, in addition to inflammation, lysosomal function had a possible role in the co-existence of the two diseases.

Prognostic value of myocardial redox signalling: a machine learning multi-omics approach

Abstract Background Oxidative stress has been proposed to be implicated in cardiovascular pathology. Studies have linked myocardial oxidative stress with the development of atrial fibrillation, but its role in the prediction of long-term outcomes and mortality is yet to be elucidated. Purpose To apply discovery network transcriptomics and genomics to atrial tissue (AT) obtained from patients undergoing cardiac surgery, to phenotype myocardial redox-state and identify potential therapeutic targets. Methods We included 1,032 patients undergoing cardiac surgery. Arm 1 included 258 patients in whom atrial tissue (right atrial appendage) was used for ex-vivo quantification of NOX-derived superoxide by lucigenin-enhanced chemiluminescence. Arm 2 included 414 patients in whom exploratory, unsupervised gene network analysis in human atrial tissue RNA sequencing data was performed to identify atrial tissue redox-sensitive signatures (blue signature). Arm 3 included 881 patients genotyped with the genome-wide SNP array UK Biobank Axiom Array and used for machine learning construction of GenRedOx, a SNP model built to predict the blue transcriptomic signature. Associations with future incidence of major adverse myocardial events (MAME: cardiovascular death and/or heart failure) was assessed across all arms using cox regression models (adjusted for age, sex, hypertension, dyslipidaemia, diabetes mellitus, body mass index, and plasma TNFa). Results Over a median follow-up of 5.27 years [IQR: 4.29-6.83] high atrial tissue (AT) NOX-derived superoxide was independently associated with MAME risk (Adj. HR[95%CI]: 11.7 [2.18 , 62.82], p=0.004, a). Unsupervised transcriptomic analysis in Arm 2 revealed 15 coexpressed gene ‘modules’ or 'signatures' (b). The blue signature was significantly associated with AT superoxide production with "immune response-regulating and activating signalling" being amongst the top enriched pathways. Patients with high eigengene values for the blue signature showed a 5.5-fold higher adjusted risk of MAME (c). In Arm 3, extreme gradient boosting of SNP data, trained using the blue transcriptomic signature as ground truth, revealed GenRedOx (d), a genomic artificial intelligence score, which was found to be prognostic of MAME in the validation stage (e). Homozygosity for the minor allele of SNP rs723897 in the Chemokine-Like Factor Super Family 7 (CMTM7) gene had the highest gain in the model. Conclusion We present for the first time two novel human myocardial transcriptomic and genomic signatures that reflect changes in redox state and identify long-term cardiovascular risk. Targeting pathways in the myocardium related with immune response signalling may lead to the development of novel therapeutics in cardiovascular disease.

Calcitonin signalling system regulates function and arhythmogenicity of atrial cardiomyocytes

Abstract Background Atrial fibrillation (AF) poses a significant therapeutic challenge due to myocardial remodelling, involving both structural and electrical alterations. Recent investigations have shed light on the role of atrial cardiomyocytes (CMs) in secreting Calcitonin (CT), a factor crucial for maintaining atrial tissue integrity. Dysregulated CT secretion in AF showed to contribute to fibrotic tissue production by atrial fibroblasts, exacerbating arrhythmogenesis [1]. However, the direct impact of CT on CM function and arrhythmogenicity remains unclear, driving the objectives of our study. Methods/Results Serum samples from 20 cardiac surgery patients revealed a noteworthy association between higher pre-operative CT levels and a significant ~2.8-fold reduction in the incidence of post-operative AF (poAF). Using freshly isolated atrial guinea pig CMs, confirmed (by qPCR and immunofluorescence) that CMs express CT-receptor (CTR) to enable CT actions in the cell. Functional studies found that CT administration inhibits spontaneous calcium (Ca2+)-release events induced by pacing and decreases the Ca2+ transients amplitude (at 2 Hz; IonOptix μstep system) in fura2-loaded CMs (n=22 cells) in a concentration-dependent manner. Atrial iPSC-CMs transduced with global RGECO sensor (Genetically encoded Ca2+ indicator) and treated with 15 pM CT showed a reduction in the beat rate when paced at 2Hz, and a significantly increased the time to 50% baseline. Evaluation of the expression and phosphorylation of selected Ca2+ handling proteins, which may potentially account for the observed changes in Ca2+ transients, showed no differences in total or phospho-(ser2808) ryanodine receptor, and SERCA2α in response to CT but an increase in phospho-(Ser16) Phospholamban. Conclusion Our findings highlight the effects of CT on atrial CM function. Maintaining physiological CT levels offer a promising approach for managing AF clinically, potentially through the use of already in clinical use CT-analogues.

Macrophage-mediated interleukin-6 signaling drives ryanodine receptor-2 calcium leak in postoperative atrial fibrillation

Abstract Background Postoperative atrial fibrillation (poAF) is self-limited AF that occurs within days after cardiac surgery in one-third of patients. Clinical and preclinical studies have demonstrated that the magnitude of the perioperative increase in systemic inflammation, in particular mediated by interleukin (IL)-6, correlates with poAF risk. However, no studies to-date have mechanistically linked IL-6 signaling to fundamental arrhythmia mechanisms or identified the specific cell types driving postoperative atrial IL-6 signaling. Methods We performed single-cell RNA sequencing (scRNAseq), followed by pseudotime trajectory and cell-cell communication analyses on atrial non-myocytes comparing mice with and without poAF. We followed up our scRNAseq findings with pharmacologic and genetic approaches in mice to validate pathways related to macrophage-mediated IL-6 signaling. We used confocal imaging to assess calcium-signaling mechanisms at the single atrial cardiomyocyte (ACM) level and performed parallel patch-clamp studies in isolated human ACMs as well as biochemical analyses of human atrial tissue to assess the translational relevance of our findings. Results Our scRNAseq results demonstrated macrophages to be the most prominently altered cell type in the atria of mice with poAF. Pseudotime trajectory analyses revealed IL-6 to be one of the top inflammatory pathways implicated in macrophage transcriptional state. Indeed, both macrophage depletion and conditional knockout of IL-6 receptors in macrophages were sufficient to prevent poAF. We found that inhibition of STAT3, which is downstream of the IL-6Ra, with FDA-approved phospho-STAT3 inhibitor TTI-101 prevented poAF in mice. Lastly, we demonstrate that enhanced STAT3 activity in poAF promotes arrhythmogenic Ca2+ sparks and waves through ryanodine receptor-2 dysfunction, and that CaMKII inhibition is sufficient to ameliorate Ca2+ mishandling at the single atrial myocyte level. Conclusions Taken together, we use an integrated approach incorporating mouse and human biochemical, functional, and single-cell sequencing data to demonstrate that infiltrating atrial macrophages are fundamentally required for poAF. IL-6 was found to be a critical pathway upregulated in poAF leading to downstream ryanodine receptor-2 dysfunction and atrial arrhythmogenesis. Our findings portend significant therapeutic utility by providing robust mechanistic evidence that targeting the IL-6 axis may be used for poAF prevention and treatment in a clinically amenable timeframe.

Secretomes from human epicardial adipocytes modulate atrial lymphatics and atrial fibrosis

Abstract Background Cardiac lymphatics maintains myocardial fluid and immune cell homeostasis. Downregulation of cardiac lymphatics leads to cardiac dysfunction through impairment of inflammation and edema. On the other hand, it is well known that adipose tissue accumulation causes lymphatic dysfunction and impairs lymphedema. Purpose We evaluated the expression of atrial lymphatics in human left atrial appendage (LAA) histologically and biologically. Subsequently, we examined secretomes from epicardial adipose tissue (EAT)-derived adipocytes and validated if they change atrial lymphatics expression using ex vivo Organo-culture system. Methods Human LAA samples were collected from forty-two patients during cardiovascular surgery. They were categorized into the sinus rhythm (SR) group (n=16, 73.1±10.4 years), the paroxysmal AF (PAF) group (n=13, 69.8±12.6 years) and the persistent AF (PeAF) group (n=13, 71.2±6.5 years). Human EAT were also excised from patients with and without AF (SR; n=5, AF; n=11) during cardiovascular surgery. Preadipocytes were extracted from EAT by homogenization and collagenase treatment, and cultured to confluence. After differentiation and maturation to adipocytes, cell culture supernatant (CCS) was collected, and was dropped onto the epicardial side of left atrial tissues excised from 8 weeks old male rats for 7 days using an ex vivo organo-culture system. Results In human LAA samples, mRNA expression of lymphangiogenesis-related genes (LYVE1, PROX1, VEGFC, and VEGFR3) was significantly lower in the PeAF group compared to the SR group (p=0.0370, <0.0001, 0.0157, and 0.0009). The number of LYVE1-positive atrial lymphatic endothelial cells (LECs) was also significantly lower in the PeAF group compared to the SR group and the PAF group (p=0.0186 and 0.038). There was a negative correlation between the number of LYVE1-positive atrial LECs and the area percentage of atrial myocardial fibrosis (r=-0.5350, p<0.001). In the experiment using organo-culture system, lymphangiogenesis-related genes expression (Lyve1, Prox1, Vegfc, and Vegfr3) of rat atria treated with CCS of adipocytes from AF patients was significantly lower than those from SR patients (p=0.0391, 0.0100, 0.0034, and 0.0338). Furthermore, the CCS of adipocytes from AF patients contained higher protein levels of leptin, which is known to suppress lymphangiogenesis (p=0.0357). Leptin treatment (100ng/ml) on rat atria also decreased lymphangiogenesis-related genes expression such as Lyve1, Prox1, Vegfc, and Vegfr3 (p=0.0413, < 0.0001, <0.0001, and 0.0190). Conclusions Our study with human LAA demonstrated that atrial lymphatics interact with atrial myocardial fibrosis/progression of AF. Furthermore, our findings indicate that secretomes from EAT-derived adipocytes regulate atrial lymphatics expression, and leptin plays an important role in modulating atrial lymphangiogenesis.

Effect of selective renal denervation guided by renal nerve stimulation on atrial remodeling

Abstract Background The renal nerves play a crucial role in regulating blood pressure (BP), and the parasympathetic nervous has been confirmed as one of the components of the renal nerves, with close connections to the central solitary nucleus. Renal nerve stimulation (RNS) can activate not only the sympathetic nerves, leading to an elevation in BP, but also the parasympathetic nerves, resulting in a reduction in BP. Multiple clinical studies have demonstrated that compared to pulmonary vein isolation (PVI), renal denervation (RDN) combined with PVI significantly increased the likelihood of freedom from atrial fibrillation, but its mechanism remains unclear. Purpose Exploring the effects of renal sympathetic denervation and renal parasympathetic denervation on atrial neural remodeling and structural remodeling from a histological perspective of atrial myocardium. Methods 24 adult healthy Kunming dogs were randomly divided into three groups: (1) RNS-guided reduced BP response sites ablation (RRA group, n=8), (2) RNS-guided elevated BP response sites ablation (ERA group, n=8), and (3) RNS only, no ablation (RSC group, n=8). Left atrial samples were obtained after a 4-week follow-up period. Results Compared to the RSC group, the ERA group showed a significant decrease in tyrosine hydroxylase (TH), while the RRA group showed a significant decrease in choline acetyltransferase (CHAT) and muscarinic acetylcholine receptor 2 (CM2) (Fig. 1A-1C). Histological results indicated that compared to the RSC group, the ERA group exhibited orderly arrangement of myocardial cells, with a significant reduction in the degree of mitochondrial swelling and a decrease in average myocardial cell area. In contrast, the RRA group showed disordered arrangement of myocardial cells, with some myofibril dissolution, noticeable swelling of cell nuclei and mitochondria, and an increase in average myocardial cell area (Fig. 1D). Further evaluation of left atrial fibrosis degree revealed that compared to the RSC group, the ERA group showed a significant decrease in Collagen I, with a reduction in interstitial fibrosis degree, while the RRA group showed a significant increase in Collagen I expression, with an increase in myocardial interstitial fibrosis degree (Fig.2). Conclusion Renal sympathetic denervation can reduce atrial sympathetic nerve, improve atrial macrostructure, ultrastructure, and fibrosis levels, which may be one of the reasons why RDN combined with PVI is more effective in maintaining sinus rhythm compared to PVI. Renal parasympathetic denervation can decrease atrial parasympathetic nerve, leading to deterioration of atrial tissue structure and exacerbation of fibrosis. This emphasizes the importance of electrical stimulation guidance during the RDN procedure to avoid "side effects" caused by renal parasympathetic nerves ablation.Figure 1Figure 2

--Connecting Transcriptomics with Computational Modeling to Reveal Developmental Adaptations in Pediatric Human Atrial Tissue.

Nearly 1% of babies are born with congenital heart disease (CHD) - many of whom will require heart surgery within the first few years of life. A detailed understanding of cardiac maturation can help to expand our knowledge on cardiac diseases that develop during gestation, identify age-appropriate drug therapies, and inform clinical care decisions related to surgical repair and postoperative management. Yet, to date, our knowledge of the temporal changes that cardiomyocytes undergo during postnatal development is limited. In this study, we collected right atrial tissue samples from pediatric patients (n=117) undergoing heart surgery. Patients were stratified into five age groups. We measured age-dependent adaptations in cardiac gene expression, and used computational modeling to simulate action potential and calcium transients. Enrichment of differentially expressed genes (DEGs) revealed age-dependent changes in several key biological processes (e.g., cell cycle, structural organization), cardiac ion channels, and calcium handling genes. Gene-associated changes in ionic currents exhibited age-dependent trends, with changes in calcium handling (INCX) and repolarization (IK1) most strongly associated with an age-dependent decrease in the action potential plateau potential and increase in triangulation, respectively. We observed a shift in repolarization reserve, with lower IKr expression in younger patients, a finding potentially tied to an increased amplitude of IKs that could be triggered by elevated sympathetic activation in pediatric patients. Collectively, this study provides valuable insights into age-dependent changes in human cardiac gene expression and electrophysiology, shedding light on molecular mechanisms underlying cardiac maturation and function throughout development.

Atrial cardiomyopathy resulting from loss of plakophilin-2 expression: Response to adrenergic stimulation and implications for the exercise response.

Atrial arrhythmias occur in 20-40% of patients with arrhythmogenic right ventricular cardiomyopathy (ARVC) and are associated with an increased risk of sustained ventricular arrhythmias and inappropriate implantable cardioverter-defibrillator shocks. The pathophysiology of atrial arrhythmias in ARVC remains unclear. Most cases of gene-positive ARVC are linked to pathogenic variants in the desmosomal gene plakophilin-2 (PKP2). Here, we test the hypothesis that loss of PKP2 expression leads to pro-arrhythmic changes in atrial cardiomyocytes. Atrial cells/tissue were obtained from a cardiac-specific, tamoxifen-activated model of PKP2 deficiency (PKP2cKO). By contrast to PKP2cKO ventricular myocytes, PKP2cKO atrial cardiomyocytes presented no significant differences in intracellular calcium (Ca2+ i) transient dynamics, sarcoplasmic reticulum load or action potential morphology. PKP2cKO atrial cardiomyocytes showed elevated reactive oxygen species levels, increased frequency and amplitude of Ca2+ sparks, and increased diastolic [Ca2+]i compared to control; the latter two parameters were further increased by isoproterenol exposure and reversed by exposure to ryanodine receptor blocker dantrolene. We speculate that these isoproterenol-dependent effects may impact on the exercise-related atrial arrhythmia risk in ARVC patients. Despite absence of changes in Ca2+ i transient dynamics, PKP2cKO atrial cardiomyocytes showed enhanced sarcomere shortening and impaired sarcomere relaxation. Orthogonal transcriptomic analysis of human(GTEx) and PKP2cKO atrial tissue led to identification of 41 transcripts depending on PKP2 expression. Biochemical follow-up confirmed reduced abundance of sarcomeric protein myosin binding protein C, potentially playing a role in cellular shortening and relaxation changes observed. Our findings provide novel insights into the role of PKP2 in atrial myocardium with potential implications to therapeutic management of atrial fibrillation in patients with PKP2-related ARVC. KEY POINTS: Atrial arrhythmias occur in a large group of patients with arrhythmogenic right ventricular cardiomyopathy (ARVC), a cardiac disease mostly caused by pathogenic variants in the desmosomal gene plakophilin-2 (PKP2). Exercise is considered to be an independent risk factor for arrhythmias consequent to PKP2 deficiency. Weshow that loss of PKP2 expression affects cellular calcium handling and electrophysiology differently in left atrial vs. ventricular myocardium and causes extensive atrial fibrosis. PKP2-deficient atrial cardiomyocytes present increased spontaneous sarcoplasmic reticulum calcium release events, furtherenhancedby isoproterenol exposure and reversiblebya ryanodine receptor blocker(dantrolene). In addition, PKP2-deficient atrial myocytes exhibit impaired relaxation and enhanced sarcomere shortening, most probably related to reduced abundance of myosin binding protein C. We speculate that cellular effects reported upon isoproterenol impact on the exercise-related atrial arrhythmia risk in ARVC patients. We further propose that therapeutic approaches aimed at mitigating ventricular damage may be effective to treat the atrial disease in ARVC.

Assessment of left atrial function using tissue motion annular displacement in healthy dogs.

Recently, tissue motion annular displacement by speckle tracking has been shown to be a reliable method for evaluating deformation of the left atrium in healthy dogs. The aim of this study was to investigate whether tissue motion annular displacement is a feasible alternative method for studying left atrial function. One hundred healthy dogs were included. Left atrial function was assessed by tissue motion annular displacement, which was correlated to the left atrial strain and biplane area-length method-derived volumes. Left atrial reservoir function was evaluated by left atrial global tissue motion annular displacement, global left atrial strain and left atrial emptying fraction, while left atrial systolic tissue motion annular displacement and left atrial ejection fraction were used to assess left atrial systolic function. A statistically significant association between body weight and the dependent variables others than age was found. Indexed global and systolic tissue motion annular displacement decreased as body weight increased. Global iTMAD_AIIometric (mm/∛kg) showed a moderate, positive correlation with left atrial emptying fraction and with global left atrial strain. Systolic iTMAD_AIIometric (mm/∛kg) showed a moderate correlation with left atrial ejection fraction. Coefficients of variation for the intraobserver and interobserver analyses were 8.3% and 20.3% for global and 10.5% and 18.9% for systolic tissue motion annular displacement, respectively. Tissue motion annular displacement is a feasible and simple method for the evaluation of left atrial function. Our study documented the effects of body weight on left atrial tissue motion annular displacement, indicating that tissue motion annular displacement must be indexed to body weight. No influence of age or heart rate was observed on tissue motion annular displacement.

The spatial overlap between left atrial epicardial adipose tissue and fibrosis is not associated to clinical stage of atrial fibrillation

Left atrial (LA) epicardial adipose tissue (EAT) and wall fibrosis are both proven to contribute to the pathogenesis and progression of atrial fibrillation (AF). The theory of LA wall fibrosis induction by local EAT infiltration, paracrine secretions, and activation of the inflammatory process is strongly advocated, but the imaging evidence for anatomical proximity of the two tissue types and its association to AF stage is lacking. Accordingly, the aim of the study was to analyse the spatial overlap between LA EAT and adjacent wall fibrosis using 3D Dixon water-fat separated late gadolinium enhancement (LGE-Dixon) MRI and correlate the findings with the clinical AF stage. Forty-two AF patients (18 paroxysmal, 10 persistent, and 14 permanent) and nine non-AF patients were scanned. The permanent AF patients had greater LA volume and EAT than the paroxysmal group. The LA fibrosis area showed the same trend. The LA EAT-fibrosis overlap area was small and there was no significant difference between the three AF stages. There was no significant relationship between LA EAT- fibrosis overlap area and AF type. The findings shed light on the complex interplay between LA fibrosis and EAT during the progression from paroxysmal to permanent AF.

Renal denervation ameliorates atrial remodeling in type 2 diabetic rats by regulating mitochondrial dynamics.

There is no effective treatment for diabetes-related atrial remodeling currently. This study aimed to investigate the effects of renal denervation (RDN) on diabetes-related atrial remodeling and explore the related mechanisms. A type 2 diabetes mellitus model was established by high-fat diet feeding and low-dose streptozotocin injection in Sprague‒Dawley rats. After successful modeling, the diabetic rats were randomly assigned to two groups according to whether they were subjected to RDN or sham RDN surgery. At the end of the experiment, cardiac function and structure were evaluated by echocardiography and histology, respectively. Mitochondrial morphology, function and mitochondrial dynamics were assessed by multiple methods. Mdivi1 was used to verify the mechanism by which RDN improves atrial remodeling. In the 10th week, diabetic rats exhibited obvious atrial remodeling, including atrial enlargement and diastolic dysfunction. Pathological staining showed that diabetic rats had cardiomyocyte hypertrophy and interstitial fibrosis in atrial tissues. In terms of mitochondrial morphology and function, diabetic rats exhibited fragmented mitochondria, reduced adenosine triphosphate production and decreased mitochondrial membrane potential levels. Abnormal mitochondrial dynamics in diabetic rats were characterized by the inhibition of mitochondrial fusion, excessive mitochondrial fission, and the suppression of mitophagy. However, RDN effectively ameliorated diabetes-induced pathological atrial remodeling. In addition, RDN significantly improved mitochondrial morphological and functional abnormalities and corrected the disorders of mitochondrial dynamics. Furthermore, the protective effects of RDN against atrial remodeling were related to the regulation of mitochondrial dynamics. RDN prevented diabetes-induced atrial remodeling. These protective effects might be related to improvements in mitochondrial dynamics.