Atrial Fibrillation Inducibility Research Articles

KCa3.1 Promotes the Migration of Macrophages From Epicardial Adipose Tissue to Induce Vulnerability to Atrial Fibrillation During Rapid Pacing

BackgroundThe relationship between local epicardial adipose tissue (EAT) macrophages and atrial fibrillation (AF) remains unclear. The purpose of this study was to investigate the role of KCa3.1 in the migration of macrophages from EAT to adjacent atrial tissue during rapid pacing. MethodsPart 1: Eighteen beagles were randomly divided into the sham group, pacing group, and pacing + clodronate liposome (CL) group. Part 2: Eighteen beagles were randomly divided into the sham group, pacing group, and pacing + TRAM-34 group. HL-1 cells and RAW264.7 cells were co-cultured to explore the specific migratory mechanism of macrophages. ResultsDepleting EAT macrophages significantly reduced macrophage infiltration in the adjacent atrium and the induction of AF in canines with rapid atrial pacing. TRAM-34 significantly inhibited the migration of macrophages from EAT to the adjacent atrium and electrical remodelling in canines with rapid atrial pacing. Compared with those of the control HL-1 cells, the secretion of CCL2 and the number of migrating macrophages in pacing HL-1 cells was significantly increased, which could be reversed by TRAM-34. Further in vitro experiments showed that KCa3.1 regulated CCL2 secretion through the p65/STAT3 signalling pathway. ConclusionsInhibiting myocardial KCa3.1 reduced the migration of EAT macrophages to adjacent atrial muscles caused by rapid atrial pacing, thereby decreasing vulnerability to AF. The mechanism by which KCa3.1 regulates CCL2 may be related to the p65/STAT3 signalling pathway.

Multiomics analysis of canine myocardium after circumferential pulmonary vein ablation: Effect of neuropeptide Y on long-term reinduction of atrial fibrillation.

Catheter ablation (CA) is an essential method for the interventional treatment of atrial fibrillation (AF), and it is very important to reduce long-term recurrence after CA. The mechanism of recurrence after CA is still unclear. We established a long-term model of beagle canines after circumferential pulmonary vein ablation (CPVA). The transcriptome and proteome were obtained using high-throughput sequencing and TMT-tagged LC-MS/LC analysis, respectively. Differentially expressed genes and proteins were screened and enriched, and the effect of fibrosis was found and verified in tissues. A downregulated protein, neuropeptide Y (NPY), was selected for validation and the results suggest that NPY may play a role in the long-term reinduction of AF after CPVA. Then, the molecular mechanism of NPY was further investigated. The results showed that the atrial effective refractory period (AERP) was shortened and fibrosis was increased after CPVA. Atrial myocyte apoptosis was alleviated by NPY intervention, and Akt activation was inhibited in cardiac fibroblasts. These results suggest that long-term suppression of NPY after CPVA may lead to induction of AF through promoting cardiomyocyte apoptosis and activating the Akt pathway in cardiac fibroblasts, which may make AF more likely to reinduce.

Inhibition of α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid Receptors Ameliorates Atrial Inflammation and Vulnerability to Atrial Fibrillation in Rats with Anxiety Disorders.

Previous studies have found that anxiety disorders may increase the incidence of atrial fibrillation (AF). More and more studies have shown that α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) are involved in the occurrence and development of cardiovascular diseases. However, the role of AMPARs in AF associated with anxiety disorder remains unclear. The aim of this study was to investigate the effect of AMPARs on AF susceptibility in rats with anxiety disorder and its possible mechanism. The anxiety disorder rat model was established by unpredictable empty bottle stimulation and was treated with AMPARs agonist and antagonist. Our results showed that AMPARs antagonist treatment significantly reduced sympathetic activity, improved heart rate variability, shortened action potential duration, prolonged effective refractory period, reduced AF induction rate, and improved cardiac electrical remodeling and the expression of inflammatory factors. In addition, inhibition of AMPARs reduced the phosphorylation of IκBα and p65. Our experimental results suggest that inhibition of AMPARs can reduce autonomic remodeling, improve atrial electrical remodeling, and suppress myocardial inflammation, which provides a potential therapeutic strategy for the treatment of AF associated with anxiety disorder.

Early inhibition of the ATM/p53 pathway reduces the susceptibility to atrial fibrillation and atrial remodeling following acute myocardial infarction

Atrial fibrillation (AF) emerges as a critical complication following acute myocardial infarction (AMI) and is associated with a significant increased risk of heart failure, stroke and mortality. Ataxia telangiectasia mutated (ATM), a key player in DNA damage repair (DDR), has been implicated in multiple cardiovascular conditions, however, its involvement in the development of AF following AMI remains unexplored. This study seeks to clarify the contribution of the ATM/p53 pathway in the onset of AF post-AMI and to investigate the underlying mechanisms. The rat model of AMI was established by ligating left anterior descending coronary artery in the presence or absence of Ku55933 (an ATM kinase inhibitor, 5 mg/kg/d) treatment. Rats receiving Ku55933 were further divided into the early administration group (administered on days 1, 2, 4, and 7 post-AMI) and the late administration group (administered on days 8, 9, 11 and 14 post-AMI). RNA-sequencing was performed 14 days post-operation. In vitro, H2O2-challenged HL-1 atrial muscle cells were utilized to evaluate the potential effects of different ATM inhibition schemes, including earlier, middle, and late periods of intervention. Fourteen days post-AMI injury, the animals exhibited significantly increased AF inducibility, exacerbated atrial electrical/structural remodeling, reduced ventricular function and exacerbated atrial DNA damage, as evidenced by enhanced ATM/p53 signaling as well as γH2AX level. These effects were partially consistent with the enrichment results of bioinformatics analysis. Notably, the deleterious effects were ameliorated by early, but not late, administration of Ku55933. Mechanistically, inhibition of ATM signaling successfully suppressed atrial NLRP3 inflammasome-mediated pyroptotic pathway. Additionally, the results were validated in the in vitro experiments demonstrating that early inhibition of Ku55933 not only attenuated cellular ATM/p53 signaling, but also mitigated inflammatory response by reducing NLRP3 activation. Collectively, hyperactivation of ATM/p53 contributed to the pathogenesis of AF following AMI. Early intervention with ATM inhibitors substantially mitigated AF susceptibility and atrial electrical/structural remodeling, highlighting a novel therapeutic avenue against cardiac arrhythmia following AMI.

SIRT3/AMPK Signaling Pathway Regulates Lipid Metabolism and Improves Vulnerability to Atrial Fibrillation in Dahl Salt-Sensitive Rats.

Hypertension may result in atrial fibrillation (AF) and lipid metabolism disorders. The Sirtuins3 (SIRT3)/AMP-activated protein kinase (AMPK) signaling pathway has the capacity to regulate lipid metabolism disorders and the onset of AF. We hypothesize that the SIRT3/AMPK signaling pathway suppresses lipid metabolism disorders, thereby mitigating salt-sensitive hypertension (SSHT)-induced susceptibility to AF. The study involved 7-week-old male Dahl salt-sensitive that were fed either a high-salt diet (8% NaCl; DSH group) or a normal diet (0.3% NaCl; DSN group). Then DSH group was administered either oral metformin (MET, an AMPK agonist) or intraperitoneal injection of Honokiol (HK, a SIRT3 agonist). This experimental model allowed for the measurement of Systolic blood pressure (SBP), the expression levels of lipid metabolism-related biomarkers, pathological examination of atrial fibrosis, and lipid accumulation, as well as AF inducibility and AF duration. DSH decrease SIRT3, phosphorylation-AMPK, and very long-chain acyl-CoA dehydrogenase, (VLCAD) expression, increased FASN and FABP4 expression and concentrations of free fatty acid and triglyceride, atrial fibrosis and lipid accumulation in atrial tissue, enhanced level of SBP, promoted AF induction rate and prolonged AF duration, which are blocked by MET and HK. Our results also showed that the degree of atrial fibrosis was negatively correlated with VLCAD expression, but positively correlated with the expression of FASN and FABP4. We have confirmed that a high-salt diet can result in hypertension, and associated atrial tissue lipid metabolism dysfunction. This condition is linked to the inhibition of the SIRT3/AMPK signaling pathway, which plays a significant role in the progression of susceptibility to AF in SSHT rats.

Polycystin-1 loss of function increases susceptibility to atrial fibrillation through impaired DNA damage response.

The increasing prevalence of atrial fibrillation (AF) and chronic kidney diseases highlights the need for a deeper comprehension of the molecular mechanisms linking them. Mutations in PKD1, the gene encoding Polycystin-1 (PKD1 or PC1), account for 85% of autosomal dominant polycystic kidney disease (ADPKD) cases. This disease often includes cardiac complications such as AF. In cardiomyocytes, PC1 deletion reduces hypertrophic response to pressure overload but promotes baseline ventricular dysfunction, while deletion in fibroblasts ameliorates post-myocardial infarction fibrosis. Despite its known cardiac impact, the role of PC1 in atrial cardiomyocytes and arrhythmias is less understood. Here, we sought to investigate the role of PC1 in AF. We used intracardiac programmed stimulation and optical mapping to evaluate AF inducibility in two mouse models, Pkd1 R3277C, which recapitulates human ADPKD progression, and cardiomyocyte-specific Pkd1 deletion, and their respective controls. Isolated adult mouse atrial cardiomyocytes, human iPSC-derived atrial cardiomyocytes (hiPSC-aCM), and HL-1 cells served as in vitro cellular models. Molecular mechanisms were evaluated using optical mapping and molecular and biochemical approaches. Loss-of-function PC1 mutations significantly increased AF susceptibility in vivo and facilitated local reentry in ex vivo left atrial appendages. Comprehensive in vitro experiments supported a direct effect of PC1 in atrial cardiomyocytes. PC1-deficient monolayers exhibited increased arrhythmic events, escalating into reentrant spiral waves post-tachypacing. Transcriptomics analysis revealed PC1-dependent regulation of DNA repair, with PC1 deficiency leading to increased DNA damage under stress. PARP1 inhibitors or nicotinamide riboside, which counteract DNA damage-related metabolic consequences, reduced in vitro arrhythmias PC1-deficient monolayers. Overexpression of the C-terminus of PC1 had the opposite effects in DNA repair genes, suggesting its regulatory effects in atrial cardiomyocytes through retinoblastoma/E2F. Analyses of human atrial tissue from non-ADPKD patients showed reduced levels of mature PC1, suggesting a broader relevance of impaired PC1 in AF. Impaired PC1 increases in vivo AF inducibility under programmed electrical stimulation and promotes in vitro arrhythmias in hiPSC-aCM and HL-1 cells. Our findings indicate that PC1 protects against DNA damage to reduce AF susceptibility.

Macrophage IL-1β mediates atrial fibrillation risk in diabetic mice.

Diabetes mellitus (DM) is an independent risk factor for atrial fibrillation (AF). The mechanisms underlying DM-associated AF are unclear. AF and DM are both related to inflammation. We investigated whether DM-associated inflammation contributed to AF risk. Mice were fed with high-fat diet to induce type II DM and were subjected to IL-1β antibodies, macrophage depletion by clodronate liposomes, a mitochondrial antioxidant (mitoTEMPO), or a cardiac ryanodine receptor 2 (RyR2) stabilizer (S107). All tests were performed at 36-38 weeks of age. DM mice presented with increased AF inducibility, enhanced mitochondrial reactive oxygen species (mitoROS) generation, and activated innate immunity in the atria, as evidenced by enhanced monocyte chemoattractant protein-1 (MCP-1) expression, macrophage infiltration, and IL-1β levels. Signs of aberrant RyR2 Ca2+ leak were observed in the atria of DM mice. IL-1β neutralization, macrophage depletion, and exposure to mitoTEMPO and S107 significantly ameliorated the AF vulnerability in DM mice. Atrial overexpression of MCP-1 increased AF occurrence in normal mice through the same mechanistic signaling cascade as observed in DM mice. In conclusion, macrophage-mediated IL-1β contributed to DM-associated AF risk through mitoROS modulation of RyR2 Ca2+ leak.

Impact of age-related gut microbiota dysbiosis and reduced short-chain fatty acids on the autonomic nervous system and atrial fibrillation in rats.

Aging is the most significant contributor to the increasing prevalence of atrial fibrillation (AF). Dysbiosis of gut microbiota has been implicated in age-related diseases, but its role in AF development remains unclear. This study aimed to investigate the correlations between changes in the autonomic nervous system, short-chain fatty acids (SCFAs), and alterations in gut microbiota in aged rats with AF. Electrophysiological experiments were conducted to assess AF induction rates and heart rate variability in rats. 16S rRNA gene sequences extracted from fecal samples were used to assess the gut microbial composition. Gas and liquid chromatography-mass spectroscopy was used to identify SCFAs in fecal samples. The study found that aged rats exhibited a higher incidence of AF and reduced heart rate variability compared to young rats. Omics research revealed disrupted gut microbiota in aged rats, specifically a decreased Firmicutes to Bacteroidetes ratio. Additionally, fecal SCFA levels were significantly lower in aged rats. Importantly, correlation analysis indicated a significant association between decreased SCFAs and declining heart rate variability in aged rats. These findings suggest that SCFAs, as metabolites of gut microbiota, may play a regulatory role in autonomic nervous function and potentially influence the onset and progression of AF in aged rats. These results provide novel insights into the involvement of SCFAs and autonomic nervous system function in the pathogenesis of AF. These results provide novel insights into the involvement of SCFAs and autonomic nervous system function in the pathogenesis of AF.

The Role of KACh Channels in Atrial Fibrillation.

This manuscript explores the intricate role of acetylcholine-activated inward rectifier potassium (KACh) channels in the pathogenesis of atrial fibrillation (AF), a common cardiac arrhythmia. It delves into the molecular and cellular mechanisms that underpin AF, emphasizing the vital function of KACh channels in modulating the atrial action potential and facilitating arrhythmogenic conditions. This study underscores the dual nature of KACh activation and its genetic regulation, revealing that specific variations in potassium channel genes, such as Kir3.4 and K2P3.1, significantly influence the electrophysiological remodeling associated with AF. Furthermore, this manuscript identifies the crucial role of the KACh-mediated current, IKACh, in sustaining arrhythmia through facilitating shorter re-entry circuits and stabilizing the re-entrant circuits, particularly in response to vagal nerve stimulation. Experimental findings from animal models, which could not induce AF in the absence of muscarinic activation, highlight the dependency of AF induction on KACh channel activity. This is complemented by discussions on therapeutic interventions, where KACh channel blockers have shown promise in AF management. Additionally, this study discusses the broader implications of KACh channel behavior, including its ubiquitous presence across different cardiac regions and species, contributing to a comprehensive understanding of AF dynamics. The implications of these findings are profound, suggesting that targeting KACh channels might offer new therapeutic avenues for AF treatment, particularly in cases resistant to conventional approaches. By integrating genetic, cellular, and pharmacological perspectives, this manuscript offers a holistic view of the potential mechanisms and therapeutic targets in AF, making a significant contribution to the field of cardiac arrhythmia research.

Laser catheter ablation of atrial zones with ganglionated plexi: impact on atrial fibrillation inducibility and the risk of esophageal damage in experimental settings

Aim. To study the potential applicability of transcatheter laser ablation for the destruction of atrial ganglionated plexi (GP) zones and the safety of this technique in relation to inadvertent esophageal damage.Methods. This was a two-stage investigation: (1) ex vivo experiments: the risk of esophageal damage during ablation on the dorsal (posterior) left atrial (LA) wall was assessed; three swine organ complexes were used, which included the heart, lungs and esophagus; (2) in vivo experiments assessing the effects of laser catheter ablation of GP zones on the inducibility of atrial fibrillation (AF) and changes in atrial effective refractory period - included 13 landrace pigs (average weight 38.8±1.2 kg).Ex vivo: laser catheter ablations were performed from the endocardial surface of the LA towards the esophagus with a power of 15 watts of varying duration; ablation was performed under thermal scanning of the LA and esophagus; then a macroscopic examination of the myocardial and esophageal walls was performed.In vivo: before and after catheter laser ablation (15 W) of the GP zones in the right atrium and atrial septum, atrial ERP was assessed with programmed stimulation, and AF induction with high-frequency (33 Hz, 2 min) stimulation was evaluated. At the end of the experiment, the animals were euthanized, and the heart and lungs were collected in a single unit.Results. Ex vivo experiments: in two cases, damage to the endocardium of the LA was detected at an exposure time of 30 s. Damage to the esophagus was observed with a longer exposure time (> 30 seconds) with a 11.3-15.4°C increase in temperature. In the in vivo experiments, 78 laser applications (6±1 in one swine) were delivered to the posterior wall of the right atrium and atrial septum. Atrial effective refractory period was not altered after ablation (183±20 ms vs 186±18 ms, P=0.99). At the baseline, AF was induced in 12 out of 13 animals (92%). After ablation, AF was induced in 7 animals (54%) (P=0.03). There was a trend toward a decrease in the duration of AF after laser ablation of GP zones (18 [5; 141] vs. 2 [0; 14] s after ablation, P=0.06). Transmural damage was observed in 46% of the hearts. No damage to extra-cardiac structures was detected.Conclusion. Ex vivo, laser ablation on the dorsal (posterior) wall of the LA with a power of 15 W and duration <30 s does not lead to visible damage to the esophagus. Laser ablation of atrial GP zones is feasible and reduces the inducibility of AF. No change in atrial effective refractory period is detected following GP zones ablation, when performed from the right atrium.

Atrial fibrillation is perpetuated by human heart secretome in ex-vivo langendorff-perfused hearts

Abstract Introduction Atrial fibrillation (AF) confers high morbidity and mortality, yet parts of the underlying pathophysiology remain elusive. Left atrial (LA) pressure is altered by the presence of AF and vice-versa. The cardiac secretome might be influenced by LA pressure and potentially alters the susceptibility of the atria to AF. We investigated the effect of the human cardiac secretome on atrial electrophysiology in a translational ex-vivo setting. Methods We obtained venous (coronary sinus) serum samples during AF and in sinus rhythm (SR) in patients hospitalized for pulmonary vein isolation (PVI). Moreover, LA tissue was collected from patients undergoing cardiac surgery and coronary sinus serum samples were collected before (CTRL) and after intraoperative volume challenge (VC). Single cardiomyocytes were isolated from human LA tissue and Ca2+ dependent excitation-contraction coupling (ECC) was studied using confocal line-scan imaging with CTRL or VC. Moreover, a modified Langendorff-Setup with the ability to monitor and control intra-cardiac pressure was utilized to perfuse mouse hearts with AF and SR serum. A multielectrode array (MEA) was placed on the epicardial aspect of the left atrium to measure electrical signals in a spatiotemporal fashion. External bipolar burst pacing protocols were applied to test AF inducibility. Results Ca2+ dependent ECC (i.e. Ca2+ amplitude and release) in human cardiomyocytes was unaltered with exposure to VC serum. Upon introducing a modified version of the Langendorff setup with the ability of linear pressure adjustment, a burst pacing protocol to test for AF inducibility was successfully implemented in mice atria. Atria perfused with human AF serum showed significantly increased AF inducibility as compared to SR serum. Moreover, both, total AF duration as well as number of AF episodes (i.e. AF burden) were increased in AF vs. SR serum upon several different pacing protocols. Conclusion Cardiac secretome during increased LA pressure had no significant effect on Ca2+ dependent ECC in human cardiomyocytes. However, secretome during AF conferred pro-arrhythmogenic properties as compared to SR, further strengthening the concept of "AF begets AF". Ongoing experiments test the hypothesis of potential differences in the multi-level omics profile of AF serum as the underlying mechanism.

The right atrium affects in silico arrhythmia vulnerability in both atria

Abstract Introduction The role of the right atrium (RA) in atrial fibrillation (AF) has long been overlooked. Computer models of the atria can aid in assessing how the RA influences arrhythmia vulnerability and in studying the role of RA drivers in the induction of AF, both aspects challenging to assess in living patients. It remains unclear if incorporating the RA influences the reentry inducibility of the model. As personalized ablation strategies rely on non-inducibility criteria, the adequacy of left atrium (LA)-only models for developing such ablation tools is uncertain. Aim To evaluate the effect of incorporating the RA in 3D patient-specific computer models on arrhythmia vulnerability. Methods Imaging data from 8 subjects were obtained to generate patient-specific computer models. We created 2 models for each subject: a monoatrial with only the LA and a biatrial with both the RA and LA. We considered 3 different states of substrate remodeling: healthy (H), mild (M), and severe (S). The Courtemanche cellular model was modified from control conditions to a setup representing AF-induced remodeling [1] with 0%, 50%, and 100% changes for H, M, and S, respectively. Conduction velocity was set to 1.2, 1.0, and 0.8m/s for each remodeling state. Fibrosis extent corresponded to Utah 2 (5-20%) and Utah 4 (>35%) stages [2] for M and S, while the H state was modeled without fibrosis. Arrhythmia vulnerability was assessed by virtual S1S2 pacing from different points separated by 2cm using openCARP [3]. A point was classified as inducing arrhythmia if reentry was maintained for at least 1s. The vulnerability ratio was defined as the number of inducing points divided by the number of stimulation points. The mean tachycardia cycle length (TCL) was assessed at the stimulation site. We compared LA vulnerability ratios in monoatrial and biatrial models. Results Incorporating the RA increased the mean LA vulnerability ratio by 115.8% (0.19±0.13 to 0.41±0.22, p=0.033) in state M and 29.0% in state S (0.31±0.14 to 0.40±0.15, p=0.219) as illustrated in Figure 1. No arrhythmia was induced in the H models. RA inclusion increased the TCL of LA reentries by 5.5% (186.9±13.3ms to 197.2±18.3ms, p=0.006) in scenario M and decreased it by 7.2% (224.3±27.6ms to 208.2±34.8ms, p=0.010) in scenario S. RA inclusion increased LA inducibility revealing 5.5±3.0 new points per patient in the LA for the biatrial model, which did not induce reentry in the monoatrial model. Conclusions LA arrhythmia vulnerability in a biatrial model differs from that in a monoatrial model. Incorporating the RA in patient-specific computational models unmasked potential inducing points in the LA. The RA had a substrate-dependent effect on reentry dynamics, altering the TCL of LA-induced reentries. Our results provide evidence for an important role of the RA in the maintenance and induction of arrhythmia in patient-specific computational models, thus suggesting the use of biatrial models.

Impact of induced atrial fibrillation during atrioventricular nodal reentrant tachycardia ablation

Abstract Ablation is the treatment of choice for atrioventricular nodal reentrant tachycardia (AV NRT). Atrial fibrillation (AF) can incidentally occur during this procedure, labeling these patients (P) as susceptible for AF in the future. Our aim was to assess the presence of new onset AF in P who presented this arrhythmia during the electrophysiological study (EPS). Methods We retrospectively analyzed 580 P that underwent AV NRT ablation between November 2008 and August 2020. Patients with previous AF were excluded. After having AF induced during the EPS, 62 P were identified as susceptible for developing AF. Data were collected by contacting P and consulting medical records. Results The studied population had 64.5% (n=40) females, 35.5% (n=22) males, with ages between 15 and 81years old (median 52.3, mean 50.1). At ablation date, 33.9% (n=21) had hypertension, 3.2% (n=2) diabetes, 6.5% (n=4) chronic kidney disease, 3.2% (n=2) obstructive sleep apnea, 6.5% (n=4) coronary artery disease and 6.5% (n=4) structural heart disease. Previously to ablation, 46.8% (n=29) were on beta-blocker, 1.6% (n=1) on amiodarone and 3.2% (n=2) on flecainide. When admitted to the procedure, 98.4% (n=61) were in sinus rhythm and 1.6% (n=1) had a pacemaker. "Slow-fast" was the most common AVNRT type (96.8%). During the EPS, other arrhythmias were induced: in 12.9% (n=8) atrial flutter and in 9.7% (n=6) atrial tachycardia. After AF induction, 12.9% (n=8) needed electrical cardioversion and 3.2% (n=2) needed both electrical and pharmacological. At the time of ablation, transient complete atrioventricular block was noted in 6.5% (n=4) P. When contacted, 100% (n=62) had 1 year of follow-up, 69.4% (n=43) 5 years and 25.8% (n=16) 10 years, with a mean follow-up of 6.6 years. It was not possible to contact 12.9% (n=8) of the P, of those, 6.5% (n=4) died and 6.5% (n=4) did not reply. Recurrence of AV NRT was documented in 6.4% (n=4) P and all underwent a successful second ablation. Almost one third, 32.3% (n=20), were symptomatic, mainly with palpitations, and 27.4% (n=17) maintained follow up with a Cardiologist. New-onset AF was documented in 1 P only (1.6%), diagnosed 9 years after the procedure. Conclusion In our cohort, the induction of AF during EPS did not translate into clinical AF during follow-up. Whether this is a nonspecific finding related to catheter manipulation or pacing maneuvers on pharmacological provocation deserves further investigation.

Spontaneous atrial fibrillation occurrence following transesophageal atrial burst pacing in rats

Abstract Purpose Animal models play a crucial role in elucidating the complex pathophysiology of atrial fibrillation (AF) and in identifying and testing novel antiarrhythmic strategies. We aimed to develop and characterize a new experimental rat model of AF, induced by long-term transesophageal atrial electrical stimulation, and to investigate whether the "AF begets AF" concept applies to small rodent hearts. Method Twelve adult male Wistar rats were randomized into two groups: Sham (n = 5) and AF (n = 7). All rats were implanted at the beginning of the study with ECG radiotelemetry devices and underwent continuous ECG monitoring throughout the study. To induce AF, the rats in the AF group underwent atrial pacing for 10 consecutive days (15 successive cycles of stimulation/day, 20 s each, with a free interval of 5 min between cycles; 4,000 stimuli/min, stimulus duration 6 ms, voltage 3 V above the diastolic threshold). A similar procedure was applied to the Sham group, but without performing the actual electrical stimulation. The number and duration of spontaneous AF episodes were evaluated based on continuous ECG monitoring prior to, during, and for one week after transesophageal atrial pacing. The inducibility of AF and the occurrence and duration of spontaneous AF episodes were evaluated and compared between the two groups. Results Atrial fibrillation was induced in 85.7% of the rats subjected to atrial electrical pacing (Figure, A), with an average global inducibility of 44.0% ± 16.9% and a mean AF duration of 123.2 ± 96.3 s. No induced or spontaneous AF episodes were recorded in any of the Sham animals. In the AF group, none of the animals presented spontaneous AF before transesophageal atrial pacing. However, in the AF rats, after atrial electrical stimulation initiation, the number of atrial premature beats significantly increased (21.3 ± 6.8 / 24-h post-stimulation vs. 7.3 ± 6.5 / 24-h at baseline; p< 0.01; Figure, B), and all rats presented spontaneous AF episodes (Figure, C). At the end of the study, AF rats presented a total number of 23.9 ± 2.3 AF episodes / 24-h (Figure, D), with a mean AF burden of 337.7 ± 25.06 s / 24-h. Conclusions Our data demonstrate that, despite the small size of the atria, the "AF begets AF" concept is applicable in small rodents. The study presents a novel rat model of AF, in which spontaneous AF occurs following long-term atrial electrical stimulation. Given that the model is relatively rapid and easy to implement, it provides a setup for further investigation of AF pathophysiology, and for identifying and testing novel therapeutic strategies for AF.Figure 1

Predictors of neuromodulation during single-shot thermal atrial fibrillation ablation: a computed tomography imaging analysis

Abstract Background Ganglionated plexi (GPs) are part of the cardiac autonomic nervous system (CANS), which play an important role in the induction and maintenance of atrial fibrillation (AF). Because of the anatomic proximity of the pulmonary veins with GPs, pulmonary vein isolation (PVI) using thermal (radiofrequency (RF) or cryo) ablation, has been shown to concomitantly affect the GPs, as suggested by increased heart rate (HR) after ablation. Right superior pulmonary vein (RSPV) isolation has been reported to have the most evident inhibitory responses to the CANS via modulation of the anterior right ganglionated plexus. Nonetheless, there are also cases with little to no effect on neuromodulation post-ablation. Purpose To assess the clinical and anatomical predictors of thermal ablation-induced CANS changes, as assessed via variations in resting HR post-ablation. Methods We retrospectively analyzed consecutive patients with symptomatic paroxysmal AF who underwent first-time PVI by cryoballoon (CB) or RF balloon (RFB) between January 2022 to November 2022. Patients who were not in sinus rhythm, had cardiac implantable electronic devices, or did not have a contrast-enhanced computed tomography before the ablation were excluded. Pre-ablation and 24-hour post-ablation ECGs in sinus rhythm were collected and analyzed to assess HR. Results A total of 83 patients (CB group, n = 43 vs RFB group, n = 40) were included in the analysis. Baseline patients’ characteristics were similar between the two groups (Table 1). A significant HR increase (ΔHR ≥ 15 bpm) at 24h post-ablation occurred in 31 patients [CB group 16 (52 %), RFB group 15 (48 %)]. Predictors of increased HR were the distance between superior vena cava (SVC) and RSPV (OR 0.51, CI 0.35 - 0.75, p value < 0.01) and age (OR 0.94, CI 0.89 - 0.99, p value < 0.01) (Table 2). Conclusions Single-shot thermal PVI influences the CANS, especially in patients with a shorter SVC - RSPV distance and in younger patients.Table 1Table 2

High efficacy and safety of endocardial pulsed electrical field ablation via contact force-controlled catheters for mitral isthmus ablation

Abstract Background A new technology of a pulsed field generator enables established contact force-controlled radiofrequency (RF) catheters to apply point by point monopolar pulsed electrical field (PEF) energy for linear lesions in atrial fibrillation (AF) ablation. Purpose We evaluated this novel monopolar PEF ablation technique for creating lateral mitral isthmus ablation lines in case of perimitral flutter or complex AF patients non responder to pulmonary vein isolation (PVI). Methods Patients (n=44, age 65±11 years) referred for ablation/re-ablation of AF with spontaneous or inducible perimitral atrial flutter (n=34, 77%) or persistent AF and severe enlarged atrium (n=7) or de novo longstanding persistent AF (n=3) without signs of atrial fibrosis were included in our patient cohort for lateral mitral isthmus ablation with PEF applications. After 3D high density voltage mapping of the left atrium with multipolar microelectrode catheters, and confirmation/completion of PVI, an endocardial lateral mitral isthmus line was performed. Using contact force sensing catheter, 25A PEF energy pulses were applied targeting a minimum of 10g contact force and an interlesion distance ≤5mm. Before PEF application 0.2 mg nitroglycerin was intravenously injected. If the inferolateral mitral isthmus line to the left inferior pulmonary vein could not be blocked, a more superior lateral line to the left superior pulmonary vein was performed. If the mitral isthmus could not be blocked by endocardial PEF application or conduction recurred after adenosine injection an additional epicardial ablation via RF application in the coronary sinus was performed. Results Exclusively endocardial PEF application blocked the lateral mitral line in 37 out of 42 cases (88%) with 23±14 PEF applications. After an unsuccessful inferior lateral mitral line, in 34% of cases a second superior lateral mitral line have to be performed. Only in five cases additional epicardial RF applications via coronary sinus were necessary to complete the mitral isthmus block. Block time between superior lateral mitral anulus and infero lateral coronary sinus was 196±48 ms. One pericardial tamponade which could be successfully drained, and no other serious complication occurred throughout all procedures (no ST segment elevation, no tamponade requiring surgery, no cerebrovascular event). Limited follow-up will be available at the time of presentation. Conclusion Blockade of left atrial mitral isthmus line with PEF application via contact force-sensing catheters for ablation of complex atrial fibrillation patients is very efficient and safe. Especially the high efficacy of exclusively endocardial PEF application for creation of a lateral mitral isthmus block in most patients is very promising. However, the long term permanence of the linear lines have to be awaited.

High-Salt Diet Inhibits the Expression of Bmal1 and Promotes Atrial Fibrosis and Vulnerability to Atrial Fibrillation in Dahl Salt-Sensitive Rats.

Hypertension is a risk factor for atrial fibrillation (AF), and brain and muscle arnt-like protein 1 (Bmal1) regulate circadian blood pressure and is implicated in several fibrotic disorders. Our hypothesis that Bmal1 inhibits atrial fibrosis and susceptibility to AF in salt-sensitive hypertension (SSHT) and our study provides a new target for the pathogenesis of AF induced by hypertension. The study involved 7-week-old male Dahl salt-sensitive that were fed either a high-salt diet (8% NaCl; DSH group) or a normal diet (0.3% NaCl; DSN group). An experimental model was used to measure systolic blood pressure (SBP), left atrial ejection fraction (LAEF), left atrial end-volume index (LAEVI), left atrial index (LAFI), AF inducibility, AF duration, and atrial fibrosis pathological examination and the expression of Baml1 and fibrosis-related proteins (TNF-α and α-SMA) in left atrial tissue. DSH increased TNF-α and α-SMA expression in atrial tissue, level of SBP and LAESVI, atrial fibrosis, AF induction rate, and AF duration, and decreased Bmal1 expression in atrial tissue, the circadian rhythm of hypertension, and level of LAEF and LAFI. Our results also showed that the degree of atrial fibrosis was negatively correlated with Bmal1 expression, but positively correlated with the expression of TNF-α and α-SMA. We demonstrated that a high-salt diet leads to circadian changes in hypertension due to a reduction of Bmal1 expression, which plays a crucial role in atrial fibrosis and increased susceptibility to AF in SSHT rats.

Spexin Diminishes Atrial Fibrillation Vulnerability by Acting on Galanin Receptor 2.

G protein-coupled receptors play a critical role in atrial fibrillation (AF). Spexin is a novel ligand of galanin receptors (GALRs). In this study, we investigated the regulation of spexin and GALRs on AF and the underlying mechanisms. Global spexin knockout (SPX-KO) and cardiomyocyte-specific GALRs knockout (GALR-cKO) mice underwent burst pacing electrical stimulation. Optical mapping was used to determine atrial conduction velocity and action potential duration. Atrial myocyte action potential duration and inward rectifying K+ current (IK1) were recorded using whole-cell patch clamps. Isolated cardiomyocytes were stained with Fluo-3/AM dye, and intracellular Ca2+ handling was examined by CCD camera. A mouse model of AF was established by Ang-II (angiotensin II) infusion. Spexin plasma levels in patients with AF were lower than those in subjects without AF, and knockout of spexin increased AF susceptibility in mice. In the atrium of SPX-KO mice, potassium inwardly rectifying channel subfamily J member 2 (KCNJ2) and sarcolipin (SLN) were upregulated; meanwhile, IK1 current was increased and Ca2+ handling was impaired in isolated atrial myocytes of SPX-KO mice. GALR2-cKO mice, but not GALR1-cKO and GALR3-cKO mice, had a higher incidence of AF, which was associated with higher IK1 current and intracellular Ca2+ overload. The phosphorylation level of CREB (cyclic AMP responsive element binding protein 1) was upregulated in atrial tissues of SPX-KO and GALR2-cKO mice. Chromatin immunoprecipitation confirmed the recruitment of p-CREB to the proximal promoter regions of KCNJ2 and SLN. Finally, spexin treatment suppressed CREB signaling, decreased IK1 current and decreased intracellular Ca2+ overload, which thus reduced the inducibility of AF in Ang-II-infused mice. Spexin reduces atrial fibrillation susceptibility by inhibiting CREB phosphorylation and thus downregulating KCNJ2 and SLN transcription by GALR2 receptor. The spexin/GALR2/CREB signaling pathway represents a novel therapeutic avenue in the development of agents against atrial fibrillation.

Transcriptomic analysis of epicardial adipose tissue reveals the potential crosstalk genes and immune relationship between type 2 diabetes mellitus and atrial fibrillation

BackgroundThe complex relationship between atrial fibrillation (AF) and type 2 diabetes mellitus (T2DM) suggests a potential role for epicardial adipose tissue (EAT) that requires further investigation. This study employs bioinformatics and experimental approaches to clarify EAT's role in linking T2DM and AF, aiming to unravel the biological mechanisms involved. MethodBioinformatics analysis initially identified common differentially expressed genes (DEGs) in EAT from T2DM and AF datasets. Pathway enrichment and network analyses were then performed to determine the biological significance and network connections of these DEGs. Hub genes were identified through six CytoHubba algorithms and subsequently validated biologically, with further in-depth analyses confirming their roles and interactions. Experimentally, db/db mice were utilized to establish a T2DM model. AF induction was executed via programmed transesophageal electrical stimulation and burst pacing, focusing on comparing the incidence and duration of AF. Frozen sections and Hematoxylin and Eosin (H&E) staining illuminated the structures of the heart and EAT. Moreover, quantitative PCR (qPCR) measured the expression of hub genes. ResultsThe study identified 106 DEGs in EAT from T2DM and AF datasets, underscoring significant pathways in energy metabolism and immune regulation. Three hub genes, CEBPZ, PAK1IP1, and BCCIP, emerged as pivotal in this context. In db/db mice, a marked predisposition towards AF induction and extended duration was observed, with HE staining verifying the presence of EAT. Additionally, qPCR validated significant changes in hub genes expression in db/db mice EAT. In-depth analysis identified 299 miRNAs and 33 TFs as potential regulators, notably GRHL1 and MYC. GeneMANIA analysis highlighted the hub genes' critical roles in stress responses and leukocyte differentiation, while immune profile correlations highlighted their impact on mast cells and neutrophils, emphasizing the genes' significant influence on immune regulation within the context of T2DM and AF. ConclusionThis investigation reveals the molecular links between T2DM and AF with a focus on EAT. Targeting these pathways, especially EAT-related ones, may enable personalized treatments and improved outcomes.

The SK4 channel allosteric blocker, BA6b9, reduces atrial fibrillation substrate in rats with reduced ejection fraction.

Atrial fibrillation (AF), the most common cardiac arrhythmia, is strongly associated with several comorbidities including heart failure (HF). AF in general, and specifically in the context of HF, is progressive in nature and associated with poor clinical outcomes. Current therapies for AF are limited in number and efficacy and do not target the underlying causes of atrial remodeling such as inflammation or fibrosis. We previously identified the calcium-activated SK4 K+ channels, which are preferentially expressed in the atria relative to the ventricles in both rat and human hearts, as attractive druggable target for AF treatment. Here, we examined the ability of BA6b9, a novel allosteric inhibitor of SK4 channels that targets the specific calmodulin-PIP2 binding domain, to alter AF susceptibility and atrial remodeling in a systolic HF rat postmyocardial infarction (post-MI) model. Daily BA6b9 injection (20 mg/kg/day) for 3 weeks starting 1-week post-MI prolonged the atrial effective refractory period, reduced AF induction and duration, and dramatically prevented atrial structural remodeling. In the post-MI left atrium (LA), pronounced upregulation of the SK4 K+ channel was observed, with corresponding increases in collagen deposition, α-SMA levels, and NLRP3 inflammasome expression. Strikingly, BA6b9 treatment reversed these changes while also significantly reducing the lateralization of the atrial connexin Cx43 in the LA of post-MI rats. Our findings indicate that the blockade of SK4 K+ channels using BA6b9 not only favors rhythm control but also remarkably reduces atrial structural remodeling, a property that is highly desirable for novel AF therapies, particularly in patients with comorbid HF.