Atrial remodeling and atrial fibrillation in acquired forms of cardiovascular disease

Atrial fibrillation is associated with higher oxygen extraction in the human heart

INTRODUCTION

Atrial fibrillation (AF) is a prevalent cardiac arrhythmia characterized by irregular atrial contractions that compromise ventricular function and cardiac output. In this study we investigated the impact of AF on myocardial oxygen utilization, hypothesizing that myocardial oxygen extraction is more pronounced in AF due to less efficient ventricular function and reduced myocardial blood flow.

METHODS

We conducted a prospective, observational study involving 45 patients undergoing AF catheter ablation at the University of Washington Medical Center between 2022 and 2024, categorizing them based on their presenting rhythm, i.e., sinus rhythm (SR; N=27) or atrial fibrillation (AF; N=18). During AF procedures blood samples for oxygen analyses were collected from the pulmonary artery, coronary sinus (CS), and left atrium. Cardiac magnetic resonance imaging assessed CS blood flow and left ventricular mass.

RESULTS

Patients in AF exhibited significantly higher myocardial oxygen extraction than those in SR (10.8 ±1.4 vs 8.9 ± 2.0 mL O2/dL blood, P=0.001). Additionally, AF patients had lower cardiac power (0.74±0.14 vs 1.07±0.32 W, P=0.004), reduced CS flow (56.2±34.0 vs 65.0±19.2 mL/s, P= 0.42), and increased heart rate (80.6±17.4 vs 64.0±10.7 bpm, P= 0.002). In the AF group, symptomatic patients had significantly higher myocardial oxygen extraction for dyspnea, exercise intolerance, and palpitations (P=0.048, P=0.018, and P=0.028, respectively), with a trend observed for fatigue (P=0.07). No significant differences were found between symptomatic and asymptomatic patients in the sinus rhythm (SR) group. Multivariable regression analyses demonstrated that AF and AF-related symptoms were strongly associated with increased myocardial oxygen extraction.

CONCLUSION

AF significantly affects myocardial oxygen utilization by reducing both myocardial blood flow and cardiac power, thereby requiring increased oxygen extraction. This two-hit mechanism-reduced supply and increased demand-highlights the symptomatic challenges in managing AF and emphasizes the need for therapeutic strategies to optimize cardiac physiology in these patients.

Noninvasive assessment of a bioconductive patch for treating atrial fibrillation with magnetic resonance imaging

Electrical and structural remodeling disrupt atrial electrical conduction, leading to atrial fibrillation (AF). Epicardially delivered conductive biomaterial patches can effectively transmit electrical signals and potentially diminish AF. However, given the progressive nature of AF development, continuous and noninvasive monitoring is essential for assessing the therapeutic efficacy of these patches over time. In this study, superparamagnetic iron oxide nanoparticles (SPIO NPs) are synthesized and used to label a bio-conductive patch made of poly-3-amino-4-methoxybenzoic acid (PAMB) conjugated to gelatin (PAMBG-NP). Incorporating SPIO NPs does not alter the mechanical, electrical, or biocompatible properties of PAMBG. PAMBG-NP restores conduction velocity, suppresses rotor generation, and prevents re-entry currents, thereby relieving AF burden in an in vitro pacing model. In vivo, a bell-shaped PAMBG-NP patch is applied to the right and left atria of KCNE1 knockout mice. Compared to its Gelatin-NP counterpart, PAMBG-NP significantly reduces AF duration and enhances post-AF recovery over a 60-day period. Furthermore, magnetic resonance imaging indicates that PAMBG-NP degrades more slowly than Gelatin-NP, along with having a reduced incidence of AF in PAMBG-NP-treated animals. Therefore, incorporating SPIO NPs into PAMBG enables real-time, in vivo monitoring, potentially facilitating the noninvasive evaluation of its therapeutic efficacy.

Identifying extra pulmonary vein targets for persistent atrial fibrillation ablation: bridging advanced and conventional mapping techniques

AIMS

Advanced technologies such as charge density mapping (CDM) show promise in guiding adjuvant ablation in patients with persistent atrial fibrillation (AF); however, their limited availability restricts widespread adoption. We sought to determine whether regions of the left atrium containing CDM-identified pivoting and rotational propagation patterns during AF could also be reliably identified using more conventional contact mapping techniques.

METHODS AND RESULTS

Twenty-two patients undergoing de novo ablation of persistent AF underwent both CDM and electroanatomic voltage mapping during AF and sinus rhythm with multiple pacing protocols. Through the use of a left atrium statistical shape model, the location of distinctive propagation patterns identified by CDM was compared with low-voltage areas (LVAs) and regions of slow conduction velocity (CV). Neither LVA nor CV mapping during paced rhythms reliably identified regions containing CDM propagation patterns. Conduction velocity mapping during AF did correlate with these regions (ρ = -0.63, P < 0.0001 for pivoting patterns; ρ = -0.54, P < 0.0001 for rotational patterns). These propagation patterns consistently occurred in two specific anatomical regions across patients: the anteroseptal and inferoposterior walls of the left atrium.

CONCLUSION

Mapping techniques during paced rhythms do not reliably correspond with regions of CDM-identified propagation patterns in persistent AF. However, these propagation patterns are consistently observed in two specific anatomical regions, suggesting a predisposition to abnormal electrophysiological properties. While further research is needed, these regions may serve as promising targets for empirical ablation, potentially reducing the reliance on complex mapping techniques.

An Evaluation of Neuron-Specific Enolase as a Biomarker of Neurological Impact in Pacemaker-Implanted Patients with Atrial High-Rate Episodes: An Observational Study from Turkey

Background and Objectives: An atrial high-rate episode (AHRE) is defined according to the European Society of Cardiology (ESC) guidelines as a heart rate of ≥175 bpm lasting at least 5 min. This study aimed to evaluate whether neuron-specific enolase (NSE) levels, an indicator of neurological impact, could serve as a surrogate biomarker for silent neurological ischemia in patients with atrial high-rate episodes (AHREs). Materials and Methods: Patients with AHRE detected in a pacemaker analysis and a control group without any arrhythmias were included. Patients with AHRE were divided into subgroups according to AHRE duration-Group 1: AHRE < 5 min, Group 2: AHRE ≥ 5 min-<1 h, Group 3: AHRE ≥ 1 h-<24 h, Group 4: AHRE ≥ 24 h. Neuron-specific enolase (NSE) levels were measured using a double-antibody enzyme-linked immunosorbent assay (ELISA) with a sensitivity of 0.05 ng/mL. Imaging techniques were not employed in this study, and NSE was used as an indirect measure of potential neurological impact. Results: There were 160 patients, including 80 (50.0%) in the AHRE group and 80 (50.0%) in the control group. According to AHRE duration, there were 24 (30.0%) patients in Group 1, 33 (41.2%) in Group 2, 19 (23.8%) in Group 3, and 4 (5.0%) in Group 4. Patients with AHRE had statistically significant differences in age, sPAP, transmitral E/A ratio, and NSE levels. The mean NSE levels of all groups were significantly different (p < 0.001). A correlation analysis in patients with AHRE showed a very strong positive correlation between AHRE duration and NSE values as well as correlations with age, virtual CHA2DS2-VASc score, and LA diameter. NSE levels were positively correlated with AHRE duration and LA diameter. AHRE duration was an independent predictor of elevated NSE levels. Conclusions: It was shown that AHRE is associated with silent neurological ischemia and that NSE levels can be used to demonstrate these neurological effects. Future studies can contribute to the development of more effective treatment strategies based on these findings by investigating the neurological effects of AHRE in more detail.

Chronic angiotensin-converting enzyme inhibition attenuates frailty and protects against atrial fibrillation in aging mice

BACKGROUND

Aging is a major risk factor for atrial fibrillation (AF); however, not all individuals age at the same rate. Frailty, which is a measure of susceptibility to adverse health outcomes, can be quantified with a frailty index (FI).

OBJECTIVE

This study aimed to determine the effects of angiotensin-converting enzyme (ACE) inhibition on AF and atrial remodeling in aging and frail mice.

METHODS

Aging mice were treated with the ACE inhibitor enalapril for 6 months beginning at 16.5 months of age and frailty was quantified. AF susceptibility and atrial structure and function were assessed by intracardiac electrophysiology in anesthetized mice, high-resolution optical mapping in intact atrial preparations, patch clamping in isolated atrial myocytes, and histology and molecular biology in atrial tissues.

RESULTS

Enalapril attenuated frailty in aging mice with larger effects in females. AF susceptibility was increased in aging mice but attenuated by enalapril. AF susceptibility and duration also increased as a function of FI score. P-wave duration was increased and atrial conduction velocity was reduced in aging mice and improved after enalapril treatment. Furthermore, P-wave duration and atrial conduction velocity were strongly correlated with FI score. Atrial action potential upstroke velocity (Vmax) and Na+ current (INa) were reduced whereas atrial fibrosis was increased in aging mice. Action potential Vmax, INa, and fibrosis were improved by enalapril and also correlated with FI scores.

CONCLUSION

ACE inhibition with enalapril attenuates frailty and reduces AF susceptibility in aging mice by preventing atrial electrical and structural remodeling.

Advancing Atrial Fibrillation Research: The Role of Animal Models, Emerging Technologies and Translational Challenges

Atrial fibrillation (AF) is the most prevalent sustained cardiac arrhythmia, presenting a significant global healthcare challenge due to its rising incidence, association with increased morbidity and mortality, and economic burden. This arrhythmia is driven by a complex interplay of electrical, structural, and autonomic remodelling, compounded by genetic predisposition, systemic inflammation, and oxidative stress. Despite advances in understanding its pathophysiology, AF management remains suboptimal, with ongoing debates surrounding rhythm control, rate control, and anticoagulation strategies. Animal models have been instrumental in elucidating AF mechanisms, facilitating preclinical research, and advancing therapeutic development. This review critically evaluates the role of animal models in studying AF, emphasizing their utility in exploring electrical, structural, and autonomic remodelling. It highlights the strengths and limitations of various models, from rodents to large animals, in replicating human AF pathophysiology and advancing translational research. Emerging approaches, including optogenetics, advanced imaging, computational modelling, and tissue engineering, are reshaping AF research, bridging the gap between preclinical and clinical applications. We also briefly discuss ethical considerations, the translational challenges of animal studies and future directions, including integrative multi-species approaches, omics technologies and personalized computational models. By addressing these challenges and addressing emerging methodologies, this review underscores the importance of refining experimental models and integrating innovative technologies to improve AF management and outcomes.

Endothelial activation, Cell-Cell Interactions, and Inflammatory Pathways in Postoperative Atrial Fibrillation Following Cardiac Surgery

BACKGROUND

Postoperative atrial fibrillation (POAF) is common after cardiac surgery and related to endothelial activation and systemic inflammation. Herein, we investigate the pathophysiological mechanisms of AF through endothelial activation and cell-cell interactions related to the development of POAF.

METHODS

Patients without previous AF undergoing cardiac surgery were studied. Permanent AF patients were included as positive controls. Interleukin (IL)-6, Von Willebrand factor (vWF), N-terminal pro-brain natriuretic peptide (NT-proBNP) and high sensitivity troponin T (hsTnT) were evaluated by electrochemiluminescence. Vascular cell adhesion molecule-1 (VCAM-1) and human Growth Differentiation Factor 15 (GDF-15) was assessed by ELISA. Connexins (Cxs) 40 and 43 were measured by tissue immunolabelling, and apoptosis by TUNEL assay.

RESULTS

We included 117 patients (median age 67: 27.8% female): 17 with permanent AF; 27 with POAF and 73 with non- AF. Patients with permanent AF and POAF had higher levels of NT-proBNP, hs-TnT, apoptotic nuclei and decrease Cx43 expression, compared to non-AF patients (all p-value <0.05). VCAM-1 and GDF-15 were significantly higher in permanent AF vs. non-AF (p=0.013 and p=0.035).

CONCLUSIONS

Greater endothelial activation and inflammation in AF patients compared to those without AF was found. The proinflammatory state in AF patients, in addition to the lower expression of Cx43, seems to be associated with atrial remodeling processes occurring in AF.

Reduced FNDC5-AMPK signaling in diabetic atrium increases the susceptibility of atrial fibrillation by impairing mitochondrial dynamics and activating NLRP3 inflammasome

Fibronectin type III domain-containing protein 5 (FNDC5) exerts potential anti-arrhythmic effects. However, the function and mechanism of FNDC5 in diabetes-associated atrial fibrillation (AF) remain unknown. In this study, bioinformatics analysis, in vivo and in vitro experiments were conducted to explore the alteration and role of FNDC5 in diabetes-related atrial remodeling and AF susceptibility. RNA sequencing data from atrial samples of permanent AF patients and diabetic mice exhibited significantly decreased FNDC5 at the transcriptional level, which was in line with the protein expression in diabetic mice as well as high glucose and palmitic acid (HG+PA) injured atrial myocytes. Diabetic mice exhibited adverse atrial remodeling and increased AF inducibility. Moreover, reduced atrial FNDC5 was accompanied with exacerbated NOD-like receptor pyrin domain containing 3 (NLRP3) activation and disturbed mitochondrial fission and fusion processes, as evidenced by decreased expressions of optic atrophy 1 (OPA-1), mitofusin (MFN-1, MFN-2) and increased phosphorylation of dynamin-related protein 1 (Ser616). These effects were validated in HG+PA-treated atrial myocytes. Critically, FNDC5 overexpression remarkably enhanced cellular antioxidant capacity by upregulating the expressions of superoxide dismutase (SOD1, SOD2) level. In addition, HG+PA-induced mitochondrial dysfunction was ameliorated by FNDC5 overexpression as evidenced by improved mitochondrial dynamics and membrane potential. Moreover, NLRP3 inflammasome-mediated inflammation was reduced by FNDC5 overexpression, and AMPK signaling might serve as the key down-stream effector. The present study demonstrated that reduced atrial FNDC5-AMPK signaling contributed to the pathogenesis of diabetes- associated AF by impairing mitochondrial dynamics and activating the NLRP3 inflammasome. These findings provide promising therapeutic avenues for diabetes-associated AF.

Echocardiographic Assessment of Left Atrial Mechanics in Patients with Atrial Fibrillation Undergoing Electrical Cardioversion: A Systematic Review

Background: To date, only a few studies have evaluated left atrial (LA) mechanics in patients with atrial fibrillation (AF) scheduled for electrical cardioversion (ECV). The present systematic review has been primarily designed to summarize the main findings of these studies and to examine the overall effect of AF on left atrial reservoir strain (LASr) in patients undergoing ECV. Methods: All the echocardiographic studies evaluating the effect of AF on LA mechanics in patients scheduled for ECV, selected from the PubMed and EMBASE databases, were included. There was no limitation of time period. The risk of bias was assessed by using the National Institutes of Health (NIH) Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. Results: The full texts of 12 studies with 880 AF patients were analyzed. The pooled ECV success rate was 91.5% (range 65.8-100%). Over a median follow-up of 5.4 months (range 0.3-12 months), 35.2% of the patients (range 5-68.8%) experienced AF recurrence. At baseline, the average LASr was 11.4% (range 6.2-17.7%). A reduced LASr before ECV was strongly correlated with reduced left atrial appendage (LAA) flow velocities and/or thrombosis. The main independent predictors of cardioversion failure were impaired LASr and previous AF history. A severe LASr deterioration was independently correlated with AF recurrence after ECV. The other independent predictors of AR relapses were LA asynchrony, reduced difference between post- and pre-ECV LASr, and reduced right atrial reservoir strain. Conclusions: LASr assessment before ECV may provide useful prognostic information about AF relapses and improve the refinement of the thromboembolic risk of AF patients scheduled for ECV.

Linking Sleep Disorders to Atrial Fibrillation: Pathways, Risks, and Treatment Implications

Sleep is a complex biobehavioural process essential for overall health, with various dimensions including duration, continuity, timing, and satisfaction. This study investigated the intricate relationships between common sleep disorders such as insomnia and obstructive sleep apnoea (OSA) and their impact on atrial fibrillation (AF), a prevalent arrhythmia with significant health implications. Using a comprehensive review of the current literature, this study examined the pathophysiological mechanisms linking sleep disorders to cardiovascular risks, focusing on autonomic nervous system disturbances, inflammation, and oxidative stress associated with OSA. These findings indicate that sleep disorders significantly elevate the risk of AF through mechanisms such as increased sympathetic activity and structural cardiac remodelling. Additionally, this study highlights the potential benefits of treating sleep disorders, particularly with continuous positive airway pressure (CPAP) therapy, in reducing AF recurrence and improving cardiovascular outcomes. This conclusion emphasises the importance of integrated therapeutic approaches that address both sleep disorders and AF to enhance patient outcomes and quality of life. Future research should explore these connections to develop more effective and holistic treatment strategies.

The Functional substrate in patients with atrial fibrillation is predictive of recurrences after catheter ablation

BACKGROUND

Enhanced characterization of the atrial electrical substrate may lead to better comprehension of atrial fibrillation (AF) pathophysiology.

OBJECTIVE

With the use of high-density substrate mapping, we sought to investigate the occurrence of functional electrophysiological phenomena in the left atrium and to assess potential association with arrhythmia recurrences after catheter ablation.

METHODS

Sixty-three consecutive patients with AF referred for ablation were enrolled. Analysis of conduction abnormalities relied on two acquired left atrial electroanatomic maps (sinus and atrial paced rhythm). We classified conduction abnormalities as fixed (if these were present in both rhythms) or functional rhythm dependent (if unmasked in one of the two rhythms). Esophagus and aorta locations were recorded to check the correspondence with abnormal conduction sites.

RESULTS

There were 234 conduction abnormalities detected, of which 125 (53.4%) were functional rhythm dependent. The most frequent anatomic site of functional phenomena was the anterior wall, followed by the posterior wall, in sinus rhythm and the pulmonary venous antra in paced rhythm. Sites of functional phenomena in 82.6% of cases corresponded with extracardiac structures, such as sinus of Valsalva of ascending aorta anteriorly and the esophagus posteriorly. Most (88%) areas with functional phenomena had normal bipolar voltage. After pulmonary vein ablation, the number of residual functional phenomena is an independent predictor of AF recurrence (hazard ratio, 2.539 [1.458-4.420]; P = .001) with a risk of recurrences at multivariable Cox analysis.

CONCLUSION

Dual high-density mapping (during sinus and paced rhythms) is able to unmask functional, rhythm-dependent phenomena that are predictive of AF recurrences during follow-up.

X-ray Radiotherapy Impacts Cardiac Dysfunction by Modulating the Sympathetic Nervous System and Calcium Transients

Recent epidemiological studies have shown that patients with right-sided breast cancer (RBC) treated with X-ray irradiation (IR) are more susceptible to developing cardiovascular diseases, such as arrhythmias, atrial fibrillation, and conduction disturbances after radiotherapy (RT). Our aim was to investigate the mechanisms induced by low to moderate doses of IR and to evaluate changes in the cardiac sympathetic nervous system (CSNS), atrial remodeling, and calcium homeostasis involved in cardiac rhythm. To mimic the RT of the RBC, female C57Bl/6J mice were exposed to X-ray doses ranging from 0.25 to 2 Gy targeting 40% of the top of the heart. At 60 weeks after RI, Doppler ultrasound showed a significant reduction in myocardial strain, ejection fraction, and atrial function, with a significant accumulation of fibrosis in the epicardial layer and apoptosis at 0.5 mGy. Calcium transient protein expression levels, such as RYR2, NAK, Kir2.1, and SERCA2a, increased in the atrium only at 0.5 Gy and 2 Gy at 24 h, and persisted over time. Interestingly, 3D imaging of the cleaned hearts showed an early reduction of CSNS spines and dendrites in the ventricles and a late reorientation of nerve fibers, combined with a decrease in SEMA3a expression levels. Our results showed that local heart IR from 0.25 Gy induced late cardiac and atrial dysfunction and fibrosis development. After IR, ventricular CSNS and calcium transient protein expression levels were rearranged, which affected cardiac contractility. The results are very promising in terms of identifying pro-arrhythmic mechanisms and preventing arrhythmias during RT treatment in patients with RBC.

Association between Inflammation and New-Onset Atrial Fibrillation in Acute Coronary Syndromes

Acute coronary syndrome (ACS) is a complex clinical syndrome that encompasses acute myocardial infarction (AMI) and unstable angina (UA). Its underlying mechanism refers to coronary plaque disruption, with consequent platelet aggregation and thrombosis. Inflammation plays an important role in the progression of atherosclerosis by mediating the removal of necrotic tissue following myocardial infarction and shaping the repair processes that are essential for the recovery process after ACS. As a chronic inflammatory disorder, atherosclerosis is characterized by dysfunctional immune inflammation involving interactions between immune (macrophages, T lymphocytes, and monocytes) and vascular cells (endothelial cells and smooth muscle cells). New-onset atrial fibrillation (NOAF) is one of the most common arrhythmic complications in the setting of acute coronary syndromes, especially in the early stages, when the myocardial inflammatory reaction is at its maximum. The main changes in the atrial substrate are due to atrial ischemia and acute infarcts that can be attributed to neurohormonal factors. The high incidence of atrial fibrillation (AF) post-myocardial infarction may be secondary to inflammation. Inflammatory response and immune system cells have been involved in the initiation and development of atrial fibrillation. Several inflammatory indexes, such as C-reactive protein and interleukins, have been demonstrated to be predictive of prognosis in patients with ACS. The cell signaling activation patterns associated with fibrosis, apoptosis, and hypertrophy are forms of cardiac remodeling that occur at the atrial level, predisposing to AF. According to a recent study, the presence of fibrosis and lymphomononuclear infiltration in the atrial tissue was associated with a prior history of AF. However, inflammation may contribute to both the occurrence/maintenance of AF and its thromboembolic complications.

Preclinical Studies on the Effects of Frailty in the Aging Heart

Age is a major risk factor for the development of cardiovascular diseases in men and in women. However, not all people age at the same rate and those who are aging rapidly are considered frail, compared with their fit counterparts. Frailty is an important clinical challenge because those who are frail are more likely to develop and die from illnesses, including cardiovascular diseases, than fit people of the same age. This increase in susceptibility to cardiovascular diseases in older individuals might occur as the cellular and molecular mechanisms involved in the aging process facilitate structural and functional damage in the heart. Consistent with this, recent studies in murine frailty models have provided strong evidence that maladaptive cardiac remodelling in older mice is the most pronounced in mice with a high level of frailty. For example, there is evidence that ventricular hypertrophy and contractile dysfunction increase as frailty increases in aging mice. Additionally, fibrosis and slowing of conduction in the sinoatrial node and atria are proportional to the level of frailty. These modifications could predispose frail older adults to diseases like heart failure and atrial fibrillation. This preclinical work also raises the possibility that emerging interventions designed to "treat frailty" might also treat or prevent cardiovascular diseases. These findings might help to explain why frail older people are most likely to develop these disorders as they age.

Leveraging 3D Atrial Geometry for the Evaluation of Atrial Fibrillation: A Comprehensive Review

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia associated with significant morbidity and mortality. Managing risk of stroke and AF burden are pillars of AF management. Atrial geometry has long been recognized as a useful measure in achieving these goals. However, traditional diagnostic approaches often overlook the complex spatial dynamics of the atria. This review explores the emerging role of three-dimensional (3D) atrial geometry in the evaluation and management of AF. Advancements in imaging technologies and computational modeling have enabled detailed reconstructions of atrial anatomy, providing insights into the pathophysiology of AF that were previously unattainable. We examine current methodologies for interpreting 3D atrial data, including qualitative, basic quantitative, global quantitative, and statistical shape modeling approaches. We discuss their integration into clinical practice, highlighting potential benefits such as personalized treatment strategies, improved outcome prediction, and informed treatment approaches. Additionally, we discuss the challenges and limitations associated with current approaches, including technical constraints and variable interpretations, and propose future directions for research and clinical applications. This comprehensive review underscores the transformative potential of leveraging 3D atrial geometry in the evaluation and management of AF, advocating for its broader adoption in clinical practice.

Repurposing Metformin for the Treatment of Atrial Fibrillation: Current Insights

Metformin is an orally effective anti-hyperglycemic drug that despite being introduced over 60 years ago is still utilized by an estimated 120 to 150 million people worldwide for the treatment of type 2 diabetes (T2D). Metformin is used off-label for the treatment of polycystic ovary syndrome (PCOS) and for pre-diabetes and weight loss. Metformin is a safe, inexpensive drug with side effects mostly limited to gastrointestinal issues. Prospective clinical data from the United Kingdom Prospective Diabetes Study (UKPDS), completed in 1998, demonstrated that metformin not only has excellent therapeutic efficacy as an anti-diabetes drug but also that good glycemic control reduced the risk of micro- and macro-vascular complications, especially in obese patients and thereby reduced the risk of diabetes-associated cardiovascular disease (CVD). Based on a long history of clinical use and an excellent safety record metformin has been investigated to be repurposed for numerous other diseases including as an anti-aging agent, Alzheimer's disease and other dementias, cancer, COVID-19 and also atrial fibrillation (AF). AF is the most frequently diagnosed cardiac arrythmia and its prevalence is increasing globally as the population ages. The argument for repurposing metformin for AF is based on a combination of retrospective clinical data and in vivo and in vitro pre-clinical laboratory studies. In this review, we critically evaluate the evidence that metformin has cardioprotective actions and assess whether the clinical and pre-clinical evidence support the use of metformin to reduce the risk and treat AF.

Weight reduction interventions for the management of atrial fibrillation in overweight and obese people

OBJECTIVES

This is a protocol for a Cochrane Review (intervention). The objectives are as follows: To evaluate the efficacy of weight loss interventions as adjunctive treatment for reducing atrial fibrillation burden.

Left atrial cardiomyopathy: Pathophysiological insights, assessment methods and clinical implications

Atrial cardiomyopathy is defined as any complex of structural, architectural, contractile or electrophysiological changes affecting atria, with the potential to produce clinically relevant manifestations. Most of our knowledge about the mechanistic aspects of atrial cardiomyopathy is derived from studies investigating animal models of atrial fibrillation and atrial tissue samples obtained from individuals who have a history of atrial fibrillation. Several noninvasive tools have been reported to characterize atrial cardiomyopathy in patients, which may be relevant for predicting the risk of incident atrial fibrillation and its related outcomes, such as stroke. Here, we provide an overview of the pathophysiological mechanisms involved in atrial cardiomyopathy, and discuss the complex interplay of these mechanisms, including aging, left atrial pressure overload, metabolic disorders and genetic factors. We discuss clinical tools currently available to characterize atrial cardiomyopathy, including electrocardiograms, cardiac imaging and serum biomarkers. Finally, we discuss the clinical impact of atrial cardiomyopathy, and its potential role for predicting atrial fibrillation, stroke, heart failure and dementia. Overall, this review aims to highlight the critical need for a clinically relevant definition of atrial cardiomyopathy to improve treatment strategies.

Functional mapping to reveal slow conduction and substrate progression in atrial fibrillation

AIMS

The aim of our study was to analyse the response to short-coupled atrial extrastimuli to identify areas of hidden slow conduction (HSC) and their relationship with the atrial fibrillation (AF) phenotype.

METHODS AND RESULTS

Twenty consecutive patients with paroxysmal AF and persistent AF (10:10) underwent the first pulmonary vein isolation procedure. Triple short-coupled extrastimuli were delivered in sinus rhythm (SR), and the evoked response was analysed: sites exhibiting double or highly fragmented electrograms (EGM) were defined as positive for HSC (HSC+). The delta of the duration of the bipolar EGM was analysed, and bipolar EGM duration maps were built. High-density maps were acquired using a multipolar catheter during AF, SR, and paced rhythm. Spatial co-localization of HSC+ and complex fractionated atrial EGMs (CFAE) during AF was evaluated. Persistent AF showed a higher number and percentage of HSC+ than paroxysmal AF (13.9% vs. 3.3%, P < 0.001). The delta of EGM duration was 53 ± 22 ms for HSC+ compared with 13 ± 11 (10) ms in sites with negative HSC (HSC-) (P < 0.001). The number and density of HSC+ were lower than CFAE during AF (19 vs. 56 per map, P < 0.001). The reproducibility and distribution of HSC+ in repeated maps were superior to CFAE (P = 0.19 vs. P < 0.001). Sites with negative and positive responses showed a similar bipolar voltage in the preceding sinus beat (1.65 ± 1.34 and 1.48 ± 1.47 mV, P = 0.12).

CONCLUSION

Functional mapping identifies more discrete and reproducible abnormal substrates than mapping during AF. The HSC+ sites in response to triple extrastimuli are more frequent in persistent AF than in paroxysmal AF.

Natriuretic Peptide Receptor B Protects Against Atrial Fibrillation by Controlling Atrial cAMP Via Phosphodiesterase 2

BACKGROUND

β-AR (β-adrenergic receptor) stimulation regulates atrial electrophysiology and Ca2+ homeostasis via cAMP-dependent mechanisms; however, enhanced β-AR signaling can promote atrial fibrillation (AF). CNP (C-type natriuretic peptide) can also regulate atrial electrophysiology through the activation of NPR-B (natriuretic peptide receptor B) and cGMP-dependent signaling. Nevertheless, the role of NPR-B in regulating atrial electrophysiology, Ca2+ homeostasis, and atrial arrhythmogenesis is incompletely understood.

METHODS

Studies were performed using atrial samples from human patients with AF or sinus rhythm and in wild-type and NPR-B-deficient (NPR-B+/-) mice. Studies were conducted in anesthetized mice by intracardiac electrophysiology, in isolated mouse atrial preparations using high-resolution optical mapping, in isolated mouse and human atrial myocytes using patch-clamping and Ca2+ imaging, and in mouse and human atrial tissues using molecular biology.

RESULTS

Atrial NPR-B protein levels were reduced in patients with AF, and NPR-B+/- mice were more susceptible to AF. Atrial cGMP levels and PDE2 (phosphodiesterase 2) activity were reduced in NPR-B+/- mice leading to larger increases in atrial cAMP in the presence of the β-AR agonist isoproterenol. NPR-B+/- mice displayed larger increases in action potential duration and L-type Ca2+ current in the presence of isoproterenol. This resulted in the occurrence of spontaneous sarcoplasmic reticulum Ca2+ release events and delayed afterdepolarizations in NPR-B+/- atrial myocytes. Phosphorylation of the RyR2 (ryanodine receptor) and phospholamban was increased in NPR-B+/- atria in the presence of isoproterenol compared with the wildtypes. C-type natriuretic peptide inhibited isoproterenol-stimulated L-type Ca2+ current through PDE2 in mouse and human atrial myocytes.

CONCLUSIONS

NPR-B protects against AF by preventing enhanced atrial responses to β-adrenergic receptor agonists.

Future Perspectives to Improve CHA2DS2VASc Score: The Role of Left Atrium Remodelling, Inflammation and Genetics in Anticoagulation of Atrial Fibrillation

In 10% of ischemic strokes, non-valvular atrial fibrillation (NVAF) is detected retroactively. Milder, or even asymptomatic forms of NVAF have shown high mortality, thrombotic risk, and deterioration of cognitive function. The current guidelines for the diagnosis and treatment of AF contain "grey areas", such as the one related to anticoagulant treatment in men with CHA2DS2-VASc score 1 and women with score 2. Moreover, parameters such as renal function, patient weight or left atrium remodelling are missing from the recommended guidelines scores. Vulnerable categories of patients including the elderly population, high hemorrhagic risk patients or patients with newly diagnosed paroxysmal episodes of atrial high rate at device interrogation are at risk of underestimation of the thrombotic risk. This review presents a systematic exposure of the most important gaps in evaluation of thrombotic and hemorrhagic risk in patients with NVAF. The authors propose new algorithms and risk factors that should be taken into consideration for an accurate thrombotic and hemorrhagic risk estimation, especially in vulnerable categories of patients.

Factors Associated with Stroke in Atrial Fibrillation. A Retrospective Study

AIM

The aim of our study was to retrospectively evaluate known factors such as CHA2DS2-VASc, but, also, new factors (such as left atrial remodeling), associated with the development of stroke in patients with atrial fibrillation (AFi).

MATERIAL AND METHODS

We performed a retrospective study in which 251 patients with AFi were included. 47 patients had an ischemic stroke before the diagnosis of AFi, at the time of diagnosis or after AFi was diagnosed. The CHA2DS2-VASc score was analyzed for all patients together with other left atrial remodeling parameters.

RESULTS

We observed that among the patients with ischemic stroke approximately 61.70% were over 72.5 years old compared to those without stroke who presented this age in a proportion of only 44.61% (OR=2.001, P=0.0367). The CHA2DS2-VASc score had the greatest statistical impact for stroke, as expected. Patients with a CHA2DS2-VASc score >4.5 presented stroke in a proportion of 87.23% compared to CHA2DS2-VASc <4.5 who had stroke only in a proportion of 12.77% (OR=11.51, P=<0.0001). Regarding left atrial remodeling parameters, low LA ejection fraction was associated with a high percentage of stroke among patients (61.70%) compared to those with LA EF>34.5% who had stroke only in a percentage of 38.30% (OR= 2.124, P=0.0238).

CONCLUSIONS

Although the CHA2DS2-VASc score remains a good factor for predicting the association of AFi with ischemic stroke, echocardiographic parameters for the evaluation of the left atrium can be used as new risk factors for predicting the occurrence of ischemic stroke in patients with AFi.

Engineered small extracellular vesicle-mediated NOX4 siRNA delivery for targeted therapy of cardiac hypertrophy

Small-interfering RNA (siRNA) therapy is considered a powerful therapeutic strategy for treating cardiac hypertrophy, an important risk factor for subsequent cardiac morbidity and mortality. However, the lack of safe and efficient in vivo delivery of siRNAs is a major challenge for broadening its clinical applications. Small extracellular vesicles (sEVs) are a promising delivery system for siRNAs but have limited cell/tissue-specific targeting ability. In this study, a new generation of heart-targeting sEVs (CEVs) has been developed by conjugating cardiac-targeting peptide (CTP) to human peripheral blood-derived sEVs (PB-EVs), using a simple, rapid and scalable method based on bio-orthogonal copper-free click chemistry. The experimental results show that CEVs have typical sEVs properties and excellent heart-targeting ability. Furthermore, to treat cardiac hypertrophy, CEVs are loaded with NADPH Oxidase 4 (NOX4) siRNA (siNOX4). Consequently, CEVs@siNOX4 treatment enhances the in vitro anti-hypertrophic effects by CEVs with siRNA protection and heart-targeting ability. In addition, the intravenous injection of CEVs@siNOX4 into angiotensin II (Ang II)-treated mice significantly improves cardiac function and reduces fibrosis and cardiomyocyte cross-sectional area, with limited side effects. In conclusion, the utilization of CEVs represents an efficient strategy for heart-targeted delivery of therapeutic siRNAs and holds great promise for the treatment of cardiac hypertrophy.

A narrative review on prediabetes or diabetes and atrial fibrillation: From molecular mechanisms to clinical practice

Based on glucose levels, people fall into three groups, normal individuals, prediabetic patients, and diabetic mellitus (DM) patients. Prediabetes (pre-DM) is an intermediate condition that exists between normal glucose levels and DM. Atrial fibrillation (AF), one of the most prevalent cardiac arrhythmias in medical practice, contributes to a considerable morbidity and mortality rate. In this review, we looked at the clinical symptoms, pathological alterations, molecular mechanisms, and associated risk factors of pre-DM, type 2 DM (T2DM), and AF. In clinical practice, pre-DM can increase the prevalence of AF. In the hyperglycemic state, oxidative stress, inflammation, and endoplasmic reticulum stress can cause alterations in atrial cell or cardiac fibroblast function through tumor necrosis factor-α/nuclear factor-κB (NF-κB)/transforming growth factor-β, mitogen-activated protein kinase-matrix metalloproteinase-9 and PARP-1 is poly (ADP-ribose) polymerase 1. IκB kinase-α/NF-κB pathways, and further cause atria undergo structural, electrical, and neural remodeling which lead to the occurrence and persistence of AF. In addition, pre-DM and T2DM may worsen as a result of obesity, obstructive sleep apnea, and arterial hypertension. Furthermore, clinical researches have demonstrated that lifestyle interventions and/or pharmacotherapy in pre-DM patients can effectively delay the progresssion of pre-DM to T2DM. Individualized glycemic management and AF management should be provided to AF patients with pre-DM or DM.

The Synergistic Relationship Between Atrial Fibrillation and Diabetes Mellitus: Implications for Cardiovascular and Metabolic Health

Type 2 diabetes mellitus (T2DM) and atrial fibrillation (AF) are widespread chronic conditions that profoundly impact public health. While the intricate mechanisms linking these two diseases remain incompletely understood, this review sets out to comprehensively analyze the current evidence about their pathophysiology, epidemiology, diagnosis, prognosis, and treatment. We reveal that T2DM can influence the electrical and structural properties of the atria through multiple pathways, including oxidative stress, inflammation, fibrosis, connexin remodeling, glycemic variability, and autonomic dysfunction. Moreover, it significantly influences AF's clinical course, elevating the risk of heart failure, stroke, and cardiovascular mortality. Our review also explores treatment options for individuals with T2DM and AF, encompassing antidiabetic and antiarrhythmic drugs and non-pharmacological interventions, such as cardioversion catheter ablation and direct current cardioversion. This review depicts an insight into the clinical interplay between T2DM and AF. It deepens our comprehension of the fundamental mechanisms, potential therapeutic interventions, and their implications for patient care. This comprehensive resource benefits researchers seeking to deepen their knowledge in this domain. Ultimately, our findings pave the way for more effective strategies in managing AF within the context of T2DM.

Sarcomeric network analysis of ex vivo cultivated human atrial appendage tissue using super-resolution microscopy

Investigating native human cardiac tissue with preserved 3D macro- and microarchitecture is fundamental for clinical and basic research. Unfortunately, the low accessibility of the human myocardium continues to limit scientific progress. To overcome this issue, utilizing atrial appendages of the human heart may become highly beneficial. Atrial appendages are often removed during open-heart surgery and can be preserved ex vivo as living tissue with varying durability depending on the culture method. In this study, we prepared living thin myocardial slices from left atrial appendages that were cultured using an air-liquid interface system for overall 10 days. Metabolic activity of the cultured slices was assessed using a conventional methyl thiazolyl tetrazolium (MTT) assay. To monitor the structural integrity of cardiomyocytes within the tissue, we implemented our recently described super-resolution microscopy approach that allows both qualitative and quantitative in-depth evaluation of sarcomere network based on parameters such as overall sarcomere content, filament size and orientation. Additionally, expression of mRNAs coding for key structural and functional proteins was analyzed by real-time reverse transcription polymerase chain reaction (qRT-PCR). Our findings demonstrate highly significant disassembly of contractile apparatus represented by degradation of [Formula: see text]-actinin filaments detected after three days in culture, while metabolic activity was constantly rising and remained high for up to seven days. However, gene expression of crucial cardiac markers strongly decreased after the first day in culture indicating an early destructive response to ex vivo conditions. Therefore, we suggest static cultivation of living myocardial slices derived from left atrial appendage and prepared according to our protocol only for short-termed experiments (e.g. medicinal drug testing), while introduction of electro-mechanical stimulation protocols may offer the possibility for long-term integrity of such constructs.

Glucagon-Like Peptide-1 Protects Against Atrial Fibrillation and Atrial Remodeling in Type 2 Diabetic Mice

Atrial fibrillation (AF) is highly prevalent in type 2 diabetes where it increases morbidity and mortality. Glucagon-like peptide (GLP)-1 receptor agonists are used in the treatment of type 2 diabetes (T2DM), but their effects on AF in T2DM are poorly understood. The present study demonstrates type 2 diabetic db/db mice are highly susceptible to AF in association with atrial electrical and structural remodeling. GLP-1, as well as the long-acting GLP-1 analogue liraglutide, reduced AF and prevented atrial remodeling in db/db mice. These data suggest that GLP-1 and related analogues could protect against AF in patients with T2DM.

An Exploration of the Relationship Between Atrial Fibrillation and Obesity

In the past 40 years, the prevalence of atrial fibrillation and obesity have skyrocketed. It has long been established that obesity can lead to adverse cardiovascular outcomes due to its myriad of effects on cardiovascular architecture, cardiovascular hemodynamics, and electrical conduction interference. The goal of this article is to explore the pathogenesis of atrial fibrillation in obese patients and examine the role of atrial enlargement, increased adipose deposits surrounding the pericardium, interstitial fibrosis, and inflammation in the development and worsening of atrial fibrillation in obese patients.

Association of bone morphogenetic protein 10 and recurrent atrial fibrillation after catheter ablation

AIMS

Atrial remodelling, defined as a change in atrial structure, promotes atrial fibrillation (AF). Bone morphogenetic protein 10 (BMP10) is an atrial-specific biomarker released to blood during atrial development and structural changes. We aimed to validate whether BMP10 is associated with AF recurrence after catheter ablation (CA) in a large cohort of patients.

METHODS AND RESULTS

We measured baseline BMP10 plasma concentrations in AF patients who underwent a first elective CA in the prospective Swiss-AF-PVI cohort study. The primary outcome was AF recurrence lasting longer than 30 s during a follow-up of 12 months. We constructed multivariable Cox proportional hazard models to determine the association of BMP10 and AF recurrence. A total of 1112 patients with AF (age 61 ± 10 years, 74% male, 60% paroxysmal AF) was included in our analysis. During 12 months of follow-up, 374 patients (34%) experienced AF recurrence. The probability for AF recurrence increased with increasing BMP10 concentration. In an unadjusted Cox proportional hazard model, a per-unit increase in log-transformed BMP10 was associated with a hazard ratio (HR) of 2.28 (95% CI 1.43; 3.62, P < 0.001) for AF recurrence. After multivariable adjustment, the HR of BMP10 for AF recurrence was 1.98 (95% CI 1.14; 3.42, P = 0.01), and there was a linear trend across BMP10 quartiles (P = 0.02 for linear trend).

CONCLUSION

The novel atrial-specific biomarker BMP10 was strongly associated with AF recurrence in patients undergoing CA for AF.

CLINICALTRIALS.GOV IDENTIFIER

NCT03718364; https://clinicaltrials.gov/ct2/show/NCT03718364.

Cannabinoid receptor agonist attenuates angiotensin II-induced enlargement and mitochondrial dysfunction in rat atrial cardiomyocytes

Pathological remodeling of atrial tissue renders the atria more prone to arrhythmia upon arrival of electrical triggers. Activation of the renin-angiotensin system is an important factor that contributes to atrial remodeling, which may result in atrial hypertrophy and prolongation of P-wave duration. In addition, atrial cardiomyocytes are electrically coupled via gap junctions, and electrical remodeling of connexins may result in dysfunction of coordinated wave propagation within the atria. Currently, there is a lack of effective therapeutic strategies that target atrial remodeling. We previously proposed that cannabinoid receptors (CBR) may have cardioprotective qualities. CB13 is a dual cannabinoid receptor agonist that activates AMPK signaling in ventricular cardiomyocytes. We reported that CB13 attenuates tachypacing-induced shortening of atrial refractoriness and inhibition of AMPK signaling in the rat atria. Here, we evaluated the effects of CB13 on neonatal atrial rat cardiomyocytes (NRAM) stimulated by angiotensin II (AngII) in terms of atrial myocyte enlargement and mitochondrial function. CB13 inhibited AngII-induced enhancement of atrial myocyte surface area in an AMPK-dependent manner. CB13 also inhibited mitochondrial membrane potential deterioration in the same context. However, AngII and CB13 did not affect mitochondrial permeability transition pore opening. We further demonstrate that CB13 increased Cx43 compared to AngII-treated neonatal rat atrial myocytes. Overall, our results support the notion that CBR activation promotes atrial AMPK activation, and prevents myocyte enlargement (an indicator that suggests pathological hypertrophy), mitochondrial depolarization and Cx43 destabilization. Therefore, peripheral CBR activation should be further tested as a novel treatment strategy in the context of atrial remodeling.

Regional and temporal progression of atrial remodeling in angiotensin II mediated atrial fibrillation

Atrial fibrillation (AF) is associated with electrical and structural remodeling in the atria; however, the regional and temporal progression of atrial remodeling is incompletely understood. The objective of this study was to investigate the regional and temporal progression of atrial remodeling leading to changes in AF susceptibility in angiotensin II (Ang II) mediated hypertension. Mice were infused with Ang II for 3, 10 or 21 days. AF susceptibility and atrial electrophysiology were studied in vivo using intracardiac electrophysiology. Right and left atrial myocyte electrophysiology was studied using patch-clamping. Atrial fibrosis was assessed histologically. P wave duration and atrial effective refractory period increased progressively from 3 to 21 days of Ang II. AF susceptibility tended to be increased at 10 days of Ang II and was elevated at 21 days of Ang II. Left, but not right, atrial AP upstroke velocity and Na+ current were reduced at 10 and 21 days of Ang II. Left atrial action potential (AP) duration increased progressively from 3 to 21 days of Ang II due to reductions in repolarizing K+ current. Right atrial AP prolongation was increased only after 21 days of Ang II. Left and right atrial fibrosis developed progressively from 3 to 21 days, but increases were larger in the left atrium. In conclusion, Ang II mediated atrial electrical and structural remodeling develop earlier and more extensively in the left atrium compared to the right atrium, providing insight into how atrial remodeling leads to enhanced AF susceptibility in Ang II mediated hypertension.

Rule-based definition of muscle bundles in patient-specific models of the left atrium

Atrial fibrillation (AF) is the most common arrhythmia encountered clinically, and as the population ages, its prevalence is increasing. Although the CHA2DS2- VASc score is the most used risk-stratification system for stroke risk in AF, it lacks personalization. Patient-specific computer models of the atria can facilitate personalized risk assessment and treatment planning. However, a challenge faced in creating such models is the complexity of the atrial muscle arrangement and its influence on the atrial fiber architecture. This work proposes a semi-automated rule-based algorithm to generate the local fiber orientation in the left atrium (LA). We use the solutions of several harmonic equations to decompose the LA anatomy into subregions. Solution gradients define a two-layer fiber field in each subregion. The robustness of our approach is demonstrated by recreating the fiber orientation on nine models of the LA obtained from AF patients who underwent WATCHMAN device implantation. This cohort of patients encompasses a variety of morphology variants of the left atrium, both in terms of the left atrial appendages (LAAs) and the number of pulmonary veins (PVs). We test the fiber construction algorithm by performing electrophysiology (EP) simulations. Furthermore, this study is the first to compare its results with other rule-based algorithms for the LA fiber architecture definition available in the literature. This analysis suggests that a multi-layer fiber architecture is important to capture complex electrical activation patterns. A notable advantage of our approach is the ability to reconstruct the main LA fiber bundles in a variety of morphologies while solving for a small number of harmonic fields, leading to a comparatively straightforward and reproducible approach.

Genetic and non-genetic risk factors associated with atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmic disorder and its prevalence in the United States is projected to increase to more than twelve million cases in 2030. AF increases the risk of other forms of cardiovascular disease, including stroke. As the incidence of atrial fibrillation increases dramatically with age, it is paramount to elucidate risk factors underlying AF pathogenesis. Here, we review tissue and cellular pathways underlying AF, as well as critical components that impact AF susceptibility including genetic and environmental risk factors. Finally, we provide the latest information on potential links between SARS-CoV-2 and human AF. Improved understanding of mechanistic pathways holds promise in preventative care and early diagnostics, and also introduces novel targeted forms of therapy that might attenuate AF progression and maintenance.

Arrhythmias as Presentation of Genetic Cardiomyopathy

There is increasing evidence regarding the prevalence of genetic cardiomyopathies, for which arrhythmias may be the first presentation. Ventricular and atrial arrhythmias presenting in the absence of known myocardial disease are often labelled as idiopathic, or lone. While ventricular arrhythmias are well-recognized as presentation for arrhythmogenic cardiomyopathy in the right ventricle, the scope of arrhythmogenic cardiomyopathy has broadened to include those with dominant left ventricular involvement, usually with a phenotype of dilated cardiomyopathy. In addition, careful evaluation for genetic cardiomyopathy is also warranted for patients presenting with frequent premature ventricular contractions, conduction system disease, and early onset atrial fibrillation, in which most detected genes are in the cardiomyopathy panels. Sudden death can occur early in the course of these genetic cardiomyopathies, for which risk is not adequately tracked by left ventricular ejection fraction. Only a few of the cardiomyopathy genotypes implicated in early sudden death are recognized in current indications for implantable cardioverter defibrillators which otherwise rely upon a left ventricular ejection fraction ≤0.35 in dilated cardiomyopathy. The genetic diagnoses impact other aspects of clinical management such as exercise prescription and pharmacological therapy of arrhythmias, and new therapies are coming into clinical investigation for specific genetic cardiomyopathies. The expansion of available genetic information and implications raises new challenges for genetic counseling, particularly with the family member who has no evidence of a cardiomyopathy phenotype and may face a potentially negative impact of a genetic diagnosis. Discussions of risk for both probands and relatives need to be tailored to their numeric literacy during shared decision-making. For patients presenting with arrhythmias or cardiomyopathy, extension of genetic testing and its implications will enable cascade screening, intervention to change the trajectory for specific genotype-phenotype profiles, and enable further development and evaluation of emerging targeted therapies.

High liver fibrosis scores in metabolic dysfunction-associated fatty liver disease patients are associated with adverse atrial remodeling and atrial fibrillation recurrence following catheter ablation

BACKGROUND

A number of epidemiological studies have suggested an association between metabolic dysfunction-associated fatty liver disease (MAFLD) and the incidence of atrial fibrillation (AF). However, the pathogenesis leading to AF in the context of MAFLD remains unclear. We therefore aimed at assessing the impact of MAFLD and liver fibrosis status on left atrium (LA) structure and function.

METHODS

Patients with a Fatty Liver Index (FLI) >60 and the presence of metabolic comorbidities were classified as MAFLD+. In MAFLD+ patients, liver fibrosis severity was defined using the non-alcoholic fatty liver disease (NAFLD) Fibrosis Score (NFS), as follows: MAFLD w/o fibrosis (NFS ≦ -1.455), MAFLD w/indeterminate fibrosis (-1.455 < NFS < 0.675), and MAFLD w/fibrosis (NFS ≧ 0.675). In the first cohort of patients undergoing AF ablation, the structural and functional impact on LA of MAFLD was assessed by LA strain analysis and endocardial voltage mapping. Histopathological assessment of atrial fibrosis was performed in the second cohort of patients undergoing cardiac surgery. Finally, the impact of MAFLD on AF recurrence following catheter ablation was assessed.

RESULTS

In the AF ablation cohort (NoMAFLD n = 123; MAFLD w/o fibrosis n = 37; MAFLD indeterm. fibrosis n = 75; MAFLD w/severe fibrosis n = 10), MAFLD patients with high risk of F3-F4 liver fibrosis presented more LA low-voltage areas as compared to patients without MAFLD (16.5 [10.25; 28] vs 5.0 [1; 11] low-voltage areas p = 0.0115), impaired LA reservoir function assessed by peak left atrial longitudinal strain (19.7% ± 8% vs 8.9% ± 0.89% p = 0.0268), and increased LA volume (52.9 ± 11.7 vs 43.5 ± 18.0 ml/m² p = 0.0168). Accordingly, among the MAFLD patients, those with a high risk of F3-F4 liver fibrosis presented a higher rate of AF recurrence during follow-up (p = 0.0179). In the cardiac surgery cohort (NoMAFLD n = 12; MAFLD w/o fibrosis n = 5; MAFLD w/fibrosis n = 3), an increase in histopathological atrial fibrosis was observed in MAFLD patients with a high risk of F3-F4 liver fibrosis (p = 0.0206 vs NoMAFLD; p = 0.0595 vs MAFLD w/o fibrosis).

CONCLUSION

In conclusion, we found that liver fibrosis scoring in MAFLD patients is associated with adverse atrial remodeling and AF recurrences following catheter ablation. The impact of the management of MAFLD on LA remodeling and AF ablation outcomes should be assessed in dedicated studies.

Medical therapies for prevention of cardiovascular and renal events in patients with atrial fibrillation and diabetes mellitus

Atrial fibrillation (AF), type 2 diabetes mellitus (DM), and chronic kidney disease (CKD) are three global epidemics with significant effects on morbidity and mortality. Diabetes is a risk factor for AF, and a risk factor for thromboembolism, comorbidity, and mortality when AF is present. The pathophysiology of diabetes-related AF and interrelationships with cardiovascular events and renal events is not fully understood but is in part related to structural, electrical, electromechanical, and autonomic remodelling. The current practice guidelines offer limited recommendations on the management of patients with AF (or risk of AF) and diabetes with its own heterogeneity for the prevention of cardiovascular and renal events. This document discusses possible clinical approaches for these patients. In the last decade, there have been major improvements for the prevention of stroke in AF patients with direct oral anticoagulants, which are preferable to vitamin K antagonists for stroke prevention in DM. Because of the increased risk rate for several cardiovascular adverse events in diabetic patients, a similar relative risk reduction generally translates into greater absolute risk reduction in the diabetic population. Recent trials with non-insulin diabetes drugs using glucagon-like peptide-1 agonists and sodium-glucose cotransporter-2 inhibitors showed a significant reduction for the risk of major adverse cardiovascular events in patients with type 2 DM. Sodium-glucose cotransporter-2 inhibitors also showed a large reduction in hospitalization for heart failure and renal events, which need to be more completely evaluated in patients with AF. Mechanisms, risks, and optimal management of AF patients with DM who have or are under risk of developing heart failure or CKD are also discussed in this document. The benefits of medical therapies for these patients still need to be put into perspective, and gaps in evidence on some of these issues are likely to be addressed in future years.

Distinct Effects of Ibrutinib and Acalabrutinib on Mouse Atrial and Sinoatrial Node Electrophysiology and Arrhythmogenesis

Background

Ibrutinib and acalabrutinib are Bruton tyrosine kinase inhibitors used in the treatment of B‐cell lymphoproliferative disorders. Ibrutinib is associated with new‐onset atrial fibrillation. Cases of sinus bradycardia and sinus arrest have also been reported following ibrutinib treatment. Conversely, acalabrutinib is less arrhythmogenic. The basis for these different effects is unclear.

Methods and Results

The effects of ibrutinib and acalabrutinib on atrial electrophysiology were investigated in anesthetized mice using intracardiac electrophysiology, in isolated atrial preparations using high‐resolution optical mapping, and in isolated atrial and sinoatrial node (SAN) myocytes using patch‐clamping. Acute delivery of acalabrutinib did not affect atrial fibrillation susceptibility or other measures of atrial electrophysiology in mice in vivo. Optical mapping demonstrates that ibrutinib dose‐dependently impaired atrial and SAN conduction and slowed beating rate. Acalabrutinib had no effect on atrial and SAN conduction or beating rate. In isolated atrial myocytes, ibrutinib reduced action potential upstroke velocity and Na⁺ current. In contrast, acalabrutinib had no effects on atrial myocyte upstroke velocity or Na⁺ current. Both drugs increased action potential duration, but these effects were smaller for acalabrutinib compared with ibrutinib and occurred by different mechanisms. In SAN myocytes, ibrutinib impaired spontaneous action potential firing by inhibiting the delayed rectifier K⁺ current, while acalabrutinib had no effects on SAN myocyte action potential firing.

Conclusions

Ibrutinib and acalabrutinib have distinct effects on atrial electrophysiology and ion channel function that provide insight into the basis for increased atrial fibrillation susceptibility and SAN dysfunction with ibrutinib, but not with acalabrutinib.

Atrial Fibrillation in Aging and Frail Mice: Modulation by Natriuretic Peptide Receptor C

[Figure: see text].

Higher long-term visit-to-visit glycemic variability predicts new-onset atrial fibrillation in patients with diabetes mellitus

Background

Atrial fibrillation (AF) is prevalent in patients with type 2 diabetes mellitus (T2DM). Glycemic variability (GV) is associated with risk of micro- and macrovascular diseases. However, whether the GV can increase the risk of AF remains unknown.

Methods

The cohort study used a database from National Taiwan University Hospital, a tertiary medical center in Taiwan. Between 2014 and 2019, a total of 27,246 adult patients with T2DM were enrolled for analysis. Each individual was assessed to determine the coefficients of variability of fasting glucose (FGCV) and HbA1c variability score (HVS). The GV parameters were categorized into quartiles. Multivariate Cox regression models were employed to estimate the relationship between the GV parameters and the risk of AF, transient ischemic accident (TIA)/ischemic stroke and mortality in patients with T2DM.

Results

The incidence rates of AF and TIA/ischemic stroke were 21.31 and 13.71 per 1000 person-year respectively. The medium follow-up period was 70.7 months. In Cox regression model with full adjustment, the highest quartile of FGCV was not associated with increased risk of AF [Hazard ratio (HR): 1.12, 95% confidence interval (CI) 0.96–1.29, p = 0.148] or TIA/ischemic stroke (HR: 1.04, 95% CI 0.83–1.31, p = 0.736), but was associated with increased risk of total mortality (HR: 1.33, 95% CI 1.12–1.58, p < 0.001) and non-cardiac mortality (HR: 1.41, 95% CI 1.15–1.71, p < 0.001). The highest HVS was significantly associated with increased risk of AF (HR: 1.29, 95% CI 1.12–1.50, p < 0.001), total mortality (HR: 2.43, 95% CI 2.03–2.90, p < 0.001), cardiac mortality (HR: 1.50, 95% CI 1.06–2.14, p = 0.024) and non-cardiac mortality (HR: 2.80, 95% CI 2.28–3.44, p < 0.001) but was not associated with TIA/ischemic stroke (HR: 0.98, 95% CI 0.78–1.23, p = 0.846). The Kaplan–Meier analysis showed significantly higher risk of AF, cardiac and non-cardiac mortality according to the magnitude of GV (log-rank test, p < 0.001).

Conclusions

Our data demonstrate that high GV is independently associated with the development of new-onset AF in patients with T2DM. The benefit of maintaining stable glycemic levels to improve clinical outcomes warrants further studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-021-01341-3.

New aspects of endocrine control of atrial fibrillation and possibilities for clinical translation

Hormones are potent endo-, para-, and autocrine endogenous regulators of the function of multiple organs, including the heart. Endocrine dysfunction promotes a number of cardiovascular diseases, including atrial fibrillation (AF). While the heart is a target for endocrine regulation, it is also an active endocrine organ itself, secreting a number of important bioactive hormones that convey significant endocrine effects, but also through para-/autocrine actions, actively participate in cardiac self-regulation. The hormones regulating heart-function work in concert to support myocardial performance. AF is a serious clinical problem associated with increased morbidity and mortality, mainly due to stroke and heart failure. Current therapies for AF remain inadequate. AF is characterized by altered atrial function and structure, including electrical and profibrotic remodelling in the atria and ventricles, which facilitates AF progression and hampers its treatment. Although features of this remodelling are well-established and its mechanisms are partly understood, important pathways pertinent to AF arrhythmogenesis are still unidentified. The discovery of these missing pathways has the potential to lead to therapeutic breakthroughs. Endocrine dysfunction is well-recognized to lead to AF. In this review, we discuss endocrine and cardiocrine signalling systems that directly, or as a consequence of an underlying cardiac pathology, contribute to AF pathogenesis. More specifically, we consider the roles of products from the hypothalamic-pituitary axis, the adrenal glands, adipose tissue, the renin–angiotensin system, atrial cardiomyocytes, and the thyroid gland in controlling atrial electrical and structural properties. The influence of endocrine/paracrine dysfunction on AF risk and mechanisms is evaluated and discussed. We focus on the most recent findings and reflect on the potential of translating them into clinical application.

Electrical and structural remodeling contribute to atrial fibrillation in type 2 diabetic db/db mice

BACKGROUND

Atrial fibrillation (AF) is highly prevalent in diabetes mellitus (DM), yet the basis for this finding is poorly understood. Type 2 DM may be associated with unique patterns of atrial electrical and structural remodeling; however, this has not been investigated in detail.

OBJECTIVE

The purpose of this study was to investigate AF susceptibility and atrial electrical and structural remodeling in type 2 diabetic db/db mice.

METHODS

AF susceptibility and atrial function were assessed in male and female db/db mice and age-matched wildtype littermates. Electrophysiological studies were conducted in vivo using intracardiac electrophysiology and programmed stimulation. Atrial electrophysiology was also investigated in isolated atrial preparations using high-resolution optical mapping and in isolated atrial myocytes using patch-clamping. Molecular biology studies were performed using quantitative polymerase chain reaction and western blotting. Atrial fibrosis was assessed using histology.

RESULTS

db/db mice were highly susceptible to AF in association with reduced atrial conduction velocity, action potential duration prolongation, and increased heterogeneity in repolarization in left and right atria. In db/db mice, atrial K⁺ currents, including the transient outward current (I_to) and the ultrarapid delayed rectifier current (I_Kur), were reduced. The reduction in I_to occurred in association with reductions in Kcnd2 mRNA expression and K_V4.2 protein levels. The reduction in I_Kur was not related to gene or protein expression changes. Interstitial atrial fibrosis was increased in db/db mice.

CONCLUSION

Our study demonstrates that increased susceptibility to AF in db/db mice occurs in association with impaired electrical conduction as well as electrical and structural remodeling of the atria.