Comprehensive evaluation of electrophysiological and 3D structural features of human atrial myocardium with insights on atrial fibrillation maintenance mechanisms

Atrial fibrillation in cancer, anticancer therapies, and underlying mechanisms

Atrial fibrillation (AF) is a common arrhythmic complication in cancer patients and can be exacerbated by traditional cytotoxic and targeted anticancer therapies. Increased incidence of AF in cancer patients is independent of confounding factors, including preexisting myocardial arrhythmogenic substrates, type of cancer, or cancer stage. Mechanistically, AF is characterized by fast unsynchronized atrial contractions with rapid ventricular response, which impairs ventricular filling and results in various symptoms such as fatigue, chest pain, and shortness of breath. Due to increased blood stasis, a consequence of both cancer and AF, concern for stroke increases in this patient population. To compound matters, cardiotoxic anticancer therapies themselves promote AF; thereby exacerbating AF morbidity and mortality in cancer patients. In this review, we examine the relationship between AF, cancer, and cardiotoxic anticancer therapies with a focus on the shared molecular and electrophysiological mechanisms linking these disease processes. We also explore the potential role of sodium-glucose co-transporter 2 inhibitors (SGLT2i) in the management of anticancer-therapy-induced AF.

[Developments of ex vivo cardiac electrical mapping and intelligent labeling of atrial fibrillation substrates]

Cardiac three-dimensional electrophysiological labeling technology is the prerequisite and foundation of atrial fibrillation (AF) ablation surgery, and invasive labeling is the current clinical method, but there are many shortcomings such as large trauma, long procedure duration, and low success rate. In recent years, because of its non-invasive and convenient characteristics, ex vivo labeling has become a new direction for the development of electrophysiological labeling technology. With the rapid development of computer hardware and software as well as the accumulation of clinical database, the application of deep learning technology in electrocardiogram (ECG) data is becoming more extensive and has made great progress, which provides new ideas for the research of ex vivo cardiac mapping and intelligent labeling of AF substrates. This paper reviewed the research progress in the fields of ECG forward problem, ECG inverse problem, and the application of deep learning in AF labeling, discussed the problems of ex vivo intelligent labeling of AF substrates and the possible approaches to solve them, prospected the challenges and future directions for ex vivo cardiac electrophysiology labeling.

Predictive value of pre-procedural N-terminal pro-B-type natriuretic peptide level for atrial fibrillation recurrence after radiofrequency catheter ablation

Introduction

N-terminal pro-B-type natriuretic peptide (NT-proBNP) has been demonstrated as a valuable risk marker for mortality and morbidity of cardiovascular disease. Recurrence after atrial fibrillation (AF) radiofrequency catheter ablation remains common.

Aim

We investigated the predictive value of the pre-procedural level of NT-proBNP to differentiate high-risk patients for post-ablation AF recurrence.

Material and methods

326 individuals with nonvalvular AF and preserved systolic function after enduring an initial radiofrequency catheter ablation (RFCA) between March 2018 and December 2019 were categorized into a recurrent group and a non-AF recurrent group. The serum NT-proBNP levels were examined before the ablation procedure. The researchers used multivariate logistic regression to find the determinants of AF recurrence.

Results

During a 14-month (interquartile range (IQR): 12-16) median follow-up, AF recurred in 84 (25.8%) patients. Patients in the recurrence group had considerably greater pre-ablation NT-proBNP levels (389.4 vs. 141.7 pg/ml, p < 0.001 in non-paroxysmal AF and 348.0 vs. 99.4 pg/ml, p < 0.001 in paroxysmal AF) as well as a greater left atrium (40 vs. 36 mm, p = 0.01 in non-paroxysmal AF and 38 vs. 36 mm, p = 0.01 in paroxysmal AF) than the non-AF recurrence group. A cut-off value of NT-proBNP ≥ 168.05 pg/ml identified AF recurrence with a sensitivity of 78.6% and specificity of 53.7% (area under ROC curve 0.68, 95% confidence interval (CI) 0.62-0.74, p < 0.001). Kaplan-Meier examination revealed that the elevated NT-proBNP (≥ 168.05 pg/ml) group presented a considerably shorter period without an occurrence compared to the low-NT-proBNP group (18.4 vs. 22.2 months, log-rank p = 0.001). Multivariate cox regression investigation showed that a level of NT-proBNP ≥ 168.05 pg/ml (hazard ratio (HR): 2.89, 95% CI: 1.71-4.903, p < 0.001) was a reliable predictor of AF recurrence after RFCA.

Conclusions

A high pre-ablation NT-proBNP level was associated with AF recurrence, and it was also discovered to be a prognostic factor of recurrence of AF following RFCA.

How synergy between mechanistic and statistical models is impacting research in atrial fibrillation

Atrial fibrillation (AF) with multiple complications, high morbidity and mortality, and low cure rates, has become a global public health problem. Although significant progress has been made in the treatment methods represented by anti-AF drugs and radiofrequency ablation, the therapeutic effect is not as good as expected. The reason is mainly because of our lack of understanding of AF mechanisms. This field has benefited from mechanistic and (or) statistical methodologies. Recent renewed interest in digital twin techniques by synergizing between mechanistic and statistical models has opened new frontiers in AF analysis. In the review, we briefly present findings that gave rise to the AF pathophysiology and current therapeutic modalities. We then summarize the achievements of digital twin technologies in three aspects: understanding AF mechanisms, screening anti-AF drugs and optimizing ablation strategies. Finally, we discuss the challenges that hinder the clinical application of the digital twin heart. With the rapid progress in data reuse and sharing, we expect their application to realize the transition from AF description to response prediction.

mTOR Modulation of IKr through hERG1b-Dependent Mechanisms in Lipotoxic Heart

In the atria, the rapid delayed rectifier channel (IKr) is a critical contributor to repolarization. In lipotoxic atria, increased activity of the serine/threonine mammalian target of rapamycin (mTOR) may remodel IKr and predispose patients to arrhythmias. To investigate whether mTOR produced defects in IKr channel function (protein expression and gating mechanisms), electrophysiology and biochemical assays in HEK293 cells stably expressing hERG1a/1b, and adult guinea pig atrial myocytes were used. Feeding with the saturated fatty acid palmitic acid high-fat diet (HFD) was used to induce lipotoxicity. Lipotoxicity-challenged HEK293 cells displayed an increased density of hERG1a/1b currents due to a targeted and significant increase in hERG1b protein expression. Furthermore, lipotoxicity significantly slowed the hERG1a/1b inactivation kinetics, while the activation and deactivation remained essentially unchanged. mTOR complex 1 (mTORC1) inhibition with rapamycin (RAP) reversed the increase in hERG1a/1b density and inactivation. Compared to lipotoxic myocytes, RAP-treated cells displayed action potential durations (APDs) and IKr densities similar to those of controls. HFD feeding triggered arrhythmogenic changes (increased the IKr density and shortened the APD) in the atria, but this was not observed in low-fat-fed controls. The data are the first to show the modulation of IKr by mTORC1, possibly through the remodeling of hERG1b, in lipotoxic atrial myocytes. These results offer mechanistic insights with implications for targeted therapeutic options for the therapy of acquired supraventricular arrhythmias in obesity and associated pathologies.

Identifying locations susceptible to micro-anatomical reentry using a spatial network representation of atrial fibre maps

Micro-anatomical reentry has been identified as a potential driver of atrial fibrillation (AF). In this paper, we introduce a novel computational method which aims to identify which atrial regions are most susceptible to micro-reentry. The approach, which considers the structural basis for micro-reentry only, is based on the premise that the accumulation of electrically insulating interstitial fibrosis can be modelled by simulating percolation-like phenomena on spatial networks. Our results suggest that at high coupling, where micro-reentry is rare, the micro-reentrant substrate is highly clustered in areas where the atrial walls are thin and have convex wall morphology, likely facilitating localised treatment via ablation. However, as transverse connections between fibres are removed, mimicking the accumulation of interstitial fibrosis, the substrate becomes less spatially clustered, and the bias to forming in thin, convex regions of the atria is reduced, possibly restricting the efficacy of localised ablation. Comparing our algorithm on image-based models with and without atrial fibre structure, we find that strong longitudinal fibre coupling can suppress the micro-reentrant substrate, whereas regions with disordered fibre orientations have an enhanced risk of micro-reentry. With further development, these methods may be useful for modelling the temporal development of the fibrotic substrate on an individualised basis.

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.

The prognostic significance of left atrial appendage peak flow velocity in the recurrence of persistent atrial fibrillation following first radiofrequency catheter ablation

Background

Atrial fibrillation (AF) relapse following radiofrequency catheter ablation (RFCA) for persistent atrial fibrillation (PeAF) continues to be a concern. This study establishes a connection between left atrial appendage peak flow velocity (LAAV) and recurrence of AF in individuals having PeAF following first RFCA.

Methods

We retrospectively studied 164 successive PeAF patients who had first RFCA between January 2018 and December 2019. Before the ablation, the LAAV was recorded using transesophageal echocardiography (TEE). The demographic and clinical data of the individuals were gathered. Participants were monitored at regular intervals to monitor for recurrence of AF. We employed Cox proportional hazards regression to determine if LAAV, as well as other clinical indicators, were predictive of AF recurrence in follow-up.

Results

In this study, AF relapse was seen in 43 patients (26.2%) following a median follow-up of 15 [interquartile range (IQR): 12–18] months. It was shown that the LAAV was decreased in individuals who had recurrences of AF (0.36±0.05 vs. 0.45±0.17 m/s, P=0.004). Using Kaplan-Meier analysis, it was discovered that the low LAAV (0.37 m/s) group had a poorer event-free survival rate compared to the high LAAV (>0.37 m/s) group (17.6 vs. 21.2 months, log-rank P=0.002) group. Based on the results of the multivariate Cox regression analysis, a LAAV of fewer than 0.37 m/s [hazard ratio (HR): 2.32; 95% confidence interval (CI): 1.177–4.227; P=0.014] was shown to be an independent predictor of AF recurrence following RFCA.

Conclusions

A low LAAV is associated with AF relapse, and it is a predictor of AF relapse following the first RFCA for PeAF. This discovery may be useful in the optimization of treatment strategies and the care of patients with PeAF.

Altered microRNA and mRNA profiles during heart failure in the human sinoatrial node

Heart failure (HF) is frequently accompanied with the sinoatrial node (SAN) dysfunction, which causes tachy-brady arrhythmias and increased mortality. MicroRNA (miR) alterations are associated with HF progression. However, the transcriptome of HF human SAN, and its role in HF-associated remodeling of ion channels, transporters, and receptors responsible for SAN automaticity and conduction impairments is unknown. We conducted comprehensive high-throughput transcriptomic analysis of pure human SAN primary pacemaker tissue and neighboring right atrial tissue from human transplanted HF hearts (n = 10) and non-failing (nHF) donor hearts (n = 9), using next-generation sequencing. Overall, 47 miRs and 832 mRNAs related to multiple signaling pathways, including cardiac diseases, tachy-brady arrhythmias and fibrosis, were significantly altered in HF SAN. Of the altered miRs, 27 are predicted to regulate mRNAs of major ion channels and neurotransmitter receptors which are involved in SAN automaticity (e.g. HCN1, HCN4, SLC8A1) and intranodal conduction (e.g. SCN5A, SCN8A) or both (e.g. KCNJ3, KCNJ5). Luciferase reporter assays were used to validate interactions of miRs with predicted mRNA targets. In conclusion, our study provides a profile of altered miRs in HF human SAN, and a novel transcriptome blueprint to identify molecular targets for SAN dysfunction and arrhythmia treatments in HF.

Understanding PITX2-Dependent Atrial Fibrillation Mechanisms through Computational Models

Atrial fibrillation (AF) is a common arrhythmia. Better prevention and treatment of AF are needed to reduce AF-associated morbidity and mortality. Several major mechanisms cause AF in patients, including genetic predispositions to AF development. Genome-wide association studies have identified a number of genetic variants in association with AF populations, with the strongest hits clustering on chromosome 4q25, close to the gene for the homeobox transcription PITX2. Because of the inherent complexity of the human heart, experimental and basic research is insufficient for understanding the functional impacts of PITX2 variants on AF. Linking PITX2 properties to ion channels, cells, tissues, atriums and the whole heart, computational models provide a supplementary tool for achieving a quantitative understanding of the functional role of PITX2 in remodelling atrial structure and function to predispose to AF. It is hoped that computational approaches incorporating all we know about PITX2-related structural and electrical remodelling would provide better understanding into its proarrhythmic effects leading to development of improved anti-AF therapies. In the present review, we discuss advances in atrial modelling and focus on the mechanistic links between PITX2 and AF. Challenges in applying models for improving patient health are described, as well as a summary of future perspectives.

Fibroblast-Specific Proteotranscriptomes Reveal Distinct Fibrotic Signatures of Human Sinoatrial Node in Nonfailing and Failing Hearts

BACKGROUND

Up to 50% of the adult human sinoatrial node (SAN) is composed of dense connective tissue. Cardiac diseases including heart failure (HF) may increase fibrosis within the SAN pacemaker complex, leading to impaired automaticity and conduction of electric activity to the atria. Unlike the role of cardiac fibroblasts in pathologic fibrotic remodeling and tissue repair, nothing is known about fibroblasts that maintain the inherently fibrotic SAN environment.

METHODS

Intact SAN pacemaker complex was dissected from cardioplegically arrested explanted nonfailing hearts (non-HF; n=22; 48.7±3.1 years of age) and human failing hearts (n=16; 54.9±2.6 years of age). Connective tissue content was quantified from Masson trichrome-stained head-center and center-tail SAN sections. Expression of extracellular matrix proteins, including collagens 1 and 3A1, CILP1 (cartilage intermediate layer protein 1), and POSTN (periostin), and fibroblast and myofibroblast numbers were quantified by in situ and in vitro immunolabeling. Fibroblasts from the central intramural SAN pacemaker compartment (≈10×5×2 mm³) and right atria were isolated, cultured, passaged once, and treated ± transforming growth factor β1 and subjected to comprehensive high-throughput next-generation sequencing of whole transcriptome, microRNA, and proteomic analyses.

RESULTS

Intranodal fibrotic content was significantly higher in SAN pacemaker complex from HF versus non-HF hearts (57.7±2.6% versus 44.0±1.2%; P<0.0001). Proliferating phosphorylated histone 3⁺/vimentin⁺/CD31^- (cluster of differentiation 31) fibroblasts were higher in HF SAN. Vimentin⁺/α-smooth muscle actin⁺/CD31^- myofibroblasts along with increased interstitial POSTN expression were found only in HF SAN. RNA sequencing and proteomic analyses identified unique differences in mRNA, long noncoding RNA, microRNA, and proteomic profiles between non-HF and HF SAN and right atria fibroblasts and transforming growth factor β1-induced myofibroblasts. Specifically, proteins and signaling pathways associated with extracellular matrix flexibility, stiffness, focal adhesion, and metabolism were altered in HF SAN fibroblasts compared with non-HF SAN.

CONCLUSIONS

This study revealed increased SAN-specific fibrosis with presence of myofibroblasts, CILP1, and POSTN-positive interstitial fibrosis only in HF versus non-HF human hearts. Comprehensive proteotranscriptomic profiles of SAN fibroblasts identified upregulation of genes and proteins promoting stiffer SAN extracellular matrix in HF hearts. Fibroblast-specific profiles generated by our proteotranscriptomic analyses of the human SAN provide a comprehensive framework for future studies to investigate the role of SAN-specific fibrosis in cardiac rhythm regulation and arrhythmias.