Computational modeling of cardiac electrophysiology and arrhythmogenesis: toward clinical translation.

The complexity of cardiac electrophysiology, involving dynamic changes in numerous components across multiple spatial (from ion channel to organ) and temporal (from milliseconds to days) scales, makes an intuitive or empirical analysis of cardiac arrhythmogenesis challenging. Multiscale mechanistic computational models of cardiac electrophysiology provide precise control over individual parameters, and their reproducibility enables a thorough assessment of arrhythmia mechanisms. This review provides a comprehensive analysis of models of cardiac electrophysiology and arrhythmias, from the single cell to the organ level, and how they can be leveraged to better understand rhythm disorders in cardiac disease and to improve heart patient care. Key issues related to model development based on experimental data are discussed, and major families of human cardiomyocyte models and their applications are highlighted. An overview of organ-level computational modeling of cardiac electrophysiology and its clinical applications in personalized arrhythmia risk assessment and patient-specific therapy of atrial and ventricular arrhythmias is provided. The advancements presented here highlight how patient-specific computational models of the heart reconstructed from patient data have achieved success in predicting risk of sudden cardiac death and guiding optimal treatments of heart rhythm disorders. Finally, an outlook toward potential future advances, including the combination of mechanistic modeling and machine learning/artificial intelligence, is provided. As the field of cardiology is embarking on a journey toward precision medicine, personalized modeling of the heart is expected to become a key technology to guide pharmaceutical therapy, deployment of devices, and surgical interventions.

Oral Anticoagulants Beyond Warfarin.

Direct oral anticoagulants (DOACs) have largely replaced vitamin K antagonists, mostly warfarin, for the main indications for oral anticoagulation, prevention and treatment of venous thromboembolism, and prevention of embolic stroke in atrial fibrillation. While DOACs offer practical, fixed-dose anticoagulation in many patients, specific restrictions or contraindications may apply. DOACs are not sufficiently effective in high-thrombotic risk conditions such as antiphospholipid syndrome and mechanical heart valves. Patients with cancer-associated thrombosis may benefit from DOACs, but the bleeding risk, particularly in those with gastrointestinal or urogenital tumors, must be carefully weighed. In patients with frailty, excess body weight, and/or moderate-to-severe chronic kidney disease, DOACs must be cautiously administered and may require laboratory monitoring. Reversal agents have been developed and approved for life-threatening bleeding. In addition, the clinical testing of potentially safer anticoagulants such as factor XI(a) inhibitors is important to further optimize anticoagulant therapy in an increasingly elderly and frail population worldwide.

Environmental Exposome and Atrial Fibrillation: Emerging Evidence and Future Directions.

There has been increased awareness of the linkage between environmental exposures and cardiovascular health and disease. Atrial fibrillation is the most common sustained cardiac arrhythmia, affecting millions of people worldwide and contributing to substantial morbidity and mortality. Although numerous studies have explored the role of genetic and lifestyle factors in the development and progression of atrial fibrillation, the potential impact of environmental determinants on this prevalent condition has received comparatively less attention. This review aims to provide a comprehensive overview of the current evidence on environmental determinants of atrial fibrillation, encompassing factors such as air pollution, temperature, humidity, and other meteorologic conditions, noise pollution, greenspace, and the social environment. We discuss the existing evidence from epidemiological and mechanistic studies, critically evaluating the strengths and limitations of these investigations and the potential underlying biological mechanisms through which environmental exposures may affect atrial fibrillation risk. Furthermore, we address the potential implications of these findings for public health and clinical practice and identify knowledge gaps and future research directions in this emerging field.

Air pollution, genetic susceptibility, and the risk of atrial fibrillation: A large prospective cohort study.

To date, no study has explored the extent to which genetic susceptibility modifies the effects of air pollutants on the risk of atrial fibrillation (AF). This study was designed to investigate the separate and joint effects of long-term exposure to air pollutants and genetic susceptibility on the risk of AF events. This study included 401,251 participants without AF at baseline from UK Biobank. We constructed a polygenic risk score and categorized it into three categories. Cox proportional hazards models were fitted to assess the separate and joint effects of long-term exposure to air pollutants and genetics on the risk of AF. Additionally, we further evaluated the effect modification of genetic susceptibility. The hazard ratios and corresponding 95% confidence intervals of incident AF for per interquartile range increase in particulate matter with an aerodynamic diameter smaller than 2.5 µm (PM2.5) or 10 µm (PM10), nitrogen dioxide (NO2), and nitrogen oxide (NOx) were 1.044 (1.025, 1.063), 1.063 (1.044, 1.083), 1.061 (1.042, 1.081), and 1.039 (1.023, 1.055), respectively. For the combined effects, participants exposed to high air pollutants levels and high genetic risk had approximately 149.2% (PM2.5), 181.7% (PM10), 170.2% (NO2), and 157.2% (NOx) higher risk of AF compared to those with low air pollutants levels and low genetic risk, respectively. Moreover, the significant additive interactions between PM10 and NO2 and genetic risk on AF risk were observed, with around 16.4% and 35.1% of AF risk could be attributable to the interactive effects. In conclusion, long-term exposure to air pollutants increases the risk of AF, particularly among individuals with high genetic susceptibility.

Mechanism of PKCε regulation of cardiac GIRK channel gating.

G-protein-gated inwardly rectifying potassium (GIRK) channel activity is regulated by the membrane phospholipid, phosphatidylinositol-4,5-bisphosphate (PI 4,5P2). Constitutive activity of cardiac GIRK channels in atrial myocytes, that is implicated in atrial fibrillation (AF), is mediated via a protein kinase C-ε (PKCε)-dependent mechanism. The novel PKC isoform, PKCε, is reported to enhance the activity of cardiac GIRK channels. Here, we report that PKCε stimulation leads to activation of GIRK channels in mouse atria and in human stem cell-derived atrial cardiomyocytes (iPSCs). We identified residue GIRK4(S418) which when mutated to Ala abolished, or to Glu, mimicked the effects of PKCε on GIRK currents. PKCε strengthened the interactions of the cardiac GIRK isoforms, GIRK4 and GIRK1/4 with PIP2, an effect that was reversed in the GIRK4(S418A) mutant. This mechanistic insight into the PKCε-mediated increase in channel activity because of GIRK4(S418) phosphorylation, provides a precise druggable target to reverse AF-related pathologies due to GIRK overactivity.

ROS in diabetic atria regulate SK2 degradation by Atrogin-1 through the NF-κB signaling pathway.

One of the independent risk factors for atrial fibrillation is diabetes mellitus (DM); however, the underlying mechanisms causing atrial fibrillation in DM are unknown. The underlying mechanism of Atrogin-1-mediated SK2 degradation and associated signaling pathways are unclear. The aim of this study was to elucidate the relationship among reactive oxygen species (ROS), the NF-κB signaling pathway, and Atrogin-1 protein expression in the atrial myocardia of DM mice. We found that SK2 expression was downregulated comitant with increased ROS generation and enhanced NF-κB signaling activation in the atrial cardiomyocytes of DM mice. These observations were mimicked by exogenously applicating H2O2 and by high glucose culture conditions in HL-1 cells. Inhibition of ROS production by diphenyleneiodonium chloride or silencing of NF-κB by siRNA decreased the protein expression of NF-κB and Atrogin-1 and increased that of SK2 in HL-1 cells with high glucose culture. Moreover, chromatin immunoprecipitation assay demonstrated that NF-κB/p65 directly binds to the promoter of the FBXO32 gene (encoding Atrogin-1), regulating the FBXO32 transcription. Finally, we evaluated the therapeutic effects of curcumin, known as a NF-κB inhibitor, on Atrogin-1 and SK2 expression in DM mice and confirmed that oral administration of curcumin for 4 weeks significantly suppressed Atrogin-1 expression and protected SK2 expression against hyperglycemia. In summary, the results from this study indicated that the ROS/NF-κB signaling pathway participates in Atrogin-1-mediated SK2 regulation in the atria of streptozotocin-induced DM mice.

Exenatide reduces atrial fibrillation susceptibility by inhibiting hKv1.5 and hNav1.5 channels.

Exenatide, a promising cardioprotective agent, protects against cardiac structural remodeling and diastolic dysfunction. Combined blockade of sodium and potassium channels is valuable for managing atrial fibrillation (AF). Here, we explored whether exenatide displayed anti-AF effects by inhibiting human Kv1.5 and Nav1.5 channels. We used the whole-cell patch-clamp technique to investigate the effects of exenatide on hKv1.5 and hNav1.5 channels expressed in human embryonic kidney 293 cells and studied the effects of exenatide on action potential (AP) and other cardiac ionic currents in rat atrial myocytes. Additionally, an electrical mapping system was used to explore the effects of exenatide on electrical properties and AF activity in isolated rat hearts. Finally, a rat AF model, established using acetylcholine and calcium chloride, was employed to evaluate the anti-AF potential of exenatide in rats. Exenatide reversibly suppressed IKv1.5 with IC50 of 3.08 µM, preferentially blocked the hKv1.5 channel in its closed state, and positively shifted the voltage-dependent activation curve. Exenatide also reversibly inhibited INav1.5 with IC50 of 3.30 µM, negatively shifted the voltage-dependent inactivation curve, and slowed its recovery from inactivation with significant use-dependency at 5 and 10 Hz. Furthermore, exenatide prolonged AP duration and suppressed the sustained K+ current (Iss) and transient outward K+ current (Ito), but without inhibition of L-type Ca2+ current (ICa,L) in rat atrial myocytes. Exenatide prevented AF incidence and duration in rat hearts and rats. These findings demonstrate that exenatide inhibits IKv1.5 and INav1.5in vitro and reduces AF susceptibility in isolated rat hearts and rats.

Risk of Stroke or Systemic Embolism According to Baseline Frequency and Duration of Subclinical Atrial Fibrillation: Insights From the ARTESiA Trial.

BACKGROUND: In the ARTESiA trial (Apixaban for the Reduction of Thromboembolism in Patients With Device-Detected Subclinical Atrial Fibrillation), apixaban, compared with aspirin, reduced stroke or systemic embolism in patients with device-detected subclinical atrial fibrillation (SCAF). Clinical guidelines recommend considering SCAF episode duration when deciding whether to prescribe oral anticoagulation for this population. METHODS: We performed a retrospective cohort study in ARTESiA. Using Cox regression adjusted for CHA2DS2-VASc score and treatment allocation (apixaban or aspirin), we assessed frequency of SCAF episodes and duration of the longest SCAF episode in the 6 months before randomization as predictors of stroke risk and of apixaban treatment effect. RESULTS: Among 3986 patients with complete baseline SCAF data, 703 (17.6%) had no SCAF episode ≥6 minutes in the 6 months before enrollment. Among 3283 patients (82.4%) with ≥1 episode of SCAF ≥6 minutes in the 6 months before enrollment, 2542 (77.4%) had up to 5 episodes, and 741 (22.6%) had ≥6 episodes. The longest episode lasted <1 hour in 1030 patients (31.4%), 1 to <6 hours in 1421 patients (43.3%), and >6 hours in 832 patients (25.3%). Higher baseline SCAF frequency was not associated with increased risk of stroke or systemic embolism: 1.1% for 1 to 5 episodes versus 1.2%/patient-year for ≥6 episodes (adjusted hazard ratio, 0.89 [95% CI, 0.59-1.34]). In an exploratory analysis, patients with previous SCAF but no episode ≥6 minutes in the 6 months before enrollment had a lower risk of stroke or systemic embolism than patients with at least one episode during that period (0.5% versus 1.1%/patient-year; adjusted hazard ratio, 0.48 [95% CI, 0.27-0.85]). The frequency of SCAF did not modify the reduction in stroke or systemic embolism with apixaban (Pinteraction=0.1). The duration of the longest SCAF episode in the 6 months before enrollment was not associated with the risk of stroke or systemic embolism during follow-up (<1 hour: 1.0%/patient-year [reference]; 1-6 hours: 1.2%/patient-year [adjusted hazard ratio, 1.27 (95% CI, 0.85-1.90)]; >6 hours: 1.0%/patient-year [adjusted hazard ratio, 1.02 (95% CI, 0.63-1.66)]). SCAF duration did not modify the reduction in stroke or systemic embolism with apixaban (Ptrend=0.1). CONCLUSIONS: In ARTESiA, baseline SCAF frequency and longest episode duration were not associated with risk of stroke or systemic embolism and did not modify the effect of apixaban on reduction of stroke or systemic embolism. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01938248.

Arterial Thromboembolism in Patients With Atrial Fibrillation and CHA2DS2-VASc Score 1: A Nationwide Study.

BACKGROUND: Oral anticoagulation is suggested in patients with atrial fibrillation and a CHA2DS2-VASc score ≥1 (congestive heart failure, hypertension, age ≥75 years, diabetes, stroke, vascular disease, age 65-74 years, and sex score). To assess granular differences within CHA2DS2-VASc 1, the incidence of arterial thromboembolism according to CHA2DS2-VASc 1 subgroups was examined. METHODS: The Danish National Patient Registry and the Danish Prescription Registry were linked on a nationwide level to identify patients with atrial fibrillation from 2000 to 2021 without oral anticoagulation and categorized according to CHA2DS2-VASc score: CHA2DS2-VASc 0 (male and female subjects); CHA2DS2-VASc 1 (hypertension, heart failure, diabetes, vascular disease, and age 65-74 years); or CHA2DS2-VASc 2 (age ≥75 years without other risk factors). Female sex was not considered a risk factor in any risk group. The outcome was arterial thromboembolism (ischemic stroke, embolism of extremity, or transient cerebral ischemia). Study groups were compared using Cox regression analysis. RESULTS: We included 26 701 patients with a CHA2DS2-VASc 0 score; 22 915 with CHA2DS2-VASc 1 (1483 patients with heart failure, 9066 with hypertension, 843 with diabetes, 770 with vascular disease, and 10 753 who were 65 to 74 years of age); and 14 525 patients with CHA2DS2-VASc 2 (≥75 years of age without other risk factors). With a median of 1 year of observation time, the cumulative incidence of arterial thromboembolism was 0.6% (n=154 [95% CI, 0.6%-0.8%]), 1.4% (n=16 [95% CI, 0.8%-2.2%]), 1.9% (n=141 [95% CI, 1.6%-2.2%]), 1.7% (n=12 [95% CI, 0.9%-2.9%]), 2.0% (n=13 [95% CI, 1.1%-3.4%]), 2.3% (n=187 [95% CI, 2.0%-2.7%]), and 4.4% (n=533 [95% CI, 4.1%-4.8%]) for CHA2DS2-VASc 0, heart failure, hypertension, diabetes, vascular disease, age 65 to 74 years (CHA2DS2-VASc 1), and age ≥75 years (CHA2DS2-VASc 2), respectively. No statistically significant difference was identified among subgroups of CHA2DS2-VASc 1 (P=0.15 for difference). CONCLUSIONS: For patients with atrial fibrillation, all subgroups of CHA2DS2-VASc 1 were associated with lower incidence of arterial thromboembolism compared with age ≥75 years without other risk factors (ie, CHA2DS2-VASc 2) and a higher incidence compared with CHA2DS2-VASc 0. No statistically significant difference was identified between the subgroups of CHA2DS2-VASc 1. These findings support current recommendations that patients within this intermediate risk group could be identified with a similar risk of arterial thromboembolism.

Clonal Hematopoiesis of Indeterminate Potential With Loss of Tet2 Enhances Risk for Atrial Fibrillation Through Nlrp3 Inflammasome Activation.

BACKGROUND: Clonal hematopoiesis of indeterminate potential (CHIP), a common age-associated phenomenon, associates with increased risk of both hematological malignancy and cardiovascular disease. Although CHIP is known to increase the risk of myocardial infarction and heart failure, the influence of CHIP in cardiac arrhythmias, such as atrial fibrillation (AF), is less explored. METHODS: CHIP prevalence was determined in the UK Biobank, and incident AF analysis was stratified by CHIP status and clone size using Cox proportional hazard models. Lethally irradiated mice were transplanted with hematopoietic-specific loss of Tet2, hematopoietic-specific loss of Tet2 and Nlrp3, or wild-type control and fed a Western diet, compounded with or without NLRP3 (NLR [NACHT, LRR {leucine rich repeat}] family pyrin domain containing protein 3) inhibitor, NP3-361, for 6 to 9 weeks. Mice underwent in vivo invasive electrophysiology studies and ex vivo optical mapping. Cardiomyocytes from Ldlr-/- mice with hematopoietic-specific loss of Tet2 or wild-type control and fed a Western diet were isolated to evaluate calcium signaling dynamics and analysis. Cocultures of pluripotent stem cell-derived atrial cardiomyocytes were incubated with Tet2-deficient bone marrow-derived macrophages, wild-type control, or cytokines IL-1ß (interleukin 1ß) or IL-6 (interleukin 6). RESULTS: Analysis of the UK Biobank showed individuals with CHIP, in particular TET2 CHIP, have increased incident AF. Hematopoietic-specific inactivation of Tet2 increases AF propensity in atherogenic and nonatherogenic mouse models and is associated with increased Nlrp3 expression and CaMKII (Ca2+/calmodulin-dependent protein kinase II) activation, with AF susceptibility prevented by inactivation of Nlrp3. Cardiomyocytes isolated from Ldlr-/- mice with hematopoietic inactivation of Tet2 and fed a Western diet have impaired calcium release from the sarcoplasmic reticulum into the cytosol, contributing to atrial arrhythmogenesis. Abnormal sarcoplasmic reticulum calcium release was recapitulated in cocultures of cardiomyocytes with the addition of Tet2-deficient macrophages or cytokines IL-1ß or IL-6. CONCLUSIONS: We identified a modest association between CHIP, particularly TET2 CHIP, and incident AF in the UK Biobank population. In a mouse model of AF resulting from hematopoietic-specific inactivation of Tet2, we propose altered calcium handling as an arrhythmogenic mechanism, dependent on Nlrp3 inflammasome activation. Our data are in keeping with previous studies of CHIP in cardiovascular disease, and further studies into the therapeutic potential of NLRP3 inhibition for individuals with TET2 CHIP may be warranted.

Pulsed Field Ablation to Treat Paroxysmal Atrial Fibrillation: Safety and Effectiveness in the AdmIRE Pivotal Trial.

BACKGROUND: Evidence from clinical trials of early pulsed field ablation (PFA) systems in treating atrial fibrillation has demonstrated their promising potential to reduce complications associated with conventional thermal modalities while maintaining efficacy. However, the lack of a fully integrated mapping system, a staple technology of most modern electrophysiology procedures, poses limitations in lesion creation and workflow options. A novel variable-loop PFA catheter integrated with an electroanatomic mapping system has been developed that allows for real-time nonfluoroscopic procedural guidance and lesion indexing as well as feedback of tissue-to-catheter proximity. AdmIRE (Assessment of Safety and Effectiveness in Treatment Management of Atrial Fibrillation With the Bosense-Webster Irreversible Electroporation Ablation System), a multicenter, single-arm, Food and Drug Administration investigational device exemption study, evaluated the long-term safety and effectiveness of this integrated PFA system in a large United States-based drug-refractory symptomatic paroxysmal atrial fibrillation patient population. METHODS: Using the PFA catheter with a compatible electroanatomic mapping system, patients with drug-refractory symptomatic paroxysmal atrial fibrillation underwent pulmonary vein isolation. The primary safety end point was primary adverse event within 7 days of ablation. The primary effectiveness end point was a composite end point that included 12-month freedom from documented atrial tachyarrhythmia (ie, atrial fibrillation, atrial tachycardia, atrial flutter) episodes, failure to achieve pulmonary vein isolation, use of a nonstudy catheter for pulmonary vein isolation, repeat procedure (except for one redo during blanking), taking a new or previously failed class I or III antiarrhythmic drug at higher dose after blanking, or direct current cardioversion after blanking. RESULTS: At 30 centers, 277 patients with paroxysmal atrial fibrillation (61.5±10.3 years of age; 64.3% male) in the pivotal cohort underwent PFA. More than 25% of the procedures were performed without fluoroscopy. Median (Q1, Q3) pulmonary vein isolation procedure, fluoroscopy, and transpired PFA application times were 81.0 (61.0, 112.0), 7.1 (0.00, 14.3), and 31.0 (24.8, 40.9) minutes, respectively. The primary adverse event rate was 2.9% (8 of 272), with the most common complication being pericardial tamponade. The 12-month primary effectiveness end point was 74.6%. The 1-year freedom from atrial fibrillation, atrial tachycardia, or atrial flutter recurrence rate after blanking was 75.4%. Substantial improvements in quality of life were observed as early as 3 months after the procedure, concurrent with a reduction in multiple health care use measures. CONCLUSIONS: AdmIRE confirmed the safety and effectiveness of the variable-loop PFA catheter, with short procedure and PFA application times and low fluoroscopy exposure. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT05293639.

Ablation Strategies for Repeat Procedures in Atrial Fibrillation Recurrences Despite Durable Pulmonary Vein Isolation: The Prospective Randomized ASTRO AF Multicenter Trial.

BACKGROUND: Ablation strategies for patients with symptomatic atrial fibrillation and isolated pulmonary veins vary and their effects on arrhythmia recurrence remain unclear. A prospective randomized German multicenter trial sought to compare 2 ablation strategies in this patient cohort. METHODS: Patients with atrial fibrillation despite durable pulmonary vein isolation were randomly assigned at 7 centers to undergo low-voltage area ablation using 3-dimensional mapping and irrigated radiofrequency current ablation (group A) or empirical left atrial appendage isolation (LAAI) using the cryoballoon followed by staged interventional left atrial appendage closure (group B). The primary end point was freedom from atrial tachyarrhythmias between 91 and 365 days after index ablation. The study was powered for superiority of LAAI compared with low-voltage area. RESULTS: Patients (40% women; mean age, 68.8±8 years) with paroxysmal (32%) or persistent atrial fibrillation (68%) were randomized to undergo low-voltage area ablation (n=79) or cryoballoon-guided LAAI (n=82). After a planned interim analysis, enrollment was halted for futility on January 10, 2023. In the LAAI group, 77 of 82 left atrial appendages were successfully isolated with subsequent left atrial appendage closure in 57 patients. Procedure-related complications occurred in 4 (5%) and 11 (13.5%) patients in group A and B, respectively (P=0.10). The median follow-up was 367 days (interquartile range, 359-378). The Kaplan-Meier point estimate for freedom from atrial tachyarrhythmias was 51.7% (CI, 40.9%-65.4%) for group A and 55.5% (CI, 44.4%-69.2%; P=0.8069) for group B. CONCLUSIONS: The current study did not detect superiority of cryoballoon-guided LAAI over low-voltage area ablation in patients with atrial fibrillation despite durable PVI. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT04056390.

Frequent Premature Atrial Contractions Lead to Adverse Atrial Remodeling and Atrial Fibrillation in a Swine Model.

BACKGROUND: Frequent premature atrial complexes (PACs) are associated with future incident atrial fibrillation (AF), but whether PACs contribute to development of AF through adverse atrial remodeling has not been studied. This study aimed to explore the effect of frequent PACs from different sites on atrial remodeling in a swine model. METHODS: Forty swine underwent baseline electrophysiologic studies and echocardiography followed by pacemaker implantations and paced PACs (50% burden) at 250-ms coupling intervals for 16 weeks in 4 groups: (1) lateral left atrium (LA) PACs by the coronary sinus (Lat-PAC; n=10), (2) interatrial septal PACs (Sep-PAC; n=10), (3) regular LA pacing at 130 beats/min (Reg-130; n=10), and (4) controls without PACs (n=10). At the final study, repeat studies were performed, followed by tissue histology and molecular analyses focusing on fibrotic pathways. RESULTS: Lat-PACs were associated with a longer P-wave duration (93.0±9.0 versus 74.2±8.2 and 58.8±7.6 ms; P<0.001) and greater echocardiographic mechanical dyssynchrony (57.5±11.6 versus 35.7±13.0 and 24.4±11.1 ms; P<0.001) compared with Sep-PACs and controls, respectively. After 16 weeks, Lat-PACs led to slower LA conduction velocity (1.1±0.2 versus 1.3±0.2 [Sep-PAC] versus 1.3±0.1 [Reg-130] versus 1.5±0.2 [controls] m/s; P<0.001) without significant change in atrial ERP. The Lat-PAC group had a significantly increased percentage of LA fibrosis and upregulated levels of extracellular matrix proteins (lysyl oxidase and collagen 1 and 8), as well as TGF-ß1 (transforming growth factor-ß1) signaling proteins (latent and monomer TGF-ß1 and phosphorylation/total ratio of SMAD2/3; P<0.05). The Lat-PAC group had the longest inducible AF duration (terminal to baseline: 131 [interquartile range 30, 192] seconds versus 16 [6, 26] seconds [Sep-PAC] versus 22 [11, 64] seconds [Reg-130] versus -1 [-16, 7] seconds [controls]; P<0.001). CONCLUSIONS: In this swine model, frequent PACs resulted in adverse atrial structural remodeling with a heightened propensity to AF. PACs originating from the lateral LA produced greater atrial remodeling and longer induced AF duration than the septal-origin PACs. These data provide evidence that frequent PACs can cause adverse atrial remodeling as well as AF, and that the location of ectopic PACs may be clinically meaningful.

Safety of Switching From a Vitamin K Antagonist to a Non-Vitamin K Antagonist Oral Anticoagulant in Frail Older Patients With Atrial Fibrillation: Results of the FRAIL-AF Randomized Controlled Trial.

BACKGROUND: There is ambiguity whether frail patients with atrial fibrillation managed with vitamin K antagonists (VKAs) should be switched to a non-vitamin K oral anticoagulant (NOAC). METHODS: We conducted a pragmatic, multicenter, open-label, randomized controlled superiority trial. Older patients with atrial fibrillation living with frailty (≥75 years of age plus a Groningen Frailty Indicator score ≥3) were randomly assigned to switch from international normalized ratio-guided VKA treatment to an NOAC or to continued VKA treatment. Patients with a glomerular filtration rate <30 mL·min-1·1.73 m-2 or with valvular atrial fibrillation were excluded. Follow-up was 12 months. The cause-specific hazard ratio was calculated for occurrence of the primary outcome that was a major or clinically relevant nonmajor bleeding complication, whichever came first, accounting for death as a competing risk. Analyses followed the intention-to-treat principle. Secondary outcomes included thromboembolic events. RESULTS: Between January 2018 and June 2022, a total of 2621 patients were screened for eligibility and 1330 patients were randomly assigned (mean age 83 years, median Groningen Frailty Indicator score 4). After randomization, 6 patients in the switch-to-NOAC arm and 1 patient in the continue-with-VKA arm were excluded due to the presence of exclusion criteria, leaving 662 patients switched from a VKA to an NOAC and 661 patients continued VKAs in the intention-to-treat population. After 163 primary outcome events (101 in the switch arm, 62 in the continue arm), the trial was stopped for futility according to a prespecified futility analysis. The hazard ratio for our primary outcome was 1.69 (95% CI, 1.23-2.32). The hazard ratio for thromboembolic events was 1.26 (95% CI, 0.60-2.61). CONCLUSIONS: Switching international normalized ratio-guided VKA treatment to an NOAC in frail older patients with atrial fibrillation was associated with more bleeding complications compared with continuing VKA treatment, without an associated reduction in thromboembolic complications. REGISTRATION: URL: https://eudract.ema.europa.eu; Unique identifier: 2017-000393-11. URL: https://eudract.ema.europa.eu; Unique identifier: 6721 (FRAIL-AF study).

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

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Association of Atrial Fibrillation Burden and Mortality Among Patients With Cardiac Implantable Electronic Devices.

BACKGROUND: Current estimates of atrial fibrillation (AF)-associated mortality rely on claims- or clinical-derived diagnoses of AF, limit AF to a binary entity, or are confounded by comorbidities. The objective of the present study is to assess the association between device-recognized AF and mortality among patients with cardiac implantable electronic devices capable of sensitive and continuous atrial arrhythmia detection. Secondary outcomes include relative mortality among cohorts with no AF, paroxysmal AF, persistent AF, and permanent AF. METHODS: Using the deidentified Optum Clinformatics US claims database (2015 to 2020) linked to the Medtronic CareLink database, we identified individuals with a cardiac implantable electronic device who transmitted data ≥6 months after implantation. AF burden was assessed during the first 6 months after implantation (baseline period). Subsequent mortality, assessed from claims data, was compared between patients with and without AF, with adjustment for age, geographic region, insurance type, Charlson Comorbidity Index, and implantation year. RESULTS: Of 21 391 patients (age, 72.9±10.9 years; 56.3% male) analyzed, 7798 (36.5%) had device-recognized AF. During a mean of 22.4±12.9 months (median, 20.1 [12.8-29.7] months) of follow-up, the overall incidence of mortality was 13.5%. Patients with AF had higher adjusted all-cause mortality than patients without AF (hazard ratio, 1.29 [95% CI, 1.20-1.39]; P<0.001). Among those with AF, patients with nonparoxysmal AF had the greatest risk of mortality (persistent AF versus paroxysmal AF: hazard ratio, 1.36 [95% CI, 1.18-1.58]; P<.001; permanent AF versus paroxysmal AF: hazard ratio, 1.23 [95% CI, 1.14-1.34]; P<.001). CONCLUSIONS: After adjustment for potential confounding factors, the presence of AF was associated with higher mortality in our cohort of patients with cardiac implantable electronic devices. Among those with AF, nonparoxysmal AF was associated with the greatest risk of mortality.

Neurofilament Light Chain and Risk of Stroke in Patients With Atrial Fibrillation.

BACKGROUND: Biomarkers reflecting brain injury are not routinely used in risk assessment of stroke in atrial fibrillation (AF). Neurofilament light chain (NFL) is a novel biomarker released into blood after cerebral insults. We investigated the association between plasma concentrations of NFL, other biomarkers, and risk of stroke and death in patients with AF not receiving oral anticoagulation. METHODS: For this observational study, baseline plasma samples were available from 3077 patients with AF randomized to aspirin in ACTIVE A (Atrial Fibrillation Clopidogrel Trial With Irbesartan for Prevention of Vascular Events; 2003 to 2008) and AVERROES (Apixaban Versus Acetylsalicylic Acid [ASA] to Prevent Stroke in Atrial Fibrillation Patients Who Have Failed or Are Unsuitable for Vitamin K Antagonist Treatment; 2007 to 2009). Median follow-up was 1.5 years. NFL was analyzed with a Single Molecule Array (Simoa). Associations with outcomes (total stroke or systemic embolism, ischemic stroke, cardiovascular death, and all-cause death) were explored with Cox regression models. RESULTS: In the combined cohort, the median NFL level was 16.9 ng/L (interquartile range, 11.1-26.5 ng/L), the median age was 71 years, 58% were men, and 13% had a history of previous stroke. NFL was associated with older age, higher creatinine, lower body mass index, previous stroke, female sex, and diabetes but not cardiac rhythm. Higher NFL was associated with a higher risk of stroke or systemic embolism (n=206) independently of clinical characteristics (hazard ratio, 1.27 [95% CI, 1.10-1.46] per doubling of NFL) and other biomarkers (hazard ratio, 1.18 [95% CI, 1.01-1.37]) and including in patients without previous stroke (hazard ratio, 1.23 [95% CI, 1.02-1.48]). NFL was also independently associated with cardiovascular (n=219) and all-cause (n=311) death. The C index for stroke using only NFL was 0.642, on par with the currently used clinical risk scores. Addition of information on NFL improved discrimination in a model also including clinical information, NT-proBNP (N-terminal pro-B-type natriuretic peptide), and high-sensitivity cardiac troponin T, yielding a C index of 0.727. CONCLUSIONS: NFL reflects overt and covert episodes of cerebral ischemia and improves risk assessment of stroke and death in patients with AF without oral anticoagulation, including in patients without previous stroke. The combination of NFL with information on age, history of stroke, and other biomarkers should be explored as a future avenue for stroke risk assessments in patients with AF.

Direct Oral Anticoagulants for Stroke Prevention in Patients With Device-Detected Atrial Fibrillation: A Study-Level Meta-Analysis of the NOAH-AFNET 6 and ARTESiA Trials.

BACKGROUND: Device-detected atrial fibrillation (also known as subclinical atrial fibrillation or atrial high-rate episodes) is a common finding in patients with an implanted cardiac rhythm device and is associated with an increased risk of ischemic stroke. Whether oral anticoagulation is effective and safe in this patient population is unclear. METHODS: We performed a systematic review of MEDLINE and Embase for randomized trials comparing oral anticoagulation with antiplatelet or no antithrombotic therapy in adults with device-detected atrial fibrillation recorded by a pacemaker, implantable cardioverter defibrillator, cardiac resynchronization therapy device, or implanted cardiac monitor. We used random-effects models for meta-analysis and rated the quality of evidence using the Grading of Recommendations Assessment, Development and Evaluation framework (GRADE). The review was preregistered (PROSPERO CRD42023463212). RESULTS: From 785 citations, we identified 2 randomized trials with relevant clinical outcome data: NOAH-AFNET 6 (Non-Vitamin K Antagonist Oral Anticoagulants in Patients With Atrial High Rate Episodes; 2536 participants) evaluated edoxaban, and ARTESiA (Apixaban for the Reduction of Thrombo-Embolism in Patients With Device-Detected Sub-Clinical Atrial Fibrillation; 4012 participants) evaluated apixaban. Meta-analysis demonstrated that oral anticoagulation with these agents reduced ischemic stroke (relative risk [RR], 0.68 [95% CI, 0.50-0.92]; high-quality evidence). The results from the 2 trials were consistent (I2 statistic for heterogeneity=0%). Oral anticoagulation also reduced a composite of cardiovascular death, all-cause stroke, peripheral arterial embolism, myocardial infarction, or pulmonary embolism (RR, 0.85 [95% CI, 0.73-0.99]; I2=0%; moderate-quality evidence). There was no reduction in cardiovascular death (RR, 0.95 [95% CI, 0.76-1.17]; I2=0%; moderate-quality evidence) or all-cause mortality (RR, 1.08 [95% CI, 0.96-1.21]; I2=0%; moderate-quality evidence). Oral anticoagulation increased major bleeding (RR, 1.62 [95% CI, 1.05-2.50]; I²=61%; high-quality evidence). CONCLUSIONS: The results of the NOAH-AFNET 6 and ARTESiA trials are consistent with each other. Meta-analysis of these 2 large randomized trials provides high-quality evidence that oral anticoagulation with edoxaban or apixaban reduces the risk of stroke in patients with device-detected atrial fibrillation and increases the risk of major bleeding.

Arrhythmic Risk in Biventricular Pacing Compared With Left Bundle Branch Area Pacing: Results From the I-CLAS Study.

BACKGROUND: Left bundle branch area pacing (LBBAP) may be associated with greater improvement in left ventricular ejection fraction and reduction in death or heart failure hospitalization compared with biventricular pacing (BVP) in patients requiring cardiac resynchronization therapy. We sought to compare the occurrence of sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) and new-onset atrial fibrillation (AF) in patients undergoing BVP and LBBAP. METHODS: The I-CLAS study (International Collaborative LBBAP Study) included patients with left ventricular ejection fraction ≤35% who underwent BVP or LBBAP for cardiac resynchronization therapy between January 2018 and June 2022 at 15 centers. We performed propensity score-matched analysis of LBBAP and BVP in a 1:1 ratio. We assessed the incidence of VT/VF and new-onset AF among patients with no history of AF. Time to sustained VT/VF and time to new-onset AF was analyzed using the Cox proportional hazards survival model. RESULTS: Among 1778 patients undergoing cardiac resynchronization therapy (BVP, 981; LBBAP, 797), there were 1414 propensity score-matched patients (propensity score-matched BVP, 707; propensity score-matched LBBAP, 707). The occurrence of VT/VF was significantly lower with LBBAP compared with BVP (4.2% versus 9.3%; hazard ratio, 0.46 [95% CI, 0.29-0.74]; P<0.001). The incidence of VT storm (>3 episodes in 24 hours) was also significantly lower with LBBAP compared with BVP (0.8% versus 2.5%; P=0.013). Among 299 patients with cardiac resynchronization therapy pacemakers (BVP, 111; LBBAP, 188), VT/VF occurred in 8 patients in the BVP group versus none in the LBBAP group (7.2% versus 0%; P<0.001). In 1194 patients with no history of VT/VF or antiarrhythmic therapy (BVP, 591; LBBAP, 603), the occurrence of VT/VF was significantly lower with LBBAP than with BVP (3.2% versus 7.3%; hazard ratio, 0.46 [95% CI, 0.26-0.81]; P=0.007). Among patients with no history of AF (n=890), the occurrence of new-onset AF >30 s was significantly lower with LBBAP than with BVP (2.8% versus 6.6%; hazard ratio, 0.34 [95% CI, 0.16-0.73]; P=0.008). The incidence of AF lasting >24 hours was also significantly lower with LBBAP than with BVP (0.7% versus 2.9%; P=0.015). CONCLUSIONS: LBBAP was associated with a lower incidence of sustained VT/VF and new-onset AF compared with BVP. This difference remained significant after adjustment for differences in baseline characteristics between patients with BVP and LBBAP. Physiological resynchronization by LBBAP may be associated with lower risk of arrhythmias compared with BVP.

Concomitant Left Atrial Appendage Occlusion and Transcatheter Aortic Valve Replacement Among Patients With Atrial Fibrillation.

BACKGROUND: Atrial fibrillation (AF) is common in patients undergoing transcatheter aortic valve replacement (TAVR) and is associated with increased risk of bleeding and stroke. While left atrial appendage occlusion (LAAO) is approved as an alternative to anticoagulants for stroke prevention in patients with AF, placement of these devices in patients with severe aortic stenosis, or when performed at the same time as TAVR, has not been extensively studied. METHODS: WATCH-TAVR (WATCHMAN for Patients with AF Undergoing TAVR) was a multicenter, randomized trial evaluating the safety and effectiveness of concomitant TAVR and LAAO with WATCHMAN in AF patients. Patients were randomized 1:1 to TAVR + LAAO or TAVR + medical therapy. WATCHMAN patients received anticoagulation for 45 days followed by dual antiplatelet therapy until 6 months. Anticoagulation was per treating physician preference for patients randomized to TAVR + medical therapy. The primary noninferiority end point was all-cause mortality, stroke, and major bleeding at 2 years between the 2 strategies. RESULTS: The study enrolled 349 patients (177 TAVR + LAAO and 172 TAVR + medical therapy) between December 2017 and November 2020 at 34 US centers. The mean age of patients was 81 years, and the mean scores for CHA2DS2-VASc and HAS-BLED (Hypertension, Abnormal renal/liver function, Stroke, Bleeding history or predisposition, Labile INR, Elderly, Drugs/alcohol concomitantly) were 4.9 and 3.0, respectively. At baseline, 85.4% of patients were taking anticoagulants and 71.3% patients were on antiplatelet therapy. The cohorts were well-balanced for baseline characteristics. The incremental LAAO procedure time was 38 minutes, and the median contrast volume used for combined procedures was 119 mL versus 70 mL with TAVR alone. At the 24-month follow-up, 82.5% compared with 50.8% of patients were on any antiplatelet therapy, and 13.9% compared with 66.7% of patients were on any anticoagulation therapy in TAVR + LAAO compared with TAVR + medical therapy group, respectively. For the composite primary end point, TAVR + LAAO was noninferior to TAVR + medical therapy (22.7 versus 27.3 events per 100 patient-years for TAVR + LAAO and TAVR + medical therapy, respectively; hazard ratio, 0.86 [95% CI, 0.60-1.22]; Pnoninferiority<0.001). CONCLUSIONS: Concomitant WATCHMAN LAAO and TAVR is noninferior to TAVR with medical therapy in severe aortic stenosis patients with AF. The increased complexity and risks of the combined procedure should be considered when concomitant LAAO is viewed as an alternative to medical therapy for patients with AF undergoing TAVR. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03173534.