Endothelial dysfunction and vascular maladaptation in atrial fibrillation

Mitochondrial calcium homeostasis and atrial fibrillation: Mechanisms and therapeutic strategies review

Atrial fibrillation (AF) is tightly linked to mitochondrial dysfunction, calcium (Ca²⁺) imbalance, and oxidative stress. Mitochondrial Ca²⁺ is essential for regulating metabolic enzymes, maintaining the tricarboxylic acid (TCA) cycle, supporting the electron transport chain (ETC), and producing ATP. Additionally, Ca²⁺ modulates oxidative balance by regulating antioxidant enzymes and reactive oxygen species (ROS) clearance. However, Ca²⁺ homeostasis disruptions, particularly overload, result in excessive ROS production, mitochondrial permeability transition pore (mPTP) opening, and oxidative stress-induced damage. These changes lead to mitochondrial dysfunction, Ca²⁺ leakage, and cardiomyocyte apoptosis, driving AF progression and atrial remodeling. Therapeutically, targeting mitochondrial Ca²⁺ homeostasis shows promise in mitigating AF. Moderate Ca²⁺ regulation enhances energy metabolism, stabilizes mitochondrial membrane potential, and bolsters antioxidant defenses by upregulating enzymes like superoxide dismutase and glutathione peroxidase. This reduces ROS generation and facilitates clearance. Proper Ca²⁺ levels also prevent electron leakage and promote mitophagy, aiding in damaged mitochondria removal and reducing ROS accumulation. Future strategies include modulating Ryanodine receptor 2 (RyR2), mitochondrial calcium uniporter (MCU), and sodium-calcium exchanger (NCLX) to control Ca²⁺ overload and oxidative damage. Addressing mitochondrial Ca²⁺ dynamics offers a compelling approach to breaking the cycle of Ca²⁺ overload, oxidative stress, and AF progression. Further research is needed to clarify the mechanisms of mitochondrial Ca²⁺ regulation and its role in AF pathogenesis. This knowledge will guide the development of innovative treatments to improve outcomes and quality of life for AF patients.

Mitochondrial Dysfunction in Atrial Fibrillation: The Need for a Strong Pharmacological Approach

Despite great progress in treating atrial fibrillation (AF), especially with the development of increasingly effective invasive techniques for AF ablation, many unanswered questions remain regarding the pathogenic mechanism of the arrhythmia and its prevention methods. The development of AF is based on anatomical and functional alterations in the cardiomyocyte resulting from altered ionic fluxes and cardiomyocyte electrophysiology. Electric instability and electrical remodeling underlying the arrhythmia may result from oxidative stress, also caused by possible mitochondrial dysfunction. The role of mitochondrial dysfunction in the pathogenesis of AF is not yet fully elucidated; however, the reduction in AF burden after therapeutic interventions that improve mitochondrial fitness tends to support this concept. This selected review aims to summarize the mechanisms of mitochondrial dysfunction related to AF and the current pharmacological treatment options that target mitochondria to prevent or improve the outcome of AF.

Association of induced atrial fibrillation in the electrophysiology laboratory with endothelial dysfunction and documented atrial fibrillation

OBJECTIVE

Atrial fibrillation (AF) is a common arrhythmia that increases morbidity and mortality, as well as healthcare costs. The induction of AF (IAF) during programmed atrial pacing in an electrophysiological study (EPS) is a prevalent phenomenon that has been underappreciated by electrophysiologists. Despite extensive research on AF, only a few studies have focused on this phenomenon. The aim of our study was to investigate the association between history of AF and IAF and the underlying pathophysiological factors such as arterial stiffness, subclinical atherosclerosis, and impaired endothelial function.

METHODS

This cross-sectional and observational study included 87 patients who had palpitations and were scheduled for EPS. Patients underwent biochemical investigations, transthoracic echocardiography, carotid ultrasound, carotid-femoral artery pulse wave velocity (PWV), and flow-mediated dilatation (FMD) measurements before EPS. Patients were divided into two groups, AF-induced and non-induced in EPS, for further statistical analysis.

RESULTS

AF was induced in 16 of 87 patients (18.3%) included in the analysis. The FMD (%) was significantly lower (16.01 ± 10.1 vs. 8.7 ± 5.7, P = 0.022) and, remarkably, the proportion of patients with a history of AF was significantly higher (2.8% vs. 37.5%, P < 0.001) in the IAF group. ROC analysis showed that a documented AF and FMD predicted IAF, with AUC of 0.741 (p = 0.012) and 0.740 (p = 0.001), respectively. Logistic regression analysis revealed that FMD and history of AF were strong predictors of IAF (odds ratio [OR], 0.853; 95% confidence interval [CI] 0.737-0.988; P = 0.034, OR: 10.1, 95% CI 4.9-20.5; P = 0.003, respectively).

CONCLUSION

Endothelial dysfunction and documented AF were associated with IAF during EPS.

Symptom Network and Clusters of the Multidimensional Symptom Experience in Patients With Atrial Fibrillation

BACKGROUND

The symptom network can provide a visual insight into the symptom mechanisms. However, few study authors have explored the multidimensional symptom network of patients with atrial fibrillation (AF).

OBJECTIVES

We aimed to identify the core symptom and symptom clusters of patients with AF by generating a symptom network. Furthermore, we wanted to identify multiple characteristics related to symptom clusters.

METHODS

This is a cross-sectional study. A total of 384 patients with AF at Tianjin Medical University General Hospital were enrolled. The University of Toronto Atrial Fibrillation Severity Scale was used to assess AF symptoms. Network analysis was used to explore the core symptom and symptom cluster.

RESULTS

Shortness of breath at rest ( rs = 1.189, rc = 0.024), exercise intolerance ( rs = 1.116), shortness of breath during physical activity ( rs = 1.055, rc = 0.022), and fatigue at rest ( rc = 0.020) have the top centrality for strength and closeness. The top 3 symptoms of bridge strength were shortness of breath at rest ( rs = 0.264), dizziness ( rs = 0.208), and palpitations ( rs = 0.207). Atrial fibrillation symptoms could be clustered into the breathless cluster and the cardiac cluster. We have identified multiple factors such as mental health status, left ventricular ejection fraction, heart failure, sex, B-type natriuretic peptide, and chronic obstructive pulmonary disease as significant contributors within the breathless cluster, whereas sex, mental health status, and history of radiofrequency ablation were strongly associated with the cardiac cluster, holding promise in elucidating the underlying mechanisms of these symptoms.

CONCLUSION

Special attention should be given to shortness of breath at rest as its core and bridging role in patients' symptoms. Furthermore, both the breathless and cardiac clusters are common among patients. Network analysis reveals direct connections between symptoms, symptom clusters, and their influencing factors, providing a foundation for clinicians to effectively manage patients' symptoms.

Exercise-based cardiac rehabilitation for adults with atrial fibrillation

BACKGROUND

Atrial fibrillation (AF), the most prevalent cardiac arrhythmia, disrupts the heart's rhythm through numerous small re-entry circuits in the atrial tissue, leading to irregular atrial contractions. The condition poses significant health risks, including increased stroke risk, heart failure, and reduced quality of life. Given the complexity of AF and its growing incidence globally, exercise-based cardiac rehabilitation (ExCR) may provide additional benefits for people with AF or those undergoing routine treatment for the condition.

OBJECTIVES

To assess the benefits and harms of ExCR compared with non-exercise controls for people who currently have AF or who have been treated for AF.

SEARCH METHODS

We searched the following electronic databases: CENTRAL in the Cochrane Library, MEDLINE Ovid, Embase Ovid, PsycINFO Ovid, Web of Science Core Collection Thomson Reuters, CINAHL EBSCO, LILACS BIREME, and two clinical trial registers on 24 March 2024. We imposed no language restrictions.

SELECTION CRITERIA

We included randomised clinical trials (RCTs) that investigated ExCR interventions compared with any type of non-exercise control. We included adults 18 years of age or older with any subtype of AF or those who had received treatment for AF.

DATA COLLECTION AND ANALYSIS

Five review authors independently screened and extracted data in duplicate. We assessed risk of bias using Cochrane's RoB 1 tool as outlined in the Cochrane Handbook for Systematic Reviews of Interventions. We assessed clinical and statistical heterogeneity by visual inspection of the forest plots and by using standard Chi² and I² statistics. We performed meta-analyses using random-effects models for continuous and dichotomised outcomes. We calculated standardised mean differences where different scales were used for the same outcome. We used the GRADE approach to assess the certainty of the evidence.

MAIN RESULTS

We included 20 RCTs involving a total of 2039 participants with AF. All trials were conducted between 2006 and 2024, with a follow-up period ranging from eight weeks to five years. We assessed the certainty of evidence as moderate to very low. Five trials assessed comprehensive ExCR programmes, which included educational or psychological interventions, or both; the remaining 15 trials compared exercise-only cardiac rehabilitation with controls. The overall risk of bias in the included studies was mixed. Details on random sequence generation, allocation concealment, and use of intention-to-treat analysis were typically poorly reported. Evidence from nine trials (n = 1173) suggested little to no difference in mortality between ExCR and non-exercise controls (risk ratio (RR) 1.06, 95% confidence interval (CI) 0.76 to 1.49; I² = 0%; 101 deaths; low-certainty evidence). Based on evidence from 10 trials (n = 825), ExCR may have little to no effect on SAEs (RR 1.30, 95% CI 0.63 to 2.67; I² = 0%; 28 events; low-certainty evidence). Evidence from four trials (n = 378) showed that ExCR likely reduced AF recurrence (measured via Holter monitoring) compared to controls (RR 0.70, 95% CI 0.56 to 0.88; I² = 2%; moderate-certainty evidence). ExCR may reduce AF symptom severity (mean difference (MD) -1.59, 95% CI -2.98 to -0.20; I² = 61%; n = 600; low-certainty evidence); likely reduces AF symptom burden (MD -1.61, 95% CI -2.76 to -0.45; I² = 0%; n = 317; moderate-certainty evidence); may reduce AF episode frequency (MD -1.29, 95% CI -2.50 to -0.07; I² = 75%; n = 368; low-certainty evidence); and likely reduces AF episode duration (MD -0.58, 95% CI -1.14 to -0.03; I² = 0%; n = 317; moderate-certainty evidence), measured via the AF Severity Scale (AFSS) questionnaire. Moderate-certainty evidence from six trials (n = 504) showed that ExCR likely improved the mental component summary measure in health-related quality of life (HRQoL) of the 36-item Short Form Health Survey (SF-36) (MD 2.66, 95% CI 1.22 to 4.11; I² = 2%), but the effect of ExCR on the physical component summary measure was very uncertain (MD 1.75, 95% CI -0.31 to 3.81; I² = 52%; very low-certainty evidence). ExCR also may improve individual components of HRQoL (general health, vitality, emotional role functioning, and mental health) and exercise capacity (peak oxygen uptake (VO2peak) and 6-minute walk test) following ExCR. The effects of ExCR on serious adverse events and exercise capacity were consistent across different models of ExCR delivery: centre compared to home-based, exercise dose, exercise only compared to comprehensive programmes, and aerobic training alone compared to aerobic plus resistance programmes. Using univariate meta-regression, there was evidence of significant association between location of trial and length of longest follow-up on exercise capacity.

AUTHORS' CONCLUSIONS

Due to few randomised participants and typically short-term follow-up, the impact of ExCR on all-cause mortality or serious adverse events for people with AF is uncertain. ExCR likely improves AF-specific measures including reduced AF recurrence, symptom burden, and episode duration, as well as the mental components of HRQoL. ExCR may improve AF symptom severity, episode frequency, and VO2peak. Future high-quality RCTs are needed to assess the benefits of ExCR for people with AF on patient-relevant outcomes including AF symptom severity and burden, AF recurrence, AF-specific quality of life, and clinical events such as mortality, readmissions, and serious adverse events. High-quality trials are needed to investigate how AF subtype and clinical setting (i.e. primary and secondary care) may influence ExCR effectiveness.

Spectrum of Non-Obstructive Coronary Artery Disease and Its Relationship with Atrial Fibrillation

This article aims to analyze the relationship between non-obstructive coronary artery disease (NOCAD) and atrial fibrillation (AF), exploring the underlying pathophysiological mechanisms and implications for clinical management. NOCAD and AF are prevalent cardiovascular conditions that often coexist, yet their interrelation is not well understood. NOCAD can lead to ischemic necrosis of cardiomyocytes and their replacement with fibrous tissue, sustaining focal ectopic activity in atrial myocardium. Atrial fibrillation, on the other hand, the most common sustained cardiac arrhythmia, is able to accelerate atherosclerosis and increase oxygen consumption in the myocardium, creating a mismatch between supply and demand, and thus promoting the development or worsening of coronary ischemia. Therefore, NOCAD and AF seem to be a complex interplay with one begets another.

Atrial Fibrillation and Cognitive Disorders

The prevalence of atrial fibrillation among older adults is increasing. Research has indicated that atrial fibrillation is linked to cognitive impairment disorders such as Alzheimer and vascular dementia, as well as Parkinson disease. Various mechanisms are believed to be shared between atrial fibrillation and cognitive impairment disorders. The specific pathologies and mechanisms of different cognitive disorders are still being studied. Potential mechanisms include cerebral hypoperfusion, ischemic or hemorrhagic infarction, and cerebrovascular reactivity to carbon dioxide. Additionally, circulatory biomarkers and certain infectious organisms appear to be involved. This review offers an examination of the overlapping epidemiology between atrial fibrillation and cognitive disorders, explores different cognitive disorders and their connections with this arrhythmia, and discusses trials and guidelines for preventing and treating atrial fibrillation in patients with cognitive disorders. It synthesizes existing knowledge on the management of atrial fibrillation and identifies areas that require further investigation to bridge the gap in understanding the complex relationship between dementia and atrial fibrillation.

One-year Aerobic Interval Training Improves Endothelial Dysfunction in Patients with Atrial Fibrillation: A Randomized Trial

Objective To evaluate the effects of one-year aerobic interval training on endothelial dysfunction in patients with atrial fibrillation. Methods Seventy-four patients with atrial fibrillation (53 men, 21 women; mean age 63±6 years old) were randomized into a 1-year continuous aerobic interval training (CT), 6-month detraining after 6 months of aerobic interval training (DT), or medical treatment only (MT) group. Aerobic interval training was performed 3 times a week for 1 year or 6 months, with an exercise intensity of 85-95% of the peak heart rate. The primary outcome was a change in biomarkers of endothelial dysfunction from baseline at six months or at the one-year follow-up. Results Six-month aerobic interval training reduced von Willebrand factor (CT: 103.7±30.7 IU/dL and DT: 106±31.2 IU/dL vs. MT: 145±47.7 IU/dL, p=0.044). Improvements were maintained with continuous aerobic interval training; however, the values increased again to the baseline levels upon detraining (CT: 84.3±39.1 IU/dL vs. DT: 122.2±27.5 IU/dL and MT: 135.9±50.4 IU/dL, p=0.002). Interleukin 1 beta levels decreased after 6 months of aerobic interval training (CT: 0.59±0.1 pg/mL and DT: 0.63±0.09 pg/mL vs. MT: 0.82±0.28 pg/mL, p=0.031), and the improvement was maintained with continuous aerobic interval training and even after detraining (CT: 0.58±0.08 pg/mL and DT: 0.62±0.09 pg/mL vs. MT: 0.86±0.28 pg/mL, p=0.015). Conclusion One-year aerobic interval training improves endothelial dysfunction in patients with atrial fibrillation and is primarily associated with the reduction in circulating thrombogenic and pro-inflammatory factors. A definitive way to sustain these improvements is the long-term continuation of aerobic training.

Ischemia with Nonobstructive Coronary Artery Disease and Atrial Cardiomyopathy-Two Sides of the Same Story?

Ischemia with nonobstructive coronary artery disease (INOCA) is increasingly recognized as a significant cause of angina, myocardial remodeling, and eventually heart failure (HF). Coronary microvascular dysfunction (CMD) is a major endotype of INOCA, and it is caused by structural and functional alterations of the coronary microcirculation. At the same time, atrial cardiomyopathy (ACM) defined by structural, functional, and electrical atrial remodeling has a major clinical impact due to its manifestations: atrial fibrillation (AF), atrial thrombosis, stroke, and HF symptoms. Both these pathologies share similar risk factors and have a high comorbidity burden. CMD causing INOCA and ACM frequently coexist. Thus, questions arise whether there is a potential link between these pathologies. Does CMD promote AF or the reverse? Which are the mechanisms that ultimately lead to CMD and ACM? Are both part of a systemic disease characterized by endothelial dysfunction? Lastly, which are the therapeutic strategies that can target endothelial dysfunction and improve the prognosis of patients with CMD and ACM? This review aims to address these questions by analyzing the existing body of evidence, offering further insight into the mechanisms of CMD and ACM, and discussing potential therapeutic strategies.

This is Your Brain, and This is Your Brain on Atrial Fibrillation: The Roles of Cardiac Malperfusion Events and Vascular Dysfunction in Cognitive Impairment

AF is an independent and strong predictor of long-term cognitive decline. However, the mechanism for this cognitive decline is difficult to define and likely multifactorial, leading to many different hypotheses. Examples include macro- or microvascular stroke events, biochemical changes to the blood-brain barrier related to anticoagulation, or hypo-hyperperfusion events. This review explores and discusses the hypothesis that AF contributes to cognitive decline and dementia through hypo-hyperperfusion events occurring during cardiac arrhythmias. We briefly explain several brain perfusion imaging techniques and further examine the novel findings associated with changes in brain perfusion in patients with AF. Finally, we discuss the implications and areas requiring more research to further understand and treat patients with cognitive decline related to AF.

Endogenous Glycosaminoglycans in Various Pathologic Plasma Samples as Measured by a Fluorescent Quenching Method

Endogenous glycosaminoglycans (GAGs) with a similar structure to heparin are widely distributed in various tissues. A fluorescence probe, namely Heparin Red, can detect polyanionic GAGs in plasma samples. The purpose of this study is to measure endogenous GAGs in various plasma samples obtained from different pathologic states in comparison to healthy controls utilizing this method. Plasma samples were obtained from patient groups including atrial fibrillation (AF), end-stage-renal-disease (ESRD), diabetes mellitus (DM), sepsis, cancer, liver disease (LD), and pulmonary embolism (PE). Normal human plasma (NHP) was used as healthy controls. The Heparin Red kit from Red Probes (Münster, Germany) was used for the quantification of endogenous GAGs in each sample before and after heparinase I degradation. All results were compiled as group means  ±  SD for comparison. NHP was found to have relatively low levels of endogenous GAGs with a mean concentration of 0.06 μg/mL. The AF, ESRD, DM, and sepsis patient samples had a mean endogenous GAG concentration of 0.55, 0.72, 0.92, and 0.94 μg/mL, respectively. The levels of endogenous GAGs were highest in cancer, LD, and PE patient plasma samples with a mean concentration of 1.95, 2.78, and 2.83 μg/mL, respectively. Heparinase I degradation resulted in a decline in GAG levels in plasma samples. These results clearly show that detectable Heparin Red sensitive endogenous GAGs are present in circulating plasma at varying levels in various patient groups. Additional studies are necessary to understand this complex pathophysiology.

Dyspnea in patients with atrial fibrillation: Mechanisms, assessment and an interdisciplinary and integrated care approach

Atrial fibrillation (AF) is the most common sustained heart rhythm disorder and is often associated with symptoms that can significantly impact quality of life and daily functioning. Palpitations are the cardinal symptom of AF and many AF therapies are targeted towards relieving this symptom. However, up to two-third of patients also complain of dyspnea as a predominant self-reported symptom. In clinical practice it is often challenging to ascertain whether dyspnea represents an AF-related symptom or a symptom of concomitant cardiovascular and non-cardiovascular comorbidities, since common AF comorbidities such as heart failure and chronic obstructive pulmonary disease share similar symptoms. In addition, therapeutic approaches specifically targeting dyspnea have not been well validated. Thus, assessing and treating dyspnea can be difficult. This review describes the latest knowledge on the burden and pathophysiology of dyspnea in AF patients. We discuss the role of heart rhythm control interventions as well as the management of AF risk factors and comorbidities with the goal to achieve maximal relief of dyspnea. Given the different and often complex mechanistic pathways leading to dyspnea, dyspneic AF patients will likely profit from an integrated multidisciplinary approach to tackle all factors and mechanisms involved. Therefore, we propose an interdisciplinary and integrated care pathway for the work-up of dyspnea in AF patients.

Atrial Fibrillation Specific Exercise Rehabilitation: Are We There Yet?

Regular physical activity and exercise training are integral for the secondary prevention of cardiovascular disease. Despite recent advances in more holistic care pathways for people with atrial fibrillation (AF), exercise rehabilitation is not provided as part of routine care. The most recent European Society of Cardiology report for AF management states that patients should be encouraged to undertake moderate-intensity exercise and remain physically active to prevent AF incidence or recurrence. The aim of this review was to collate data from primary trials identified in three systematic reviews and recent real-world cohort studies to propose an AF-specific exercise rehabilitation guideline. Collating data from 21 studies, we propose that 360–720 metabolic equivalent (MET)-minutes/week, corresponding to ~60–120 min of exercise per week at moderate-to-vigorous intensity, could be an evidence-based recommendation for patients with AF to improve AF-specific outcomes, quality of life, and possibly prevent long-term major adverse cardiovascular events. Furthermore, non-traditional, low-moderate intensity exercise, such as Yoga, seems to have promising benefits on patient quality of life and possibly physical capacity and should, therefore, be considered in a personalised rehabilitation programme. Finally, we discuss the interesting concepts of short-term exercise-induced cardioprotection and ‘none-response’ to exercise training with reference to AF rehabilitation.