Atrial Fibrillation Promotion by Endurance Exercise

Excessive Blood Pressure Rise and Cardiovascular Remodeling in Marathon Runners

Exercise-induced hypertension (EIH) is thought to be associated with increased cardiovascular (CV) risks. However, no previous studies have investigated the effects of EIH on CV systems in marathon runners without CV risk factors using both 24-hr ambulatory blood pressure (BP) monitoring and exercise stress echocardiography (ESE). This study firstly described differences in CV adaptations according to EIH assessed by both exams. Marathon runners between 35 and 64 years of age without CV risk factors were eligible. All the participants underwent both 24-hr ambulatory BP monitoring and ESE. EIH was defined as a maximal exercise systolic BP≥210 mmHg. The EIH group (n=19) had shorter training history and higher exercise intensity compared to the non-EIH group (n=23). The average systolic BP was higher in the EIH group than in the non-EIH group. Left cardiac chamber size and left ventricular mass (LVM) were also higher in the EIH group compared to the non-EIH group. Maximal BP during ESE was positively correlated with both parameters. Exaggerated BP response during exercise needs to be monitored for pre-emptive measurements before it results in progressive cardiovascular maladaptation.

2024 HRS expert consensus statement on arrhythmias in the athlete: Evaluation, treatment, and return to play

Youth and adult participation in sports continues to increase, and athletes may be diagnosed with potentially arrhythmogenic cardiac conditions. This international multidisciplinary document is intended to guide electrophysiologists, sports cardiologists, and associated health care team members in the diagnosis, treatment, and management of arrhythmic conditions in the athlete with the goal of facilitating return to sport and avoiding the harm caused by restriction. Expert, disease-specific risk assessment in the context of athlete symptoms and diagnoses is emphasized throughout the document. After appropriate risk assessment, management of arrhythmias geared toward return to play when possible is addressed. Other topics include shared decision-making and emergency action planning. The goal of this document is to provide evidence-based recommendations impacting all areas in the care of athletes with arrhythmic conditions. Areas in need of further study are also discussed.

Sex-specific and polygenic effects underlying resting heart rate and associated risk of cardiovascular disease

AIMS

Resting heart rate (RHR) is associated with cardiovascular disease (CVD) and mortality. This study aimed to identify genetic loci associated with RHR, develop a genome-wide polygenic risk score (PRS) for RHR, and assess associations between the RHR PRS and CVD outcomes, to better understand the biological mechanisms linking RHR to disease. Sex-specific analyses were conducted to potentially elucidate different pathways between the sexes.

METHODS AND RESULTS

We performed a genome-wide meta-analysis of RHR (n = 550 467) using two independent study populations, The Trøndelag Health Study (HUNT) and the UK Biobank (UKB), comprising 69 155 and 481 312 participants, respectively. We also developed a genome-wide PRS for RHR using UKB and tested for association between the PRS and 13 disease outcomes in HUNT. We identified 403, 253, and 167 independent single nucleotide polymorphisms (SNPs) significantly associated with RHR in the total population, women, and men, respectively. The sex-specified analyses indicated differences in the genetic contribution to RHR and revealed loci significantly associated with RHR in only one of the sexes. The SNPs were mapped to genes enriched in heart tissue and cardiac conduction pathways, as well as disease-pathways, including dilated cardiomyopathy. The PRS for RHR was associated with increased risk of hypertension and dilated cardiomyopathy, and decreased risk of atrial fibrillation.

CONCLUSION

Our findings provide insight into the pleiotropic effects of the RHR variants, contributing towards an improved understanding of mechanisms linking RHR and disease. In addition, the sex-specific results might contribute to a more refined understanding of RHR as a risk factor for the different diseases.

PANoptosis and cardiovascular disease: The preventive role of exercise training

Regulated cell death, including pyroptosis, apoptosis, and necroptosis, is vital for the body's defense system. Recent research suggests that these three types of cell death are interconnected, giving rise to a new concept called PANoptosis. PANoptosis has been linked to various diseases, making it crucial to comprehend its mechanism for effective treatments. PANoptosis is controlled by upstream receptors and molecular signals, which form polymeric complexes known as PANoptosomes. Cell death combines necroptosis, apoptosis, and pyroptosis and cannot be fully explained by any of these processes alone. Understanding pyroptosis, apoptosis, and necroptosis is essential for understanding PANoptosis. Physical exercise has been shown to suppress pyroptotic, apoptotic, and necroptotic signaling pathways by reducing inflammatory factors, proapoptotic factors, and necroptotic factors such as caspases and TNF-alpha. This ultimately leads to a decrease in cardiac structural remodeling. The beneficial effects of exercise on cardiovascular health may be attributed to its ability to inhibit these cell death pathways.

Associated Factors and Mortality of Arrhythmia in Emergency Department: A Narrative Review

Cardiac arrhythmias represent a major concern in the emergency department (ED), particularly given their association with significant morbidity and mortality. This narrative review examines the various factors influencing arrhythmias and their impact on patient outcomes in emergency settings. Managing complex supraventricular and ventricular arrhythmias (VAs) during acute myocardial infarction (AMI) and severe cardiovascular conditions remains challenging, despite advancements in diagnostic and therapeutic techniques. Ventricular arrhythmias frequently forecast worse outcomes during hospital stays and heighten the chances of sudden cardiac death and cardiac arrest, especially within the initial 30 days after a heart attack. The incidence of arrhythmias in ED is increasing due to demographic changes and higher rates of chronic illnesses such as diabetes, hypertension, and chronic kidney disease. These comorbidities, coupled with lifestyle factors such as smoking and alcohol consumption, complicate arrhythmia management, especially among older adults and males. Rapid and precise ECG interpretation in the ED is crucial for identifying specific arrhythmia types and initiating appropriate treatments. Atrial fibrillation (AF), the most prevalent form of rapid heart rhythm originating above the ventricles, notably impacts patient outcomes, particularly in cases of AMI and heart failure. In the ED, managing AF focuses on preventing strokes with thromboprophylaxis and employing risk assessment tools such as CHA2DS2-VASc and HAS-BLED scores. The analysis highlights how risk factors like hypertension, obesity, obstructive sleep apnea (OSA), and diabetes intricately influence the development and worsening of AF. Optimizing AF treatment outcomes requires a multidisciplinary approach involving cardiologists, emergency physicians, and critical care specialists. Future research should prioritize evaluating the effectiveness of preventive and therapeutic interventions for AF, integrating new risk factors and genetic insights to enhance prediction and management strategies. Understanding the factors contributing to arrhythmias and mortality in the ED underscores the importance of timely and accurate diagnostic and therapeutic measures to improve patient care and outcomes.

Reduced plakoglobin increases the risk of sodium current defects and atrial conduction abnormalities in response to androgenic anabolic steroid abuse

Androgenic anabolic steroids (AAS) are commonly abused by young men. Male sex and increased AAS levels are associated with earlier and more severe manifestation of common cardiac conditions, such as atrial fibrillation, and rare ones, such as arrhythmogenic right ventricular cardiomyopathy (ARVC). Clinical observations suggest a potential atrial involvement in ARVC. Arrhythmogenic right ventricular cardiomyopathy is caused by desmosomal gene defects, including reduced plakoglobin expression. Here, we analysed clinical records from 146 ARVC patients to identify that ARVC is more common in males than females. Patients with ARVC also had an increased incidence of atrial arrhythmias and P wave changes. To study desmosomal vulnerability and the effects of AAS on the atria, young adult male mice, heterozygously deficient for plakoglobin (Plako+/-), and wild type (WT) littermates were chronically exposed to 5α-dihydrotestosterone (DHT) or placebo. The DHT increased atrial expression of pro-hypertrophic, fibrotic and inflammatory transcripts. In mice with reduced plakoglobin, DHT exaggerated P wave abnormalities, atrial conduction slowing, sodium current depletion, action potential amplitude reduction and the fall in action potential depolarization rate. Super-resolution microscopy revealed a decrease in NaV1.5 membrane clustering in Plako+/- atrial cardiomyocytes after DHT exposure. In summary, AAS combined with plakoglobin deficiency cause pathological atrial electrical remodelling in young male hearts. Male sex is likely to increase the risk of atrial arrhythmia, particularly in those with desmosomal gene variants. This risk is likely to be exaggerated further by AAS use. KEY POINTS: Androgenic male sex hormones, such as testosterone, might increase the risk of atrial fibrillation in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC), which is often caused by desmosomal gene defects (e.g. reduced plakoglobin expression). In this study, we observed a significantly higher proportion of males who had ARVC compared with females, and atrial arrhythmias and P wave changes represented a common observation in advanced ARVC stages. In mice with reduced plakoglobin expression, chronic administration of 5α-dihydrotestosterone led to P wave abnormalities, atrial conduction slowing, sodium current depletion and a decrease in membrane-localized NaV1.5 clusters. 5α-Dihydrotestosterone, therefore, represents a stimulus aggravating the pro-arrhythmic phenotype in carriers of desmosomal mutations and can affect atrial electrical function.

The impact of lifestyle factors on atrial fibrillation

Atrial fibrillation (AF), with its significant associated morbidity and mortality contributes to significant healthcare utilisation and expenditure. Given its progressively rising incidence, strategies to limit AF development and progression are urgently needed. Lifestyle modification is a potentially potent but underutilised weapon against the AF epidemic. The purpose of this article is to review the role of lifestyle factors as risk factors for AF, outline potential mechanisms of pathogenesis and examine the available evidence for lifestyle intervention in primary and secondary AF prevention. It will also highlight the need for investment by physicians, researchers, health services and governments in order to facilitate delivery of the comprehensive, multidisciplinary AF care that is required to manage this complex and multifactorial disease.

Histological evaluation of cardiac remodelling in equine athletes

Approximately 1-2 per 100,000 young athletes die from sudden cardiac death (SCD) and extreme exercise may be associated with myocardial scar and arrhythmias. Racehorses have a high prevalence of atrial fibrillation (AF) and SCD but the presence of myocardial scar and inflammation has not been evaluated. Cardiac tissues from the left (LAA) and right (RAA) atrial appendages, left ventricular anterior (LVAPM) and posterior (LVPPM) papillary muscles, and right side of the interventricular septum (IVS-R) were harvested from racehorses with sudden cardiac death (SCD, n = 16) or other fatal injuries (OFI, n = 17), constituting the athletic group (ATH, n = 33), and compared to sedentary horses (SED, n = 10). Horses in the ATH group had myocyte hypertrophy at all sites; increased fibrosis at all sites other than the LAA; increased fibroblast infiltration but a reduction in the overall extracellular matrix (ECM) volume in the RAA, LVAPM, and IVS-R compared to SED horses. In this horse model, athletic conditioning was associated with myocyte hypertrophy and a reduction in ECM. There was an excess of fibrocyte infiltration and focal fibrosis that was not present in non-athletic horses, raising the possibility of an exercise-induced pro-fibrotic substrate.

The Role of KACh Channels in Atrial Fibrillation

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

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.

Exercise-Dependent Modulation of Immunological Response Pathways in Endurance Athletes With and Without Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF) is a common arrhythmia characterized by uncoordinated atrial electrical activity. Lone AF occurs in the absence of traditional risk factors and is frequently observed in male endurance athletes, who face a 2- to 5-fold higher risk of AF compared with healthy, moderately active males. Our understanding of how endurance exercise contributes to the pathophysiology of lone AF remains limited. This study aimed to characterize the circulating protein fluctuations during high-intensity exercise as well as explore potential biomarkers of exercise-associated AF.

METHODS AND RESULTS

A prospective cohort of 12 male endurance cyclists between the ages of 40 and 65 years, 6 of whom had a history of exercise-associated AF, were recruited to participate using a convenience sampling method. The circulating proteome was subsequently analyzed using multiplex immunoassays and aptamer-based proteomics before, during, and after an acute high-intensity endurance exercise bout to assess temporality and identify potential markers of AF. The endurance exercise bout resulted in significant alterations to proteins involved in immune modulation (eg, growth/differentiation factor 15), skeletal muscle metabolism (eg, α-actinin-2), cell death (eg, histones), and inflammation (eg, interleukin-6). Subjects with AF differed from those without, displaying modulation of proteins previously known to have associations with incident AF (eg, C-reactive protein, insulin-like growth factor-1, and angiopoietin-2), and also with proteins having no previous association (eg, tapasin-related protein and α2-Heremans-Schmid glycoprotein).

CONCLUSIONS

These findings provide insights into the proteomic response to acute intense exercise, provide mechanistic insights into the pathophysiology behind AF in athletes, and identify targets for future study and validation.

Associations of Dietary and Lifestyle Components with Atrial Fibrillation

Atrial fibrillation (AF) is a prevalent cardiac arrhythmia that still remains a significant health concern, especially due to its consequences, including stroke and heart failure. This review explores the intricate interplay between AF, lifestyle choices, and dietary habits. It is particularly focused on findings from diverse studies about non-pharmacological methods of managing AF. Moreover, its purpose is to elucidate the implementation of lifestyle changes such as physical activity or proper diet choices in the integrated treatment strategy of patients with AF.

Vigorous physical activity and atrial fibrillation in healthy individuals: What is the correct approach?

Sport activity compared to sedentary life is associated with improved wellbeing and risk reduction in many different health conditions including atrial fibrillation (AF). Vigorous physical activity is associated with increased AF risk. We describe four individuals, who regularly perform endurance sport activity and developed AF. We discuss the changes occurring in the heart of endurance athletes and the possible etiology for AF, as well as currently available treatment options in this seemingly healthy population. Although the etiology of AF in the general population differs from the one in the usually younger endurance sport activity population, the treatment options are similar. There are several factors unique to those involved in vigorous physical activity that can influence their management. Despite a lack of evidence, endurance athletes with AF have traditionally been advised to "de-training," to reduce both the amount and intensity of exercise. Some of the current offered treatment options (beta-blockers, class III antiarrhythmic) have a varied range of adverse effect, hindering them unattractive for these individuals. Depending on risk stratification tools, anticoagulation may be indicated. Some suggest an intermittent dosing therapy, while others recommend following current guidelines. AF ablation is recommended in exercising individuals with recurrent, symptomatic AF and/or in those who do not want drug therapy, given its impact on athletic performance, AF treatment decisions should be individualized for those engaging vigorous physical activity, while considering the potential risks, the urgency of returning to training, and the will and expectations of the patient.

Effects of different exercise methods and intensities on the incidence and prognosis of atrial fibrillation

Atrial fibrillation (AF), the most common sustained arrhythmia in clinical practice, exhibits a higher risk of cardiovascular adverse events. Exercise plays a crucial role in AF prevention, but the effects of different exercise types and doses are inconclusive. This review aims to comprehensively explore the most recent evidence and possible mechanisms of diverse exercise modalities concerning AF incidence and therapeutic outcomes. Multiple studies underscore the efficacy of moderate-intensity continuous training (MICT) in reducing AF incidence and symptom burden, rendering it the currently favored exercise therapy for AF patients. High-intensity interval training (HIIT) shows promise, potentially surpassing MICT, especially in reducing age-related AF susceptibility and improving symptoms and exercise capacity. Conversely, prolonged high-intensity endurance exercise exacerbates AF risk due to excessive exercise volume, with potential mechanisms encompassing irreversible atrial remodeling, heightened inflammation, and increased vagal tone. In summation, MICT is a secure strategy for populations in mitigating the risk associated with AF incidence and secondary cardiovascular events and should be encouraged. Also, it is recommended to initiate large-scale clinical intervention trials encompassing a variety of exercise types to delineate the optimal exercise prescription for cardiovascular patients, including those afflicted with AF.

Exercise and Atrial Fibrillation: The Dose Makes the Poison? A Narrative Review

"All things are poison, and nothing is without poison; the dosage alone makes it so a thing is not a poison" (Paracelsus, ~ 1538 AD). This well-known quote seems to aptly summarize the current understanding of the interaction between exercise and atrial fibrillation (AF). A host of data strongly suggests that regular exercise has a protective effect against developing AF. A small but well-conducted group of trials also demonstrates beneficial effects of exercise in the treatment of AF. Recently, however, potentially detrimental effects of large volumes of high-intensity exercise on the probability of developing AF have moved into the sports-cardiological focus. This effect is well documented for elite athletes; data regarding the general population is less clear. This review presents the current data regarding the protective, therapeutic and potentially risk-enhancing effects of exercise regarding AF. The authors demonstrate that the benefits are clear and strongly outweigh the potential disadvantages.

Cardiomyocyte and endothelial cells play distinct roles in the tumour necrosis factor (TNF)-dependent atrial responses and increased atrial fibrillation vulnerability induced by endurance exercise training in mice

AIMS

Endurance exercise is associated with an increased risk of atrial fibrillation (AF). We previously established that adverse atrial remodelling and AF susceptibility induced by intense exercise in mice require the mechanosensitive and pro-inflammatory cytokine tumour necrosis factor (TNF). The cellular and mechanistic basis for these TNF-mediated effects is unknown.

METHODS AND RESULTS

We studied the impact of Tnf excision, in either atrial cardiomyocytes or endothelial cells (using Cre-recombinase expression controlled by Nppa or Tie2 promoters, respectively), on the cardiac responses to six weeks of intense swim exercise training. TNF ablation, in either cell type, had no impact on the changes in heart rate, autonomic tone, or left ventricular structure and function induced by exercise training. Tnf excision in atrial cardiomyocytes did, however, prevent atrial hypertrophy, fibrosis, and macrophage infiltration as well as conduction slowing and increased AF susceptibility arising from exercise training. In contrast, endothelial-specific excision only reduced the training-induced atrial hypertrophy. Consistent with these cell-specific effects of Tnf excision, inducing TNF loss from atrial cardiomyocytes prevented activation of p38MAPKinase, a strain-dependent downstream mediator of TNF signalling, without affecting the atrial stretch as assessed by atrial pressures induced by exercise. Despite TNF's established role in innate immune responses and inflammation, neither acute nor chronic exercise training caused measurable NLRP3 inflammasome activation.

CONCLUSIONS

Our findings demonstrate that adverse atrial remodelling and AF vulnerability induced by intense exercise require TNF in atrial cardiomyocytes whereas the impact of endothelial-derived TNF is limited to hypertrophy modulation. The implications of the cell autonomous effects of TNF and crosstalk between cells in the atria are discussed.

Keeping the Heart Healthy: The Role of Exercise in Cardiac Repair and Regeneration

Significance: Heart failure is often accompanied by a decrease in the number of cardiomyocytes. Although the adult mammalian hearts have limited regenerative capacity, the rate of regeneration is extremely low and decreases with age. Exercise is an effective means to improve cardiovascular function and prevent cardiovascular diseases. However, the molecular mechanisms of how exercise acts on cardiomyocytes are still not fully elucidated. Therefore, it is important to explore the role of exercise in cardiomyocytes and cardiac regeneration. Recent Advances: Recent advances have shown that the effects of exercise on cardiomyocytes are critical for cardiac repair and regeneration. Exercise can induce cardiomyocyte growth by increasing the size and number. It can induce physiological cardiomyocyte hypertrophy, inhibit cardiomyocyte apoptosis, and promote cardiomyocyte proliferation. In this review, we have discussed the molecular mechanisms and recent studies of exercise-induced cardiac regeneration, with a focus on its effects on cardiomyocytes. Critical Issues: There is no effective way to promote cardiac regeneration. Moderate exercise can keep the heart healthy by encouraging adult cardiomyocytes to survive and regenerate. Therefore, exercise could be a promising tool for stimulating the regenerative capability of the heart and keeping the heart healthy. Future Directions: Although exercise is an important measure to promote cardiomyocyte growth and subsequent cardiac regeneration, more studies are needed on how to do beneficial exercise and what factors are involved in cardiac repair and regeneration. Thus, it is important to clarify the mechanisms, pathways, and other critical factors involved in the exercise-mediated cardiac repair and regeneration. Antioxid. Redox Signal. 39, 1088-1107.

Insight into the relationship between resting heart rate and atrial fibrillation: a Mendelian randomization study

AIMS

A low resting heart rate (RHR) implies a more efficient heart function and a lower risk of cardiovascular disease. However, observational studies have reported a U-shaped association between RHR and atrial fibrillation (AF). In contrast, Mendelian randomization (MR) studies have found an inverse causal association between RHR and AF. Hence, the causal nature of the relationship is not clear. The aim is to investigate the causal association and its shape between RHR on AF using linear and non-linear MR (NLMR).

METHODS AND RESULTS

Linear and non-linear MR were performed on individual-level data in the Trøndelag Health Study (HUNT) and UK Biobank (UKB). HUNT consists of 69 155 individuals with 7,062 AF cases, while UKB provides data on 431 852 individuals with 20 452 AF cases. The linear MR found an inverse relationship between RHR and AF with an OR = 0.95 [95% confidence interval (CI): 0.93-0.98] and OR = 0.96 (95% CI: 0.95-0.97) per unit decrease in RHR in HUNT and UKB, respectively. The NLMR was supportive of an inverse linear relationship in both HUNT and UKB for RHR values <90 beats per minute (bpm). Several sensitivity analyses were also consistent.

CONCLUSION

In contrast with the current observational knowledge of RHR and AF, an inverse causal association between RHR and AF was demonstrated in both linear and non-linear MR for RHR values up to 90 bpm. Further exploring the underlying mechanisms of the genetic instrument for RHR may shed light on whether pleiotropy is biasing this association.

Influence of exercise training on the left atrium: implications for atrial fibrillation, heart failure, and stroke

The left atrium (LA) plays a critical role in receiving pulmonary venous return and modulating left ventricular (LV) filling. With the onset of exercise, LA function contributes to the augmentation in stroke volume. Due to the growing focus on atrial imaging, there is now evidence that structural remodeling and dysfunction of the LA is associated with adverse outcomes including incident cardiovascular disease. In patients with established disease, pathological changes in atrial structure and function are associated with exercise intolerance, increased hospital admissions and mortality, independent of left ventricular function. Exercise training is widely recommended in patients with cardiovascular disease to improve patient outcomes and maintain functional capacity. There are widely documented changes in LV function with exercise, yet less attention has been given to the LA. In this review, we first describe LA physiology at rest and during exercise, before exploring its association with cardiac disease outcomes including atrial fibrillation, heart failure, and stroke. The adaptation of the LA to short- and longer-term exercise training is evaluated through review of longitudinal studies of exercise training in healthy participants free of cardiovascular disease and athletes. We then consider the changes in LA structure and function among patients with established disease, where adverse atrial remodeling may be implicated in the disease process. Finally, we consider important future directions for assessment of atrial structure and function using novel imaging modalities, in response to acute and chronic exercise.

Autoimmune Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF) is by far the most common cardiac arrhythmia. In about 3% of individuals, AF develops as a primary disorder without any identifiable trigger (idiopathic or historically termed lone AF). In line with the emerging field of autoantibody-related cardiac arrhythmias, the objective of this study was to explore whether autoantibodies targeting cardiac ion channels can underlie unexplained AF.

METHODS

Peptide microarray was used to screen patient samples for autoantibodies. We compared patients with unexplained AF (n=37 pre-existent AF; n=14 incident AF on follow-up) to age- and sex-matched controls (n=37). Electrophysiological properties of the identified autoantibody were then tested in vitro with the patch clamp technique and in vivo with an experimental mouse model of immunization.

RESULTS

A common autoantibody response against Kir3.4 protein was detected in patients with AF and even before the development of clinically apparent AF. Kir3.4 protein forms a heterotetramer that underlies the cardiac acetylcholine-activated inwardly rectifying K+ current, IKACh. Functional studies on human induced pluripotent stem cell-derived atrial cardiomyocytes showed that anti-Kir3.4 IgG purified from patients with AF shortened action potentials and enhanced the constitutive form of IKACh, both key mediators of AF. To establish a causal relationship, we developed a mouse model of Kir3.4 autoimmunity. Electrophysiological study in Kir3.4-immunized mice showed that Kir3.4 autoantibodies significantly reduced atrial effective refractory period and predisposed animals to a 2.8-fold increased susceptibility to AF.

CONCLUSIONS

To our knowledge, this is the first report of an autoimmune pathogenesis of AF with direct evidence of Kir3.4 autoantibody-mediated AF.

Masters athlete screening study (MASS): incidence of cardiovascular disease and major adverse cardiac events and efficacy of screening over five years

BACKGROUND

The efficacy of cardiovascular screening in Masters athletes (MAs) (≥35 y), and whether screening decreases their risk of major adverse cardiac events (MACEs) is unknown.

PURPOSE

To evaluate the effectiveness of yearly cardiovascular screening, and the incidence of cardiovascular disease (CVD) and MACE over five years.

METHODS AND RESULTS

MAs (≥35 y) without previous history of CVD underwent yearly cardiovascular screening. Participants with an abnormal screen underwent further evaluations. In the initial year, 798 MAs (62.7% male, 55 ± 10 y) were screened; 11.4% (n = 91) were diagnosed with CVD. Coronary artery disease (CAD) was the most common diagnosis (n = 64; 53%). During follow-up, there were an additional 89 CVD diagnoses with an incidence rate of 3.58/100, 4.14/100, 3.74/100, 1.19/100, for years one to four, respectively. The most common diagnoses during follow-up were arrhythmias (n = 33; 37%). Increasing age (OR = 1.047, 95% confidence interval (CI): 1.003-1.094; P = 0.0379), Framingham Risk Score (FRS) (OR = 1.092, 95% CI: 1.031-1.158; P = 0.003), and LDL cholesterol (OR = 1.709, 95% CI: 1.223-2.401; P = 0.002) were predictive of CAD, whereas moderate intensity activity (min/wk) (OR = 0.997, 95% CI: 0.996-0.999; P = 0.002) was protective. Ten MACE (2.8/1000 athlete-years) occurred. All of these MAs were male, and 90% had ≥10% FRS. All underwent further evaluations with only two identified to have obstructive CAD.

CONCLUSION

MACE occurred despite yearly screening. All MAs who had an event had an abnormal screen; however, cardiac functional tests failed to detect underlying CAD in most cases. It may be appropriate to offer computed coronary tomography angiography in MAs with ≥10% FRS to overcome the limitations of functional testing, and to assist with lifestyle and treatment modifications.

Clinical pharmacology of cardiac cyclic AMP in human heart failure: too much or too little?

INTRODUCTION

Cyclic 3', 5'-adenosine monophosphate (cAMP) is a major signaling hub in cardiac physiology. Although cAMP signaling has been extensively studied in cardiac cells and animal models of heart failure (HF), not much is known about its actual amount present inside human failing or non-failing cardiomyocytes. Since many drugs used in HF work via cAMP, it is crucial to determine the status of its intracellular levels in failing vs. normal human hearts.

AREAS COVERED

Only studies performed on explanted/excised cardiac tissues from patients were examined. Studies that contained no data from human hearts or no data on cAMP levels per se were excluded from this perspective's analysis.

EXPERT OPINION

Currently, there is no consensus on the status of cAMP levels in human failing vs. non-failing hearts. Several studies on animal models may suggest maladaptive (e.g. pro-apoptotic) effects of cAMP on HF, advocating for cAMP lowering for therapy, but human studies almost universally indicate that myocardial cAMP levels are deficient in human failing hearts. It is the expert opinion of this perspective that intracellular cAMP levels are too low in human failing hearts, contributing to the disease. Strategies to increase (restore), not decrease, these levels should be pursued in human HF.

The Complex but Fascinating Relationship between Sport and Atrial Fibrillation: From Pathophysiology to the Clinical Scenario

Atrial fibrillation (AF) is the most common cause of hospital admission among all arrhythmias in the general population. Moreover, AF represents the most common arrhythmia in the athletic population as well. The complex but fascinating relationship between sport and atrial fibrillation has not yet been fully clarified. Although the benefits of moderate physical activity in controlling cardiovascular risk factors and in reducing the risk of atrial fibrillation have been widely demonstrated, some concerns have been raised about the potential adverse effects of physical activity. Endurance activity in middle-aged men athletes appears to increase the risk of AF. Several different physiopathological mechanisms may explain the increased risk of AF in endurance athletes, including the imbalance of the autonomic nervous system, changes in left atrial size and function and presence of atrial fibrosis. The goal of this article is to review the epidemiology, pathophysiology and clinical management for AF in athletes, including pharmacological and electrophysiological strategies.

Long-Term Sports Practice and Atrial Fibrillation: An Updated Review of a Complex Relationship

Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice, and it is an enormous burden worldwide because of its high morbidity, disability and mortality. It is generally acknowledged that physical activity (PA) is strongly associated with a significant reduction in the risk of cardiovascular (CV) disease and all-cause mortality. Moreover, it has been observed that moderate and regular physical activity has the potential to reduce the risk of AF, in addition to improving overall well-being. Nevertheless, some studies have associated intense physical activity with an increased risk of AF. This paper aims to review the main related literature to investigate the association between PA and AF incidence and draw pathophysiological and epidemiological conclusions.

The AFLETES Study: Atrial Fibrillation in Veteran Athletes and the Risk of Stroke

OBJECTIVES

Endurance athletes are at an increased risk of atrial fibrillation (AF) when compared with the general population. However, the risk of stroke in athletes with AF is unknown.

DESIGN AND SETTING

We aimed to assess this risk using an international online survey.

PATIENTS

Individuals that had competed in ≥1 competitive events and were ≥40 years old were included.

INTERVENTIONS

Self-reported demographic, medical history, and training history data were collected, and a CHA 2 DS 2 -VASc was calculated.

MAIN OUTCOME MEASURES

Binary logistic regression was used to assess variables associated with AF and stroke.

RESULTS

There were 1002 responses from participants in 41 countries across Africa, Asia, Australasia, Europe, and North and South America, and 942 were included in the final analysis. The average age was 52.4 ± 8.5 years, and 84% were male. The most common sports were cycling (n = 677, 72%), running (n = 558, 59%), and triathlon (n = 245, 26%). There were 190 (20%) individuals who reported AF and 26 individuals (3%) who reported stroke; of which, 14 (54%) had AF. Lifetime exercise dose [odds ratio (OR), 1.02, 95% confidence interval (95% CI),1.00-1.03, P = 0.02] and swimming (OR, 1.56, 95% CI, 1.02-2.39, P = 0.04) were associated with AF in multivariable analysis, independent of other risk factors. Atrial fibrillation was associated with stroke (OR, 4.18, 95% CI, 1.80-9.72, P < 0.01), even in individuals with a low (0/1) CHA 2 DS 2 -VASc score (OR, 4.20, 95% CI, 1.83-9.66, P < 0.01).

CONCLUSIONS

This survey provides early evidence that veteran endurance athletes who develop AF may be at an increased risk of developing stroke, even in those deemed to be at low risk by CHA 2 DS 2 -VASc score.

Effects of training adaption in endurance athletes with atrial fibrillation: protocol for a multicentre randomised controlled trial

Endurance athletes have a high prevalence of atrial fibrillation (AF), probably caused by exercise-induced cardiac remodelling. Athletes diagnosed with AF are often advised to reduce the intensity and amount of training but the efficacy of this intervention has not been investigated in endurance athletes with AF. Effects of detraining in endurance athletes with atrial fibrillation is a two-arm international multicentre randomised (1:1) controlled trial on the effects of a period of training adaption on AF burden in endurance athletes with paroxysmal AF. One-hundred-and-twenty endurance athletes diagnosed with paroxysmal AF are randomised to a 16-week period of intervention (training adaption) or a control group. We define training adaption as training with a heart rate (HR) not exceeding 75% of the individual maximum HR (HRmax), and total duration of weekly training not exceeding 80% of the self-reported average before the study. The control group is instructed to uphold training intensity including sessions with HR ≥85% of HRmax. AF burden is monitored with insertable cardiac monitors, and training intensity with HR chest-straps and connected sports watches. The primary endpoint, AF burden, will be calculated as the cumulative duration of all AF episodes lasting ≥30sec divided by total duration of monitoring. Secondary endpoints include number of AF episodes, adherence to training adaption, exercise capacity, AF symptoms and health-related quality of life, echocardiographic signs of cardiac remodelling and risk of cardiac arrhythmias related to upholding training intensity.

Trial registration number

NCT04991337.

Study protocol version

4.7 (Date 9 March 2023).

Cardiac RGS Proteins in Human Heart Failure and Atrial Fibrillation: Focus on RGS4

The regulator of G protein signaling (RGS) proteins are crucial for the termination of G protein signals elicited by G protein-coupled receptors (GPCRs). This superfamily of cell membrane receptors, by far the largest and most versatile in mammals, including humans, play pivotal roles in the regulation of cardiac function and homeostasis. Perturbations in both the activation and termination of their G protein-mediated signaling underlie numerous heart pathologies, including heart failure (HF) and atrial fibrillation (AFib). Therefore, RGS proteins play important roles in the pathophysiology of these two devasting cardiac diseases, and several of them could be targeted therapeutically. Although close to 40 human RGS proteins have been identified, each RGS protein seems to interact only with a specific set of G protein subunits and GPCR types/subtypes in any given tissue or cell type. Numerous in vitro and in vivo studies in animal models, and also in diseased human heart tissue obtained from transplantations or tissue banks, have provided substantial evidence of the roles various cardiomyocyte RGS proteins play in cardiac normal homeostasis as well as pathophysiology. One RGS protein in particular, RGS4, has been reported in what are now decades-old studies to be selectively upregulated in human HF. It has also been implicated in protection against AFib via knockout mice studies. This review summarizes the current understanding of the functional roles of cardiac RGS proteins and their implications for the treatment of HF and AFib, with a specific focus on RGS4 for the aforementioned reasons but also because it can be targeted successfully with small organic molecule inhibitors.

Assessment of P Wave Indices in Healthy Standardbred Horses

P wave indices are used as non-invasive electrocardiographic markers of atrial remodelling in humans. Few studies have investigated their use in animals. The aim of this study was to measure P wave duration and P wave dispersion (Pd) in healthy standardbred horses and investigate variables that might influence these measurements. A 12-lead electrocardiogram was recorded at rest and P wave indices were calculated in 53 horses. A general linear model was used to investigate the main effects: age, bodyweight, sex, resting heart rate, presence of a murmur, exercise status and the number of years raced. There were significant associations with exercise status for both the maximum P wave duration and Pd, with both values being increased in strenuously exercising versus non-active horses. Furthermore, a significant moderate positive correlation was identified between the duration of exercise (number of years raced) and both Pmax and Pd. No other significant associations were identified. These findings are similar to those reported in elite human athletes versus sedentary individuals. The increases in these P wave indices most likely occur due to prolongation and heterogeneity in atrial conduction time, which are associated with structural and electrical remodelling, and may explain the increased risk of atrial fibrillation in athletic horses.

Cardiac electrophysiological remodeling associated with enhanced arrhythmia susceptibility in a canine model of elite exercise

The health benefits of regular physical exercise are well known. Even so, there is increasing evidence that the exercise regimes of elite athletes can evoke cardiac arrhythmias including ventricular fibrillation and even sudden cardiac death (SCD). The mechanism of exercise-induced arrhythmia and SCD is poorly understood. Here, we show that chronic training in a canine model (12 sedentary and 12 trained dogs) that mimics the regime of elite athletes induces electrophysiological remodeling (measured by ECG, patch-clamp, and immunocytochemical techniques) resulting in increases of both the trigger and the substrate for ventricular arrhythmias. Thus, 4 months sustained training lengthened ventricular repolarization (QTc: 237.1±3.4 ms vs. 213.6±2.8 ms, n=12; APD90: 472.8±29.6 ms vs. 370.1±32.7 ms, n=29 vs. 25), decreased transient outward potassium current (6.4±0.5 pA/pF vs. 8.8±0.9 pA/pF at 50 mV, n=54 vs. 42), and increased the short-term variability of repolarization (29.5±3.8 ms vs. 17.5±4.0 ms, n=27 vs. 18). Left ventricular fibrosis and HCN4 protein expression were also enhanced. These changes were associated with enhanced ectopic activity (number of escape beats from 0/hr to 29.7±20.3/hr) in vivo and arrhythmia susceptibility (elicited ventricular fibrillation: 3 of 10 sedentary dogs vs. 6 of 10 trained dogs). Our findings provide in vivo, cellular electrophysiological and molecular biological evidence for the enhanced susceptibility to ventricular arrhythmia in an experimental large animal model of endurance training.

Epidemiology and modifiable risk factors for atrial fibrillation

The global prevalence of atrial fibrillation (AF) has increased substantially over the past three decades and is currently approximately 60 million cases. Incident AF and its clinical consequences are largely the result of risk factors that can be modified by lifestyle changes. In this Review, we provide evidence that the lifetime risk of AF is modified not only by sex and race but also through the clinical risk factor and comorbidity burden of individual patients. We begin by summarizing the epidemiology of AF, focusing on non-modifiable and modifiable risk factors, as well as targets and strategies for the primary prevention of AF. Furthermore, we evaluate the role of modifiable risk factors in the secondary prevention of AF as well as the potential effects of risk factor interventions on the frequency and severity of subsequent AF episodes. We end the Review by proposing strategies that require evaluation as well as global policy changes that are needed for the prevention of incident AF and the management of recurrent episodes in patients already affected by AF.

Overview of programmed electrical stimulation to assess atrial fibrillation susceptibility in mice

Atrial fibrillation (AF) is the most common human arrhythmia and is associated with increased risk of stroke, dementia, heart failure, and death. Among several animal models that have been used to investigate the molecular determinants of AF, mouse models have become the most prevalent due to low cost, ease of genetic manipulation, and similarity to human disease. Programmed electrical stimulation (PES) using intracardiac or transesophageal atrial pacing is used to induce AF as most mouse models do not develop spontaneous AF. However, there is a lack of standardized methodology resulting in numerous PES protocols in the literature that differ with respect to multiple parameters, including pacing protocol and duration, stimulus amplitude, pulse width, and even the definition of AF. Given this complexity, the selection of the appropriate atrial pacing protocol for a specific model has been arbitrary. Herein we review the development of intracardiac and transesophageal PES, including commonly used protocols, selected experimental models, and advantages and disadvantages of both techniques. We also emphasize detection of artifactual AF induction due to unintended parasympathetic stimulation, which should be excluded from results. We recommend that the optimal pacing protocol to elicit an AF phenotype should be individualized to the specific model of genetic or acquired risk factors, with an analysis using several definitions of AF as an endpoint.

The therapeutic potential of targeting cardiac RGS4

G protein-coupled receptors (GPCRs) play pivotal roles in regulation of cardiac function and homeostasis. To function properly, every cell needs these receptors to be stimulated only when a specific extracellular stimulus is present, and to be silenced the moment that stimulus is removed. The regulator of G protein signaling (RGS) proteins are crucial for the latter to occur at the cell membrane, where the GPCR normally resides. Perturbations in both activation and termination of G protein signaling underlie numerous heart pathologies. Although more than 30 mammalian RGS proteins have been identified, each RGS protein seems to interact only with a specific set of G protein subunits and GPCR types/subtypes in any given tissue or cell type, and this applies to the myocardium as well. A large number of studies have provided substantial evidence for the roles various RGS proteins expressed in cardiomyocytes play in cardiac physiology and heart disease pathophysiology. This review summarizes the current understanding of the functional roles of cardiac RGS proteins and their implications for the treatment of specific heart diseases, such as heart failure and atrial fibrillation. We focus on cardiac RGS4 in particular, since this isoform appears to be selectively (among the RGS protein family) upregulated in human heart failure and is also the target of ongoing drug discovery efforts for the treatment of a variety of diseases.

Physical inactivity by tail suspension alters markers of metabolism, structure, and autophagy of the mouse heart

Sedentary behavior has become ingrained in our society and has been linked to cardiovascular diseases. Physical inactivity is the main characteristic of sedentary behavior. However, its impact on cardiovascular disease is not clear. Therefore, we investigated the effect of physical inactivity in an established mouse model on gene clusters associated with cardiac fibrosis, electrophysiology, cell regeneration, and tissue degradation/turnover. We investigated a sedentary group (CTR, n = 10) versus a tail suspension group (TS, n = 11) that caused hindlimb unloading and consequently physical inactivity. Through histological, protein content, and transcript analysis approaches, we found that cardiac fibrosis-related genes partly change, with significant TS-associated increases in Tgfb1, but without changes in Col1a1 and Fn1. These changes are not translated into fibrosis at tissue level. We further detected TS-mediated increases in protein degradation- (Trim63, p < 0.001; Fbxo32, p = 0.0947 as well as in biosynthesis-related [P70s6kb1, p < 0.01]). Corroborating these results, we found increased expression of autophagy markers such as Atg7 (p < 0.01) and ULK1 (p < 0.05). Two cardiomyocyte regeneration- and sarcomerogenesis-related genes, Yap (p = 0.0535) and Srf (p < 0.001), increased upon TS compared to CTR conditions. Finally, we found significant upregulation of Gja1 (p < 0.05) and a significant downregulation of Aqp1 (p < 0.05). Our data demonstrate that merely 2 weeks of reduced physical activity induce changes in genes associated with cardiac structure and electrophysiology. Hence, these data should find the basis for novel research directed to evaluate the interplay of cardiac functioning and physical inactivity.

An Exercise and Physical Activity Program in Patients With Atrial Fibrillation: The ACTIVE-AF Randomized Controlled Trial

BACKGROUND

There are limited data on the effect of exercise interventions on atrial fibrillation (AF) recurrence and symptoms.

OBJECTIVES

The aim of this study was to determine the efficacy of an exercise and physical activity intervention on AF burden and symptoms among patients with symptomatic AF.

METHODS

This prospective, randomized controlled trial included 120 patients with paroxysmal or persistent, symptomatic AF, randomized 1:1 to receive an exercise intervention, combining home and supervised aerobic exercise over 6 months, or to receive usual care. The coprimary outcomes were: 1) AF recurrence, off antiarrhythmic medications and without catheter ablation; and 2) symptom severity assessed by using a validated questionnaire.

RESULTS

By 12 months, freedom from AF was achieved in 24 (40%) of 60 patients in the exercise group and 12 (20%) of 60 patients in the control group (HR: 0.50: 95% CI: 0.33 to 0.78). At 6 months, AF symptom severity was lower in the exercise group compared with the control group (mean difference -2.3; 95% CI: -4.3 to -0.2; P = 0.033). This difference persisted at 12 months (-2.3; 95% CI: -4.5 to -0.1; P = 0.041). Total symptom burden was lower at 6 months in the exercise group but not at 12 months. Peak oxygen consumption was increased in the exercise group at both 6 and 12 months. There were no between-group differences in cardiac structure or function, body mass index, or blood pressure.

CONCLUSIONS

Participation in an exercise-based intervention over 6 months reduced arrhythmia recurrence and improved symptom severity among patients with AF. (A Lifestyle-based, PhysiCal AcTIVity IntErvention for Patients With Symptomatic Atrial Fibrillation [the ACTIVE-AF Study]; ACTRN12615000734561).

Characterization of arrhythmia substrate to ablate persistent atrial fibrillation (COAST-AF): Randomized controlled trial design and rationale

BACKGROUND

Atrial low voltage area (LVA) catheter ablation has emerged as a promising strategy for ablation of persistent atrial fibrillation (AF). It is unclear if catheter ablation of atrial LVA increases treatment success rates in patients with persistent AF.

OBJECTIVE

The primary aim of this trial is to assess the potential benefit of adjunctive catheter ablation of atrial LVA in addition to pulmonary vein isolation (PVI) in patients with persistent AF, when compared to PVI alone. The secondary aims are to evaluate safety outcomes, the quality of life and the healthcare resource utilization.

METHODS/DESIGN

A multicenter, prospective, parallel-group, 2-arm, single-blinded randomized controlled trial is under way (NCT03347227). Patients who are candidates for catheter ablation for persistent AF will be randomly assigned (1:1) to either PVI alone or PVI + atrial LVA ablation. The primary outcome is 18-month documented event rate of atrial arrhythmia (AF, atrial tachycardia or atrial flutter) post catheter ablation. Secondary outcomes include procedure-related complications, freedom from atrial arrhythmia at 12 months, AF burden, need for emergency department visits/hospitalization, need for repeat ablation for atrial arrhythmia, quality of life at 12 and 18 months, ablation time, and procedure duration.

DISCUSSION

Characterization of Arrhythmia Mechanism to Ablate Atrial Fibrillation (COAST-AF) is a multicenter randomized trial evaluating ablation strategies for catheter ablation. We hypothesize that catheter ablation of atrial LVA in addition to PVI will result in higher procedural success rates when compared to PVI alone in patients with persistent AF.

Intense long-term training impairs brain health compared with moderate exercise: Experimental evidence and mechanisms

The consequences of extremely intense long-term exercise for brain health remain unknown. We studied the effects of strenuous exercise on brain structure and function, its dose-response relationship, and mechanisms in a rat model of endurance training. Five-week-old male Wistar rats were assigned to moderate (MOD) or intense (INT) exercise or a sedentary (SED) group for 16 weeks. MOD rats showed the highest motivation and learning capacity in operant conditioning experiments; SED and INT presented similar results. In vivo MRI demonstrated enhanced global and regional connectivity efficiency and clustering as well as a higher cerebral blood flow (CBF) in MOD but not INT rats compared with SED. In the cortex, downregulation of oxidative phosphorylation complex IV and AMPK activation denoted mitochondrial dysfunction in INT rats. An imbalance in cortical antioxidant capacity was found between MOD and INT rats. The MOD group showed the lowest hippocampal brain-derived neurotrophic factor levels. The mRNA and protein levels of inflammatory markers were similar in all groups. In conclusion, strenuous long-term exercise yields a lesser improvement in learning ability than moderate exercise. Blunting of MOD-induced improvements in CBF and connectivity efficiency, accompanied by impaired mitochondrial energetics and, possibly, transient local oxidative stress, may underlie the findings in intensively trained rats.

The Athlete's Heart-Challenges and Controversies: JACC Focus Seminar 4/4

Regular exercise promotes structural, functional, and electrical remodeling of the heart, often referred to as the "athlete's heart," with intense endurance sports being associated with the greatest degree of cardiac remodeling. However, the extremes of exercise-induced cardiac remodeling are potentially associated with uncommon side effects. Atrial fibrillation is more common among endurance athletes and there is speculation that other arrhythmias may also be more prevalent. It is yet to be determined whether this arrhythmic susceptibility is a result of extreme exercise remodeling, genetic predisposition, or other factors. Gender may have the greatest influence on the cardiac response to exercise, but there has been far too little research directed at understanding differences in the sportsman's vs sportswoman's heart. Here in part 4 of a 4-part seminar series, the controversies and ambiguities regarding the athlete's heart, and in particular, its arrhythmic predisposition, genetic, and gender influences are reviewed in depth.

Influence of endurance sports on atrial fibrillation ablation outcomes

Objectives

We aimed to investigate the outcomes of pulmonary vein isolation in athletes.

Methods

We retrospectively identified endurance athletes who underwent catheter ablation at our institution (2004-2018). Endurance athletes were defined as participating in competitive athletics for at least 1500 lifetime hours in sports at the IB or IIA Bethesda classification or higher. Primary endpoints were freedom from atrial arrhythmias at 12, 24, and 36 months after the procedure. Secondary endpoints were defined as qualitative improvement in symptoms allowing athletes to return to their previous level of activity. Athletes were compared with a control group of nonathletes in a 3-to-1 matched analysis by age and sex.

Results

A total of 39 endurance athletes who underwent catheter ablation were identified during the study period. At 12 months, there was no difference in treatment outcomes for athletes versus nonathletes (relative risk [RR], 1.06; 95% CI, 0.92-1.22; p = .40). Freedom from atrial arrhythmias was 35% less likely in athletes than nonathletes at 24 months (RR, 0.65; 95% CI, 0.50-0.83; p < .001) and 42% less likely at 36 months (RR, 0.58; 95% CI, 0.41-0.79; p < .001). Overall, 77% of the athletes were able to return to their previous level of activity following catheter ablation.

Conclusion

Endurance athletes with atrial fibrillation appear to have higher rates of atrial arrhythmia recurrence than nonathletes after catheter ablation, with higher rates of atypical flutter. The majority of athletes were able to return to their previous level of activity after ablation.

Protective effect of low-intensity treadmill exercise against acetylcholine-calcium chloride-induced atrial fibrillation in mice

Atrial fibrillation (AF) is the most common supraventricular arrhythmia, and it corresponds highly with exercise intensity. Here, we induced AF in mice using acetylcholine (ACh)-CaCl₂ for 7 days and aimed to determine the appropriate exercise intensity (no, low, moderate, high) to protect against AF by running the mice at different intensities for 4 weeks before the AF induction by ACh-CaCl₂. We examined the AF-induced atrial remodeling using electrocardiogram, patch-clamp, and immunohistochemistry. After the AF induction, heart rate, % increase of heart rate, and heart weight/body weight ratio were significantly higher in all the four AF groups than in the normal control; highest in the high-ex AF and lowest in the low-ex (lower than the no-ex AF), which indicates that low-ex treated the AF. Consistent with these changes, G protein-gated inwardly rectifying K⁺ currents, which were induced by ACh, increased in an exercise intensity-dependent manner and were lower in the low-ex AF than the no-ex AF. The peak level of Ca²⁺ current (at 0 mV) increased also in an exercise intensity-dependent manner and the inactivation time constants were shorter in all AF groups except for the low-ex AF group, in which the time constant was similar to that of the control. Finally, action potential duration was shorter in all the four AF groups than in the normal control; shortest in the high-ex AF and longest in the low-ex AF. Taken together, we conclude that low-intensity exercise protects the heart from AF, whereas high-intensity exercise might exacerbate AF.

CArdiac MagnEtic resonance assessment of bi-Atrial fibrosis in secundum atrial septal defects patients: CAMERA-ASD study

AIMS

Atrial septal defects (ASD) are associated with atrial arrhythmias, but the arrhythmia substrate in these patients is poorly defined. We hypothesized that bi-atrial fibrosis is present and that right atrial fibrosis is associated with atrial arrhythmias in ASD patients. We aimed to evaluate the extent of bi-atrial fibrosis in ASD patients and to investigate the relationships between bi-atrial fibrosis, atrial arrhythmias, shunt fraction, and age.

METHODS AND RESULTS

Patients with uncorrected secundum ASDs (n = 36; 50.4 ± 13.6 years) underwent cardiac magnetic resonance imaging with atrial late gadolinium enhancement. Comparison was made to non-congenital heart disease patients (n = 36; 60.3 ± 10.5 years) with paroxysmal atrial fibrillation (AF). Cardiac magnetic resonance parameters associated with atrial arrhythmias were identified and the relationship between bi-atrial structure, age, and shunt fraction studied. Bi-atrial fibrosis burden was greater in ASD patients than paroxysmal AF patients (20.7 ± 14% vs. 10.1 ± 8.6% and 14.8 ± 8.5% vs. 8.6 ± 6.1% for right and left atria respectively, P = 0.001 for both). In ASD patients, right atrial fibrosis burden was greater in those with than without atrial arrhythmias (33.4 ± 18.7% vs. 16.8 ± 10.3%, P = 0.034). On receiver operating characteristic analysis, a right atrial fibrosis burden of 32% had a 92% specificity and 71% sensitivity for predicting the presence of atrial arrhythmias. Neither age nor shunt fraction was associated with bi-atrial fibrosis burden.

CONCLUSION

Bi-atrial fibrosis burden is greater in ASD patients than non-congenital heart disease patients with paroxysmal AF. Right atrial fibrosis is associated with the presence of atrial arrhythmias in ASD patients. These findings highlight the importance of right atrial fibrosis to atrial arrhythmogenesis in ASD patients.

Immune remodeling and atrial fibrillation

Atrial fibrillation (AF) is a highly prevalent arrhythmia that causes high morbidity and mortality. However, the underlying mechanism of AF has not been fully elucidated. Recent research has suggested that, during AF, the immune system changes considerably and interacts with the environment and cells involved in the initiation and maintenance of AF. This may provide a new direction for research and therapeutic strategies for AF. In this review, we elaborate the concept of immune remodeling based on available data in AF. Then, we highlight the complex relationships between immune remodeling and atrial electrical, structural and neural remodeling while also pointing out some research gaps in these field. Finally, we discuss several potential immunomodulatory treatments for AF. Although the heterogeneity of existing evidence makes it ambiguous to extrapolate immunomodulatory treatments for AF into the clinical practice, immune remodeling is still an evolving concept in AF pathophysiology and further studies within this field are likely to provide effective therapies for AF.

Age impacts left atrial functional remodeling in athletes

Aim

Age-associated changes in cardiac filling and function are well known in the general population. Yet, the effect of aging on left atrial (LA) function, and its interaction with left ventricular (LV) adaptation, remain less described when combined with high-intensity chronic training. We aimed to analyze the effects of aging on LA and LV functions in trained athletes.

Methods and results

Ninety-five healthy highly-trained athletes referred for resting echocardiography were included. Two groups of athletes were retrospectively defined based on age: young athletes aged <35 years (n = 54), and master athletes aged ≥35 years (n = 41). All subjects were questioned about their sports practice. Echocardiographic analysis of LV systolic and diastolic functions (2D-echo, 3D-echo, and Doppler), as well as LA 2D dimensions and phasic deformations assessed by speckle tracking, were analyzed. Master athletes (mean age = 46.3 ± 8.3 years, mean duration of sustained training = 13.7 ± 8.9 years) exhibited significantly stiffer LV and LA with reduced LV early diastolic functional parameters (ratio E/A, peak e’, and ratio e’/a’), LA reservoir and conduit strain, whereas LA volume, LA contractile strain and LV peak a’ were higher, compared to young athletes. Multivariate regression analysis confirmed that age was predictive of peak e’, LA reservoir strain and LA conduit strain, independently of training variables. LA phasic strains were strongly associated with LV diastolic function.

Conclusions

Regardless of chronic sports practice, master athletes exhibited age-related changes in LA function closely coupled to LV diastolic properties, which led to LV filling shifts to late diastole.

Long-Term Strenuous Exercise Promotes Vascular Injury by Selectively Damaging the Tunica Media

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Long-term strenuous endurance training promotes a deleterious vascular remodeling, in contrast to the beneficial effects of moderate exercise.

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Tunica media fibrosis, possibly mediated by miR-212, miR-132, and miR-146b down-regulation, and intrinsic vascular smooth muscle cell stiffening may contribute to aortic stiffening.

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Endothelial function improves in a similar intensity after moderate and strenuous training. However, in the INT group, a larger NO-mediated vasorelaxation is compensated by more intense vasoconstriction, leading to a potentially unstable balance.

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Strenuous exercise-induced vascular stiffening and changes in endothelial function remain after ceasing physical activity.

Moderate exercise has well-founded benefits in cardiovascular health. However, increasing, yet controversial, evidence suggests that extremely trained athletes may not be protected from cardiovascular events as much as moderately trained individuals. In our rodent model, intensive but not moderate training promoted aorta and carotid stiffening and elastic lamina ruptures, tunica media thickening of intramyocardial arteries, and an imbalance between vasoconstrictor and relaxation agents. An up-regulation of angiotensin-converter enzyme, miR-212, miR-132, and miR-146b might account for this deleterious remodeling. Most changes remained after a 4-week detraining. In conclusion, our results suggest that intensive training blunts the benefits of moderate exercise.

Imaging assessment of the right atrium: anatomy and function

The right atrium (RA) is the cardiac chamber that has been least well studied. Due to recent advances in interventional cardiology, the need for greater understanding of the RA anatomy and physiology has garnered significant attention. In this article, we review how a comprehensive assessment of RA dimensions and function using either echocardiography, cardiac computed tomography, and magnetic resonance imaging may be used as a first step towards a better understanding of RA pathophysiology. The recently published normative data on RA size and function will likely shed light on RA atrial remodelling in atrial fibrillation (AF), which is a complex phenomenon that occurs in both atria but has only been studied in depth in the left atrium. Changes in RA structure and function have prognostic implications in pulmonary hypertension (PH), where the increased right ventricular (RV) afterload first induces RV remodelling, predominantly characterized by hypertrophy. As PH progresses, RV dysfunction and dilatation may begin and eventually lead to RV failure. Thereafter, RV overload and increased RV stiffness may lead to a proportional increase in RA pressure. This manuscript provides an in-depth review of RA anatomy, function, and haemodynamics with particular emphasis on the changes in structure and function that occur in AF, tricuspid regurgitation, and PH.

Electrocardiographic characteristics of trained and untrained standardbred racehorses

Background

Long‐term exercise induces cardiac remodeling that potentially influences the electrical properties of the heart.

Hypothesis/objectives

We assessed whether training alters cardiac conduction in Standardbred racehorses.

Animals

Two hundred one trained and 52 untrained Standardbred horses.

Methods

Cross‐sectional study. Resting ECG recordings were analyzed to assess heart rate (HR) along with standard ECG parameters and for identification of atrial and ventricular arrhythmias. An electrophysiological study was performed in 13 horses assessing the effect of training on sinoatrial (SA) and atrioventricular (AV) nodal function by sinus node recovery time (SNRT) and His signal recordings. Age and sex adjustments were implemented in multiple and logistic regression models for comparison.

Results

Resting HR in beats per minute (bpm) was lower in trained vs untrained horses (mean, 30.8 ± 2.6 bpm vs 32.9 ± 4.2 bpm; P = .001). Trained horses more often displayed second‐degree atrioventricular block (2AVB; odds ratio, 2.59; P = .04). No difference in SNRT was found between groups (n = 13). Mean P‐A, A‐H, and H‐V intervals were 71 ± 20, 209 ± 41, and 134 ± 41 ms, respectively (n = 7). We did not detect a training effect on AV‐nodal conduction intervals. His signals were present in 1 horse during 2AVB with varying H‐V interval preceding a blocked beat.

Conclusions and Clinical Importance

We identified decreased HR and increased frequency of 2AVB in trained horses. In 5 of 7 horses, His signal recordings had variable H‐V intervals within each individual horse, providing novel insight into AV conduction in horses.

Arrhythmogenesis of Sports: Myth or Reality?

Regular exercise confers health benefits with cardiovascular mortality risk reduction through a variety of mechanisms. At a population level, evidence suggests that undertaking more exercise has greater benefits. In the modern era of sport, there has been an exponential rise in professional and amateur athletes participating in endurance events, with a progressively better understanding of the associated cardiac adaptations, collectively termed 'athletes heart'. However, emerging data raise questions regarding the risk of potential harm from endurance exercise, with an increased risk of arrhythmia from adverse cardiac remodelling. Cross-sectional studies have demonstrated that athletes may exhibit a higher burden of AF, conduction tissue disease, ventricular arrhythmias, a cardiomyopathy-like phenotype and coronary artery disease. In an attempt to separate myth from reality, this review reports on the evidence supporting the notion of 'too much exercise', the purported mechanisms of exercise-induced cardiac arrhythmia and complex interplay with sporting discipline, demographics, genetics and acquired factors.

Electrical and Structural Adaption of Athlete’s Heart and the Impact on Training and Recovery Management in Professional Basketball Players: A Retrospective Observational Study

Introduction

We analyzed data of 27 professional basketball players to prove cardiac remodeling referring echocardiographic parameters, cardiopulmonary exercise testing (CPET), and 12-lead electrocardiogram (ECG) analyses. The aim of our study was to present different characteristics in the athletes, on the one hand signs of a high vagal tone in the 12-lead ECG as criteria of early repolarization (ER), furthermore echocardiographic remodeling parameters and finally the performance in CPET. Therefore, we divided the cohort into a group with signs of ER pattern in the 12-lead ECG and without these criteria and presented the differences in detail.

Materials and Methods

This was a single-center, retrospective study performed in 27 professional basketball players (age: 26.5 ± 7.5 years, male: 27, height: 197.2 ± 12 cm, weight: 100 ± 17 kg, BMI: 25.7 ± 3.4 kg/m2). All participants underwent a sports medicine checkup, ECG analysis, transthoracic echocardiographic examination, and a CPET on a cycle ergometer between 2015 and 2019 during their pre-season preparation time. All individuals were healthy people without cardiological advance anamnesis. After assessment, two groups were built based on electrocardiographic criteria of ER pattern and a group without these criteria and compared against each other for parameters of echocardiographic assessment, CPET, and 12-lead ECG analysis. Data were analyzed with Minitab statistic program (Minitab Inc., State College, PA, United States) and Graph Pad Prism 8.2.1 (279; Graph Pad Software, San Diego, CA, United States) using ANOVA testing with post-hoc testing and unpaired t-testing (p ≤ 0.05).

Retrospectively additional information was collected referring to the management of training sessions, recovery time, and nutrition by interviewing the athletic training staff in order to understand the principles for individual athlete’s training management and physiological and cardiopulmonary interactions.

Results

Comparing professional basketball players with ER pattern to those with no ER pattern, significant differences were found for CPET, echocardiographic, and ECG analysis (p &lt; 0.05). Absolute and relativized peak oxygen uptake (VO2 peak; ER 4120 ± 750 ml/min (39 ± 5.4 ml/kg/min) vs. non-ER 3556 ± 393 ml/min (37.2 ± 5.3 ml/kg/min), p = 0.018) and maximum workload during CPET (ER 310 ± 51.5 Watt (2.94 ± 0.35 W/kg) vs. non-ER 271 ± 32 Watt (2.85 ± 0.49 W/kg), p = 0.026) was higher in athletes with an ER pattern. Furthermore, ER pattern athletes showed a higher enddiastolic left ventricular diameter (LVedd; ER 58.3 ± 7.9 mm vs. non-ER 53.6 ± 3.6 mm, p = 0.048) and a significantly enlarged left atrial (LA) endsystolic diameter (ER 23.33 ± 2.71 mm vs. non-ER 20.47 ± 2.29 mm, p = 0.006) as well as a significantly enlarged right atrial (RA) endsystolic diameter (ER 23.42 ± 2.15 mm vs. non-ER 20.93 ± 3.28 mm, p = 0.033). Significant differences between the two compared groups could be revealed for left ventricular mass Index (LVMI gr/m2; LVMI ER 113 gr/m2 ± 17.5 vs. LVMI non-ER 91.3 gr/m2 ± 15.1, p = 0.002), but no significant differences for the relative wall thickness were found (RWT; RWT ER 0.49 ± 0.11 vs. RWT non-ER 0.38 ± 0.06, p = 0.614).

Conclusion

Professional basketball players with criteria of ER pattern showed different results in CPET and cardiac remodeling as athletes with no ER pattern. These findings should encourage the athletic training staff to emphasize the quality of an individual training schedule for each athlete based on the cardiopulmonary pre-season sport medicine checkup. Nevertheless, echocardiographic findings, ER pattern, and performance in CPET have to be interpreted referring the sport-specific and athlete’s ethnical background.