Increase in vulnerability of atrial fibrillation in an acute intermittent hypoxia model: Importance of autonomic imbalance

The Autonomic Coumel Triangle: A New Way to Define the Fascinating Relationship between Atrial Fibrillation and the Autonomic Nervous System

Arrhythmogenic substrate, modulating factors, and triggering factors (the so-called Coumel's triangle concept) play a primary role in atrial fibrillation (AF) pathophysiology. Several years have elapsed since Coumel and co-workers advanced the concept of the relevance of autonomic nervous system (ANS) influences on atrial cells' electrophysiological characteristics. The ANS is not only associated with cardiac rhythm regulation but also exerts an important role in the triggering and maintenance of atrial fibrillation. This review aims to describe in detail the autonomic mechanisms involved in the pathophysiology of atrial fibrillation (AF), starting from the hypothesis of an "Autonomic Coumel Triangle" that stems from the condition of the fundamental role played by the ANS in all phases of the pathophysiology of AF. In this article, we provide updated information on the biomolecular mechanisms of the ANS role in Coumel's triangle, with the molecular pathways of cardiac autonomic neurotransmission, both adrenergic and cholinergic, and the interplay between the ANS and cardiomyocytes' action potential. The heterogeneity of the clinical spectrum of the ANS and AF, with the ANS playing a relevant role in situations that may promote the initiation and maintenance of AF, is highlighted. We also report on drug, biological, and gene therapy as well as interventional therapy. On the basis of the evidence reviewed, we propose that one should speak of an "Autonomic Coumel's Triangle" instead of simply "Coumel's Triangle".

Vagal milieu or electrophysiologic substrate? The link between atrial fibrillation and obstructive sleep apnea

Atrial fibrillation is the most common cardiac arrhythmia with its prevalence expected to increase to 12.1 million people in the United States by 2030. Chronic underlying conditions that affect the heart and lungs predispose patients to develop atrial fibrillation. Obstructive sleep apnea is strongly associated with atrial fibrillation. Several pathophysiological mechanisms have been proposed to elucidate this relationship which includes electrophysiological substrate modification and the contribution of the autonomic nervous system. In this comprehensive review, we highlight important relationships and plausible causality between obstructive sleep apnea and atrial fibrillation which will improve our understanding in the evaluation, management, and prevention of atrial fibrillation. This is the most updated comprehensive review of the relationship between obstructive sleep apnea and atrial fibrillation.

Sleep apnea and atrial fibrillation: challenges in clinical and translational research

INTRODUCTION

Sleep-disordered breathing (SDB) is present in 21-74% of all patients with atrial fibrillation (AF). Treatment of SDB by positive airway pressure may help to prevent recurrence of AF after electrical cardioversion and help to improve AF ablation success rates in non-randomized studies.

AREAS COVERED

In this review, the current understanding of the atrial arrhythmogenic pathophysiology of SDB is summarized, and diagnostic and therapeutic challenges in AF patients are discussed. Current international recommendations are presented, and a comprehensive literature search is undertaken.

EXPERT OPINION

AF patients with SDB rarely report SDB-related symptoms such as daytime sleepiness. Therefore, systematic home sleep testing evaluation should be considered for all patients eligible for rhythm control strategy. A close interdisciplinary collaboration between the electrophysiologist/cardiologist, nurses and sleep-specialists are required for the management of SDB in AF patients. An arrhythmia-orientated assessment of SDB may better quantify SDB-related AF risk in an individual patient and may help to better guide targeted and personalized SDB treatment in AF patients as a component of rhythm and symptom control strategies. Finally, randomized controlled trials are needed to confirm the relationship between SDB and AF, and the benefits of routine testing and treatment of SDB in AF patients.

Contemporary approach to understand and manage COVID-19-related arrhythmia

Arrhythmia, one of the most common complications of COVID-19, was reported in nearly one-third of diagnosed COVID-19 patients, with higher prevalence rate among ICU admitted patients. The underlying etiology for arrhythmia in these cases are mostly multifactorial as those patients may suffer from one or more of the following predisposing mechanisms; catecholamine surge, hypoxia, myocarditis, cytokine storm, QTc prolongation, electrolyte disturbance, and pro-arrhythmic drugs usage. Obviously, the risk for arrhythmia and the associated lethal outcome would rise dramatically among patients with preexisting cardiac disease such as myocardial ischemia, heart failure, cardiomyopathy, and hereditary arrhythmias. Considering all of these variables, the management strategy of COVID-19 patients should expand from managing a viral infection and related host immune response to include the prevention of predictable causes for arrhythmia. This may necessitate the need to investigate the role of some drugs that modulate the pathway of arrhythmia generation. Of these drugs, we discuss the potential role of adrenergic antagonists, trimetazidine, ranolazine, and the debatable angiotensin converting enzyme inhibitors drugs. We also recommend monitoring the level of: unbound free fatty acids, serum electrolytes, troponin, and QTc (even in the absence of apparent pro-arrhythmic drug use) as these may be the only indicators for patients at risk for arrhythmic complications.

Obstructive Sleep Apnea and Cardiac Arrhythmias: A Contemporary Review

Obstructive sleep apnea (OSA) is a highly prevalent disorder with a growing incidence worldwide that closely mirrors the global obesity epidemic. OSA is associated with enormous healthcare costs in addition to significant morbidity and mortality. Much of the morbidity and mortality related to OSA can be attributed to an increased burden of cardiovascular disease, including cardiac rhythm disorders. Awareness of the relationship between OSA and rhythm disorders is variable among physicians, a fact that can influence patient care, since the presence of OSA can influence the incidence, prevalence, and successful treatment of multiple rhythm disorders. Herein, we provide a review of this topic that is intentionally broad in scope, covering the relationship between OSA and rhythm disorders from epidemiology and pathophysiology to diagnosis and management, with a particular focus on the recognition of undiagnosed OSA in the general clinical population and the intimate relationship between OSA and atrial fibrillation.

Long-Term High-Altitude Exposure Does Not Increase the Incidence of Atrial Fibrillation Associated with Organic Heart Diseases

Wang, Man, Mengxue Liu, Jia Huang, Dan Fan, Shengzhong Liu, Tao Yu, Keli Huang, Xinchuan Wei, and Qian Lei. Long-term high-altitude exposure does not increase the incidence of atrial fibrillation associated with organic heart diseases. High Alt Med Biol. 00:000-000, 2021.- Background: Atrial fibrillation (AF) is one of the most common arrhythmias and is associated with several complications following cardiac surgery. However, the differences in the incidence of AF associated with organic heart diseases between highland and lowland populations have not been comprehensively studied. Methods: In this retrospective study, a total of 2,316 highland and lowland patients who underwent cardiac surgery between January 2013 and December 2018 in a single center were enrolled. According to the altitude of residence, patients were divided into high-altitude (>1,500 m) and low-altitude (<1,500 m) groups. A propensity score matching analysis was performed to estimate the association of lifetime high-altitude exposure with AF. Results: Among the enrolled patients, 239 (10.9%) were from a high-altitude plateau, while 1,946 (89.1%) were from a low-altitude area. There were statistical differences in age, gender, European System for Cardiac Operative Risk Evaluation, and other factors, between the two groups (p < 0.05). According to the propensity score, 237 patients in the high-altitude group were successfully matched to 237 patients in the low-altitude group without significant difference in baseline data (p > 0.05). Among the matched patients, 125 patients (26.4%) suffered from AF, with 66 (27.8%) in the high-altitude group and 59 (24.9%) in the low-altitude group. The incidence of AF was statistically similar between the two groups and not significantly influenced by long-term high-altitude exposure (odds ratio 1.07; 95% confidence interval 0.71-1.60, p > 0.05). Conclusion: Long-term high-altitude exposure did not significantly increase the occurrence of AF in patients with organic heart diseases. Clinical Trial No. ChiCTR1900028612.

Association between Respiratory Sleep Indices and Cardiovascular Disease in Sleep Apnea-A Community-Based Study in Cyprus

Obstructive sleep apnea (OSA) is a chronic and prevalent disorder, strongly associated with cardiovascular disease (CVD). The apnea-hypopnea index (AHI), or respiratory event index (REI), and the oxygen desaturation index (ODI) are the clinical metrics of sleep apnea in terms of diagnosis and severity. However, AHI, or REI, does not quantify OSA-related hypoxemia and poorly predicts the consequences of sleep apnea in cardiometabolic diseases. Moreover, it is unclear whether ODI correlates with CVD in OSA. Our study aimed to examine the possible associations between respiratory sleep indices and CVD in OSA, in a non-clinic-based population in Cyprus. We screened 344 subjects of a stratified, total sample of 4118 eligible responders. All participants were adults (age 18+), residing in Cyprus. Each patient answered with a detailed clinical history in terms of CVD. A type III sleep test was performed on 282 subjects (81.97%). OSA (REI ≥ 15) was diagnosed in 92 patients (32.62%, Group A). REI < 15 was observed in the remaining 190 subjects (67.37%, Group B). In OSA group A, 40 individuals (43%) reported hypertension, 17 (18.5%) arrhythmias, 10 (11%) heart failure, 9 (9.8%) ischemic heart disease and 2 (2%) previous stroke, versus 46 (24%), 21 (11%), 7 (3.7%), 12 (6.3%) and 6 (3%), in Group B, respectively. Hypertension correlated with REI (p = 0.001), ODI (p = 0.003) and mean SaO₂ (p < 0.001). Arrhythmias correlated with mean SaO₂ (p = 0.001) and time spent under 90% oxygen saturation (p = 0.040). Heart failure correlated with REI (p = 0.043), especially in the supine position (0.036). No statistically significant correlations were observed between ischemic heart disease or stroke and REI, ODI and mean SaO₂. The pathogenesis underlying CVD in OSA is variable. According to our data, hypertension correlated with REI, ODI and mean SaO₂. Arrhythmias correlated only with hypoxemia (mean SaO₂), whereas heart failure correlated only with REI, especially in the supine position.

Cardiac Sympathetic Denervation Suppresses Atrial Fibrillation and Blood Pressure in a Chronic Intermittent Hypoxia Rat Model of Obstructive Sleep Apnea

Background Chronic intermittent hypoxia ( CIH ) is a distinct pathological mechanism of obstructive sleep apnea ( OSA ), which is recognized as an independent risk factor for cardiovascular diseases. The aims of this study were to ascertain whether CIH induces atrial fibrillation ( AF ), to determine whether cardiac sympathetic denervation ( CSD ) can prevent it and suppress blood pressure, and to explore the potential molecular mechanisms involved. Methods and Results Sixty Sprague-Dawley male rats were randomly divided into 4 groups: sham, CSD , CIH , CIH + CSD . The rats were exposed either to CIH 8 hours daily or normoxia for 6 weeks. Cardiac pathology and structure were analyzed by hematoxylin and eosin staining and echocardiogram. ECG, blood pressure, body weight, and blood gas were recorded. Connexin 43 and tyrosine hydroxylase were detected by western blot, immunohistochemistry, and immunofluorescence. CIH induced atrial remodeling, and increased AF inducibility. CSD treatment reduced postapneic blood pressure rises and AF susceptibility, which could attenuate CIH -associated structural atrial arrhythmogenic remodeling. In addition, CIH -induced sympathetic nerve hyperinnervation and CSD treatment reduced sympathetic innervation, which may affect CIH -induced AF -associated sympathovagal imbalance. Connexin 43 was specifically downregulated in CIH , whereas CSD treatment increased its expression. Conclusions These results suggested CIH induces atrial remodeling, increases AF inducibility, results in sympathetic nerve hyperinnervation, and decreases connexin 43 expression, but CSD treatment reduces AF susceptibility, postapneic blood pressure increase, sympathetic innervation, and the alteration of Cx43, which may be a key point in the genesis of CIH -induced AF .

Atrial fibrillation in obstructive sleep apnea: Neural mechanisms and emerging therapies

Obstructive sleep apnea (OSA) has been reproducibly identified as a risk factor for initiation and progression of atrial fibrillation (AF) and reduces the efficacy of antiarrhythmic drugs, electrical cardioversion, and catheter ablation in AF. It is still controversial whether continuous positive airway pressure ventilation (CPAP) could improve the successful rate of AF treatment in OSA patients. Besides, CPAP has shown relative low compliance in patients with OSA. Therefore, novel optional therapies might be needed to improve the control of AF associated with OSA. A growing body of evidence suggests that autonomic activation contributes to the pathogenesis of AF in OSA. Acute apneic episodes result in sympathovagal co-activation, shortening atrial refractoriness and promoting the initiation of AF. Chronic OSA-induced sympathetic activation plays a crucial role in atrial autonomic, structural, and electrical remodeling, thus providing substrates for AF maintenance and recurrence. Therefore, the autonomic nervous system may be a promising therapeutic target for OSA and AF. Autonomic modulation as a treatment for OSA-associated AF has been well established in several preclinical studies. Further clinical studies are needed to provide a more precise definition of the role of autonomic modulation in the treatment of AF in OSA.

Connexins and Atrial Fibrillation in Obstructive Sleep Apnea

PURPOSE OF THE REVIEW

To summarize the potential interactions between obstructive sleep apnea (OSA), atrial fibrillation (AF), and connexins.

RECENT FINDINGS

OSA is highly prevalent in patients with cardiovascular disease, and is associated with increased risk for end-organ substantial morbidities linked to autonomic nervous system imbalance, increased oxidative stress and inflammation, ultimately leading to reduced life expectancy. Epidemiological studies indicate that OSA is associated with increased incidence and progression of coronary heart disease, heart failure, stroke, as well as arrhythmias, particularly AF. Conversely, AF is very common among subjects referred for suspected OSA, and the prevalence of AF increases with OSA severity. The interrelationships between AF and OSA along with the well-known epidemiological links between these two conditions and obesity may reflect shared pathophysiological pathways, which may depend on the intercellular diffusion of signaling molecules into either the extracellular space or require cell-to-cell contact. Connexin signaling is accomplished via direct exchanges of cytosolic molecules between adjacent cells at gap membrane junctions for cell-to-cell coupling. The role of connexins in AF is now quite well established, but the impact of OSA on cardiac connexins has only recently begun to be investigated. Understanding the biology and regulatory mechanisms of connexins in OSA at the transcriptional, translational, and post-translational levels will undoubtedly require major efforts to decipher the breadth and complexity of connexin functions in OSA-induced AF.

SUMMARY

The risk of end-organ morbidities has initiated the search for circulating mechanistic biomarker signatures and the implementation of biomarker-based algorithms for precision-based diagnosis and risk assessment. Here we summarize recent findings in OSA as they relate to AF risk, and also review potential mechanisms linking OSA, AF and connexins.

The Interplay between Obstructive Sleep Apnea and Atrial Fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Obstructive sleep apnea (OSA) is also an increasingly common condition. Both entities are risk factors for ischemic stroke and both conditions are linked with increased mortality. Mechanical effects of obesity and sleep apnea can lead to increased afterload, left ventricular hypertrophy, and left atrial fibrosis and remodeling. These changes can result in an increased risk of AF development. The current paper summarizes the evidence for the bidirectional relationship between AF and OSA. The merits of selective screening for these two conditions are also discussed.

Obesity as an Effect Modifier in Sleep-Disordered Breathing and Postcardiac Surgery Atrial Fibrillation

BACKGROUND

Because the interrelationships of objectively ascertained sleep-disordered breathing (SDB), postcardiac surgery atrial fibrillation (PCSAF), and obesity remain unclear, we aimed to further investigate the interrelationships in a clinic-based cohort.

METHODS

Patients with polysomnography and cardiac surgery (coronary artery bypass surgery and/or valvular surgery) within 3 years, from January 2009 to January 2014, were identified, excluding those with preexisting atrial fibrillation. Logistic models were used to determine the association of SDB (apnea hypopnea index [AHI] per 5-unit increase) and secondary predictors (central sleep apnea [CSA] [central apnea index ≥ 5] and oxygen desaturation index [ODI]) with PCSAF. Models were adjusted for age, sex, race, BMI, and hypertension. Statistical interaction and stratification by median BMI was performed. ORs and 95% CIs are presented.

RESULTS

There were 190 patients who comprised the analytic sample (mean age, 60.6 ± 11.4 years; 36.1% women; 80% white; BMI, 33.3 ± 7.5 kg/m²; 93.2% had an AHI ≥ 5; 30% had PCSAF). Unlike unadjusted analyses (OR, 1.06; 95% CI, 1.01-1.1), in the adjusted model, increasing AHI was not significantly associated with increased odds of PCSAF (OR, 1.04; 95% CI, 0.98-1.1). Neither CSA nor ODI was associated with PCSAF. A significant interaction with median BMI was noted (P = .015). Effect modification by median BMI was observed; those with a higher BMI > 32 kg/m² had 15% increased odds of PCSAF (OR, 1.15; 95% CI, 1.05-1.26; P < .003).

CONCLUSIONS

SDB was significantly associated with PCSAF in unadjusted analyses, but not after taking into account obesity; those with both SDB and obesity may represent a vulnerable subgroup to target to reduce PCSAF and its associated morbidity.

OSA and Cardiac Arrhythmogenesis: Mechanistic Insights

A surge of data has reproducibly identified strong associations of OSA with cardiac arrhythmias. As an extension of epidemiologic and clinic-based findings, experimental investigations have made strides in advancing our understanding of the putative OSA and cardiac arrhythmogenesis mechanistic underpinnings. Although most studies have focused on the links between OSA and atrial fibrillation (AF), relationships with ventricular arrhythmias have also been characterized. Key findings implicate OSA-related autonomic nervous system fluctuations typified by enhanced parasympathetic activation during respiratory events and sympathetic surges subsequent to respiratory events, which contribute to augmented arrhythmic propensity. Other more immediate pathophysiologic influences of OSA-enhancing arrhythmogenesis include intermittent hypoxia, intrathoracic pressure swings leading to atrial stretch, and hypercapnia. Intermediate pathways by which OSA may trigger arrhythmia include increased systemic inflammation, oxidative stress, enhanced prothrombotic state, and vascular dysfunction. Long-term OSA-associated sequelae such as hypertension, atrial enlargement and fibrosis, ventricular hypertrophy, and coronary artery disease also predispose to cardiac arrhythmia. These factors can lead to a reduction in atrial effective refractory period, triggered and abnormal automaticity, and promote slowed and heterogeneous conduction; all of these mechanisms increase the persistence of reentrant arrhythmias and prolong the QT interval. Cardiac electrical and structural remodeling observed in OSA animal models can progress the arrhythmogenic substrate to further enhance arrhythmia generation. Future investigations clarifying the contribution of specific OSA-related mechanistic pathways to arrhythmia generation may allow targeted preventative therapies to mitigate OSA-induced arrhythmogenicity. Furthermore, interventional studies are needed to clarify the impact of OSA pathophysiology reversal on cardiac arrhythmogenesis and related adverse outcomes.

Atrial Fibrillation And Sleep Apnea: Considerations For A Dual Epidemic

Atrial fibrillation (AF) is the most common cardiac arrhythmia and shares many of the same risk factors as another common clinical condition, sleep apnea. The estimated prevalence of sleep apnea has increased over the past decade, and reflects a parallel increase in the most prominent risk factors of obesity and overweight. Both obstructive and central sleep apnea have been associated with AF in multiple studies, with the risk of AF increasing 2-4-fold compared to those without sleep breathing disorder. Continuous positive airway pressure (CPAP) has been shown to reduce the rate of AF recurrence following catheter ablation in patients with sleep apnea. However, the mechanisms by which sleep apnea precipitates AF or vice versa, remain unclear. In this Review, we examine the current date linking AF and sleep apnea, discuss the existing data supporting a mechanistic link between the two conditions, present the existing evidence for the effectiveness of CPAP in this growing population, and suggest approaches to screen AF patients for sleep breathing disorders.

Chemoreflexes, sleep apnea, and sympathetic dysregulation

Obstructive sleep apnea (OSA) and hypertension are closely linked conditions. Disordered breathing events in OSA are characterized by increasing efforts against an occluded airway while asleep, resulting in a marked sympathetic response. This is predominantly due to hypoxemia activating the chemoreflexes, resulting in reflex increases in sympathetic neural outflow. In addition, apnea - and the consequent lack of inhibition of the sympathetic system that occurs with lung inflation during normal breathing - potentiates central sympathetic outflow. Sympathetic activation persists into the daytime, and is thought to contribute to hypertension and other adverse cardiovascular outcomes. This review discusses chemoreflex physiology and sympathetic modulation during normal sleep, as well as the sympathetic dysregulation seen in OSA, its extension into wakefulness, and changes after treatment. Evidence supporting the role of the peripheral chemoreflex in the sympathetic dysregulation seen in OSA, including in the context of comorbid obesity, metabolic syndrome, and systemic hypertension, is reviewed. Finally, alterations in cardiovascular variability and other potential mechanisms that may play a role in the autonomic imbalance in OSA are also discussed.

The histology of human right atrial tissue in patients with high-risk Obstructive Sleep Apnea and underlying cardiovascular disease: A pilot study

Background

Obstructive Sleep Apnea (OSA) results in intermittent hypoxia leading to atrial remodeling, which, among other things, facilitates development of atrial fibrillation. While much data exists on the macrostructural changes in cardiac physiology induced by OSA, there is a lack of studies looking for histologic changes in human atrial tissue induced by OSA which might lead to the observed macrostructural changes.

Methods

A case control study was performed. Patients undergoing coronary artery bypass grafting (CABG) were evaluated for OSA and categorized as high-risk or low-risk. The right atrial tissue samples were obtained during CABG and both microscopic histological analysis and Sirius Red staining were performed.

Results

18 patients undergoing CABG were included; 10 high-risk OSA and 8 low-risk OSA in evenly matched populations. No statistically significant difference between the two groups was observed in amount of myocytolysis (p = 0.181), nuclear hypertrophy (p = 0.671), myocardial inflammation (p = n/a), amyloid deposition (p = n/a), or presence of thrombi (p = n/a), as measured through routine H&E staining. As well, no statistically significant difference in interstitial and epicardial collagen was observed, as measured by Sirius Red staining (for total tissue: p = 0.619: for myocardium: p = 0.776).

Conclusions

In this pilot study there were no observable histological differences in human right atrial tissue from individuals at high- and low-risk for OSA. Further investigation would be required for more definitive results.

Low-level vagosympathetic trunk stimulation inhibits atrial fibrillation in a rabbit model of obstructive sleep apnea

BACKGROUND

Atrial fibrillation (AF) is highly associated with obstructive sleep apnea (OSA) in which AF is triggered by hyperactivity of the cardiac autonomic nervous system. Previous studies showed that low-level vagosympathetic trunk stimulation (LLVS), at voltages not slowing sinus rate or AV conduction, inhibits AF by suppressing the cardiac autonomic nervous system.

OBJECTIVE

The purpose of this study was to investigate whether LLVS delivered at the right vagosympathetic trunk suppresses AF in a rabbit model of OSA.

METHODS

Eleven rabbits received a tracheostomy under general anesthesia. The endotracheal tube was clamped at end expiration for 1 minute to simulate OSA. Over a period of 4 hours, OSA was delivered every 6 minutes. Effective refractory period (ERP), blood pressure, intraesophageal pressure, and blood gases (O2, CO2, pH) were measured before and after each episode of OSA. AF duration and ERP were measured by programmed stimulation. Group 1 rabbits (n = 6) received LLVS (50% below that which slowed the sinus rate) in the first 3 hours. Group 2 rabbits (n = 5) only received OSA.

RESULTS

Group 1 ERP began to lengthen progressively from the second hour compared to group 2. AF duration increased in the first hour for both groups but began to shorten progressively after the first hour in group 1 rabbits. Blood pH, O2 or CO2 level, intraesophageal pressure, and hypertensive response during OSA were not different between the 2 groups.

CONCLUSION

LLVS is capable of suppressing ERP shortening and AF induced by OSA. LLVS may serve as a new therapeutic approach to treat OSA-induced AF.