Is structural remodeling of fibrillated atria the consequence of tissue hypoxia?

Oxidative Stress, Inflammation, and Mitochondrial Dysfunction: A Link between Obesity and Atrial Fibrillation

The adipose tissue has long been thought to represent a passive source of triglycerides and fatty acids. However, extensive data have demonstrated that the adipose tissue is also a major endocrine organ that directly or indirectly affects the physiological functions of almost all cell types. Obesity is recognized as a risk factor for multiple systemic conditions, including metabolic syndrome, type 2 diabetes mellitus, sleep apnea, cardiovascular disorders, and many others. Obesity-related changes in the adipose tissue induce functional and structural changes in cardiac myocytes, promoting a wide range of cardiovascular disorders, including atrial fibrillation (AF). Due to the wealth of epidemiologic data linking AF to obesity, the mechanisms underlying AF occurrence in obese patients are an area of rich ongoing investigation. However, progress has been somewhat slowed by the complex phenotypes of both obesity and AF. The triad inflammation, oxidative stress, and mitochondrial dysfunction are critical for AF pathogenesis in the setting of obesity via multiple structural and functional proarrhythmic changes at the level of the atria. The aim of this paper is to provide a comprehensive view of the close relationship between obesity-induced oxidative stress, inflammation, and mitochondrial dysfunction and the pathogenesis of AF. The clinical implications of these mechanistic insights are also discussed.

Identification and validation of potential biomarkers for atrial fibrillation based on integrated bioinformatics analysis

Background: Globally, the most common form of arrhythmias is atrial fibrillation (AF), which causes severe morbidity, mortality, and socioeconomic burden. The application of machine learning algorithms in combination with weighted gene co-expression network analysis (WGCNA) can be used to screen genes, therefore, we aimed to screen for potential biomarkers associated with AF development using this integrated bioinformatics approach. Methods: On the basis of the AF endocardium gene expression profiles GSE79768 and GSE115574 from the Gene Expression Omnibus database, differentially expressed genes (DEGs) between AF and sinus rhythm samples were identified. DEGs enrichment analysis and transcription factor screening were then performed. Hub genes for AF were screened using WGCNA and machine learning algorithms, and the diagnostic accuracy was assessed by the receiver operating characteristic (ROC) curves. GSE41177 was used as the validation set for verification. Subsequently, we identified the specific signaling pathways in which the key biomarkers were involved, using gene set enrichment analysis and reverse prediction of mRNA-miRNA interaction pairs. Finally, we explored the associations between the hub genes and immune microenvironment and immune regulation. Results: Fifty-seven DEGs were identified, and the two hub genes, hypoxia inducible factor 1 subunit alpha inhibitor (HIF1AN) and mitochondrial inner membrane protein MPV17 (MPV17), were screened using WGCNA combined with machine learning algorithms. The areas under the receiver operating characteristic curves for MPV17 and HIF1AN validated that two genes predicted AF development, and the differential expression of the hub genes was verified in the external validation dataset. Enrichment analysis showed that MPV17 and HIF1AN affect mitochondrial dysfunction, oxidative stress, gap junctions, and other signaling pathway functions. Immune cell infiltration and immunomodulatory correlation analyses showed that MPV17 and HIF1AN are strongly correlated with the content of immune cells and significantly correlated with HLA expression. Conclusion: The identification of hub genes associated with AF using WGCNA combined with machine learning algorithms and their correlation with immune cells and immune gene expression can elucidate the molecular mechanisms underlying AF occurrence. This may further identify more accurate and effective biomarkers and therapeutic targets for the diagnosis and treatment of AF.

Vascular Endothelial Barrier Protection Prevents Atrial Fibrillation by Preserving Cardiac Nanostructure

BACKGROUND

Atrial fibrillation (AF), the most common cardiac arrhythmia, is widely associated with inflammation, vascular dysfunction, and elevated levels of the vascular leak-inducing cytokine, vascular endothelial growth factor (VEGF). Mechanisms underlying AF are poorly understood and current treatments only manage this progressive disease, rather than arresting the underlying pathology. The authors previously identified edema-induced disruption of sodium channel (NaV1.5)-rich intercalated disk nanodomains as a novel mechanism for AF initiation secondary to acute inflammation. Therefore, we hypothesized that protecting the vascular barrier can prevent vascular leak-induced atrial arrhythmias.

OBJECTIVES

In this study the authors tested the hypothesis that protecting the vascular barrier can prevent vascular leak-induced atrial arrhythmias. They identified 2 molecular targets for vascular barrier protection, connexin43 (Cx43) hemichannels and pannexin-1 (Panx1) channels, which have been implicated in cytokine-induced vascular leak.

METHODS

The authors undertook in vivo electrocardiography, electron microscopy, and super-resolution light microscopy studies in mice acutely treated with a clinically relevant level of VEGF.

RESULTS

AF incidence was increased in untreated mice exposed to VEGF relative to vehicle control subjects. VEGF also increased the average number of AF episodes. VEGF shifted NaV1.5 signal to longer distances from Cx43 gap junctions, measured by a distance transformation-based spatial analysis of 3-dimensional confocal images of intercalated disks. Similar effects were observed with NaV1.5 localized near mechanical junctions composed of neural cadherin. Blocking connexin43 hemichannels (αCT11 peptide) or Panx1 channels (PxIL2P peptide) significantly reduced the duration of AF episodes compared with VEGF alone with no treatment. Concurrently, both peptide therapies preserved NaV1.5 distance from gap junctions to control levels and reduced mechanical junction-adjacent intermembrane distance in these hearts. Notably, similar antiarrhythmic efficacy was also achieved with clinically-relevant small-molecule inhibitors of Cx43 and Panx1.

CONCLUSIONS

These results highlight vascular barrier protection as an antiarrhythmic strategy following inflammation-induced vascular leak.

Downregulation of FKBP5 Promotes Atrial Arrhythmogenesis

BACKGROUND

Atrial fibrillation (AF), the most common arrhythmia, is associated with the downregulation of FKBP5 (encoding FKBP5 [FK506 binding protein 5]). However, the function of FKBP5 in the heart remains unknown. Here, we elucidate the consequences of cardiomyocyte-restricted loss of FKBP5 on cardiac function and AF development and study the underlying mechanisms.

METHODS

Right atrial samples from patients with AF were used to assess the protein levels of FKBP5. A cardiomyocyte-specific FKBP5 knockdown mouse model was established by crossbreeding Fkbp5flox/flox mice with Myh6MerCreMer/+ mice. Cardiac function and AF inducibility were assessed by echocardiography and programmed intracardiac stimulation. Histology, optical mapping, cellular electrophysiology, and biochemistry were employed to elucidate the proarrhythmic mechanisms due to loss of cardiomyocyte FKBP5.

RESULTS

FKBP5 protein levels were lower in the atrial lysates of patients with paroxysmal AF or long-lasting persistent (chronic) AF. Cardiomyocyte-specific knockdown mice exhibited increased AF inducibility and duration compared with control mice. Enhanced AF susceptibility in cardiomyocyte-specific knockdown mice was associated with the development of action potential alternans and spontaneous Ca2+ waves, and increased protein levels and activity of the NCX1 (Na+/Ca2+-exchanger 1), mimicking the cellular phenotype of chronic AF patients. FKBP5-deficiency enhanced transcription of Slc8a1 (encoding NCX1) via transcription factor hypoxia-inducible factor 1α. In vitro studies revealed that FKBP5 negatively modulated the protein levels of hypoxia-inducible factor 1α by competitively interacting with heat-shock protein 90. Injections of the heat-shock protein 90 inhibitor 17-AAG normalized protein levels of hypoxia-inducible factor 1α and NCX1 and reduced AF susceptibility in cardiomyocyte-specific knockdown mice. Furthermore, the atrial cardiomyocyte-selective knockdown of FKBP5 was sufficient to enhance AF arrhythmogenesis.

CONCLUSIONS

This is the first study to demonstrate a role for the FKBP5-deficiency in atrial arrhythmogenesis and to establish FKBP5 as a negative regulator of hypoxia-inducible factor 1α in cardiomyocytes. Our results identify a potential molecular mechanism for the proarrhythmic NCX1 upregulation in chronic AF patients.

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.

Hypoxia signaling in human health and diseases: implications and prospects for therapeutics

Molecular oxygen (O₂) is essential for most biological reactions in mammalian cells. When the intracellular oxygen content decreases, it is called hypoxia. The process of hypoxia is linked to several biological processes, including pathogenic microbe infection, metabolic adaptation, cancer, acute and chronic diseases, and other stress responses. The mechanism underlying cells respond to oxygen changes to mediate subsequent signal response is the central question during hypoxia. Hypoxia-inducible factors (HIFs) sense hypoxia to regulate the expressions of a series of downstream genes expression, which participate in multiple processes including cell metabolism, cell growth/death, cell proliferation, glycolysis, immune response, microbe infection, tumorigenesis, and metastasis. Importantly, hypoxia signaling also interacts with other cellular pathways, such as phosphoinositide 3-kinase (PI3K)-mammalian target of rapamycin (mTOR) signaling, nuclear factor kappa-B (NF-κB) pathway, extracellular signal-regulated kinases (ERK) signaling, and endoplasmic reticulum (ER) stress. This paper systematically reviews the mechanisms of hypoxia signaling activation, the control of HIF signaling, and the function of HIF signaling in human health and diseases. In addition, the therapeutic targets involved in HIF signaling to balance health and diseases are summarized and highlighted, which would provide novel strategies for the design and development of therapeutic drugs.

Vascular endothelial growth factor modulates pulmonary vein arrhythmogenesis via vascular endothelial growth factor receptor 1/NOS pathway

Atrial fibrillation (AF) is a common form of arrhythmia with serious public health impacts, but its underlying mechanisms are not yet fully understood. Vascular endothelial growth factor (VEGF) is highly expressed in the atrium of patients with AF, but whether VEGF affects AF pathogenesis remains unclear. Pulmonary veins (PVs) are important sources for the genesis of atrial tachycardia or AF. Therefore, this study assessed the effects of VEGF on PV electrophysiological properties and evaluated its underlying mechanisms. Conventional microelectrodes and whole-cell patch clamps were performed using isolated rabbit PV preparations or single isolated PV cardiomyocytes before and after VEGF or VEGF receptor (VEGFR), Akt, NOS inhibitor administration. We found that VEGF (0.1, 1, and 10 ng/mL) reduced the PV beating rate in a dose-dependent manner. Furthermore, VEGF (10 ng/mL) reduced late diastolic depolarization and diastolic tension. Isoproterenol increased PV beating and burst firing, which was attenuated by VEGF (1 ng/mL). In the presence of VEGFR-1 inhibition (ZM306416 at 10 μM) and L-NAME (100 μM), VEGF (1 ng/mL) did not alter PV spontaneous activity. In isolated PV cardiomyocytes, VEGF (1 ng/mL) decreased L-type calcium, sodium/calcium exchanger, and late sodium currents. In conclusion, we found that VEGF reduces PV arrhythmogenesis by modulating sodium/calcium homeostasis through VEGFR-1/NOS signaling pathway.

Atrial fibrillation before heart transplantation is a risk factor for post-transplant atrial fibrillation and mortality

AIMS

Atrial fibrillation (AF) after heart transplantation (HTX) is associated with worse clinical outcomes. The current study aimed to analyse the association between AF before HTX and AF within 30 days after HTX.

METHODS AND RESULTS

This study included 639 adults who received HTX at Heidelberg Heart Center. Patients were subdivided into four groups depending on the status of AF before and after HTX. Analyses comprised recipient and donor data, medication, echocardiographic features, permanent pacemaker implantation, stroke, and mortality after HTX. Three hundred thirty-two patients (52.0%) had neither AF before nor after HTX, 15 patients (2.3%) had no AF before HTX but showed AF after HTX, 219 patients (34.3%) showed AF before HTX but had no AF after HTX, and 73 patients (11.4%) had AF before and after HTX. Patients with AF before and after HTX had a higher 1 year post-transplant mortality (39.7%) than patients without AF before or after HTX (18.1%, P < 0.01). Secondary outcomes showed a higher percentage of enlarged atria, ventricular dysfunction, mitral regurgitation, 1-year stroke, and 1-year permanent pacemaker implantation in patients with AF before and after HTX. Multivariate analysis revealed a six-fold elevated risk for post-transplant AF in patients with AF before HTX (hazard ratio: 6.59, confidence interval: 3.72-11.65; P < 0.01). Further risk factors for post-transplant AF were higher donor age and prolonged ischaemic time, whereas total orthotopic HTX was associated with a two-fold lower risk for post-transplant AF.

CONCLUSIONS

Atrial fibrillation before HTX is a risk factor for post-transplant AF, permanent pacemaker implantation, and mortality after HTX.

Association of Nocturnal Hypoxemia and Pulse Rate Variability with Incident Atrial Fibrillation in Patients Investigated for Obstructive Sleep Apnea

Rationale: Nocturnal hypoxemia and sympathetic/parasympathetic imbalance might contribute to the occurrence or atrial fibrillation (AF) in patients with obstructive sleep apnea (OSA). During sleep recordings, pulse rate variability (PRV) derived from oximetry might provide an accurate estimation of heart rate variability, which reflects the autonomic cardiovascular control. Objectives: We aimed to evaluate whether indices of oxygen desaturation and PRV derived from nocturnal oximetry were associated with AF incidence in patients investigated for OSA. Methods: Data from a large multicenter cohort of AF-free patients investigated for OSA between May 15, 2007, and December 31, 2017, were linked to health administrative data to identify hospitalized and nonhospitalized patients with new-onset AF. Cox proportional hazards models were used to evaluate the association between AF incidence and oximetry-derived indices automatically generated from sleep recordings. Results: After a median (interquartile range) follow-up of 5.34 (3.3-8.0) years, 181 of 7,205 patients developed AF (130 were hospitalized for AF). After adjusting for confounders, including anthropomorphic data, alcohol intake, cardiac, metabolic and respiratory diseases, β blocker/calcium channel blocker medications, type of sleep study, study site, and positive airway pressure adherence, AF risk was associated with increasing nocturnal hypoxemia (P trend = 0.004 for quartiles of percentage of recording time with oxygen saturation <90%) and PRV (P trend < 0.0001 for quartiles of root mean square of the successive normal-normal beat interval differences), and decreasing sympathetic/parasympathetic tone (P trend = 0.0006 for quartiles of low-frequency power/high-frequency power ratio). The highest risk of AF was observed in patients with the highest quartiles of both the percentage of recording time with oxygen saturation <90% and the root mean square of the successive normal-normal beat interval differences compared with those with neither of these conditions (adjusted hazard ratio, 3.61; 95% confidence interval, 2.10-6.22). Similar associations were observed when the analyses were restricted to hospitalized AF. Conclusions: In patients investigated for OSA, nocturnal hypoxemia and PRV indices derived from single-channel pulse oximetry were independent predictors of AF incidence. Patients with both marked nocturnal hypoxemia and high PRV were at higher risk of AF. Oximetry may be used to identify patients with OSA at greatest risk of developing AF.

Atrial fibrillation: the role of hypoxia-inducible factor-1-regulated cytokines

Atrial fibrillation (AF) is a common arrhythmia that has major morbidity and mortality. Hypoxia plays an important role in AF initiation and maintenance. Hypoxia-inducible factor (HIF), the master regulator of oxygen homeostasis in cells, plays a fundamental role in the regulation of multiple chemokines and cytokines that are involved in different physiological and pathophysiological pathways. HIF is also involved in the pathophysiology of AF induction and propagation mostly through structural remodeling such as fibrosis; however, some of the cytokines discussed have even been implicated in electrical remodeling of the atria. In this article, we highlight the association between HIF and some of its related cytokines with AF. Additionally, we provide an overview of the potential diagnostic benefits of using the mentioned cytokines as AF biomarkers. Research discussed in this review suggests that the expression of these cytokines may correlate with patients who are at an increased risk of developing AF. Furthermore, cytokines that are elevated in patients with AF can assist clinicians in the diagnosis of suspect paroxysmal AF patients. Interestingly, some of the cytokines have been elevated specifically when AF is associated with a hypercoagulable state, suggesting that they could be helpful in the clinician's and patient's decision to begin anticoagulation. Finally, more recent research has demonstrated the promise of targeting these cytokines for the treatment of AF. While still in its early stages, tools such as neutralizing antibodies have proved to be efficacious in targeting the HIF pathway and treating or preventing AF.

Vascular endothelial growth factor promotes atrial arrhythmias by inducing acute intercalated disk remodeling

Atrial fibrillation (AF) is the most common arrhythmia and is associated with inflammation. AF patients have elevated levels of inflammatory cytokines known to promote vascular leak, such as vascular endothelial growth factor A (VEGF). However, the contribution of vascular leak and consequent cardiac edema to the genesis of atrial arrhythmias remains unknown. Previous work suggests that interstitial edema in the heart can acutely promote ventricular arrhythmias by disrupting ventricular myocyte intercalated disk (ID) nanodomains rich in cardiac sodium channels (Na_V1.5) and slowing cardiac conduction. Interestingly, similar disruption of ID nanodomains has been identified in atrial samples from AF patients. Therefore, we tested the hypothesis that VEGF-induced vascular leak can acutely increase atrial arrhythmia susceptibility by disrupting ID nanodomains and slowing atrial conduction. Treatment of murine hearts with VEGF (30–60 min, at clinically relevant levels) prolonged the electrocardiographic P wave and increased susceptibility to burst pacing-induced atrial arrhythmias. Optical voltage mapping revealed slower atrial conduction following VEGF treatment (10 ± 0.4 cm/s vs. 21 ± 1 cm/s at baseline, p < 0.05). Transmission electron microscopy revealed increased intermembrane spacing at ID sites adjacent to gap junctions (GJs; 64 ± 9 nm versus 17 ± 1 nm in controls, p < 0.05), as well as sites next to mechanical junctions (MJs; 63 ± 4 nm versus 27 ± 2 nm in controls, p < 0.05) in VEGF–treated hearts relative to controls. Importantly, super-resolution microscopy and quantitative image analysis revealed reorganization of Na_V1.5 away from dense clusters localized near GJs and MJs to a more diffuse distribution throughout the ID. Taken together, these data suggest that VEGF can acutely predispose otherwise normal hearts to atrial arrhythmias by dynamically disrupting Na_V1.5-rich ID nanodomains and slowing atrial conduction. These data highlight inflammation-induced vascular leak as a potential factor in the development and progression of AF.

Spirometry Assessment and Correlation With Postoperative Pulmonary Complications in Cardiac Surgery Patients

Objective

To observe spirometry and its correlation with postoperative pulmonary complications in cardiac surgery patients.

Study design

Prospective observational study

Place and duration of the study

Chaudhary Pervaiz Elahi Institute of Cardiology (CPEIC) Multan, from January 1, 2017, to June 30, 2020

Methodology

Written informed consent was taken from 357 patients. Spirometry was performed in all the patients using the conventional method. Baseline data, including gender, age, body mass index (BMI), living area, smoking history, known lung illness, six-minute walk distance, predicted forced vital capacity (FVC) %, predicted forced expiratory volume in one second (FEV1) %, and type of the procedure such as aortic valve replacement (AVR), coronary artery bypass grafting (CABG), double-valve replacement (DVR), and mitral valve replacement (MVR) were documented for all the patients. Outcome data included postoperative ICU length of stay (LOS), respiratory failure, respiratory infection, atelectasis, and mortality.

Results

The most common procedure was CABG and MVR proceeded by n=254 (71.1%) and n=83 (23.2%) patients, respectively. Postoperative complications, such as respiratory failure, respiratory infection, and atelectasis, was noted in n=29 (8.1%), n=28 (7.8 %), and n=127 (35.6 %) patients, respectively, while n=5 (1.4%) patients died.

Conclusion

Deranged pulmonary function tests (PFTs) are associated with poor prognosis following elective cardiac surgery in terms of postoperative pulmonary complications such as pulmonary infection, respiratory failure, and atelectasis. There is a significant difference in percentage predicted of FVC and FEV1 in patients who developed atelectasis and respiratory tract infection.

Vascular endothelial growth factor enhances profibrotic activities through modulation of calcium homeostasis in human atrial fibroblasts

Vascular endothelial growth factor (VEGF), a pivotal activator of angiogenesis and calcium (Ca²⁺) signaling in endothelial cells, was shown to increase collagen production in atrial fibroblasts. In this study, we evaluated whether VEGF may regulate Ca²⁺ homeostasis in atrial fibroblasts and contribute to its profibrogenesis. Migration, and proliferation analyses, patch-clamp assay, Ca²⁺ fluorescence imaging, and western blotting were performed using VEGF-treated (300 pg/mL or 1000 pg/mL) human atrial fibroblasts with or without coadministration of Ethylene glycol tetra-acetic acid (EGTA, 1 mmol/L), or KN93 (a Ca²⁺/calmodulin-dependent protein kinase II [CaMKII] inhibitor, 10 μmol/L). VEGF (1000 pg/mL) increased migration, myofibroblast differentiation, pro-collagen type I, pro-collagen type III production, and phosphorylated VEGF receptor 1 expression of fibroblasts. VEGF (1000 pg/mL) increased the nonselective cation current (I_NSC) of transient receptor potential (TRP) channels and potassium current of intermediate-conductance Ca²⁺-activated K⁺ (K_Ca3.1) channels thereby upregulating Ca²⁺ entry. VEGF upregulated phosphorylated ERK expression. An ERK inhibitor (PD98059, 50 μmol/L) attenuated VEGF-activated I_NSC of TRP channels. The presence of EGTA attenuated the profibrotic effects of VEGF on pro-collagen type I, pro-collagen type III production, myofibroblast differentiation, and migratory capabilities of fibroblasts. VEGF upregulated the expression of phosphorylated CaMKII in fibroblasts, which was attenuated by EGTA. In addition, KN93 reduced VEGF-increased pro-collagen type I, pro-collagen type III production, myofibroblast differentiation, and the migratory capabilities of fibroblasts. In conclusion, we found that VEGF increases atrial fibroblast activity through CaMKII signaling by enhancing Ca²⁺ entry. Our findings provide benchside evidence leading to a potential novel strategy targeting atrial myopathy and arrhythmofibrosis.

Fibrosis independent atrial fibrillation in older patients is driven by substrate leukocyte infiltration: diagnostic and prognostic implications to patients undergoing cardiac surgery

Background

The objectives of the study were to characterize and quantify cellular inflammation and structural remodeling of human atria and correlate findings with molecular markers of inflammation and patient surrogate outcome.

Methods

Voluntary participants undergoing heart surgery were enrolled in the study and blood samples were collected prior to surgery, and right atrium samples were harvested intraoperatively. Blood samples were analyzed by flow cytometry and complete blood counts. Atrial samples were divided for fixed fibrosis analysis, homogenized for cytokine analysis and digested for single cell suspension flow cytometry.

Results

A total of 18 patients were enrolled and samples assessed. Isolated cells from the atria revealed a CD45+ population of ~ 20%, confirming a large number of leukocytes. Further characterization revealed this population as 57% lymphocytes and 26% monocyte/macrophages (MoΦ), with the majority of the latter cells being classical (CD14++/CD16−). Interstitial fibrosis was present in 87% of samples and correlated significantly with patient age. Older patients (> 65) had significantly more atrial fibrosis and cellular inflammation. AFib patients had no distinguishing feature of atrial fibrosis and had significantly greater CD45+ MoΦ, increased expression of MMP9 and presented with a significant correlation in length of stay to CCL-2/MCP-1 and NLR (neutrophil-to-lymphocyte ratio).

Conclusion

Atrial fibrosis is correlated with age and not determinate to AFib. However, severity of atrial leukocyte infiltration and markers of matrix degradation are determinant to AFib. This also correlated with CCL2 (or MCP-1) and NLR-indicative of marked inflammation. These data show the potential importance of diagnostic and prognostic assessments that could inform clinical decision making in regard to the intensity of AFib patient management.

Does an imbalance in circulating vascular endothelial growth factors (VEGFs) cause atrial fibrillation in patients with valvular heart disease?

Background

The pathogenesis of atrial fibrillation (AF) remains unclear. Vascular endothelial growth factors (VEGFs) can stimulate fibrosis within the atrium and ventricle. We hypothesized that there is a relationship between the serum VEGFs/soluble vascular endothelial growth factor receptor (sVEGFRs) levels and AF in patients with valvular heart disease (VHD). This provides a new paradigm for studying AF.

Methods

The plasma levels of VEGF-A, VEGF-C, sVEGFR-1 and sVEGFR-2 were detected by enzyme-linked immunosorbent assay (ELISA). A total of 100 people, consisting of AF patients (long-standing, persistent AF; n=49), sinus rhythm (SR) patients (n=31) and healthy controls (n=20), were included in this study.

Results

The plasma levels of VEGF-A were significantly higher in AF patients compared to healthy control (P<0.05). The plasma levels of sVEGFR-1 were significantly higher in AF compared to SR (P<0.05). The plasma levels of sVEGFR-2 were significantly lower in AF patients compared to SR patients and healthy controls (both P<0.05). There was a significant and negative correlation between AF and the sVEGFR-2 levels in the groups (r=-0.432, P=0.000).

Conclusions

An imbalance in VEGFs and sVEGFRs may contribute to AF by breaking the balance of angiogenesis and lymphangiogenesis. Additionally, sVEGFR-2 may be an important biomarker of AF.

Abnormal pulmonary function tests are associated with prolonged ventilation and risk of complications following elective cardiac surgery

Elective cardiac surgery accounts for a significant proportion of perioperative resource allocation in Australasia. Preoperative pulmonary function testing (PFT) is routinely undertaken in some centres to identify patients who may require prolonged ventilation and intensive care unit (ICU) stay, although there are currently no data supporting this practice. Routine PFT places a burden on respiratory diagnostic laboratories, is inconvenient to patients and may delay surgery. We aimed to identify whether PFT parameters identify patients requiring prolonged mechanical ventilation after elective cardiac surgery. Adult patients admitted to the Royal Adelaide Hospital ICU following elective cardiac surgery between July 2013 and December 2017 were identified retrospectively from the local ICU database. Preoperative PFT and operative and postoperative outcome data were retrieved from local databases, and multivariable logistic regression was undertaken to identify which PFT variables were associated with prolonged mechanical ventilation. PFT data were available for 835/1139 (73%) elective cardiac surgical cases. The best independent predictors of prolonged mechanical ventilation were post-bronchodilator forced vital capacity (FVC) and single-breath diffusing capacity for carbon monoxide (DLCO). Patients with FVC <80% predicted and DLCO <60% predicted had an odds ratio for prolonged postoperative ventilation of 7.5 (95% confidence intervals 3.6–15.6; P < 0.001). The area under the receiver operating characteristic curve derived from this model was 0.68. Abnormal PFT results were associated with prolonged postoperative mechanical ventilation. A PFT-based prediction tool does not accurately predict individual patient outcome but identifies a cohort of patients at higher risk of requiring prolonged ventilation, potentially informing ICU resource allocation and surgical planning.

Acute Exacerbation of Chronic Obstructive Pulmonary Disease and Subsequent Risk of Emergency Department Visits and Hospitalizations for Atrial Fibrillation

Background Although emerging evidence has suggested the relationship of chronic obstructive pulmonary disease with atrial fibrillation (AF), little is known about whether acute exacerbation of chronic obstructive pulmonary disease (AECOPD) increases the risk of repeated AF-related healthcare utilization. Methods This is a self-controlled case series study using the population-based emergency department (ED) and inpatient databases of 5 US states from 2007 through 2012. Among patients with existing AF, we identified patients with an AECOPD hospitalization and at least 1 ED visit or hospitalization for AF during the observation period. We constructed conditional Poisson regression models to compare the rate of AF-related ED visits or hospitalizations during sequential 90-day periods after the AECOPD hospitalization, with pre-AECOPD days 1 to 90 as the reference. Results We analyzed 944 patients who were hospitalized for AECOPD and had an ED visit or hospitalization for AF during a 450-day period. The median age was 77 years, and 41% were men. Compared with the reference period, the rate of AF-related ED visits or hospitalizations significantly increased in the post-AECOPD days 1 to 90 (7.3 versus 14.1 per 100 person-months; rate ratio, 1.93; 95% CI, 1.63-2.29; P<0.001). Then, the rate decreased to the reference level in the post-AECOPD days 91 to 180 (7.5 per 100 person-months; rate ratio, 1.03; 95% CI, 0.85-1.25; P=0.77) and remained at the reference level during post-AECOPD days 181 to 270 (rate ratio, 0.84; 95% CI, 0.68-1.03; P=0.09) and days 271 to 360 (rate ratio, 0.90; 95% CI, 0.73-1.10; P=0.29). These temporal associations persisted with stratification by age, sex, and season. Conclusions Among patients with existing AF, AECOPD was associated with a higher risk of AF-related ED visit or hospitalization in the first 90-day post-AECOPD period.

The Warburg effect: A new insight into atrial fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia. Atrial remodeling, including electrical/structural/autonomic remodeling, plays a vital role in AF pathogenesis. All of these have been shown to contribute continuously to the self-perpetuating nature of AF. The Warburg effect was found to play important roles in tumor and non-tumor disease. Recently, lots of studies documented altered atrial metabolism in AF, but the specific mechanism and the impact of these changes upon AF initiation/progression remain unclear. In this article, we review the metabolic consideration in AF comprehensively and observe the footprints of the Warburg effect. We also summarize the signaling pathway involved in the Warburg effect during AF-HIF-1α and AMPK, and discuss their potential roles in AF maintenance and progression. In conclusion, we give the innovative idea that the Warburg effect exists in AF and promotes the progression of AF. Targeting it may provide new therapies for AF treatment.

A prospective study of the clinical outcomes and prognosis associated with comorbid COPD in the atrial fibrillation population

Background

Patients with COPD are at higher risk of presenting with atrial fibrillation (AF). Information about clinical outcomes and optimal medical treatment of AF in the setting of COPD remains missing. We aimed to describe the prevalence of COPD in a sizeable cohort of real-world AF patients belonging to the same healthcare area and to examine the relationship between comorbid COPD and AF prognosis.

Methods

Prospective analysis performed in a specific healthcare area. Data were obtained from several sources within the “data warehouse of the Galician Healthcare Service” using multiple analytical tools. Statistical analyses were completed using SPSS 19 and STATA 14.0.

Results

A total of 7,990 (2.08%) patients with AF were registered throughout 2013 in our healthcare area (n=348,985). Mean age was 76.83±10.51 years and 937 (11.7%) presented with COPD. COPD patients had a higher mean CHA₂DS₂-VASc (4.21 vs 3.46; P=0.02) and received less beta-blocker and more digoxin therapy than those without COPD. During a mean follow-up of 707±103 days, 1,361 patients (17%) died. All-cause mortality was close to two fold higher in the COPD group (28.3% vs 15.5%; P<0.001). Independent predictive factors for all-cause mortality were age, heart failure, diabetes, previous thromboembolic event, dementia, COPD, and oral anticoagulation (OA). There were nonsignificant differences in thromboembolic events (1.7% vs 1.5%; P=0.7), but the rate of hemorrhagic events was significantly higher in the COPD group (3.3% vs 1.9%; P=0.004). Age, valvular AF, OA, and COPD were independent predictive factors for hemorrhagic events. In COPD patients, age, heart failure, vasculopathy, lack of OA, and lack of beta-blocker use were independent predictive factors for all-cause mortality.

Conclusion

AF patients with COPD have a higher incidence of adverse events with significantly increased rates of all-cause mortality and hemorrhagic events than AF patients without COPD. However, comorbid COPD was not associated with differences in cardiovascular death or stroke rate. OA and beta-blocker treatment presented a risk reduction in mortality while digoxin use exerted a neutral effect.

COPD in patients after heart transplantation is associated with a prolonged hospital stay, early posttransplant atrial fibrillation, and impaired posttransplant survival

Objectives

COPD is associated with reduced physical activity, an increased risk for pulmonary infections, and impaired survival in nontransplant patients. The aim of this study was to investigate the influence of COPD in patients after heart transplantation (HTX).

Methods

We performed an observational retrospective single-center study of 259 patients receiving HTX at Heidelberg University Hospital between 2003 and 2012. Patients were stratified by the Tiffeneau index (forced expiratory volume in 1 second/forced vital capacity [FEV1/FVC]) <0.70 before HTX. The analysis included demographics, posttransplant medication, length of the initial hospital stay after HTX, early posttransplant atrial fibrillation (AF), mortality, and causes of death.

Results

In total, 63 (24.3%) patients had an FEV1/FVC <0.70. These patients showed a prolonged hospital stay after HTX (52.0 days vs 43.4 days, mean difference (MD) = 8.6 days, 95% CI: 0.2, 17.0 days), a higher rate of early posttransplant AF (19.0% vs 8.2%, MD = 10.8%, 95% CI: 0.4%, 21.2%), and an increased 30-day mortality (9.5% vs 2.6%, HR = 3.79, 95% CI: 1.16, 12.40). Kaplan– Meier analysis showed a significant inferior 5-year survival in patients with an FEV1/FVC <0.70, along with a higher percentage of death due to transplant failure and infection/sepsis. In addition, a multivariate analysis for mortality within 5 years after HTX indicated an FEV1/FVC <0.70 as a significant risk factor for impaired 5-year posttransplant survival (HR =4.77, 95% CI: 2.76, 8.22).

Conclusion

COPD in patients after HTX is associated with a prolonged hospital stay, early posttransplant AF, and impaired posttransplant survival.

The impact of atrial fibrillation in patients with COPD during hospitalization

Background

Atrial fibrillation (AF) occurs frequently in patients with COPD. There are limited data about the impact of AF in hospitalized COPD patients on other serious health outcomes, such as acute organ dysfunction, severe sepsis, and respiratory failure. The aim of our study was to delineate the impact of AF in hospitalized COPD patients.

Methods

We defined COPD populations with and without AF from the National Health Insurance database in Taiwan. The control subjects (patients with COPD without AF) were selected from the population of COPD patients who had no history of AF and were matched to the COPD patients with AF by age (±1 year), gender, and the year of COPD diagnosis (±1 year). The primary outcome was the time to any first event, which included acute organ dysfunction, severe sepsis, respiratory failure, and death during the hospitalization period. Secondary outcomes, which also included acute organ dysfunction, severe sepsis, respiratory failure, and death, were estimated separately over time.

Results

The primary outcome probability was higher in COPD patients with AF than in COPD patients without AF, with an adjusted HR (aHR) of 1.169 (95% confidence interval [CI]: 1.034–1.320), and higher risks of acute organ dysfunction and respiratory failure were also observed in the former group, with aHRs of 1.179 (95% CI: 1.0370–1.339) and 1.176 (95% CI: 1.006–1.374), respectively.

Conclusion

Compared with COPD patients without AF, those with AF had a higher risk of hepatic dysfunction and respiratory failure.

The progression in atrial fibrillation patients with COPD: a systematic review and meta-analysis

AIM

Chronic Obstructive Pulmonary Disease (COPD) and atrial fibrillation (AF) share pathophysiological links, as supported by the high prevalence of AF within COPD patients. AF progression and recurrence can increase the risks of mortality, morbidity and adverse cardiovascular events. The present systematic review and meta-analysis aims to assess the risk for AF progression and recurrence for COPD patients, to further demonstrate the risk of COPD in AF patients.

METHODS AND RESULTS

A systematic review was conducted in MEDLINE / PubMed and Cochrane Library and Embase, Web of science. Prospective studies including AF patients with COPD were screened and included if matching inclusion and exclusion criteria. 7 studies were included, adding up to 10761 AF patients (1556 with AF and COPD, 9205 without COPD). Mean age from each study ranged from 51 to 81 years, and 57.2% were male. Hypertension accounted for 75.5% of the population, and 20.7% had the comorbidity of diabetes mellitus. The pool analysis showed that COPD could promote AF progression (OR = 1.90; 95% CI, 1.34-2.68, I² = 77%, p = 0.0003). For subgroup analysis, we found that COPD could increase the risk of AF recurrence (OR = 2.35; 95% CI, 1.86-2.97, I² = 0%, p = 0.39). Besides, in the younger group, at the median age of 64, COPD was still a risk factor for AF progression (OR = 2.22; 95% CI, 1.80-2.74, I² = 0%, p = 0.69).

CONCLUSIONS

COPD is an independent risk for AF progression and recurrence, COPD patients with AF carry a worse prognosis than those in sinus rhythm (SR).

Incidence and risk factors of atrial fibrillation in Asian COPD patients

Objective

To investigate the incidence and risk factors of atrial fibrillation (AF) in Asian chronic obstructive pulmonary disease (COPD) patients.

Patients and methods

We selected a study population older than 40 years with a COPD diagnosis and who had used at least one inhaled bronchodilator medication between 1998 and 2012. The date of the index COPD diagnosis was defined as the index date. We excluded patients with a history of AF, significant mitral valve disease, disorders of the thyroid gland, or ischemic heart disease before the index date. We followed all patients from the index date to the day of AF occurrence, the day of death, or the date of December 31, 2013. The baseline of comorbidities was identified before the index date. Comorbidities included hypertension, diabetes mellitus, end-stage renal disease, congenital heart failure, stroke, peripheral arterial occlusive disease, and malignancy.

Results

We included 6,208 COPD patients and 12,409 patients without COPD. The incidence of AF was higher in COPD patients than in those without COPD. The adjusted hazard ratio (HR) for AF among those with COPD was 2.23 with a 95% confidence interval (CI) of 1.98–2.51 compared to those without COPD. After multiple analyses, patients with hypertension (HR 1.43 [95% CI =1.26–1.62]) or heart failure (HR 2.36 [95% CI =1.81–3.08]) were found to have a significantly higher incidence of AF than those without these conditions.

Conclusion

It is important for physicians to monitor, prevent, and provide early intervention for AF in COPD patients with hypertension or heart failure.

Chronic obstructive pulmonary disease and atrial fibrillation: An unknown relationship

Chronic obstructive pulmonary disease (COPD) is independently associated with atrial fibrillation (AF). Decreased oxygenation, hypercapnia, pulmonary hypertension, diastolic dysfunction, oxidative stress, inflammation, changes in atrial size by altered respiratory physiology, increased arrhythmogenicity from nonpulmonary vein foci commonly located in the right atrium, and respiratory drugs have been implicated in the pathogenesis of AF in COPD. The understanding of the relationship between COPD and AF is of particular importance, as the presence of the arrhythmia has significant impact on mortality, especially in COPD exacerbations. On the other hand, COPD in AF is associated with AF progression, success of cardioversion, recurrence of AF after catheter ablation, and increased cardiovascular and all-cause mortality. Treatment of the underlying pulmonary disease and correction of hypoxia and acid-base imbalance represents first-line therapy for COPD patients who develop AF. Cardioselective β-blockers are safe and can be routinely used in COPD. In addition, AF ablation was proved to be efficient and safe, and improves quality of life in these patients. This review presents the association between COPD and AF, describes the pathophysiological mechanisms implicated in AF development in COPD, underlines the prognostic significance of AF in COPD patients and vice versa, and highlights emerging therapeutic approaches in this setting.

Bioptic Study of Left and Right Atrial Interstitium in Cardiac Patients with and without Atrial Fibrillation: Interatrial but Not Rhythm-Based Differences

One of the generally recognized factors contributing to the initiation and maintenance of atrial fibrillation (AF) is structural remodeling of the myocardium that affects both atrial cardiomyocytes as well as interstitium. The goal of this study was to characterize morphologically and functionally interstitium of atria in patients with AF or in sinus rhythm (SR) who were indicated to heart surgery. Patient population consisted of 46 subjects (19 with long-term persistent AF, and 27 in SR) undergoing coronary bypass or valve surgery. Peroperative bioptic samples of the left and the right atria were examined using immunohistochemistry to visualize and quantify collagen I, collagen III, elastin, desmin, smooth muscle actin, endothelium and Vascular Endothelial Growth Factor (VEGF). The content of interstitial elastin, collagen I, and collagen III in atrial tissue was similar in AF and SR groups. However, the right atrium was more than twofold more abundant in elastin as compared with the left atrium and similar difference was found for collagen I and III. The right atrium showed also higher VEGF expression and lower microvascular density as compared to the left atrium. No significant changes in atrial extracellular matrix fiber content, microvascular density and angiogenic signaling, attributable to AF, were found in this cohort of patients with structural heart disease. This finding suggests that interstitial fibrosis and other morphological changes in atrial tissue are rather linked to structural heart disease than to AF per se. Significant regional differences in interstitial structure between right and left atrium is a novel observation that deserves further investigation.

Dynamic regulation of atrial coronary blood flow in healthy adult pigs

BACKGROUND

There are several indications for a mismatch between atrial oxygen supply and demand during atrial fibrillation (AF), but atrial coronary flow regulation has not been investigated extensively.

OBJECTIVE

The purpose of this study was to characterize the dynamic regulation of atrial coronary flow in pigs.

METHODS

In anesthetized open-chest pigs, Doppler flow probes were placed around left atrial (LA) and left ventricular (LV) branches of the circumflex artery. Pressures and work indices were measured simultaneously. Systolic and diastolic flow contribution, flow response kinetics, and relationship between pressures, work, and flow were investigated during sinus rhythm, atrial pacing, and acute AF.

RESULTS

During atrial systole, LA flow decreased. Only 2% of total LA flow occurred during atrial systole. Pacing with 2:1 AV block and infusion of acetylcholine revealed that atrial contraction itself impeded atrial coronary flow. The response to sudden changes in heart rate was slower in LA compared to LV. Both LA and LV vascular conductance were positively correlated with work. After the cessation of acute AF, the LA showed a more pronounced phase of supranormal vascular conductance than the LV, indicating a period of atrial reactive hyperemia.

CONCLUSION

In healthy adult pigs, atrial coronary flow is impeded by atrial contraction. Although atrial coronary blood flow is positively correlated with atrial external work, it reacts more slowly to changes in rate than ventricular flow. The occurrence of a pronounced hyperemic phase after acute AF supports the notion of a significant supply-demand mismatch during AF.

Arrhythmia risk associated with sleep disordered breathing in chronic heart failure

The intersecting relationships of sleep disordered breathing (SDB), arrhythmogenic risk and chronic heart failure (HF) are complex and most likely multi-directional and synergistic. Autonomic dysfunction is a common pathophysiological feature of each of these entities. Intermittent hypoxia, hypercapnia, mechanical cardiac influences due to upper airway obstruction and rostral fluid shifts are SDB-specific mechanisms which may trigger, perpetuate and exacerbate HF and arrhythmogenesis. Specific pathophysiological mechanisms will vary according to the predominance of central as compared to obstructive sleep apnea. The risk of cardiac arrhythmias and HF attributable to SDB may be considerable given the high prevalence of SDB and its likely physiologic burden. The current review focuses on the data, which have accrued elucidating the specific contributory mechanisms of SDB in cardiac arrhythmias and HF, highlighting the clinical relevance and effects of standard SDB treatment on these outcomes, and describing the role of novel therapeutics.

Significance of hypoxia-inducible factor-1α expression with atrial fibrosis in rats induced with isoproterenol

Atrial interstitial fibrosis plays a dual role in inducing and maintaining atrial fibrillation (AF). Hypoxia-inducible factor-1α (HIF-1α) has been reported as closely associated with renal, liver and pulmonary fibrosis diseases. However, whether HIF-1α is involved in myocardial fibrosis, and the associations between HIF-1α, transforming growth factor-β₁ (TGF-β₁) and matrix metalloproteinase-9 (MMP-9) remain unknown. Therefore, this area warrants studying for the significance of AF diagnosis and treatment. The present study investigated the expression of HIF-1α in atrial fibrosis and its possible mechanism in isoproterenol (ISO)-induced rats. The three groups of rats; control, ISO and ISO plus sirolimus [also known as rapamycin (Rapa)], were treated for 15 days and sacrificed to remove the myocardial tissues. The expression levels of HIF-1α, TGF-β₁ and MMP-9 and their associations with atrial fibrosis were examined through histomorphology and protein and mRNA levels. The protein and mRNA levels of HIF-1α, TGF-β₁ and MMP-9 in the ISO group were increased markedly (P<0.01) compared with the control group, while those in the Rapa group were clearly decreased (P<0.01) compared with the ISO group. The protein and mRNA levels of HIF-1α, TGF-β₁ and MMP-9 were positively correlated (P<0.01) with atrial fibrosis (collagen volume fraction index), as were the HIF-1α, TGF-β₁ and MMP-9 mRNA levels (P<0.01) and the mRNA levels between MMP-9 and TGF-β₁ (P<0.01). During the process of atrial fibrosis in ISO-induced rats, HIF-1α promotes the expression of TGF-β₁ and MMP-9 protein, and thus is involved in in atrial fibrosis.