Atrial expression of endothelial nitric oxide synthase in patients with and without atrial fibrillation

Developing Pharmacological Therapies for Atrial Fibrillation Targeting Mitochondrial Dysfunction and Oxidative Stress: A Scoping Review

Atrial fibrillation (AF) is a cardiac arrhythmia caused by electrophysiological anomalies in the atrial tissue, tissue degradation, structural abnormalities, and comorbidities. A direct relationship exists between AF and altered mitochondrial activity resulting from membrane potential loss, contractile dysfunction, or decreased ATP levels. This review aimed to elucidate the role of mitochondrial oxidative mechanisms in AF pathophysiology, the impact of mitochondrial oxidative stress on AF initiation and perpetuation, and current therapies. This review followed the Preferred Reporting Items for Systematic Reviews and the Meta-Analysis Extension for Scoping Reviews. PubMed, Excerpta Medica Database, and Scopus were explored until June 2023 using "MESH terms". Bibliographic references to relevant papers were also included. Oxidative stress is an imbalance that causes cellular damage from excessive oxidation, resulting in conditions such as AF. An imbalance in reactive oxygen species production and elimination can cause mitochondrial damage, cellular apoptosis, and cardiovascular diseases. Oxidative stress and inflammation are intrinsically linked, and inflammatory pathways are highly correlated with the occurrence of AF. AF is an intricate cardiac condition that requires innovative therapeutic approaches. The involvement of mitochondrial oxidative stress in the pathophysiology of AF introduces novel strategies for clinical treatment.

Relationship Between Fibrosis, Endocardial Endothelial Damage, and Thrombosis of Left Atrial Appendage in Atrial Fibrillation

BACKGROUND

Left atrial appendage (LAA) thrombus (LAAT) and ischemic stroke are considered important in atrial cardiomyopathy with progressive atrial fibrosis and endocardial endothelial damage.

OBJECTIVES

This study aimed to obtain histological evidence to clarify the association between LAA fibrosis and endocardial endothelial damage with LAAT, ischemic stroke, and clinical risk factors.

METHODS

Ninety-six patients with atrial fibrillation (AF) scheduled to undergo LAA excision during surgery were enrolled. They underwent transesophageal echocardiography before the surgery to validate the LAA function/morphology and LAAT presence or absence. The resected LAAs were subjected to Azan-Mallory staining and CD31 immunohistochemistry to quantify the degree of fibrosis and endocardial endothelial damage staged as F1-F4 and E1-E4 per the quantiles.

RESULTS

Patients with an LAAT and/or ischemic stroke history had higher fibrosis degrees (18.4% ± 9.9% vs 10.4% ± 7.0%, P < 0.0001) and lower CD31 expressions (0.27 [IQR: 0.05-0.57] vs 1.02 [IQR: 0.49-1.65]; P < 0.0001). Also, higher CHADS₂ was associated with a higher degree of fibrosis and lower CD31 expression. Multivariate logistic regression analysis revealed that endothelial damage (E4) was associated with an LAAT and/or ischemic stroke history independent of AF type (paroxysmal or nonparoxysmal) with an OR of 3.47. Among patients with nonparoxysmal AF, fibrosis (F4, OR: 3.66), endothelial damage (E4, OR: 4.62), and LAA morphology (non-chicken-wing, OR: 3.79) were independently associated with LAAT and/or stroke. The degree of fibrosis correlated significantly with endothelial damage (R = -0.38, P = 0.0001).

CONCLUSIONS

These histological findings may be essential in considering the pathophysiology of LAAT and stroke within the atrial cardiomyopathy context.

Left Atrial Cardiomyopathy - A Challenging Diagnosis

Left atrial cardiomyopathy (LACM) has been an ongoing focus of research for several years. There is evidence that LACM is responsible for atrial fibrillation and embolic strokes of undetermined sources. Therefore, the correct diagnosis of LACM is of clinical importance. Various techniques, including electrocardiography, echocardiography, cardiac magnetic resonance imaging, computed tomography, electroanatomic mapping, genetic testing, and biomarkers, can both identify and quantify structural, mechanical as well as electrical dysfunction in the atria. However, the question arises whether these techniques can reliably diagnose LACM. Because of its heterogeneity, clinical diagnosis is challenging. To date, there are no recommendations for standardized diagnosis of suspected LACM. However, standardization could help to classify LACM more precisely and derive therapeutic directions to improve individual patient management. In addition, uniform diagnostic criteria for LACM could be important for future studies. Combining several parameters and relating them seems beneficial to approach the diagnosis of LACM. This review provides an overview of the current evidence regarding the diagnosis of LACM, in which several potential parameters are discussed and, consequently, a proposal for a diagnostic algorithm is presented.

Hypertension and Arrhythmias: A Clinical Overview of the Pathophysiology-Driven Management of Cardiac Arrhythmias in Hypertensive Patients

Because of demographic aging, the prevalence of arterial hypertension (HTN) and cardiac arrhythmias, namely atrial fibrillation (AF), is progressively increasing. Not only are these clinical entities strongly connected, but, acting with a synergistic effect, their association may cause a worse clinical outcome in patients already at risk of ischemic and/or haemorrhagic stroke and, consequently, disability and death. Despite the well-known association between HTN and AF, several pathogenetic mechanisms underlying the higher risk of AF in hypertensive patients are still incompletely known. Although several trials reported the overall clinical benefit of renin–angiotensin–aldosterone inhibitors in reducing incident AF in HTN, the role of this class of drugs is greatly reduced when AF diagnosis is already established, thus hinting at the urgent need for primary prevention measures to reduce AF occurrence in these patients. Through a thorough review of the available literature in the field, we investigated the basic mechanisms through which HTN is believed to promote AF, summarising the evidence supporting a pathophysiology-driven approach to prevent this arrhythmia in hypertensive patients, including those suffering from primary aldosteronism, a non-negligible and under-recognised cause of secondary HTN. Finally, in the hazy scenario of AF screening in hypertensive patients, we reviewed which patients should be screened, by which modality, and who should be offered oral anticoagulation for stroke prevention.

Atrial Cardiomyopathy: Pathophysiology and Clinical Consequences

Around the world there are 33.5 million patients suffering from atrial fibrillation (AF) with an annual increase of 5 million cases. Most AF patients have an established form of an atrial cardiomyopathy. The concept of atrial cardiomyopathy was introduced in 2016. Thus, therapy of underlying diseases and atrial tissue changes appear as a cornerstone of AF therapy. Furthermore, therapy or prevention of atrial endocardial changes has the potential to reduce atrial thrombogenesis and thereby cerebral stroke. The present manuscript will summarize the underlying pathophysiology and remodeling processes observed in the development of an atrial cardiomyopathy, thrombogenesis, and atrial fibrillation. In particular, the impact of oxidative stress, inflammation, diabetes, and obesity will be addressed.

The CHA2DS2-VASc score predicts chronic kidney disease among patients with atrial fibrillation

BACKGROUND

It is unclear how the CHA2DS2-VASc score can predict subsequent chronic kidney disease (CKD) and end-stage renal disease (ESRD) among atrial fibrillation (AF) patients.

METHODS

We identified incident AF patients without CKD between 2000 and 2013 from the National Health Insurance Research Database (NHIRD) of Taiwan and calculated the CHA₂DS₂-VASc score for each patient. Adjusted hazard ratio (HR) with 95% confidence interval (CI) was estimated from multivariate cause-specific Cox models to assess the risk of CKD and ESRD associated with the CHA₂DS₂-VASc score.

RESULTS

A total of 8764 participants with AF who did not have CKD were included in the analysis. The mean age was 69.63 ± 13.48 years and 4800 (54.8%) were males. The adjusted HR of CKD displayed a stepwise increase with the increase in the CHA₂DS₂-VASc score. When compared with those with a CHA₂DS₂-VASc score of 0, the adjusted HRs of CKD were 1.57 (95% CI 1.09-2.26), 2.04 (95% CI 1.42-2.94), 2.48 (95% CI 1.70-3.62), 2.88 (95% CI 1.95-4.26), 3.29 (95% CI 2.18-4.95) and 4.00 (95% CI 2.61-6.13) for the AF patients with a CHA₂DS₂-VASc score of 1, 2, 3, 4, 5 and ≥ 6, respectively. Similarly, as the CHA₂DS₂-VASc score increased, the adjusted HR of ESRD showed a gradual increase.

CONCLUSIONS

Patients with a higher CHA₂DS₂-VASc score were linked to a higher risk of CKD and ESRD in a dose-dependent effect, i.e. the incidence of CKD/ESRD increased with the increasing CHA₂DS₂-VASc score.

Under-recognized post-stroke acute kidney injury: risk factors and relevance for stroke outcome of a frequent comorbidity

BACKGROUND

Acute kidney injury (AKI) is emerging as a predictor of poor stroke outcome, however, it is often not recognized. The aim of our study was to evaluate post-stroke AKI burden, AKI risk factors and their influence in post-stroke outcome.

METHODS

From 2013 to 2016, 440 individuals with stroke diagnosis admitted in Stroke Unit, Foundation IRCCS Policlinico San Matteo (Pavia, Italy), were retrospectively enrolled. AKI cases identified by KDIGO criteria through the electronic database and hospital chart review were compared with the ones reported in discharge letters or in administrative hospital data base. Mortality data were provided by Agenzia Tutela della Salute of Pavia.

RESULTS

We included 430 patients in the analysis. Median follow-up was 19.2 months. We identified 79 AKI cases (18% of the enrolled patients, 92% classified as AKI stage 1), a fivefold higher number of cases than the ones reported at discharge. 37 patients had AKI at the admission in the hospital, while 42 developed AKI during the hospitalization. Cardioembolic (p = 0.01) and hemorrhagic (p = 0.01) stroke types were associated with higher AKI risk. Admission National Institutes of Health Stroke Scale (NIHSS, p < 0.05) and Charlson Comorbidity Index (p < 0.01) were independently associated with overall AKI, while admission NIHSS (p < 0.05) and eGFR (p < 0.005) were independently associated with AKI developed during the hospitalization. AKI was associated to longer in-hospital stay (p = 0.01), worse Rankin Neurologic Disability Score at discharge (p < 0.0001) and discharge disposition other than home (p = 0.03). AKI was also independently associated to higher in-hospital mortality (OR 3.9 95% CI 1.2-12.9 p = 0.023) but not with long-term survival.

CONCLUSIONS

Post-stroke AKI diagnosis needs to be improved by strictly monitoring individuals with cardioembolic or hemorrhagic stroke, reduced kidney function, higher Charlson Comorbidity Index and worse NIHSS at presentation.

The CHA2DS2-VASc score strongly correlates with glomerular filtration rate and predicts renal function decline over time in elderly patients with atrial fibrillation and chronic kidney disease

BACKGROUND

The decline of renal function affects stroke risk in patients with atrial fibrillation (AF). Here, we aim to study the predictive value of the CHA₂DS₂-VASc score, a stroke-risk stratification model in AF, for renal function and renal decline in patients with AF and chronic kidney disease (CKD).

METHODS

Two electronic health record cohorts with AF and CKD stage III/IV were evaluated (Cohort #1 (IMS-DA, Germany): 18,539 patients with 125,149 estimated glomerular filtration rate (eGFR) measurements; Cohort #2 (IMS-THIN, United Kingdom): 18,240 patients with 133,676 eGFR measurements). The eGFR trajectories were analysed with multi-level mixed-effects regression and joint models for longitudinal and survival data.

RESULTS

In IMS-DA, the mean baseline eGFR was 52.0ml/min/1.73m², and declined by 1.03ml/min/1.73m²/year (95%CI: 0.86-1.19, p<0.0001). In IMS-THIN, the mean baseline eGFR was 48.0ml/min/1.73m², and declined by 0.44ml/min/1.73m²/year (95%CI: 0.37-0.51, p<0.0001). In both datasets, higher CHA₂DS₂-VASc scores (median: 4 points) were strongly associated with both lower baseline eGFR (p<0.0001) and faster progression of CKD (p=0.002). Mean baseline eGFR values were higher in patients with a CHA₂DS₂-VASc score of 0 compared to patients with a score of 8 points. Conversely, the annual declines in eGFR were lower in patients with a score of 0 compared to patients with a score of 8 points in both databases.

CONCLUSION

The CHA₂DS₂-VASc score can identify AF patient subgroups with lower baseline eGFR and a higher risk of CKD progression, which has important implications for the management of anticoagulation in these patients.

The role of reactive oxygen species in the pathophysiology of cardiovascular diseases and the clinical significance of myocardial redox

Acute and chronic excessive intracellular increase of reactive oxygen species (ROS) is involved in the development and progression of cardiovascular diseases. ROS are by-products of various oxidative physiological and biochemical processes. Sources of ROS are mitochondrial respiration, NADH/NADPH oxidase, xanthine oxidoreductase or the uncoupling of nitric oxide synthase (NOS) in vascular cells. ROS mediate various signaling pathways that underlie cardiovascular pathophysiology. The delicate equilibrium between free-radical generation and antioxidant defense is altered in favor of the former, thus leading to redox imbalance, oxidative stress, and increased cellular injury. An understanding of the pathophysiological mechanisms mediated by oxidative stress is crucial to the prevention and treatment of cardiovascular diseases.

Redox control of cardiac remodeling in atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is the most common arrhythmia in clinical practice and is a potential cause of thromboembolic events. AF induces significant changes in the electrophysiological properties of atrial myocytes and causes alterations in the structure, metabolism, and function of the atrial tissue. The molecular basis for the development of structural atrial remodeling of fibrillating human atria is still not fully understood. However, increased production of reactive oxygen or nitrogen species (ROS/RNS) and the activation of specific redox-sensitive signaling pathways observed both in patients with and animal models of AF are supposed to contribute to development, progression and self-perpetuation of AF.

SCOPE OF REVIEW

The present review summarizes the sources and targets of ROS/RNS in the setting of AF and focuses on key redox-sensitive signaling pathways that are implicated in the pathogenesis of AF and function either to aggravate or protect from disease.

MAJOR CONCLUSIONS

NADPH oxidases and various mitochondrial monooxygenases are major sources of ROS during AF. Besides direct oxidative modification of e.g. ion channels and ion handling proteins that are crucially involved in action potential generation and duration, AF leads to the reversible activation of redox-sensitive signaling pathways mediated by activation of redox-regulated proteins including Nrf2, NF-κB, and CaMKII. Both processes are recognized to contribute to the formation of a substrate for AF and, thus, to increase AF inducibility and duration.

GENERAL SIGNIFICANCE

AF is a prevalent disease and due to the current demographic developments its socio-economic relevance will further increase. Improving our understanding of the role that ROS and redox-related (patho)-mechanisms play in the development and progression of AF may allow the development of a targeted therapy for AF that surpasses the efficacy of previous general anti-oxidative strategies. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Normal and abnormal development of the aortic wall and valve: correlation with clinical entities

Dilation of the wall of the thoracic aorta can be found in patients with a tricuspid (TAV) as well as a bicuspid aortic valve (BAV) with and without a syndromic component. BAV is the most common congenital cardiovascular malformation, with a population prevalence of 0.5–2 %. The clinical course is often characterised by aneurysm formation and in some cases dissection. The non-dilated aortic wall is less well differentiated in all BAV as compared with TAV, thereby conferring inherent developmental susceptibility. Furthermore, a turbulent flow, caused by the inappropriate opening of the bicuspid valve, could accelerate the degenerative process in the aortic wall. However, not all patients with bicuspidy develop clinical complications during their life. We postulate that the increased vulnerability for aortic complications in a subset of patients with BAV is caused by a defect in the early development of the aorta and aortic valve. This review discusses histological and molecular genetic aspects of the normal and abnormal development of the aortic wall and semilunar valves. Aortopathy associated with BAV could be the result of a shared developmental defect during embryogenesis.

Impact of aldosterone antagonists on the substrate for atrial fibrillation: aldosterone promotes oxidative stress and atrial structural/electrical remodeling

Atrial fibrillation (AF), the most common cardiac arrhythmia, is an electrocardiographic description of a condition with multiple and complex underlying mechanisms. Oxidative stress is an important driver of structural remodeling that creates a substrate for AF. Oxidant radicals may promote increase of atrial oxidative damage, electrical and structural remodeling, and atrial inflammation. AF and other cardiovascular morbidities activate angiotensin (Ang-II)-dependent and independent cascades. A key component of the renin-angiotensin-aldosterone system (RAAS) is the mineralocorticoid aldosterone. Recent studies provide evidence of myocardial aldosterone synthesis. Aldosterone promotes cardiac oxidative stress, inflammation and structural/electrical remodeling via multiple mechanisms. In HF patients, aldosterone production is enhanced. In patients and in experimental HF and AF models, aldosterone receptor antagonists have favorable influences on cardiac remodeling and oxidative stress. Therapeutic approaches that seek to reduce AF burden by modulating the aldosterone system are likely beneficial but underutilized.

Tackling endothelial dysfunction by modulating NOS uncoupling: new insights into its pathogenesis and therapeutic possibilities

Endothelial nitric oxide synthase (eNOS) serves as a critical enzyme in maintaining vascular pressure by producing nitric oxide (NO); hence, it has a crucial role in the regulation of endothelial function. The bioavailability of eNOS-derived NO is crucial for this function and might be affected at multiple levels. Uncoupling of eNOS, with subsequently less NO and more superoxide generation, is one of the major underlying causes of endothelial dysfunction found in atherosclerosis, diabetes, hypertension, cigarette smoking, hyperhomocysteinemia, and ischemia/reperfusion injury. Therefore, modulating eNOS uncoupling by stabilizing eNOS activity, enhancing its substrate, cofactors, and transcription, and reversing uncoupled eNOS are attractive therapeutic approaches to improve endothelial function. This review provides an extensive overview of the important role of eNOS uncoupling in the pathogenesis of endothelial dysfunction and the potential therapeutic interventions to modulate eNOS for tackling endothelial dysfunction.