Atrial fibrillation in β‐thalassemia patients with a focus on the role of iron‐overload and oxidative stress: A review

Effects of Inflammatory Cell Death Caused by Catheter Ablation on Atrial Fibrillation

Atrial fibrillation (AF) poses a serious healthcare burden on society due to its high morbidity and the resulting serious complications such as thrombosis and heart failure. The principle of catheter ablation is to achieve electrical isolation by linear destruction of cardiac tissue, which makes AF a curable disease. Currently, catheter ablation does not have a high long-term success rate. The current academic consensus is that inflammation and fibrosis are central mechanisms in the progression of AF. However, artificially caused inflammatory cell death by catheter ablation may have a significant impact on structural and electrical remodeling, which may affect the long-term prognosis. This review first focused on the inflammatory response induced by apoptosis, necrosis, necroptosis, pyroptosis, ferroptosis and their interaction with arrhythmia. Then, we compared the differences in cell death induced by radiofrequency ablation, cryoballoon ablation and pulsed-field ablation. Finally, we discussed the structural and electrical remodeling caused by inflammation and the association between inflammation and the recurrence of AF after catheter ablation. Collectively, pulsed-field ablation will be a revolutionary innovation with faster, safer, better tissue selectivity and less inflammatory response induced by apoptosis-dominated cell death.

Oxido-Reduction Potential as a Method to Determine Oxidative Stress in Semen Samples

There are different estimates for the incidence of infertility. Its occurrence may vary from area to area, but on average, it affects 15% of couples and 10-12% of men worldwide. Many aspects of infertility can be linked to reactive oxygen species (ROS) and the process of oxidative stress (OS). The association between poor semen quality and OS is well known. Unfortunately, there is no accepted protocol for the diagnosis and treatment of OS in andrology. Oxido-reduction potential (ORP) measurement is a new method for determining the ratio between oxidant and antioxidant molecules. Currently, ORP measurement is one of the fastest and most user-friendly methods of andrological OS determination and our goals were to confirm published correlations between ORP values and sperm parameters, examine how sperm concentration influences these results, and investigate whether intracellular ROS formations are also manifested in the ORP values or not after artificial ROS induction. Intracellular ROS formations were induced by menadione (superoxide anion inducer), hydrogen peroxide, and tert-butyl hydroperoxide (lipid peroxidation inducer) treatments; sperm parameters like motility and viability were determined with an SCA Scope system, and ORP changes were recorded by the Mioxsys system. Significant correlations were noticed among the ORP, spermatozoa concentration, motility, progressive motility, and viability. Nevertheless, only the ORP value after normalization with the sperm count correlated with these parameters. Due to normalization, very low and very high sperm concentrations can give misleading results. The means of the non-normalized ORP values were almost the same. All of the applied treatments resulted in decreases in the viability, motility, and progressive motility, and interestingly, altered ORP levels were detected. In addition, it was determined that seminal plasma had a significant protective effect on spermatozoa. The elimination of seminal plasma caused higher sensitivity of spermatozoa against used OS inducers, and higher ORP levels and decreased viabilities and motilities were measured. The ORP level could be a good indicator of male OS; however, in cases of low and high sperm counts, its result can be misleading. Overall, the conclusion can be drawn that ORP determination is a suitable method for detecting intracellular ROS accumulation, but it has limitations that still need to be clarified.

Cardiovascular Complications in β-Thalassemia: Getting to the Heart of It

Beta thalassemia is an inherited disorder resulting in abnormal or decreased production of hemoglobin, leading to hemolysis and chronic anemia. The long-term complications can affect multiple organ systems, namely the liver, heart, and endocrine. Myocardial iron overload is a common finding in β-thalassemia. As a result, different cardiovascular complications in the form of cardiomyopathy, pulmonary hypertension, arrhythmias, and vasculopathies can occur, and in extreme cases, sudden cardiac death. Each of these complications pertains to underlying etiologies and risk factors, which highlights the importance of early diagnosis and prevention. In this review, we will discuss different types of cardiovascular complications that can manifest in patients with β-thalassemia, in addition to the current diagnostic modalities, preventive and treatment modalities for these complications.

Genetic support of a causal relationship between iron status and atrial fibrillation: a Mendelian randomization study

Background

Atrial fibrillation is the most common arrhythmia disease. Animal and observational studies have found a link between iron status and atrial fibrillation. However, the causal relationship between iron status and AF remains unclear. The purpose of this investigation was to use Mendelian randomization (MR) analysis, which has been widely applied to estimate the causal effect, to reveal whether systemic iron status was causally related to atrial fibrillation.

Methods

Single nucleotide polymorphisms (SNPs) strongly associated (P < 5 × 10−8) with four biomarkers of systemic iron status were obtained from a genome-wide association study involving 48,972 subjects conducted by the Genetics of Iron Status consortium. Summary-level data for the genetic associations with atrial fibrillation were acquired from the AFGen (Atrial Fibrillation Genetics) consortium study (including 65,446 atrial fibrillation cases and 522,744 controls). We used a two-sample MR analysis to obtain a causal estimate and further verified credibility through sensitivity analysis.

Results

Genetically instrumented serum iron [OR 1.09; 95% confidence interval (CI) 1.02–1.16; p = 0.01], ferritin [OR 1.16; 95% CI 1.02–1.33; p = 0.02], and transferrin saturation [OR 1.05; 95% CI 1.01–1.11; p = 0.01] had positive effects on atrial fibrillation. Genetically instrumented transferrin levels [OR 0.90; 95% CI 0.86–0.97; p = 0.006] were inversely correlated with atrial fibrillation.

Conclusion

In conclusion, our results strongly elucidated a causal link between genetically determined higher iron status and increased risk of atrial fibrillation. This provided new ideas for the clinical prevention and treatment of atrial fibrillation.

Gut Microbiota Dysbiosis Induced by a High-Fat Diet Increases Susceptibility to Atrial Fibrillation

BACKGROUND

Obesity is a significant risk factor for atrial fibrillation (AF), and the gut microbiota is closely related to obesity-induced diseases. However, whether the gut microbiota is involved in regulating obesity-induced AF has not been studied. This study investigated whether gut microbiota dysbiosis affects obesity-related AF.

METHODS

Fecal microbes derived from normal diet (ND)-fed and high-fat diet (HD)-fed mice were transplanted into those fed normally. Morphologic, biochemical, functional, histologic, electrophysiological studies, molecular analysis, 16S rRNA gene amplicon sequencing, and RNA-sequencing were performed.

RESULTS

Transplantation of the HD gut microbes in ND-maintained (THD) mice led to a significant increase in the susceptibility to AF. Gut microbiota analysis showed a significant increase in Desulfovibrionaceae, which generated metabolic endotoxemia in THD mice. Transplantation with HD microbes also resulted in significantly increased levels of circulating lipopolysaccharide (LPS), significant disruption in the histologic architecture of the intestinal tissue, and significantly increased proinflammatory cytokines in the left atrium, indicating that atrial inflammation likely contributed to AF susceptibility. RNA-sequencing showed that the THD group had enhanced activation of ferroptosis and TLR4/NF-κB/NLRP3 inflammasome signalling pathway. Inhibiting the ferroptosis or NLRP3 inflammasome signalling pathway significantly improved atrial fibrosis and reduced susceptibility to obesity-related gut dysbiosis-induced AF.

CONCLUSIONS

This study provides evidence showing an original causal role of gut microbiota dysbiosis in the pathogenesis of obesity-related AF, which showed elevated LPS and dysregulation of atrial pathologic remodelling by activating ferroptosis and the TLR4/NF-κB/NLRP3 inflammasome signalling pathway.

Left atrial deformation indices in β-thalassemia major patients

The presence of atrial cardiomyopathy in β-thalassemia major (β-TM) patients complicates their clinical condition. The diagnosis is challenging even with cardiac magnetic resonance (CMR) imaging. Novel echocardiographic techniques are applied to increase the diagnostic yield. Fifty-six β-TM patients and thirty age and sex-matched controls were included in the present cross-sectional study. Heart rate, PR duration, and P axis were measured by electrocardiography, left ventricular ejection fraction (LVEF) and end-diastolic diameter (LVEDD), ratio between early mitral inflow velocity and mitral annular early diastolic velocity (E/e'), left atrial volume index (LAVI), left atrial strain at reservoir (LASr), conduit (LAScd) and contraction (LASct) phases respectively, left ventricular global longitudinal strain (GLS) by echocardiography, and T2* calculation in patient group by CMR. PR duration, LVEF, LAVI, E/e', GLS, and left atrial deformation parameters differed between patients and controls (p <0.05). In patient group, left atrial strain was correlated with PR duration, LAVI, E/e', GLS, and T2* (p <0.05). T2* was correlated only with left atrial deformation indices (p <0.05). Patients with a history of atrial fibrillation were older, had lower heart rate, prolonged PR, increased E/e' and LAVI, and impaired left atrial strain (p <0.05). LASct differed relative to the presence of atrial fibrillation and myocardial iron overload. Atrial strain could be of clinical use in the early detection of atrial cardiomyopathy. An impaired LASct could identify β-TM patients with undetected episodes of atrial fibrillation. Finally, left atrial strain may be helpful in myocardial iron load estimation.

Atrial Fibrillation in β-Thalassemia: Overview of Mechanism, Significance and Clinical Management

Thalassemia is an inherited blood disorder with worldwide distribution. Transfusion and chelation therapy have radically improved the prognosis of β-thalassemic patients in the developed world, but this has led to the development of new chronic cardiac complications like atrial fibrillation (AF). Prevalence of AF in patients with β-thalassemia is higher than in the general population, ranging from 2 to 33%. Studies are lacking, and the little evidence available comes from a small number of observational studies. The pathophysiology is not well understood but, while iron overload seems to be the principal mechanism, AF could develop even in the absence of iron deposition. Furthermore, the clinical presentation is mainly paroxysmal, and patients are highly symptomatic. The underlying disease, the pathophysiology, and the clinical presentation require a different management of AF in β-thalassemia than in the general population. Rhythm control should be preferred over rate control, and the most important antiarrhythmic therapy is represented by chelation drugs. Thromboembolic risk is high, but the available risk scores are not validated in β-thalassemia, and the choice of anticoagulation therapy should be considered early. The main purpose of this review is to summarize the actual knowledge about AF in β-thalassemia, with a specific focus on the clinical management of these complex patients.

Evaluation of electrocardiography, echocardiography and cardiac T2* for cardiac complications in beta thalassemia major

Cardiac complications such as heart failure and arrhythmias caused by "iron-induced" cardiomyopathy are considered as the primary cause of death in the patients with β-thalassemia major. The aim of this study was to evaluate electrocardiography, echocardiography according cardiac T2* and ferritin findings of patients followed-up for β-thalassemia major, and to investigate the importance of these findings for early detection of cardiac complications. The study included 41 patients and 25 healthy individuals with matched age and gender. The cardiac T2* results revealed a cardiac iron load below 20 ms in 12 (29.27%) patients, and above 20 ms in 29 (70.73%) patients. All electrocardiography parameters significantly increased in the patient group when compared to the control group (p < 0.05). All parameters except P wave segment in electrocardiography and T peak-end/QT ratio were significantly higher in the group with cardiac T2* < 20 ms than the group with cardiac T2* > 20 ms (p < 0.05). Intraventricular septum thickness, left ventricular posterior wall thickness, left ventricular mass and left ventricular mass index detected by echocardiography were significantly higher in the group with T2* < 20 ms (p < 0.05). Electrocardiography, echocardiography, cardiac T2* and ferritin findings should be carefully evaluated in these patients in order to detect early signs of cardiac complications.

Thrombotic Events and Anticoagulants in Beta-thalassemia Patients with Focus on Anticoagulants for Atrial Fibrillation: A Brief Review

Despite many advances in the diagnosis and treatment of beta-thalassemia patients in recent years and their longevity and quality of life which has been greatly increased, many of these patients have other life-threatening risks. The prevalence of atrial fibrillation in beta-thalassemia patients and its related thromboembolism, stroke, and mortality have been increased in the last few years. Appropriate anticoagulant therapy may help to prevent the incidence or recurrence of thromboembolism. So far warfarin is the most widely used drug. Aspirin should use with caution in these patients because of its resistance to aspirin over time, which can increase the risk of thromboembolism. Direct oral anticoagulants (DOACs) are widely used to prevent embolism in coronary artery disease and venous thromboembolism, but their use in thalassemia patients is still very limited. More high-quality researches and clinical trials are needed to prove their effectiveness and safety for atrial fibrillation in beta-thalassemia patients.

Combination of ponatinib with deferoxamine synergistically mitigates ischemic heart injury via simultaneous prevention of necroptosis and ferroptosis

Necroptosis, ferroptosis and cyclophilin D (Cyp D)-dependent necrosis contribute to myocardial ischemia/reperfusion (I/R) injury, and ponatinib, deferoxamine and cyclosporine are reported to inhibit necroptosis, ferroptosis and Cyp D-dependent necrosis, respectively. This study aims to explore whether the any two combination between ponatinib, deferoxamine and cyclosporine exerts a better cardioprotective effect on I/R injury than single medicine does. The H9c2 cells were subjected to 10 h of hypoxia (H) plus 4 h of reoxygenation (R) to establish H/R injury model. The effects of any two combination between ponatinib, deferoxamine and cyclosporine on H/R injury were examined. On this basis, a I/R injury model in rat hearts was established to focus on the effect of ponatinib, deferoxamine and their combination on myocardial I/R injury and the underlying mechanisms. In H/R-treated H9c2 cells, all three medicines can attenuate H/R injury (decrease in LDH release and necrosis percent). However, only the combination of ponatinib with deferoxamine exerted synergistic effect on reducing H/R injury, showing simultaneous suppression of necroptosis and ferroptosis. Expectedly, administration of ponatinib or deferoxamine either before or after ischemia could suppress necroptosis or ferroptosis in the I/R-treated rat hearts as they did in vitro, concomitant with a decrease in myocardial infarct size and creatine kinase release, and the combination therapy is more efficient than single medication. Based on these observations, we conclude that the combination of ponatinib with deferoxamine reduces myocardial I/R injury via simultaneous inhibition of necroptosis and ferroptosis.

Keeping heart homeostasis in check through the balance of iron metabolism

Highly active cardiomyocytes need iron for their metabolic activity. In physiological conditions, iron turnover is a delicate process which is dependent on global iron supply and local autonomous regulatory mechanisms. Though less is known about the autonomous regulatory mechanisms, data suggest that these mechanisms can preserve cellular iron turnover even in the presence of systemic iron disturbance. Therefore, activity of local iron protein machinery and its relationship with global iron metabolism is important to understand cardiac iron metabolism in physiological conditions and in cardiac disease. Our knowledge in this respect has helped in designing therapeutic strategies for different cardiac diseases. This review is a synthesis of our current knowledge concerning the regulation of cardiac iron metabolism. In addition, different models of cardiac iron dysmetabolism will be discussed through the examples of heart failure (cardiomyocyte iron deficiency), myocardial infarction (acute changes in cardiac iron turnover), doxorubicin-induced cardiotoxicity (cardiomyocyte iron overload in mitochondria), thalassaemia (cardiomyocyte cytosolic and mitochondrial iron overload) and Friedreich ataxia (asymmetric cytosolic/mitochondrial cardiac iron dysmetabolism). Finally, future perspectives will be discussed in order to resolve actual gaps in knowledge, which should be helpful in finding new treatment possibilities in different cardiac diseases.