Effects of experimental heart failure on atrial cellular and ionic electrophysiology

Characterization of remodeling processes in the atria of atrioventricular block dogs: Utility as an early-stage atrial fibrillation model

To characterize utility of atrioventricular block (AVB) dogs as atrial fibrillation (AF) model, we studied remodeling processes occurring in their atria in acute (<2 weeks) and chronic (>4 weeks) phases. Fifty beagle dogs were used. Holter electrocardiogram demonstrated that paroxysmal AF occurred immediately after the production of AVB, of which duration tended to be prolonged in chronic phase. Electrophysiological analysis showed that inter-atrial conduction time and duration of burst pacing-induced AF increased in the chronic phase compared with those in the acute phase, but that atrial effective refractory period was hardly altered. Echocardiographic study revealed that diameters of left atrium, right pulmonary vein and inferior vena cava increased similarly in the acute and chronic phases. Histological evaluation indicated that hypertrophy and fibrosis in atrial tissue increased in the chronic phase. Electropharmacological characterization showed that i.v. pilsicainide effectively suppressed burst pacing-induced AF with increasing atrial conduction time and refractoriness of AVB dogs in chronic phase, but that i.v. amiodarone did not exert such electrophysiological effects. Taken together, AVB dogs in chronic phase appear to possess such pathophysiology as developed in the atria of early-stage AF patients, and therefore they can be used to evaluate drug candidates against early-stage AF.

Failure of intravenous nifekalant cardioversion as an independent predictor for persistent atrial fibrillation recurrence after catheter ablation

AIMS

Nifekalant is a class III antiarrhythmic drug that exerts antiarrhythmic effects by inhibiting rapid rectifying potassium channels and extending the effective refractory period of cardiomyocytes. It has a high success rate in converting atrial fibrillation (AF) to sinus rhythm. Whether the failure of intravenous nifekalant cardioversion is an independent predictor for persistent AF recurrence after catheter ablation has not been reported.

METHODS

A total of 92 patients with drug-refractory persistent AF were retrospectively enrolled. After all ablations, intravenous nifekalant was administrated. Patients were assigned to the success group (group 1) and failure group (group 2) based on nifekalant cardioversion results and followed for 12 months to note any episode of atrial arrhythmia recurrence.

RESULTS

Each group included 46 patients. After 12 months of follow-up, nine (19.6%) patients from group 1 and 23 (50.0%) patients from group 2 had a recurrence of atrial tachyarrhythmia (P = 0.002). AF duration and type 2 diabetes were strongly associated with failure of intravenous nifekalant cardioversion. Univariable Cox proportional hazard regression showed that failure of intravenous nifekalant cardioversion, AF duration, and type 2 diabetes were potential risk factors. Multivariable Cox proportional hazard regression showed that failure of nifekalant cardioversion was statistically associated with AF recurrence (adjusted RR = 2.257, 95% CI: 1.006-5.066, P = 0.048). Failure of intravenous nifekalant cardioversion could bring a positive effect on the prognostic differentiation when added into the multivariable model (0.767 ± 0.042 vs. 0.774 ± 0.045, P = 0.025).

CONCLUSION

Failure of nifekalant cardioversion is an independent predictor for persistent AF recurrence after catheter ablation.

Increased Risk for Atrial Alternans in Rabbit Heart Failure: The Role of Ca2+/Calmodulin-Dependent Kinase II and Inositol-1,4,5-trisphosphate Signaling

Heart failure (HF) increases the probability of cardiac arrhythmias, including atrial fibrillation (AF), but the mechanisms linking HF to AF are poorly understood. We investigated disturbances in Ca2+ signaling and electrophysiology in rabbit atrial myocytes from normal and failing hearts and identified mechanisms that contribute to the higher risk of atrial arrhythmias in HF. Ca2+ transient (CaT) alternans-beat-to-beat alternations in CaT amplitude-served as indicator of increased arrhythmogenicity. We demonstrate that HF atrial myocytes were more prone to alternans despite no change in action potentials duration and only moderate decrease of L-type Ca2+ current. Ca2+/calmodulin-dependent kinase II (CaMKII) inhibition suppressed CaT alternans. Activation of IP3 signaling by endothelin-1 (ET-1) and angiotensin II (Ang II) resulted in acute, but transient reduction of CaT amplitude and sarcoplasmic reticulum (SR) Ca2+ load, and lowered the alternans risk. However, prolonged exposure to ET-1 and Ang II enhanced SR Ca2+ release and increased the degree of alternans. Inhibition of IP3 receptors prevented the transient ET-1 and Ang II effects and by itself increased the degree of CaT alternans. Our data suggest that activation of CaMKII and IP3 signaling contribute to atrial arrhythmogenesis in HF.

The Arrhythmogenicity of Sotalol and its Role in Heart Failure: A Literature Review

ABSTRACT

According to the American Heart Association, approximately 6 million adults have been afflicted with heart failure in the United States in 2020 and are more likely to have sudden cardiac death accounting for approximately 50% of the cause of mortality. Sotalol is a nonselective β-adrenergic receptor antagonist with class III antiarrhythmic properties that has been mostly used for atrial fibrillation treatment and suppressing recurrent ventricular tachyarrhythmias. The use of sotalol in patients with left ventricular dysfunction is not recommended by the American College of Cardiology or American Heart Association because studies are inconclusive with conflicting results regarding safety. This article aims to review the mechanism of action of sotalol, the β-blocking effects on heart failure, and provide an overview of clinical trials on sotalol use and its effects in patients with heart failure. Small- and large-scale clinical trials have been controversial and inconclusive about the use of sotalol in heart failure. Sotalol has been shown to reduce defibrillation energy requirements and reduce shocks from implantable cardioverter-defibrillators. Torsades de Pointes is the most life-threatening arrhythmia that has been documented with sotalol use and occurs more commonly in women and heart failure patients. Thus far, mortality benefits have not been demonstrated with sotalol use and larger multicenter studies are required going forward.

Diversity of cells and signals in the cardiovascular system

This white paper is the outcome of the seventh UC Davis Cardiovascular Research Symposium on Systems Approach to Understanding Cardiovascular Disease and Arrhythmia. This biannual meeting aims to bring together leading experts in subfields of cardiovascular biomedicine to focus on topics of importance to the field. The theme of the 2022 Symposium was 'Cell Diversity in the Cardiovascular System, cell-autonomous and cell-cell signalling'. Experts in the field contributed their experimental and mathematical modelling perspectives and discussed emerging questions, controversies, and challenges in examining cell and signal diversity, co-ordination and interrelationships involved in cardiovascular function. This paper originates from the topics of formal presentations and informal discussions from the Symposium, which aimed to develop a holistic view of how the multiple cell types in the cardiovascular system integrate to influence cardiovascular function, disease progression and therapeutic strategies. The first section describes the major cell types (e.g. cardiomyocytes, vascular smooth muscle and endothelial cells, fibroblasts, neurons, immune cells, etc.) and the signals involved in cardiovascular function. The second section emphasizes the complexity at the subcellular, cellular and system levels in the context of cardiovascular development, ageing and disease. Finally, the third section surveys the technological innovations that allow the interrogation of this diversity and advancing our understanding of the integrated cardiovascular function and dysfunction.

IKACh is constitutively active via PKC epsilon in aging mediated atrial fibrillation

Atrial fibrillation (AF), the most common abnormal heart rhythm, is a major cause for stroke. Aging is a significant risk factor for AF; however, specific ionic pathways that can elucidate how aging leads to AF remain elusive. We used young and old wild-type and PKC epsilon- (PKCϵ) knockout mice, whole animal, and cellular electrophysiology, as well as whole heart, and cellular imaging to investigate how aging leads to the aberrant functioning of a potassium current, and consequently to AF facilitation. Our experiments showed that knocking out PKCϵ abrogates the effects of aging on AF by preventing the development of a constitutively active acetylcholine sensitive inward rectifier potassium current (IKACh). Moreover, blocking this abnormal current in the old heart reduces AF inducibility. Our studies demonstrate that in the aging heart, IKACh is constitutively active in a PKCϵ-dependent manner, contributing to the perpetuation of AF.

The predictive value of galectin-3 levels on left atrial low voltage areas assessed by high-density mapping in patients with paroxysmal atrial fibrillation

Aims

Galectin-3 is an inflammation biomarker that is associated with atrial fibrosis and plays a role in the development of atrial fibrillation (AF). Low voltage areas (LVAs) identified using an electroanatomical mapping system represent the presence of fibrotic tissue. The present study aimed to determine the relationship between coronary sinus (CS) serum sampling of galectin-3 levels and the presence and extent of LVA in patients with paroxysmal AF.

Methods

A total of 115 consecutive paroxysmal AF patients underwent pulmonary vein isolation (PVI) included prospectively in the study. Voltage mapping was performed before PVI during sinus rhythm guided by multipolar high-density mapping catheter and LVAs were defined as regions where bipolar peak to peak voltage was <0.5 mV. Galectin-3 levels were measured via enzyme-linked immunosorbent assay.

Results

CS serum sampling of galectin-3 levels was significantly higher in paroxysmal AF patients with LVA than those without LVA (16.5 ± 3.7 ng/ml vs. 10.2 ±2.7 ng/ml, respectively, p < .001). CS serum sampling of galectin-3 levels was significantly higher in paroxysmal AF patients with moderate and severe LVA than in paroxysmal AF patients with mild LVA (17 ± 3.5 ng/ml and 20.1 ± 1.3 ng/ml vs. 13.3 ± 2.3 ng/ml, respectively, p = .002). In the multivariate analysis female gender (odds ratio [OR] = 7.537, 95% confidence interval [CI]: 1.011-56.195; p = .049), left atrium volume (OR = 1.326, 95% CI: 1.052-1.67; p = .017), and CS serum sampling of galectin-3 levels (OR = 1.704, 95% CI: 1.169-2.483; p = .006) were significant and independent predictors for LVAs.

Conclusion

In this study, we found that the CS serum sampling of galectin-3 levels increased with the extent of LVA and was an independent predictor for the presence of LVA.

Atrial AMP-activated protein kinase is critical for prevention of dysregulation of electrical excitability and atrial fibrillation

Metabolic stress is an important cause of pathological atrial remodeling and atrial fibrillation. AMPK is a ubiquitous master metabolic regulator, yet its biological function in the atria is poorly understood in both health and disease. We investigated the impact of atrium-selective cardiac AMPK deletion on electrophysiological and structural remodeling in mice. Loss of atrial AMPK expression caused atrial changes in electrophysiological properties and atrial ectopic activity prior to the onset of spontaneous atrial fibrillation. Concomitant transcriptional downregulation of connexins and atrial ion channel subunits manifested with delayed left atrial activation and repolarization. The early molecular and electrophysiological abnormalities preceded left atrial structural remodeling and interstitial fibrosis. AMPK inactivation induced downregulation of transcription factors (Mef2c and Pitx2c) linked to connexin and ion channel transcriptional reprogramming. Thus, AMPK plays an essential homeostatic role in atria, protecting against adverse remodeling potentially by regulating key transcription factors that control the expression of atrial ion channels and gap junction proteins.

Ranolazine: An Old Drug with Emerging Potential; Lessons from Pre-Clinical and Clinical Investigations for Possible Repositioning

Ischemic heart disease is a significant public health problem with high mortality and morbidity. Extensive scientific investigations from basic sciences to clinics revealed multilevel alterations from metabolic imbalance, altered electrophysiology, and defective Ca²⁺/Na⁺ homeostasis leading to lethal arrhythmias. Despite the recent identification of numerous molecular targets with potential therapeutic interest, a pragmatic observation on the current pharmacological R&D output confirms the lack of new therapeutic offers to patients. By contrast, from recent trials, molecules initially developed for other fields of application have shown cardiovascular benefits, as illustrated with some anti-diabetic agents, regardless of the presence or absence of diabetes, emphasizing the clear advantage of “old” drug repositioning. Ranolazine is approved as an antianginal agent and has a favorable overall safety profile. This drug, developed initially as a metabolic modulator, was also identified as an inhibitor of the cardiac late Na⁺ current, although it also blocks other ionic currents, including the hERG/Ikr K⁺ current. The latter actions have been involved in this drug’s antiarrhythmic effects, both on supraventricular and ventricular arrhythmias (VA). However, despite initial enthusiasm and promising development in the cardiovascular field, ranolazine is only authorized as a second-line treatment in patients with chronic angina pectoris, notwithstanding its antiarrhythmic properties. A plausible reason for this is the apparent difficulty in linking the clinical benefits to the multiple molecular actions of this drug. Here, we review ranolazine’s experimental and clinical knowledge on cardiac metabolism and arrhythmias. We also highlight advances in understanding novel effects on neurons, the vascular system, skeletal muscles, blood sugar control, and cancer, which may open the way to reposition this “old” drug alone or in combination with other medications.

Simultaneous analyses of hemodynamic and electrophysiological effects of oseltamivir along with its pharmacokinetic profile using the canine paroxysmal atrial fibrillation model

Since information of antiviral drug oseltamivir on the anti-atrial fibrillation (AF) property is still limited, we assessed it using the canine paroxysmal AF model. Oseltamivir in doses of 3 and 30 mg/kg/10 min was intravenously infused to the isoflurane-anesthetized, chronic atrioventricular block dogs (n = 6) with monitoring hemodynamic and electrophysiological variables, in which AF was induced by 10 s of burst pacing on atrial septum. Oseltamivir decreased AF incidence and AF duration, and prolonged AF cycle length in a dose-dependent manner. The low and high doses attained the peak plasma drug concentrations of 9.7 and 96.5 μg/mL, which were approximately 100 and 1000 times greater than those observed in human clinical cases, respectively. The low dose of oseltamivir decreased mean blood pressure without altering sinoatrial or idioventricular rate, whereas its high dose reduced each of them. Oseltamivir delayed inter-atrial conduction in dose- and frequency-dependent manners, whereas it prolonged atrial effective refractory period in dose-dependent but frequency-independent manners. The high dose prolonged ventricular effective refractory period, which was not detected with the low dose. These findings can be used for repurposing oseltamivir as an anti-AF drug candidate.

Arrhythmogenic Remodeling in the Failing Heart

Chronic heart failure is a clinical syndrome with multiple etiologies, associated with significant morbidity and mortality. Cardiac arrhythmias, including ventricular tachyarrhythmias and atrial fibrillation, are common in heart failure. A number of cardiac diseases including heart failure alter the expression and regulation of ion channels and transporters leading to arrhythmogenic electrical remodeling. Myocardial hypertrophy, fibrosis and scar formation are key elements of arrhythmogenic structural remodeling in heart failure. In this article, the mechanisms responsible for increased arrhythmia susceptibility as well as the underlying changes in ion channel, transporter expression and function as well as alterations in calcium handling in heart failure are discussed. Understanding the mechanisms of arrhythmogenic remodeling is key to improving arrhythmia management and the prevention of sudden cardiac death in patients with heart failure.

Effect of ivabradine in heart failure: a meta-analysis of heart failure patients with reduced versus preserved ejection fraction

In clinical trials of heart failure reduced ejection fraction (HFrEF), ivabradine seemed to be an effective heart rate lowering agent associated with lower risk of cardiovascular death. In contrast, ivabradine failed to improve cardiovascular outcomes in heart failure preserved ejection fraction (HFpEF) despite the significant effect on heart rate. This meta-analysis is the first to compare the effects of ivabradine on heart rate and mortality parameters in HFpEF versus HFrEF. We screened three databases: PubMed, Embase, and Cochrane Library. The outcomes of these studies were mortality, reduction in heart rate, and left ventricular function improvement. We compared the efficacy of ivabradine treatment in HFpEF versus HFrEF. Heart rate analysis of pooled data showed decrease in both HFrEF (-17.646 beats/min) and HFpEF (-11.434 beats/min), and a tendency to have stronger bradycardic effect in HFrEF (p = 0.094) in randomized clinical trials. Left ventricular ejection fraction analysis revealed significant improvement in HFrEF (5.936, 95% CI: [4.199-7.672], p < 0.001) when compared with placebo (p < 0.001). We found that ivabradine significantly improves left ventricular performance in HFrEF, at the same time it exerts a tendency to have improved bradycardic effect in HFrEF. These disparate effects of ivabradine and the higher prevalence of non-cardiac comorbidities in HFpEF may explain the observed beneficial effects in HFrEF and the unchanged outcomes in HFpEF patients after ivabradine treatment.

Sensitivity Analysis of Ion Channel Conductance on Myocardial Electromechanical Delay: Computational Study

It is well known that cardiac electromechanical delay (EMD) can cause dyssynchronous heart failure (DHF), a prominent cardiovascular disease (CVD). This work computationally assesses the conductance variation of every ion channel on the cardiac cell to give rise to EMD prolongation. The electrical and mechanical models of human ventricular tissue were simulated, using a population approach with four conductance reductions for each ion channel. Then, EMD was calculated by determining the difference between the onset of action potential and the start of cell shortening. Finally, EMD data were put into the optimized conductance dimensional stacking to show which ion channel has the most influence in elongating the EMD. We found that major ion channels, such as L-type calcium (CaL), slow-delayed rectifier potassium (Ks), rapid-delayed rectifier potassium (Kr), and inward rectifier potassium (K1), can significantly extend the action potential duration (APD) up to 580 ms. Additionally, the maximum intracellular calcium (Cai) concentration is greatly affected by the reduction in channel CaL, Ks, background calcium, and Kr. However, among the aforementioned major ion channels, only the CaL channel can play a superior role in prolonging the EMD up to 83 ms. Furthermore, ventricular cells with long EMD have been shown to inherit insignificant mechanical response (in terms of how strong the tension can grow and how far length shortening can go) compared with that in normal cells. In conclusion, despite all variations in every ion channel conductance, only the CaL channel can play a significant role in extending EMD. In addition, cardiac cells with long EMD tend to have inferior mechanical responses due to a lack of Cai compared with normal conditions, which are highly likely to result in a compromised pump function of the heart.

Remodeling of the Purkinje Network in Congestive Heart Failure in the Rabbit

Supplemental Digital Content is available in the text.

Background:

Purkinje fibers (PFs) control timing of ventricular conduction and play a key role in arrhythmogenesis in heart failure (HF) patients. We investigated the effects of HF on PFs.

Methods:

Echocardiography, electrocardiography, micro-computed tomography, quantitative polymerase chain reaction, immunohistochemistry, volume electron microscopy, and sharp microelectrode electrophysiology were used.

Results:

Congestive HF was induced in rabbits by left ventricular volume- and pressure-overload producing left ventricular hypertrophy, diminished fractional shortening and ejection fraction, and increased left ventricular dimensions. HF baseline QRS and corrected QT interval were prolonged by 17% and 21% (mean±SEMs: 303±6 ms HF, 249±11 ms control; n=8/7; P=0.0002), suggesting PF dysfunction and impaired ventricular repolarization. Micro-computed tomography imaging showed increased free-running left PF network volume and length in HF. mRNA levels for 40 ion channels, Ca²⁺-handling proteins, connexins, and proinflammatory and fibrosis markers were assessed: 50% and 35% were dysregulated in left and right PFs respectively, whereas only 12.5% and 7.5% changed in left and right ventricular muscle. Funny channels, Ca²⁺-channels, and K⁺-channels were significantly reduced in left PFs. Microelectrode recordings from left PFs revealed more negative resting membrane potential, reduced action potential upstroke velocity, prolonged duration (action potential duration at 90% repolarization: 378±24 ms HF, 249±5 ms control; n=23/38; P<0.0001), and arrhythmic events in HF. Similar electrical remodeling was seen at the left PF-ventricular junction. In the failing left ventricle, upstroke velocity and amplitude were increased, but action potential duration at 90% repolarization was unaffected.

Conclusions:

Severe volume- followed by pressure-overload causes rapidly progressing HF with extensive remodeling of PFs. The PF network is central to both arrhythmogenesis and contractile dysfunction and the pathological remodeling may increase the risk of fatal arrhythmias in HF patients.

Acute atrial ischemia associates with early but not late new-onset atrial fibrillation in STEMI patients treated with primary PCI: relationship with in-hospital outcomes

BACKGROUND

New-onset atrial fibrillation (NOAF), both early (EAF) or late (LAF), may complicate ST-segment elevation myocardial infarction (STEMI). The mechanisms underlying EAF or LAF are poorly described. We investigated atrial branch occlusion and EAF or LAF onset in STEMI patients undergoing primary percutaneous coronary intervention.

METHODS

This was a retrospective cohort study including 155 STEMI patients. Patients were divided into 3 groups: sinus rhythm (SR), EAF, or LAF. Clinical characteristics, angiographic features including occlusion of atrial branches, namely ramus ostia cavae superioris (ROCS), atrio-ventricular node artery (AVNA), right intermediate atrial artery (RIAA), and left intermediate atrial artery, were assessed. We also investigated in-hospital adverse events (AEs) and death.

RESULTS

Mean age was 63.8±11.9 years; 78.7% were men. NOAF was detected in 22 (14.2%) patients: 10 (6.4%) EAF and 12 LAF (7.7%). Compared to EAF, LAF patients were older (p=0.013), with higher GRACE risk score (p=0.014) and Killip class (p=0.015), depressed ejection fraction (p=0.007), elevated filling pressures (p=0.029), higher C-reactive protein (p=0.014) and more with thrombolysis in myocardial infarction flow <3 (p=0.015). Compared to SR, EAF was associated with higher prevalence of occluded ROCS (p=0.010), AVNA (p=0.005), and RIAA (p<0.001). Moreover, EAF patients had more frequently ≥2 diseased atrial branches than SR (19.5%, p<0.001) and LAF (25%, p<0.030) patients. LAF patients had a higher in-hospital AEs (p=0.019 vs SR; p=0.029 vs EAF) and death (p=0.004 vs SR).

CONCLUSIONS

The occlusion of atrial branches is associated with EAF but not LAF following STEMI. LAF patients had worse in-hospital AEs and mortality.

Atrial fibrillation in patients with systolic heart failure: pathophysiology mechanisms and management

Heart failure (HF) and atrial fibrillation (AF) demonstrate a constantly increasing prevalence during the 21^st century worldwide, as a result of the aging population and the successful interventions of the clinical practice in the deterioration of adverse cardiovascular outcomes. HF and AF share common risk factors and pathophysiological mechanisms, creating the base of a constant interrelation. AF impairs systolic and diastolic function, resulting in the increasing incidence of HF, whereas the structural and neurohormonal changes in HF with preserved or reduced ejection fraction increase the possibility of the AF development. The temporal relationship of the development of either condition affects the diagnostic algorithms, the prognosis and the ideal therapeutic strategy that leads to euvolaemia, management of non-cardiovascular comorbidities, control of heart rate or restoration of sinus rate, ventricular synchronization, prevention of sudden death, stroke, embolism, or major bleeding and maintenance of a sustainable quality of life. The indicated treatment for the concomitant HF and AF includes rate or/and rhythm control as well as thromboembolism prophylaxis, while the progress in the understanding of their pathophysiological interdependence and the introduction of the genetic profiling, create new paths in the diagnosis, the prognosis and the prevention of these diseases.

Cardiac transmembrane ion channels and action potentials: cellular physiology and arrhythmogenic behavior

Cardiac arrhythmias are among the leading causes of mortality. They often arise from alterations in the electrophysiological properties of cardiac cells and their underlying ionic mechanisms. It is therefore critical to further unravel the pathophysiology of the ionic basis of human cardiac electrophysiology in health and disease. In the first part of this review, current knowledge on the differences in ion channel expression and properties of the ionic processes that determine the morphology and properties of cardiac action potentials and calcium dynamics from cardiomyocytes in different regions of the heart are described. Then the cellular mechanisms promoting arrhythmias in congenital or acquired conditions of ion channel function (electrical remodeling) are discussed. The focus is on human-relevant findings obtained with clinical, experimental, and computational studies, given that interspecies differences make the extrapolation from animal experiments to human clinical settings difficult. Deepening the understanding of the diverse pathophysiology of human cellular electrophysiology will help in developing novel and effective antiarrhythmic strategies for specific subpopulations and disease conditions.

The Potential Effects of Aliskiren on Atrial Remodeling Induced by Chronic Intermittent Hypoxia in Rats

Purpose

Atrial remodeling takes part in the pathogenesis of atrial fibrillation (AF). Aliskiren, as a direct renin inhibitor, has been shown to exert protective effects against arrhythmia. The aim of this study was to investigate the potential role of aliskiren in atrial remodeling in a chronic intermittent hypoxia (CIH) rat model.

Methods

A total of 45 Sprague–Dawley rats were randomly assigned into three groups (n=15 per group): control group; CIH group; and CIH with aliskiren (CIH-A) group. CIH and CIH-A rats were subjected to CIH for 6 h per day for 4 weeks. Atrial fibrosis was evaluated using Masson’s trichrome staining. Electrophysiological tests were conducted in the isolated perfused hearts to assess the atrial effective refractory period and inducibility of AF. Atrial ionic remodeling was measured using the whole-cell patch-clamp technique, and Western blotting and real-time quantitative polymerase chain reactionwere performed to evaluate changes in ion channels.

Results

CIH induced obvious collagen deposition, and the abnormal fibrosis was significantly attenuated by aliskiren. The inducibility of AF was increased significantly in the CIH group compared with the control and CIH-A groups (23±24.5% vs 2.0±4.2% vs 5.0±7.0%, respectively; P<0.05). Compared with the control group, the densites of the calcium current (I_CaL) and sodium current (I_Na) were reduced significantly in the CIH group (I_CaL: −3.16±0.61 pA/pF vs −7.13±1.98 pA/pF; I_Na: −50.97±8.71 pA/pF vs −132.58±25.34 pA/pF, respectively; all P<0.05). Following intervention with aliskiren, the reductions in I_CaL and I_Na were significantly improved, and the ionic modeling changes assessed at the mRNA and protein levels were also significantly improved.

Conclusion

CIH could alter atrial modeling and subsequently promote the occurrence and development of AF, which could be attenuated by treatment with aliskiren.

Neurohormonal Regulation of IKs in Heart Failure: Implications for Ventricular Arrhythmogenesis and Sudden Cardiac Death

Heart failure (HF) results in sustained alterations in neurohormonal signaling, including enhanced signaling through the sympathetic nervous system and renin-angiotensin-aldosterone system pathways. While enhanced sympathetic nervous system and renin-angiotensin-aldosterone system activity initially help compensate for the failing myocardium, sustained signaling through these pathways ultimately contributes to HF pathophysiology. HF remains a leading cause of mortality, with arrhythmogenic sudden cardiac death comprising a common mechanism of HF-related death. The propensity for arrhythmia development in HF occurs secondary to cardiac electrical remodeling that involves pathological regulation of ventricular ion channels, including the slow component of the delayed rectifier potassium current, that contribute to action potential duration prolongation. To elucidate a mechanistic explanation for how HF-mediated electrical remodeling predisposes to arrhythmia development, a multitude of investigations have investigated the specific regulatory effects of HF-associated stimuli, including enhanced sympathetic nervous system and renin-angiotensin-aldosterone system signaling, on the slow component of the delayed rectifier potassium current. The objective of this review is to summarize the current knowledge related to the regulation of the slow component of the delayed rectifier potassium current in response to HF-associated stimuli, including the intracellular pathways involved and the specific regulatory mechanisms.

Exendin-4 inhibits atrial arrhythmogenesis in a model of myocardial infarction-induced heart failure via the GLP-1 receptor signaling pathway

Glucagon-like peptide-1 receptor (GLP-1 receptor) agonists are considered to exert cardioprotective effects in models of acute and chronic heart disease. The present study aimed to investigate the role of exendin-4 (a GLP-1 receptor agonist) in atrial arrhythmogenesis in a model of myocardial infarction (MI)-induced heart failure and to elucidate the mechanisms underlying its effects. For this purpose, male Sprague-Dawley rats underwent sham surgery or left anterior descending artery ligation prior to being treated with saline/exendin-4/exendin-4 plus exendin9-39 (an antagonist of GLP-1 receptor) for 4 weeks. The effects of exendin-4 on atrial electrophysiology, atrial fibrosis and PI3K/AKT signaling were assessed. Rats with MI exhibited depressed left ventricular function, an enlarged left atrium volume, prolonged action potential duration, elevated atrial tachyarrhythmia inducibility, decreased conduction velocity and an increased total activation time, as well as total activation time dispersion and atrial fibrosis. However, these abnormalities were attenuated by treatment with the GLP-1 receptor agonist, exendin-4. Moreover, the expression levels of collagen I, collagen III, transforming growth factor-β1, phosphorylated PI3K and AKT levels in atrial tissues were upregulated in rats with MI. These changes were also attenuated by exendin-4. It was also found that these exedin-4-mediated attenutations were mitigated by the co-administration of exendin9-39 with exendin-4. Overall, the findings of the present study suggested that exendin-4 decreases susceptibility to atrial arrhythmogenesis, improves conduction properties and exerts antifibrotic effects via the GLP-1 receptor signaling pathway. These findings provide evidence for the potential use of GLP-1R in the treatment of atrial fibrillation.

Heart failure-induced atrial remodelling promotes electrical and conduction alternans

Heart failure (HF) is associated with an increased propensity for atrial fibrillation (AF), causing higher mortality than AF or HF alone. It is hypothesized that HF-induced remodelling of atrial cellular and tissue properties promotes the genesis of atrial action potential (AP) alternans and conduction alternans that perpetuate AF. However, the mechanism underlying the increased susceptibility to atrial alternans in HF remains incompletely elucidated. In this study, we investigated the effects of how HF-induced atrial cellular electrophysiological (with prolonged AP duration) and tissue structural (reduced cell-to-cell coupling caused by atrial fibrosis) remodelling can have an effect on the generation of atrial AP alternans and their conduction at the cellular and one-dimensional (1D) tissue levels. Simulation results showed that HF-induced atrial electrical remodelling prolonged AP duration, which was accompanied by an increased sarcoplasmic reticulum (SR) Ca²⁺ content and Ca²⁺ transient amplitude. Further analysis demonstrated that HF-induced atrial electrical remodelling increased susceptibility to atrial alternans mainly due to the increased sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) Ca²⁺ reuptake, modulated by increased phospholamban (PLB) phosphorylation, and the decreased transient outward K⁺ current (I_to). The underlying mechanism has been suggested that the increased SR Ca²⁺ content and prolonged AP did not fully recover to their previous levels at the end of diastole, resulting in a smaller SR Ca²⁺ release and AP in the next beat. These produced Ca²⁺ transient alternans and AP alternans, and further caused AP alternans and Ca²⁺ transient alternans through Ca²⁺→AP coupling and AP→Ca²⁺ coupling, respectively. Simulation of a 1D tissue model showed that the combined action of HF-induced ion channel remodelling and a decrease in cell-to-cell coupling due to fibrosis increased the heart tissue’s susceptibility to the formation of spatially discordant alternans, resulting in an increased functional AP propagation dispersion, which is pro-arrhythmic. These findings provide insights into how HF promotes atrial arrhythmia in association with atrial alternans.

Atrial Fibrillation (AF) is the most common arrhythmia in adults, especially in the elderly, with the increased incidence of stroke being a major complication that increases morbidity and mortality. The occurrence of AF is often accompanied by heart failure (HF). AF and HF are also known to have the bidirectional relationship that AF worsens HF and HF promotes AF. HF can induce atrial remodelling, including electrical remodelling, atrial fibrosis, stretch and dilatation, and oxidative stress, in which many factors are associated with arrhythmogenic atrial alternans. HF-induced atrial remodelling varies during various stages and complications of HF, but possible mechanisms underlying their pro-susceptibility to alternans have not been completely elucidated. In this study, we investigated the effects of HF-induced atrial remodelling with prolonged action potential duration (APD) and decreased cell-to-cell coupling on susceptibility to atrial alternans. Simulation results showed that HF-induced an increase in sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) Ca²⁺ reuptake caused by increased phospholamban phosphorylation and a decrease in transient outward K⁺ current played significant roles in the genesis of Ca²⁺ transient alternans and action potential alternans at the single-cell level. The HF-induced decline of cell-to-cell coupling and APD prolongation promoted the genesis of spatially discordant alternans in atrial tissue. This provides insights into how HF facilitates atrial arrhythmia in relation to atrial alternans.

Atrial remodeling and atrial fibrillation in acquired forms of cardiovascular disease

Atrial fibrillation (AF) is prevalent in common conditions and acquired forms of heart disease, including diabetes mellitus (DM), hypertension, cardiac hypertrophy, and heart failure. AF is also prevalent in aging. Although acquired heart disease is common in aging individuals, age is also an independent risk factor for AF. Importantly, not all individuals age at the same rate. Rather, individuals of the same chronological age can vary in health status from fit to frail. Frailty can be quantified using a frailty index, which can be used to assess heterogeneity in individuals of the same chronological age. AF is thought to occur in association with electrical remodeling due to changes in ion channel expression or function as well as structural remodeling due to fibrosis, myocyte hypertrophy, or adiposity. These forms of remodeling can lead to triggered activity and electrical re-entry, which are fundamental mechanisms of AF initiation and maintenance. Nevertheless, the underlying determinants of electrical and structural remodeling are distinct in different conditions and disease states. In this focused review, we consider the factors leading to atrial electrical and structural remodeling in human patients and animal models of acquired cardiovascular disease or associated risk factors. Our goal is to identify similarities and differences in the cellular and molecular bases for atrial electrical and structural remodeling in conditions including DM, hypertension, hypertrophy, heart failure, aging, and frailty.

Various subtypes of phosphodiesterase inhibitors differentially regulate pulmonary vein and sinoatrial node electrical activities

Phosphodiesterase (PDE)3-5 are expressed in cardiac tissue and play critical roles in the pathogenesis of heart failure and atrial fibrillation. PDE inhibitors are widely used in the clinic, but their effects on the electrical activity of the heart are not well understood. The aim of the present study was to examine the effects of various PDE inhibitors on spontaneous cardiac activity and compare those effects between sinoatrial nodes (SANs) and pulmonary veins (PVs). Conventional microelectrodes were used to record action potentials in isolated rabbit SAN and PV tissue preparations, before and after administration of different concentrations (0.1, 1 and 10 µM) of milrinone (PDE3 inhibitor), rolipram (PDE4 inhibitor) and sildenafil (PDE5 inhibitor), with or without the application of isoproterenol (cAMP and PKA activator), KT5823 (PKG inhibitor) or H89 (PKA inhibitor). Milrinone (1 and 10 µM) increased the spontaneous activity in PVs by 10.6±4.9 and 16.7±5.3% and in SANs by 9.3±4.3 and 20.7±4.6%, respectively. In addition, milrinone (1 and 10 µM) induced the occurrence of triggered activity (0/8 vs. 5/8; P<0.005) in PVs. Rolipram increased PV spontaneous activity by 7.5±1.3-9.5±4.0%, although this was not significant, and did not alter SAN spontaneous activity. Sildenafil reduced spontaneous activity in PVs to a greater extent than that seen in SANs. Both KT5823 and H89 suppressed milrinone-increased PV spontaneous activity. In the presence of isoproterenol, milrinone did not alter isoproterenol-induced PV arrhythmogenesis, suggesting that the effects of PDE3 are mediated by the protein kinase G and protein kinase A signaling pathways. In conclusion, inhibitors of different PDE subtypes exert diverse electrophysiological effects on PV and SAN activities.

Animal models of arrhythmia: classic electrophysiology to genetically modified large animals

Arrhythmias are common and contribute substantially to cardiovascular morbidity and mortality. The underlying pathophysiology of arrhythmias is complex and remains incompletely understood, which explains why mostly only symptomatic therapy is available. The evaluation of the complex interplay between various cell types in the heart, including cardiomyocytes from the conduction system and the working myocardium, fibroblasts and cardiac immune cells, remains a major challenge in arrhythmia research because it can be investigated only in vivo. Various animal species have been used, and several disease models have been developed to study arrhythmias. Although every species is useful and might be ideal to study a specific hypothesis, we suggest a practical trio of animal models for future use: mice for genetic investigations, mechanistic evaluations or early studies to identify potential drug targets; rabbits for studies on ion channel function, repolarization or re-entrant arrhythmias; and pigs for preclinical translational studies to validate previous findings. In this Review, we provide a comprehensive overview of different models and currently used species for arrhythmia research, discuss their advantages and disadvantages and provide guidance for researchers who are considering performing in vivo studies.

Impact of Transcatheter Device Closure of Atrial Septal Defect on Atrial Arrhythmias Propensity in Young Adults

Atrial septal defect (ASD) is a condition that requires early intervention because of the consequences over the right-side heart. Chronic atrial stretching promotes atrial conduction delay and the imbalance of the conduction homogeneity, which lead to the propensity to atrial arrhythmias (AA). We aim to evaluate the impact of transcatheter closure of ASD on atrial vulnerability markers leading to late AA in young adults. We conducted a prospective, longitudinal study in one hundred patients (mean age 25.2 ± 5.4 years) who underwent transcatheter closure of ASD at Cardiocentro Pediátrico William Soler. P-wave maximum (P_max) and P-wave dispersion (P_d) were analyzed from 12-lead electrocardiogram. Left-side and right-side intraatrial and interatrial electromechanical delay (EMD) were measured with tissue Doppler imaging. Both electrocardiographic and echocardiographic analyses were performed during the study period. Compared to baseline, there was a significant reduction in P max (p ≤ 0.001) and P_d (p ≤ 0.001) after 3 months of procedure. All atrial electromechanical coupling parameters significantly reduced at 6 months of ASD closure and tend to remain at lower values till the last evaluation. Over 9.2 ± 1.6 years of follow-up, 15 subjects (15%) developed AA, of which intraatrial reentrant tachycardia (66.6%) became the main rhythm disturbance. Intra-right atrial EMD ≥ 16 ms (HR 4.08, 95% CI 1.15-14.56; p = 0.03) and P_d 45 ms (HR 1.66, 95% CI 1.06-2.59; p = 0.02) were identified as predictors of late AA. Transcatheter device closure of ASD in young adults promotes a significant reduction of electrocardiographic and echocardiographic markers of AA vulnerability, which persist during the long-term follow-up. Nevertheless, P_d and interatrial EMD were identified as independent risk factors of AA.

Lemnalol Modulates the Electrophysiological Characteristics and Calcium Homeostasis of Atrial Myocytes

Sepsis, an inflammatory response to infection provoked by lipopolysaccharide (LPS), is associated with high mortality, as well as ischemic stroke and new-onset atrial arrhythmia. Severe bacterial infections causing sepsis always result in profound physiological changes, including fever, hypotension, arrhythmia, necrosis of tissue, systemic multi-organ dysfunction and finally death. LPS challenge-induced inflammatory responses during sepsis may increase the likelihood of the arrhythmogenesis. Lemnalol is known to possess potent anti-inflammatory effects. This study examined whether Lemnalol (0.1 μM) could modulate the electrophysiological characteristics and calcium homeostasis of atrial myocytes under the influence of LPS (1μg/mL). Under challenge with LPS, Lemnalol-treated LA myocytes, had a longer AP duration at 20%, 50% and 90% repolarization of the amplitude, compared to the LPS-treated cells. LPS-challenged LA myocytes showed increased late sodium current, Na⁺-Ca²⁺ exchanger current, transient outward current, rapid component of delayed rectifier potassium current, tumor necrosis factor-α, NF-κB and increased phosphorylation of ryanodine receptor (RyR), but a lower L-type Ca²⁺ current than the control LA myocytes. Exposure to Lemnalol reversed the LPS-induced effects. The LPS-treated and control groups of LA myocytes, with or without the existence of Lemnalol. showed no apparent alterations in the sodium current amplitude or Cav1.2 expression. The expression of sarcoendoplasmic reticulum calcium transport ATPase (SERCA2) was reduced by LPS treatment, while Lemnalol ameliorated the LPS-induced alterations. The phosphorylation of RyR was enhanced by LPS treatment, while Lemnalol attenuated the LPS-induced alterations. In conclusion, Lemnalol modulates LPS-induced alterations of LA calcium homeostasis and blocks the NF-κB pathways, which may contribute to the attenuation of LPS-induced arrhythmogenesis.

Atrial Fibrillation – An Orchestra of Classic and Modern Risk Factors

Over the past years, prevention and control of risk factors has begun to play an important role in the management of patients prone to develop atrial fibrillation (AF). A considerable number of risk factors that contribute to the creation of a predisposing substrate for AF has been identified over the years. Although certain AF risk factors such as age, gender, genetic predisposition, or race are unmodifiable, controlling modifiable risk factors may represent an invaluable tool in the management of AF patients. In the recent decades, numerous studies have evaluated the mechanisms linking different risk factors to AF, but the exact degree of atrial remodeling induced by each factor remains unknown. Elucidating these mechanisms is essential for initiating personalized therapies in patients prone to develop AF. The present review aims to provide an overview of the most relevant modifiable risk factors involved in AF occurrence, with a focus on the mechanisms by which these factors lead to AF initiation and perpetuation.

Effect of ablation at high-dominant frequency sites overlapping with low-voltage areas after pulmonary vein isolation of nonparoxysmal atrial fibrillation

BACKGROUND

The relationship between high-dominant frequency (DF) sites and low-voltage areas (LVAs) in nonparoxysmal atrial fibrillation (AF) patients still remains unknown.

OBJECTIVE

This study aimed to evaluate the effect of ablation at high-DF sites overlapping with LVAs after pulmonary vein ablation (PVI) of nonparoxysmal AF.

METHODS

A total of 128 consecutive nonparoxysmal patients with atrial fibrillation (53 persistent AF) were retrospectively investigated. The patients with AF were divided into two groups: patients with circumferential PVI alone (PVI group, n = 57) and those with PVI followed by a DF-based ablation (DF group, n = 71).

RESULTS

The patient characteristics did not significantly differ between the two groups. However, the LVA ( < 0.5 mV)/left atrial (LA) surface was significantly greater in the DF than the PVI group (22% vs 16%, P = .02). The total max-DF sites overlapping with LVAs in the LA were significantly greater in the DF than the PVI group (91% vs 10%, P = .001). The atrial arrhythmia freedom on antiarrhythmic drugs in the DF group was significantly greater than that in the PVI group during 10.0 ± 3.2 months of follow-up (83.1% vs 64.9%, log-rank test P = .021). The event-free survival in the PVI group decreased according to the LVA extent while it was > 80% in the DF group. The event-free survival in patients with AF especially with extensive LVAs ( ≥ 30%) in the DF group was significantly greater than that in the PVI group (81.0% vs 45.5%, log-rank test P = .035).

CONCLUSIONS

High-DF sites overlapping with LVAs after the PVI may be potential selective targets for modification of atrial substrates in nonparoxysmal AF patients.

Invasive therapies for patients with concomitant heart failure and atrial fibrillation

Atrial fibrillation (AF) and heart failure (HF) are two clinical entities that can present either separately or concurrently. One entity can lead to the other and vice versa as AF can not only be the underlying etiology of HF but also exacerbate HF due to other cardiac diseases. Besides prevention of cerebral and systemic embolism and elimination of AF-related symptoms, restoration of sinus rhythm for AF patients helps to avoid or reduce HF, irrespective of their underlying heart disease. Successful rates of medical therapy for AF are low in persistent AF, and much lower in long-standing AF, while invasive procedures for AF yield promising results. In this review, the authors evaluate the value of invasive therapies for HF patients complicated with non-valvular AF. We examine this clinical problem by interpreting the relationships between these two entities: the mechanism of tachycardia-induced cardiomyopathy (TIC), past opinions about rhythm control and rate control of AF, discrimination of HF-related AF and AF-induced HF, how to identify the AF patients that could benefit from invasive therapies, and how to select invasive therapies for different AF patients and peri-operative treatments.

Atrial Fibrillation Ablation Should Be First-Line Therapy in Heart Failure Patients: CON

Heart failure (HF) and atrial fibrillation (AF) are the epidemics of the twenty-first century. These often coexist and are the cause of major morbidity and mortality. Management of these patients has posed a significant challenge to the medical community. Guideline-directed pharmacologic therapy for heart failure is important; however, there is no clear consensus on how best to treat AF with concomitant HF. In this article, we provide an in-depth review of the management of AF in patients with HF and provide insight as to why catheter ablation should not be the first line of therapy in this population.

Association between echocardiographic parameters and biomarkers in probands with atrial fibrillation and different PR interval lengths: Insight from the epidemiologic LIFE Adult Study

Background

PR interval prolongation is associated with increased risk for atrial fibrillation (AF). Different biomarkers are used to predict AF incidence and its outcomes. The aim of this study was to investigate the association between echocardiographic parameters and blood biomarkers in PR interval groups and AF.

Methods

The LIFE-Adult-Study is a population-based cohort study of randomly selected participants from Leipzig, Germany. In this cross-sectional analysis, individuals ≥40 years with available echocardiographic (LA diameter, EF) and laboratory data (creatinine, Troponin, NT-proBNP) were included.

Results

The study population comprised 1.429 individuals (median age 56 (IQR 48–66) years, 40% males) with complete ECG, echocardiographic and laboratory data. There were 48 (3.4%) individuals with AF, 177 (12.4%) with short, 138 (9.7%) with prolonged and 1.066 (74.5%) with normal PR interval. Individuals with PR interval prolongation had larger LA diameter, higher Troponin and NT-proBNP levels than individuals with normal PR interval, but lower than AF group (p<0.001). In contrast, eGFR was significantly higher in the group with PR interval prolongation than in AF, but lower than in individuals with normal PR interval (p<0.001). In the multivariate analysis, PR interval prolongation and AF shared similar characteristics, the only parameter different between both groups was NT-proBNP.

Conclusions

Individuals with PR interval prolongation and AF showed similarities in echocardiographic parameters, renal function and blood biomarker levels. Longitudinal studies are necessary to prove whether the PR interval prolongation may be considered as preliminary stage for AF.

Anticoagulation in atrial fibrillation with heart failure

Heart failure (HF) and atrial fibrillation (AF) frequently coexist, and they can beget one another due to similar factors and shared pathophysiology. These pathophysiologic changes promote the episodes of AF, while they in turn predispose to the exacerbation of HF. In this review, we will discuss pathophysiological mechanisms shared by AF and HF. Patients with concomitant HF and AF are at a particularly high risk of thromboembolism, which contribute to even worse symptoms and poorer prognosis. Vitamin K antagonists (VKA) (warfarin) were the traditional medication in AF patients for the prevention of stroke, whereas the advance of novel non-VKA oral anticoagulants (NOACs) (dabigatran, apixaban, rivaroxaban, and edoxaban) is challenging these standard prescriptions. NOACs' potential advantages over warfarin, including fixed dosing regimens, wide therapeutic window, and more sustained anticoagulant response, promote clinicians to consider these novel agents in the first place. However, some data suggested patients with AF and HF may receive different therapeutic response than those with AF alone in anticoagulant treatment. Accordingly, we aim to assess the potential role of oral anticoagulants, especially NOACs, in the management of patients with concomitant AF and HF.

Pathophysiological and therapeutic implications in patients with atrial fibrillation and heart failure

Heart failure and atrial fibrillation are common and responsible for significant mortality of patients. Both share the same risk factors like hypertension, ischemic heart disease, diabetes, obesity, arteriosclerosis, and age. A variety of microscopic and macroscopic changes favor the genesis of atrial fibrillation in patients with preexisting heart failure, altered subcellular Ca²⁺ homeostasis leading to increased cellular automaticity as well as concomitant fibrosis that are induced by pressure/volume overload and altered neurohumoral states. Atrial fibrillation itself promotes clinical deterioration of patients with preexisting heart failure as atrial contraction significantly contributes to ventricular filling. In addition, atrial fibrillation induced tachycardia can even further compromise ventricular function by inducing tachycardiomyopathy. Even though evidence has been provided that atrial functions significantly and independently of confounding ventricular pathologies, correlate with mortality of heart failure patients, rate and rhythm controls have been shown to be of equal effectiveness in improving mortality. Yet, it also has been shown that cohorts of patients with heart failure benefit from a rhythm control concept regarding symptom control and hospitalization. To date, amiodarone is the most feasible approach to restore sinus rhythm, yet its use is limited by its extensive side-effect profile. In addition, other therapies like catheter-based pulmonary vein isolation are of increasing importance. A wide range of heart failure-specific therapies are available with mixed impact on new onset or perpetuation of atrial fibrillation. This review highlights pathophysiological concepts and possible therapeutic approaches to treat patients with heart failure at risk for or with atrial fibrillation.

Oxidative stress creates a unique, CaMKII-mediated substrate for atrial fibrillation in heart failure

The precise mechanisms by which oxidative stress (OS) causes atrial fibrillation (AF) are not known. Since AF frequently originates in the posterior left atrium (PLA), we hypothesized that OS, via calmodulin-dependent protein kinase II (CaMKII) signaling, creates a fertile substrate in the PLA for triggered activity and reentry. In a canine heart failure (HF) model, OS generation and oxidized-CaMKII-induced (Ox-CaMKII-induced) RyR2 and Nav1.5 signaling were increased preferentially in the PLA (compared with left atrial appendage). Triggered Ca2+ waves (TCWs) in HF PLA myocytes were particularly sensitive to acute ROS inhibition. Computational modeling confirmed a direct relationship between OS/CaMKII signaling and TCW generation. CaMKII phosphorylated Nav1.5 (CaMKII-p-Nav1.5 [S571]) was located preferentially at the intercalated disc (ID), being nearly absent at the lateral membrane. Furthermore, a decrease in ankyrin-G (AnkG) in HF led to patchy dropout of CaMKII-p-Nav1.5 at the ID, causing its distribution to become spatially heterogeneous; this corresponded to preferential slowing and inhomogeneity of conduction noted in the HF PLA. Computational modeling illustrated how conduction slowing (e.g., due to increase in CaMKII-p-Nav1.5) interacts with fibrosis to cause reentry in the PLA. We conclude that OS via CaMKII leads to substrate for triggered activity and reentry in HF PLA by mechanisms independent of but complementary to fibrosis.

Effect of autonomic influences to induce triggered activity in muscular sleeves extending into the coronary sinus of the canine heart and its suppression by ranolazine

INTRODUCTION

Extrasystoles arising from the muscular sleeves associated with the pulmonary veins (PV), superior vena cava (SVC), and coronary sinus (CS) are known to precipitate atrial fibrillation (AF). The late sodium channel current (I_Na ) inhibitor ranolazine has been reported to exert antiarrhythmic effects in canine PV and SVC sleeves by suppressing late phase 3 early and delayed after depolarization (EAD and DAD)-induced triggered activity induced by parasympathetic and/or sympathetic stimulation. The current study was designed to extend our existing knowledge of the electrophysiological and pharmacologic properties of canine CS preparations and assess their response to inhibition of late I_Na following autonomic stimulation.

METHODS

Transmembrane action potentials were recorded from canine superfused CS using standard microelectrode techniques. Acetylcholine (ACh, 1 µM), isoproterenol (Iso, 1 µM), high calcium ([Ca²⁺ ]_o  = 5.4 mM), or a combination were used to induce EADs, DADs, and triggered activity.

RESULTS

Action potentials (AP) recorded from the CS displayed short and long AP durations (APD), with and without phase 4 depolarization (n = 19). Iso induced DAD-mediated triggered activity. The combination of sympathetic and parasympathetic agonists resulted in late phase 3 EAD-induced triggered activity in all CS preparations. Ranolazine (5-10 µM) suppressed late phase 3 EAD- and DAD-induced triggered activity in 8 of 8 preparations. Subthreshold stimulation induced a prominent hyperpolarization that could be suppressed by atropine.

CONCLUSIONS

Our results suggest the important role of parasympathetic innervation in the activity of the CS. Autonomic influences promote DAD- and late phase-3-EAD-mediated triggered activity in canine CS, thus generating extrasystolic activity capable of initiating atrial arrhythmias. Ranolazine effectively suppresses these triggers.

Profibrotic, Electrical, and Calcium-Handling Remodeling of the Atria in Heart Failure Patients With and Without Atrial Fibrillation

Atrial fibrillation (AF) and heart failure (HF) are common cardiovascular diseases that often co-exist. Animal models have suggested complex AF-promoting atrial structural, electrical, and Ca²⁺-handling remodeling in the setting of HF, but data in human samples are scarce, particularly regarding Ca²⁺-handling remodeling. Here, we evaluated atrial remodeling in patients with severe left ventricular (LV) dysfunction (HFrEF), long-standing persistent ('chronic') AF (cAF) or both (HFrEF-cAF), and sinus rhythm controls with normal LV function (Ctl) using western blot in right-atrial tissue, sharp-electrode action potential (AP) measurements in atrial trabeculae and voltage-clamp experiments in isolated right-atrial cardiomyocytes. Compared to Ctl, expression of profibrotic markers (collagen-1a, fibronectin, periostin) was higher in HFrEF and HFrEF-cAF patients, indicative of structural remodeling. Connexin-43 expression was reduced in HFrEF patients, but not HFrEF-cAF patients. AP characteristics were unchanged in HFrEF, but showed classical indices of electrical remodeling in cAF and HFrEF-cAF (prolonged AP duration at 20% and shorter AP duration at 50% and 90% repolarization). L-type Ca²⁺ current (I_Ca,L) was significantly reduced in HFrEF, cAF and HFrEF-cAF, without changes in voltage-dependence. Potentially proarrhythmic spontaneous transient-inward currents were significantly more frequent in HFrEF and HFrEF-cAF compared to Ctl, likely resulting from increased sarcoplasmic reticulum (SR) Ca²⁺ load (integrated caffeine-induced current) in HFrEF and increased ryanodine-receptor (RyR2) single-channel open probability in HFrEF and HFrEF-cAF. Although expression and phosphorylation of the SR Ca²⁺-ATPase type-2a (SERCA2a) regulator phospholamban were unchanged in HFrEF and HFrEF-cAF patients, protein levels of SERCA2a were increased in HFrEF-cAF and sarcolipin expression was decreased in both HFrEF and HFrEF-cAF, likely increasing SR Ca²⁺ uptake and load. RyR2 protein levels were decreased in HFrEF and HFrEF-cAF patients, but junctin levels were higher in HFrEF and relative Ser2814-RyR2 phosphorylation levels were increased in HFrEF-cAF, both potentially contributing to the greater RyR2 open probability. These novel insights into the molecular substrate for atrial arrhythmias in HF-patients position Ca²⁺-handling abnormalities as a likely trigger of AF in HF patients, which subsequently produces electrical remodeling that promotes the maintenance of the arrhythmia. Our new findings may have important implications for the development of novel treatment options for AF in the context of HF.

Calcium in the Pathophysiology of Atrial Fibrillation and Heart Failure

Atrial fibrillation (AF) is commonly associated with heart failure. A bidirectional relationship exists between the two-AF exacerbates heart failure causing a significant increase in heart failure symptoms, admissions to hospital and cardiovascular death, while pathological remodeling of the atria as a result of heart failure increases the risk of AF. A comprehensive understanding of the pathophysiology of AF is essential if we are to break this vicious circle. In this review, the latest evidence will be presented showing a fundamental role for calcium in both the induction and maintenance of AF. After outlining atrial electrophysiology and calcium handling, the role of calcium-dependent afterdepolarizations and atrial repolarization alternans in triggering AF will be considered. The atrial response to rapid stimulation will be discussed, including the short-term protection from calcium overload in the form of calcium signaling silencing and the eventual progression to diastolic calcium leak causing afterdepolarizations and the development of an electrical substrate that perpetuates AF. The role of calcium in the bidirectional relationship between heart failure and AF will then be covered. The effects of heart failure on atrial calcium handling that promote AF will be reviewed, including effects on both atrial myocytes and the pulmonary veins, before the aspects of AF which exacerbate heart failure are discussed. Finally, the limitations of human and animal studies will be explored allowing contextualization of what are sometimes discordant results.

Atrial Fibrillation in Patients with Heart Failure: Current State and Future Directions

Heart failure affects nearly 26 million people worldwide. Patients with heart failure are frequently affected with atrial fibrillation, and the interrelation between these pathologies is complex. Atrial fibrillation shares the same risk factors as heart failure. Moreover, it is associated with a higher-risk baseline clinical status and higher mortality rates in patients with heart failure. The mechanisms by which atrial fibrillation occurs in a failing heart are incompletely understood, but animal studies suggest they differ from those that occur in a healthy heart. Data suggest that heart failure-induced atrial fibrosis and atrial ionic remodeling are the underlying abnormalities that facilitate atrial fibrillation. Therapeutic considerations for atrial fibrillation in patients with heart failure include risk factor modification and guideline-directed medical therapy, anticoagulation, rate control, and rhythm control. As recommended for atrial fibrillation in the non-failing heart, anticoagulation in patients with heart failure should be guided by a careful estimation of the risk of embolic events versus the risk of hemorrhagic episodes. The decision whether to target a rate-control or rhythm-control strategy is an evolving aspect of management. Currently, both approaches are good medical practice, but recent data suggest that rhythm control, particularly when achieved through catheter ablation, is associated with improved outcomes. A promising field of research is the application of neurohormonal modulation to prevent the creation of the "structural substrate" for atrial fibrillation in the failing heart.

Role of ion channels in heart failure and channelopathies

Heart failure (HF) is a complication of multiple cardiac diseases and is characterized by impaired contractile and electric function. Patients with HF are not only limited by reduced contractile function but are also prone to life-threatening ventricular arrhythmias. HF itself leads to remodeling of ion channels, gap junctions, and intracellular calcium handling abnormalities that in combination with structural remodeling, e.g., fibrosis, produce a substrate for an arrhythmogenic disorders. Not only ventricular life-threatening arrhythmias contribute to increased morbidity and mortality but also atrial arrhythmias, especially atrial fibrillation (AF), are common in HF patients and contribute to morbidity and mortality. The distinct ion channel remodeling processes in HF and in channelopathies associated with HF will be discussed. Further basic research and clinical studies are needed to identify underlying molecular pathways of HF pathophysiology to provide the basis for improved patient care and individualized therapy based on individualized ion channel composition and remodeling.

Evaluation of the atrial substrate based on low-voltage areas and dominant frequencies after pulmonary vein isolation in nonparoxysmal atrial fibrillation

BACKGROUND

This study aimed to evaluate the atrial substrate in the left atrium (LA) by low-voltage areas (LVAs) and high-dominant frequencies (DFs) after circumferential pulmonary vein isolation (PVI) in nonparoxysmal atrial fibrillation (AF).

METHODS

In 70 patients with nonparoxysmal AF patients (41 persistent AF), LA voltage maps were created during sinus rhythm by external cardioversion after PVI and DF mapping. The patients were divided into AF-free and AF-recurrent groups.

RESULTS

The AF freedom rate without antiarrhythmic drugs was 69.0% after PVI after 1 procedure during a 12-month follow-up. There was a significant difference in the LVA (<0.5 mV)/LA surface area after PVI between the AF-free and AF-recurrent groups (15% vs 23%, P = .033). AF freedom was significantly greater in those with LVAs of ≤24% than in those with LVAs of >24% during 12 months of follow-up (78.6% vs 53.8%, Log-rank test P = .020). Fifty-six (72%) of the 78 high-DF sites (≥8 Hz) overlapped with LVAs. Thirty-one (55%) of 56 high-DF sites overlapped with LVAs that existed at LVA border zones. There were no significant differences in number of high-DF sites that overlapped with LVAs in the LA between the two groups. However, in persistent AF patients, the max-DF value in the LA exhibited a significant difference between the two groups (P = .008).

CONCLUSIONS

LVAs were associated with AF recurrences after PVI in nonparoxysmal AF patients and overlapped with many high-DF sites. PVI alone may be enough to treat patients with mild-to-moderate extent (≤24%) of LVAs.

Xanthine Oxidase Inhibitor Allopurinol Prevents Oxidative Stress-Mediated Atrial Remodeling in Alloxan-Induced Diabetes Mellitus Rabbits

Background

There are several mechanisms, including inflammation, oxidative stress and abnormal calcium homeostasis, involved in the pathogenesis of atrial fibrillation. In diabetes mellitus (DM), increased oxidative stress may be attributable to higher xanthine oxidase activity. In this study, we examined the relationship between oxidative stress and atrial electrical and structural remodeling, and calcium handling abnormalities, and the potential beneficial effects of the xanthine oxidase inhibitor allopurinol upon these pathological changes.

Methods and Results

Ninety rabbits were randomly and equally divided into 3 groups: control, DM, and allopurinol‐treated DM group. Echocardiographic and hemodynamic assessments were performed in vivo. Serum and tissue markers of oxidative stress and atrial fibrosis, including the protein expression were examined. Atrial interstitial fibrosis was evaluated by Masson trichrome staining. I_CaL was measured from isolated left atrial cardiomyocytes using voltage‐clamp techniques. Confocal microscopy was used to detect intracellular calcium transients. The Ca²⁺ handling protein expression was analyzed by Western blotting. Mitochondrial‐related proteins were analyzed as markers of mitochondrial function. Compared with the control group, rabbits with DM showed left ventricular hypertrophy, increased atrial interstitial fibrosis, oxidative stress and fibrosis markers, I_CaL and intracellular calcium transient, and atrial fibrillation inducibility. These abnormalities were alleviated by allopurinol treatment.

Conclusions

Allopurinol, via its antioxidant effects, reduces atrial mechanical, structural, ion channel remodeling and mitochondrial synthesis abnormalities induced by DM‐related increases in oxidative stress.

Increased left atrial size is associated with higher atrial fibrillation recurrence in patients treated with antiarrhythmic medications

BACKGROUND

Atrial fibrillation (AF) is highly prevalent, and antiarrhythmic therapy is often used to help with rhythm control. Some common echocardiographic parameters may be useful in predicting AF recurrence among these patients. The purpose of this study was to evaluate the association between 3 common echocardiographic parameters (left atrial [LA] size, left ventricular ejection fraction [LVEF], and mitral regurgitation [MR]) and AF recurrence among patients treated with antiarrhythmic medications.

HYPOTHESIS

We hypothesized that LA size, LVEF, and severity of MR are predictors of AF recurrence in this population.

METHODS

A real-world cohort of AF patients who had transthoracic echocardiograms was analyzed. Data on LA size, LVEF, and MR were collected retrospectively from echocardiography reports. Patients were followed from the time of the echocardiogram until first recurrence of AF.

RESULTS

A total of 2522 patients had echocardiography reports available for review. LA size showed the strongest prognostic relationship with AF recurrence; neither LVEF nor MR was significantly associated with AF recurrence. These results persisted after adjusting for age, sex, race, tobacco use, alcohol use, drug use, body mass index, and Charlson Comorbidity Index in a multivariable model.

CONCLUSIONS

In a cohort of patients treated with antiarrhythmic medications that had transthoracic echocardiogram data, LA size was a significant predictor of AF recurrence. The clinical utility of this finding would be strengthened by replication in a multicenter setting.

Loss of p21-activated kinase 1 (Pak1) promotes atrial arrhythmic activity

BACKGROUND

Atrial fibrillation (AF) is initiated through arrhythmic atrial excitation from outside the sinus node or remodeling of atrial tissue that allows reentry of excitation. Angiotensin II (AngII) has been implicated in the initiation and maintenance of AF through changes in Ca²⁺ handling and production of reactive oxygen species (ROS).

OBJECTIVE

We aimed to determine the role of p21-activated kinase 1 (Pak1), a downstream target in the AngII signaling cascade, in atrial electrophysiology and arrhythmia.

METHODS

Wild-type and Pak1^-/- mice were used to determine atrial function in vivo on the organ and cellular level by quantification of electrophysiological and Ca²⁺ handling properties.

RESULTS

We demonstrate that reduced Pak1 activity increases the inducibility of atrial arrhythmia in vivo and in vitro. On the cellular level, Pak1^-/- atrial myocytes (AMs) exhibit increased basal and AngII (1 μM)-induced ROS production, sensitivity to the NADPH oxidase-2 (NOX2) inhibitors gp91ds-tat and apocynin (1 μM), and enhanced membrane translocation of Ras-related C3 substrate 1 (Rac1) that is part of the multimolecular NOX2 complex. Upon stimulation with AngII, Pak1^-/- AMs exhibit an exaggerated increase in the intracellular Calcium concentration ([Ca²⁺]_i) and arrhythmic events that were sensitive to sodium-calcium exchanger (NCX) inhibitors (KB-R7943 and SEA0400; 1 μM) and suppressed in AMs from NOX2-deficient (gp91^phox-/-) mice. Pak1 stimulation (FTY720; 200 nM) in wild-type AMs and AMs from a canine model of ventricular tachypacing-induced AF prevented AngII-induced arrhythmic Ca²⁺ overload by attenuating NCX activity in a NOX2-dependent manner.

CONCLUSION

The experimental results support that Pak1 stimulation can attenuate NCX-dependent Ca²⁺ overload and prevent triggered arrhythmic activity by suppressing NOX2-dependent ROS production.