Atrial Electrophysiology Research Articles

A Plasma-Based, Amiodarone-Impregnated Material Decreases Susceptibility to Atrial Fibrillation in a Post-Cardiac Surgery Model.

This study aimed to test the impact of a plasma-based, material (PBM) impregnated with amiodarone on atrial electrophysiology and atrial fibrillation susceptibility in a porcine post-cardiac surgery model. Ten healthy pigs underwent implantation of transvenous pacing systems, after which sterile talc was infused into the pericardial sac via a pericardiotomy. In five animals, PBM was applied to the atrial epicardial surface just before talc infusion. Electrophysiologic evaluations were performed using the pacing system immediately after chest closure and 7 days later. Atrial histologic evaluations were performed. Immediately after chest closure, there were no significant differences in electrophysiologic parameters between talc-only and talc + PBM animals, and atrial fibrillation was largely noninducible. On postsurgical day 7, electrophysiologic evaluation revealed significantly shorter sinus cycle length and atrioventricular nodal refractoriness among talc-only animals relative to talc + PBM animals, possibly suggesting attenuated sympathetic nervous system activation in the latter. Atrial fibrillation inducibility and duration were significantly greater among talc-only animals. No significant differences in atrial refractoriness or conduction time between groups were apparent. Histologic evaluation revealed a relative reduction in epicardial inflammation and less myolysis among talc + PBM animals. Epicardial application of a plasma-based, amiodarone-impregnated material was associated with a significant reduction in atrial inflammation and susceptibility to fibrillation.

Computational models of atrial cellular electrophysiology and calcium handling, and their role in atrial fibrillation.

The complexity of the heart makes an intuitive understanding of the relative contribution of ion channels, transporters and signalling pathways to cardiac electrophysiology challenging. Computational modelling of cardiac cellular electrophysiology has proven useful to integrate experimental findings, extrapolate results obtained in expression systems or animal models to other systems, test quantitatively ideas based on experimental data and provide novel hypotheses that are experimentally testable. While the bulk of computational modelling has traditionally been directed towards ventricular bioelectricity, increasing recognition of the clinical importance of atrial arrhythmias, particularly atrial fibrillation, has led to widespread efforts to apply computational approaches to understanding atrial electrical function. The increasing availability of detailed, atrial-specific experimental data has stimulated the development of novel computational models of atrial-cellular electrophysiology and Ca(2+) handling. To date, more than 300 studies have employed mathematical simulations to enhance our understanding of atrial electrophysiology, arrhythmogenesis and therapeutic responses. Future modelling studies are likely to move beyond current whole-cell models by incorporating new data on subcellular architecture, macromolecular protein complexes, and localized ion-channel regulation by signalling pathways. At the same time, more integrative multicellular models that take into account regional electrophysiological and Ca(2+) handling properties, mechano-electrical feedback and/or autonomic regulation will be needed to investigate the mechanisms governing atrial arrhythmias. A combined experimental and computational approach is expected to provide the more comprehensive understanding of atrial arrhythmogenesis that is required to develop improved diagnostic and therapeutic options. Here, we review this rapidly expanding area, with a particular focus on Ca(2+) handling, and provide ideas about potential future directions.

Effects of Persistent Atrial Fibrillation-Induced Electrical Remodeling on Atrial Electro-Mechanics - Insights from a 3D Model of the Human Atria.

AimsAtrial stunning, a loss of atrial mechanical contraction, can occur following a successful cardioversion. It is hypothesized that persistent atrial fibrillation-induced electrical remodeling (AFER) on atrial electrophysiology may be responsible for such impaired atrial mechanics. This simulation study aimed to investigate the effects of AFER on atrial electro-mechanics.Methods and ResultsA 3D electromechanical model of the human atria was developed to investigate the effects of AFER on atrial electro-mechanics. Simulations were carried out in 3 conditions for 4 states: (i) the control condition, representing the normal tissue (state 1) and the tissue 2–3 months after cardioversion (state 2) when the atrial tissue recovers its electrophysiological properties after completion of reverse electrophysiological remodelling; (ii) AFER-SR condition for AF-remodeled tissue with normal sinus rhythm (SR) (state 3); and (iii) AFER-AF condition for AF-remodeled tissue with re-entrant excitation waves (state 4). Our results indicate that at the cellular level, AFER (states 3 & 4) abbreviated action potentials and reduced the Ca2+ content in the sarcoplasmic reticulum, resulting in a reduced amplitude of the intracellular Ca2+ transient leading to decreased cell active force and cell shortening as compared to the control condition (states 1 & 2). Consequently at the whole organ level, atrial contraction in AFER-SR condition (state 3) was dramatically reduced. In the AFER-AF condition (state 4) atrial contraction was almost abolished.ConclusionsThis study provides novel insights into understanding atrial electro-mechanics illustrating that AFER impairs atrial contraction due to reduced intracellular Ca2+ transients.

Unmasking atrial repolarization to assess alternans, spatiotemporal heterogeneity, and susceptibility to atrial fibrillation

Detection of atrial repolarization waves free of far-field signal contamination by ventricular activation would allow investigation of atrial electrophysiology and factors that influence susceptibility to atrial tachycardia and atrial fibrillation (AF). The purpose of this study was to identify means for high-resolution intracardiac recording of atrial repolarization (Ta) waves using standard clinical electrocatheters and to assess fundamental electrophysiologic properties relevant to AF risk. In alpha-chloralose anesthetized Yorkshire pigs, we studied effects of vagus nerve stimulation (VNS) on PTa and QT intervals and effects of acute atrial ischemia or administration of intrapericardial acetylcholine followed by intravenous epinephrine on susceptibility to AF. Electrocatheters with closely spaced (1-mm) electrode pairs yielded high-resolution tracings of atrial repolarization waves. These recordings permitted detection of differential effects of right or left VNS, which shortened atrial PTa interval by 30% vs. 21% (P <.01) and lengthened QT interval by 1.5% vs. 9%, respectively (P < .05). During atrial ischemia, STa segments were elevated 3.4-fold (P < .01), and the threshold for inducing AF was reduced 3.1-fold (P = .004). Ischemia amplified atrial T-wave alternans (TWAa) and spatiotemporal heterogeneity (TWHa) by 23- and 13-fold, respectively, in inverse correlation to AF threshold (r = 0.74, P <.01; r = 0.61, P = .03). TWAa and TWHa increased by 4.5- and 2-fold shortly before autonomically triggered atrial premature beats and AF. This study used standard electrocatheters to demonstrate that TWAa and TWHa analysis provides means to assess vulnerability to AF without provocative electrical stimuli. These parameters could be evaluated in the clinical electrophysiology laboratory to determine risk for this prevalent arrhythmia and efficacy of contemporary and new agents.

Optical mapping design for murine atrial electrophysiology

Optical mapping is an important tool for assessment of cardiac electrophysiology. We demonstrate a system for quantification and automatic measurement of electrophysiological parameters in isolated cardiac tissue. The system makes use of voltage sensitive fluorescent dyes. These shift in wavelength in response to millivolt changes in potential across cell membranes located on the left atrium. Automated analysis of the pixel-wise measurements yields information on action potential durations and isochronal maps allowing for high throughput of data analysis. The algorithms that we propose reliably describe activation sequences and allow for quantification of conduction velocities.

Cardiac pacing in 21 patients with Emery-Dreifuss muscular dystrophy: a single-centre study with a 39-year follow-up.

Emery-Dreifuss muscular dystrophy (EDMD) is a genetic condition associated with cardiac arrhythmias. The patients typically develop early, asymptomatic bradyarrhythmia, which may lead to sudden death, preventable with a cardiac implantable electronic device (CIED). EDMD may be characterised by atrial electrical silence. Intra-operative electrophysiological evaluation of the myocardium helps ultimately determine the true nature of the disorder and select an appropriate CIED. To analyse permanent electrotherapy procedures in EDMD patients: atrial pacing limitations that stem from the electrophysiological properties of the myocardium and long-term follow-up of implanted devices. A total of 21 EDMD patients (mean age 29 ± 9 years) with a CIED implanted (1976-2014) due to bradyarrhythmia were included in the study. The implantation procedures and factors determining the CIED type selection were analysed. CIEDs were implanted in five women and in 16 men with EDMD types 1 and 2 (mean follow-up: 11 ± 8 years). Intra-operatively assessed atrial electrophysiology resulted in changing the planned CIED type during the procedure in three men with EDMD type 1. Eventually, we implanted: eight DDD, one VDD, 11 VVI, and one CD-DR device, with four of the patients' devices switched later from DDD to VVI mode in response to electrophysiological changes in the atria. Intra-operative assessment of atrial electrophysiological properties resulted in changing the planned DDD mode for VVI in 19% of patients with EDMD type 1. Progression of the underlying disease over a 39-year follow-up resulted in a later change of the initially selected pacing mode from DDD to VVI in 40% of cases.

The Past, Present, and Potential Future of Sodium Channel Block as an Atrial Fibrillation Suppressing Strategy.

Despite major advances in arrhythmia therapy, atrial fibrillation (AF) remains a challenge. A significant limitation in AF management is the lack of safe and effective drugs to restore and/or maintain sinus rhythm. The rational design of a new generation of AF-selective Na(+) channel blockers (NCBs) is emerging as a promising AF-suppressing strategy. Recent theoretical and experimental advances have generated insights into the mechanisms underlying AF maintenance and termination by antiarrhythmic drugs. Our understanding of antiarrhythmic drug-induced proarrhythmia has also grown in sophistication. These discoveries have created new possibilities in therapeutic targeting and renewed interest in improved NCB antiarrhythmic drugs. Recently described differences in atrial versus ventricular electrophysiology can be exploited in the prospective design of atrial-selective NCBs. Furthermore, state-dependent block has been shown to be an important modulator of NCB rate selectivity. Together, differential atrial-ventricular electrophysiological actions and state-dependent block form the backbone for the rational design of an AF-selective NCB. Synergistic combinations incorporating both NCB and block of K(+) currents may allow for further enhancement of AF selectivity. Future work on translating these basic research advances into the development of an optimized AF-selective NCB has the potential to provide safer and more effective pharmacotherapeutic options for AF, thereby fulfilling a major unmet clinical need.

Effects of Wild-Type and Mutant Forms of Atrial Natriuretic Peptide on Atrial Electrophysiology and Arrhythmogenesis.

Atrial natriuretic peptide (ANP) is a hormone with numerous beneficial cardiovascular effects. Recently, a mutation in the ANP gene, which results in the generation of a mutant form of ANP (mANP), was identified and shown to cause atrial fibrillation in people. The mechanism(s) through which mANP causes atrial fibrillation is unknown. Our objective was to compare the effects of wild-type ANP and mANP on atrial electrophysiology in mice and humans. Action potentials (APs), L-type Ca(2+) currents (ICa,L), and Na(+) current were recorded in atrial myocytes from wild-type or natriuretic peptide receptor C knockout (NPR-C(-/-)) mice. In mice, ANP and mANP (10-100 nmol/L) had opposing effects on atrial myocyte AP morphology and ICa,L. ANP increased AP upstroke velocity (Vmax), AP duration, and ICa,L similarly in wild-type and NPR-C(-/-) myocytes. In contrast, mANP decreased Vmax, AP duration, and ICa,L, and these effects were completely absent in NPR-C(-/-) myocytes. ANP and mANP also had opposing effects on ICa,L in human atrial myocytes. In contrast, neither ANP nor mANP had any effect on Na(+) current in mouse atrial myocytes. Optical mapping studies in mice demonstrate that ANP sped electric conduction in the atria, whereas mANP did the opposite and slowed atrial conduction. Atrial pacing in the presence of mANP induced arrhythmias in 62.5% of hearts, whereas treatment with ANP completely prevented the occurrence of arrhythmias. These findings provide mechanistic insight into how mANP causes atrial fibrillation and demonstrate that wild-type ANP is antiarrhythmic.

LKB1 deletion causes early changes in atrial channel expression and electrophysiology prior to atrial fibrillation.

Liver kinase B1 (LKB1) is a protein kinase that activates the metabolic regulator AMP-activated protein kinase (AMPK) and other related kinases. Deletion of LKB1 in mice leads to cardiomyopathy and atrial fibrillation (AF). However, the specific role of the LKB1 pathway in early atrial biology remains unknown. Thus, we investigated whether LKB1 deletion altered atrial channel expression and electrophysiological function in a cardiomyocyte-specific knockout mouse model. We performed a systematic comparison of αMHC-Cre LKB1(fl/fl) and littermate LKB1(fl/fl) male mice. This included analysis of gene expression, histology, and echocardiography, as well as cellular and tissue-level electrophysiology using patch-clamp recordings in vitro, optical mapping ex vivo, and ECG recordings in vivo. At postnatal day 1, atrial depolarization was prolonged, and Nav1.5 and Cx40 expression were markedly down-regulated in MHC-Cre LKB1(fl/fl) mice. Inward sodium current density was significantly decreased in MHC-Cre LKB1(fl/fl) neonatal atrial myocytes.Subsequently, additional alterations in atrial channel expression, atrial fibrosis, and spontaneous onset of AF developed by 2 weeks of age. In adult mice, abnormalities of interatrial conduction and bi-atrial electrical coupling were observed, likely promoting the perpetuation of AF. Mice with AMPK-inactivated hearts demonstrated modest overlap in channel expression with MHC-Cre LKB1(fl/fl) hearts, but retained normal structure, electrophysiological function and contractility. Deletion of LKB1 causes early defects in atrial channel expression, action potential generation and conduction, which precede widespread atrial remodelling, fibrosis and AF. LKB1 is critical for normal atrial growth and electrophysiological function.

Circulation : Clinical Summaries

<i>Circulation</i> : Clinical Summaries

168 Atrial arrhythmias and electrical remodelling after endurance training in a mouse model of arrhythmogenic right ventricular cardiomyopathy

<h3>Background and purpose</h3> Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited disorder that causes ventricular arrhythmias and sudden death. The disease manifests predominantly in the right heart and is more common in endurance athletes. ARVC patients also show increased atrial arrhythmias. Loss-of-function mutations in desmosomal proteins such as plakoglobin are associated with ARVC, and endurance training exacerbates ventricular arrhythmias and right ventricular enlargement in mice with reduced expression of plakoglobin (Plako^+/–). Chronic intensive endurance training has recently been observed to increase susceptibility to atrial arrhythmias in rats. We therefore tested whether standardised endurance training affects atrial electrophysiology or increases in mice with heterozygous plakoglobin deficiency (Plako^+/–). <h3>Methods</h3> Plako^+/– and WT mice group swim-trained for 5 d/week over 8 weeks, gradually increased from 2 to 90 min/d (average swim times 50h). Atrial size and function was assessed by echocardiography. Left atrial (LA) monophasic action potentials (MAPs) were recorded from Langendorff-perfused hearts. Action potential durations (APDs) were measured during RA pacing at 100ms paced cycle lengths (CL). Atrial arrhythmias were provoked by programmed stimulation (S1-S2). Atrial arrhythmias were defined as fast irregular atrial activity &gt;1s). Transmembrane action potentials (TAPs) were recorded at 100ms CL from isolated, superfused LA using floating glass microelectrodes. All continuous parameters are expressed as mean±SEM. <h3>Results</h3> Swim-training increased atrial arrhythmia susceptibility in Plako^+/–but not WT mice (Plako^+/– sedentary: 1/9 vs trained: 9/17 hearts),(WT sedentary: 3/11 hearts vs trained: 1/11 hearts). Training induced mild leftventricular hypertrophy in both genotypes (LV mass increase 6–14%, p &lt; 0.05). As shown previously, training also increased right ventricular size in Plako^+/– vs. trained WT, e.g. Parasternal RV diameter Plako^+/– (1.79 ± 0.03 mm) vs. WT (1.66 ± 0.02 mm) after training, p &lt; 0.05. Training increased LA size as assessed in echocardiography in both genotypes versus sedentary (LA size WT: 3.11 ± 0.14 sedentary vs 3.79 ± 0.17 mm² trained, p &lt; 0.05; Plako^+/–: 3.23 ± 0.1 mm² sedentary vs 4.14 ± 0.23 mm² trained, p &lt; 0.05). LA APD from MAPs tended to be shorter in trained WT and were significantly shorter in trained Plako^+/- mice (Figure 2). RA APD90s measured from TAPs were also shorter after training (WT: 22 ± 1 sedentary vs 19 ± 1 ms trained; Plako^+/- 24 ± 1 sedentary vs 18 ± 1 ms trained). <h3>Conclusion</h3> Our observations suggest that endurance training shortens atrial action potential duration and increases left atrial size in both WT and plakoglobin deficient atria. Endurance training increased atrial arrhythmia susceptibility in mice with a deficiency in the mechanical cell-cell contact protein plakoglobin.

Right Ventricular Outflow Tract Septal Pacing Is Superior to Right Ventricular Apical Pacing

BackgroundThe effects of right ventricular apical pacing (RVAP) and right ventricular outflow tract (RVOT) septal pacing on atrial and ventricular electrophysiology have not been thoroughly compared.Methods and ResultsTo identify a more favorable pacing strategy with fewer adverse effects, 80 patients who had complete atrioventricular block with normal cardiac function and who were treated with either RVAP (n=42) or RVOT septal pacing (n=38) were recruited after an average of 2 years of follow‐up. The data from electrocardiography and echocardiography performed before pacemaker implantation and at the end of follow‐up were collected. The patients in the RVOT septal pacing and RVAP groups showed similar demographic and clinical characteristics before pacing treatments. After a mean follow‐up of 2 years, the final maximum P‐wave duration; P‐wave dispersion; Q‐, R‐, and S‐wave complex duration; left atrial volume index; left ventricular end‐systolic diameter; ratio of transmitral early diastolic filling velocity to mitral annular early diastolic velocity; and interventricular mechanical delay in the RVOT septal pacing group were significantly less than those in the RVAP group (P<0.05). The final left ventricular ejection fraction of the RVOT septal pacing group was significantly higher than that of the RVAP group (P<0.05).ConclusionsCompared with RVAP, RVOT septal pacing has fewer adverse effects regarding atrial electrical activity and structure in patients with normal cardiac function.

Effects of low-level carotid baroreflex stimulation on atrial electrophysiology.

This study aimed to investigate the effects of low-level carotid baroreflex stimulation (LL-CBS) on atrial electrophysiology. In protocol 1 (LL-CBS on physiological state), anesthetized rabbits were subjected to LL-CBS (n = 10) or surgical exposure (n = 6) for 1 h. In protocol 2 (LL-CBS on acute rapid atrial pacing), anesthetized rabbits underwent 3 h of rapid atrial pacing (RAP) with concomitant LL-CBS in the third hour (n = 7) or 3h-RAP without LL-CBS (n = 6). Carotid baroreceptor surrounded by electrodes allowed LL-CBS at 20 % below the voltage required to reduce systolic blood pressure or heart rate. Effective refractory period (ERP) and monophasic action potential duration (MAPD) were determined, and power spectral of heart rate variability (HRV) was analyzed at baseline as well as after interventions in all groups, respectively. In protocol 1, LL-CBS significantly prolonged the ERPs, MAPD90, and MAPD50 and increased high-frequency (HF) HRV component but it decreased low-frequency (LF) HRV component and LF/HF ratio. In protocol 2, 3h-RAP significantly shortened ERPs, MAPD90, and MAPD50 and decreased HF but it increased LF and LF/HF ratio. However, LL-CBS reversed the variations caused by RAP. LL-CBS prolongs ERPs and MAPD of the left atrium and attenuates RAP-induced atrial electrical remodeling including the shortening of ERPs and MAPD, probably by modulating the autonomic nervous system.

Obstructive respiratory events and premature atrial contractions after cardioversion

Recurrence of atrial fibrillation (AF) after electrical cardioversion (ECV) is increased in patients with obstructive sleep apnoea (OSA). In patients with persistent AF, with (n=40) and without (n=32) obstructive respiratory events (OREs) during sedation for ECV, we determined the occurrence of premature atrial contractions (PACs) before and after insertion of a nasopharyngeal tube. The influence of acute obstructive respiratory events on atrial electrophysiology after termination of AF was studied in pigs. Incidence of PACs directly after ECV was higher in patients with OREs compared to those without OREs (7±2 versus 1±1 per 10 s, respectively; p<0.01). Occurrence of PACs could be reduced by 79% by insertion of a nasopharyngeal tube. In a subsequent sleeping study, patients with OREs had higher apnoea-hypopnoea indices and more PACs during night. 16 patient with and four patients without OREs had a relapse of AF during 1 week after ECV (p<0.01). In pigs, acute OREs after 30 min of AF increased occurrence of PACs and vulnerability for reinduction of AF, which could be attenuated by atropine, beta-blockers and renal denervation. OREs are associated with increased occurrence of PACs and more early relapse of AF. OREs increase occurrence of PACs and vulnerability for reinduction of AF by sympathovagal imbalance.

Virtual electrophysiological study of atrial fibrillation in fibrotic remodeling.

Research has indicated that atrial fibrillation (AF) ablation failure is related to the presence of atrial fibrosis. However it remains unclear whether this information can be successfully used in predicting the optimal ablation targets for AF termination. We aimed to provide a proof-of-concept that patient-specific virtual electrophysiological study that combines i) atrial structure and fibrosis distribution from clinical MRI and ii) modeling of atrial electrophysiology, could be used to predict: (1) how fibrosis distribution determines the locations from which paced beats degrade into AF; (2) the dynamic behavior of persistent AF rotors; and (3) the optimal ablation targets in each patient. Four MRI-based patient-specific models of fibrotic left atria were generated, ranging in fibrosis amount. Virtual electrophysiological studies were performed in these models, and where AF was inducible, the dynamics of AF were used to determine the ablation locations that render AF non-inducible. In 2 of the 4 models patient-specific models AF was induced; in these models the distance between a given pacing location and the closest fibrotic region determined whether AF was inducible from that particular location, with only the mid-range distances resulting in arrhythmia. Phase singularities of persistent rotors were found to move within restricted regions of tissue, which were independent of the pacing location from which AF was induced. Electrophysiological sensitivity analysis demonstrated that these regions changed little with variations in electrophysiological parameters. Patient-specific distribution of fibrosis was thus found to be a critical component of AF initiation and maintenance. When the restricted regions encompassing the meander of the persistent phase singularities were modeled as ablation lesions, AF could no longer be induced. The study demonstrates that a patient-specific modeling approach to identify non-invasively AF ablation targets prior to the clinical procedure is feasible.

Resveratrol, a red wine antioxidant, reduces atrial fibrillation susceptibility in the failing heart by PI3K/AKT/eNOS signaling pathway activation.

Resveratrol has shown benefits in reducing ventricular remodeling and arrhythmias. This study aimed to assess the therapeutic efficacy of resveratrol in reducing atrial fibrillation (AF) in a heart failure (HF) model and to explore the underlying mechanisms. HF rabbits were created 4 weeks after undergoing coronary ligation. Group 1 (n = 6) was divided into subgroups of (a) normal rabbits, (b) HF sham rabbits, and (c) HF rabbits treated for 1 week with intraperitoneal injections of resveratrol, (d) resveratrol plus wortmannin, or (e) resveratrol plus diphenyleneiodonium chloride (DPI). All rabbits underwent epicardial catheter stimulation. Collagen content, messenger RNA and protein expression in ion channels, and phosphoinositide 3-kinase (PI3K)/AKT/endothelial nitric oxide synthase (eNOS) signaling pathways were studied in left atrial appendage (LAA) preparations. To investigate acute drug effects on left atrial electrophysiology, groups 2 a through 2e (n = 6 per group) were subjected to Langendorff perfusion. Higher AF inducibility was found in the HF group and groups that were given PI3K and eNOS inhibitors than in the normal and resveratrol-treated groups (P < .001). Histologic analysis of the LAA revealed a decrease in fibrosis in resveratrol-treated groups compared with the HF group (8.95% ± 1.53% vs 26.62% ± 2.19%, P < .001). In real-time polymerase chain reaction analysis, ion channels including Kv1.4, Kv1.5, KvLQT1, Kir2.1, Nav1.5, Cav1.2, NCX, SERCA2a, and phospholamban were upregulated by resveratrol. PI3K, AKT, and eNOS messenger RNA and protein expression were upregulated by resveratrol but were inhibited by the coadministration of wortmannin and DPI. Resveratrol decreases left atrial fibrosis and regulates variation in ion channels to reduce AF through the PI3K/AKT/eNOS signaling pathway.

Inflammation and the pathogenesis of atrial fibrillation.

Atrial fibrillation (AF) is the most common cardiac arrhythmia. However, the development of preventative therapies for AF has been disappointing. The infiltration of immune cells and proteins that mediate the inflammatory response in cardiac tissue and circulatory processes is associated with AF. Furthermore, the presence of inflammation in the heart or systemic circulation can predict the onset of AF and recurrence in the general population, as well as in patients after cardiac surgery, cardioversion, and catheter ablation. Mediators of the inflammatory response can alter atrial electrophysiology and structural substrates, thereby leading to increased vulnerability to AF. Inflammation also modulates calcium homeostasis and connexins, which are associated with triggers of AF and heterogeneous atrial conduction. Myolysis, cardiomyocyte apoptosis, and the activation of fibrotic pathways via fibroblasts, transforming growth factor-β and matrix metalloproteases are also mediated by inflammatory pathways, which can all contribute to structural remodelling of the atria. The development of thromboembolism, a detrimental complication of AF, is also associated with inflammatory activity. Understanding the complex pathophysiological processes and dynamic changes of AF-associated inflammation might help to identify specific anti-inflammatory strategies for the prevention of AF.

Long-Term Modulation of Ion Channels by Aldosterone in Adult Rat Atrial Myocytes

In recent years, both aldosterone and mineralocorticoid receptor (MR) have drawn attention as important factors that promote structural remodeling of the atrium. Here, we investigated effects of chronic aldosterone treatment on both intracellular Ca2+ and ion channels. Atrial myocytes were cultured in either the absence or presence of aldosterone, and then the activity of ion channels was studied, under whole-cell patch-clamp conditions. Aldosterone increased both the cell membrane capacitance (Cm) and the maximal conductance of ion channels that give rise to IKsus, INa, ICaT, and ICaL (30-100%). Except for inactivation curves of INa, which were shifted by −10 mV, aldosterone produced no major alterations in the biophysical properties of the channels. Interestingly, at resting membrane potentials the increase in INa was cancelled by a greater fraction of inactivation. The onset and recovery of the changes -in ICaT, ICaL, and Cm- were also assessed. In general, they required 2d to be noticeable, reached their maximal value in 6d, and returned to basal values after 1-3d of aldosterone removal. The effects on both Cm and ICaL were further studied -to explore both a potential dose-response relationship and a possible implication of the MR. In fact, co-incubating with 10 µM of spironolactone (an MR antagonist) abolished both effects. Furthermore, their corresponding magnitudes fitted well with the Hill equation, being the EC50 values for Cm and ICaL 20 and 130 (nM), respectively. Interestingly, aldosterone did not alter expression levels of Cav1.2, suggesting that the action on ICaL arises from a stimulus in open probability. The hormone also produced a 40% increase in the amplitude of Ca2+ transients along with a higher proportion of arrhythmic cells (2.5-fold increase). These results contribute to understanding the role of the MR and aldosterone in atrial electrophysiology.

The effect of endothelin-receptor blockade on atrial electrophysiology in obesity

The effect of endothelin-receptor blockade on atrial electrophysiology in obesity

The effect of different rates of weight gain on atrial electrophysiology

The effect of different rates of weight gain on atrial electrophysiology