Electrical, morphological, and ultrastructural remodeling and reverse remodeling in a canine model of chronic atrial fibrillation

Dynamic changes of left atrial substrate over time following pulmonary vein isolation: the Progress-AF study

AIMS

Little is known about dynamic changes of the left atrial (LA) substrate over time in patients with atrial fibrillation (AF). This study aims to evaluate substrate changes following pulmonary vein isolation (PVI).

METHODS AND RESULTS

In our prospective observational study, consecutive patients undergoing first PVI-only and redo ablation were included. High-density maps of the two procedures were compared. Progression or regression was diagnosed if a significant concordant decrease or increase in bipolar voltages in ≥2 segments was observed, respectively. In 28 patients (61.2 ± 9.5 years, 39% female, 53.5% persistent AF), 111.013 voltage points from 56 high-density LA maps (1.982 points/patient) were analysed. Comparing the high-density maps of the first and second procedures, in the progression group (17 patients, 61%), there was a decrease in global (-35%, P < 0.001) and all regional voltages. In the regression group (11 patients, 39%), there was an increase in global (+43%, P < 0.001) and regional voltages. Comparing the progression with the regression group, the area of low-voltage zone (LVZ) increased (+3.5 vs. -4.5 cm2, P < 0.001) and LA activation time prolonged (+8.0 vs. -9.1 ms, P = 0.005). Baseline clinical parameters did not predict progression or regression. In patients with substrate progression, pulmonary veins (PVs) were more frequently isolated (P = 0.02) and the AF pattern at recurrence was more frequently persistent (P = 0.005).

CONCLUSION

Our study describes bidirectional dynamic properties of the LA substrate with concordant either progressive or regressive changes. Regression occurs with reduced AF burden after the first procedure, while progression is associated with persistent AF recurrence despite durable PV isolation. The dynamic nature of LA substrate poses questions about LVZ-based ablation strategies.

Prevention of Atrial Fibrillation: Putting Proteostasis Derailment Back on Track

Despite the many attempts to treat atrial fibrillation (AF), the most common cardiac tachyarrhythmia in the Western world, the treatment efficacy of AF is still suboptimal. A plausible reason for the suboptimal efficacy is that the current treatments are not directed at the underlying molecular mechanisms that drive AF. Recent discoveries revealed that the derailment of specific molecular proteostasis pathways drive electrical conduction disorders, contractile dysfunction and AF. The degree of this so-called 'electropathology' corresponds to the response to anti-AF treatment. Hence, to develop effective therapies to prevent AF, understanding the molecular mechanisms is of key importance. In this review, we highlight the key modulators of proteostasis derailment and describe the mechanisms that explain how they affect electrical and contractile function in atrial cardiomyocytes and AF. The key modulators of proteostasis derailment include (1) exhaustion of cardioprotective heat shock proteins (HSPs), (2) excessive endoplasmic reticulum (ER) stress and downstream autophagic protein degradation, (3) histone deacetylase 6 (HDAC6)-induced microtubule disruption, (4) activation of DNA damage-PARP1 activation and NAD⁺ axis and (5) mitochondrial dysfunction. Furthermore, we discuss druggable targets within these pathways that are involved in the prevention of proteostasis derailment, as well as the targets that aid in the recovery from AF. Finally, we will elaborate on the most favorable druggable targets for (future) testing in patients with AF, as well as drugs with potential benefits for AF recovery.

Does conduction heterogeneity determine the supervulnerable period after atrial fibrillation?

Atrial fibrillation (AF) resumes within 90 s in 27% of patients after sinus rhythm (SR) restoration. The aim of this study is to compare conduction heterogeneity during the supervulnerable period immediately after electrical cardioversion (ECV) with long-term SR in patients with AF. Epicardial mapping of both atria was performed during SR and premature atrial extrasystoles in patients in the ECV (N = 17, age: 73 ± 7 years) and control group (N = 17, age: 71 ± 6 years). Inter-electrode conduction times were used to identify areas of conduction delay (CD) (conduction times 7-11 ms) and conduction block (CB) (conduction times ≥ 12 ms). For all atrial regions, prevalences and length of longest CB and continuous CDCB lines, magnitude of conduction disorders, conduction velocity, biatrial activation time, and voltages did not differ between the ECV and control group during both SR and premature atrial extrasystoles (p ≥ 0.05). Hence, our data suggest that there may be no difference in biatrial conduction characteristics between the supervulnerable period after ECV and long-term SR in AF patients. The supervulnerable period after AF termination is not determined by conduction heterogeneity during SR and PACs. It is unknown to what extent intra-atrial conduction is impaired during the supervulnerable period immediately after ECV and whether different right and left atrial regions are equally affected. This high-resolution epicardial mapping study (upper left panel) of both atria shows that during SR the prevalences and length of longest CB and cCDCB lines (upper middle panel), magnitude of conduction disorders, CV and TAT (lower left panel), and voltages did not differ between the ECV and control group. Likewise, these parameters were comparable during PACs between the ECV and control group (lower left panel). †Non-normally distributed. cm/s = centimeters per second; mm = millimeter; ms = millisecond; AF = atrial fibrillation; AT = activation time; BB = Bachmann's bundle; cCDCB = continuous lines of conduction delay and block; CB = conduction block; CD = conduction delay; CT = conduction time; CV = conduction velocity; ECV = electrical cardioversion; LA = left atrium; LAT = local activation times; PAC = premature atrial complexes; PVA = pulmonary vein area; RA = right atrium; SR = sinus rhythm; TAT = total activation time.

Pulmonary vein isolation alone or in combination with substrate modulation after electrical cardioversion failure in patients with persistent atrial fibrillation: The PACIFIC trial: Study design

INTRODUCTION

Pulmonary vein isolation (PVI) is effective at treating 50% of unselected patients with persistent atrial fibrillation (AF). Alternatively, PVI combined with a new ablation strategy entitled the Marshall-PLAN ensures a 78% 1-year sinus rhythm (SR) maintenance rate in the same population. However, a substantial subset of patients could undergo the Marshall-PLAN unnecessarily. It is therefore essential to identify those patients who can be treated with PVI alone versus those who may truly benefit from the Marshall-PLAN before ablation is performed. In this context, we hypothesized that electrical cardioversion (EC) could help to select the most appropriate strategy for each patient.

METHODS

In this multicentre, prospective, randomized study, patients with AF recurrence within 4 weeks after EC will be randomized 1:1 to PVI alone or the Marshall-PLAN. Conversely, patients in whom SR is maintained for ≥4 weeks after EC will be treated with PVI only and included in a prospective registry. The primary endpoint will be the 1-year SR maintenance rate after a single ablation procedure.

RESULTS AND CONCLUSION

The Marshall-PLAN might be necessary in patients with an advanced degree of persistent AF (i.e., where SR is not maintained for ≥4 uninterrupted weeks after EC). Conversely, in patients with mild or moderate persistent AF (i.e., where SR is maintained for ≥4 weeks after EC), PVI alone might be a sufficient ablation strategy. The PACIFIC trial is the first study designed to assess whether rhythm monitoring after EC could help to identify patients who should undergo adjunctive ablation strategies beyond PVI.

Atrial fibrillatory rate as predictor of recurrence of atrial fibrillation in horses treated medically or with electrical cardioversion

BACKGROUND

The recurrence rate of atrial fibrillation (AF) in horses after cardioversion to sinus rhythm (SR) is relatively high. Atrial fibrillatory rate (AFR) derived from surface ECG is considered a biomarker for electrical remodelling and could potentially be used for the prediction of successful AF cardioversion and AF recurrence.

OBJECTIVES

Evaluate if AFR was associated with successful treatment and could predict AF recurrence in horses.

STUDY DESIGN

Retrospective multicentre study.

METHODS

Electrocardiograms (ECG) from horses with persistent AF admitted for cardioversion with either medical treatment (quinidine) or transvenous electrical cardioversion (TVEC) were included. Bipolar surface ECG recordings were analysed by spatiotemporal cancellation of QRST complexes and calculation of AFR from the remaining atrial signal. Kaplan-Meier survival curve and Cox regression analyses were performed to assess the relationship between AFR and the risk of AF recurrence.

RESULTS

Of the 195 horses included, 74 received quinidine treatment and 121 were treated with TVEC. Ten horses did not cardiovert to SR after quinidine treatment and AFR was higher in these, compared with the horses that successfully cardioverted to SR (median [interquartile range]), (383 [367-422] vs 351 [332-389] fibrillations per minute (fpm), P < .01). Within the first 180 days following AF cardioversion, 12% of the quinidine and 34% of TVEC horses had AF recurrence. For the horses successfully cardioverted with TVEC, AFR above 380 fpm was significantly associated with AF recurrence (hazard ratio = 2.4, 95% confidence interval 1.2-4.8, P = .01).

MAIN LIMITATIONS

The treatment groups were different and not randomly allocated, therefore the two treatments cannot be compared. Medical records and the follow-up strategy varied between the centres.

CONCLUSIONS

High AFR is associated with failure of quinidine cardioversion and AF recurrence after successful TVEC. As a noninvasive marker that can be retrieved from surface ECG, AFR can be clinically useful in predicting the probability of responding to quinidine treatment as well as maintaining SR after electrical cardioversion.

Electrical Posterior Box Isolation in Repeat Ablation for Atrial Fibrillation: A Prospective Randomized Clinical Study

OBJECTIVES

This study investigated whether additional electrical posterior box isolation (POBI) may improve the rhythm outcome of repeat ablation in atrial fibrillation (AF).

BACKGROUND

Although electrically reconnected pulmonary veins (PVs) are the main mechanism of AF recurrence, it is unclear whether linear ablation in addition to circumferential PV isolation (CPVI) improves rhythm outcomes after repeat ablation.

METHODS

The authors prospectively randomized 150 patients with PV reconnection undergoing redo procedures to either a CPVI-alone group (n = 75) or an additional POBI group (n = 75). The primary endpoint was AF recurrence after a single procedure, and the secondary endpoints were recurrence pattern, cardioversion rate, and response to antiarrhythmic drugs.

RESULTS

After a median follow-up of 17 months, the clinical recurrence rate did not significantly differ between the CPVI-alone and additional-POBI groups (30.7% vs 30.7%; log-rank P =0.828). Of the 46 patients with clinical recurrence, the recurrences as atrial tachycardia (8.7% vs 30.4%; P =0.137) and cardioversion rates (21.7% vs 47.8%; P =0.122) were not significantly different between the CPVI-alone and additional-POBI groups. Major complication rates did not differ between the 2 groups (1.3% vs 5.3%; P = 0.363), but the total ablation time was significantly longer in the additional-POBI group than in the CPVI-alone group (median: 1,084 [IQR: 704-1,664] vs 1,595 [IQR: 1,244-2,302] seconds; P < 0.001).

CONCLUSIONS

Among patients undergoing redo AF ablation with reconnected PVs, the addition of POBI to CPVI did not improve rhythm outcomes or influence overall safety, whereas leading to a longer ablation time than that with CPVI alone. (Comparison of Circumferential Pulmonary Vein Isolation and Complex Pulmonary Vein Isolation Additional Linear Ablation for Recurred Atrial Fibrillation After Previous Catheter Ablation: Prospective Randomized Trial [RILI Trial]; NCT02747498).

Transvenous electrical cardioversion of atrial fibrillation in horses: Horse and procedural factors correlated with success and recurrence

Background

Transvenous electrical cardioversion (TVEC) is 1 of the main treatment options for atrial fibrillation (AF) in horses. Large‐scale studies on factors affecting success and prognosis have primarily been performed in Standardbred populations.

Hypothesis/Objectives

To determine factors affecting cardioversion success, cardioversion difficulty and recurrence in a predominant Warmblood study sample.

Animals

TVEC records of 199 horses.

Methods

Retrospective study of TVEC procedures of horses admitted for AF without severe echocardiographic abnormalities. Horse and procedural factors for success and cumulative amount of energy (≤ 600 J vs > 600 J) were determined using multivariable logistic regression. A survival analysis was performed to determine risk factors for recurrence.

Results

Two hundred and thirty‐one TVEC procedures were included, with a 94.4% success rate and 31.9% recurrence rate (51/160). Mitral regurgitation (OR 0.151, 95% CI 0.032‐0.715, P = .02) and AF cycle length (OR 1.05, 95% CI 1.01‐1.09, P = .02) were independent determinants for success. Catheter type (OR 0.154, 95% CI 0.074‐0.322, P < .001), previous AF episode (OR 3.10, 95% CI 1.20‐8.01, P = .02), tricuspid regurgitation (OR 2.54, 95% CI 1.25‐5.13, P = .01), and body weight (OR 1.009, 95% CI 1.003‐1.015, P = .004) were significantly correlated with cumulative amount of energy delivered. Significant risk factors for recurrence after a first AF episode were sex (stallion; HR 3.05, 95% CI 1.34‐6.95, P = .008), mitral regurgitation (HR 1.91, 95% CI 1.08‐3.38, P = .03), and AF duration (HR 1.001, 95% CI 1.0001‐1.0026, P = .04).

Conclusions and Clinical Importance

Both horse and procedural factors should be considered when assessing treatment options and prognosis in horses with AF.

A Review on Atrial Fibrillation (Computer Simulation and Clinical Perspectives)

Atrial fibrillation (AF), a heart condition, has been a well-researched topic for the past few decades. This multidisciplinary field of study deals with signal processing, finite element analysis, mathematical modeling, optimization, and clinical procedure. This article is focused on a comprehensive review of journal articles published in the field of AF. Topics from the age-old fundamental concepts to specialized modern techniques involved in today’s AF research are discussed. It was found that a lot of research articles have already been published in modeling and simulation of AF. In comparison to that, the diagnosis and post-operative procedures for AF patients have not yet been totally understood or explored by the researchers. The simulation and modeling of AF have been investigated by many researchers in this field. Cellular model, tissue model, and geometric model among others have been used to simulate AF. Due to a very complex nature, the causes of AF have not been fully perceived to date, but the simulated results are validated with real-life patient data. Many algorithms have been proposed to detect the source of AF in human atria. There are many ablation strategies for AF patients, but the search for more efficient ablation strategies is still going on. AF management for patients with different stages of AF has been discussed in the literature as well but is somehow limited mostly to the patients with persistent AF. The authors hope that this study helps to find existing research gaps in the analysis and the diagnosis of AF.

The Relationship Between Atrial Fibrillation, Mitral Regurgitation, and Heart Failure Subtype: The ARIC Study

BACKGROUND

Atrial fibrillation (AF) and mitral regurgitation (MR) are closely interrelated in the setting of heart failure (HF). Here we investigate the prevalence and prognostic significance of AF in patients with acute decompensated HF (ADHF) stratified by MR severity.

METHODS AND RESULTS

The Atherosclerosis Risk in Communities Study investigated ADHF hospitalizations in residents greater than or equal to 55 years of age in 4 US communities. ADHF cases were stratified by MR severity (none/mild or moderate/severe) and HF subtype (HF with reduced [HFrEF] or preserved [HFpEF] ejection fraction). The odds of AF in patients with increasing MR severity was estimated using multivariable logistic regression, adjusting for age, race, sex, diabetes, hypertension, coronary artery disease, hemodialysis, stroke, and anemia. Cox regression models were used to assess the association of AF with 1-year mortality in patients with HFpEF and HFrEF, stratified by MR severity and adjusted as described, also adjusting for the year of hospitalization. From 2005 to 2014, there were 3,878 ADHF hospitalizations (17,931 weighted). AF was more likely in those with higher MR severity regardless of HF subtype; more so in HFpEF (odds ratio [OR] 1.38, 95% confidence interval [CI], 1.31-1.45) than in HFrEF (OR, 1.19, 95% CI, 1.13-1.25) (interaction P [by HF subtype] < .01). When stratified by HF type, association between AF and 1-year mortality was noted in patients with HFpEF (OR, 1.28, 95% CI 1.04-1.56) but not HFrEF (OR 0.96, 95% CI 0.79-1.16) (interaction by EF subtype, P = .02).

CONCLUSIONS

In patients with ADHF, AF prevalence increased with MR severity and this effect was more pronounced in HFpEF compared with HFrEF. AF was associated with an increased 1-year mortality only in patients with HFpEF and concomitant moderate/severe MR.

REGISTRATION

NCT00005131, https://clinicaltrials.gov/ct2/show/NCT00005131.

Size matters in atrial fibrillation: the underestimated importance of reduction of contiguous electrical mass underlying the effectiveness of catheter ablation

Evidence has accumulated over the last century of the importance of a critical electrical mass in sustaining atrial fibrillation (AF). AF ablation certainly reduces electrically contiguous atrial mass, but this is not widely accepted to be an important part of its mechanism of action. In this article, we review data showing that atrial size is correlated in many settings with AF propensity. Larger mammals are more likely to exhibit AF. This is seen both in the natural world and in animal models, where it is much easier to create a goat model than a mouse model of AF, for example. This also extends to humans-athletes, taller people, and obese individuals all have large atria and are more likely to exhibit AF. Within an individual, risk factors such as hypertension, valvular disease and ischaemia can enlarge the atrium and increase the risk of AF. With respect to AF ablation, we explore how variations in ablation strategy and the relative effectiveness of these strategies may suggest that a reduction in electrical atrial mass is an important mechanism of action. We counter this with examples in which there is no doubt that mass reduction is less important than competing theories such as ganglionated plexus ablation. We conclude that, when considering future strategies for the ablative therapy of AF, it is important not to discount the possibility that contiguous electrical mass reduction is the most important mechanism despite the disappointing consequence being that enhancing success rates in AF ablation may involve greater tissue destruction.

Conduction Heterogeneity: Impact of Underlying Heart Disease and Atrial Fibrillation

OBJECTIVES

The goal of this study is to investigate the impact of various underlying heart diseases (UHDs) and prior atrial fibrillation (AF) episodes on conduction heterogeneity.

BACKGROUND

It is unknown whether intra-atrial conduction during sinus rhythm differs between various UHD or is influenced by AF episodes.

METHODS

Epicardial sinus rhythm mapping of the right atrium, Bachmann's bundle (BB), left atrium and pulmonary vein area was performed in 447 participants (median age: 67 [interquartile range (IQR): 59 to 73] years) with or without AF undergoing cardiac surgery for ischemic heart disease, (ischemic and) valvular heart disease, or congenital heart disease. Conduction times (CTs) were defined as Δ local activation time between 2 adjacent electrodes and used to assess frequency (CTs ≥ 4 ms) and magnitude of conduction disorders (in increments of 10 ms).

RESULTS

When comparing the 3 types of UHD, there were no differences in frequencies and magnitude of CTs at all locations (p ≥ 0.017 and p ≥ 0.005, respectively). Prior AF episodes were associated with conduction slowing throughout both atria (14.9% [IQR: 11.8 to 17.0] vs. 12.8% [IQR: 10.9 to 14.6]; p < 0.001). At BB, CTs with magnitudes ≥30 ms were more common in patients with AF (n = 56.2% vs. n = 36.0%; p < 0.004).

CONCLUSIONS

UHD has no impact on the frequency and severity of conduction disorders. AF episodes are associated with more conduction disorders throughout both atria and with more severe conduction disorders at BB. The next step will be to determine the relevance of these conduction disorders for AF development and maintenance.

Update on the efficacy of statins in primary and secondary prevention of atrial fibrillation

Atrial fibrillation is the most common arrhythmia in adults and its prevalence is growing rapidly. It has been shown that AF is associated with increased risk of heart failure, ischemic and hemorrhagic stroke, and mortality. Hence, there is growing interest among researchers in seeking preventive and therapeutic interventions regarding AF. In recent decades, it has been suggested that statins may decrease the incidence of AF and may also decrease its recurrence after cardioversion and catheter ablation. These effects are thought to be mediated by different mechanisms such as modulating inflammation, altering the properties of transmembrane ion channels, interfering with activation of matrix metalloproteinases, and acting on endothelial function. In this article, we review and update current knowledge about the role of statins in primary and secondary prevention of AF in general and specific populations.

Update on the efficacy of statins in primary and secondary prevention of atrial fibrillation

Atrial fibrillation is the most common arrhythmia in adults and its prevalence is growing rapidly. It has been shown that AF is associated with increased risk of heart failure, ischemic and hemorrhagic stroke, and mortality. Hence, there is growing interest among researchers in seeking preventive and therapeutic interventions regarding AF. In recent decades, it has been suggested that statins may decrease the incidence of AF and may also decrease its recurrence after cardioversion and catheter ablation. These effects are thought to be mediated by different mechanisms such as modulating inflammation, altering the properties of transmembrane ion channels, interfering with activation of matrix metalloproteinases, and acting on endothelial function. In this article, we review and update current knowledge about the role of statins in primary and secondary prevention of AF in general and specific populations.

Reduction of Conduction Velocity in Patients with Atrial Fibrillation

It is unknown to what extent atrial fibrillation (AF) episodes affect intra-atrial conduction velocity (CV) and whether regional differences in local CV heterogeneities exist during sinus rhythm. This case-control study aims to compare CV assessed throughout both atria between patients with and without AF. Patients (n = 34) underwent intra-operative epicardial mapping of the right atrium (RA), Bachmann’s bundle (BB), left atrium (LA) and pulmonary vein area (PVA). CV vectors were constructed to calculate median CV in addition to total activation times (TAT) and unipolar voltages. Biatrial median CV did not differ between patients with and without AF (90 ± 8 cm/s vs. 92 ± 6 cm/s, p = 0.56); only BB showed a CV reduction in the AF group (79 ± 12 cm/s vs. 88 ± 11 cm/s, p = 0.02). In patients without AF, there was no predilection site for the lowest CV (P₅) (RA: 12%; BB: 29%; LA: 29%; PVA: 29%). In patients with AF, lowest CV was most often measured at BB (53%) and ranged between 15 to 22 cm/s (median: 20 cm/s). Lowest CVs were also measured at the LA (18%) and PVA (29%), but not at the RA. AF was associated with a prolonged TAT (p = 0.03) and decreased voltages (P₅) at BB (p = 0.02). BB was a predilection site for slowing of conduction in patients with AF. Prolonged TAT and decreased voltages were also found at this site. The next step will be to determine the relevance of a reduced CV at BB in relation to AF development and maintenance.

Role of Oxidative DNA Damage and Repair in Atrial Fibrillation and Ischemic Heart Disease

Atrial fibrillation (AF) and ischemic heart disease (IHD) represent the two most common clinical cardiac diseases, characterized by angina, arrhythmia, myocardial damage, and cardiac dysfunction, significantly contributing to cardiovascular morbidity and mortality and posing a heavy socio-economic burden on society worldwide. Current treatments of these two diseases are mainly symptomatic and lack efficacy. There is thus an urgent need to develop novel therapies based on the underlying pathophysiological mechanisms. Emerging evidence indicates that oxidative DNA damage might be a major underlying mechanism that promotes a variety of cardiac diseases, including AF and IHD. Antioxidants, nicotinamide adenine dinucleotide (NAD⁺) boosters, and enzymes involved in oxidative DNA repair processes have been shown to attenuate oxidative damage to DNA, making them potential therapeutic targets for AF and IHD. In this review, we first summarize the main molecular mechanisms responsible for oxidative DNA damage and repair both in nuclei and mitochondria, then describe the effects of oxidative DNA damage on the development of AF and IHD, and finally discuss potential targets for oxidative DNA repair-based therapeutic approaches for these two cardiac diseases.

The Role of Oxidative Stress in Cardiovascular Aging and Cardiovascular Diseases

Aging can be seen as process characterized by accumulation of oxidative stress induced damage. Oxidative stress derives from different endogenous and exogenous processes, all of which ultimately lead to progressive loss in tissue and organ structure and functions. The oxidative stress theory of aging expresses itself in age-related diseases. Aging is in fact a primary risk factor for many diseases and in particular for cardiovascular diseases and its derived morbidity and mortality. Here we highlight the role of oxidative stress in age-related cardiovascular aging and diseases. We take into consideration the molecular mechanisms, the structural and functional alterations, and the diseases accompanied to the cardiovascular aging process.

Canine atrial fibrillation: Pathophysiology, epidemiology and classification

Atrial fibrillation (AF) is the most common non-physiological arrhythmia in dogs and humans. Its high prevalence in both species and the impact it has on survival time and quality of life of affected patients, makes it a very relevant topic of medical research. Significant developments in understanding the mechanisms underlying this arrhythmia in humans has occurred over the last decades and some of this knowledge is being applied to veterinary medicine, despite the many differences between species. This article reviews the current understanding of the pathophysiology of AF. The epidemiology and classification of AF in dogs will also be discussed.

Atrial fibrillation in horses part 1: Pathophysiology

Atrial fibrillation (AF) is the most common clinically relevant arrhythmia in horses, with a reported prevalence up to 2.5%. The pathophysiology has mainly been investigated in experimental animal models and human medicine, with limited studies in horses. Atrial fibrillation results from the interplay between electrical triggers and a susceptible substrate. Triggers consist of atrial premature depolarizations due to altered automaticity or triggered activity, or local (micro)reentry. The arrhythmia is promoted by atrial myocardial ion channel alterations, Ca²⁺ handling alterations, structural abnormalities, and autonomic nervous system imbalance. Predisposing factors include structural heart disease such as valvular regurgitation resulting in chronic atrial stretch, although many horses show so-called 'lone AF' or idiopathic AF in which no underlying cardiac abnormalities can be detected using routine diagnostic techniques. These horses may have underlying ion channel dysfunction or undiagnosed myocardial (micro)structural alterations. Atrial fibrillation itself results in electrical, contractile and structural remodelling, fostering AF maintenance. Electrical remodelling leads to shortening of the atrial effective refractory period, promoting reentry. Contractile remodelling consists of decreased myocardial contractility, while structural remodelling includes the development of interstitial fibrosis and atrial enlargement. Reverse remodelling occurs after cardioversion to sinus rhythm, but full recovery may take weeks to months depending on duration of AF. The clinical signs of AF depend on the aerobic demands during exercise, ventricular rhythm response and presence of underlying cardiac disease. In horses with so-called 'lone AF', clinical signs are usually absent at rest but during exercise poor performance, exercise-induced pulmonary hemorrhage, respiratory distress, weakness or rarely collapse may develop.

Association Between Plasma Intact Parathyroid Hormone Levels and the Prevalence of Atrial Fibrillation in Patients With Chronic Kidney Disease - The Fukuoka Kidney Disease Registry Study

BACKGROUND

Parathyroid hormone (PTH) has been associated with cardiovascular disorders; however, it is unknown whether plasma PTH concentrations are associated with atrial fibrillation (AF) in patients with chronic kidney disease (CKD).Methods and Results:The present cross-sectional study analyzed baseline data of 3,384 patients registered in the Fukuoka Kidney Disease Registry Study, a Japanese multicenter prospective cohort study of patients with non-dialysis-dependent CKD. The outcome was prevalence of AF, and the main risk factor was plasma intact PTH concentration. Associations between plasma intact PTH concentration quartiles (Q1-Q4, from lowest to highest) and the presence of AF were analyzed using logistic regression. In all, 185 patients had AF; 22, 34, 59, and 70 patients were in Q1, Q2, Q3, and Q4 of PTH concentrations, respectively. The prevalence of AF increased incrementally with increases in plasma intact PTH. In the logistic regression model, patients with higher plasma intact PTH concentrations (Q2-Q4) had higher adjusted odds ratios (95% confidence intervals) for the prevalence of AF relative to the reference group (Q1), namely 1.33 (0.76-2.34), 1.82 ([1.06-3.13), and 1.99 (1.08-3.64), respectively (P=0.016).

CONCLUSIONS

Higher plasma intact PTH concentrations were significantly and incrementally associated with an increased prevalence of AF in non-dialysis-dependent CKD patients.

Change in Atrial Fibrillation Burden over Time in Patients with Nonpermanent Atrial Fibrillation

Introduction

The natural course of atrial fibrillation (AF) is not well defined. We aimed to investigate the change in AF burden over time and its associated risk factors among AF patients.

Methods

Fifty-four participants with recently documented paroxysmal or persistent AF were enrolled. Main exclusion criteria were permanent AF or previous catheter ablation for AF. AF burden was calculated as time in AF divided by total recording time using yearly continuous 7-day Holter-ECG recordings. A relative change ≥10% or an absolute change >0.5% in AF burden between two yearly Holter-ECG recordings was considered significant.

Results

Mean age was 67 years, 72% were men. The proportion of patients with no recorded AF increased from 53.7% at baseline to 78.6% (p=0.1) after 4 years of follow-up. In 7-day Holter-ECG recordings performed after baseline, 23.7% of participants had a decrease and 23.7% an increase in AF burden. In separate mixed effect models, AF burden over time was associated with prior stroke (β 42.59, 95% CI (23.40; 61.77); p < 0.0001), BNP (β 0.05, CI (0.02; 0.09); p=0.005) end-diastolic (β 0.49, CI (0.23; 0.74); p=0.0003) as well as end-systolic (β 0.25, CI (0.05; 0.46); p=0.02) left atrial volume, left atrial ejection fraction (β −0.43, CI (−0.76;−0.10); p=0.01), E-wave (β 36.67, CI (12.96; 60.38); p=0.003), and deceleration time (β −0.1, CI (−0.16; −0.05); p=0.002). In a multivariable model, a history of prior stroke (β 29.87, CI (2.61; 57.13); p=0.03) and BNP levels (β 0.05, CI (0.01; 0.08); p=0.007) remained significantly associated with AF burden.

Conclusions

Few patients with paroxysmal or persistent AF have AF episodes on yearly 7-day Holter-ECG recordings, and AF progression is rare. AF burden was independently associated with a history of prior stroke and BNP levels.

Molecular Mechanisms, Diagnostic Aspects and Therapeutic Opportunities of Micro Ribonucleic Acids in Atrial Fibrillation

Micro ribonucleic acids (miRNAs) are short non-coding RNA molecules responsible for regulation of gene expression. They are involved in many pathophysiological processes of a wide spectrum of diseases. Recent studies showed their involvement in atrial fibrillation. They seem to become potential screening biomarkers for atrial fibrillation and even treatment targets for this arrhythmia. The aim of this review article was to summarize the latest knowledge about miRNA and their molecular relation to the pathophysiology, diagnosis and treatment of atrial fibrillation.

Correlation between the left atrial low-voltage area and the cardiac function improvement after catheter ablation for paroxysmal atrial fibrillation

BACKGROUND

The impact of the left atrial low-voltage area (LVA) on the cardiac function improvement following ablation for atrial fibrillation (AF) is unclear.

METHODS

In 49 patients with paroxysmal AF who underwent ablation, the left ventricular stroke volume index (SVI) was repeatedly measured using an impedance cardiography until 6 months after ablation. We defined the cardiac function improvement as a 20% increase in the SVI. The LVA (the area with the voltage amplitude of <0.5 mV) was assessed before ablation.

RESULTS

The reduced baseline SVI (<33 mL/m2) was observed in 18 (37%) patients. The SVI increased following ablation (from 36 ± 5 to 39 ± 6 mL/m2, P < .001). We observed the cardiac function improvement in 14 (29%) patients. The LVA was smaller in patients with the improved cardiac function than in those without (8.3% ± 5.2% vs 14.0% ± 8.5%, P = .026). The multivariate analysis revealed that only the LVA was independently associated with the cardiac function improvement (odds ratio, 0.878; 95% confidence interval: 0.778-0.991, P = .036). Furthermore, LVAs of the anterior (7.9% ± 7.6% vs 18.2% ± 15.5%, P = .022), septal (12.0 ± 7.3% vs 20.7% ± 13.8%, P = .031), and roof walls (6.9% ± 6.0% vs 16.9% ± 15.2%, P = .022) were smaller in patients with the improved cardiac function than in those without.

CONCLUSIONS

The LVA was related to the cardiac function improvement following ablation in patients with paroxysmal AF.

Reverse electrical and structural remodeling of the left atrium occurs early after pulmonary vein isolation for persistent atrial fibrillation

PURPOSE

Adverse left atrial (LA) remodeling is known to be associated with persistent atrial fibrillation (PeAF). The time course and pattern of reversal of LA remodeling following catheter ablation is poorly understood. We aimed to evaluate LA chamber volumes and dimensions, LA conduction velocities, and LA bipolar voltages at baseline and at 2 months after catheter ablation for PeAF.

METHODS

Twenty-three patients with PeAF underwent detailed LA mapping during fixed rate atrial pacing using the CARTO3 navigation system prior to undergoing pulmonary vein isolation. All patients returned for protocol-mandated repeat electrophysiology study at 2 months, irrespective of symptoms or arrhythmia recurrence, during which all measurements were repeated using an identical mapping protocol. Patients then underwent daily ECG monitoring for 12 months.

RESULTS

Nineteen out of twenty-three (83.6%) patients had durable PVI of all veins at repeat electrophysiology study, while 4 (17.4%) patients had late reconnection of a single vein each. In the blinded offline analysis, LA volume at follow-up was significantly lower as compared with baseline (55 ± 14 mL/m² vs. 65 ± 15 mL/m², P < 0.001). LA conduction velocities were significantly greater at 2 months (0.90 ± 0.13 m/s vs. 0.78 ± 0.13 m/s, P = 0.01). There was non-uniform regional LA voltage evolution, with a significant increase in bipolar voltages observed on the LA posterior wall (2.18 ± 0.85 mV vs. 1.83 ± 0.49 mV, P = 0.04), but not elsewhere. Individual variables of remodeling were not associated with AF recurrence.

CONCLUSION

Significant structural and electrical reverse remodeling of the LA can be seen as early as 2 months following successful catheter ablation for PeAF.

Biomarkers Associated with Atrial Fibrosis and Remodeling

Atrial fibrillation is the most common rhythm disturbance encountered in clinical practice. Although often considered as solely arrhythmic in nature, current evidence has established that atrial myopathy constitutes both the substrate and the outcome of atrial fibrillation, thus initiating a vicious, self-perpetuating cycle. This myopathy is triggered by stress-induced (including pressure/volume overload, inflammation, oxidative stress) responses of atrial tissue, which in the long term become maladaptive, and combine elements of both structural, especially fibrosis, and electrical remodeling, with contemporary approaches yielding potentially useful biomarkers of these processes. Biomarker value becomes greater given the fact that they can both predict atrial fibrillation occurrence and treatment outcome. This mini-review will focus on the biomarkers of atrial remodeling (both electrical and structural) and fibrosis that have been validated in human studies, including biochemical, histological and imaging approaches.

Use of wearable cardioverter-defibrillator in association with catheter ablation for atrial fibrillation-related tachycardiomyopathy

Implantable cardioverter-defibrillator (ICD) is an effective therapy in patients known to be at high risk for sudden cardiac death (SCD). Nevertheless, ICD implantation is not indicated in transient or reversible causes of SCD. Wearable cardioverter-defibrillator is increasingly used for SCD prevention in patients with a transient risk of ventricular arrhythmia.

Bipolar Voltage Mapping for the Evaluation of Atrial Substrate: Can We Overcome the Challenge of Directionality?

The relationship between atrial fibrosis and atrial fibrillation (AF) has been proven. Patient specific substrate ablation targeting fibrotic tissue estimated by bipolar voltage mapping has emerged as an alternative strategy for additional substrate modification beyond pulmonary vein isolation. The primary mechanism of a low-voltage electrogram has been suggested to be atrial fibrosis, however, no direct correlation between histological fibrosis and low-voltage zone has been confirmed. Furthermore, the definition of low-voltage zone is still controversial, and bipolar voltage amplitudes depend on multiple variables including electrodes orientation relative to direction of wavefront, electrode length, interelectrode spacing, and tissue contact. The aim of this article is to review the role and limitation of voltage mapping, and to share our initial experience of a newly released grid-pattern designed mapping catheter to make the voltage mapping more reliable to guide patient specific AF ablation.

Association Between Cardiovascular Magnetic Resonance-Derived Left Atrial Dimensions, Electroanatomical Substrate and NT-proANP Levels in Atrial Fibrillation

Background Enlargement of left atrial ( LA ) size indicates advanced disease stage in patients with atrial fibrillation ( AF ) and is associated with poor success of different AF therapies. Two dimensional echocardiographic LA measurements do not reliably reflect the true size of LA anatomy. The aim of the current study was: 1) to analyze cardiovascular magnetic resonance ( CMR )-derived LA dimensions and their association with low voltage areas ( LVA ); and 2) to investigate the association between these parameters and NT -pro ANP (N-terminal proatrial natriuretic peptide) levels. Methods and Results Patients undergoing first AF catheter ablation were included. All patients underwent CMR imaging (Ingenia 1.5T Philips) before intervention. CMR data ( LA volume, superior-inferior, transversal and anterior-posterior LA diameters) were measured in all patients. LVA were determined using high-density maps and a low voltage threshold <0.5 mV. Blood plasma samples from femoral vein were collected before catheter ablation. NT -pro ANP levels were studied using commercially available assays. There were 216 patients (65±11 years, 59% males, 56% persistent AF , 26% LVA ) included into analyses. NT -pro ANP levels in patients with LVA were significantly higher than in those without (median/interquartile range 22 [13-29] versus 15 [9-22] pg/mL, P=0.004). All CMR derived LA diameters correlated significantly with persistent AF ( r²=0.291-0.468, all P<0.001), LVA ( r²=0.187-0.306, all P<0.001), and NT -pro ANP levels ( r²=0.258-0.352, P<0.01). On logistic regression multivariable analysis, age (odds ratio=1.090, 95% confidence interval: 1.030-1.153, P=0.003), females (odds ratio=2.686, 95% confidence interval: 1.047-6.891, P=0.040), and LA volume (odds ratio=1.022, 95% confidence interval: 1.009-1.035, P=0.001) remained significant predictors for LVA . Conclusions Left atrial CMR parameters are associated with persistent AF , low voltage areas and NT -pro ANP levels. LA volume is the most significant predictor for LVA .

Comparison of chronological changes in blood characteristics in the atrium and peripheral vessels after the development of non-valvular atrial fibrillation

INTRODUCTION

Changes in blood characteristics in the atrium and peripheral vessels in patients with non-valvular atrial fibrillation (NVAF) are unclear. We investigated chronological changes in blood characteristics in the atrium and peripheral vessels in a dog model of NVAF by using a total thrombus-formation analysis system (T-TAS).

MATERIALS AND METHODS

In NVAF model dogs (n = 8, 390 bpm rapid atrial pacing), atrial and peripheral blood samples were collected. Using this blood, T-TAS was performed before and 1, 2, and 3 weeks after the onset of rapid atrial pacing.

RESULTS

Occlusion time (OT: time to +80 and +60 kPa in the AR and PL chips, respectively) and area under the flow pressure curve (AUC) were measured using the AR chip (for mixed white thrombus analysis) and PL chip (for platelet thrombus analysis). OT of the AR chip showed shortening as early as 1 week after NVAF onset, which continued for 3 weeks. OT of the PL chip showed significant shortening in atrium blood only 3 weeks after NVAF onset. By contrast, peripheral blood showed no significant changes in OT or AUC with both AR and PL chips.

CONCLUSIONS

In our dog model of NVAF, thrombus formation accelerated in the atrium as early as 1 week after NVAF onset and continued for 3 weeks, but no significant changes were found in peripheral blood. We conclude that antithrombotic therapy should be started early after NVAF onset even if no changes in coagulation activity are observed in peripheral blood.

Efficacy of pentamidine analogue 6 in dogs with chronic atrial fibrillation

Background

The inward rectifier inhibitor pentamidine analogue 6 (PA‐6) is effective in cardioversion of goats with persistent rapid pacing induced atrial fibrillation (AF) and is not proarrhythmic in dogs with experimental chronic 3rd‐degree AV block. Efficacy and safety in the clinical setting are unknown.

Hypothesis

That PA‐6 would be effective in converting AF to sinus rhythm (SR) in dogs with naturally occurring AF, without the presence of overt adverse effects.

Animals

Ten client‐owned large and giant breed dogs.

Methods

Animals with persistent or permanent AF were recruited for our prospective study. PA‐6 was administered IV as a bolus of 2.5 mg/kg 10 min⁻¹ followed by a maintenance infusion of 0.04 mg/kg min⁻¹ for a maximum of 50 minutes in conscious dogs. Standard 6 lead limb ECG was recorded during the infusion. Visible and audible signs of adverse effects were scored during the entire procedure.

Results

PA‐6 did not induce changes in QRS duration (54.7 ± 4.6 versus 56.7 ± 6.1 ms, P = .42), QTc interval (241.1 ± 19.5 versus 258.7 ± 19.8 ms, P = .061) or RR interval (363.4 ± 84.6 versus 440.8 ± 96.3 ms, P = .072) at the end of the bolus. No cardioversion to SR was observed in any dog. Three dogs displayed no adverse effects. Five dogs had premature ventricular depolarizations during PA‐6 infusion on the ECG. Respiratory distress with laryngeal stridor, subtle muscle twitching, and mild generalized muscular weakness were noncardiac adverse effects observed in 5 dogs. Adverse effects resolved spontaneously.

Conclusions and Clinical importance

Chronic naturally occurring AF in large and giant breed dogs could not be cardioverted to SR by PA‐6.

Aging-Induced Biological Changes and Cardiovascular Diseases

Aging is characterized by functional decline in homeostatic regulation and vital cellular events. This process can be linked with the development of cardiovascular diseases (CVDs). In this review, we discussed aging-induced biological alterations that are associated with CVDs through the following aspects: (i) structural, biochemical, and functional modifications; (ii) autonomic nervous system (ANS) dysregulation; (iii) epigenetic alterations; and (iv) atherosclerosis and stroke development. Aging-mediated structural and biochemical modifications coupled with gradual loss of ANS regulation, vascular stiffening, and deposition of collagen and calcium often disrupt cardiovascular system homeostasis. The structural and biochemical adjustments have been consistently implicated in the progressive increase in mechanical burden and functional breakdown of the heart and vessels. In addition, cardiomyocyte loss in this process often reduces adaptive capacity and cardiovascular function. The accumulation of epigenetic changes also plays important roles in the development of CVDs. In summary, the understanding of the aging-mediated changes remains promising towards effective diagnosis, discovery of new drug targets, and development of new therapies for the treatment of CVDs.

The characteristics of a porcine mitral regurgitation model

The porcine mitral regurgitation (MR) model is a common cardiovascular animal model. Standardized manufacturing processes can improve the uniformity and success rate of the model, and systematic research can evaluate its potential use. In this study, 17 pigs were divided into an experimental group (n=11) and a control group (n=6). We used a homemade retractor to cut the mitral chordae via the left atrial appendage to establish a model of MR; the control group underwent a sham surgery. The model animals were followed for 30 months after the surgery. Enlargement and fibrosis of the left atrium were significant in the experimental group compared with those in the control group, and left atrial systolic function decreased significantly. In addition, model animals showed preserved left ventricular systolic function. There were no differences in left atrial potential or left ventricular myocardial fibrosis between the two groups. Atrial fibrillation susceptibility in the experimental group was higher than that in the control group. Our method enables the simple and effective production of a MR model with severe reflux that can be used for pathophysiological studies of MR, as well as for the development of preclinical surgical instruments and their evaluation. This model could also be used to study atrial fibrillation and myocardial fibrosis but is not suitable for studies of heart failure.

Usefulness of the WCD in patients with suspected tachymyopathy

AIMS

The wearable cardioverter defibrillator (WCD) is used for temporary protection of patients deemed to be at high risk for sudden death. There is limited experience regarding the clinical development of patients with tachymyopathy. We aimed to evaluate the clinical development of tachymyopathy patients protected with a WCD in a single-center non-randomized patient cohort.

METHODS AND RESULTS

We fitted 130 consecutive patients deemed to be at high risk for ventricular tachyarrhythmias with the WCD. Of these, 20 patients (15%) presenting with newly diagnosed heart failure in the setting of rapidly conducted atrial fibrillation/flutter were suspected to suffer from tachymyopathy. The control group consisted of the remaining 110 patients with other indications for WCD therapy. LVEF increased by more than 10% in 13/20 (65%) tachymyopathy patients compared to 40/110 (36%) patients in the control population (p = 0.01). Similarly, BNP levels decreased in 15/20 (75%) tachymyopathy patients compared to 41/110 (37%) in the control group (p = 0.05). ICD implantation rates were lower in the tachymyopathy group (3/20) compared to the control population (40/110; p = 0.04). On further follow-up (mean 12 ± 8 months), patients with suspected tachymyopathy had no sustained ventricular arrhythmias. Compared to 5/110 patients in the control group, no tachymyopathy patient died.

CONCLUSION

Most of the patients with suspected tachymyopathy have a favorable clinical outcome. The WCD is useful for temporary protection while LV function recovers.

Association between connexin 40 and potassium voltage-gated channel subfamily A member 5 expression in the atrial myocytes of patients with atrial fibrillation

Structural and electrical remodeling within the atrium mediate the pathogenesis of atrial fibrillation (AF). Two key genes that sever a role in this remodeling are connexin 40 (Cx40) and potassium voltage-gated channel subfamily A member 5 (KCNA5), respectively. Electrical remodeling is considered to induce structural remodeling during AF. In the present study, the left atrial appendage section and atrial myocytes of patients with AF were evaluated. It was observed that Cx40 and KCNA5 mRNA (P<0.05) and protein (P<0.01) expression was significantly downregulated in AF compared with rheumatic heart disease. In addition, a positive correlation between the mRNA expression Cx40 and KCNA5 was observed in the atrial myocytes of patients with AF (P<0.05; r=0.42). The association between Cx40 and KCNA5 expression was subsequently investigated in primary cultured atrial myocytes using siRNA transfection. In atrial myocytes, downregulation of Cx40 inhibited the expression of KCNA5. Similarly, silencing of KCNA5 suppressed the expression of Cx40. These results indicate that synergistic regulation may occur between Cx40 and KCNA5 expression. Furthermore, the combined effects of electrical and structural remodeling in the atrial myocytes of patients with AF may contribute to the pathogenesis of AF.

Relationship between lesion formation and electrophysiological responses using catheters equipped with mini-electrodes in chronic atrial fibrillation

BACKGROUND

The study focuses on the electrophysiological changes associated with lesion formation using 4.5-mm irrigated and 8-mm standard catheters equipped with mini-electrodes (MEs) positioned circumferentially on the tip.

OBJECTIVE

The aim of the study was to test the relationship between the maximal electrogram (EGM) reduction, frequency spectrum shift, and their impact on atrial lesion formation in the atrial fibrillation (AF) model. Furthermore, we hypothesize that the high fidelity recording from the MEs allows improved discrimination of ablated tissues from nonablated tissues.

METHODS

Under fluoroscopic and NavX guidance, atrial ablation lesions were placed in 4 canines in chronic AF (>12 months in AF) to achieve intercaval, cavotricuspid isthmus, and left atrial contiguous lesions. Lesion times were titrated to the maximal loss of EGM amplitude as recorded from the MEs. Radiofrequency (RF) lesions were sequentially connected on the basis of the ME recordings of tissue viability.

RESULTS

In lesions formed using a 4.5-mm irrigated catheter (172 lesions) and in those formed using an 8-mm catheter (155 lesions), the time to nadir of the EGM reduction was 22 ± 12 and 22 ± 9 seconds (NS:p>0.05). Contiguous transmural lesions were successfully placed and guided by the ME EGMs and confirmed by frequency spectra.

CONCLUSION

In the chronic AF model, EGM reduction and frequency spectrum shift recorded from the MEs are twice the reduction recorded using the 4.5mm and 8mm tip to ring electrodes. RF titration based on the maximal EGM diminution is an effective approach to monitor lesion formation and may improve safety by preventing unnecessarily prolonged RF application. The ME EGM recording greatly facilitates placement of contiguous transmural linear lesions.

Aliskiren protecting atrial structural remodeling from rapid atrial pacing in a canine model

Atrial fibrillation (AF) contributing to the increasing mortality risk is the most common disease in clinical practice. Owing to the side effects and relative inefficacy of current antiarrhythmic drugs, some research focuses on renin-angiotensin-aldosterone system (RAS) for finding out the new treatment of AF. The purpose of this study is to confirm whether aliskiren as a proximal inhibitor of renin, which completely inhibits RAS, has beneficial effects on atrial structural remodeling in AF. In this study, rapid atrial pacing was induced at 500 beats per minute for 2 weeks in a canine model. A different dose of aliskiren was given orally for 2 weeks before rapid atrial pacing. HE staining and Masson's staining were used for analysis of myocardial fibrosis. TGF-β1, signal pathways, and pro-inflammatory cytokines were shown for the mechanism of structural remodeling after the treatment of aliskiren. Serious atrial fibrosis was induced by rapid atrial pacing, followed by the elevated TGF-β1, upregulated MEK and ERK1/2, and increased inflammatory factors. Aliskiren could apparently improve myocardial fibrosis by reducing the expression of TGF-β1, inhibiting MEK and ERK1/2 signal pathways, and decreasing IL-18 and TLR4 in both serum and atrial tissue. In conclusion, aliskiren could prevent atrial structural remodeling from rapid atrial pacing for 2 weeks. Aliskiren may play a potential beneficial role in the treatment of AF induced by rapid atrial pacing.

A Stochastic Individual-Based Model of the Progression of Atrial Fibrillation in Individuals and Populations

Models that represent the mechanisms that initiate and sustain atrial fibrillation (AF) in the heart are computationally expensive to simulate and therefore only capture short time scales of a few heart beats. It is therefore difficult to embed biophysical mechanisms into both policy-level disease models, which consider populations of patients over multiple decades, and guidelines that recommend treatment strategies for patients. The aim of this study is to link these modelling paradigms using a stylised population-level model that both represents AF progression over a long time-scale and retains a description of biophysical mechanisms. We develop a non-Markovian binary switching model incorporating three different aspects of AF progression: genetic disposition, disease/age related remodelling, and AF-related remodelling. This approach allows us to simulate individual AF episodes as well as the natural progression of AF in patients over a period of decades. Model parameters are derived, where possible, from the literature, and the model development has highlighted a need for quantitative data that describe the progression of AF in population of patients. The model produces time series data of AF episodes over the lifetimes of simulated patients. These are analysed to quantitatively describe progression of AF in terms of several underlying parameters. Overall, the model has potential to link mechanisms of AF to progression, and to be used as a tool to study clinical markers of AF or as training data for AF classification algorithms.

Mapping Atrial Fibrillation: 2015 Update

Atrial fibrillation requires a trigger that initiates the arrhythmia and substrate that favors perpetuation. Cardiac mapping is necessary to locate triggers and substrate so that an ablation strategy can be optimized. The most commonly used cardiac mapping approach is isochronal or activation mapping, which aims to create a spatial model of electrical wavefront propagation. Historically, activation mapping has been successful for mapping point source and single or double wave reentrant arrhythmias, while mapping multiple wavelets or driving sources that underlie most episodes of atrial fibrillation remains challenging. In the multiple wavelet model of AF there is no particular area critical to sustain atrial fibrillation, and a "critical mass" of atrium is required to maintain AF. Recent studies suggest endocardial and epicardial dissociation may play an important role. Investigation of driving sources that sustain AF has focused on the presence of rotors. Rotors in human AF have now been observed using multiple imaging modalities, however ablation strategies targeting rotors remain of unproven benefit. In addition, substrate mapping of AF is now feasible. Increasing degrees of atrial fibrosis on delayed enhancement magnetic resonance imaging (DE-MRI) has been shown to correlate with poor procedural outcomes for AF ablation, which suggests the increased burden of scar promotes more complex and extensive arrhythmia substrate. Atrial fibrosis is also identifiable using electrogram voltage tagging in an electro-anatomic mapping system. Patient-specific ablation strategies targeting areas of fibrosis are currently under investigation. Recent technological advances have facilitated greater understanding of the potential role for AF mapping and has allowed initiation of clinical studies to evaluate the effectiveness of mapping-based intervention. Multi-modality mapping is likely to play an increasingly important role in AF ablation, but is currently limited by the inability to simultaneously record and interpret electrical signals from both atria and from both the epicardium and endocardium.

Making better scar: Emerging approaches for modifying mechanical and electrical properties following infarction and ablation

Following myocardial infarction (MI), damaged myocytes are replaced by collagenous scar tissue, which serves an important mechanical function - maintaining integrity of the heart wall against enormous mechanical forces - but also disrupts electrical function as structural and electrical remodeling in the infarct and borderzone predispose to re-entry and ventricular tachycardia. Novel emerging regenerative approaches aim to replace this scar tissue with viable myocytes. Yet an alternative strategy of therapeutically modifying selected scar properties may also prove important, and in some cases may offer similar benefits with lower risk or regulatory complexity. Here, we review potential goals for such modifications as well as recent proof-of-concept studies employing specific modifications, including gene therapy to locally increase conduction velocity or prolong the refractory period in and around the infarct scar, and modification of scar anisotropy to improve regional mechanics and pump function. Another advantage of scar modification techniques is that they have applications well beyond MI. In particular, ablation treats electrical abnormalities of the heart by intentionally generating scar to block aberrant conduction pathways. Yet in diseases such as atrial fibrillation (AF) where ablation can be extensive, treating the electrical disorder can significantly impair mechanical function. Creating smaller, denser scars that more effectively block conduction, and choosing the location of those lesions by balancing their electrical and mechanical impacts, could significantly improve outcomes for AF patients. We review some recent advances in this area, including the use of computational models to predict the mechanical effects of specific lesion sets and gene therapy for functional ablation. Overall, emerging techniques for modifying scar properties represents a potentially important set of tools for improving patient outcomes across a range of heart diseases, whether used in place of or as an adjunct to regenerative approaches.

Cardiac Fibrosis in Patients With Atrial Fibrillation: Mechanisms and Clinical Implications

Atrial fibrillation (AF) is associated with structural, electrical, and contractile remodeling of the atria. Development and progression of atrial fibrosis is the hallmark of structural remodeling in AF and is considered the substrate for AF perpetuation. In contrast, experimental and clinical data on the effect of ventricular fibrotic processes in the pathogenesis of AF and its complications are controversial. Ventricular fibrosis seems to contribute to abnormalities in cardiac relaxation and contractility and to the development of heart failure, a common finding in AF. Given that AF and heart failure frequently coexist and that both conditions affect patient prognosis, a better understanding of the mutual effect of fibrosis in AF and heart failure is of particular interest. In this review paper, we provide an overview of the general mechanisms of cardiac fibrosis in AF, differences between fibrotic processes in atria and ventricles, and the clinical and prognostic significance of cardiac fibrosis in AF.

Angiotensin II activates signal transducers and activators of transcription 3 via Rac1 in the atrial tissue in permanent atrial fibrillation patients with rheumatic heart disease

Patients with rheumatic heart disease (RHD) often experience persistent atrial fibrillation (AF) associated with adverse atrial structural remodeling (ASR) manifested by atrial fibrosis and left atrial enlargement. The aim of this study was to explore the potential molecular signaling mechanisms for atrial fibrosis and ASR. Twenty RHD patients with persistent AF and 10 RHD patients with sinus rhythm (Group A) were recruited in our study, which all underwent transthoracic echocardiography. Right atrial appendage (RAA) tissue samples were obtained from these patients during mitral/aortic valve replacement operation. The AF patients were further divided into two groups according to left atrial diameter (LAD): Group B with LAD ranging 50-65 mm and Group C with LAD >65 mm. Histological examinations were performed with hematoxylin-eosin staining and Masson's trichrome staining. Atrial angiotensin II (AngII) content was measured by ELISA. Rac1 and STAT3 protein levels were determined by Western blot analysis. Hematoxylin-eosin staining demonstrated highly organized arrangement of atrial muscles in control Group A and significant derangement in both Group B and C AF patients with reduced cell density and increased cell size. Moreover, Masson's trichrome staining showed that atrial myocytes were surrounded by large trunks of collagen fibers in both Group B and C, but not in Group A. There was a positive correlation between atrial tissue fibrosis and LAD. AngII content was markedly higher in Group C than in Group B than in Group A, which was positively correlated with LAD. Similarly, Rac1 and STAT3 protein levels were found considerably higher in Group C and B than in Group A with excellent correlation to LAD. Our study unraveled for the first time the AngII/Rac1/STAT3 signaling as a mechanism for ASR thereby AF in a particular clinical setting-RHD patients with persistent AF and indicated inhibition of this pathway may help ameliorating adverse ASR.

Atrial fibrillation: recent advances in understanding the role of microRNAs in atrial remodeling with an electrophysiological overview

Atrial fibrillation (AF) is a highly prevalent condition associated with pronounced cardiovascular-related morbidity, mortality and socioeconomic burden. It accounts for more hospitalization days than does any other arrhythmia. This article reviews the basic electrophysiology of AF, electrical and structural remodeling in AF and recent advances in understanding the molecular mechanisms of AF in relation to specific microRNAs. This paper also reviews the potential role of microRNAs as novel therapeutic targets as well as biomarkers in the management of AF. AF shows characteristics typical of altered electrophysiology that promote ectopic activity and facilitate reentry, thereby contributing to the progression from short paroxysmal AF to a persistent, permanent form via atrial remodeling, even in the absence of progressive underlying heart disease. MicroRNAs have been suggested to influence the development of AF by regulating gene expression at the post-transcriptional level. Increasing evidence has identified various microRNA modifications and their impacts on AF initiation and maintenance through electrical and structural remodeling. The discovery of specific microRNAs as novel therapeutic targets and some experimental evidence implicating microRNAs as potential molecular diagnostic markers have had a significant impact on the diagnosis and management of AF and demand further research.

Effect of valsartan on atrial fibrillation recurrence following pulmonary vein isolation in patients

Pulmonary venous isolation has emerged as an effective therapy for atrial fibrillation (AF); however, AF recurrence is common. The aim of the present study was to investigate the effect of angiotensin receptor blockers (ARBs) on the recurrence rate of AF following ablation therapy. In total, 120 patients, who were scheduled for ablation, were randomly selected. The patients were randomly divided into three groups, which received treatment with a placebo (n=40), 80 mg valsartan daily (n=40) or with 160 mg valsartan daily (n=40). The demographic characteristics, comorbidities, AF type and information regarding treatment with ARBs were recorded and analyzed. Following a mean follow-up period of 13.8±8.6 months, 66.7% of patients were found to be free of AF. Kaplan-Meier analysis of the time until the first recurrence during the follow-up period revealed that patients treated with 160 mg/day valsartan presented a higher probability of remaining free of AF (88%, vs. 47% for the control and 65% for the 80 mg/day valsartan groups). In addition, multivariate analysis demonstrated that treatment with ARB was associated with lower AF recurrence rates (hazard ratio, 0.46; 95% confidence interval, 0.20–0.93] P=0.01). In conclusion, treatment with 160 mg/day valsartan markedly reduced the risk of recurrence of AF in a dose-dependent manner in AF patients following ablation.

Variability of P-wave morphology predicts the outcome of circumferential pulmonary vein isolation in patients with recurrent atrial fibrillation

INTRODUCTION

Severe atrial structural remodeling may reflect irreversible damage of the atrial tissue in patients with atrial fibrillation (AF) and is associated with changes of P-wave duration and morphology. Our aim was to study whether variability of P-wave morphology (PMV) is associated with outcome in patients with AF after circumferential PV isolation (CPVI).

METHODS AND RESULTS

70 consecutive patients (aged 60±9years, 46 men) undergoing CPVI due to symptomatic AF were studied. After cessation of antiarrhythmic therapy, standard 12-lead ECG during sinus rhythm was recorded for 10min at baseline and transformed to orthogonal leads. Beat-to-beat P-wave morphology was subsequently defined using a pre-defined classification algorithm. The most commonly observed P-wave morphology in a patient was defined as the dominant morphology. PMV was defined as the percentage of P waves with non-dominant morphology in the 10-min sample. At the end of follow-up, 53 of 70 patients had no arrhythmia recurrence. PMV was greater in patients without recurrence (19.5±17.1% vs. 8.2±6.7%, p<0.001). In the multivariate logistic regression model, PMV≥20% (upper tertile) was the only independent predictor of ablation success (OR=11.4, 95% CI 1.4-92.1, p=0.023). A PMV≥20% demonstrated a sensitivity of 41.5%, a specificity of 94.1%, a PPV of 96.7%, and an NPV of 34.0% for free of AF after CPVI.

CONCLUSIONS

We report a significant association between increased PMV and 6-month CPVI success. PMV may help to identify patients with very high likelihood of freedom of AF 6-months after CPVI.