Structural remodeling and conduction velocity dynamics in the human left atrium: Relationship with reentrant mechanisms sustaining atrial fibrillation

Identifying extra pulmonary vein targets for persistent atrial fibrillation ablation: bridging advanced and conventional mapping techniques

AIMS

Advanced technologies such as charge density mapping (CDM) show promise in guiding adjuvant ablation in patients with persistent atrial fibrillation (AF); however, their limited availability restricts widespread adoption. We sought to determine whether regions of the left atrium containing CDM-identified pivoting and rotational propagation patterns during AF could also be reliably identified using more conventional contact mapping techniques.

METHODS AND RESULTS

Twenty-two patients undergoing de novo ablation of persistent AF underwent both CDM and electroanatomic voltage mapping during AF and sinus rhythm with multiple pacing protocols. Through the use of a left atrium statistical shape model, the location of distinctive propagation patterns identified by CDM was compared with low-voltage areas (LVAs) and regions of slow conduction velocity (CV). Neither LVA nor CV mapping during paced rhythms reliably identified regions containing CDM propagation patterns. Conduction velocity mapping during AF did correlate with these regions (ρ = -0.63, P < 0.0001 for pivoting patterns; ρ = -0.54, P < 0.0001 for rotational patterns). These propagation patterns consistently occurred in two specific anatomical regions across patients: the anteroseptal and inferoposterior walls of the left atrium.

CONCLUSION

Mapping techniques during paced rhythms do not reliably correspond with regions of CDM-identified propagation patterns in persistent AF. However, these propagation patterns are consistently observed in two specific anatomical regions, suggesting a predisposition to abnormal electrophysiological properties. While further research is needed, these regions may serve as promising targets for empirical ablation, potentially reducing the reliance on complex mapping techniques.

Multi-modal integration of MRI and global chamber charge density mapping for the evaluation of atrial fibrillation

Atrial fibrillation (AF) is the most prevalent clinical arrhythmia, posing significant mortality and morbidity challenges. Outcomes of current catheter ablation treatment strategies are suboptimal, highlighting the need for innovative approaches. A major obstacle lies in the inability to comprehensively assess both structural and functional remodelling in AF. Combining magnetic resonance imaging (MRI)'s detailed structural insights with global chamber charge density mapping (CDM)'s functional mapping capabilities holds promise for advancing AF management. Our research introduces a novel tool for three-dimensional reconstruction of left atrial geometries from MRI, facilitating integration into CDM systems. We comprehensively assess our tool by generating three-dimensional left atrial meshes from MRIs of eight patients with AF and compare them with the established CDM intra-chamber ultrasound approach utilizing both geometric and clinical parameters. We apply the CDM inverse algorithm to both sets of reconstructions in order to compare derived conductions across various heart rhythms and AF conduction patterns. Finally, we explore the potential utility of our integrated pipeline through an exploration of the relationship between AF conduction patterns and their proximity to adjacent thoracic structures. Ultimately, this multifaceted approach aims to unveil insights into AF mechanisms, potentially improving treatment outcomes through personalized ablation strategies targeting arrhythmogenic atrial substrate.

The impact of atrial voltage and conduction velocity phenotypes on atrial fibrillation recurrence

Introduction

Low atrial voltage and slow conduction velocity (CV) have been associated with atrial fibrillation (AF); however, their interaction and relative importance as early disease markers remain incompletely understood. We aimed to elucidate the relationship between atrial voltage and CV using high-density electroanatomic (HDE) maps of patients with AF.

Methods

HDE maps obtained during sinus rhythm in 52 patients with AF and five healthy controls were analysed. Atrial voltage and CV maps were generated, and their correlations were assessed. Subgroup analyses were performed based on clinically relevant factors such as AF type, CV, and voltage levels. Finally, cluster analysis was conducted to identify distinct phenotypes within the population, reflecting different patterns of conduction and voltage.

Results

A moderate positive correlation was found between the mean atrial voltage and CV (r = 0.570). Subgroup analysis revealed differences in voltage (p = 0.0044) but not in global CV (p = 0.42), with no significant differences between AF types. Three distinct phenotypes emerged: normal voltage/normal CV, normal voltage/low CV, and low voltage/low CV, with distinct recurrence rates, suggesting different disease progression paths. Slower atrial CV was identified as a significant predictor of arrhythmia recurrence at 12 and 24 months after AF ablation, surpassing the predictive potential of atrial voltage.

Conclusion

Atrial voltage and CV analyses revealed distinct phenotypes. Lower atrial CV emerged as a significant predictor of AF recurrence, exceeding the predictive significance of atrial voltage. These findings emphasise the importance of considering CV and voltage in managing AF and offer potential insights for personalised strategies.

Functional and Structural Remodeling as Atrial Fibrillation Progresses in a Persistent Atrial Fibrillation Canine Model

BACKGROUND

Contractile, electrical, and structural remodeling has been associated with atrial fibrillation (AF), but the progression of functional and structural changes as AF sustains has not been previously evaluated serially.

OBJECTIVES

Using a rapid-paced persistent AF canine model, the authors aimed to evaluate the structural and functional changes serially as AF progresses.

METHODS

Serial electrophysiological studies in a chronic rapid-paced canine model (n = 19) prior to AF sustaining and repeated at 1, 3, and 6 months of sustained AF were conducted to measure changes in atrial conduction speed and direction. Cardiac late gadolinium enhancement magnetic resonance imaging was performed prior to and following sustained AF to evaluate structural remodeling.

RESULTS

As AF progressed, the overall area of the left atrium with fibrosis increased. Over time, conduction speeds slowed, with speeds decreasing by 0.15 m/s after 3 months and 0.26 m/s after 6 months of sustained AF. Regions that developed fibrosis experienced greater slowing compared with healthy regions (0.32 ± 0.01 m/s decrease vs 0.21 ± 0.01 m/s decrease; P < 0.001). Conduction directions became more aligned (conduction direction heterogeneity decreased from 19.7 ± 0.1° to 17.5 ± 0.1° after 6 months of sustained AF; P < 0.001). Fibrotic regions had a greater decrease in conduction direction heterogeneity (2.7 ± 0.3° vs 2.0 ± 0.2°; P = 0.008).

CONCLUSIONS

As AF progressed, functional changes occurred globally throughout the left atrium. Conduction speed slowed, and conduction directions became more aligned over time, with the greatest changes occurring within regions that developed fibrosis.

The effect of fixed and functional remodelling on conduction velocity, wavefront propagation, and rotational activity formation in atrial fibrillation

AIMS

Pathophysiology of atrial fibrillation (AF) remains unclear. Interactions between scar and conduction velocity (CV) and their impact on wavefront propagation in sinus rhythm (SR) and rotational activity burden in AF were evaluated.

METHODS AND RESULTS

Local activation times (LATs) and voltage data were obtained from patients undergoing ablation for persistent AF. Omnipolar voltage (OV) and bipolar voltage (BV) data were obtained during AF and SR at pacing intervals of 600 and 250 ms. Local activation times were used to determine CV dynamics and their relationship to the underlying voltage and pivot points in SR. Computational modelling studies were performed to evaluate the impact of CVs and fibrosis on rotational activity burden in AF. Data from 60 patients with a total of 2 768 400 LAT and voltage points were analysed (46 140 ± 5689 points/patient). Voltage determined CV dynamics. Enhanced CV heterogeneity sites were predominantly mapped to low-voltage zones (LVZs) (0.2-0.49 mV) (128/168, 76.2%) rather than LVZs (<0.2 mV) and frequently co-located to pivot points (151/168, 89.9%). Atrial fibrillation OV maps correlated better with SR BV 250 ms than 600 ms maps, thereby representing fixed and functional remodelling. Sinus rhythm maps at 250 ms compared with 600 ms harboured a greater number of pivot points. Increased CV slowing and functional remodelling on computational models resulted in a greater rotational activity burden.

CONCLUSION

Conduction velocity dynamics are impacted by the degree of scar. Conduction velocity heterogeneity and functional remodelling impacts wavefront propagation in SR and rotational activity burden in AF. This study provides insight into the pathophysiology of AF and identifies potential novel ablation targets.

Atrial Fibrillation and Underlying Structural and Electrophysiological Heterogeneity

As atrial fibrillation (AF) progresses from initial paroxysmal episodes to the persistent phase, maintaining sinus rhythm for an extended period through pharmacotherapy and catheter ablation becomes difficult. A major cause of the deteriorated treatment outcome is the atrial structural and electrophysiological heterogeneity, which AF itself can exacerbate. This heterogeneity exists or manifests in various dimensions, including anatomically segmental structural features, the distribution of histological fibrosis and the autonomic nervous system, sarcolemmal ion channels, and electrophysiological properties. All these types of heterogeneity are closely related to the development of AF. Recognizing the heterogeneity provides a valuable approach to comprehending the underlying mechanisms in the complex excitatory patterns of AF and the determining factors that govern the seemingly chaotic propagation. Furthermore, substrate modification based on heterogeneity is a potential therapeutic strategy. This review aims to consolidate the current knowledge on structural and electrophysiological atrial heterogeneity and its relation to the pathogenesis of AF, drawing insights from clinical studies, animal and cell experiments, molecular basis, and computer-based approaches, to advance our understanding of the pathophysiology and management of AF.

Pacing cycle length-dependent electrophysiologic changes in left atrium: Poor validity of using low-voltage area and slow conduction area under specific pacing cycle length as absolute substrates of atrial fibrillation

BACKGROUND

Pacing cycle length (PCL)-dependent changes in left atrial (LA) electrophysiologic properties have not been fully elucidated.

OBJECTIVE

We aimed to elucidate these changes using a high-resolution mapping system.

METHODS

Forty-eight patients underwent atrial fibrillation ablation with RHYTHMIA HDx. Paired LA maps under a baseline PCL (600 ms) and rapid PCL (300 ms) were acquired after pulmonary vein isolation under right atrial appendage pacing. The PCL-dependent change in the low-voltage area (LVA; area with <0.5 mV bipolar voltage), LA activation time (interval from first LA activation to wavefront collision at lateral wall), regional mean voltage, regional mean wave propagation velocity, and slow conduction area (area with <0.3 m/s wave propagation velocity) were quantitatively analyzed.

RESULTS

Under the rapid PCL, the total LVA was significantly increased (7.6 ± 9.5 cm2 vs 6.7 ± 7.6 cm2; P = .031), especially in patients with a 10 cm2 LVA on the baseline PCL map (21.5 ± 9.1 cm2 vs 18.1 ± 6.5 cm2; P = .013). The LA activation time was also prolonged (87.9 ± 16.2 ms vs 84.0 ± 14.0 ms; P < .0001). Although the rapid PCL did not decrease the regional mean voltage, it significantly decreased the regional mean wave propagation velocity and increased the slow conduction area in all measured regions.

CONCLUSION

LVA and slow conduction area can be emphasized by rapid PCL LA mapping. There may be poor validity in using these areas as absolute atrial fibrillation substrates without considering the PCL-dependent changes.

Beyond pulmonary vein isolation: approaches to treat patients with persistent atrial fibrillation

INTRODUCTION

Atrial fibrillation (AF) is the most common arrhythmia. Catheter ablation is a successful rhythm control strategy in paroxysmal AF, but it has demonstrated dramatically lower AF-free survival rates in patients with persistent AF. In recent years, myriad novel rhythm control strategies have been developed, each with the promise of improved persistent AF ablation success.

AREAS COVERED

This review discusses multiple novel techniques and approaches to persistent AF. Authors identified relevant papers by searching PubMed and Google Scholar databases and considered all papers identified, regardless of publication date. It begins by discussing recent advances in electrogram analysis that yielded improved AF-free survival following persistent AF catheter ablation. Next, it discusses several trials revealing the shortcomings of MRI in guiding persistent AF ablation. Finally, it discusses one nascent technique (Vein of Marshall ablation) and technology (AI-assisted electrogram analysis) who have shown promise in improving persistent AF ablation.

EXPERT OPINION

In the authors' expert opinions, upcoming persistent AF ablations will utilize a stepwise approach of (1) ensuring PV isolation, (2) Vein of Marshall ablation and (3) AI-assisted ablation to optimize future persistent AF ablation outcomes. This approach systematically addresses arrhythmogenic sources beyond the pulmonary veins, the historical treatment target.

Development and validation of the Atri-Risk Conduction Index risk score to predict risk of atrial fibrillation after typical atrial flutter ablation

BACKGROUND

Identification of patients at risk for atrial fibrillation (AF) after typical atrial flutter (tAFL) ablation is important to guide monitoring and treatment.

OBJECTIVE

The purpose of this study was to create and validate a risk score to predict AF after tAFL ablation METHODS: We identified patients who underwent tAFL ablation with no AF history between 2017 and 2022 and randomly allocated to derivation and validation cohorts. We collected clinical variables and measured conduction parameters in sinus rhythm on an electrophysiology recording system (CardioLab, GE Healthcare). Univariate and multivariate logistic regressions (LogR) were used to evaluate association with AF development.

RESULTS

A total of 242 consecutive patients (81% male; mean age 66 ± 11 years) were divided into derivation (n =142) and validation (n = 100) cohorts. Forty-two percent developed AF over median follow-up of 330 days. In multivariate LogR (derivation cohort), proximal to distal coronary sinus time (pCS-dCS) ≥70 ms (odds ratio [OR] 16.7; 95% confidence interval [CI] 5.6-49), pCS time ≥36 ms (OR 4.5; 95% CI 1.5-13), and CHADS2-VASc score ≥3 (OR 4.3; 95% CI 1.6-11.8) were independently associated with new AF during follow-up. The Atri-Risk Conduction Index (ARCI) score was created with 0 as minimal and 4 as high-risk using pCS-dCS ≥70 ms = 2 points; pCS ≥36 ms = 1 point; and CHADS2-VASc score ≥3 = 1 point. In the validation cohort, 0% of patients with ARCI score = 0 developed AF, whereas 89% of patients with ARCI score = 4 developed AF.

CONCLUSION

We developed and validated a risk score using atrial conduction parameters and clinical risk factors to predict AF after tAFL ablation. It stratifies low-, moderate-, and high-risk patients and may be helpful in individualizing approaches to AF monitoring and anticoagulation.

Autonomic modulation impacts conduction velocity dynamics and wavefront propagation in the left atrium

AIMS

Atrial fibrosis and autonomic remodelling are proposed pathophysiological mechanisms in atrial fibrillation (AF). Their impact on conduction velocity (CV) dynamics and wavefront propagation was evaluated.

METHODS AND RESULTS

Local activation times (LATs), voltage, and geometry data were obtained from patients undergoing ablation for persistent AF. LATs were obtained at three pacing intervals (PIs) in sinus rhythm (SR). LATs were used to determine CV dynamics and their relationship to local voltage amplitude. The impact of autonomic modulation- pharmacologically and with ganglionated plexi (GP) stimulation, on CV dynamics, wavefront propagation, and pivot points (change in wavefront propagation of ≥90°) was determined in SR. Fifty-four patients were included. Voltage impacted CV dynamics whereby at non-low voltage zones (LVZs) (≥0.5 mV) the CV restitution curves are steeper [0.03 ± 0.03 m/s ΔCV PI 600-400 ms (PI1), 0.54 ± 0.09 m/s ΔCV PI 400-250 ms (PI2)], broader at LVZ (0.2-0.49 mV) (0.17 ± 0.09 m/s ΔCV PI1, 0.25 ± 0.11 m/s ΔCV PI2), and flat at very LVZ (<0.2 mV) (0.03 ± 0.01 m/s ΔCV PI1, 0.04 ± 0.02 m/s ΔCV PI2). Atropine did not change CV dynamics, while isoprenaline and GP stimulation resulted in greater CV slowing with rate. Isoprenaline (2.7 ± 1.1 increase/patient) and GP stimulation (2.8 ± 1.3 increase/patient) promoted CV heterogeneity, i.e. rate-dependent CV (RDCV) slowing sites. Most pivot points co-located to RDCV slowing sites (80.2%). Isoprenaline (1.3 ± 1.1 pivot increase/patient) and GP stimulation (1.5 ± 1.1 increase/patient) also enhanced the number of pivot points identified.

CONCLUSION

Atrial CV dynamics is affected by fibrosis burden and influenced by autonomic modulation which enhances CV heterogeneity and distribution of pivot points. This study provides further insight into the impact of autonomic remodelling in AF.

Conduction velocity mapping in atrial fibrillation using omnipolar technology

BACKGROUND

Recent studies have shown that atrial slow conduction velocity (CV) is associated with the perpetuation of atrial fibrillation (AF). However, the criteria of CV measurement have not been standardized. The aim of this study was to evaluate the relationship between the slow CV area (SCVA) measured by novel omnipolar technology (OT) and AF recurrence.

METHODS

This study included 90 patients with AF who underwent initial pulmonary vein isolation (PVI). The segmented surface area of the SCVA was measured by left atrial (LA) electrophysiological mapping using OT before the PVI. The proportion of the SCVA at each cutoff value of CV (from < 0.6 to < 0.9 m/s) was compared between the patients with and without AF recurrence.

RESULTS

During a mean follow-up period of 516 ± 197 days, the recurrence of AF after the initial PVI was observed in 23 (25.5%) patients. In patients with AF recurrence, the proportion of the SCVA in the LA posterior, LA appendage (LAA), and LA anterior were significantly higher than those without AF recurrence. The multivariate analysis indicated that the proportion of the low voltage area and the SCVA in the LA anterior (local CV < 0.7 m/s) were independent predictors of AF recurrence (hazard ratio [HR], 1.07; 95% confidence interval [CI], 1.01-1.14; p = 0.03; HR, 1.40; 95% CI, 1.07-1.83; p = 0.01, respectively).

CONCLUSION

By evaluating the local CV using OT, it was indicated that SCVA with CV < 0.7 m/s in the LA anterior is strongly associated with AF recurrence after PVI.

Characterization of airborne particulate matter and its toxic and proarrhythmic effects: A case study in Aburrá Valley, Colombia

Particle matter (PM) is a complex mixture of particles suspended in the air, mainly caused by fuel combustion from vehicles and industry, and has been related to pulmonary and cardiovascular diseases. The Metropolitan Area of Aburrá Valley in Colombia is the second most populous urban agglomeration in the country and the third densest in the world, composed of ten municipalities. Examining the physicochemical properties of PM is crucial in comprehending its composition and its effects on human health, as it varies based on the socioeconomic dynamics specific to each city. This study characterized the PM collected from the north, south, and central zones to evaluate its chemical composition and morphology. Different elements such as silicon, carbon, aluminum, potassium, calcium, sodium, iron, magnesium, and copper and the presence of unburned fuel, motor oil, and silicon fibers were identified. In vitro and in silico studies were conducted to evaluate the toxicity of the PM, and it was found that the PM collected from the central zone had the greatest impact on cell viability and caused DNA damage. The in silico study demonstrated that PM has concentration-dependent proarrhythmic effects, reflected in an action potential duration shortening and an increased number of reentries, which may contribute to the development of cardiac arrhythmias. Overall, the results suggest that the size and chemical composition of ambient PM can induce toxicity and play an important role in the generation of arrhythmias.

What determines the optimal pharmacological treatment of atrial fibrillation? Insights from in silico trials in 800 virtual atria

The best pharmacological treatment for each atrial fibrillation (AF) patient is unclear. We aim to exploit AF simulations in 800 virtual atria to identify key patient characteristics that guide the optimal selection of anti-arrhythmic drugs. The virtual cohort considered variability in electrophysiology and low voltage areas (LVA) and was developed and validated against experimental and clinical data from ionic currents to ECG. AF sustained in 494 (62%) atria, with large inward rectifier K+ current (IK1 ) and Na+ /K+ pump (INaK ) densities (IK1 0.11 ± 0.03 vs. 0.07 ± 0.03 S mF-1 ; INaK 0.68 ± 0.15 vs. 0.38 ± 26 S mF-1 ; sustained vs. un-sustained AF). In severely remodelled left atrium, with LVA extensions of more than 40% in the posterior wall, higher IK1 (median density 0.12 ± 0.02 S mF-1 ) was required for AF maintenance, and rotors localized in healthy right atrium. For lower LVA extensions, rotors could also anchor to LVA, in atria presenting short refractoriness (median L-type Ca2+ current, ICaL , density 0.08 ± 0.03 S mF-1 ). This atrial refractoriness, modulated by ICaL and fast Na+ current (INa ), determined pharmacological treatment success for both small and large LVA. Vernakalant was effective in atria presenting long refractoriness (median ICaL density 0.13 ± 0.05 S mF-1 ). For short refractoriness, atria with high INa (median density 8.92 ± 2.59 S mF-1 ) responded more favourably to amiodarone than flecainide, and the opposite was found in atria with low INa (median density 5.33 ± 1.41 S mF-1 ). In silico drug trials in 800 human atria identify inward currents as critical for optimal stratification of AF patient to pharmacological treatment and, together with the left atrial LVA extension, for accurately phenotyping AF dynamics. KEY POINTS: Atrial fibrillation (AF) maintenance is facilitated by small L-type Ca2+ current (ICaL ) and large inward rectifier K+ current (IK1 ) and Na+ /K+ pump. In severely remodelled left atrium, with low voltage areas (LVA) covering more than 40% of the posterior wall, sustained AF requires higher IK1 and rotors localize in healthy right atrium. For lower LVA extensions, rotors can also anchor to LVA, if the atria present short refractoriness (low ICaL ) Vernakalant is effective in atria presenting long refractoriness (high ICaL ). For short refractoriness, atria with fast Na+ current (INa ) up-regulation respond more favourably to amiodarone than flecainide, and the opposite is found in atria with low INa . The inward currents (ICaL and INa ) are critical for optimal stratification of AF patient to pharmacological treatment and, together with the left atrial LVA extension, for accurately phenotyping AF dynamics.

Personalized biomechanical insights in atrial fibrillation: opportunities & challenges

INTRODUCTION

Atrial fibrillation (AF) is an increasingly prevalent and significant worldwide health problem. Manifested as an irregular atrial electrophysiological activation, it is associated with many serious health complications. AF affects the biomechanical function of the heart as contraction follows the electrical activation, subsequently leading to reduced blood flow. The underlying mechanisms behind AF are not fully understood, but it is known that AF is highly correlated with the presence of atrial fibrosis, and with a manifold increase in risk of stroke.

AREAS COVERED

In this review, we focus on biomechanical aspects in atrial fibrillation, current and emerging use of clinical images, and personalized computational models. We also discuss how these can be used to provide patient-specific care.

EXPERT OPINION

Understanding the connection betweenatrial fibrillation and atrial remodeling might lead to valuable understanding of stroke and heart failure pathophysiology. Established and emerging imaging modalities can bring us closer to this understanding, especially with continued advancements in processing accuracy, reproducibility, and clinical relevance of the associated technologies. Computational models of cardiac electromechanics can be used to glean additional insights on the roles of AF and remodeling in heart function.

Experimental study on the effect of chlorhexidine gluconate (CG)-induced atrial fibrillation on renal water and sodium metabolism

To construct an animal model of atrial fibrillation and observe the effect of acute atrial fibrillation on renal water and sodium metabolism in mice. A total of 20 C57 mice were randomly assigned to 2 groups (n = 10/group): control group (CON) and atrial fibrillation group (AF). The mice model of atrial fibrillation was induced by chlorhexidine gluconate (CG) in combination with transesophageal atrial spacing. The urine of the two groups of mice was collected, and then we calculate the urine volume and urine sodium content. The expression of TGF-β and type III collagen in the atrial myocardium of the two groups was detected by immunohistochemistry and Western Blot. The levels of CRP and IL-6 in blood were observed by ELISA, and the NF-κB, TGF-β, collagen type III, AQP2, AQP3, AQP4, ENaC-β, ENaC-γ, SGK1 and NKCC proteins in the kidneys of the two groups of mice was observed by Western Blot. Compared with CON, the expression of TGF-β and type III collagen in the atrial myocardium of the mice in AF were increased, the levels of CRP and IL-6 in the blood in AF were increased, and the renal NF-κB, TGF-β, type III collagen AQP2, AQP3, ENaC-β, ENaC-γ, SGK1 and NKCC protein expression in AF were up-regulated. The level of urine volume and urine sodium content in AF were significantly reduced. In the acute attack of atrial fibrillation, the formation of renal inflammatory response and fibrosis is activated, and the renal water and sodium metabolism is hindered, which is related to the up-regulated of the expressions of renal NKCC, ENaC and AQPs.

Cellular electrophysiological effects of botulinum toxin A on neonatal rat cardiomyocytes and on cardiomyocytes derived from human-induced pluripotent stem cells

Botulinum toxin A is a well-known neurotransmitter inhibitor with a wide range of applications in modern medicine. Recently, botulinum toxin A preparations have been used in clinical trials to suppress cardiac arrhythmias, especially in the postoperative period. Its antiarrhythmic action is associated with inhibition of the nervous system of the heart, but its direct effect on heart tissue remains unclear. Accordingly, we investigate the effect of botulinum toxin A on isolated cardiac cells and on layers of cardiac cells capable of conducting excitation. Cardiomyocytes of neonatal rat pups and human cardiomyocytes obtained through cell reprogramming were used. A patch-clamp study showed that botulinum toxin A inhibited fast sodium currents and L-type calcium currents in a dose-dependent manner, with no apparent effect on potassium currents. Optical mapping showed that in the presence of botulinum toxin A, the propagation of the excitation wave in the layer of cardiac cells slows down sharply, conduction at high concentrations becomes chaotic, but reentry waves do not form. The combination of botulinum toxin A with a preparation of chitosan showed a stronger inhibitory effect by an order of magnitude. Further, the inhibitory effect of botulinum toxin A is not permanent and disappears after 12 days of cell culture in a botulinum toxin A-free medium. The main conclusion of the work is that the antiarrhythmic effect of botulinum toxin A found in clinical studies is associated not only with depression of the nervous system but also with a direct effect on heart tissue. Moreover, the combination of botulinum toxin A and chitosan reduces the effective dose of botulinum toxin A.

Matrix Metalloproteinases in Cardioembolic Stroke: From Background to Complications

Matrix metalloproteinases (MMPs) are endopeptidases participating in physiological processes of the brain, maintaining the blood-brain barrier integrity and playing a critical role in cerebral ischemia. In the acute phase of stroke activity, the expression of MMPs increase and is associated with adverse effects, but in the post-stroke phase, MMPs contribute to the process of healing by remodeling tissue lesions. The imbalance between MMPs and their inhibitors results in excessive fibrosis associated with the enhanced risk of atrial fibrillation (AF), which is the main cause of cardioembolic strokes. MMPs activity disturbances were observed in the development of hypertension, diabetes, heart failure and vascular disease enclosed in CHA₂DS₂VASc score, the scale commonly used to evaluate the risk of thromboembolic complications risk in AF patients. MMPs involved in hemorrhagic complications of stroke and activated by reperfusion therapy may also worsen the stroke outcome. In the present review, we briefly summarize the role of MMPs in the ischemic stroke with particular consideration of the cardioembolic stroke and its complications. Moreover, we discuss the genetic background, regulation pathways, clinical risk factors and impact of MMPs on the clinical outcome.

Consequences and Mechanisms of Left Atrium Remodeling in Aging Rabbits

To investigate the consequences and mechanisms of myocardium remodeling of aging left atrium, we analyzed the main cardiac electrophysiological parameters such as rest membrane potential, action potential amplitude, maximum rate of action potential increase (max dV/dt), action potential plateau, and 30, 50, and 90% action potential duration (APD₃₀, APD₅₀, and APD₉₀, respectively), as well as the inducibility and duration of atrial arrhythmias in adult and aging rabbits. L-type calcium current was also recorded. The collagen content in the myocardium and ultrastructure of left atrial cells were also studied. Significant changes were detected in the electrophysiological parameters and structure in aged left atrium, which can contribute to atrial susceptibility to arrhythmia in aged rabbits.

Coronary sinus electrogram characteristics predict termination of AF with ablation and long-term clinical outcome

INTRODUCTION

Markers predicting atrial fibrillation (AF) termination and freedom from AF/atrial tachycardia (AT) has been proposed. This study aimed to evaluate the role of novel coronary sinus (CS) electrogram characteristics in predicting the acute ablation response and freedom from AF/AT during follow-up.

METHODS

Patients undergoing ablation for persistent AF as part of the Stochastic Trajectory Analysis of Ranked signals mapping study were included. Novel CS electrogram characteristics including CS cycle length variability (CLV) and CS activation pattern stability (APS) and proportion of low voltage zones (LVZs) were reviewed as potential predictors for AF termination on ablation and freedom from AF/AT during follow-up. The relationship between localized driver characteristics and CS electrogram characteristics was also assessed.

RESULTS

Sixty-five patients were included. AF termination was achieved in 51 patients and 80% of patients were free from AF/AT during a follow-up of 29.5 ± 3.7 months. CS CLV of <30 ms, CS APS of ≥30% and proportion of LVZ < 30% showed high diagnostic accuracy in predicting AF termination on ablation and freedom from AF/AT during follow-up (CS CLV odds ratio [OR] 25.6, area under the curve [AUC] 0.91; CS APS OR 15.9, AUC 0.94; proportion of LVZs OR 21.4, AUC 0.88). These markers were independent predictors of AF termination on ablation and AF/AT recurrence during follow-up. Ablation of a smaller number of drivers that demonstrate greater dominance strongly correlate with greater CS organization.

CONCLUSION

Novel CS electrogram characteristics were independent predictors of AF termination and AF/AT recurrence during follow-up. These markers can potentially aid in predicting outcomes and guide ablation and follow-up strategies.

Driver characteristics associated with structurally and electrically remodeled atria in persistent atrial fibrillation

Background

Recent studies suggest persistent atrial fibrillation (AF) is maintained by localized focal or rotational electrical activations termed drivers.

Objective

The purpose of this study was to evaluate how left atrial (LA) dilation and time in AF impact persistent AF mechanisms.

Methods

Patients with persistent AF <2 years underwent electrocardiographic image mapping. Potential drivers (PDs) were defined as rotational wavefront activity ≥1.5 revolutions or focal activations. Distribution of PDs was recorded using an 18-segment model.

Results

One hundred patients were enrolled (age 61.3 ± 12.1 years). Of these patients, 47 were hypertensive, 14 had diabetes mellitus, and 10 had ischemic heart disease. AF duration was 8 [5-15] months. Median LA diameter was 39 [33-43] mm. Although LA dimensions did not correlate with overall PD burden or distribution, there was a modest correlation between increasing LA area (r = 0.235; P = .024) and LA volume (r = 0.216; P = .039) with proportion of PDs that were rotational. Although time in AF did not correlate with overall PD burden or distribution, there was a correlation between time in AF and the number of focal PDs (r = 0.203; P = .044). Female gender, increasing age, and hypertension also were associated with an increase in focal PDs.

Conclusion

This is the first study to demonstrate different AF mechanisms in patient subgroups. Greater understanding of patient-specific AF mechanisms may facilitate a tailored approach to AF mapping and ablation.

A systematic review and meta-analysis of the safety and efficacy of left atrial substrate modification in atrial fibrillation patients with low voltage areas

Background

The left atrial low-voltage areas (LVAs) are associated with atrial fibrosis; however, it is not clear how the left atrial LVAs affect the recurrence of arrhythmias after catheter ablation, and the efficacy and safety of the left atrial substrate modification based on LVAs as a strategy for catheter ablation of atrial fibrillation (AF) are not evident for AF patients with LVAs.

Methods

We performed a systematic search to compare the arrhythmia recurrence in AF patients with and without LVAs after conventional ablation and arrhythmia recurrence in LVAs patients after conventional ablation with and without substrate modification based on LVAs.

Result

A total of 6 studies were included, involving 1,175 patients. The arrhythmia recurrence was higher in LVA patients after conventional ablation (OR: 5.14, 95% CI: [3.11, 8.49]; P < 0.00001). Additional LVAs substrate modification could improve the freedom of arrhythmia in LVAs patients after the first procedure (OR: 0.30, 95% CI: [0.15, 0.62]; P = 0.0009). However, there was no significant difference after multiple procedures (P = 0.19). The procedure time (MD: 26.61, 95% CI [15.79, 37.42]; P < 0.00001) and fluoroscopy time (MD: 6.90, 95% CI [4.34, 9.47]; P < 0.00001) in LVAs patients with additional LVAs substrate modification were significantly increased compared to LVAs patients' without substrate modification. Nevertheless, there were no higher LVAs substrate modification-related complications (P = 0.93) between LVAs patients with and without additional LVAs substrate modification. In the subgroup analysis, the additional LVAs substrate modification reduced the risk of arrhythmia recurrence in LVAs patients during the follow-up time, which was 12 months (OR: 0.32, 95% CI (0.17, 0.58); P = 0.002), and box isolation (OR: 0.37, 95% CI (0.20, 0.69); P = 0.002) subgroups, but the type of AF, follow up >12 months and homogenization subgroups were not statistically significant. Trial sequential analysis shows conclusive evidence for the LVAs ablation.

Conclusion

This study has shown that LVAs could improve the risk of arrhythmia recurrence in AF patients after conventional ablation. And additional LVAs substrate modification after conventional ablation could increase the freedom of arrhythmia recurrence in LVAs patients. Interestingly, the box isolation approach appeared more promising.

Systematic review registration

[http://www.crd.york.ac.uk/prospero], identifier [CRD42021239277].

Atrial Fibrosis, Ischaemic Stroke and Atrial Fibrillation

Atrial fibrosis is an important component of the arrhythmic substrate in AF. Evidence suggests that atrial fibrosis also plays a role in increasing the risk of stroke in patients with the arrhythmia. Patients with embolic stroke of undetermined source (ESUS), who are suspected to have AF but are rarely shown to have it, frequently demonstrate evidence of atrial fibrosis; measured using late-gadolinium enhancement MRI, this manifests as atrial remodelling encompassing structural, functional and electrical properties. In this review, the authors discuss the available evidence linking atrial disease, including fibrosis, with the risk of ischaemic stroke in AF, as well as in the ESUS population, in whom it has been linked to recurrent stroke and new-onset AF. They also discuss the implications of this association on future research that may elucidate the mechanism of stroke and stroke prevention strategies in the AF and ESUS populations.

P wave duration ≥150 ms predicts poor left atrial function and ablation outcomes in non-paroxysmal atrial fibrillation

BACKGROUND

It remains unknown whether P wave duration (PWD) ≥ 150 ms measured after extensive radiofrequency catheter ablation (RFCA) can identify non-paroxysmal atrial fibrillation (non-PAF) patients at increased risk of atrial tachyarrhythmia recurrence. We investigated the predicting power of PWD and its association with left atrial (LA) reverse remodeling in patients with non-PAF undergoing pulmonary vein isolation with LA linear ablation.

METHODS

We retrospectively evaluated 136 patients who underwent RFCA for drug-refractory non-PAF. Electroanatomic mapping was acquired during AF. Low-voltage area (LVA) was defined as an area with bipolar voltage ≤0.5 mV. Electrocardiography and echocardiography were performed during sinus rhythm 1 day and 3 months after RFCA. PWD was measured using amplified 12‑lead electrocardiography. Prolonged PWD was defined as maximum PWD ≥ 150 ms.

RESULTS

Over a mean follow-up duration of 48 ± 35 months, 28 patients experienced atrial tachyarrhythmia recurrence. PWD was positively correlated with LVA (r = 0.527, p < 0.001) and inversely correlated with LA emptying fraction (r = -0.399, p < 0.001). PWD was shortened and LA emptying fraction (LAEF) was increased in patients without atrial tachyarrhythmia recurrence during follow-up. Atrial tachyarrhythmia-free survival was significantly more likely in patients without a prolonged PWD (83.5% vs 60.7%, p = 0.002). Multivariate analysis showed that LAEF and PWD were independent predictors of atrial tachyarrhythmia recurrence.

CONCLUSIONS

PWD ≥ 150 ms measured after RFCA can identify patients with non-PAF at increased risk of atrial tachyarrhythmia recurrence. PWD is correlated with LVA and LAEF and reflects LA reverse remodeling.

Atrial slow conduction develops and dynamically expands during premature stimulation in an animal model of persistent atrial fibrillation

Slow conduction areas and conduction block in the atria are considered pro-arrhythmic conditions. Studies examining the size and distribution of slow conduction regions in the context of persistent atrial fibrillation (AF) may help to develop improved therapeutic strategies for patients with AF. In this work, we studied the differences of size and number in slow conduction areas between control and persistent AF goats and the influence of propagation direction on the development of these pathological conduction areas. Epicardial atrial electrical activations from the left atrial roof were optically mapped with physiological pacing cycle lengths and for the shortest captured cycle lengths. The recordings were converted to local activation times and conduction velocity measures. Regions with slow conduction velocity (less than [Formula: see text]) were identified. The size of the connected regions and the number of non-connected regions were counted for propagation from different orthogonal directions. We found that regions of slow conduction significantly increases in our 15 persistent AF goat recordings in response to premature stimulation (24.4±4.3% increase to 36.6±4.4%, p < 0.001). This increase is driven by an increase of size from (3.70±0.89[mm2] to 6.36±0.91[mm2], p = 0.014) for already existing regions and not by generation of new slow conduction regions (11.6±1.8 vs. 13±1.9, p = 0.242). In 12 control goat recordings, no increase from baseline pacing to premature pacing was found. Similarly, size of the slow conduction areas and the count did not change significantly in control animals.

Classification of Left Atrial Diseased Tissue Burden Determined by Automated Voltage Analysis Predicts Outcomes after Ablation for Atrial Fibrillation

Background

The burden and persistence of atrial fibrillation (AF) have been associated with the presence and extent of left atrial (LA) fibrosis. Recent reports have implicated an association between the extent of LA fibrosis and the outcome of pulmonary vein isolation (PVI). We aimed to analyse the value of an automated scar quantification method in the prediction of success following PVI.

Methods

One hundred and nine consecutive patients undergoing PVI for paroxysmal or persistent AF were included in our observational study with a 2-year follow-up. Prior to PVI, patients underwent high-definition LA electroanatomical mapping, and scar burden was quantified by automated software (Voltage Histogram Analysis, CARTO 3, Biosense Webster), then classified into 4 subgroups (Dublin Classes I-IV). Recurrence rates were analysed on and off antiarrhythmic drug therapy (AAD), respectively.

Results

The overall success rate was 74% and 67% off AAD at 1- and 2-year follow-up, respectively. Patients with Dublin Class IV had significantly lower success rates (p = 0.008, off AAD). Dublin Class IV (OR = 2.27, p = 0.022, off AAD) and the presence of arrhythmia in the blanking period (OR = 3.28, p = 0.001, off AAD) were the only significant predictors of recurrence. The use of AAD did not affect these results.

Conclusions

We propose a classification of low voltage areas based on automated quantification by software during 3D mapping prior to PVI. Patients with high burden of low voltage areas (>31% of <0.5 mV, Dublin Class IV) have a higher risk of recurrence following PVI. Information gathered during electroanatomical mapping may have important prognostic value.

Ventricular fibrillation mechanism and global fibrillatory organization are determined by gap junction coupling and fibrosis pattern

AIMS

Conflicting data exist supporting differing mechanisms for sustaining ventricular fibrillation (VF), ranging from disorganized multiple-wavelet activation to organized rotational activities (RAs). Abnormal gap junction (GJ) coupling and fibrosis are important in initiation and maintenance of VF. We investigated whether differing ventricular fibrosis patterns and the degree of GJ coupling affected the underlying VF mechanism.

METHODS AND RESULTS

Optical mapping of 65 Langendorff-perfused rat hearts was performed to study VF mechanisms in control hearts with acute GJ modulation, and separately in three differing chronic ventricular fibrosis models; compact fibrosis (CF), diffuse fibrosis (DiF), and patchy fibrosis (PF). VF dynamics were quantified with phase mapping and frequency dominance index (FDI) analysis, a power ratio of the highest amplitude dominant frequency in the cardiac frequency spectrum. Enhanced GJ coupling with rotigaptide (n = 10) progressively organized fibrillation in a concentration-dependent manner; increasing FDI (0 nM: 0.53 ± 0.04, 80 nM: 0.78 ± 0.03, P < 0.001), increasing RA-sustained VF time (0 nM: 44 ± 6%, 80 nM: 94 ± 2%, P < 0.001), and stabilized RAs (maximum rotations for an RA; 0 nM: 5.4 ± 0.5, 80 nM: 48.2 ± 12.3, P < 0.001). GJ uncoupling with carbenoxolone progressively disorganized VF; the FDI decreased (0 µM: 0.60 ± 0.05, 50 µM: 0.17 ± 0.03, P < 0.001) and RA-sustained VF time decreased (0 µM: 61 ± 9%, 50 µM: 3 ± 2%, P < 0.001). In CF, VF activity was disorganized and the RA-sustained VF time was the lowest (CF: 27 ± 7% vs. PF: 75 ± 5%, P < 0.001). Global fibrillatory organization measured by FDI was highest in PF (PF: 0.67 ± 0.05 vs. CF: 0.33 ± 0.03, P < 0.001). PF harboured the longest duration and most spatially stable RAs (patchy: 1411 ± 266 ms vs. compact: 354 ± 38 ms, P < 0.001). DiF (n = 11) exhibited an intermediately organized VF pattern, sustained by a combination of multiple-wavelets and short-lived RAs.

CONCLUSION

The degree of GJ coupling and pattern of fibrosis influences the mechanism sustaining VF. There is a continuous spectrum of organization in VF, ranging between globally organized fibrillation sustained by stable RAs and disorganized, possibly multiple-wavelet driven fibrillation with no RAs.

Using machine learning to identify local cellular properties that support re-entrant activation in patient-specific models of atrial fibrillation

AIMS

Atrial fibrillation (AF) is sustained by re-entrant activation patterns. Ablation strategies have been proposed that target regions of tissue that may support re-entrant activation patterns. We aimed to characterize the tissue properties associated with regions that tether re-entrant activation patterns in a validated virtual patient cohort.

METHODS AND RESULTS

Atrial fibrillation patient-specific models (seven paroxysmal and three persistent) were generated and validated against local activation time (LAT) measurements during an S1-S2 pacing protocol from the coronary sinus and high right atrium, respectively. Atrial models were stimulated with burst pacing from three locations in the proximity of each pulmonary vein to initiate re-entrant activation patterns. Five atria exhibited sustained activation patterns for at least 80 s. Models with short maximum action potential durations (APDs) were associated with sustained activation. Phase singularities were mapped across the atria sustained activation patterns. Regions with a low maximum conduction velocity (CV) were associated with tethering of phase singularities. A support vector machine (SVM) was trained on maximum local conduction velocity and action potential duration to identify regions that tether phase singularities. The SVM identified regions of tissue that could support tethering with 91% accuracy. This accuracy increased to 95% when the SVM was also trained on surface area.

CONCLUSION

In a virtual patient cohort, local tissue properties, that can be measured (CV) or estimated (APD; using effective refractory period as a surrogate) clinically, identified regions of tissue that tether phase singularities. Combing CV and APD with atrial surface area further improved the accuracy in identifying regions that tether phase singularities.

Pathophysiology and therapeutic relevance of PI3K(p110α) protein in atrial fibrillation: A non-interventional molecular therapy strategy

Genetically modified animal studies have revealed specific expression patterns and unequivocal roles of class I PI3K isoenzymes. PI3K(p110α), a catalytic subunit of class I PI3Ks is ubiquitously expressed and is well characterised in the cardiovascular system. Given that genetic inhibition of PI3K(p110α) causes lethal phenotype embryonically, the catalytic subunit is critically important in housekeeping and biological processes. A growing number of studies underpin crucial roles of PI3K(p110α) in cell survival, proliferation, hypertrophy and arrhythmogenesis. While the studies provide great insights, the precise mechanisms involved in PI3K(p110α) hypofunction and atrial fibrillation (AF) are not fully known. AF is a well recognised clinical problem with significant management limitations. In this translational review, we attempted a narration of PI3K(p110α) hypofunction in the molecular basis of AF pathophysiology. We sought to cautiously highlight the relevance of this molecule in the therapeutic approaches for AF management per se (i.e without conditions associate with cell proliferation, like cancer), and in mitigating effects of clinical risk factors in atrial substrate formation leading to AF progression. We also considered PI3K(p110α) in AF gene association, with the aim of identifying mechanistic links between the ever increasingly well-defined genetic loci (regions and genes) and AF. Such mechanisms will aid in identifying new drug targets for arrhythmogenic substrate and AF.

Focal and pseudo/rotational activations in human atrial fibrillation defined with automated periodicity mapping

INTRODUCTION

Defining atrial fibrillation (AF) wave propagation is challenging unless local signal features are discrete or periodic. Periodic focal or rotational activity may identify AF drivers. Our objective was to characterize AF propagation at sites with periodic activation to evaluate the prevalence and relationship between focal and rotational activation.

METHODS

We included 80 patients (61 ± 10 years, persistent AF 49%) from the FaST randomized trial that compared the efficacy of adjunctive focal site ablation versus pulmonary vein isolation. Patients underwent left atrial (LA) activation mapping with a 20-pole circular catheter during spontaneous or induced AF. Five-second bipolar and unipolar electrograms in AF were analyzed. Periodic sites were identified by spectral analysis of the bipolar electrogram. Activation maps of periodic sites were constructed using an automated, validated tracking algorithm, and classified into three patterns: focal sites (FS), rotation (RO), or pseudo-rotation (pRO).

RESULTS

The most common propagation pattern at periodic sites was FS for 5-s in all patients (4.9 ± 1.9 per patient). RO and pRO were observed in two and seven patients, respectively, but were all transient (3-5 cycles). Activation from a FS evolved into transient RO/pRO in five patients. No patient had autonomous RO/pRO activations. Patients with RO/pRO had greater LA surface area with periodicity (78 ± 7 vs. 63 ± 16%, p = .0002) and shorter LA periodicity CL (166 ± 10 vs. 190±28 ms, p = .0001) than the rest.

CONCLUSION

Using automated, regional AF periodicity mapping, FS is more prevalent and temporally stable than RO/pRO. Most RO/pRO evolve from neighboring FS. These findings and their implications for AF maintenance require verification with global, panoramic mapping.

A practical guide for investigating cardiac physiology using living myocardial slices

Ex vivo multicellular preparations are essential tools to study tissue physiology. Among them, the recent methodological and technological developments in living myocardial slices (LMS) are attracting increasing interest by the cardiac research field. Despite this, this research model remains poorly perceived and utilized by most research laboratories. Here, we provide a practical guide on how to use LMS to interrogate multiple aspects of cardiac function, structure and biochemistry. We discuss issues that should be considered to conduct successful experiments, including experimental design, sample preparation, data collection and analysis. We describe how laboratory setups can be adapted to accommodate and interrogate this multicellular research model. These adaptations can often be achieved at a reasonable cost with off-the-shelf components and operated reliably using well-established protocols and freely available software, which is essential to broaden the utilization of this method. We will also highlight how current measurements can be improved to further enhance data quality and reliability to ensure inter-laboratory reproducibility. Finally, we summarize the most promising biomedical applications and envision how living myocardial slices can lead to further breakthroughs.

Dynamic Local Activation Time Mapping in Heavily Scarred Left Atrium and Persistent Atrial Fibrillation: A proof of concept case report

We report the case of a 68-year-old male, presenting with persistent atrial fibrillation (Pe AF) refractory to anti arrhythmic medications and cardioversion, on a background history of ischaemic heart disease. Pre and post standard pulmonary vein isolation (PVI), left atrial (LA) voltageanalyses wereperformed, followed by dynamic local activation time (DLAT) mapping in addition to focal activity identification.Thisdemonstrated a heavily scarred LA, and a number ofareas of focal activity. The patient remained in atrial fibrillation (AF) post rotor (focal activity) targeting,howevernotable changes in AF cycle length (CL)werenotedandslowed by an average of 25.3 milliseconds. Comparison between DLAT mappingpre and post PVI were anatomically similar but not identical. The anatomical distribution of heavy scar areas in the LA did not correspond to the DLAT areas of interest. The patient subsequentlyremained in normal sinus rhythm (SR) for 6 monthson a low dose Beta blockade in a short follow up period. DLAT mapping and its characteristics in heavily scarred LA are reported in this case.

Atrial Myopathy Underlying Atrial Fibrillation

While AF most often occurs in the setting of atrial disease, current assessment and treatment of patients with AF does not focus on the extent of the atrial myopathy that serves as the substrate for this arrhythmia. Atrial myopathy, in particular atrial fibrosis, may initiate a vicious cycle in which atrial myopathy leads to AF, which in turn leads to a worsening myopathy. Various techniques, including ECG, plasma biomarkers, electroanatomical voltage mapping, echocardiography, and cardiac MRI, can help to identify and quantify aspects of the atrial myopathy. Current therapies, such as catheter ablation, do not directly address the underlying atrial myopathy. There is emerging research showing that by targeting this myopathy we can help decrease the occurrence and burden of AF.

Ripple map guided catheter ablation targeting abnormal atrial potentials during sinus rhythm for non-paroxysmal atrial fibrillation

BACKGROUND

Abnormal atrial potential (AAP) during sinus rhythm may be a critical ablation target for atrial fibrillation. However, the assessment of local electrograms throughout the left atrium is difficult. Thus, we sought to investigate the effectiveness of Ripple map guided AAP ablation.

METHODS AND RESULTS

AAP areas were determined by Ripple mapping on the CARTO system in 35 patients (Ripple group) by marking the area where small deflections persisted after the first deflection wavefront had passed. Following pulmonary vein isolation, AAP areas were ablated. If AAP areas were located on the left atrial posterior wall, the posterior wall was isolated. The outcome of this approach was compared with that of 66 patients who underwent an empirical linear ablation approach (control group). There were no differences in patient characteristics between the groups. The total radiofrequency application time and procedure time were shorter in the Ripple group than in the control group (radiofrequency application time, 48 ± 14 minutes vs 61 ± 13 minutes, P < .001; procedure time, 205 ± 30 minutes vs 221 ± 27 minutes, P = .013). Gastroparesis occurred in one patient in each group (P = .645), but in both cases this was relieved with conservative therapy. Kaplan-Meier analysis revealed that rate of freedom from atrial arrhythmia was higher in the Ripple group than in the control group (91% vs 74% during the 12 months' follow up; P = .040).

CONCLUSION

Ripple map guided AAP ablation effectively suppressed atrial arrhythmia in patients with non-paroxysmal AF.

Drivers in AF colocate to sites of electrogram organization and rapidity: Potential synergy between spectral analysis and STAR mapping approaches in prioritizing drivers for ablation

INTRODUCTION

Stochastic trajectory analysis of ranked signals (STAR) mapping has recently been used to ablate persistent atrial fibrillation (AF) with high rates of AF termination and long-term freedom from AF in small, single-arm studies. We hypothesized that rapidity and organization markers would correlate with early sites of activation (ESA).

METHODS

Patients undergoing persistent AF ablation as part of the STAR mapping study were included. Five-minute unipolar basket recordings used to create STAR maps were used to determine the minimum-cycle length (Min-CL) and CL variability (CLV) at each electrode to identify the site of the fastest Min-CL and lowest CLV across the left atrium (LA). The location of ESA targeted with ablation was compared with these sites. Dominant frequency was assessed at ESA and compared with that of neighboring electrodes to assess for regional gradients.

RESULTS

Thirty-two patients were included with 83 ESA ablated, with an ablation response at 73 sites (24 AF termination and 49 CL slowing ≥30 ms). Out of these, 54 (74.0%) and 56 (76.7%) colocated to sites of fastest Min-CL and lowest CLV, respectively. Regional CL and frequency gradients were demonstrable at majority of ESA. ESA colocating to sites of fastest Min-CL and lowest CLV were more likely to terminate AF with ablation (odds ratio, 34 and 29, respectively, P = .02). These showed a moderate sensitivity (74.0% Min-CL and 75.3% CLV) and specificity (66.7% Min-CL and 76.9% CLV) in predicting ESA with an ablation response.

CONCLUSIONS

ESA correlate with rapidity and organization markers. Further work is needed to clarify any role for spectral analysis in prioritizing driver ablation.

Visualization of Inflammation After Cryoballoon Ablation in Atrial Fibrillation Patients - Protocol for Proof-of-Concept Feasibility Trial

Background: Atrial fibrosis and inflammation play important roles in perpetuating and initiating atrial fibrillation (AF). Although the fibrotic area can be visualized as a delayed enhancement area on late gadolinium enhancement magnetic resonance imaging (LGE-MRI), atrial inflammation has not yet been visualized on any imaging modality. We describe the protocol for a feasibility study to visualize atrial inflammation on positron emission tomography/MRI (PET/MRI).

Methods and Results: This is a single-arm, prospective, open-label proof-of concept trial, involving AF patients after cryoballoon ablation (CBA). A total of 30 paroxysmal AF patients will be enrolled and undergo simultaneous PET/MRI for the assessment of regional ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) uptake 1 day after the CBA. Furthermore, LGE-MRI will be performed before CBA, and at 1 and 4 weeks after assessing the regional LGE area. The main outcome measures will be (1) the feasibility of imaging inflammation in the left atrium on PET/MRI; and (2) the safety of the intervention.

Conclusions: There are few data on the visualization of atrial inflammation using PET/MRI. Establishing the visualization methodology will contribute to elucidating the fundamental histopathologic findings of the progress to fibrosis, and to the planning and execution of a larger definitive trial to test the usefulness of PET/MRI.

Challenges Associated with Interpreting Mechanisms of AF

Determining optimal treatment strategies for complex arrhythmogenesis in AF is confounded by the lack of consensus regarding the mechanisms causing AF. Studies report different mechanisms for AF, ranging from hierarchical drivers to anarchical multiple activation wavelets. Differences in the assessment of AF mechanisms are likely due to AF being recorded across diverse models using different investigational tools, spatial scales and clinical populations. The authors review different AF mechanisms, including anatomical and functional re-entry, hierarchical drivers and anarchical multiple wavelets. They then describe different cardiac mapping techniques and analysis tools, including activation mapping, phase mapping and fibrosis identification. They explain and review different data challenges, including differences between recording devices in spatial and temporal resolutions, spatial coverage and recording surface, and report clinical outcomes using different data modalities. They suggest future research directions for investigating the mechanisms underlying human AF.

Interatrial conduction times in paroxysmal atrial fibrillation patients with normal atrial volume and their correlation with areas of local prolonged bipolar electrograms

BACKGROUND

Recent evidence has shown that the presence of abnormal substrate can be demonstrated also among patients with "lone" AF.

OBJECTIVES

Interatrial conduction slowing is likely to characterize patients with paroxysmal atrial fibrillation (AF) and it could be correlated to the left atrium area of prolonged local bipolar endocardial electrograms.

METHODS

P-wave duration (PWD), amplified PWD and endocavitary interatrial conduction time (IACT), were analyzed in 60 patients; 30 undergoing de novo ablation for paroxysmal AF with normal atrial volumes and without any other cardiac disease and 30 of similar age undergoing electrophysiological study for atrioventricular nodal reentrant tachycardia or atrioventricular re- entrant tachycardia. In patients with AF, voltage maps and local bipolar electrograms (LBE) duration map were evaluated.

RESULTS

Although PWD was <120 ms in 28 patients with AF and in 29 controls, patients with AF exhibited longer PWD, amplified-PWD and IACT. Although low-voltage areas (<0.5 mV) were not found in the study population, 28 of them demonstrated areas with LBE longer than 60 ms. These LBE were found mainly in the roof of the left atrium and their extension was correlated to IACT (R = 0.51, p = 0.004). IACT >135.5 ms identified the subjects who experienced AF with 90% sensitivity and 97% specificity.

CONCLUSION

A subclinical interatrial conduction disturbance is demonstrable in subjects with paroxysmal AF and normal left atrial volume. IACT has a good correlation to the areas of abnormal LBE in the left atrium. IACT >135 ms identified subjects who have experienced AF.

The stationary wavelet transform as an efficient reductor of powerline interference for atrial bipolar electrograms in cardiac electrophysiology

OBJECTIVE

The most relevant source of signal contamination in the cardiac electrophysiology (EP) laboratory is the ubiquitous powerline interference (PLI). To reduce this perturbation, algorithms including common fixed-bandwidth and adaptive-notch filters have been proposed. Although such methods have proven to add artificial fractionation to intra-atrial electrograms (EGMs), they are still frequently used. However, such morphological alteration can conceal the accurate interpretation of EGMs, specially to evaluate the mechanisms supporting atrial fibrillation (AF), which is the most common cardiac arrhythmia. Given the clinical relevance of AF, a novel algorithm aimed at reducing PLI on highly contaminated bipolar EGMs and, simultaneously, preserving their morphology is proposed.

APPROACH

The method is based on the wavelet shrinkage and has been validated through customized indices on a set of synthesized EGMs to accurately quantify the achieved level of PLI reduction and signal morphology alteration. Visual validation of the algorithm's performance has also been included for some real EGM excerpts.

MAIN RESULTS

The method has outperformed common filtering-based and wavelet-based strategies in the analyzed scenario. Moreover, it possesses advantages such as insensitivity to amplitude and frequency variations in the PLI, and the capability of joint removal of several interferences.

SIGNIFICANCE

The use of this algorithm in routine cardiac EP studies may enable improved and truthful evaluation of AF mechanisms.

Ablation in Persistent Atrial Fibrillation Using Stochastic Trajectory Analysis of Ranked Signals (STAR) Mapping Method

OBJECTIVES

The aim of this study was to demonstrate that a stochastic vector-based mapping approach could guide ablation of atrial fibrillation (AF) drivers as evidenced by ablation response and long-term follow-up outcomes.

BACKGROUND

The optimal method for mapping and ablation of AF drivers is yet to be defined.

METHODS

Patients undergoing persistent AF ablation were recruited. Patients underwent pulmonary vein isolation (PVI) with further ablation guided by the stochastic trajectory analysis of ranked signals (STAR) mapping method. The proportion of the time an electrode's activation was seen to precede its neighboring electrodes activation was used to determine early sites of activation (ESA). A positive ablation response at ESA was defined as AF termination or cycle length slowing of ≥30 ms. Clinical outcome was defined as recurrence of AF/atrial tachycardia (AT) during a follow-up of 12 months.

RESULTS

Thirty-five patients were included (AF duration of 14.4 ± 5.3 months). After PVI, an average of 2.6 ± 0.8 ESA were ablated per patient with study-defined ablation response achieved in all patients. Of the 86 STAR maps created post-PVI, the same ESA was identified on 73.8 ± 26.1% of maps. ESA that resulted in AF termination were more likely to be identified on both pre- and post-PVI maps than those associated with cycle length slowing (23 of 24 vs. 16 of 49; p < 0.001). During a follow-up of 18.5 ± 3.7 months, 28 (80%) patients were free from AF/AT.

CONCLUSIONS

The ablation response at ESA suggests they may be drivers of AF. Ablation guided by STAR mapping produced a favorable clinical outcome and warrants testing through a randomized controlled trial. (Identification, Electro-mechanical Characterisation and Ablation of Driver Regions in Persistent Atrial Fibrillation [STAR MAPPING]; NCT02950844).

Development, in vitro validation and human application of a novel method to identify arrhythmia mechanisms: The stochastic trajectory analysis of ranked signals mapping method

Introduction

Methods and Results

Conclusions

A technique for measuring anisotropy in atrial conduction to estimate conduction velocity and atrial fibre direction

BACKGROUND

Cardiac conduction properties exhibit large variability, and affect patient-specific arrhythmia mechanisms. However, it is challenging to clinically measure conduction velocity (CV), anisotropy and fibre direction. Our aim is to develop a technique to estimate conduction anisotropy and fibre direction from clinically available electrical recordings.

METHODS

We developed and validated automated algorithms for estimating cardiac CV anisotropy, from any distribution of recording locations on the atrial surface. The first algorithm is for elliptical wavefront fitting to a single activation map (method 1), which works well close to the pacing location, but decreases in accuracy further from the pacing location (due to spatial heterogeneity in the conductivity and fibre fields). As such, we developed a second methodology for measuring local conduction anisotropy, using data from two or three activation maps (method 2: ellipse fitting to wavefront propagation velocity vectors from multiple activation maps).

RESULTS

Ellipse fitting to CV vectors from two activation maps (method 2) leads to an improved estimation of longitudinal and transverse CV compared to method 1, but fibre direction estimation is still relatively poor. Using three activation maps with method 2 provides accurate estimation, with approximately 70% of atrial fibres estimated within 20∘. We applied the technique to clinical activation maps to demonstrate the presence of heterogeneous conduction anisotropy, and then tested the effects of this conduction anisotropy on predicted arrhythmia dynamics using computational simulation.

CONCLUSIONS

We have developed novel algorithms for calculating CV and measuring the direction dependency of atrial activation to estimate atrial fibre direction, without the need for specialised pacing protocols, using clinically available electrical recordings.