Multimodal Examination of Atrial Fibrillation Substrate: Correlation of Left Atrial Bipolar Voltage Using Multi-Electrode Fast Automated Mapping, Point-by-Point Mapping, and Magnetic Resonance Image Intensity Ratio

Unipolar voltage electroanatomical mapping detects structural atrial remodeling identified by LGE-MRI

BACKGROUND

In atrial fibrillation (AF) management, understanding left atrial (LA) substrate is crucial. While both electroanatomical mapping (EAM) and late gadolinium enhancement MRI (LGE-MRI) are accepted methods for assessing the atrial substrate and are associated with ablation outcome, recent findings have highlighted discrepancies between low voltage areas (LVAs) in EAM and LGE-areas.

OBJECTIVE

Explore the relationship between LGE regions and unipolar and bipolar-LVAs utilizing multipolar high-density (HD) mapping.

METHODS

20 patients scheduled for AF ablation underwent pre-ablation LGE-MRI. LA segmentation was conducted using a deep learning approach, which subsequently generated a 3D mesh integrating the LGE data. HD-EAM was performed in sinus rhythm for each patient. The EAM map and LGE-MRI mesh were co-registered. LVAs were defined using voltage cut-offs of 0.5mV for bipolar and 2.5mV for unipolar. Correspondence between LGE-areas and LVAs in the LA was analyzed using confusion matrices and performance metrics.

RESULTS

A considerable 87.3% of LGE regions overlapped with unipolar-LVAs, compared to only 16.2% overlap observed with bipolar-LVAs. Across all performance metrics, unipolar-LVAs outperformed bipolar-LVAs in identifying LGE-areas [precision (78.6% vs. 61.1%); sensitivity (87.3% vs. 16.2%); F1 score (81.3% vs. 26.0%); accuracy (74.0% vs. 35.3%)].

CONCLUSION

Our findings demonstrate that unipolar-LVAs highly correlate with LGE regions. These findings support the integration of unipolar mapping alongside bipolar mapping into clinical practice. This would offer a nuanced approach to diagnose and manage atrial fibrillation by revealing critical insights into the complex architecture of the atrial substrate.

Practical approach for atrial cardiomyopathy characterization in patients with atrial fibrillation

Atrial fibrillation (AF) causes progressive structural and electrical changes in the atria that can be summarized within the general concept of atrial remodeling. In parallel, other clinical characteristics and comorbidities may also affect atrial tissue properties and make the atria susceptible to AF initiation and its long-term persistence. Overall, pathological atrial changes lead to atrial cardiomyopathy with important implications for rhythm control. Although there is general agreement on the role of the atrial substrate for successful rhythm control in AF, the current classification oversimplifies clinical management. The classification uses temporal criteria and does not establish a well-defined strategy to characterize the individual-specific degree of atrial cardiomyopathy. Better characterization of atrial cardiomyopathy may improve the decision-making process on the most appropriate therapeutic option. We review current scientific evidence and propose a practical characterization of the atrial substrate based on 3 evaluation steps starting with a clinical evaluation (step 1), then assess outpatient complementary data (step 2), and finally include information from advanced diagnostic tools (step 3). The information from each of the steps or a combination thereof can be used to classify AF patients in 4 stages of atrial cardiomyopathy, which we also use to estimate the success on effective rhythm control.

Left atrial volume affects the correlation of voltage map with magnetic resonance imaging

BACKGROUND

The low-voltage area detected by electroanatomic mapping (EAM) is a surrogate marker of left atrial fibrosis. However, the correlation between the EAM and late gadolinium enhancement magnetic resonance imaging (LGE-MRI) has been inconsistent among studies. This study aimed to investigate how LA size affects the correlation between EAM and LGE-MRI.

METHODS

High-density EAMs of the LA during sinus rhythm were collected in 22 patients undergoing AF ablation. The EAMs were co-registered with pre-ablation LGE-MRI models. Voltages in the areas with and without LGE were recorded. Left atrial volume index (LAVI) was calculated from MRI, and LAVI > 62 ml/m2 was defined as significant LA enlargement (LAE).

RESULTS

Atrial bipolar voltage negatively correlates with the left atrial volume index. The median voltages in areas without LGE were 1.1 mV vs 2.0 mV in patients with vs without significant LAE (p = 0.002). In areas of LGE, median voltages were 0.4 mV vs 0.8 mV in patients with vs without significant LAE (p = 0.02). A voltage threshold of 1.7 mV predicted atrial LGE in patients with normal or mildly enlarged LA (sensitivity and specificity of 74% and 59%, respectively). In contrast, areas of voltage less than 0.75 mV correlated with LGE in patients with significant LA enlargement (sensitivity 68% and specificity 66%).

CONCLUSIONS

LAVI affects left atrial bipolar voltage, and the correlation between low-voltage areas and LGE-MRI. Distinct voltage thresholds according to the LAVI value might be considered to identify atrial scar by EAM.

Multi-modal characterization of the left atrium by a fully automated integration of pre-procedural cardiac imaging and electro-anatomical mapping

Background

The combination of information obtained from pre-procedural cardiac imaging and electro-anatomical mapping (EAM) can potentially help to locate new ablation targets. In this study we developed and evaluated a fully automated technique to align left atrial (LA) anatomies obtained from CT- and MRI-scans with LA anatomies obtained from EAM.

Methods

Twenty-one patients scheduled for a pulmonary vein (PV) isolation with a pre-procedural MRI were enrolled. Additionally, a recent computed tomography (CT) scan was available in 12 patients. LA anatomies were segmented from MRI-scans using ADAS-AF (Galgo Medical, Barcelona) and from the CT-scans using Slicer3D. MRI and CT anatomies were aligned with the EAM anatomy using an iterative closest plane-to-plane algorithm. Initially, the algorithm included the PVs, LA appendage and mitral valve anulus as they are the most distinctive landmarks. Subsequently, the algorithm was applied again, excluding these structures, with only three iterative steps to refine the alignment of the true LA surface. The result of the alignments was quantified by the Euclidian distance between the aligned anatomies after excluding PVs, LA appendage and mitral anulus.

Results

Our algorithm successfully aligned 20/21 MRI anatomies and 11/12 CT anatomies with the corresponding EAM anatomies. The average median residual distances were 1.9 ± 0.6 mm and 2.5 ± 0.8 mm for MRI and CT anatomies respectively. The average LA surface with a residual distance less than 5.00 mm was 89 ± 9% and 89 ± 10% for MRI and CT anatomies respectively.

Conclusion

An iterative closest plane-to-plane algorithm is a reliable method to automatically align pre-procedural cardiac images with anatomies acquired during ablation procedures.

Gender Differences in Atrial Fibrosis and Cardiomyopathy Assessed by Left Atrial Low-Voltage Areas During Catheter Ablation of Atrial Fibrillation

Atrial myocardial degeneration predisposes to atrial fibrillation (AF), ischemic stroke, and heart failure. Studies suggest the presence of gender differences in atrial myocardial degeneration. This study aimed to delineate gender differences in the prevalence, predictors, and prognostic impact of left atrial low-voltage areas (LVAs). This observational study included 1,488 consecutive patients who underwent initial ablation for AF. Voltage mapping was performed after pulmonary vein isolation during sinus rhythm. LVAs were defined as regions where bipolar peak-to-peak voltage was <0.50 mV. LVA prevalence was higher in women (38.7%) than in men (16.0%). High age, persistent form of AF, diabetes mellitus, and a large left atrium were shown to be common predictors in both gender categories. Heart failure and history of stroke/thromboembolic events were men-specific predictors of LVA existence. Women experienced more AF recurrence than men (31.1% vs 25.7%, p = 0.027). LVA existence was significantly associated with increased AF recurrence in each gender category, with a respective hazard ratio, 95% confidence interval, and p value of 2.45, 1.87 to 3.22, and <0.0001 in men and 1.82, 1.33 to 2.49, and <0.0001 in women. In conclusion, LVA was more frequent in women than men, and predicted frequent AF recurrence irrespective of gender category.

C. Silva T, Ambale-Venkatesh B, Xie E, Ostovaneh MR, Habibi M, Bluemke DA, Soliman EZ, Wu CO, Heckbert SR, Nazarian S, Lima JAC. Association between Left Atrial Late Gadolinium Enhancement and Atrial Fibrillation: The Multi-Ethnic Study of Atherosclerosis (MESA)

Purpose

To determine the prevalence and correlates of left atrial (LA) late gadolinium enhancement (LGE) at cardiac MRI and its association with atrial fibrillation (AF) in a population-based sample from the Multi-Ethnic Study of Atherosclerosis (MESA).

Materials and Methods

In this secondary post hoc analysis of the MESA cohort (ClinicalTrials.gov no. NCT00005487), participants without AF underwent LGE cardiac MRI at the fifth examination (2010-2012). LA LGE burden was quantified using the image intensity ratio technique on biplane long-axis two-dimensional (2D) LGE images without fat saturation. Survival analysis was performed with log-rank testing and Cox regression.

Results

Of 1697 participants (mean age, 67 years ± 9 [SD]; 872 men), 1035 (61%) had LA LGE, and 75 (4.4%) developed AF during follow-up (median, 3.95 years). At univariable analysis, LA LGE was associated with age (β = .010 [95% CI: .005, .015], P < .001), diastolic blood pressure (β = .005 [95% CI: .001, .009], P = .02), HbA1c level (β = .06 [95% CI: .02, .11], P = .009), heart failure (β = .60 [95% CI: .11, 1.08], P = .02), LA volume (β = .008 [95% CI: .004, .012], P < .001), and LA function (emptying fraction, LA global longitudinal strain, LA early diastolic peak longitudinal strain rate, and LA late diastolic peak strain rate; all P < .05). After adjusting for the variables in the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) AF score, LA LGE independently helped predict incident AF (hazard ratio = 1.46 [95% CI: 1.13, 1.88], P = .003). The highest tertile (LGE > 2%) was twice as likely to develop AF.

Conclusion

Although limited by the 2D LGE technique employed, LA LGE was associated with adverse atrial remodeling and helped predict AF in a multiethnic population-based sample.Clinical trial registration no. NCT00005487Keywords: MR Imaging, Cardiac, Epidemiology Supplemental material is available for this article. © RSNA, 2023.

Left atrial late gadolinium enhancement in patients with ischaemic stroke

AIMS

To evaluate the extent of left atrial (LA) fibrosis in patients with a recent stroke without atrial fibrillation and controls without established cardiovascular disease.

METHODS AND RESULTS

This prospectively designed study used cardiac magnetic resonance to detect LA late gadolinium enhancement as a proxy for LA fibrosis. Between 2019 and 2021, we consecutively included 100 patients free of atrial fibrillation with recent ischaemic stroke (<30 days) and 50 age- and sex-matched controls. LA fibrosis assessment was achieved in 78 patients and 45 controls. Blinded to the cardiac magnetic resonance results, strokes were adjudicated according to modified Trial of Org 10172 in Acute Stroke Treatment classification as undetermined aetiology (n = 42) or as attributable to large- or small-vessel disease (n = 36). Patients with stroke had a larger extent of LA fibrosis [6.9%, interquartile range (IQR) 3.6-15.4%] than matched controls (4.2%, IQR 2.3-7.5%; P = 0.007). No differences in LA fibrosis were observed between patients with stroke of undetermined aetiology and those with large- or small-vessel disease (6.6%, IQR 3.8-16.0% vs. 6.9%, IQR 3.4-14.6%; P = 0.73).

CONCLUSION

LA fibrosis was more extensive in patients with stroke than in age- and sex-matched controls. A similar extent of LA fibrosis was observed in patients with stroke of undetermined aetiology and stroke classified as attributable to large- or small-vessel disease. Our findings suggest that LA structural abnormality is more frequent in patients with stroke than in controls independent of aetiological classification.

Atrial electrogram amplitude variability during atrial fibrillation ablation

INTRODUCTION

Variability of the bipolar atrial electrogram amplitude may affect voltage maps created during ablation procedures, and thus also the extent of ablations. Therefore, the aim of the study was to assess the beat-to-beat electrogram amplitude variability in the left atrium in patients undergoing atrial fibrillation ablation.

METHODS

In 11 patients undergoing ablation for atrial fibrillation, 362 mapping points were collected in two series. At each point, three consecutive beats were recorded and verified including the bipolar electrogram amplitude, contact force (CF), and orientation of the catheter tip. The repeatability and reproducibility of obtained measurements between consecutive beats and series were assessed by the Pearson correlation coefficient (r), the Bland-Altman test, repeatability coefficient (RC), relative standard deviation (RSD), and concordance correlation coefficient (CCC).

RESULTS

A total of 1086 beats were analyzed. The correlation coefficient for bipolar atrial electrogram amplitude for the first two beats, and for the first and the third beats were 0.94 and 0.86, respectively. The average of differences between the first two beats and between the first and the third beats were 0.06 and 0.13 mV with 95% limits of agreement (LoA) within ±0.98 and ±1.74 mV, respectively. For CF values ≤5 and ≥20 g, the 95% LoA were narrower compared to other CF ranges and were ±0.49 and ±0.71 mV from the average value, respectively. When the analyzes were performed within the predefined ranges of bipolar electrogram amplitude: 0.05-1; 1-2; 2-3 mV, the 95% LoA were within ±0.33, ±0.98, and ±0.84 mV from the average value, respectively. RC and RSD were 1.41 mV and 20.8%, respectively. For repeated measurement between series, CCC ranged from 0.67 to 0.71 and the 95% LoA were within ±2.7 to 2.9 mV from the average value.

CONCLUSION

Bipolar atrial electrogram amplitude recorded at a given site during ablation procedures is variable to an extent that may be clinically relevant. The magnitude of the observed variability is greater during remapping.

Correlation between Cardiac MRI and Voltage Mapping in Evaluating Atrial Fibrosis: A Systematic Review

Purpose

To provide an overview of existing literature on the association between late gadolinium enhancement (LGE) cardiac MRI and low voltage areas (LVA) obtained with electroanatomic mapping (EAM) or histopathology when assessing atrial fibrosis.

Materials and Methods

A systematic literature search was conducted in the PubMed, Embase, and Cochrane Library databases to identify all studies published until June 7, 2022, comparing LGE cardiac MRI to LVA EAM and/or histopathology for evaluation of atrial fibrosis. The study protocol was registered at PROSPERO (registration no. CRD42022338243). Two reviewers independently evaluated the studies for inclusion. Risk of bias and applicability for each included study were assessed using Quality Assessment of Diagnostic Accuracy Studies–2 (QUADAS-2) criteria. Data regarding demographics, electrophysiology, LGE cardiac MRI, and study outcomes were extracted.

Results

The search yielded 1048 total results, of which 22 studies were included. Nineteen of the 22 included studies reported a significant correlation between high signal intensity at LGE cardiac MRI and LVA EAM or histopathology. However, there was great heterogeneity between included studies regarding study design, patient samples, cardiac MRI performance and postprocessing, and EAM performance.

Conclusion

Current literature suggests a correlation between LGE cardiac MRI and LVA EAM or histopathology when evaluating atrial fibrosis but high heterogeneity between studies, demonstrating the need for uniform choices regarding cardiac MRI and EAM acquisition in future studies.

Keywords: Cardiac, MR Imaging, Left Atrium

Supplemental material is available for this article.

© RSNA, 2022

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.

Evaluation of Isolation Area, Myocardial Injury and Left Atrial Function Following High-Power Short-Duration Radiofrequency or Second-Generation Cryoballoon Ablation for Atrial Fibrillation

This randomized study aims to compare the left atrial (LA) lesion size, function, and tissue damage following pulmonary vein isolation (PVI) by high-power short-duration (HPSD) radiofrequency (RF) and second-generation cryoballoon (CB2) ablation. We enrolled 40 patients with paroxysmal atrial fibrillation who underwent PVI by HPSD RF (n = 21) or CB2 (n = 19). Every patient underwent LA CT angiography and transthoracic echocardiography (TTE) to assess the LA anatomy and function. Biomarker levels (hs-cTnT, hs-CRP, LDH) were compared pre- and post-procedurally. Pre- and post-ablation high-density mapping (HDM) was performed. The isolation area was defined under 0.2 mV bipolar voltage (low voltage area, LVA). We calculated the post-PVI LVA/LA surface ratio using LA CT-HDM merge images. At 3-month follow-up, TTE was performed to assess the changes in LA function. Post-ablation hs-cTnT level was significantly higher in the RF group (RF: 1249 ± 469 ng/L, CB2: 995 ± 280 ng/L, p = 0.024). Post-PVI hs-CRP (RF: 9.53 ± 10.30 mg/L, CB2: 12.36 ± 5.76 mg/L, p = 0.034) and LDH levels (RF: 349.9 ± 65.6 U/L, CB2: 451.6 ± 91.3 U/L, p < 0.001) were significantly higher following CB2 ablation. Post-PVI LVA/LA surface ratios were 8.37 ± 6.42% in the RF group and 13.58 ± 8.92% in the CB2 group (p = 0.022). LA function did not change significantly after the PVI procedure. Our data indicate that second-generation cryoballoon ablation produces a significantly larger LA lesion size compared to “point-by-point” HPSD radiofrequency. Both techniques preserve LA function. The myocardial component of tissue loss appears to be higher using HPSD radiofrequency ablation, with less collateral damage.

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].

Prediction of Left Atrial Fibrosis and Success of Catheter Ablation by Speckle Tracking Echocardiography in Patients Imaged in Persistent Atrial Fibrillation

Background

Non-invasive evaluation of left atrial structural and functional remodeling should be considered in all patients with persistent atrial fibrillation (AF) to optimal management. Speckle tracking echocardiography (STE) has been shown to predict AF recurrence after catheter ablation; however in most studies, patients had paroxysmal AF, and STE was performed while patients were in sinus rhythm.

Aim

The aim of this study was to evaluate the ability of STE parameters acquired during persistent AF to assess atrial fibrosis measured by low voltage area, and to predict maintenance of sinus rhythm of catheter ablation.

Methods

A total of 94 patients (69 men, 65 ± 9 years) with persistent AF prospectively underwent measurement of Global Peak Atrial Longitudinal Strain (GPALS), indexed LA Volume (LAVI), E/e′ ratio, and LA stiffness index (the ratio of E/e′ to GPALS) by STE prior to catheter ablation, while in AF. Low-voltage area (LVA) was assessed by electro-anatomical mapping and categorized into absent, moderate (&gt;0 to &lt;15%), and high (≥15%) atrial extent. AF recurrence was evaluated after 3 months of blanking.

Results

Multivariable regression showed that LAVI, GPALS, and LA stiffness independently predicted LVA extent after correcting for age, glomerular filtration rate, and CHA2DS2-VASc score. Of all the parameters, LA stiffness index had the highest diagnostic accuracy (AUC 0.85), allowing using a cut-off value ≥0.7 to predict moderate or high LVA with 88% sensitivity and 47% specificity, respectively. In multivariable Cox analysis, both GPALS and LA stiffness were able to significantly improve the c statistic to predict AF recurrence (n = 40 over 9 months FU) over CHARGE-AF (p &lt; 0.001 for GPALS and p = 0.01 for LA stiffness) or CHA2DS2-VASc score (p &lt; 0.001 for GPALS and p = 0.02 for LA stiffness). GPALS and LA stiffness also improved the net reclassification index (NRI) over the CHARGE-AF index (NRI 0.67, 95% CI [0.33–1.13] for GPALS and NRI 0.73, 95% CI [0.12–0.91] for LA stiffness, respectively), and over the CHA2DS2-VASc score (NRI 0.43, 95% CI [−0.14 to 0.69] for GPALS and NRI 0.52, 95% CI [0.10–0.84], respectively) for LA stiffness to predict AF recurrence at 9 months.

Conclusion

STE parameters acquired during AF allow prediction of LVA extent and AF recurrence in patients with persistent AF undergoing catheter ablation. Therefore, STE could be a valuable approach to select candidates for catheter ablation.

Comparison of various late gadolinium enhancement magnetic resonance imaging methods with high-definition voltage and activation mapping for detection of atrial cardiomyopathy

AIMS

Atrial cardiomyopathy (ACM) is associated with increased arrhythmia recurrence rates after pulmonary vein isolation (PVI). We compare the most common left atrial (LA) late gadolinium enhancement magnetic resonance imaging (LGE-MRI)-methods [Utah-method and image intensity ratio (IIR)-methods] and endocardial voltage mapping for ACM-detection and outcome prediction after PVI for atrial fibrillation (AF).

METHODS AND RESULTS

In this prospective observational study, 37 ablation-naive patients (66 ± 9 years, 84% male) with persistent AF underwent LA-LGE-MRI and high-definition voltage and activation mapping (2129 ± 484 sites) in sinus rhythm prior to PVI. The MRI-post-processing-analyses were performed by two independent expert laboratories. Arrhythmia recurrence was recorded within 12 months following PVI. The global ACM-extent was highly variable: median LA low-voltage substrate (LA-LVS) was 12.9% at <1.0 mV and 2.7% at <0.5 mV; median LA-LGE-extent using the Utah-method was 18.3% and 0.03-93.1% using the IIR-methods. The LA activation time was significantly correlated with LA-LVS (r = 0.76 at <0.5 mV and r = 0.82 at <1.0 mV, both P < 0.0001), but not with LA-LGE-extent. The highest regional matching between LA-LVS <0.5 mV and LA-LGE was found for the anterior wall in 57% of patients using the Utah-method and in 59% using IIR 1.20. The corresponding values for the posterior wall were 19% and 38%, respectively. Arrhythmia recurrence occurred in 15(41%) patients. Freedom from arrhythmia was significantly lower in those with LA-LVS ≥2 cm2 at 0.5 mV but not in those with LGE ≥20% (Utah-stages III and IV): 43% vs. 81%, P = 0.009 and 50% vs. 67%, P = 0.338, respectively.

CONCLUSION

Comparison of the most common LA-LGE-MRI methods and endocardial voltage mapping revealed large discrepancies in global and regional ACM-extent.

Atrial Structural Remodeling in Patients With Atrial Fibrillation Is a Diffuse Fibrotic Process: Evidence From High-Density Voltage Mapping and Atrial Biopsy

Background

Low‐voltage areas (LVAs) in the atria of patients with atrial fibrillation are considered local fibrosis. We hypothesized that voltage reduction in the atria is a diffuse process associated with fibrosis and that the presence of LVAs reflects a global voltage reduction.

Methods and Results

We examined 140 patients with atrial fibrillation and 13 patients with a left accessory pathway (controls). High‐density bipolar voltage mapping was performed using a grid‐mapping catheter during high right atrial pacing. Global left atrial (LA) voltage (V_GLA) in the whole LA and regional LA voltage (V_RLA) in 6 anatomic regions were evaluated with the mean of the highest voltage at a sampling density of 1 cm². Patients with atrial fibrillation were categorized into quartiles by V_GLA. LVAs were evaluated at voltage cutoffs of 0.1, 0.5, 1.0, and 1.5 mV. Twenty‐eight patients with atrial fibrillation also underwent right atrial septum biopsy, and the fibrosis extent was quantified. Voltage at the biopsy site (V_biopsy) was recorded. V_GLA results by category were Q1 (<4.2 mV), Q2 (4.2–5.6 mV), Q3 (5.7–7.0 mV), and Q4 (≥7.1 mV). V_RLA at any region was reduced as V_GLA decreased. V_GLA and V_RLA did not differ between Q4 and controls. The presence of LVAs increased as V_GLA decreased at any voltage cutoff. Biopsies revealed 11±6% fibrosis, which was inversely correlated with both V_biopsy and V_GLA (r=–0.71 and –0.72, respectively). V_biopsy was correlated with V_GLA (r=0.82).

Conclusions

Voltage reduction in the LA is a diffuse process associated with fibrosis. Presence of LVAs reflects diffuse voltage reduction of the LA.

Sex-Related Differences in Atrial Remodeling in Patients With Atrial Fibrillation: Relationship to Ablation Outcomes

BACKGROUND

Population studies have demonstrated a range of sex differences including a higher prevalence of atrial fibrillation (AF) in men and a higher risk of AF recurrence in women. However, the underlying reasons for this higher recurrence are unknown. This study evaluated whether sex-based electrophysiological substrate differences exist to account for worse AF ablation outcomes in women.

METHODS

High-density electroanatomic mapping of the left atrium was performed in 116 consecutive patients with AF. Regional analysis was performed across 6 left atrium segments. High-density maps were created using a multipolar catheter (Biosense Webster) during distal coronary sinus pacing at 600 and 300 ms. Mean voltage and conduction velocity was determined. Complex fractionated signals and double potentials were manually annotated.

RESULTS

Overall, 42 (36%) were female, mean age was 61±8 years and AF was persistent in 52%. Global mean voltage was significantly lower in females compared with males at 600 ms (1.46±0.17 versus 1.84±0.15 mV, P<0.001) and 300 ms (1.27±0.18 versus 1.57±0.18 mV, P=0.013) pacing. These differences were seen uniformly across the left atrium. Females demonstrated significant conduction velocity slowing (34.9±6.1 versus 44.1±6.9 cm/s, P=0.002) and greater proportion of complex fractionated signals (9.9±1.7% versus 6.0±1.7%, P=0.014). After a median follow-up of 22 months (Q1-Q3: 15-29), females had significantly lower single-procedure (22 [54%] versus 54 [75%], P=0.029) and multiprocedure (24 [59%] versus 60 [83%], P=0.005) arrhythmia-free survival. Female sex and persistent AF were independent predictors of single and multiprocedure arrhythmia recurrence.

CONCLUSIONS

Female patients demonstrated more advanced atrial remodeling on high-density electroanatomic mapping and greater post-AF ablation arrhythmia recurrence compared with males. These changes may contribute to sex-based differences in the clinical course of females with AF and in part explain the higher risk of recurrence.

Identifying Atrial Fibrillation Mechanisms for Personalized Medicine

Atrial fibrillation (AF) is a major cause of heart failure and stroke. The early maintenance of sinus rhythm has been shown to reduce major cardiovascular endpoints, yet is difficult to achieve. For instance, it is unclear how discoveries at the genetic and cellular level can be used to tailor pharmacotherapy. For non-pharmacologic therapy, pulmonary vein isolation (PVI) remains the cornerstone of rhythm control, yet has suboptimal success. Improving these therapies will likely require a multifaceted approach that personalizes therapy based on mechanisms measured in individuals across biological scales. We review AF mechanisms from cell-to-organ-to-patient from this perspective of personalized medicine, linking them to potential clinical indices and biomarkers, and discuss how these data could influence therapy. We conclude by describing approaches to improve ablation, including the emergence of several mapping systems that are in use today.

Electrophysiological Consequences of Cardiac Fibrosis

For both the atria and ventricles, fibrosis is generally recognized as one of the key determinants of conduction disturbances. By definition, fibrosis refers to an increased amount of fibrous tissue. However, fibrosis is not a singular entity. Various forms can be distinguished, that differ in distribution: replacement fibrosis, endomysial and perimysial fibrosis, and perivascular, endocardial, and epicardial fibrosis. These different forms typically result from diverging pathophysiological mechanisms and can have different consequences for conduction. The impact of fibrosis on propagation depends on exactly how the patterns of electrical connections between myocytes are altered. We will therefore first consider the normal patterns of electrical connections and their regional diversity as determinants of propagation. Subsequently, we will summarize current knowledge on how different forms of fibrosis lead to a loss of electrical connectivity in order to explain their effects on propagation and mechanisms of arrhythmogenesis, including ectopy, reentry, and alternans. Finally, we will discuss a histological quantification of fibrosis. Because of the different forms of fibrosis and their diverging effects on electrical propagation, the total amount of fibrosis is a poor indicator for the effect on conduction. Ideally, an assessment of cardiac fibrosis should exclude fibrous tissue that does not affect conduction and differentiate between the various types that do; in this article, we highlight practical solutions for histological analysis that meet these requirements.

Considerations for the Assessment of Substrates, Genetics and Risk Factors in Patients with Atrial Fibrillation

Successful translation of research focussing on atrial arrhythmogenic mechanisms has potential to provide a mechanism-tailored classification and to support personalised treatment approaches in patients with AF. The clinical uptake and clinical implementation of new diagnostic techniques and treatment strategies require translational research approaches on various levels. Diagnostic translation involves the development of clinical diagnostic tools. Additionally, multidisciplinary teams are required for collaborative translation to describe genetic mechanisms, molecular pathways, electrophysiological characteristics and concomitant risk factors. In this article, current approaches for AF substrate characterisation, analysis of genes potentially involved in AF and strategies for AF risk factor assessment are summarised. The authors discuss challenges and obstacles to clinical translation and implementation into clinical practice.

[Pulmonary vein isolation using radiofrequency ablation]

Catheter ablation represents the primary treatment for most arrhythmias. The effectiveness of catheter ablation for the treatment of atrial fibrillation is superior to drug therapy. Therefore, catheter ablation has been established as an increasingly common procedure in clinical routine. In this context, the electrical isolation of the pulmonary veins (PVI) constitutes the cornerstone of the interventional therapy of paroxysmal and persistent atrial fibrillation. This article describes the procedure of pulmonary vein isolation utilizing radiofrequency point-by-point ablation. It shall be a practical guide for the staff in the electrophysiological laboratory. This article continues a series of manuscripts focusing on interventional electrophysiology topics in the course of EP (electrophysiology) training.This article describes the procedure of pulmonary vein isolation utilizing radiofrequency point-by-point ablation. It shall be a practical guide for the staff in the electrophysiological laboratory. This article continues a series of manuscripts dealing with topics of interventional electrophysiology in the course of EP training.

Atrial fibrosis as a dominant factor for the development of atrial fibrillation: facts and gaps

Atrial fibrillation (AF), the most commonly diagnosed arrhythmia, affects a notable percentage of the population and constitutes a major risk factor for thromboembolic events and other heart-related conditions. Fibrosis plays an important role in the onset and perpetuation of AF through structural and electrical remodelling processes. Multiple molecular pathways are involved in atrial substrate modification and the subsequent maintenance of AF. In this review, we aim to recapitulate underlying molecular pathways leading to atrial fibrosis and to indicate existing gaps in the complex interplay of atrial fibrosis and AF.

Atrial fibrillation and cardiac fibrosis

The understanding of atrial fibrillation (AF) evolved from a sole rhythm disturbance towards the complex concept of a cardiomyopathy based on arrhythmia substrates. There is evidence that atrial fibrosis can be visualized using late gadolinium enhancement cardiac magnetic resonance imaging and that it is a powerful predictor for the outcome of AF interventions. However, a strategy of an individual and fibrosis guided management of AF looks promising but results from prospective multicentre trials are pending. This review gives an overview about the relationship between cardiac fibrosis and AF focusing on translational aspects, clinical observations, and fibrosis imaging to emphasize the concept of personalized paths in AF management taking into account the individual amount and distribution of fibrosis.

Easily available ECG and echocardiographic parameters for prediction of left atrial remodeling and atrial fibrillation recurrence after pulmonary vein isolation: A multicenter study

BACKGROUND

The assessment of noninvasive markers of left atrial (LA) low-voltage substrate (LVS) enables the identification of atrial fibrillation (AF) patients at risk for arrhythmia recurrence after pulmonary vein isolation (PVI).

METHODS

In this prospective multicenter study, 292 consecutive AF patients (72% male, 62 ± 11 years, 65% persistent AF) underwent high-density LA voltage mapping in sinus rhythm. LA-LVS (<0.5 mV) was considered as significant at 2 cm²  or above. Preprocedural clinical electrocardiogram and echocardiographic data were assessed to identify predictors of LA-LVS. The role of the identified LA-LVS markers in predicting 1-year arrhythmia freedom after PVI was assessed in 245 patients.

RESULTS

Significant LA-LVS was identified in 123 (42%) patients. The amplified sinus P-wave duration (APWD) best predicted LA-LVS, with a 148-ms value providing the best-balanced sensitivity (0.81) and specificity (0.88). An APWD over 160 ms was associated with LA-LVS in 96% of patients, whereas an APWD under 145 ms in 15%. Remaining gray zones improved their accuracy by introduction of systolic pulmonary artery pressure (sPAP) of 35 mmHg or above, age, and sex. According to COX regression, the risk of arrhythmia recurrence 12 months following PVI was twofold and threefold higher in patients with APWD 145-160 and over 160 ms, compared to APWD under 145 ms. Integration of pulmonary hypertension further improved the outcome prediction in the intermediate APWD group: Patients with APWD 145-160 ms and normal sPAP had similar outcome than patients with APWD under 145 ms (hazard ratio [HR] 1.62, p = .14), whereas high sPAP implied worse outcome (HR 2.56, p < .001).

CONCLUSIONS

The APWD identifies LA-LVS and risk for arrhythmia recurrence after PVI. Our prediction model becomes optimized by means of integration of the pulmonary artery pressure.

Atrial fibrosis and substrate based characterization in atrial fibrillation: Time to move forwards

Atrial fibrillation (AF) is the most commonly encountered cardiac arrhythmia in clinical practice. However, current therapeutic interventions for atrial fibrillation have limited clinical efficacy as a consequence of major knowledge gaps in the mechanisms sustaining atrial fibrillation. From a mechanistic perspective, there is increasing evidence that atrial fibrosis plays a central role in the maintenance and perpetuation of atrial fibrillation. Electrophysiologically, atrial fibrosis results in alterations in conduction velocity, cellular refractoriness, and produces conduction block promoting meandering, unstable wavelets and micro-reentrant circuits. Clinically, atrial fibrosis has also linked to poor clinical outcomes including AF-related thromboembolic complications and arrhythmia recurrences post catheter ablation. In this article, we review the pathophysiology behind the formation of fibrosis as AF progresses, the role of fibrosis in arrhythmogenesis, surrogate markers for detection of fibrosis using cardiac magnetic resonance imaging, echocardiography and electroanatomic mapping, along with their respective limitations. We then proceed to review the current evidence behind therapeutic interventions targeting atrial fibrosis, including drugs and substrate-based catheter ablation therapies followed by the potential future use of electro phenotyping for AF characterization to overcome the limitations of contemporary substrate-based methodologies.

Multimodality imaging for atrial fibrosis detection in the era of precision medicine

In recent years, atrial fibrillation (AF) has increasingly become a focus of attention because it represents the most encountered arrhythmia in clinical practice and a major cause of morbidity and mortality. Issues underlying AF have long been debated; nevertheless, electrical, contractile, and structural remodeling is demonstrated to be the pivotal contributor to arrhythmic substrate. Fibrosis is a hallmark of arrhythmogenic structural remodeling, resulting from an accumulation of fibrillar collagen deposits, as a reparative process to replace degenerating myocardium with concomitant reactive fibrosis, which causes interstitial expansion. Although the precise role of fibrosis in AF initiation and maintenance remains to be fully elucidated, a better definition of its extent and distribution may assist in designing individually tailored ablation approaches and improving procedure outcomes by targeting the fibrotic substrates with an organized strategy employing imaging resources. A deep comprehension of the mechanisms underlying atrial fibrosis could be crucial to setting up improved strategies for preventing AF-promoting structural remodeling. Imaging modalities such as echocardiography, cardiac computed tomography, and cardiac magnetic resonance, combined sometimes with invasive electroanatomical mapping, could provide valuable information for the optimal patients’ management if their use is not limited to cardiac anatomy study but extended to characterize abnormal left atrial substrate. Although pulmonary vein isolation is usually efficacious in treating paroxysmal AF, it is not sufficient for many patients with nonparoxysmal arrhythmias, particularly those with longstanding persistent AF. Noninvasive imaging techniques play a pivotal role in the planning of arrhythmic substrates ablation and show a strong correlation with electro-anatomic mapping, whose novel multipolar mapping catheters allow nowadays a more precise comprehension of atrial substrate. This review aims to explore the impact of the various imaging modalities for the detection of atrial fibrosis and their role in the management of AF.

Left atrial scar identification and quantification in sinus rhythm and atrial fibrillation

Identification and quantification of low voltage areas (LVA) in atrial fibrillation (AF), identified by their bipolar voltages (BiV) via electro-anatomical voltage mapping is an area of interest to prognosis of AF free burden. LVAs have been linked to diseased left atrial (LA) tissue which results in pro-fibrillatory potentials. These LVAs are dominantly found within the pulmonary veins, however, as the disease progresses other areas of the LA show low voltage. The scar burden of the LA is linked to recurrence of the arrhythmia and can be a target of further modification. This burden is classically assessed once sinus rhythm (SR) is attained, but this is susceptible to operator variability with overestimated dense LA scar (<0.2 mV) and underestimated diseased LA tissue (<0.5 mV). The novel automated voltage histogram analysis (VHA) tool may increase accuracy, however, is yet to be fully validated. A recent study indicates that LVAs can be assessed just as reliably in AF as SR, but BiV is lower with linear correlation to SR values (0.24-0.5 mV respectively). In this paper, we review current data as well as review current methods of identifying, quantifying, and grading LA scar. We also compared AF vs SR voltages of a patient undergoing catheter ablation in our site using our VHA tool to compare the results. In keeping with the cited papers, we found lower voltages in our patient measured in AF. This area warrants further study to assess correlation in more patients, with view to developing prognostic and therapeutic grading systems.

Atrial Fibrillation Structural Substrates: Aetiology, Identification and Implications

Atrial remodelling in AF underlines the electrical, structural and mechanical changes in the atria of patients with AF. Several risk factors for AF contribute to the development of the atrial substrate, with some evidence that atrial remodelling reversal is possible with targeted intervention. In this article, the authors review the electrophysiological changes that characterise the atrial substrate in patients with AF risk factors. They also discuss the pitfalls of mapping the atrial substrate and the implications for developing tailored ablation strategies to improve outcomes in patients with AF.

Reduction of mapping time in pulmonary vein isolation using atrial pacing during left atrial voltage map acquisition

INTRODUCTION

3D mapping systems are used during radiofrequency (RF) pulmonary vein isolation (PVI) to facilitate catheter navigation and to provide additional electroanatomical information as a surrogate marker for the presence and location of fibrotic atrial myocardium. Electric voltage information can only be measured when the myocardium is depolarized. Low heart rates or frequent premature atrial beats can significantly prolong creation of detailed left atrial voltage maps. This study was designed to evaluate the potential advantage of voltage information collection during atrial pacing instead of acquisition during sinus rhythm.

METHODS AND RESULTS

A total of 40 patients were included in the study, in 20 consecutive patients voltage mapping was performed during sinus rhythm, and in the following 20 patients during atrial pacing. The average age of the included patients was 69.5 ± 9.4, 17 of 40 patients (43%) were male. All procedures were performed using the Carto 3D Mapping system. For LA voltage mapping, a multipolar circular mapping catheter was used. The atrium was paced via the proximal coronary sinus catheter electrodes with a fixed cycle length of 600 ms. By mapping during atrial pacing mapping time was reduced by 35% (441 s. (±141) vs. 683 s. (±203) p = 0.029) while a higher number of total mapping points were acquired (908 ± 560 vs. 581 ± 150, p = 0.008).

CONCLUSION

Acquiring left atrial low voltage maps during atrial pacing significantly reduces mapping time. As pacing also improves comparability of left atrial electroanatomical maps we suggest that this approach may be considered as a standard during these procedures.

Galectin-3, N-terminal Propeptides of Type I and III Procollagen in Patients with Atrial Fibrillation and Metabolic Syndrome

The aim of this study was to determine the concentration of galectin-3, PINP and PIIINP in patients with metabolic syndrome (MS) and atrial fibrillation (AF) with an assessment of the relationship with severity of left atrium fibrosis. A total of 480 subjects were included in the case-control study: MS patients (n = 337), 176 of whom had AF, 72 patients with AF without MS and 71 healthy subjects. Galectin-3, PINP and PIIINP blood concentrations and metabolic parameters were compared with the severity of left atrium fibrosis, measured by CARTO3. Galectin-3 in AF and MS patients is higher than in MS without AF and in healthy subjects (10.3 (4.8–15.4), 5.1 (4.3–8.8), 3.2 (2.4–4.2) ng/mL, p < 0.0001). Galectin-3 serum concentration in AF patients with MS is higher than in patients without MS: 10.3 (4.8–15.4), 6.8 (5.2–8.1) ng/mL, p = 0.0001. PINP and PIIINP concentration were higher in patients with AF and MS than in MS without AF: 3499.1 (2299.2–4567.3), 2130.9 (1425.3–2861.8) pg/mL, p < 0.0001, 94.9 (64.8–123.5), 57.6 (40.5–86.9) ng/mL, p < 0.0001. Galectin-3 correlates with PINP (r = 0.496, p < 0.001) and PIIINP concentration (r = 0.451, p < 0.0001). The correlation between galectin-3, PINP and the severity of left atrium fibrosis was found (r = 0.410, p < 0.001; r = 0.623, p < 0.001). Galectin-3 higher than 12.6 ng/mL increased the risk of AF more than five-fold. High galectin-3, PINP and PIIINP concentrations were associated with heart remodeling in MS patients and increased the risk of AF.

Prospective cross-sectional study using Poisson renewal theory to study phase singularity formation and destruction rates in atrial fibrillation (RENEWAL-AF): Study design

BACKGROUND

Unstable functional reentrant circuits known as rotors have been consistently observed in atrial fibrillation and are mechanistically believed critical to the maintenance of the arrhythmia. Recently, using a Poisson renewal theory-based quantitative framework, we have demonstrated that rotor formation (λf) and destruction rates (λd) can be measured using in vivo electrophysiologic data. However, the association of λf and λd with clinical, electrical, and structural markers of atrial fibrillation phenotype is unknown.

METHODS

RENEWAL-AF is a multicenter prospective cross-sectional study recruiting adult patients with paroxysmal or persistent atrial fibrillation undergoing clinically indicated catheter ablation. Patients will undergo intraprocedural electrophysiologic atrial fibrillation mapping, with λf and λd to be determined from 2-minute unipolar electrogram recordings acquired before ablation. The primary objective will be to determine the association of λf and λd as markers of fibrillatory dynamics with clinical, electrical, and structural markers of atrial fibrillation clinical phenotype, measured by preablation transthoracic echocardiogram and cardiac magnetic resonance imaging. An exploratory objective is the noninvasive assessment of λf and λd using surface ECG characteristics via a machine learning approach.

RESULTS

Not applicable.

CONCLUSION

This pilot study will provide insight into the correlation between λf/λd with clinical, electrophysiological, and structural markers of atrial fibrillation phenotype and provide a foundation for the development of noninvasive assessment of λf/λd using surface ECG characteristics will help expand the use of λf/λd in clinical practice.

Tailoring the Approach to Embolic Stroke of Undetermined Source: A Review

Importance

One-third of ischemic strokes have no identifiable cause after standard evaluation. In 2014, researchers termed these embolic strokes of undetermined source (ESUS) and argued that this entity would respond to anticoagulation. Two recent randomized clinical trials have not upheld this hypothesis, leading to questions about the ESUS concept.

Observations

This article proposes that ESUS remains a useful concept, the clinical effect of which can be enhanced by considering 2 subsets defined by their likelihood of responding to anticoagulation. Recent studies indicate that some ESUS cases result from subclinical atrial fibrillation, atrial cardiopathy, unrecognized myocardial infarction, patent foramen ovale, or cancer, while other cases result from nonstenosing large-artery atherosclerosis, aortic atherosclerosis, or nonatherosclerotic vasculopathies. Evidence suggests that anticoagulation will prove superior to antiplatelet therapy for cases in the first group of causative mechanisms but not those in the second group, suggesting the need for personalized therapy.

Conclusions and Relevance

Although the ESUS concept as currently constructed cannot guide treatment, efforts to better understand ESUS and develop therapies tailored to specific mechanisms are likely to help reduce the burden of stroke.

Left Atrial Structural Remodelling in Non-Valvular Atrial Fibrillation: What Have We Learnt from CMR?

Left atrial structural, functional and electrical remodelling are linked to atrial fibrillation (AF) pathophysiology and mirror the phrase “AF begets AF”. A structurally remodelled left atrium (LA) is fibrotic, dysfunctional and enlarged. Fibrosis is the hallmark of LA structural remodelling and is associated with increased risk of stroke, heart failure development and/or progression and poorer catheter ablation outcomes with increased recurrence rates. Moreover, increased atrial fibrosis has been associated with higher rates of stroke even in sinus-rhythm individuals. As such, properly assessing the fibrotic atrial cardiomyopathy in AF patients becomes necessary. In this respect, late-gadolinium enhancement cardiac magnetic resonance (LGE-CMR) imaging is the gold standard in imaging myocardial fibrosis. LA structural remodelling extension offers both diagnostic and prognostic information and influences therapeutic choices. LGE-CMR scans can be used before the procedure to better select candidates and to aid in choosing the ablation technique, during the procedure (full CMR-guided ablations) and after the ablation (to assess the ablation scar). This review focuses on imaging several LA structural remodelling CMR parameters, including size, shape and fibrosis (both extension and architecture) and their impact on procedure outcomes, recurrence risk, as well as their utility in relation to the index procedure timing.

Ablation of persistent atrial fibrillation and beyond

PURPOSE OF REVIEW

Percutaneous catheter ablation is an effective treatment for atrial fibrillation. However, catheter ablation for the treatment of persistent atrial fibrillation or long-standing persistent atrial fibrillation is associated with unsatisfying success rates. This review aims to summarize the recent literature on the progress of catheter ablation among patients with persistent atrial fibrillation RECENT FINDINGS: In this review, we outline the potential future therapeutic techniques of catheter ablation of persistent atrial fibrillation. We highlight the innovative techniques (rotor mapping, substrate mapping, delayed enhancement MRI, and high-resolution mapping catheter) of current approaches and optimal procedural endpoint for persistent atrial fibrillation.

SUMMARY

In summary, the optimal catheter ablation strategy for persistent atrial fibrillation remains unknown. Current data highlight the need for a better understanding of the substrate and mechanisms of arrhythmia maintenance in this population. Current mapping technologies offer additional tools (improved automatic algorithm for annotation, multiple electrode mapping, high-resolution mapping, and application of different processing techniques) for identifying the putative mechanism underlying atrial fibrillation. Further prospective studies are needed for the optimal procedural endpoint and the recent innovative techniques and their clinical benefits in ablation strategies.

Association of Left Atrial High-Resolution Late Gadolinium Enhancement on Cardiac Magnetic Resonance With Electrogram Abnormalities Beyond Voltage in Patients With Atrial Fibrillation

BACKGROUND

Conflicting data have been reported on the association of left atrial (LA) late gadolinium enhancement (LGE) with atrial voltage in patients with atrial fibrillation. The association of LGE with electrogram fractionation and delay remains to be examined. We sought to examine the association between LA LGE on cardiac magnetic resonance and electrogram abnormalities in patients with atrial fibrillation.

METHODS

High-resolution LGE cardiac magnetic resonance was performed before electrogram mapping and ablation in atrial fibrillation patients. Cardiac magnetic resonance features were quantified using LA myocardial signal intensity Z score (SI-Z), a continuous normalized variable, as well as a dichotomous LGE variable based on previously validated methodology. Electrogram mapping was performed pre-ablation during sinus rhythm or LA pacing, and electrogram locations were coregistered with cardiac magnetic resonance images. Analyses were performed using multilevel patient-clustered mixed-effects regression models.

RESULTS

In the 40 patients with atrial fibrillation (age, 63.2±9.2 years; 1312.3±767.3 electrogram points per patient), lower bipolar voltage was associated with higher SI-Z in patients who had undergone previous ablation (coefficient, -0.049; P<0.001) but not in ablation-naive patients (coefficient, -0.004; P=0.7). LA electrogram activation delay was associated with SI-Z in patients with previous ablation (SI-Z: coefficient, 0.004; P<0.001 and LGE: coefficient, 0.04; P<0.001) but not in ablation-naive patients. In contrast, increased LA electrogram fractionation was associated with SI-Z (coefficient, 0.012; P=0.03) and LGE (coefficient, 0.035; P<0.001) only in ablation-naive patients.

CONCLUSIONS

The association of LA LGE with voltage is modified by ablation. Importantly, in ablation-naive patients, atrial LGE is associated with electrogram fractionation even in the absence of voltage abnormalities.

Extent and spatial distribution of left atrial arrhythmogenic sites, late gadolinium enhancement at magnetic resonance imaging, and low-voltage areas in patients with persistent atrial fibrillation: comparison of imaging vs. electrical parameters of fibrosis and arrhythmogenesis

Aims

Atrial fibrosis contributes to arrhythmogenesis in atrial fibrillation and can be detected by MRI or electrophysiological mapping. The current study compares the spatial correlation between delayed enhancement (DE) areas to low-voltage areas (LVAs) and to arrhythmogenic areas with spatio-temporal dispersion (ST-Disp) or continuous activity (CA) in atrial fibrillation (AF).

Methods and results

Sixteen patients with persistent AF (nine long-standing) underwent DE-magnetic resonance imaging (1.25 mm × 1.25 mm × 2.5 mm) prior to pulmonary vein isolation. Left atrial (LA) voltage mapping was acquired in AF and the regional activation patterns of 7680 AF wavelets were analysed. Sites with ST-Disp or CA were characterized (voltage, duration) and their spatial relationship to DE areas and LVAs <0.5 mV was assessed. Delayed enhancement areas and LVAs covered 55% and 24% (P < 0.01) of total LA surface, respectively. Delayed enhancement area was present at 61% of LVAs, whereas low voltage was present at 28% of DE areas. Most DE areas (72%) overlapped with atrial high-voltage areas (>0.5 mV). Spatio-temporal dispersion and CA more frequently co-localized with LVAs than with DE areas (78% vs. 63%, P = 0.02). Regional bipolar voltage of ST-Disp vs. CA was 0.64 ± 0.47 mV vs. 0.58 ± 0.51 mV. All 28 ST-Disp and 56 CA areas contained electrograms with prolonged duration (115 ± 14 ms) displaying low voltage (0.34 ± 0.11 mV).

Conclusion

A small portion of DE areas and LVAs harbour the arrhythmogenic areas displaying ST-Disp or CA. Most arrhythmogenic activities co-localized with LVAs, while there was less co-localization with DE areas. There is an important mismatch between DE areas and LVAs which needs to be considered when used as target for catheter ablation.

Atrial Fibrosis: Translational Considerations for the Management of AF Patients

Fibrosis plays a fundamental role in the initiation and maintenance of AF, mainly due to enhanced automaticity and anisotropy-related re-entry. The identification and quantification of atrial fibrosis is achieved either preprocedurally by late gadolinium enhancement MRI or intraprocedurally using electroanatomic voltage mapping. The presence and extent of left atrial fibrosis among AF patients may influence relevant decision making regarding the need for anticoagulation, the adoption of rate versus rhythm control and mainly the type of ablation strategy that will be followed during interventional treatment. Several types of individualised substrate modifications targeting atrial fibrotic areas have been proposed, although their impact on patient outcome needs to be further investigated in adequately powered prospective randomised controlled clinical trials.

Decreased platelet-to-lymphocyte ratio as predictor of thrombogenesis in nonvalvular atrial fibrillation

BACKGROUND

Inflammation plays a key role in the progression of atrial fibrillation and its related prothrombotic state. The platelet-to-lymphocyte ratio (PLR) is an easily obtainable biomarker of inflammatory burden. Decreased left atrial appendage flow velocity (LAA-FV) reflects blood stasis, and left atrial strain is a manifestation of atrial remodeling. This study examined the role of PLR in reflecting decreased LAA-FV and its correlation with impaired left atrial strain.

METHODS

In 54 patients with nonvalvular atrial fibrillation, LAA-FV and left atrial strain were measured by echocardiography. The PLR was calculated from a complete blood count.

RESULTS

The PLR was lower in the group of patients with decreased LAA-FV (84.22 [IQR, 69.87-98.17 cm/s] vs. 103.27 [IQR, 90.37-127.16 cm/s]; p = 0.018). PLR was predictive of decreased LAA-FV with a sensitivity of 66.7% and a specificity of 83.3%. In a receiver operator characteristic curve analysis, using a cut-off value of 88.16, the area under the curve for PLR as a predictor of decreased LAA-FV was 0.726 (p = 0.018). Furthermore, the patients with a PLR of < 88.16 had a lower left atrial strain than those with a PLR of > 88.16 (0.38 vs. 0.77, p = 0.02).

CONCLUSION

The PLR was lower in patients with nonvalvular atrial fibrillation and with a decreased LAA-FV. Its correlation with left atrial strain might indicate the role of inflammation in the progression of atrial remodeling and in the prothrombotic state.

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 .

Targeting the Substrate in Ablation of Persistent Atrial Fibrillation: Recent Lessons and Future Directions

While isolation of the pulmonary veins is firmly established as effective treatment for the majority of paroxysmal atrial fibrillation (AF) patients, there is recognition that patients with persistent AF have substrate for perpetuation of arrhythmia existing outside of the pulmonary veins. Various computational approaches have been used to identify targets for effective ablation of persistent AF. This paper aims to discuss the clinical aspects of computational approaches that aim to identify critical sites for treatment. Various analyses of electrogram characteristics have been performed with this aim. Leading techniques for electrogram analysis are Complex Fractionated Atrial Electrograms (CFAE) and Dominant Frequency (DF). These techniques have been the subject of clinical trials of which the results are discussed. Evaluation of the activation patterns of atria in AF has been another avenue of research. Focal Impulse and Rotor Modulation (FIRM) mapping and forms of Body Surface Mapping aim to characterize multiple atrial wavelets, macro-reentry and focal sources which have been proposed as basic mechanisms perpetuating AF. Both invasive and non-invasive activation mapping techniques are reviewed. The presence of atrial fibrosis causes non-uniform anisotropic impulse propagation. Therefore, identification of fibrosis by imaging techniques is an avenue of potential research. The leading contender for imaging-based techniques is Cardiac Magnetic Resonance (CMR). As this technology advances, improvements in resolution and scar identification have positioned CMR as the mode of choice for analysis of atrial structure. AF has been demonstrated to be associated with obesity, inactivity and diseases of modern life. An opportunity exists for detailed computational analysis of the impact of risk factor modification on atrial substrate. This ranges from microstructural investigation through to examination at a population level via registries and public health interventions. Computational analysis of atrial substrate has moved from basic science toward clinical application. Future directions and potential limitations of such analyses are examined in this review.