Left atrial voltage mapping: defining and targeting the atrial fibrillation substrate

Effectiveness of a Standardized Approach to Repeat Paroxysmal Atrial Fibrillation Ablation: Insights Into the Value of Extrapulmonary Vein Targets

BACKGROUND

The optimal approach to repeat catheter ablation for recurrent paroxysmal atrial fibrillation (PAF) is unknown.

METHODS

Consecutive patients undergoing repeat PAF ablation were studied. The following 6-step approach was used in all cases: re-isolation of reconnected pulmonary veins (PVs); ablation of left atrial low-voltage areas (LVAs); targeted ablation of clinical or inducible atrial flutter/tachycardia; non-PV trigger ablation; ablation of inducible supraventricular tachycardia; and additional empirical ablation based on operator judgement. The primary study outcome was atrial arrhythmia-free survival at 1 year.

RESULTS

One hundred thirteen patients were included in the study (mean age 63.7 ± 8.6 years, 28.3% women). In this cohort, 73.5% had PV reconnection(s), 31.9% had LVAs, 10.6% had identifiable non-PV triggers, 5.3% had inducible atrioventricular nodal re-entrant tachycardia, 31.9% underwent atrial flutter/tachycardia ablation, and 12.4% had additional empirical ablation performed. Arrhythmia-free survival at 1 year was 53.1%. Patients with arrhythmia recurrence were more likely to be older, female, have hypertension, have durably isolated PVs, and to have undergone LVA ablation. In multivariable analysis, female sex and LVA ablation remained predictive of arrhythmia recurrence. Among patients with durably isolated PVs, only female sex was (negatively) associated with procedural success.

CONCLUSIONS

A comprehensive protocol for repeat PAF ablation resulted in arrhythmia-free survival at 1 year in 53% of patients. Durably isolated PVs were observed in 26.5% of cases. None of the ablation protocol's steps was suggested to independently improve procedural success. Further research to determine the optimal ablation strategy in patients undergoing repeat ablation for PAF is needed, a growing proportion of whom are expected to have durably isolated PVs.

Quantification of atrial cardiomyopathy disease severity by electroanatomic voltage mapping and cardiac magnetic resonance imaging

INTRODUCTION

Atrial late gadolinium enhancement (Atrial-LGE) and electroanatomic voltage mapping (Atrial-EAVM) quantify the anatomical and functional extent of atrial cardiomyopathy. We aimed to explore the relationships between, and outcomes from, these modalities in patients with atrial fibrillation undergoing ablation.

METHODS

Patients undergoing first-time ablation had disease severities quantified using both Atrial-LGE and Atrial-EAVM. Correlations between modalities and their relationships with clinical features and arrhythmia recurrence were assessed.

RESULTS

In 123 atrial fibrillation patients (60 ± 10 years), Atrial-EAVM was moderately correlated with Atrial-LGE (r = .34, p < .001), with a mean fibrosis burden of 47.2% ± 14.91%. Agreement was strongest in the highest tertile of fibrosis burden (mean of differences 16.8% (95% CI = -24.4% to 57.9%, p = .433). Fibrosis burden was greater for Atrial-LGE than Atrial-EAVM (50.7% ± 10.7% vs. 13.7% ± 7.13%, p < .005) for patients in the lowest tertile who were younger, had smaller atria and a greater frequency of paroxysmal atrial fibrillation. Both Atrial EAVM and Atrial LGE were associated with recurrence of arrhythmia following ablation (Atrial-LGE HR = 1.02 (95% CI = 1.01-1.04), p = .047; Atrial-EAVM HR = 1.02 (95% CI = 1.005-1.03), p = .007). A low fibrosis burden (<15%) by Atrial-EAVM identified patients with very low arrhythmia recurrence. In contrast, a much higher fibrosis burden (>66%) by Atrial-LGE identified patients failing to respond to ablation.

CONCLUSIONS

We demonstrate for the first time that the level of agreement between Atrial-EAVM and Atrial-LGE is dependent on the level of atrial cardiomyopathy disease severity. The functional consequences of atrial cardiomyopathy are most evident in patients with the highest anatomical extent of disease.

Electrophysiological Markers of Ex-Situ Heart Performance in a Porcine Model of Cardiac Donation After Circulatory Death

Normothermic ex-situ heart perfusion (ESHP) enables assessment of hearts donated after circulatory death (DCD) prior to transplantation. However, sensitive parameters of cardiac function of DCD hearts on ESHP are needed. This study proposes a novel approach using electrophysiological (EP) parameters derived from electrical mapping as biomarkers of post-ischemic cardiac performance. Porcine slaughterhouse hearts (PSH) were divided in two groups based on the type of warm ischemia (Group 1: 10 ± 1 min with animal depilation vs. Group 2: ≤5 min without depilation). Electrical mapping of the right (RV) and left ventricle (LV) was performed on ESHP. Potential voltages, slopes and conduction velocities were computed from unipolar electrograms and compared between groups. Voltages were lower in Group 1 compared to Group 2 (RV: 3.6 vs. 15.3 mV, p = 0.057; LV: 10.8 vs. 23.6 mV, p = 0.029). In addition, the percentage of low-voltage potentials was higher and potential slopes were flatter in Group 1. Voltages and slopes strongly correlated with the visual contractile performance of PSH, but showed weaker correlation with lactate profiles. In conclusion, unipolar potential voltages and potential slopes were decreased in hearts with severe warm ischemia. As such, EP parameters could aid transplantation teams in decision-making on transplantability of DCD hearts.

Functional substrate analysis in patients with persistent atrial fibrillation

OBJECTIVES

The aim of this study was to describe the correlation between atrial electrogram duration map (AEDUM), spatiotemporal electrogram dispersion (STED) and low voltage areas (LVA) in patients with persistent atrial fibrillation (PsAF).

BACKGROUND

The degree of left atrial (LA) tissue remodelling and augmented anisotropic conduction is one of the major issues related to PsAF ablation outcome.

METHODS

This study enrolled consecutive patients with PsAF undergoing pulmonary vein isolation. In all patients, voltage, AEDUM and STED maps were created, and the correlation was reported between these three mapping methods.

RESULTS

A total of 40 patients with PsAF were enrolled. The mean age was 62.2 ± 7.4 years, and males were 72.5% (n = 29). The overall bipolar voltage of the LA was 3.06 ± 1.87 mV. All patients had at least one AEDUM area (overall AEDUM area: 21.8 ± 8.2 cm2); the mean longest electrogram (EGMs) duration was 90 ± 19 ms. STED areas with < 120 ms was 46.3 ± 20.2 cm2 which covered 45 ± 22% of the LA surface. AEDUM and STED areas were most frequently reported on the roof, the anterior wall and the septum. The extension of the AEDUM areas was significantly smaller than STED areas with CL < 120 ms (21.8 ± 8.2 vs 46.3 ± 20.2; p-value < 0.0001). In 24 patients (60%), AEDUM areas was entirely included in the STED areas with CL < 120 ms. In the three (7.5%) patients with LVA, no correspondence with STED and AEDUM was noted.

CONCLUSION

AEDUM and STED maps allow to identify areas of conductive dysfunction as a possible atrial substrate even if a normal voltage is detected.

Myeloperoxidase and N-terminal proatrial natriuretic peptide as predictors for atrial fibrillation recurrence in patients undergoing redo ablation

Background

Atrial fibrillation (AF) is a progressively developing arrhythmia. Electroanatomic remodeling may play an important role, both in the development of the disease and in the perpetuation and thus in the recurrence of AF.

Objective

This study aimed to investigate potential biomarkers myeloperoxidase (MPO), N-terminal proatrial natriuretic peptide (NT-proANP), intercellular adhesion molecule-1, and matrix metalloproteinase-2 and their predictive value for AF recurrence in patients undergoing redo ablation.

Methods

In this single-center prospective cohort study, 50 consecutive patients underwent ultra high-density mapping and redo ablation. Biomarkers were determined before ablation and at 6-month follow-up. Seven-day Holter was conducted to check for AF recurrence (>30 seconds).

Results

Eleven (22%) patients showed AF recurrence after redo ablation. Receiver-operating characteristic curve analysis revealed venous MPO and NT-proANP (area under the curve [AUC] 0.755, 95% CI 0.599-0.912, P = .010; and AUC 0.752, 95% CI 0.551-0.953, P = .011) as acceptable predictors for intermediate AF recurrence, whereas matrix metalloproteinase-2, intercellular adhesion molecule-1, and established cardiovascular biomarkers such as N-terminal pro-B-type natriuretic peptide, troponin T, and C-reactive protein were not (all AUC <0.600). MPO and NT-proANP correlated with AF burden (ρ = 0.365, P = .005; and ρ = 0.362, P = .005). While MPO was associated with atrial fibrosis in the endocardial map (ρ = 0.280, P = .024), NT-proANP correlated with left atrial volume index (ρ = 0.256, P = .037). There were no significant differences in biomarkers concentrations with regard to venous and coronary sinus samples.

Conclusion

MPO and NT-proANP are of predictive value for AF recurrence in patients undergoing redo ablation. While MPO correlated with endocardial fibrosis, NT-proANP was associated with left atrial volume.

Left Atrial Low-Voltage Extent Predicts the Recurrence of Supraventricular Arrhythmias

The incidence of left atrial (LA) supraventricular arrhythmias is increasing. Even after LA ablation, recurrence of these tachycardias is common. MRI studies show that LA cardiomyopathy is a significant risk factor for recurrence and correlates with low voltage areas detected via 3D electroanatomic mapping (EAM). There are limited data on the impact of low voltage extent detected by EAM on recurrence-free survival. Voltage thresholds defining low voltage vary across different studies. This study aims to investigate the impact of the extent of low voltage areas in the LA on recurrence-free survival and to assess whether defining low voltage areas using thresholds of 0.5, 0.4, or 0.3 mV offers better predictive performance. Patients with atrial arrhythmia who underwent LA EAM at Ulm University Heart Center between September 2018 and September 2022 were included from the ATRIUM registry. ROC analysis determined the voltage threshold for predicting recurrence-free survival. Kaplan-Meier and logistic regression models adjusted for patient variables were used to analyze recurrence-free survival. Of 1089 screened patients, 108 met the inclusion criteria. ROC analysis indicated that a 0.4 mV threshold for low voltage provided the best predictive performance. Logistic regression showed a 1.039-fold increase in recurrence risk per percent increase in LA low voltage area (odds ratio = 1.039, 95% CI 1.014-1.064). Low voltage extent in EAM correlates with 1-year recurrence rate after ablation of left atrial supraventricular arrhythmias. The threshold of 0.4 mV is the most suitable for predicting recurrences of those examined.

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.

Ablation of persistent atrial fibrillation based on atrial electrogram duration map: methodology and clinical outcomes from the AEDUM pilot study

BACKGROUND

Catheter ablation of persistent atrial fibrillation (PsAF) represents a challenge for the electrophysiologist and there are still divergences regarding the best ablative approach to adopt. Create a new map of the duration of atrial bipolar electrograms (Atrial Electrogram DUration Map, AEDUM) to recognize a functional substrate during sinus rhythm and guide a patient-tailored ablative strategy for PsAF.

METHODS

Forty PsAF subjects were assigned in a 1:1 ratio to either for PVI alone (Group B1) or PVI+AEDUM areas ablation (Group B2). A cohort of 15 patients without AF history undergoing left-sided accessory pathway ablation was used as a control group (Group A). In all patients, voltage and AEDUM maps were created during sinus rhythm. The minimum follow-up was 12 months, with rhythm monitoring via 48-h ECG Holter or by implantable cardiac device.

RESULTS

Electrogram (EGM) duration was higher in Group B than in Group A (49±16.2ms vs 34.2±3.8ms; p-value<0.001). In Group B the mean cumulative AEDUM area was 21.8±8.2cm2; no difference between the two subgroups was observed (22.3±9.1cm2 vs 21.2±7.2cm2; p-value=0.45). The overall bipolar voltage recorded inside the AEDUM areas was lower than in the remaining atrial areas [median: 1.30mV (IQR: 0.71-2.38mV) vs 1.54mV (IQR: 0.79-2.97mV); p-value: <0.001)]. Low voltage areas (<0.5mV) were recorded in three (7.5%) patients in Group B. During the follow-up [median 511 days (376-845days)] patients who underwent PVI-only experienced more AF recurrence than those receiving a tailored approach (65% vs 35%; p-value= 0.04).

CONCLUSIONS

All PsAF patients exhibited AEDUM areas. An ablation approach targeting these areas resulted in a more effective strategy compared with PVI only.

Sex-related differences in left atrial substrate among patients with atrial fibrillation: evidence from high-density voltage mapping

BACKGROUND

There is sufficient evidence that women with atrial fibrillation (AF) have a greater symptom burden than men with AF and are more likely to experience recurrence after catheter ablation. However, the mechanisms underlying these sex differences are unclear.

METHODS

We prospectively enrolled 125 consecutive patients, including 40 non-AF patients and 85 AF patients, who underwent high-density voltage mapping during sinus rhythm and AF patients who underwent first ablation.

RESULTS

Overall, 37 (44%) female patients with AF and 24 (60%) female non-AF patients with a mean age of 61.7 ± 11.6 years and 53.6 ± 16.7 years, respectively, were enrolled in this study. The results showed that the atrial voltage of female AF patients was significantly lower than that of male AF patients (1.11 ± 0.58 mV vs. 1.53 ± 0.65 mV; P = 0.003), while there were no significant sex differences in non-AF patients (3.02 ± 0.86 mV vs. 3.21 ± 0.84 mV; P = 0.498). Multiple linear regression analysis revealed that female sex (- 0.29, 95% confidence interval [CI] - 0.64 to - 0.13, P = 0.004) and AF type (- 0.32, 95% CI - 0.69 to - 0.13, P = 0.004) were the only factors independently associated with voltage. Compared with men, women in the paroxysmal AF group had a 3.5-fold greater incidence of recurrence (adjusted hazard ratio 4.49; 95% CI 1.101-18.332, P = 0.036). Both globally and regionally, the results showed that sex-related differences in voltage values occurred prominently in paroxysmal AF patients but not in nonparoxysmal AF patients.

CONCLUSION

Sex-related differences in atrial substrates and arrhythmia-free survival were found in paroxysmal AF patients, suggesting the existence of sex-related pathophysiological factors.

Association of beat-to-beat P-wave analysis index to the extent of left atrial low-voltage areas in patients with paroxysmal atrial fibrillation

BACKGROUND

Left atrial (LA) fibrosis has been shown to be associated with atrial fibrillation (AF) recurrence. Beat-to-beat (B2B) index is a non-invasive classifier, based on B2B P-wave morphological and wavelet analysis, shown to be associated with AF incidence and recurrence. In this study, we tested the hypothesis that the B2B index is associated with the extent of LA low-voltage areas (LVAs) on electroanatomical mapping.

METHODS

Patients with paroxysmal AF scheduled for pulmonary vein isolation, without evident structural remodeling, were included. Pre-ablation electroanatomical voltage maps were used to calculate the surface of LVAs (<0.5 mV). B2B index was compared between patients with small versus large LVAs.

RESULTS

35 patients were included (87% male, median age 62). The median surface area of LVAs was 7.7 (4.4-15.8) cm2 corresponding to 5.6 (3.3-12.1) % of LA endocardial surface. B2B index was 0.57 (0.52-0.59) in patients with small LVAs (below the median) compared to 0.65 (0.56-0.77) in those with large LVAs (above the median) (p = 0.009). In the receiver operator characteristic curve analysis for predicting large LVAs, the c-statistic was 0.75 (p = 0.006) for B2B index and 0.81 for the multivariable model including B2B index (multivariable p = 0.04) and P-wave duration.

CONCLUSION

In patients with paroxysmal AF without overt atrial myopathy, B2B P-wave analysis appears to be a useful non-invasive correlate of low-voltage areas-and thus fibrosis-in the LA. This finding establishes a pathophysiological basis for B2B index and its potential usefulness in the selection process of patients who are likely to benefit most from further invasive treatment.

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

AIMS

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

METHODS AND RESULTS

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

CONCLUSION

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

P-Wave Duration/Amplitude Ratio Quantifies Atrial Low-Voltage Area and Predicts Atrial Arrhythmia Recurrence After Pulmonary Vein Isolation

BACKGROUND

Atrial low-voltage areas (LVAs) in patients with atrial fibrillation increase the risk of atrial arrhythmia (AA) recurrence after pulmonary vein isolation (PVI). Contemporary LVA prediction scores (DR-FLASH, APPLE) do not include P-wave metrics. We aimed to evaluate the utility of P-wave duration/amplitude ratio (PWR) in quantifying LVA and predicting AA recurrence after PVI.

METHODS

In 65 patients undergoing first-time PVI, 12-lead ECGs were recorded during sinus rhythm. PWR was calculated as the ratio between the longest P-wave duration and P-wave amplitude in lead I. High-resolution biatrial voltage maps were collected and LVAs included bipolar electrogram amplitudes < 0.5 mV or < 1.0 mV. An LVA quantification model was created with the use of clinical variables and PWR, and then validated in a separate cohort of 24 patients. Seventy-eight patients were followed for 12 months to evaluate AA recurrence.

RESULTS

PWR strongly correlated with left atrial (LA) (< 0.5 mV: r = 0.60; < 1.0 mV: r = 0.68; P < 0.001) and biatrial LVA (< 0.5 mV: r = 0.63; < 1.0 mV: r = 0.70; P < 0.001). Addition of PWR to clinical variables improved model quantification of LA LVA at the < 0.5 mV (adjusted R2 = 0.59 to 0.68) and < 1.0 mV (adjusted R2 = 0.59 to 0.74) cutoffs. In the validation cohort, PWR model-predicted LVA correlated strongly with measured LVA (< 0.5 mV: r = 0.78; < 1.0 mV: r = 0.81; P < 0.001). PWR model was superior to DR-FLASH (area under the receiver operating characteristic curve [AUC] 0.90 vs 0.78; P = 0.030) and APPLE (AUC 0.90 vs 0.67; P = 0.003) at detecting LA LVA and similar at predicting AA recurrence after PVI (AUC 0.67 vs 0.65 and 0.60).

CONCLUSION

Our novel PWR model accurately quantifies LVA and predicts AA recurrence after PVI. PWR model-predicted LVA may help guide patient selection for PVI.

Left atrial conduction times and regional velocities in persistent atrial fibrillation patients with and without fibrotic atrial cardiomyopathy

Despite the progress in understanding left atrial substrate and arrhythmogenesis, only little is known about conduction characteristics in atrial fibrillation patients with various stages of fibrotic atrial cardiomyopathy (FACM). This study evaluates left atrial conduction times and conduction velocities based on high-density voltage and activation maps in sinus rhythm (CARTO®3 V7) of 53 patients with persistent atrial fibrillation (LVEF 60% (55-60 IQR), LAVI 39 ml/m2 (31-47 IQR), LApa 24 ± 6 cm2). Measurements were made in low voltage areas (LVA ≤ 0.5 mV) and normal voltage areas (NVA ≥ 1.5 mV) at the left atrial anterior and posterior walls. Maps of 28 FACM and 25 no FACM patients were analyzed (19 FACM I/II, 9 FACM III/IV, LVA 14 ± 11 cm2). Left atrial conduction time averaged to 110 ± 24 ms but was shown to be prolonged in FACM (119 ms, + 17%) when compared to no FACM patients (101 ms, p = 0.005). This finding was pronounced in high-grade FACM (III/IV) (133 ms, + 31.2%, p = 0.001). In addition, the LVA extension correlated significantly with the left atrial conduction time (r = 0.56, p = 0.002). Conduction velocities were overall slower in LVA than in NVA (0.6 ± 0.3 vs. 1.3 ± 0.5 m/s, -51%, p < 0.001). Anterior conduction appeared slower than posterior, which was significant in NVA (1 vs. 1.4 m/s, -29%, p < 0.001) but not in LVA (0.6 vs. 0.8 m/s, p = 0.096). FACM has a significant influence on left atrial conduction characteristics in patients with persistent atrial fibrillation. Left atrial conduction time prolongs with the grade of FACM and the quantitative expanse of LVA up to 31%. LVAs show a 51% conduction velocity reduction compared to NVA. Moreover, regional conduction velocity differences are present in the left atrium when comparing anterior to posterior walls. Our data may influence individualized ablation strategies.

Impact of Obesity on Atrial Electrophysiological Substrate

(1) Background. Obesity is a well-established worldwide recognised risk factor for atrial fibrillation (AF). Prior review papers reported on the associations between obesity and AF development, but not on the relation between obesity and atrial electrophysiology. We therefore conducted a systematic review to describe the current knowledge of the characteristics of the atrial electrophysiological substrate in obese individuals and how they relate to the development of AF. (2) Methods. A search was conducted in Pubmed, Embase, and the Cochrane Library for publications evaluating the impact of obesity on atrial electrophysiology, electrical substrates, and their relation to the development of AF. (3) Results. A systematic literature search retrieved 477 potential publications based on the inclusion criteria; 76 full-text articles were selected for the present systematic review. The literature demonstrated that obesity predisposes to not only a higher AF incidence but also to more extensive atrial electrophysiological abnormalities increasing susceptibility to AF development. (4) Conclusion. Obesity may predispose to an overall increase in atrial electropathology, consisting of an increase in the slowing of the conduction, conduction block, low-voltage areas, and complex fractionated electrograms. To determine the impact of obesity-induced atrial electrical abnormalities on the long-term clinical outcome, further prospective studies are mandatory.

Baseline left atrial low-voltage area predicts recurrence after pulmonary vein isolation: WAVE-MAP AF results

AIMS

Electro-anatomical mapping may be critical to identify atrial fibrillation (AF) subjects who require substrate modification beyond pulmonary vein isolation (PVI). The objective was to determine correlations between pre-ablation mapping characteristics and 12-month outcomes after a single PVI-only catheter ablation of AF.

METHODS AND RESULTS

This study enrolled paroxysmal AF (PAF), early persistent AF (PsAF; 7 days-3 months), and non-early PsAF (>3-12 months) subjects undergoing de novo PVI-only radiofrequency catheter ablation. Sinus rhythm (SR) and AF voltage maps were created with the Advisor HD Grid™ Mapping Catheter, Sensor Enabled™ for each subject, and the presence of low-voltage area (LVA) (low-voltage cutoffs: 0.1-1.5 mV) was investigated. Follow-up visits were at 3, 6, and 12 months, with a 24-h Holter monitor at 12 months. A Cox proportional hazards model identified associations between mapping data and 12-month recurrence after a single PVI procedure. The study enrolled 300 subjects (113 PAF, 86 early PsAF, and 101 non-early PsAF) at 18 centres. At 12 months, 75.5% of subjects were free from AF/atrial flutter (AFL)/atrial tachycardia (AT) recurrence. Univariate analysis found that arrhythmia recurrence did not correlate with AF diagnosis, but LVA was significantly correlated. Low-voltage area (<0.5 mV) >28% of the left atrium in SR [hazard ratio (HR): 4.82, 95% confidence interval (CI): 2.08-11.18; P = 0.0003] and >72% in AF (HR: 5.66, 95% CI: 2.34-13.69; P = 0.0001) was associated with a higher risk of AF/AFL/AT recurrence at 12 months.

CONCLUSION

Larger extension of LVA was associated with an increased risk of arrhythmia recurrence. These subjects may benefit from substrate modification beyond PVI.

High-resolution mapping of reentrant atrial tachycardias: Relevance of low bipolar voltage

BACKGROUND

Bipolar voltage is widely used to characterize the atrial substrate but has been poorly validated, particularly during clinical tachycardias.

OBJECTIVE

The purpose of this study was to evaluate the diagnostic performance of voltage thresholds for identifying regions of slow conduction during reentrant atrial tachycardias (ATs).

METHODS

Thirty bipolar voltage and activation maps created during reentrant ATs were analyzed to (1) examine the relationship between voltage amplitude and conduction velocity (CV), (2) measure the diagnostic ability of voltage thresholds to predict CV, and (3) identify determinants of AT circuit dimensions. Voltage amplitude was categorized as "normal" (>0.50 mV), "abnormal" (0.05-0.50 mV), or "scar" (<0.05 mV); slow conduction was defined as <30 cm/s.

RESULTS

A total of 266,457 corresponding voltage and CV data points were included for analysis. Voltage and CV were moderately correlated (r = 0.407; P < .001). Bipolar voltage predicted regions of slow conduction with an area under the receiver operating characteristic curve of 0.733 (95% confidence interval 0.731-0.735). A threshold of 0.50 mV had 91% sensitivity and 35% specificity for identifying slow conduction, whereas 0.05 mV had 36% sensitivity and 87% specificity, with an optimal voltage threshold of 0.15 mV. Analyses restricted to the AT circuits identified weaker associations between voltage and CV and an optimal voltage threshold of 0.25 mV.

CONCLUSION

Widely used bipolar voltage amplitude thresholds to define "abnormal" and "scar" tissue in the atria are, respectively, sensitive and specific for identifying regions of slow conduction during reentrant ATs. However, overall, the association of voltage with CV is modest. No clinical predictors of AT circuit dimensions were identified.

Living myocardial slices: Advancing arrhythmia research

Living myocardial slices (LMS) are ultrathin (150-400 µm) sections of intact myocardium that can be used as a comprehensive model for cardiac arrhythmia research. The recent introduction of biomimetic electromechanical cultivation chambers enables long-term cultivation and easy control of living myocardial slices culture conditions. The aim of this review is to present the potential of this biomimetic interface using living myocardial slices in electrophysiological studies outlining advantages, disadvantages and future perspectives of the model. Furthermore, different electrophysiological techniques and their application on living myocardial slices will be discussed. The developments of living myocardial slices in electrophysiology research will hopefully lead to future breakthroughs in the understanding of cardiac arrhythmia mechanisms and the development of novel therapeutic options.

Reverse structural left atrial remodeling and atrial tachycardia in patients with repeat ablation for atrial fibrillation

BACKGROUND

Catheter ablation has been evolved to a cornerstone in the therapy of atrial fibrillation (AF); however, atrial tachycardias (AT) after AF ablation are still an important issue. Besides the electrical recurrence of atrial tachyarrhythmia after ablation, left atrial (LA) remodeling has received attention as a consequence of AF.

OBJECTIVE

The aim of this study is to evaluate predictors for AT recurrence and LA remodeling in patients with repeat AF ablation procedures.

METHODS AND RESULTS

One hundred thirteen patients who underwent repeat AF ablation with 3D electro-anatomical mapping system were evaluated. Mean age was 63.1 ± 9.3 years, and 2.3 ± 0.5 ablation procedures were performed during a time period of 22 [IQR 7;48] months. Reverse structural LA remodeling (LA volume decreased more than 15%) was observed in 25 (22.1%) patients. LA volume index (LAVI) during first procedure was the only predictor for positive reverse structural LA remodeling (hazard ratio (HR): 1.03, 95% CI: 1.00-1.07, p = .036) in multivariate analysis. Fifty-nine (52.2%) patients experienced only AF and 54 (47.8%) patients AT after first procedure. Female gender (HR: 5.21, 95% CI: 1.66-18.08, p = .006), LAVI (HR: 1.06, 95% CI: 1.02-1.11, p = .008) and LA scar percentage (HR: 1.08, 95% CI: 1.02-1.17, p = .019) were independent significant predictors for AT recurrence in multivariate analysis.

CONCLUSIONS

Reverse structural LA remodeling occurred in a quarter of patients with repeat ablation procedures for AF. Only larger LAVI during first procedure predicted reverse structural LA remodeling. Half of the patients experienced AT between first and last ablation procedure. Female gender, larger LAVI and larger scar area were significant predictors for AT after catheter ablation for AF.

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.

Clinical and Structural Factors Affecting Ablation Outcomes in Atrial Fibrillation Patients - A Review

Catheter ablation is an effective and durable treatment option for patients with atrial fibrillation (AF). Ablation outcomes vary widely, with optimal results in patients with paroxysmal AF and diminishing results in patients with persistent or long-standing persistent AF. A number of clinical factors including obesity, hypertension, diabetes, obstructive sleep apnea, and alcohol use contribute to AF recurrence following ablation, likely through modulation of the atrial electroanatomic substrate. In this article, we review the clinical risk factors and the electro-anatomic features that contribute to AF recurrence in patients undergoing ablation for AF.

Characterization of Atrial Substrate to Predict the Success of Pulmonary Vein Isolation: The Prospective, Multicenter MASH-AF II (Multipolar Atrial Substrate High Density Mapping in Atrial Fibrillation) Study

Background Left atrial substrate may have mechanistic relevance for ablation of atrial fibrillation (AF). We sought to analyze the relationship between low-voltage zones (LVZs), transition zones, and AF recurrence in patients undergoing pulmonary vein isolation. Methods and Results We conducted a prospective multicenter study on consecutive patients undergoing pulmonary vein isolation-only approach. LVZs and transition zones (0.5-1 mV) were analyzed offline on high-density electroanatomical maps collected before pulmonary vein isolation. Overall, 262 patients (61±11 years, 31% female) with paroxysmal (130 pts) or persistent (132 pts) AF were included. After 28 months of follow-up, 73 (28%) patients experienced recurrence. An extension of more than 5% LVZ in paroxysmal AF and more than 15% in persistent AF was associated with recurrence (hazard ratio [HR], 4.4 [95% CI, 2.0-9.8], P<0.001 and HR, 1.9 [95% CI, 1.1-3.7], P=0.04, respectively). Significant association was found between LVZs and transition zones and between LVZs and left atrial volume index (LAVI) (both P<0.001). Thirty percent of patients had significantly increased LAVI without LVZs. Eight percent of patients had LVZs despite normal LAVI. Older age, female sex, oncological history, and increased AF recurrence characterized the latter subgroup. Conclusions In patients undergoing first pulmonary vein isolation, the impact of LVZs on outcomes occurs with lower burden in paroxysmal than persistent AF, suggesting that not all LVZs have equal prognostic implications. A proportional area of moderately decreased voltages accompanies LVZs, suggesting a continuous substrate instead of the dichotomous division of healthy or diseased tissue. LAVI generally correlates with LVZs, but a small subgroup of patients may present with disproportionate atrial remodeling, despite normal LAVI.

Talk like a duck, walk like a duck: A cardiac surgeon's understanding of complex imaging in the management of atrial fibrillation

The treatment of atrial fibrillation continues to evolve. The Heart Team Hybrid Ablation Approach is the latest iteration of Electrophysiology and Arrythmia surgeon collaboration that is focused on the treatment of complex (persistent and long-standing persistent) atrial fibrillation patients. Critical to this team approach is the ability to converse regarding atrial anatomy, atrial substrate and transmurality of ablation lesions. The cornerstone of these dialogs is advanced imaging techniques including; transesophageal echocardiography, enhanced magnetic resonance imaging, endocardial voltage mapping, and epicardial electrogram mapping. We herein review these techniques and their clinic implications.

Atrial fibrillation: Insights from animal models, computational modeling, and clinical studies

Atrial fibrillation (AF) is the most common human arrhythmia, affecting millions of patients worldwide. A combination of risk factors and comorbidities results in complex atrial remodeling, which increases AF vulnerability and persistence. Insights from animal models, clinical studies, and computational modeling have advanced the understanding of the mechanisms and pathophysiology of AF. Areas of heterogeneous pathological remodeling, as well as altered electrophysiological properties, serve as a substrate for AF drivers and spontaneous activations. The complex and individualized presentation of this arrhythmia suggests that mechanisms-based personalized approaches will likely be needed to overcome current challenges in AF management. In this paper, we review the insights on the mechanisms of AF obtained from animal models and clinical studies and how computational models integrate this knowledge to advance AF clinical management. We also assess the challenges that need to be overcome to implement these mechanistic models in clinical practice.

Detection of endo-epicardial atrial low-voltage areas using unipolar and omnipolar voltage mapping

Background: Low-voltage areas (LVA) can be located exclusively at either the endocardium or epicardium. This has only been demonstrated for bipolar voltages, but the value of unipolar and omnipolar voltages recorded from either the endocardium and epicardium in predicting LVAs at the opposite layer remains unknown. The goal of this study was therefore to compare simultaneously recorded endo-epicardial unipolar and omnipolar potentials and to determine whether their voltage characteristics are predictive for opposite LVAs.

Methods: Intra-operative simultaneous endo-epicardial mapping (256 electrodes, interelectrode distances 2 mm) was performed during sinus rhythm at the right atrium in 93 patients (67 ± 9 years, 73 male). Cliques of four electrodes (2 × 2 mm) were used to define maximal omnipolar (Vomni,max) and unipolar (Vuni,max) voltages. LVAs were defined as Vomni,max ≤0.5 mV or Vuni,max ≤1.0 mV.

Results: The majority of both unipolar and omnipolar LVAs were located at only the endocardium (74.2% and 82.0% respectively) or epicardium (52.7% and 47.6% respectively). Of the endocardial unipolar LVAs, 25.8% were also located at the opposite layer and 47.3% vice-versa. In omnipolar LVAs, 18.0% of the endocardial LVAs were also located at the epicardium and 52.4% vice-versa. The combination of epicardial Vuni,max and Vomni,max was most accurate in identifying dual-layer LVAs (50.4%).

Conclusion: Unipolar and omnipolar LVAs are frequently located exclusively at either the endocardium or epicardium. Endo-epicardial LVAs are most accurately identified using combined epicardial unipolar and omnipolar voltages. Therefore, a combined endo-epicardial unipolar and omnipolar mapping approach is favoured as it may be more indicative of possible arrhythmogenic substrates.

Provocation and localization of atrial ectopy in patients with atrial septal defects

BACKGROUND

Atrial fibrillation (AF) is associated with atrial septal defects (ASDs), but the mechanism of arrhythmia in these patients is poorly understood. We hypothesised that right-sided atrial ectopy may predominate in this cohort. Here, we aimed to localise the origin of spontaneous and provoked atrial ectopy in ASD patients.

METHODS

Following invasive calibration of P-wave axes, 24-h Holter monitoring was used to determine the chamber of origin of spontaneous atrial ectopy. Simultaneous electrogram recording from multiple intra-cardiac catheters was used to determine the chamber of origin of isoprenaline-provoked ectopy. Comparison was made to a group of non-congenital heart disease AF patients.

RESULTS

Amongst ASD patients, a right-sided origin for spontaneous atrial ectopy was significantly more prevalent than a left-sided origin (24/30 patients with right-sided ectopy vs. 14/30 with left-sided ectopy, P = 0.015). Amongst AF patients, there was no difference in the prevalence of spontaneous right vs. left-sided ectopy. For isoprenaline-provoked ectopy, there was no significant difference in the proportions of patients with right-sided or left-sided ectopy in either group.

CONCLUSIONS

When spontaneous atrial ectopy occurs in ASD patients, it is significantly more prevalent from a right-sided than left-sided origin. Isoprenaline infusion did not reveal the predilection for right-sided ectopy during electrophysiology study.

Atrial fibrosis identification with unipolar electrogram eigenvalue distribution analysis in multi-electrode arrays

Abstract

Atrial fibrosis plays a key role in the initiation and progression of atrial fibrillation (AF). Atrial fibrosis is typically identified by a peak-to-peak amplitude of bipolar electrograms (b-EGMs) lower than 0.5 mV, which may be considered as ablation targets. Nevertheless, this approach disregards signal spatiotemporal information and b-EGM sensitivity to catheter orientation. To overcome these limitations, we propose the dominant-to-remaining eigenvalue dominance ratio (EIGDR) of unipolar electrograms (u-EGMs) within neighbor electrode cliques as a waveform dispersion measure, hypothesizing that it is correlated with the presence of fibrosis. A simulated 2D tissue with a fibrosis patch was used for validation. We computed EIGDR maps from both original and time-aligned u-EGMs, denoted as \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathcal {R}$$\end{document}R and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathcal{R}^{\mathcal{A}}$$\end{document}RA, respectively, also mapping the gain in eigenvalue concentration obtained by the alignment, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta \mathcal{R}^{\mathcal{A}}$$\end{document}ΔRA. The performance of each map in detecting fibrosis was evaluated in scenarios including noise and variable electrode-tissue distance. Best results were achieved by \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathcal{R}^{\mathcal{A}}$$\end{document}RA, reaching 94% detection accuracy, versus the 86% of b-EGMs voltage maps. The proposed strategy was also tested in real u-EGMs from fibrotic and non-fibrotic areas over 3D electroanatomical maps, supporting the ability of the EIGDRs as fibrosis markers, encouraging further studies to confirm their translation to clinical settings.

Graphical Abstract

Upper panels: map of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathcal {R}^{\mathcal {A}}$$\end{document}RA from 3×3 cliques for Ψ= 0^∘ and bipolar voltage map V^b-m, performed assuming a variable electrode-to-tissue distance and noisy u-EGMs (noise level σ_v = 46.4 μV ). Lower panels: detected fibrotic areas (brown), using the thresholds that maximize detection accuracy of each map

The Atrium in Atrial Fibrillation - A Clinical Review on How to Manage Atrial Fibrotic Substrates

Atrial fibrillation (AF) is the most common sustained arrhythmia in the population and is associated with a significant clinical and economic burden. Rigorous assessment of the presence and degree of an atrial arrhythmic substrate is essential for determining treatment options, predicting long-term success after catheter ablation, and as a substrate critical in the pathophysiology of atrial thrombogenesis. Catheter ablation of AF has developed into an essential rhythm-control strategy. Nowadays is one of the most common cardiac ablation procedures performed worldwide, with its success inversely related to the extent of atrial structural disease. Although atrial substrate evaluation remains complex, several diagnostic resources allow for a more comprehensive assessment and quantification of the extent of left atrial structural remodeling and the presence of atrial fibrosis. In this review, we summarize the current knowledge on the pathophysiology, etiology, and electrophysiological aspects of atrial substrates promoting the development of AF. We also describe the risk factors for its development and how to diagnose its presence using imaging, electrocardiograms, and electroanatomic voltage mapping. Finally, we discuss recent data regarding fibrosis biomarkers that could help diagnose atrial fibrotic substrates.

Clinical Relevance of Sinus Rhythm Mapping to Quantify Electropathology Related to Atrial Fibrillation

Progression of AF is accompanied by structural and electrical remodelling, resulting in complex electrical conduction disorders. This is defined as electropathology and it increases with the progression of AF. The severity of electropathology, thus, defines the stage of AF and is a major determinant of effectiveness of AF therapy. As specific features of AF-related electropathology are still unknown, it is essential to first quantify the electrophysiological properties of atrial tissue and then to examine the inter- and intra-individual variation during normal sinus rhythm. Comparison of these parameters between patients with and without a history of AF unravels quantified electrophysiological features that are specific to AF patients. This can help to identify patients at risk for early onset or progression of AF. This review summarises current knowledge on quantified features of atrial electrophysiological properties during sinus rhythm and discusses its relevance in identifying AF-related electropathology.

Fixed complex electrograms during sinus rhythm and local pacing: potential ablation targets for persistent atrial fibrillation

In atrial fibrillation (AF) patients, complex electrograms during sinus rhythm (C-EGMs) could be pathological or not. We aimed to demonstrate whether local pacing was helpful to discern pathological C-EGMs. 126 persistent AF patients and 27 patients with left-side accessory pathway (LAP) underwent left atrial mapping during sinus rhythm. If C-EGMs were detected, local pacing was performed. If the electrograms turned normal, we defined them as non-fixed C-EGMs, otherwise as fixed C-EGMs. No difference was detected in the incidence and proportion of non-fixed C-EGMs between AF patients and LAP patients (101/126 vs. 19/27, P = 0.26; 9.1 ± 6.0% vs. 7.7 ± 5.7%, P = 0.28). However, the incidence and proportion of fixed C-EGMs were higher in persistent AF patients (87/126 vs. 1/27, P < 0.01; 4.3 ± 3.4% vs. 0.1 ± 0.5%, P < 0.01). Compared with non-fixed C-EGMs, fixed C-EGMs had lower amplitudes, longer electrogram durations and longer Stimuli-P wave internals. All AF patients received circumferential pulmonary vein isolation. Among AF patients with fixed C-EGMs, 45 patients received fixed C-EGMs ablation and 42 patients underwent linear ablation. Compared with linear ablation, fixed C-EGMs ablation reduced recurrence (HR: 0.43; 95% CI 0.21‐0.81; P = 0.011). Among patients without fixed C-EGMs ablation, the proportion of fixed C-EGMs was an independent predictor of ablation outcomes (HR for per percent: 1.13, 95% CI 1.01–1.28, P = 0.038). C-EGMs could be classified into fixed and non-fixed C-EGMs through local pacing. Fixed rather than non-fixed C-EGMs might indicate abnormal atrial substrates and fixed C-EGMs ablation improve outcomes of persistent AF ablation.

Prediction of Type and Recurrence of Atrial Fibrillation after Catheter Ablation via Left Atrial Electroanatomical Voltage Mapping Registration and Multilayer Perceptron Classification: A Retrospective Study

Atrial fibrillation (AF) is a common cardiac arrhythmia and affects one to two percent of the population. In this work, we leverage the three-dimensional atrial endocardial unipolar/bipolar voltage map to predict the AF type and recurrence of AF in 1 year. This problem is challenging for two reasons: (1) the unipolar/bipolar voltages are collected at different locations on the endocardium and the shapes of the endocardium vary widely in different patients, and thus the unipolar/bipolar voltage maps need aligning to the same coordinate; (2) the collected dataset size is very limited. To address these issues, we exploit a pretrained 3D point cloud registration approach and finetune it on left atrial voltage maps to learn the geometric feature and align all voltage maps into the same coordinate. After alignment, we feed the unipolar/bipolar voltages from the registered points into a multilayer perceptron (MLP) classifier to predict whether patients have paroxysmal or persistent AF, and the risk of recurrence of AF in 1 year for patients in sinus rhythm. The experiment shows our method classifies the type and recurrence of AF effectively.

Atrial CARdiac Magnetic resonance imaging in patients with embolic stroke of unknown source without documented Atrial Fibrillation (CARM-AF): Study design and clinical protocol

Background

Initiation of anticoagulation therapy in ischemic stroke patients is contingent on a clinical diagnosis of atrial fibrillation (AF). Results from previous studies suggest thromboembolic risk may predate clinical manifestations of AF. Early identification of this cohort of patients may allow early initiation of anticoagulation and reduce the risk of secondary stroke.

Objective

This study aims to produce a substrate-based predictive model using cardiac magnetic resonance imaging (CMR) and baseline noninvasive electrocardiographic investigations to improve the identification of patients at risk of future thromboembolism.

Methods

CARM-AF is a prospective, multicenter, observational cohort study. Ninety-two patients will be recruited following an embolic stroke of unknown source (ESUS) and undergo atrial CMR followed by insertion of an implantable loop recorder (ILR) as per routine clinical care within 3 months of index stroke. Remote ILR follow-up will be used to allocate patients to a study or control group determined by the presence or absence of AF as defined by ILR monitoring.

Results

Baseline data collection, noninvasive electrocardiographic data analysis, and imaging postprocessing will be performed at the time of enrollment. Primary analysis will be performed following 12 months of continuous ILR monitoring, with interim and delayed analyses performed at 6 months and 2 and 3 years, respectively.

Conclusion

The CARM-AF Study will use atrial structural and electrocardiographic metrics to identify patients with AF, or at high risk of developing AF, who may benefit from early initiation of anticoagulation.

Critical appraisal of technologies to assess electrical activity during atrial fibrillation: a position paper from the European Heart Rhythm Association and European Society of Cardiology Working Group on eCardiology in collaboration with the Heart Rhythm Society, Asia Pacific Heart Rhythm Society, Latin American Heart Rhythm Society and Computing in Cardiology

We aim to provide a critical appraisal of basic concepts underlying signal recording and processing technologies applied for (i) atrial fibrillation (AF) mapping to unravel AF mechanisms and/or identifying target sites for AF therapy and (ii) AF detection, to optimize usage of technologies, stimulate research aimed at closing knowledge gaps, and developing ideal AF recording and processing technologies. Recording and processing techniques for assessment of electrical activity during AF essential for diagnosis and guiding ablative therapy including body surface electrocardiograms (ECG) and endo- or epicardial electrograms (EGM) are evaluated. Discussion of (i) differences in uni-, bi-, and multi-polar (omnipolar/Laplacian) recording modes, (ii) impact of recording technologies on EGM morphology, (iii) global or local mapping using various types of EGM involving signal processing techniques including isochronal-, voltage- fractionation-, dipole density-, and rotor mapping, enabling derivation of parameters like atrial rate, entropy, conduction velocity/direction, (iv) value of epicardial and optical mapping, (v) AF detection by cardiac implantable electronic devices containing various detection algorithms applicable to stored EGMs, (vi) contribution of machine learning (ML) to further improvement of signals processing technologies. Recording and processing of EGM (or ECG) are the cornerstones of (body surface) mapping of AF. Currently available AF recording and processing technologies are mainly restricted to specific applications or have technological limitations. Improvements in AF mapping by obtaining highest fidelity source signals (e.g. catheter-electrode combinations) for signal processing (e.g. filtering, digitization, and noise elimination) is of utmost importance. Novel acquisition instruments (multi-polar catheters combined with improved physical modelling and ML techniques) will enable enhanced and automated interpretation of EGM recordings in the near future.

Degree of Fibrosis in Human Atrial Tissue Is Not the Hallmark Driving AF

Background: The current paradigm is that fibrosis promotes electrophysiological disorders and drives atrial fibrillation (AF). In this current study, we investigated the relation between the degree of fibrosis in human atrial tissue samples of controls and patients in various stages of AF and the degree of electrophysiological abnormalities. Methods: The degree of fibrosis was measured in the atrial tissue and serum of patients in various stages of AF and the controls. Hereto, picrosirius and H&E staining were performed to quantify degree of total, endo-perimysial fibrosis, and cardiomyocyte diameter. Western blot quantified fibrosis markers: neural cell adhesion molecule, tissue inhibitor of metalloproteinase, lysyl oxidase, and α-smooth muscle actin. In serum, the ratio carboxyl-terminal telopeptide of collagen/matrix-metalloproteinase1 was determined. High-resolution epicardial mapping evaluated low-voltage areas and conduction abnormalities. Results: No significant differences were observed in the degree of fibrosis between the groups. Finally, no significant correlation—absolute nor spatial—was observed between all electrophysiological parameters and histological fibrosis markers. Conclusions: No differences in the degree of fibrosis were observed in patients from various stages of AF compared to the controls. Moreover, electrophysiological abnormalities did not correlate with any of the fibrosis markers. The findings indicate that fibrosis is not the hallmark of structural remodeling in AF.

Absence of detectable effect of radiotherapy and chemotherapy for breast cancer on the presence of low voltage areas in patients receiving left atrial catheter ablation

PURPOSE

Radiation and chemotherapy for breast cancer are known to cause side effects to the heart. However, it still remains unclear whether those therapies affect left atrium fibrosis. We sought to examine the effects of radiation and chemotherapy on the electroanatomic features of the left atrium (LA) in patients who received catheter ablation for LA arrhythmias and underwent radiation and/or chemotherapy prior to the procedure.

METHODS AND RESULTS

We compared 38 patients who underwent catheter ablation for LA arrhythmias and had a previous diagnosis of breast cancer with 38 patients without breast cancer. LA low voltage zones (LVZ) were analysed during the electrophysiological (EP) study. The existence of LA LVZ did not differ significantly between both groups (71.1% vs. 76.3%, p = .602; 13.7cm² (IQR 0;20.6cm²) vs. 7.0cm² (IQR 1.6;21.1cm²), p = .690). Also scar distribution revealed no difference between both groups. However, an involvement of the anterior wall was common in both groups (65.8% vs. 73.7%, p = .454). Patients with breast cancer and persistent AF showed a trend towards greater LA scar areas 14.5% vs. 6.9%, p = .383) compared to the control group. Age and LA volume index were the only independent predictors for greater LA scarring.

CONCLUSIONS

Thoracic irradiation and chemotherapy for breast cancer do not lead to an increase in LA scar area or a changed distribution of LA scarring. However, patient with breast cancer showed a tendency towards greater LA scar areas. Patient's age and LA volume index were identified as independent predictors for LA scar development.

Characterization of Atrial Propagation Patterns and Fibrotic Substrate With a Modified Omnipolar Electrogram Strategy in Multi-Electrode Arrays

Introduction: The omnipolar electrogram method was recently proposed to try to generate orientation-independent electrograms. It estimates the electric field from the bipolar electrograms of a clique, under the assumption of locally plane and homogeneous propagation. The local electric field evolution over time describes a loop trajectory from which omnipolar signals in the propagation direction, substrate and propagation features, are derived. In this work, we propose substrate and conduction velocity mapping modalities based on a modified version of the omnipolar electrogram method, which aims to reduce orientation-dependent residual components in the standard approach. Methods: A simulated electrical propagation in 2D, with a tissue including a circular patch of diffuse fibrosis, was used for validation. Unipolar electrograms were calculated in a multi-electrode array, also deriving bipolar electrograms along the two main directions of the grid. Simulated bipolar electrograms were also contaminated with real noise, to assess the robustness of the mapping strategies against noise. The performance of the maps in identifying fibrosis and in reproducing unipolar reference voltage maps was evaluated. Bipolar voltage maps were also considered for performance comparison. Results: Results show that the modified omnipolar mapping strategies are more accurate and robust against noise than bipolar and standard omnipolar maps in fibrosis detection (accuracies higher than 85 vs. 80% and 70%, respectively). They present better correlation with unipolar reference voltage maps than bipolar and original omnipolar maps (Pearson's correlations higher than 0.75 vs. 0.60 and 0.70, respectively). Conclusion: The modified omnipolar method improves fibrosis detection, characterization of substrate and propagation, also reducing the residual sensitivity to directionality over the standard approach and improving robustness against noise. Nevertheless, studies with real electrograms will elucidate its impact in catheter ablation interventions.

Relationship between left atrial scar and P wave dispersion in patients undergoing atrial fibrillation catheter ablation

BACKGROUND

Left atrial scar is an important entity in the atrial fibrillation substrate. P wave dispersion (PWD) is an indicator of slow and inhomogeneous conduction in the atria. In this study, we aim to investigate the relation between PWD and left atrial scars identified by electroanatomical mapping.

METHODS

Patients who had an electroanatomical map obtained during sinus rhythm as well as at least one electrocardiogram in sinus rhythm prior to the procedure were included in the study. Left atrial scar (defined as <0.5 mV) area was calculated on the electroanatomical map. Maximum and minimum P wave duration and PWD were compared between patients with and without left atrial scar.

RESULTS

A total of 224 patients were enrolled in the study. Of them, 47.9% of the patients were female. On the electroanatomical map, left atrial scar was identified in 103 patients, and no scar was present in 121 patients. PWD was significantly increased in patients with left atrial scar when compared to the no-scar group (46 ms ± 20 vs. 38 ms ± 15, respectively, p < 0.001). Similarly, PWD was significantly increased in patients with moderate-to-severe scar, when compared to patients with mild scar (50 ms ± 19 vs. 41 ms ± 19, respectively, p = 0.026). PWD was found not to be a good predictor of left atrial scar with an AUC of 0.625 for scar vs. no scar.

CONCLUSION

PWD is significantly increased in patients with left atrial scar identified by electroanatomical mapping, however, the receiver operating characteristic analysis showed that PWD is not a good predictor of presence of left atrial scar.

Sinus rhythm voltage fingerprinting in patients with mitral valve disease using a high-density epicardial mapping approach

Aims

Unipolar voltage (UV) mapping is increasingly used for guiding ablative therapy of atrial fibrillation (AF) as unipolar electrograms (U-EGMs) are independent of electrode orientation and atrial wavefront direction. This study was aimed at constructing individual, high-resolution sinus rhythm (SR) UV fingerprints to identify low-voltage areas and study the effect of AF episodes in patients with mitral valve disease (MVD).

Methods and results

Intra-operative epicardial mapping (interelectrode distance 2 mm) of the right and left atrium, Bachmann’s bundle (BB), and pulmonary vein area was performed in 67 patients (27 male, 67 ± 11 years) with or without a history of paroxysmal AF (PAF). In all patients, there were considerable regional variations in voltages. UVs at BB were lower in patients with PAF compared with those without [no AF: 4.94 (3.56–5.98) mV, PAF: 3.30 (2.25–4.57) mV, P = 0.006]. A larger number of low-voltage potentials were recorded at BB in the PAF group [no AF: 2.13 (0.52–7.68) %, PAF: 12.86 (3.18–23.59) %, P = 0.001]. In addition, areas with low-voltage potentials were present in all patients, yet we did not find any predilection sites for low-voltage potentials to occur.

Conclusion

Even in SR, advanced atrial remodelling in MVD patients shows marked inter-individual and regional variation. Low UVs are even present during SR in patients without a history of AF indicating that low UVs should carefully be used as target sites for ablative therapy.

Ablation of persistent atrial fibrillation based on high density voltage mapping and complex fractionated atrial electrograms: A randomized controlled trial

INTRODUCTION

Pulmonary vein isolation (PVI) is the cornerstone of atrial fibrillation (AF) catheter ablation. However, a PVI alone has been considered insufficient for persistent AF. This study aimed to evaluate the efficacy of persistent AF ablation targeting complex fractionated atrial electrogram (CFAE) areas within low voltage zones identified by high-resolution mapping in addition to the PVI.

METHODS

We randomized 50 patients (mean age 58.4 ± 9.5 years old, 86.0% males) with persistent AF to a PVI + CFAE group and PVI only group in a 1:1 ratio. CFAE and voltage mapping was performed simultaneously using a Pentaray Catheter with the CARTO3 CONFIDENSE module (Biosense Webster, CA, USA). The PVI + CFAE group, in addition to the PVI, underwent ablation targeting low voltage areas (<0.5 mV during AF) containing CFAEs.

RESULTS

The mean persistent AF duration was 24.0 ± 23.1 months and mean left atrial dimension 4.9 ± 0.5 cm. In the PVI + CFAE group, AF converted to atrial tachycardia (AT) or sinus rhythm in 15 patients (60%) during the procedure. The PVI + CFAE group had a higher 1-year AF free survival (84.0% PVI + CFAE vs 44.0 PVI only, P = .006) without antiarrhythmic drugs. However, there was no difference in the AF/AT free survival (60.0% PVI + CFAE vs 40.0% PVI only, P = .329).

CONCLUSION

Persistent AF ablation targeting CFAE areas within low voltage zones using high-density voltage mapping had a higher AF free survival than a PVI only. Although recurrence with AT was frequent in the PVI+CFAE group, the sinus rhythm maintenance rate after redo procedures was 76%.

[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.

Identification of Low-Voltage Areas: A Unipolar, Bipolar, and Omnipolar Perspective

Low-voltage areas (LVAs) are commonly considered surrogate markers for an arrhythmogenic substrate underlying tachyarrhythmias. It remains challenging to define a proper threshold to classify LVA, and it is unknown whether unipolar, bipolar, and the recently introduced omnipolar voltage mapping techniques are complementary or contradictory in classifying LVAs. Therefore, this study examined similarities and dissimilarities in unipolar, bipolar, and omnipolar voltage mapping and explored the relation between various types of voltages and conduction velocity (CV).

Reduction of Conduction Velocity in Patients with Atrial Fibrillation

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

Incidence, electrophysiological characteristics, and long-term follow-up of perimitral atrial flutter in patients with previously confirmed mitral isthmus block

INTRODUCTION

After mitral isthmus (ΜΙ) catheter ablation, perimitral atrial flutter (PMF) circuits can be maintained due to the preservation of residual myocardial connections, even if conventional pacing criteria for complete MI block are apparently met (MI pseudo-block). We aimed to study the incidence, the electrophysiological characteristics, and the long-term outcome of these patients.

METHODS

Seventy-two consecutive patients (mean age 62.4 ± 10.2, 62.5% male) underwent MI ablation, either as part of an atrial fibrillation (AF) ablation strategy (n = 35), or to treat clinical reentrant atrial tachycardia (AT) (n = 32), or to treat AT that occurred during ablation for AF (n = 5). Ιn all patients, the electrophysiological characteristics of PMF circuits were studied by high-density mapping.

RESULTS

Mitral isthmus block was successfully achieved in 69/72 patients (95.6%). Five patients developed PMF after confirming MI block. In these patients, high-density mapping during the PMF showed a breakthrough in MI with extremely low impulse conduction velocity (CV). In contrast, in usual PMF circuits that occurred after AF ablation, the lowest CV of the reentrant circuit was of significantly higher value (0.07 ± 0.02 m/s vs 0.25 ± 0.07 m/s, respectively; P < .001). Patients presented with clinical AT had better prognosis in maintaining sinus rhythm after MI ablation compared with patients presented with AF.

CONCLUSION

Perimitral atrial flutter with MI pseudo-block may be present after MI ablation and has specific electrophysiological features characterized by remarkably slow CV in the MI. Thus, even after MI block is achieved, a more detailed mapping in the boundaries of the ablation line or reinduction attempts may be needed to exclude residual conduction.

A new interpretation of nonpulmonary vein substrates of the left atrium in patients with atrial fibrillation

BACKGROUND

Substrate analysis of the left atrium in patients undergoing atrial fibrillation ablation has limitations when performed by means of simple bipolar acquisition.

OBJECTIVE

To evaluate the incidence of low-voltage zones (LVZs) through maps constructed by means of various catheters: multipolar (MC), omnipolar (OC), and circular catheters (CMCs) with the 3D electro-anatomical systems (3d-S) CARTO3 and EnSite Precision.

METHODS

To assess LVZs, we acquired maps by means of CMC and MC in the voltage range 0.05-0.5 mV in 70 consecutive patients in sinus rhythm. In the case of OC only, we made an intra-patient comparison of bipolar maps constructed by means of the along and across, and HD-Wave configurations of the EnSite 3d-S in the ranges of 0.05-0.5 and 0.5-1.0 mV. On the basis of this comparison, we chose the range that best identified LVZs as a set of different colors (SDC) compatible with patchy fibrosis (qualitative analysis). Subsequently, we detected the voltage values corresponding to purple and gray points, close to SDC, and the value inside corresponding to blue, green, and red colors, and we evaluated the color change in other voltage ranges. Finally, we performed a quantitative analysis of LVZs by applying the qualitative characteristics described above.

RESULTS

On the basis of our settings, for OC, the optimal range identifying LVZs was 0.3-0.6 mV. OC revealed smaller LVZs than MC (P < .05 or P < .001), except in the lateral wall. No significant differences were observed between CMCs.

CONCLUSIONS

In our experience, OC does not present the limits of bipolar HD maps, though further studies are needed in order to confirm that 0.3-0.6 mV is the optimal voltage range within which to identify LVZs.

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.