Impact of atrial fibrillation on the voltage of bipolar signals acquired from the left and right atria

Device-detected atrial sensing amplitudes as a marker of increased risk for new onset and progression of atrial high-rate episodes

BACKGROUND

Atrial high-rate episodes (AHREs) are frequent in patients with cardiac implantable electronic devices. A decrease in device-detected P-wave amplitude may be an indicator of periods of increased risk of AHRE.

OBJECTIVE

The objective of this study was to assess the association between P-wave amplitude and AHRE incidence.

METHODS

Remote monitoring data from 2579 patients with no history of atrial fibrillation (23% pacemakers and 77% implantable cardioverter-defibrillators, of which 40% provided cardiac resynchronization therapy) were used to calculate the mean P-wave amplitude during 1 month after implantation. The association with AHRE incidence according to 4 strata of daily burden duration (≥15 minutes, ≥6 hours, ≥24 hours, ≥7 days) was investigated by adjusting the hazard ratio with the CHA2DS2-VASc score.

RESULTS

The adjusted hazard ratio for 1-mV lower mean P-wave amplitude during the first month increased from 1.10 (95% confidence interval [CI], 1.05-1.15; P < .001) to 1.18 (CI, 1.09-1.28; P < .001) with AHRE duration strata from ≥15 minutes to ≥7 days independent of the CHA2DS2-VASc score. Of 871 patients with AHREs, those with 1-month P-wave amplitude <2.45 mV had an adjusted hazard ratio of 1.51 (CI, 1.19-1.91; P = .001) for progression of AHREs from ≥15 minutes to ≥7 days compared with those with 1-month P-wave amplitude ≥2.45 mV. Device-detected P-wave amplitudes decreased linearly during the 1 year before the first AHRE by 7.3% (CI, 5.1%-9.5%; P < .001 vs patients without AHRE).

CONCLUSION

Device-detected P-wave amplitudes <2.45 mV were associated with an increased risk of AHRE onset and progression to persistent forms of AHRE independent of the patient's risk profile.

Comparison of voltages between atria: differences in sinus rhythm and atrial fibrillation

BACKGROUND

Ultra high-density mapping systems allow for comparison of atrial electroanatomical maps in unprecedented detail. Atrial scar determined by voltages and surface area between atria, rhythm and atrial fibrillation (AF) types was assessed.

METHODS

Left (LA) and right atrial (RA) maps were created using Rhythmia HDx in patients listed for ablation for paroxysmal (PAF, sinus rhythm (SR) maps only) or persistent AF (PeAF, AF and SR maps). Electrograms on corresponding SR/AF maps were paired for direct comparison. Percentage surface area of scar was assigned low- (LVM, ≤ 0.05 mV), intermediate- (IVM, 0.05-0.5 mV) or normal voltage myocardium, (NVM, > 0.5 mV).

RESULTS

Thirty-eight patients were recruited generating 96 maps using 913,480 electrograms. Paired SR-AF bipolar electrograms showed fair correlation in LA (Spearman's ρ = 0.32) and weak correlation in RA (ρ = 0.19) and were significantly higher in SR in both (LA: 0.61 mV (0.20-1.67) vs 0.31 mV (0.10-0.74), RA: 0.68 mV (0.19-1.88) vs 0.47 mV (0.14-1.07), p < 0.0005 both). Voltages were significantly higher in patients with PAF over PeAF, (LA: 1.13 mV (0.39-2.93) vs 0.52 mV (0.16-1.49); RA: 0.93 mV (0.24-2.46) vs 0.57 mV (0.17-1.69)). Minimal differences were seen in electrogram voltages between atria. Significantly more IVM/LVM surface areas were seen in AF over SR (LA only, p < 0005), and PeAF over PAF (LA: p = 0.01, RA: p = 0.04). There was minimal difference between atria within patients.

CONCLUSIONS

Ultra high-density mapping shows paired electrograms correlate poorly between SR and AF. SR electrograms are typically (but not always) larger than those in AF. Patients with PeAF have a lower global electrogram voltage than those with PAF. Electrogram voltages are similar between atria within individual patients.

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.

Comparing Left Atrial Low Voltage Areas in Sinus Rhythm and Atrial Fibrillation Using Novel Automated Voltage Analysis: A Pilot Study

BACKGROUND

Low voltage areas (LVAs) have been proposed as surrogate markers for left atrial (LA) scar. Correlation between voltages in sinus rhythm (SR) and atrial fibrillation (AF) have previously been measured via point-by-point analysis. We sought to compare LA voltage composition measured in SR to AF, utilizing a high-density automated voltage histogram analysis (VHA) tool in those undergoing pulmonary vein isolation (PVI) for persistent AF (PeAF).

METHODS

We retrospectively analyzed patients with PeAF undergoing de novo PVI. Maps required ≥ 1,000 voltage points in each rhythm and had a standardized procedure (mapped in AF then remapped in SR post-PVI). We created six anatomical segments (AS) from each map: anterior, posterior, roof, floor, septal and lateral AS. These were analyzed by VHA, categorizing atrial LVAs into 10 voltage aliquots 0 - 0.5 mV. Data were analyzed using SPSS v.26.

RESULTS

We acquired 58,342 voltage points (n = 10 patients, mean age: 67 ± 13 years, three females). LVA burdens of ≤ 0.2 mV, designated as "severe LVAs", were comparable between most AS (except on the posterior wall) with good correlation. Mapped voltages between the ranges of 0.21 and 0.5 mV were labeled as "diseased LA tissue", and these were found significantly more in AF than SR. Significant differences were seen on the roof, anterior, posterior, and lateral AS.

CONCLUSIONS

Diseased LA tissue (0.21 - 0.5 mV) burden is significantly higher in AF than SR, mainly in the anterior, roof, lateral, and posterior wall. LA "severe LVA" (≤ 0.2 mV) burden is comparable in both rhythms, except with respect to the posterior wall. Our findings suggest that mapping rhythm has less effect on the LA with voltages < 0.2 mV than 0.2 - 0.5 mV across all anatomical regions, excluding the posterior wall.

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.

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.

Atrial low voltage areas: A comparison between atrial fibrillation and sinus rhythm

BACKGROUND

Atrial fibrosis can promote atrial fibrillation (AF). Electroanatomic mapping (EAM) can provide information regarding local voltage abnormalities that may be used as a surrogate marker for fibrosis. Specific voltage cut-off values have been reproduced accurately to identify fibrosis in the ventricles, but these values are not well defined in atrial tissue.

METHODS

This study is a prospective single-center study. Patients with persistent AF referred for ablation were included. EAM was performed before ablation. We recorded bipolar signals, first in AF and later in sinus rhythm (SR). Two thresholds delimited low-voltage areas (LVA), 0.5 and 0.3 mV. We compared LVA extension between maps in SR and AF in each patient.

RESULTS

A total of 23 patients were included in the study. The percentage of points with voltage lower than 0.5 mV and 0.3 mV was significantly higher in maps in AF compared with maps in SR: 38.2% of points < 0.5 mV in AF vs. 22.9% in SR (p < 0.001); 22.3% of points < 0.3 mV in AF vs. 14% in SR (p < 0.001). Areas with reduced voltage were significantly larger in maps in AF (0.5 mV threshold, mean area in AF 41.3 ± 42.5 cm2 vs. 11.7 ± 17.9 cm2 in SR, p < 0.001; 0.3 mV threshold, mean area in AF 15.6 ± 22.1 cm2 vs. 6.2 ± 11.5 cm2 in SR, p < 0.001).

CONCLUSIONS

Using the same voltage thresholds, LVA extension in AF is greater than in SR in patients with persistent AF. These findings provide arguments for defining a different atrial fibrosis threshold based on EAM rhythm.

Alterations in atrial electrogram amplitude as steady sinus rhythm transitions to paroxysmal atrial fibrillation during continuous monitoring in patients with implantable cardiac devices: Insights from the IMPACT study

OBJECTIVES

We aimed to evaluate whether device measured amplitudes of atrial electrogram (AEGM) would change when measured in sinus rhythm (SR) transitioning to paroxysmal atrial fibrillation (AF) from previous steady SR, and significance of such change.

METHODS

From the IMPACT trial's database we selected two groups; (A) those who developed AF (n = 164), and (B) propensity-matched control (n = 459) who stayed in SR during continuous Home Monitoring (HM) to compare AEGMs amplitudes at baseline SR and transition phase.

RESULTS

During 420.0 ± 349.2 days (mean ± SD) from first postenrollment HM transmission to AF event transmission in Group A, and corresponding 515.3 ± 407.0 days in Group B, baseline and transition AEGM amplitude were 2.88 ± 1.146 and 2.74 ± 1.186 mV, respectively, for Group A (p = .1), and 2.88 ± 1.155 and 2.79 ± 1.145, respectively, for Group B (p < .005). Comparison of differences of AEGM amplitude, 0.14 ± 1.072 mV in Group A and 0.09 ± 0.893 mV in Group B were insignificant (p = .3). Age, sex, and hypertension identified as confounders had no association to AEGM changes (p = NS).

CONCLUSIONS

Independent of age, sex, and hypertension, AEGMs amplitudes decline over a long period of time in patients with defibrillators and substrate for AF. The significance of such change remains unclear as it occurs whether patients develop AF or not, but raises a possibility of progressive atrial myopathy that patients with substrate for AF may be predisposed to.

How, When, and Why: High-Density Mapping of Atrial Fibrillation

High-density (HD) mapping presents opportunities to enhance delineation of atrial fibrillation (AF) substrate, improve efficiency of the mapping procedure without sacrificing safety, and afford new mechanistic insights regarding AF. Innovations in hardware, software algorithms, and development of novel multielectrode catheters have allowed HD mapping to be feasible and reliable. Patients to particularly benefit from this technology are those with paroxysmal AF in setting of preexisting atrial scar, persistent AF, and AF in the setting of complex congenital heart disease. The future will bring refinements in automated HD mapping including evolution of noncontact methodologies and artificial intelligence to supplant current techniques.

Voltage during atrial fibrillation is superior to voltage during sinus rhythm in localizing areas of delayed enhancement on magnetic resonance imaging: An assessment of the posterior left atrium in patients with persistent atrial fibrillation

BACKGROUND

Bipolar electrogram voltage during sinus rhythm (VSR) has been used as a surrogate for atrial fibrosis in guiding catheter ablation of persistent atrial fibrillation (AF), but the fixed rate and wavefront characteristics present during sinus rhythm may not accurately reflect underlying functional vulnerabilities responsible for AF maintenance.

OBJECTIVE

The purpose of this study was determine whether, given adequate temporal sampling, the spatial distribution of mean AF voltage (VmAF) better correlates with delayed-enhancement magnetic resonance imaging (MRI-DE)-detected atrial fibrosis than VSR.

METHODS

AF was mapped (8 seconds) during index ablation for persistent AF (20 patients) using a 20-pole catheter (660 ± 28 points/map). After cardioversion, VSR was mapped (557 ± 326 points/map). Electroanatomic and MRI-DE maps were co-registered in 14 patients.

RESULTS

The time course of VmAF was assessed from 1-40 AF cycles (∼8 seconds) at 1113 locations. VmAF stabilized with sampling >4 seconds (mean voltage error 0.05 mV). Paired point analysis of VmAF from segments acquired 30 seconds apart (3667 sites; 15 patients) showed strong correlation (r = 0.95; P <.001). Delayed enhancement (DE) was assessed across the posterior left atrial (LA) wall, occupying 33% ± 13%. VmAF distributions were (median [IQR]) 0.21 [0.14-0.35] mV in DE vs 0.52 [0.34-0.77] mV in non-DE regions. VSR distributions were 1.34 [0.65-2.48] mV in DE vs 2.37 [1.27-3.97] mV in non-DE. VmAF threshold of 0.35 mV yielded sensitivity of 75% and specificity of 79% in detecting MRI-DE compared with 63% and 67%, respectively, for VSR (1.8-mV threshold). CONCLUSION: The correlation between low-voltage and posterior LA MRI-DE is significantly improved when acquired during AF vs sinus rhythm. With adequate sampling, mean AF voltage is a reproducible marker reflecting the functional response to the underlying persistent AF substrate.

Changes in atrial electrophysiological and structural substrate and their relationship to histology in a long-term chronic canine atrial fibrillation model

BACKGROUND

Atrial fibrillation (AF) is related to numerous electrophysiological changes; however, the extent of structural and electrophysiological remodeling with long-term AF is not well characterized.

METHODS

Dogs (n = 6) were implanted with a neurostimulator in the right atrium (AF group). No implantation was done in the Control group (n = 3). Electroanatomical mapping was done prior to and following more than 6 months of AF. Magnetic resonance imaging was also done to assess structural remodeling. Animals were euthanized and tissue samples were acquired for histological analysis.

RESULTS

A significant increase was seen in the left atrial (LA) volume among all AF animals (22.25 ± 12.60 cm3 vs 34.00 ± 12.23 cm3 , P = .01). Also, mean bipolar amplitude in the LA significantly decreased from 5.96 ± 2.17 mV at baseline to 3.23 ± 1.51 mV (P < .01) after chronic AF. Those significant changes occurred in each anterior, lateral, posterior, septal, and roof regions as well. Additionally, the dominant frequency (DF) in the LA increased from 7.02 ± 0.37 Hz to 10.12 ± 0.28 Hz at chronic AF (P < .01). Moreover, the percentage of fibrosis in chronic AF animals was significantly larger than that of control animals in each location (P < .01).

CONCLUSIONS

Canine chronic AF is accompanied by a significant decrease in intracardiac bipolar amplitudes. These decreased electrogram amplitude values are still higher than traditional cut-off values used for diseased myocardial tissue. Despite these "normal" bipolar amplitudes, there is a significant increase in DF and tissue fibrosis.

Identification of optimal reference genes for transcriptomic analyses in normal and diseased human heart

Aims

Quantitative real-time RT-PCR (RT-qPCR) has become the method of choice for mRNA quantification, but requires an accurate normalization based on the use of reference genes showing invariant expression across various pathological conditions. Only few data exist on appropriate reference genes for the human heart. The objective of this study was to determine a set of suitable reference genes in human atrial and ventricular tissues, from right and left cavities in control and in cardiac diseases.

Methods and results

We assessed the expression of 16 reference genes (ACTB, B2M, GAPDH, GUSB, HMBS, HPRT1, IPO8, PGK1, POLR2A, PPIA, RPLP0, TBP, TFRC, UBC, YWHAZ, 18S) in tissues from: right and left ventricles from healthy controls and heart failure (HF) patients; right-atrial tissue from patients in sinus rhythm with (SRd) or without (SRnd) atrial dilatation, patients with paroxysmal (pAF) or chronic (cAF) atrial fibrillation or with HF; and left-atrial tissue from patients in SR or cAF. Consensual analysis (by geNorm and Normfinder algorithms, BestKeeper software tool and comparative delta-Ct method) of the variability scores obtained for each reference gene expression shows that the most stably expressed genes are: GAPDH, GUSB, IPO8, POLR2A, and YWHAZ when comparing either right and left ventricle or ventricle from healthy controls and HF patients; GAPDH, IPO8, POLR2A, PPIA, and RPLP0 when comparing either right and left atrium or right atria from all pathological groups. ACTB, TBP, TFRC, and 18S genes were identified as the least stable.

Conclusions

The overall most stable reference genes across different heart cavities and disease conditions were GAPDH, IPO8, POLR2A and PPIA. YWHAZ or GUSB could be added to this set for some specific experiments. This study should provide useful guidelines for reference gene selection in RT-qPCR studies in human heart.

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

Low atrial endocardial bipolar voltage, measured during catheter ablation for atrial fibrillation (AF), is a commonly used surrogate marker for the presence of atrial fibrosis. Low voltage shows many useful associations with clinical outcomes, comorbidities and has links to trigger sites for AF. Several contemporary trials have shown promise in targeting low voltage areas as the substrate for AF ablation; however, the results have been mixed. In order to understand these results, a thorough understanding of voltage mapping techniques, the relationship between low voltage and the pathophysiology of AF, as well as the inherent limitations in voltage measurement are needed. Two key questions must be answered in order to optimally apply voltage mapping as the road map for ablation. First, are the inherent limitations of voltage mapping small enough as to be ignored when targeting specific tissue based on voltage? Second, can conventional criteria, using a binary threshold for voltage amplitude, truly define the extent of the atrial fibrotic substrate? Here, we review the latest clinical evidence with regard to voltage-based ablation procedures before analysing the utility and limitations of voltage mapping. Finally, we discuss omnipole mapping and dynamic voltage attenuation as two possible approaches to resolving these issues.

Standardized unfold mapping: a technique to permit left atrial regional data display and analysis

PURPOSE

Left atrial arrhythmia substrate assessment can involve multiple imaging and electrical modalities, but visual analysis of data on 3D surfaces is time-consuming and suffers from limited reproducibility. Unfold maps (e.g., the left ventricular bull's eye plot) allow 2D visualization, facilitate multimodal data representation, and provide a common reference space for inter-subject comparison. The aim of this work is to develop a method for automatic representation of multimodal information on a left atrial standardized unfold map (LA-SUM).

METHODS

The LA-SUM technique was developed and validated using 18 electroanatomic mapping (EAM) LA geometries before being applied to ten cardiac magnetic resonance/EAM paired geometries. The LA-SUM was defined as an unfold template of an average LA mesh, and registration of clinical data to this mesh facilitated creation of new LA-SUMs by surface parameterization.

RESULTS

The LA-SUM represents 24 LA regions on a flattened surface. Intra-observer variability of LA-SUMs for both EAM and CMR datasets was minimal; root-mean square difference of 0.008 ± 0.010 and 0.007 ± 0.005 ms (local activation time maps), 0.068 ± 0.063 gs (force-time integral maps), and 0.031 ± 0.026 (CMR LGE signal intensity maps). Following validation, LA-SUMs were used for automatic quantification of post-ablation scar formation using CMR imaging, demonstrating a weak but significant relationship between ablation force-time integral and scar coverage (R ² = 0.18, P < 0.0001).

CONCLUSIONS

The proposed LA-SUM displays an integrated unfold map for multimodal information. The method is applicable to any LA surface, including those derived from imaging and EAM systems. The LA-SUM would facilitate standardization of future research studies involving segmental analysis of the LA.

Resolving Bipolar Electrogram Voltages During Atrial Fibrillation Using Omnipolar Mapping

Background:

Low-voltage–guided substrate modification is an emerging strategy in atrial fibrillation (AF) ablation. A major limitation to contemporary bipolar electrogram (EGM) analysis in AF is the resultant lower peak-to-peak voltage (V pp ) from variations in wavefront direction relative to electrode orientation and from fractionation and collision events. We aim to compare bipole V pp with novel omnipolar peak-to-peak voltages (V max ) in sinus rhythm (SR) and AF.

Methods and Results:

A high-density fixed multielectrode plaque was placed on the epicardial surface of the left atrium in dogs. Horizontal and vertical orientation bipolar EGMs, followed by omnipolar EGMs, were obtained and compared in both SR and AF. Bipole orientation has significant impact on bipolar EGM voltages obtained during SR and AF. In SR, vertical values were on average 66±119% larger than horizontal ( P =0.004). In AF, vertical values were on average 31±96% larger than horizontal ( P =0.07). Omnipole V max values were 99.9±125% larger than both horizontal (99.9±125%; P <0.001) and vertical (41±78%; P <0.0001) in SR and larger than both horizontal (76±109%; P <0.001) and vertical (52±70%; P value <0.0001) in AF. Vector field analysis of AF wavefronts demonstrates that omnipolar EGMs can account for collision and fractionation and record EGM voltages unaffected by these events.

Conclusions:

Omnipolar EGMs can extract maximal voltages from AF signals which are not influenced by directional factors, collision or fractionation, compared with contemporary bipolar techniques.

Wavefront direction and cycle length affect left atrial electrogram amplitude

BACKGROUND

The relationship between atrial electrogram (EGM) characteristics in atrial fibrillation (AF) and those in sinus rhythm (SR) are generally unknown. The activation rate and direction may affect EGM characteristics. We examined characteristics of left atrial (LA) EGMs obtained during pacing from different sites.

METHODS

The study included 10 patients undergoing pulmonary vein isolation for AF. Atrial EGMs were recorded from a 64-pole basket catheter placed in the LA, and bipolar EGM amplitudes from the distal electrode pair (1-2) and proximal electrode pair (6-7) from 8 splines were averaged. The high right atrium (HRA), proximal coronary sinus (CSp), and distal coronary sinus (CSd) were paced at 600 ms and 300 ms.

RESULTS

When the LA voltage at SR was ≥1.5 mV, bipolar voltages of the HRA were greater than those of the CSp, which were greater than those of the CSd, regardless of the pacing cycle length. The shorter pacing cycle length resulted in a reduction of the LA EGM voltage at sites of SR voltage ≥1.5 mV, but no significant difference was seen at sites where the SR EGM amplitude was between >0.5 and <1.5 mV. No significant differences were seen in intra-basket conduction times between pacing cycle lengths of 600 ms and 300 ms at any pacing site.

CONCLUSION

The rate and direction-dependent reduction of the amplitude of atrial EGMs may explain, in part, the voltage discordance during SR and AF.

Focal Impulse And Rotor Mapping (FIRM): Conceptualizing And Treating Atrial Fibrillation

Current approaches for the ablation of atrial fibrillation are often effective, but only partially rooted in mechanistic understanding. Accordingly, they are unable to predict whether a given patient will or will not do well, or which lesions sets should or should not be performed - in any given patient. This goal would require clearer mechanistic definition of what sustains AF after it has been triggered (i.e. electrophysiological substrates). There are two schools of thought. The first proposes disorganized activity that self-sustains with no 'driver', and the second describes drivers that then cause disorganization. Interestingly, these mechanisms can be separated in human studies by mapping approach - proponents of the disorganized hypothesis studying small atrial areas at high resolution, and proponents of the driver model studying wide fields-of-view at varying resolutions. Focal impulse and rotor modulation (FIRM) mapping combines a wide field of view with physiologically based signal filtering and phase analysis, and has revealed that human AF is often sustained by rotors. In the CONFIRM Trial, targeting stable AF rotors/sources for ablation improved the single-procedure efficacy for paroxysmal and persistent AF over conventional ablation alone, as now confirmed by independent laboratories. FIRM mapping gives a mechanistic foundation to predict whether any selected lesions should intersect AF sources in any given patient and which mechanisms may cause recurrence. Rotors of varying characteristics have now been shown by many groups. These insights have reinvigorated interest in AF mapping, and rationalizing these findings will likely translate into improved therapy for our patients.

Consistency of the automatic algorithm in detecting complex fractionated electrograms using an electroanatomical navigation system

BACKGROUND

The different settings of the automatic algorithm in the Carto system (Carto XP, Biosense Webster, Diamond Bar, CA, USA) used for detecting complex fractionated electrograms (CFEs) during atrial fibrillation (AF) may influence the identification of the fragmented electrograms.

OBJECTIVES

We aimed to evaluate the impact of the different parameters on the detection of CFEs and the efficacy of the substrate modification after pulmonary vein isolation (PVI).

METHODS

A total of 1,159 electrograms were analyzed from 11 consecutive patients (age = 56 ± 12 years). The effect of the different algorithm factors, such as the high-voltage thresholds (0.12, 0.25, 0.5, 20 mV), detection algorithms (average complex interval [ACI] vs interval confidence level), and recording duration (2.5 seconds vs 5 seconds), on the disparities of the CFEs was investigated.

RESULTS

The proportion of the different grades of CFEs depended on the detection algorithm and recording duration. The high-voltage threshold would not affect the consistency of the CFEs irrespective of the different settings of the detection algorithm or recording duration. High-grade CFEs were most consistent with an ACI algorithm and recording duration of 5 seconds (Cronbach's alpha = 0.952). Ablation consisting of a PVI and high-grade CFE sites converted AF directly to sinus rhythm in eight of 11 patients or into atrial tachycardia in one of 11.

CONCLUSIONS

The distribution and consistency of the CFE detection depended on the detection algorithm and recording duration, but not on the high-voltage threshold. Under the ACI algorithm and a recording duration of 5 seconds, high-grade CFE sites remained highest consistency.

Left Atrial Wall Stress Distribution and Its Relationship to Electrophysiologic Remodeling in Persistent Atrial Fibrillation

Background—

Atrial stretch causes remodeling that predisposes to atrial fibrillation. We tested the hypothesis that peaks in left atrial (LA) wall stress are associated with focal remodeling.

Methods and Results—

Nineteen patients underwent LA mapping before catheter ablation for persistent atrial fibrillation. Finite Element Analysis was used to predict wall stress distribution based on LA geometry from CT. The relationship was assessed between wall stress and (1) electrogram voltage and (2) complex fractionated atrial electrograms (CFAE), using CFAE mean (the mean interval between deflections). Wall stress varied widely within atria and between subjects (median, 36 kPa; interquartile range, 26–51 kP). Peaks in wall stress (≥90th percentile) were common at the pulmonary vein (PV) ostia (93%), the appendage ridge (100%), the high posterior wall (84%), and the anterior wall and septal regions (42–84%). Electrogram voltage showed an inverse relationship across quartiles for wall stress (19% difference across quartiles, P =0.016). There was no effect on CFAE mean across quartiles of wall stress. Receiver operating characteristic analysis showed high wall stress was associated with low voltage (ie, <0.5 mV) and electrical scar (ie, <0.05 mV; both P <0.0001) and with absence of CFAE (ie, CFAE mean <120 ms; P <0.0001). However, peaks in wall stress and CFAE were found at 88% of PV ostia.

Conclusions—

Peaks in wall stress were associated with areas of low voltage, suggestive of focal remodeling. Although peaks in wall stress were not associated with LA CFAE, the PV ostia may respond differently.