Different patterns of atrial activation in idiopathic atrial fibrillation: simultaneous multisite atrial mapping in patients with paroxysmal and chronic atrial fibrillation

Atrial fibrillation fundamentals: from physiopathology to transcatheter ablation

Atrial fibrillation (AF) is a common and harmful arrhythmia. Its complex pathogenesis can be outlined using Coumel's Triangle, that considers at the base of AF three different factors: substrate, trigger, and catalyst factor. The triangle can serve as a guide to understand the mechanism of action of the different possible treatments. Anti-arrhythmic drug therapies have a modest efficacy and no proven benefit on prognosis. Interventional therapy is more effective, especially if employed in the first stages of the disease, and can reduce mortality in selected populations. Ablative schemes must be different depending on the type of AF (paroxysmal, persistent) and the presence or absence of atrial dilation.

Sustained and self-terminating atrial fibrillation induced immediately after pulmonary vein isolation exhibit differences in coronary sinus electrical activity from onset

INTRODUCTION

Little data exists on the electrophysiological differences between sustained atrial fibrillation (sAF; >5 minutes) vs self-terminating nonsustained AF (nsAF; <5 minutes). We sought to investigate the electrophysiological characteristics of coronary sinus (CS) activity during postpulmonary vein isolation (PVI) sAF vs nsAF.

METHODS AND RESULTS

We studied 142 patients post-PVI for paroxysmal AF (PAF). In a 50-patient subset, CS electrograms in the first 30 seconds of induced AF were analyzed manually. A custom-made algorithm for automated electrogram annotation was derived for validation on the whole patient set. In patients with sAF post-PVI, CS fractionated potentials were ablated. Manual analysis showed that patients with sAF exhibited higher activation pattern variability (2.1 vs 0.5 changes/sec; P < .001); fewer proximal-to-distal wavefronts (25 vs 61%; P < .001); fewer unidirectional wavefronts (60 vs 86%; P < .001); more pivot locations (4.3 vs 2.1; P < .001); shorter cycle lengths (190 vs 220 ms; P < .001); and shorter cumulative isoelectric segments (35 vs 44%; P = .045) compared to nsAF. These observations were confirmed on the whole study population by automated electrogram annotation and sample entropy computation (SampEn: 0.29 ± 0.15 in sAF vs 0.15 ± 0.05 in nsAF; P < .0001). The derived model predicted sAF with 78% sensitivity, 88% specificity; agreement with manual model: 88% (Cohen's kappa= 0.76). CS defragmentation resulted in AF termination or noninducibility in 49% of sAF.

CONCLUSION

In PAF patients post-PVI, induced sAF shows greater activation sequence variability, shorter cycle length, and higher SampEn in the CS compared to nsAF. Automated electrogram annotation confirmed these results and accurately distinguished self-terminating nsAF episodes from sAF based on 30-second recordings at AF onset.

Biatrial versus Isolated Left Atrial Ablation in Atrial Fibrillation: A Systematic Review and Meta-Analysis

Objective

The outcomes of biatrial ablation (BA) and isolated left atrial ablation (LA) in atrial fibrillation remain inconclusive. In this meta-analysis, we assess the currently available evidence to compare outcomes between BA and LA.

Methods

Electronic searches were performed from database inception to December 2016, and relevant studies were accessed. Odds ratios and weight mean differences with 95% confidence intervals are reported. Twenty-one studies comprising 3609 patients were included in the present meta-analysis.

Results

The prevalence of sinus rhythm in the BA cohort was similar to that in the LA cohort at discharge, at 12 months, and after more than 1 year of follow-up. However, at 6 months, the prevalence of sinus rhythm was higher in the BA cohort than in the LA cohort. The rate of permanent pacemaker implantation was higher in the BA cohort than in the LA cohort. However, 30-day and late mortality and neurological events were similar between the BA and LA groups.

Conclusion

There was no significant difference in the rate of restored sinus rhythm, the risk of death, and cerebrovascular events between BA and LA, but BA had a higher rate of permanent pacemaker implantation.

Effects of refractory gradients and ablation on fibrillatory activity

BACKGROUND

The mechanisms involved in onset, maintenance, and termination of atrial fibrillation are not well understood. A biophysical model could be useful to determine how the events unfold.

METHOD

A two-dimensional cellular automaton consisting of 576 × 576 grid nodes was implemented to demonstrate the types of electrical activity that may occur in compromised atrial substrate. Electrical activation between nodes was made anisotropic (2:1), and the refractory period (RP) was adjusted from 74 to 192 ms in the spatial domain. Presence of collagen fibers were simulated as short lines of conduction block at many random grid sites, while ablation lesions were delineated as longer lines of block. An S1-S2 pulse from one grid corner was utilized to initiate simulated electrical activity. Simulations were done in which 1. no ablation lines, 2. random ablation lines, and 3. parallel ablation lines were added to the grid to determine how this affected the formation and annihilation of rotational activity after S1-S2 stimulation.

RESULTS

As the premature (S2) wavefront traversed the grid, rotational activity formed near boundaries where wavefronts propagated from shorter to longer refractory regions, causing unidirectional block, and were anchored by fiber clusters. Multiple wavelets appeared when wavefronts originating from different driving rotational features collided, and/or by their encounter with RP discontinuities. With the addition of randomly orientated simulated ablation lesions, followed by reinduction of fibrillatory activity, mean activation interval (AI) prolonged from a baseline level of 144.2 ms-160.3 ms (p < 0.001 in most comparisons). During fibrillatory activity, when parallel ablation lines were added to short RP regions, AI prolonged to 150.4 ms (p < 0.001), and when added to long RP regions, AI prolonged to 185.3 ms (p < 0.001). In all cases, AI prolongation after simulated ablation resulted from reduced number and/or from the isolation of local drivers, so that distant drivers in short RP regions activated long RP regions N:1, while distant drivers in long RP regions activated short RP regions at a relatively slow rate.

CONCLUSIONS

An automaton model was found useful to generate and test hypotheses concerning fibrillatory activity, which can then be validated in the clinical electrophysiology laboratory.

Additional linear ablation from the superior vena cava to right atrial septum after pulmonary vein isolation improves the clinical outcome in patients with paroxysmal atrial fibrillation: prospective randomized study

AIMS

Although circumferential pulmonary vein isolation (CPVI) has been considered as the cornerstone for paroxysmal atrial fibrillation (PAF) ablation, there has been a substantial recurrence rate. We conducted a prospectively randomized study to evaluate whether additional linear ablation from the superior vena cava (SVC) to the right atrial (RA) septum (SVC-L) improves the clinical outcome.

METHODS AND RESULTS

This study enroled 200 patients with PAF (male 74.5%, 56.8 ± 11.7 years old) randomly assigned to either the CPVI (n = 100) or CPVI + SVC-L (n = 100) groups. An RA isthmus ablation was performed in all patients. The CPVI + SVC-L group required a longer ablation procedure time (82.7 ± 17.9 min) than the CPVI group (63.6 ± 16.8 min, P < 0.001). The complication rates were 5% in CPVI + SVC-L group and 2% in CPVI group, respectively (P = 0.445). Two CPVI + SVC-L group patients had post-procedural sinus node dysfunction, which recovered within 24 h. During 12.2 ± 5.3 months of follow-up, the recurrence rate was significantly lower in the CPVI + SVC-L group (6%) than the CPVI group (27%, P < 0.001). The post-procedural 3-month follow-up heart rate variability in the CPVI + SVC-L group showed a significantly greater reduction in the rMSSD (25.2 ± 13.7 vs. 13.7 ± 8.5 ms, P < 0.001), HF (10.2 ± 7.1 vs. 5.5 ± 5.8 ms(2), P < 0.001), and LF/HF (1.6 ± 0.5 vs. 0.9 ± 0.3, P < 0.001) than in the CPVI group.

CONCLUSION

In spite of a longer procedure time and risk of transient sinus node dysfunction, an SVC-L in addition to CPVI improved the clinical outcome of catheter ablation, and was associated with post-procedural autonomic neural remodelling in patients with PAF.

Evaluation of time course and predicting factors of progression of paroxysmal or persistent atrial fibrillation to permanent atrial fibrillation

BACKGROUND

To evaluate time course and predictors of progression of paroxysmal or persistent atrial fibrillation (AF) to permanent AF.

METHODS AND RESULTS

We included 460 patients referred for paroxysmal (n = 337) or persistent (n = 123) AF between 1994 and 2012. Mean follow-up was 13.2 ± 6.5 years. AF progression rate was 3.7% per year, 19.7% at 5 years, and 38.1% at 10 years. Lone AF was diagnosed in 217 patients (47%). Predictors of permanent AF were: age, persistent AF, left atrial (LA) size, left ventricular-fractional shortening (LV-FS), lack of antiarrhythmic (AA) drugs, VVI pacing (P < 0.001 for all), and valvular disease (P < 0.02). Independent predictors were age (P < 0.001), persistent AF (P < 0.001), LA diameter (P < 0.005), lack of AA drugs (P < 0.005), and VVI pacing (P < 0.01). When adjusted at means of covariates, persistent AF and age >75 years remained highly significant (P < 0.01). LA dimension >50 mm was highly significant at univariate model (P < 0.001) but to a lesser extent when adjusted (P < 0.05). In patients with paroxysmal AF-with age <75 years-on AA drugs, progression rate to permanent AF was 6.5% at 5 years and 23.7% at 10 years. Among four predictors (age, LA size, LV-FS, and VVI pacing), only age (P < 0.01) and LA size (P < 0.005) remained independently significant, but LA size was not significant when adjusted.

CONCLUSIONS

Progression to permanent AF is a slow process. Aging, LA size, VVI pacing, lack of AA therapy, and a persistent form of AF independently increased the progression to permanent AF.

Validation of novel 3-dimensional electrocardiographic mapping of atrial tachycardias by invasive mapping and ablation: a multicenter study

OBJECTIVES

This study prospectively evaluated the role of a novel 3-dimensional, noninvasive, beat-by-beat mapping system, Electrocardiographic Mapping (ECM), in facilitating the diagnosis of atrial tachycardias (AT).

BACKGROUND

Conventional 12-lead electrocardiogram, a widely used noninvasive tool in clinical arrhythmia practice, has diagnostic limitations.

METHODS

Various AT (de novo and post-atrial fibrillation ablation) were mapped using ECM followed by standard-of-care electrophysiological mapping and ablation in 52 patients. The ECM consisted of recording body surface electrograms from a 252-electrode-vest placed on the torso combined with computed tomography-scan-based biatrial anatomy (CardioInsight Inc., Cleveland, Ohio). We evaluated the feasibility of this system in defining the mechanism of AT-macro-re-entrant (perimitral, cavotricuspid isthmus-dependent, and roof-dependent circuits) versus centrifugal (focal-source) activation-and the location of arrhythmia in centrifugal AT. The accuracy of the noninvasive diagnosis and detection of ablation targets was evaluated vis-à-vis subsequent invasive mapping and successful ablation.

RESULTS

Comparison between ECM and electrophysiological diagnosis could be accomplished in 48 patients (48 AT) but was not possible in 4 patients where the AT mechanism changed to another AT (n = 1), atrial fibrillation (n = 1), or sinus rhythm (n = 2) during the electrophysiological procedure. ECM correctly diagnosed AT mechanisms in 44 of 48 (92%) AT: macro-re-entry in 23 of 27; and focal-onset with centrifugal activation in 21 of 21. The region of interest for focal AT perfectly matched in 21 of 21 (100%) AT. The 2:1 ventricular conduction and low-amplitude P waves challenged the diagnosis of 4 of 27 macro-re-entrant (perimitral) AT that can be overcome by injecting atrioventricular node blockers and signal averaging, respectively.

CONCLUSIONS

This prospective multicenter series shows a high success rate of ECM in accurately diagnosing the mechanism of AT and the location of focal arrhythmia. Intraprocedural use of the system and its application to atrial fibrillation mapping is under way.

Preferential conduction patterns along the coronary sinus during atrial fibrillation in humans and their modification by pulmonary vein isolation

INTRODUCTION

Correlation function analysis applied to endocardial electrograms has earlier been used for analysis of agreement between signals and direction of activation during atrial fibrillation (AF). This study was aimed at evaluating whether preferential activation patterns along the coronary sinus (CS) exist in patients with AF.

METHODS

Twenty-seven patients (57 ± 10 years old) admitted for electrophysiological (EP) study (10 patients) and/or AF ablation (17 patients) were studied, 8 with permanent and 19 with persistent AF. Unipolar signals were recorded during 60 seconds from a 10-pole CS catheter during AF at baseline (BL) and after isolation of left and right pulmonary veins and after additional lines in the left atrium (LA) (End). Correlation function analysis was applied to signals from each pair of adjacent electrodes, and graphs of cumulated time delay were made to enable interpretation of direction of activation.

RESULTS

Correlation between paired signals was highest in the distal and middle parts of CS and lowest in the proximal CS. In 21 patients, correlation values greater than 0.8 between closely spaced electrodes suggested uniform propagation of the fibrillatory waves. In 18 of 21 patients, preferential conduction pattern along CS was seen. Of those, 15 patients had left-to-right conduction, and 3 had right-to-left conduction. During ablation, atrial fibrillation cycle length increased from 184 ± 32 milliseconds at BL to 193 ± 39 milliseconds after pulmonary vein isolation and 215 ± 39 milliseconds at the end of ablation (P = .03, BL vs End). Because of ablation, preferential conduction along CS changed in 4 patients from left to right at BL to simultaneous CS activation or right to left. In 1 of 3 patients with simultaneous activation at BL, the direction changed to right to left. No direction change was observed in any of the 3 patients with right-to-left activation at BL.

CONCLUSIONS

Atrial activation during AF exhibits a high degree of organization in distal and middle CS. Preferential conduction patterns observed in most patients may indicate either relatively dominant stable reentry circuits in the LA or activation spread from a focal source. The changes in preferential conduction during ablation of AF may reflect modification of AF substrate and indicate persistent right atrial sources not affected by ablation in the LA only.

Challenges in the classification of atrial fibrillation

The incidence and prevalence of atrial fibrillation (AF) are increasing worldwide. AF is of public health importance because it accounts for substantial morbidity, mortality, and health-care costs. AF may be transient initially, but many patients have progressive disease marked by increasing frequency and duration of episodes. Various classification schemes for AF have been proposed, although current guidelines are based on temporal rhythm-based patterns. We discuss existing schemes for the classification of AF, focusing on the advantages and limitations of the pattern-based scheme, in the context of new knowledge about AF pathophysiology, AF patterns, and clinical outcomes. Furthermore, we address gaps in knowledge that present opportunities to re-examine the current pattern-based classification of AF. A future classification scheme should ideally combine elements such as the risk of stroke, an assessment of symptoms, and the degree of impairment of the atrial substrate.

Noninvasive assessment of the complexity and stationarity of the atrial wavefront patterns during atrial fibrillation

A novel automated approach to quantitatively evaluate the degree of spatio-temporal organization in the atrial activity (AA) during atrial fibrillation (AF) from surface recordings, obtained from body surface potential maps (BSPM), is presented. AA organization is assessed by measuring the reflection of the spatial complexity and temporal stationarity of the wavefront patterns propagating inside the atria on the surface ECG, by means of principal component analysis (PCA). Complexity and stationarity are quantified through novel parameters describing the structure of the mixing matrices derived by the PCA of the different AA segments across the BSPM recording. A significant inverse correlation between complexity and stationarity is highlighted by this analysis. The discriminatory power of the parameters in identifying different groups in the set of patients under study is also analyzed. The obtained results present analogies with earlier invasive studies in terms of number of significant components necessary to describe 95% of the variance in the AA (four for more organized AF, and eight for more disorganized AF). These findings suggest that automated analysis of AF organization exploiting spatial diversity in surface recordings is indeed possible, potentially leading to an improvement in clinical decision making and AF treatment.

An automatic system for the analysis and classification of human atrial fibrillation patterns from intracardiac electrograms

This paper presents an automatic system for the analysis and classification of atrial fibrillation (AF) patterns from bipolar intracardiac signals. The system is made up of: 1) a feature-extraction module that defines and extracts a set of measures potentially useful for characterizing AF types on the basis of their degree of organization; 2) a feature-selection module (based on the Jeffries-Matusita distance and a branch and bound search algorithm) identifying the best subset of features for discriminating different AF types; and 3) a support vector machine technique-based classification module that automatically discriminates the AF types according to the Wells' criteria. The automatic system was applied on 100 intracardiac AF signal strips and on a selection of 11 representative features, demonstrating: a) the possibility to properly identify the most significant features for the discrimination of AF types; b) higher accuracy (97.7% using the seven most informative features) than the traditional maximum likelihood classifier; and c) effectiveness in AF classification also with few training samples (accuracy = 88.3% with only five training signals). Finally, the system identifies a combination of indices characterizing changes of morphology of atrial activation waves and perturbation of the isoelectric line as the most effective in separating the AF types.

The Time Interval from the Initiation of the P-Wave to the Start of Left Atrial Appendage Ejection Flow: Does It Reflect ?nteratrial Conduction Time?

Recurrence of atrial fibrillation is more common in patients with atrial conduction delay. In the present study, we evaluated whether findings obtained from transesophageal echocardiography (TEE), a semi-invasive method, correlate with those from an invasive method, electrophysiologic study (EPS), in measuring interatrial conduction time.

METHODS AND RESULTS

We compared two methods of calculating interatrial conduction time in a group of 33 patients. The origin of the P-wave on the surface electrocardiogram (ECG) was taken as the onset of atrial activation. The time interval from this point to the commencement of the left atrial appendage ejection flow (P-LAA) was measured by TEE. Meanwhile, simultaneous recordings of the left atrial appendage were obtained with a catheter positioned in the LAA, and an invasive interatrial conduction time was measured from the origin of the surface's earliest P-wave (I-IACT). The mean I-IACT (46.27 +/- 13.25 ms) correlated strongly with the mean P-LAA (49.91 +/- 12.72 ms; r = 0.839, P < 0.0001).

CONCLUSION

The interatrial conduction time can be estimated with a relatively noninvasive method using P-LAA measurements. This technique can be applied widely in predicting AF recurrence, and appropriate therapy may be applied.

Deterioration of Organization in the First Minutes of Atrial Fibrillation: A Beat-to-Beat Analysis of Cycle Length and Wave Similarity

INTRODUCTION

It has been recently suggested that many episodes of atrial fibrillation (AF) may be partially organized at the onset and thus more suitable for antitachycardia pacing therapy. Nevertheless, the time course of organization in the first minutes of AF has not been quantified yet.

METHODS AND RESULTS

Twenty episodes of paroxysmal AF were studied. Electrograms were recorded from the right atrium (RA), distal (CSd), and proximal coronary sinus (CSp). The time course of AF cycle length (AFCL) and the regularity of wave morphology (similarity index S) were beat-to-beat measured at each recording site during the first 7 minutes of AF. AFCL and S showed a decreasing trend after the onset of AF. AFCL decreased from 208 +/- 31 to 171 +/- 21 msec (P < 0.001), from 206 +/- 40 to 169 +/- 23 msec (P < 0.001) and from 190 +/- 42 to 152 +/- 18 msec (P < 0.05), respectively, in RA, CSd, and CSp. Similarly, the similarity index decreased in CSd from 0.37 +/- 0.27 to 0.12 +/- 0.09 (P < 0.01) and in RA from 0.40 +/- 0.18 to 0.17 +/- 0.16 (P < 0.001). The 80% of the decrease occurred during the first 3 minutes of the arrhythmia, while after this time both cycle length and similarity index did not change significantly anymore. Conversely, the electrical activity in CSp was highly disorganized (S = 0.05 +/- 0.03) even in the first minute of AF, and no decreasing temporal trend was observed.

CONCLUSION

Higher levels of organization and longer fibrillation intervals exist at the onset of AF. The degree of organization of the electrical activity decays within less than 3 minutes. Since antitachycardia pacing success rate increases with high levels of organization, these results suggest an early delivery of pacing treatment.

Spectral Analysis of Atrial Fibrillation Cycle Lengths Comparison Between Fast Fourier Transform Analysis and Autocorrelation Function Analysis Using Multipurpose Physio-Informatic Analysis Software

BACKGROUND

Fast Fourier transform (FFT) analysis is a popular method of spectral analysis of atrial fibrillation cycle lengths (AFCL). Autocorrelation function (ACF) analysis is also available, so the aim of this study was to elucidate the relationship between FFT and ACF analyses in the spectral analysis of AFCLs.

METHODS AND RESULTS

A total of 75 atrial fibrillation (AF) data from 39 patients were subjected to analysis. The dominant frequencies (DFs) from 4 different spectral resolutions of the FFT and peak AFCL from the ACF analysis were compared. In the FFT analysis using rectified signals, the DF was influenced by spectral resolution, no matter how the signals were tapered by the Hanning or Hamming window or filtered with the low-pass filter. There was a significant relationship between the DF from each spectral resolution and the peak AFCL. The DF from the 4,096-point FFT analysis had the strongest relationship to the peak AFCL with the smallest difference, when using 30-s AF data. In a study of the different lengths of the atrial fibrillation data, the DF also had a strong correlation to the peak AFCL with a small difference.

CONCLUSIONS

The peak AFCL obtained from ACF analysis was not of the same quality as that from FFT analysis, but had the same value as the DF from FFT analysis.

Left Atrial Ablation Versus Biatrial Ablation for Persistent and Permanent Atrial Fibrillation

OBJECTIVES

The aim of this study was to compare--in patients with persistent and permanent atrial fibrillation (AF)--the efficacy and safety of left atrial ablation with that of a biatrial approach.

BACKGROUND

Left atrium-based catheter ablation of AF, although very effective in the paroxysmal form of the arrhythmia, has an insufficient efficacy in patients with persistent and permanent AF.

METHODS

Eighty highly symptomatic patients (age, 58.6 +/- 8.9 years) with persistent (n = 43) and permanent AF (n = 37), refractory to antiarrhythmic drugs, were randomized to two different ablation approaches guided by electroanatomical mapping. A procedure including circumferential pulmonary vein, mitral isthmus, and cavotricuspid isthmus ablation was performed in 41 cases (left atrial ablation group). In the remaining 39 patients (biatrial ablation group), the aforementioned approach was integrated by the following lesions in the right atrium: intercaval posterior line, intercaval septal line, and electrical disconnection of the superior vena cava.

RESULTS

During follow-up (mean duration 14 +/- 5 months), AF recurred in 39% of patients in the left atrial ablation group and in 15% of patients in the biatrial ablation group (p = 0.022). Multivariable Cox regression analysis showed that ablation technique was an independent predictor of AF recurrence during follow-up.

CONCLUSIONS

In patients with persistent and permanent AF, circumferential pulmonary vein ablation, combined with linear lesions in the right atrium, is feasible, safe, and has a significantly higher success rate than left atrial and cavotricuspid ablation alone.

Wave Similarity Mapping Shows the Spatiotemporal Distribution of Fibrillatory Wave Complexity in the Human Right Atrium During Paroxysmal and Chronic Atrial Fibrillation

INTRODUCTION

The complexity of waveforms during atrial fibrillation may reflect critical activation patterns for the arrhythmia perpetuation. In this study, we introduce a novel concept of map, based on the analysis of the wave morphology, which gives a direct evidence in the human right atrium on the spatiotemporal distribution of fibrillatory wave complexity in paroxysmal (PAF) and chronic (CAF) atrial fibrillation.

METHODS AND RESULTS

Electrograms were recorded from a 64-electrode catheter in the right atrium of 15 patients during PAF (n = 8) and CAF (n = 7). Wave similarity maps were constructed by calculating the degree of morphological similarity of activation waves (S) at each atrial site and by following its temporal evolution. During PAF the spatiotemporal distribution of the waveforms was highly consistent across the subjects and was determined by the anatomic location. Wave similarity maps showed the existence of an extended area with low similarity index, which covered the low posteroseptal atrium (S = 0.28 +/- 0.09) and the septal region (S = 0.22 +/- 0.04), and the presence of a large tongue with high similarity index, which penetrated the lateral wall (S = 0.55 +/- 0.08) starting from the high anterolateral atrium (S = 0.54 +/- 0.06). A completely different spatiotemporal pattern was seen during CAF. No distinct regions with different similarity indexes were recognized, but a uniformly distributed low similarity index (S = 0.27 +/- 0.07) was found. The spatial pattern was highly stable in time with fluctuations of S < 0.04.

CONCLUSION

Quantification of the spatiotemporal distribution of fibrillatory wave complexity is feasible in humans by wave similarity mapping. Anatomic anchoring of waveforms during PAF and pattern destruction during CAF was determined.

Quantification of synchronization during atrial fibrillation by Shannon entropy: validation in patients and computer model of atrial arrhythmias

Atrial fibrillation (AF), a cardiac arrhythmia classically described as completely desynchronized, is now known to show a certain amount of synchronized electrical activity. In the present work a new method for quantifying the level of synchronization of the electrical activity recorded in pairs of atrial sites during atrial fibrillation is presented. A synchronization index (Sy) was defined by quantifying the degree of complexity of the distribution of the time delays between sites by Shannon entropy estimation. The capability of Sy to discriminate different AF types in patients was assessed on a database of 60 pairs of endocardial recordings from a multipolar basket catheter. The analysis showed a progressive and significant decrease of Sy with increasing AF complexity classes as defined by Wells (AF type I Sy = 0.73 +/- 0.07, type II Sy = 0.56 +/- 0.07, type III Sy = 0.36 +/- 0.04, p < 0.001). The extension of Sy calculation to the whole right atrium showed the existence of spatial heterogeneities in the synchronization level. Moreover, experiments simulated by a computer model of atrial arrhythmias showed that propagation patterns with different complexity could be the basis of different synchronization levels found in patients. In conclusion the quantification of synchronization by Shannon entropy estimation of time delay dispersion may facilitate the identification of different propagation patterns associated with AF, thus enhancing our understanding of AF mechanisms and helping in its treatment.

Prevalence of pulmonary vein disconnection after anatomical ablation for atrial fibrillation: consequences of wide atrial encircling of the pulmonary veins

AIMS

Anatomical and wide atrial encircling of the pulmonary veins (PVs) has been proposed as a cure of atrial fibrillation (AF). We evaluated the acute achievement of electrical PV isolation using this approach. In addition, the consequences of wide encircling of the PVs with isolation were assessed.

METHODS AND RESULTS

Twenty patients with paroxysmal AF were studied. Anatomically guided ablation was performed utilizing the CARTO system to deliver coalescent lesions circumferentially around each PV to produce a voltage reduction to <0.1 mV, with the operator blinded to recordings of circumferential PV mapping. After achieving the anatomical endpoint, the incidence of residual conduction and the amplitude and conduction delay of residual PV potentials were determined. Electrical isolation of the PV was then performed and the residual far-field potentials evaluated. Individual PV ablation was performed in all PVs. Anatomically guided PV ablation was performed for 47.3+/-11 min, after which 44 (55%) PVs were electrically isolated. In the remaining 45%, despite abolition of the local potential at the ablation site, PV potentials [amplitude 0.2 mV (range 0.09-0.75) and delay of 50.3+/-12.6 ms] were identified by circumferential mapping. After electrical isolation (12.2+/-11.7 min ablation), 55 (69%) PVs demonstrated far-field potentials; with a greater incidence (P=0.015) and amplitude (P=0.021) on the left compared with the right PVs. At 13.2+/-8.3 months follow-up, 13 patients (65%) remained arrhythmia-free without anti-arrhythmics. In four patients (20%), spontaneous sustained left atrial macrore-entry required re-mapping and ablation. Macrore-entry was observed to utilize regions around or bordering the previous ablation as its substrate.

CONCLUSION

Anatomically guided circumferential PV ablation results in apparently coalescent but electrically incomplete lesions with residual conduction in 45% of PVs. Wide encircling of the PVs was associated with left atrial macrore-entry in 20% of patients.

Assessment of the dynamics of atrial signals and local atrial period series during atrial fibrillation: effects of isoproterenol administration

Background

The autonomic nervous system (ANS) plays an important role in the genesis and maintenance of atrial fibrillation (AF), but quantification of its electrophysiologic effects is extremely complex and difficult. Aim of the study was to evaluate the capability of linear and non-linear indexes to capture the fine changing dynamics of atrial signals and local atrial period (LAP) series during adrenergic activation induced by isoproterenol (a sympathomimetic drug) infusion.

Methods

Nine patients with paroxysmal or persistent AF (aged 60 ± 6) underwent electrophysiological study in which isoproterenol was administered to patients. Atrial electrograms were acquired during i) sinus rhythm (SR); ii) sinus rhythm during isoproterenol (SRISO) administration; iii) atrial fibrillation (AF) and iv) atrial fibrillation during isoproterenol (AFISO) administration. The level of organization between two electrograms was assessed by the synchronization index (S), whereas the degree of recurrence of a pattern in a signal was defined by the regularity index (R). In addition, the level of predictability (LP) and regularity of LAP series were computed.

Results

LAP series analysis shows a reduction of both LP and R index during isoproterenol infusion in SR and AF (R_SR = 0.75 ± 0.07 R_SRISO = 0.69 ± 0.10, p < 0.0001; R_AF = 0.31 ± 0.08 R_AFISO = 0.26 ± 0.09, p < 0.0001; LP_SR = 99.99 ± 0.001 LP_SRISO = 99.97 ± 0.03, p < 0.0001; LP_AF = 69.46 ± 21.55 LP_AFISO = 55 ± 24.75; p < 0.0001). Electrograms analysis shows R index reductions both in SR (R_SR = 0.49 ± 0.08 R_SRISO = 0.46 ± 0.09 p < 0.0001) and in AF (R_AF = 0.29 ± 0.09 R_AFISO = 0.28 ± 0.08 n.s.).

Conclusions

The proposed parameters succeeded in discriminating the subtle changes due to isoproterenol infusion during both the rhythms especially when considering LAP series analysis. The reduced value of analyzed parameters after isoproterenol administration could reflect an important pro-arrhythmic influence of adrenergic activation on favoring maintenance of AF.

On the Atrial Response to Focal Discharges in Man

INTRODUCTION

Triggers and vulnerability are key factors for the occurrence of atrial fibrillation (AF). The aim of this study was to assess spatial dispersion of atrial refractoriness and vulnerability in response to both focal discharges as well as programmed electrical stimulation in patients undergoing ablation of atrial arrhythmogenic foci.

METHODS AND RESULTS

Twenty-nine patients were studied, and 12 right atrial unipolar electrograms were recorded. Inducibility of AF was assessed by a pacing protocol that started with one extrastimulus, followed by more aggressive pacing until AF was obtained. Mean fibrillatory intervals were used to assess the local refractoriness of each recording site. Spatial dispersion of refractoriness was calculated as the coefficient of dispersion (CD value: standard deviation of the mean of all local mean fibrillatory intervals as a percentage of the overall mean fibrillatory interval). Based on our previous study, a CD value </= 3.0 was defined as normal, whereas a CD value >3.0 was considered enhanced spatial dispersion of refractoriness. Fifteen of 29 patients had normal dispersion of refractoriness (mean CD value 1.65 +/- 0.43), and AF was inducible with burst pacing only. These patients had focal discharges causing rapid atrial tachycardia with a focal activation pattern. Activation mapping of focal activity was possible in 14 of 15 patients. Focal triggering of AF occurred in only 1 of 15 patients. Fourteen of 29 patients had enhanced dispersion (mean CD value 4.2 +/- 0.72). AF was inducible with a single extrastimulus in 11 of 14 patients (P < 0.001). Focal triggering of AF occurred in all 14 patients.

CONCLUSION

Spatial dispersion of atrial refractoriness determines whether focal atrial discharges trigger AF with disorganized activity or, alternatively, only rapid atrial tachycardia.

Long-Term Follow-Up of Right Atrial Ablation in Patients with Atrial Fibrillation:

INTRODUCTION

The aim of this study was to evaluate the efficacy and the impact on quality of life of a new ablative approach to the right atrium in patients with atrial fibrillation (AF).

METHODS AND RESULTS

Seventy-four symptomatic patients with paroxysmal (n = 49) or permanent (n = 25) refractory AF underwent radiofrequency ablation. A nonfluoroscopic electroanatomic mapping system was used to perform the following lesions: (1) an isthmus line between the tricuspid annulus and the inferior vena cava; (2) a posterior intercaval line from the superior vena cava and the inferior vena cava; (3) a septal line from the superior vena cava to the fossa ovalis, proceeding to the coronary sinus ostium where a circumferential line around the ostium was performed, and then on to the inferior vena cava; and (4) a transversal lesion connecting the posterior intercaval and the septal lesions. In addition, electrical disconnection of the superior vena cava was performed. There were no complications. Postablation remapping showed the absence of discrete electrical activity inside and just around the ablation lines. Electrical disconnection of the superior vena cava was obtained in all patients. After 21 +/- 6 months, 49 patients (66%) had stable sinus rhythm with continuation of the previous antiarrhythmic drug therapy, 13 patients (18%) were considered improved, and 12 (16%) received no benefit (unsuccessful procedure). After ablation, quality of life was significantly improved, reaching the levels of the general Italian population. Ejection fraction and the extent of the low-voltage area were found by multivariate analysis to be independent predictors of AF recurrence.

CONCLUSION

The results of the present study suggest that this ablative approach in combination with antiarrhythmic drugs is safe and effective in treating AF, leading to a marked increase in quality of life in patients with refractory AF.

Circadian variation of arrhythmia onset patterns in patients with persistent atrial fibrillation

BACKGROUND

The circadian onset patterns and cycle lengths of atrial tachyarrhythmias (AT) were determined in a group of patients with persistent atrial fibrillation.

METHODS

Fifteen patients, mean age 63 +/- 14 years and 80% male, were implanted with the Jewel AF atrial defibrillator (Medtronic, Minneapolis, Minn) for persistent atrial fibrillation only. Onset times of AT and median onset atrial cycle lengths were determined from device memory.

RESULTS

Over a follow-up period of 23.3 +/- 7 months, 227 episodes of persistent AT were treated by patient-activated atrial defibrillation. The peak onset of persistent AT was nocturnal, with 74% of episodes initiating between 8 pm and 8 am. Eighty-seven percent of the patients experienced an additional 403 paroxysmal AT episodes. These episodes showed a "double-peaked" pattern with the least number of episodes occurring between midnight and 8 am. The mean onset atrial cycle length of persistent AT was significantly shorter than the paroxysmal AT episodes (200 +/- 37 ms vs 240 +/- 39 ms, P <.005). The atrial cycle lengths at arrhythmia onset of both paroxysmal and persistent AT episodes also demonstrated circadian variation.

CONCLUSION

There is a circadian distribution of onsets for persistent AT with predominance at night. Patients with persistent AF have >1 type of atrial arrhythmia with differences in the onset patterns and atrial cycle lengths, suggesting different triggers and onset mechanisms.

Pulmonary vein internal electrical activity does not contribute to the maintenance of atrial fibrillation

Whether the electrical activity generated in the pulmonary veins (PVs) during atrial fibrillation (AF) contributes to the maintenance of arrhythmia is not known. The study population consisted of 22 patients (mean age 58 +/- 9.5 years, 16 men) with persistent (12 patients) or intermittent (10 patients) AF. Mapping of the left atrium (LA) was performed with a 64-electrode basket catheter. PVs were mapped simultaneously with the LA with a quadripolar catheter. PV were defined as arrhythmogenic (if frequent ectopic activity induced AF) or nonarrhythmogenic (if no ectopic activity was observed during the procedure). AF cycle lengths in arrhythmogenic and nonarrhythmogenic PV were 130 +/- 50 ms and 152 +/- 42 ms, respectively (P < 0.001). Both were significantly longer than simultaneous AF activity recorded from the posterior wall of the LA (116 +/- 49 ms, P < 0.001). AF cycle lengths in arrhythmogenic PVs as compared to nonarrhythmogenic PVs were: right superior PV 125 +/- 49 ms versus 148 +/- 51 ms; left superior PV 140 +/- 52 ms versus 161 +/- 30 ms; left inferior PV 127 +/- 48 ms versus 147 +/- 45 ms; and right inferior PV 129 +/- 38 versus 152 +/- 44 ms (P < 0.001 for all four comparisons). AF activity in the PV was more organized than in the posterior wall of the LA and the veins were activated in a proximal-to-distal direction during sustained AF episodes. In patients with AF not related to rheumatic heart disease, the posterior wall of the LA has faster activity than the PVs. The AF activity generated inside the PV during sustained AF episodes originates from the posterior wall of the LA rather than from focal firing.

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

A detailed analysis of the impact of atrial fibrillation (AF) on the voltage of the atrial signals acquired from various right and left atrial regions has not been reported. Thirteen patients (mean age 55 +/- 11 years, range 39-67 years, 5 women) with AF were included in this study. Mapping of the left and the right atrium was performed with 64-electrode basket catheters. AF cycle lengths were calculated over 10-second time intervals using a custom-made software. Voltage of the bipolar signals during AF was calculated by measuring the amplitudes of 30 consecutive signals in the left and the right atria. During sinus rhythm voltage differences between the left (3 +/- 2.9 mV) and the right atrium (2.8 +/- 2.4 mV, P = 0.15) were insignificant. During AF, as compared to sinus rhythm, voltages of the bipolar signals were significantly reduced in the left (0.9 +/- 0.6 mV) and the right (1.3 +/- 1.1 mV) atria (P < 0.001 compared with sinus rhythm). In the left atrium, the posterior wall showed the most pronounced voltage reduction (1.1 +/- 0.8 mV vs 5.3 +/- 4.6 mV, P < 0.001). In the right atrium the septal wall showed the greatest reduction in voltage amplitude (0.8 +/- 0.6 mV vs 2.5 +/- 1.5 mV, P < 0.001). There was a close correlation between the voltage values and the AF cycle length. The smallest voltage values and greatest amplitude reductions were observed during faster and more disorganized AF activity. It is concluded that during AF, the voltage of bipolar signals is significantly reduced as compared to sinus rhythm. The reduction in voltage expresses atrial and regional disparity and correlates strongly with local AF cycle lengths and the degree of AF disorganization.

Decrease in the Spatial Dispersion at the Termination of Atrial Fibrillation by Intravenous Cibenzoline

Atrial electrograms were recorded from the high right atrium, coronary sinus, and right lateral wall in 15 patients with induced atrial fibrillation (AF). Intravenous cibenzoline terminated AF in 8 patients (T group), but not in 7 patients (non-T group). The cycle length of the AF (AFCL) obtained by the autocorrelation function was measured every 5 s during the 30 s prior to the cibenzoline administration, and just before the termination of AF or at the end of the cibenzoline infusion in the non-T group. The mean AFCL, and spatial and temporal dispersion of the AFCL were then compared between the 2 groups (dispersion = standard deviation x 100 /mean AFCL). Cibenzoline significantly increased the mean AFCL and decreased the spatial dispersion in both groups. No significant difference in either the mean AFCL or temporal dispersion before or after cibenzoline was observed between the 2 groups. In addition, no significant difference in the spatial dispersion before the cibenzoline was observed, but the spatial dispersion after the cibenzoline was significantly smaller in the T group than in the non-T group. The mean AFCL, and the spatial and temporal dispersion before the cibenzoline did not predict the termination of AF. The decrease in the spatial dispersion may be the most important mechanism by which intravenous cibenzoline terminates AF.

A method for quantifying atrial fibrillation organization based on wave-morphology similarity

A new method for quantifying the organization of single bipolar electrograms recorded in the human atria during atrial fibrillation (AF) is presented. The algorithm relies on the comparison between pairs of local activation waves (LAWs) to estimate their morphological similarity, and returns a regularity index (rho) which measures the extent of repetitiveness over time of the detected activations. The database consisted of endocardial data from a multipolar basket catheter during AF and intraatrial recordings during atrial flutter. The index showed maximum regularity (rho = 1) for all atrial flutter episodes and decreased significantly when increasing AF complexity as defined by Wells (type I: rho = 0.75 +/- 0.23; type II: rho = 0.35 +/- 0.11; type III: rho = 0.15 +/- 0.08; P < 0.01). The ability to distinguish different AF episodes was assessed by designing a classification scheme based on a minimum distance analysis, obtaining an accuracy of 85.5%. The algorithm was able to discriminate among AF types even in presence of few depolarizations as no significant rho changes were observed by reducing the signal length down to include five LAWs. Finally, the capability to detect transient instances of AF complexity and to map the local regularity over the atrial surface was addressed by the dynamic and multisite evaluation of rho, suggesting that our algorithm could improve the understanding of AF mechanisms and become useful for its clinical treatment.

Use of global atrial fibrillation organization to optimize the success of burst pace termination

OBJECTIVES

The purpose of this study was to determine if burst atrial pacing would have an effect on terminating atrial fibrillation.

BACKGROUND

We hypothesized that frequency domain analysis of a filtered wide bipolar atrial electrogram describes the global organization of atrial fibrillation (AF) and should vary over time. Timing burst pacing to periods of high organization of AF should promote regional atrial conduction block and terminate AF.

METHODS

Nine dogs were conditioned with rapid atrial pacing for 48 h. Electrogram recordings were made from a wide right atrium (RA) to left atrium (LA) bipole and digitally filtered. A fast-Fourier transform was performed every 0.5 s on a sliding 2-s window, and the organization index (OI) was calculated as a ratio of the area of the first four harmonic peaks to the total power of the spectrum. Organization indexes >0.5 indicated more organized AF activity. Right atrium and LA burst pacing (burst) (cycle length 50 ms, 9.9 ms, 9.9 mA, 1 to 4 s) was performed through decapolar catheters. Burst was either random or synchronized to OI >0.5.

RESULTS

Burst termination was attempted 1,814 times (889 OI sync, 925 random) and succeeded in seven of nine dogs. Burst had an overall success rate of 11.1% versus 6.3% for random (p < 0.0003). Biatrial pacing had the highest efficacy for terminating AF, with a success rate of 16.5% for OI sync versus 8.2% for random (p < 0.0001).

CONCLUSIONS

Timing the delivery of the burst pace when the OI is >0.5 increases the efficacy of burst pace termination of AF. Biatrial pacing is more effective than either RA or LA pacing alone.

Principal component analysis and cluster analysis for measuring the local organisation of human atrial fibrillation

The distribution of atrial electrogram types has been proposed to characterise human atrial fibrillation. The aim of this study was to provide computer procedures for evaluating the local organisation of intracardiac recordings during AF as an alternative to off-line manual classification. Principal component analysis (PCA) reduced the data set to a few representative activations, and cluster analysis (CA) measured the average dissimilarity between consecutive activations of an intracardiac signal. The data set consisted of 106 bipolar signals recorded on 11 patients during electrophysiological studies for catheter ablation. Performances of PCA and CA in distinguishing between organised (type I) and disorganised (type II/III, Wells criteria) were assessed, in comparison with manual reading, by evaluating the predictive parameters of the classification analysis. Both methods gave high accuracy (92% for PCA and 89% for CA), confirming the feasibility of on-line characterisation of AF. Sensitivity was lower than specificity (81% against 98% for PCA, and 77% against 97% for CA), with seven out of eight misclassifications of PCA in common with CA. Differences between manual and computer analysis may be related to the higher resolution of PCA and CA in the measurement of the organisation of atrial activations. These procedures are suitable for providing automatic (by CA) or semi-automatic (by PCA) measures of the extent of local organisation of AF in the pre-ablation treatment phase.