Clinical evaluation of disorganization during atrial fibrillation as a guide to radiofrequency ablation

Aim of this study was to investigate the spatial patterns of organization of fibrillation in the right atrium using bipolar recordings from a basket catheter. Study population consists of 17 patients with persistent atrial fibrillation (AF), selected a priori for low energy internal cardioversion. Organization was measured by the number of occurrences--i.e. the percentage number of points laying on the baseline--which has been demonstrated to match Wells' criteria for the classification of AF. Well-defined and stable patterns of organization characterize the electrical activity of the right atrium in these patients. The organization in the entire right atrium showed an individual rather than common distribution. This may have implications in the choice of regions candidate for ablation.

Different atrial regional patterns of activation during atrial fibrillation: is there any relationship with the anatomy?

Right atrial (RA) mapping has been recently more carefully examined in patients with idiopathic atrial fibrillation (AF) in order to improve radiofrequency (RF) catheter-mediated ablation lines to control recurrences. The aim of this study was to map right atrial activation during AF to analyze relationship between anatomy and atrial activation for specific sites. Twenty-four patients with recurrent, drug-refractory, paroxysmal AF underwent an extensive mapping of the RA before attempting RF linear lesion catheter ablation. A typical pattern of atrial activation was recorded in all patients which was consistent with a more regular activity on the trabeculated right atrium (type I AF) and a more fragmented and complex activation on the posterior and the anterior septum (type II and III AF). This paper helps to understand the influence of the anatomic barriers to atrial activation during atrial fibrillation.

Deterministic patterns and coupling of bipolar recordings from the right atrium

The presence of organization of atrial activation processes during atrial fibrillation has been investigated to assess whether the activation sequences are wholly random or are governed by deterministic mechanisms. We performed a linear analysis based on the cross correlation function and a non linear analysis based on two algorithms. The first one detects and qualifies recurrent patterns of the coupling between atrial period time series by means of the recurrence plot quantification approach; the second one estimates the non linear coupling between activation sequences in two sites following a multivariate embedding approach. The detection of spatio-temporal recurrent patterns and of non linear coupling together with the surrogate data results indicate that during atrial fibrillation a certain degree of local organization exists, likely caused by deterministic mechanisms of activation.

Extraction of physiological and clinical information from intra-atrial electrograms during atrial fibrillation: review of methods

This paper presents a review of the evolution of methods and algorithms for the analysis of intra-atrial recordings, with special emphasis to the extraction of physiological and clinical information during atrial fibrillation. The principal time-domain and frequency-domain methods of electrogram analyses are described, and their physiological interpretation and clinical applications are discussed. In addition, the recent findings from complex system theory and chaos theory approaches are highlighted.

Management of patients with atrial fibrillation: different therapeutic options and role of electrophysiology-guided approaches

At present the approach to atrial fibrillation treatment is based on the electrophysiological patterns of atrial fibrillation (on the basis of multiple intra-atrial recordings or sophisticated new mapping techniques) only in a restricted minority of patients, those who are candidate to ablation of the substrate and/or of the triggers. Atrial fibrillation has a broad spectrum of clinical presentations and a heterogeneous electrophysiological pattern. The treatment of this arrhythmia, both with drugs and non pharmacological treatments, has been based, classically, on empirical basis and on a clinically-guided staged-approach. The limitations of pharmacological treatment led in recent years to the development of a wide spectrum of non pharmacological treatments. This implies a change in the approach to atrial fibrillation and the need to identify potentially ideal candidates to complex and expensive treatments. In this view it is currently under investigation the possibility to identify potential responders to a definitive treatment or a combination of treatments (both pharmacological and non-pharmacological) on the basis of the electrophysiological pattern.

Effect of atrial fibrillation organization on internal defibrillation threshold

Aim of the present study is to assess the effect of the organization of atrial fibrillation in the right atrium on the minimum effective cardioversion energy. Thirteen patients were studied, selected a priori for low-energy internal cardioversion (LEIC). LEIC was carried out at increasing energy levels. All patients were monitored by a multipolar basket catheter in basal condition and during cardioversion. Our results showed that the mean organization correlates with the energy of successful cardioversion, and that after each shock no significant differences (Kruskal-Wallis test) were observed in the level of organization. Similar results have been obtained for the differences of organization values, immediately before and after each shock. These results prompt for further studies aimed at measuring electrophysiological properties to predict energy thresholds.

Discrimination of atrial rhythms by linear and non-linear methods

The discrimination among atrial rhythms is obtained through the analysis of linear and non-linear dynamics of atria electrograms and local atrial period (LAP) series. Linear and non-linear degree of coupling between atrial electrograms have been assessed using cross-correlation (CCI) and synchronization indexes. Dynamics of LAP series were investigated using level of predictability (LP) and regularity indexes. Atrial fibrillation (AF) episodes, classified according to Wells' criteria, were investigated. We found that metrics obtained from LAP series provide the best performance in the classification of AF rhythms. The LP index misclassified only 12 AF episodes over 87. Synchronization index was the most performing metric in the discrimination between organized and not-organized fibrillation: detection of organized rhythm; sensitivity (SE) > 95%; positive predictability (+P) > 95%. LP (SE: 89%; +P: 89%) and CCI (SE: 87%; +P: 83%) provide slightly lower performances.

Relaxation processes in an epoxy resin studied by time-resolved optical Kerr effect

The dynamics of the epoxy resin phenyl glycidyl ether, a fragile glass-forming liquid, is investigated in the liquid and supercooled phases by time-resolved optical Kerr effect experiment with an heterodyne detection technique. We tested the mode-coupling theory and found that the predicted dynamic scenario allows to reproduce properly the measured signal, for t>1 ps, in the whole temperature interval investigated. Furthermore, the values of T(c) and lambda, obtained from the analysis of three different and independent dynamic regimes (alpha regime, von Schweidler, beta regime), are in remarkable agreement. Moreover, relaxation times obtained from optical Kerr effect and dielectric spectroscopy measurements are compared. The two time scales differ only for a constant factor in the whole temperature interval investigated.

Spontaneous and forced non-linear oscillations in heart period: role of the sino-atrial node

The aim of this study is to investigate whether and to which extent the non-linearity of the sino-atrial node contributes to the complex interactions between autonomic control and heart period. A non-linear model of the autonomic control on the sino-atrial node has been analyzed under particular experimental conditions: the autonomic nervous system was forced to act at established frequencies, by a controlled breathing procedure and a non-invasive periodic modulation of carotid baroreceptors. We quantify the non-linear coupling between the stimuli and both the experimental and the simulated heart period fluctuations by using the recurrence plot quantification analysis. Our results show that the non-linear interaction between external stimuli and heart period fluctuations is due to a certain extent to the non-linear features of the sino-atrial node.

Measure of synchronisation of right atrial depolarisation wavefronts during atrial fibrillation

A new index of synchronisation (IS) between the electrical activity of pairs of close atrial sites during atrial fibrillation (AF) is introduced. The index assesses the probability of finding synchronous activations in intra-atrial bipolar electrograms and is based on the assumption that two activations closely spaced in time are likely to belong to the same depolarisation wavefront. A dedicated statistical treatment to test this hypothesis is also illustrated. Experimental data were obtained using a multipolar basket catheter in the right atrium in 20 patients during normal sinus rhythm (NSR), atrial flutter (AFL, one patient), high-frequency pacing (HFP, two patients) and chronic AF (17 patients), and 30 segments were obtained from each. From the 24 pairs of bipoles, a single averaged IS and its standard deviation were extracted. The IS was 1 in NSR and HFP and 0.95 +/- 0.02 during AFL. During AF, the IS provided a quantitative measure of the degree of coupling of various atrial sites. The IS varied significantly among the recording sites (range 0.38-0.96), showing a patient-dependent pattern, and decreased as the arrhythmia complexity increases. No temporal trends were observed for the IS values in any chronic AF patient. On average, in each site, the dispersion of the IS over time was lower than 32% of the mean, for all patients. Additional relevant features of the proposed index are its high temporal resolution (2s) and robustness to activation time estimation error, to missing or false detections and to the ever-changing pattern of propagation. The index of synchronisation is a descriptor of the electrophysiological properties of atrial tissues.

Non-linear coupling of atrial activation processes during atrial fibrillation in humans

The activation patterns underlying the electrical activity of the heart during atrial fibrillation (AF) are not entirely random. The aim of this study was to assess the local organization of the activation processes during AF by estimating the non-linear coupling between activation sequences (ASs) in two atrial sites. To quantitatively estimate the degree of non-linear coupling we extracted two indices based on a multivariate embedding procedure and on the estimation of the correlation dimension (CD) and correlation entropy (CE), termed independence of complexity and of independence of predictability, respectively. We analysed AS in two atrial sites in 30 informed subjects during chronic AF of type I, II and III (Wells' classification), ten 6-s-long episodes of each type. Surrogates were used to reject the hypothesis that the time series were generated by linear stochastic dynamics. We estimated CD and CE according to the coarse-grained approach, which leads to a fixed high value for the embedding dimension in all the analysed ASs, and a typical value for the distance between the two ASs in the phase space. Various degrees of organization, ranging from completely synchronized to fully de-coupled signals, were observed: significant degrees of non-linear coupling were found in segments belonging in types I and II AF, whereas type III electrograms always turned out to be weakly coupled. This finding links the morphology of single electrograms to the synchronization between pairs of closely spaced electrograms. Our bivariate approach suggests that the measurement of organization during AF should be based on the estimation of the non-linear coupling between two sites. This approach appears to be more reliable and sensitive than non-linear analysis of single electrograms or linear analysis of their coupling.

Mapping the organization of atrial fibrillation with basket catheters. Part II: Regional patterns in chronic patients

The aim of this study was to investigate the spatial patterns of organization of fibrillation in the right atrium using bipolar recordings from a basket catheter in a population of 17 patients with persistent AF. The number of occurrences (NO) (i.e., the number of points laying on the baseline) was used as an objective measure of organization. This parameter significantly matches Wells' criteria for the classification of bipolar recordings during AF. The anatomic correspondence of the splines with eight atrial regions (namely anterior free wall, lateral free wall, posterolateral free wall, posterior free wall, posterior atrial septum, atrial septum, tricuspid valve, and anterior tricuspid valve) was assessed by fluoroscopic projections and electrogram morphology. Each region was further divided into high, mid-high, mid-low, and low segments. It was observed that individual and well-defined patterns of organization characterize the electrical activity of the right atrium in patients with persistent AF. When observed over 10 minutes, these patterns are rather stable in time. In each patient, the NO measurements were significantly different in the various right atrium regions (P < 0.0001 for all patients, Friedman test). The NO averaged over the population was significantly different among the regions (P < 0.001, Kruskal-Wallis test), owing to a common disorganized pattern observed in the tricuspid valve and anterior tricuspid valve regions. When these regions were removed from the analysis, the differences among the remaining regions were not statistically significant (P = 0.77). In conclusion, the quantitative assessment of organization in the entire right atrium showed an individual rather than common distribution. This may have implications in the choice of regions candidate for ablation.

Mapping the organization of atrial fibrillation with basket catheters. Part I: Validation of a real-time algorithm

The authors proposed a real-time algorithm to quantify AF organization from multielectrode basket catheter (MBC) recordings. The algorithm is based on a fast method to estimate the number of points along the baseline of a single bipolar electrogram (number of occurrences, NO). They have already proven this parameter to be effective at discriminating AF organization according to Wells' criteria. Special attention has been paid to ventricular far-field artifacts, as they proved they can significantly bias the degree of organization. To fulfill the constraints of a real-time application, a ventricular blanking procedure was implemented and validated. Bipolar electrograms were obtained from MBC in the right atrium in 17 informed patients with chronic AF. The results of NO computations were displayed as three-dimensional color-coded maps of organization by interpolating the measurements obtained at the locations of catheter bipoles. The proposed method allows real-time estimation of the organization of the atrial electrograms according to Wells' criteria. The estimation has a temporal resolution of 2 seconds, is robust to far-field ventricular artifacts, and interpolates the data available to furnish a single global map of the entire atrium. Further studies devoted to the analysis of individual and common patterns of the regional distribution of AF organization are needed to assess the usefulness of this approach for electrophysiological studies and therapeutic applications.

Linear and non-linear analysis of atrial signals and local activation period series during atrial-fibrillation episodes

Linear and non-linear indexes for the characterisation of the dynamics in atrial signals (AS) and local atrial period (LAP) series are assessed in different atrial fibrillation (AF) episodes as defined by Wells. Parameters include the linear index obtained from the cross-correlation function (CCF) between ASs and the non-linear synchronisation (S) index based on the mutual corrected conditional entropy (MCCE). Regularity (R) was computed on single-lead AS. In addition, the level of predictability (LP) and the regularity of LAP series were computed. It was found that the level of synchronisation between ASs decreased passing from type-I to type-II AF when using linear (CCF: 0.90 +/- 0.10 against 0.44 +/- 0.18; p<0.001) and non-linear (S: 0.22 +/- 0.10 against 0.05 +/- 0.03; p<0.001) indexes. The regularity index (in normal sinus rhythm (NSR): 0.30 +/- 0.08; in AF-I: 0.19 +/- 0.10; in AF-II: 0.09 +/- 0.02; NSR against AF-I p<0.001; AF-I against AF-II p<0.001) and level of predictability (in NSR: 65 +/- 18; in AF-I: 27 +/- 13; in AF-II 7 +/- 6; NSR against AF-I p<0.001; AF-I against AF-II p<0.001) significantly decreased in the LAP series passing from NSR to AF-II. The proposed parameters succeeded in discriminating the different dynamics which characterised AS and LAP series during different kinds of AF episodes.

High-level synthesis of human prolactin in Chinese-Hamster ovary cells

Two eukaryotic human prolactin (hPRL) expression vectors, based on a selectable dihydrofolate reductase (dhfr) marker, were used to transfect dhfr(-) Chinese- hamster ovary (CHO) cells. One vector, p658-hPRL, contains the hepatitis-B virus-X cDNA coding for a viral transactivator and sequences mediating dhfr mRNA degradation. The other, pEDdc-hPRL, carries the encephalomyocarditis virus leader sequence coupled to hPRL cDNA to provide high-level protein expression, possibly via a mechanism of internal translation initiation in dicistronic mRNA. Without methotrexate (MTX) amplification, p658-hPRL-transfected stable cell lines, secreting up to approximately 10 microg of hPRL/10(6) cells per day, could be rapidly obtained; production by pEDdc-hPRL-transfected cells was about 10-fold lower. However, a three-step MTX amplification of the latter led to clones secreting up to approximately 30 microg of hPRL/10(6) cells per day. A pilot production using a hollow-fibre bioreactor indicated that highly concentrated hormone levels in the medium could be obtained, with a production of up to 150 microg of hPRL/ml per day. SDS/PAGE analysis indicated that recombinant hPRL contained approximately 10% glycosylated PRL. Chromatographically purified non-glycosylated and glycosylated recombinant hPRL had bioactivities of 35 and 16 i.u./mg, respectively (Nb2 cell bioassay). This appears to be the first report describing production and purification of recombinant hPRL from CHO cells, secreted at levels higher than reported thus far in eukaryotic systems.

Electromagnetic interference by GSM cellular phones and UHF radios with intensive-care and operating-room ventilators

The aim of this study was to evaluate the risks deriving from the interference by radio handsets (GSM cellular phones and UHF radios) with intensive-care and operating-room ventilators. Tests were conducted in three hospitals in Rome on 22 lung ventilators in accordance with the recommended practice ANSI C63.18-1997. When electromagnetic interference (EMI) effects occurred, the authors determined maximum interference distances. They also evaluated the distances at which the use of a given handset would result in a 5% and a 95% probability of interference. The degree of risk posed by each observed event was estimated, and safe distances are suggested. EMI events of varying degrees and natures were observed even with transmitters placed at a considerable distance. All observed effects were temporary. Only three ventilators of a certain model stopped working altogether and had to be reset.

Single-step purification of recombinant human growth hormone (hGH) directly from bacterial osmotic shock fluids, for the purpose of (125)I-hGH preparation

A good quality tracer, to be used in the radioimmunoassay of human growth hormone, was prepared by applying the chloramine-T iodination technique to the recombinant product obtained after a single-step high-performance size-exclusion chromatography purification of a bacterial osmotic shock fluid. The labeling reaction presented a yield of about 65% and the purified tracer exhibited an antibody binding of approximately 50% (NIDDK reference antiserum diluted 1:600,000). These values are very similar to those obtained by radioiodinating highly purified clinical-grade recombinant human growth hormone obtained from the same periplasmic extract after the regular six-step purification process. Both tracers provided the same accuracy, when evaluated with the use of commercial-quality control samples in a classical radioimmunoassay methodology, their stability being practically identical: about 18% decrease in antibody binding after 2 months of storage at -20 degrees C. The novel approach permits the utilization of transformed Escherichia coli strains as a source of freshly prepared, radioiodination-grade recombinant proteins, capable of providing better reproducibility and reagent continuity.

Automated classification of human atrial fibrillation from intraatrial electrograms

The assessment of the degree of organization and the classification of atrial fibrillation (AF) according to the types defined by Wells usually resorts to the visual inspection of bipolar intraatrial electrograms. The focus of this study was to test seven parameters aimed to quantify the degree of organization of the electrograms, and then to design a final classification scheme based on a multidimensional, minimum-distance analysis. The following parameters were tested: mean atrial period (AP) and its coefficient of variation (CV); number of points lying at the baseline (NO) and the Shannon entropy (EN) of the amplitude probability density function (APDF); depolarization width (F-WIDTH); and correlation waveform analysis (CWA) and electrogram bandwidth (BW). The signal database consisted in a set of 160 AF strips of Type I, II, and III AF, scored by an expert cardiologist (60 Type I, 40 Type II, 60 Type III) and further divided in a training set (60) and a test set (100). Strips were 6 seconds long and were recorded with 5-mm interspace bipolar catheters from electrically induced (n = 13) and chronic (n = 10) patients. A classification algorithm based on a minimum-distance (Mahalanobis distance) discriminant analysis was tested. Using a single parameter, the best discriminations were provided by NO, F-WIDTH, and CV. F-WIDTH was found strongly inversely correlated to NO (r = -0.90). Of all the two-parameter combinations, CV-NO provided the best classification: 92 of 100 segments were correctly classified with sensitivity > 90% and specificity > 92%. A further improvement was obtained by including BW as a third parameter (93/100 correctly classified). The use of more than three parameters not only failed to improve, but even degraded the classification.

Recurrent patterns of atrial depolarization during atrial fibrillation assessed by recurrence plot quantification

The aim of this study was to determine the presence of organization of atrial activation processes during atrial fibrillation (AF) by assessing whether the activation sequences are wholly random or are governed by deterministic mechanisms. We performed both linear and nonlinear analyses based on the cross correlation function (CCF) and recurrence plot quantification (RPQ), respectively. Recurrence plots were quantified by three variables: percent recurrence (PR), percent determinism (PD), and entropy of recurrences (ER). We recorded bipolar intra-atrial electrograms in two atrial sites during chronic AF in 19 informed subjects, following two protocols. In one, both recording sites were in the right atrium; in the other protocol, one site was in the right atrium, the other one in the left atrium. We extracted 19 episodes of type I AF (Wells' classification). RPQ detected transient recurrent patterns in all the episodes, while CCF was significant only in ten episodes. Surrogate data analysis, based on a cross-phase randomization procedure, decreased PR, PD, and ER values. The detection of spatiotemporal recurrent patterns together with the surrogate data results indicate that during AF a certain degree of local organization exists, likely caused by deterministic mechanisms of activation.