Biomedical subjects

G Calcagnini

Publications and source records attributed to G Calcagnini.

At least 19 recordsLinked to original sources

PubMed2006

Evaluation of electromagnetic interference of GSM mobile phones with pacemakers featuring remote monitoring functions.

UNLABELLED: The aim of this study was to evaluate whether global system for mobile communication (GSM) cellular phones can affect the home monitoring (HM) function implemented in last generation pacemakers (PM). METHODS: We performed in vitro and in vivo tests on the BA03 PM (Biotronik GmbH, Berlin, Germany). In vitro we evaluated whether an improper HM procedure or an altered patient-activated HM function occurred. We used two cellular phone models, with a fixed external or internal antenna, positioned close to both the PM and the mobile phone-like device, during handover, ringing, and talking. All the tests were done with the PM in air, at 900 and 1,800 MHz GSM bands, under worst case conditions. A subset of these tests was repeated in 17 patients: the mobile phones were moved both around the PM implant site and the mobile cell phone-like device, during talking. RESULTS: In vitro, neither the HM procedure nor PM functioning were corrupted by the GSM communications: all the transmissions were correctly received, with a maximum transmission delay of about 110 seconds. In vivo, the rate of successful transmissions was 93%. CONCLUSION: Our data show that HM function does not call for specific restrictions on the use of GSM cellular phones.

Artifacts↗

PubMed2005

Multidisciplinary approach for diagnosing syncope: a retrospective study on 521 outpatients.

OBJECTIVES: To describe causes of syncope in outpatients in whom structural heart disease was ruled out as a cause, and to analyse the role of a multidisciplinary approach in a syncope unit for the diagnosis of patients with syncope of unknown origin. METHODS: Cardiovascular autonomic nervous system (ANS) function was evaluated extensively in 521 outpatients by careful history, physical examination including orthostatic blood pressure measurement and standard ECG, and tilt testing. RESULTS: Causes of syncope remained unknown in 29.2% of cases. ANS dysfunction was found in 58.6% of those presenting with either neurally mediated syncope (53.6%) or chronic autonomic failure (5%); 3.8% of the patients suffered from syncope of cardiogenic origin (2.5%) or non-neurogenic hypotension (1.3%), and 8.4% had loss of consciousness of non-syncopal origin. Loss of consciousness was confirmed as being related to seizures in under 30% of patients initially diagnosed as having epilepsy. CONCLUSIONS: Neurally mediated syncope represents the commonest type of syncope. ANS evaluation including tilt testing should be considered as preliminary screening in patients with syncope in the absence of definite heart abnormalities. Neurologists should consider syncope from ANS failure as a comorbid factor in patients with seizures where the clinical characteristics are not straightforward.

Adult↗

PubMed2004

Effects of subthreshold shocks on wavelet propagation during atrial fibrillation in humans.

OBJECTIVES: Our objectives are: first to investigate the effects of internal cardioversion energies on the wave fronts propagation in the right atrium immediately after the energy delivery; second, to track the time course of these effects. METHODS: The study is based on a measure of organization of the endoatrial electrograms obtained by a multipolar basket catheter inserted in the right atrium. We estimated the level of organization by computing the percentage of points laying on the signal baseline (i.e., number of occurrences, NO). NO values were computed on two-second long windows. Six non-overlapped windows were selected, one just before and five just after the last unsuccessful shock. RESULTS: Immediately after the shock most of the patients exhibited an increase in the organization patterns. This increase was more evident in those patients with rather disorganized patterns and higher energy threshold. This effect fades within a few seconds after the shock delivery. CONCLUSIONS: Our data confirm the idea that the electrical shock causes a widespread extinction of electrical wavefronts, which regenerates after the shock. Since an increase of organization may lead to a reduction of energy threshold, a potential application of these findings might consist in the delivery of multiple subthreshold shocks instead of a single one.

Atrial Fibrillation↗

PubMed2003

On the mechanisms of interference between mobile phones and pacemakers: parasitic demodulation of GSM signal by the sensing amplifier.

The aim of this study was to investigate the mechanisms by which the radiated radiofrequency (RF) GSM (global system for mobile communication) signal may affect pacemaker (PM) function. We measured the signal at the output of the sensing amplifier of PMs with various configurations of low-pass filters. We used three versions of the same PM model: one with a block capacitor which short circuits high-frequency signals; one with a ceramic feedthrough capacitor, a hermetically sealed mechanism connecting the internal electronics to the external connection block, and one with both. The PMs had been modified to have an electrical shielded connection to the output of the sensing amplifier. For each PM, the output of the sensing amplifier was monitored under exposure to modulated and non-modulated RF signals, and to GSM signals (900 and 1800 MHz). Non-modulated RF signals did not alter the response of the PM sensing amplifier. Modulated RF signals showed that the block capacitor did not succeed in short circuiting the RF signal, which is somehow demodulated by the PM internal non-linear circuit elements. Such a demodulation phenomenon poses a critical problem because digital cellular phones use extremely low-frequency modulation (as low as 2 Hz). which can be mistaken for normal heartbeat.

Amplifiers, Electronic↗

PubMed2003

A novel heart/trunk simulator for the study of electromagnetic interference with active implantable devices.

This paper describes a portable heart simulator for the study of electromagnetic interference with active implantable devices. The simulator consists of plexiglas box divided into three chambers simulating the left atrium and the ventricles, plus a lateral compartment for the implantable device. The box is linked to a laptop computer by an analogue-to-digital convertor board, and the three chambers are monitored and driven by dedicated hardware and software interfaces. Synthetic endocardial atrial and ventricle signals for 13 cardiac rhythms are stored in the computer. They are applied to the cardiac chambers by AgCl plates. Sensing electrodes are in the form of AgCl needles inserted in saline. The simulator was able to demonstrate the behaviour of three pacemakers tested in the absence and presence of electromagnetic interference, generated by mobile phones (European GSM 900 and 1800 MHz) that emitted up to 2W (1 W at 1800 MHz). Pacemakers can be programmed with sensitivity from 0.1 mV to 5 mV, pulse width from 0.1 ms to 1.5 ms and pulse amplitude from 0.5 V to 5 V. The structural separation in three cardiac chambers (plus the one for the device) allowed a fast analysis procedure for dual- and tri-chamber implantable devices.

Cell Phone↗

PubMed2003

Nonlinear coupling among heart rate, blood pressure, and respiration in patients susceptible to neuromediated syncope.

The aim of this study is to evaluate the degree of coupling between the cardiovascular variability series and the respiration in subjects susceptible to neurally mediated syncope. Twenty-one informed patients susceptible to syncope and ten sex- and age-matched control subjects were enrolled in the study. ECG, respiration activity, and arterial blood pressure were simultaneously recorded at rest (controlled and free breathing) and during the 70 degrees head-up TILT test (free breathing). The degree of nonlinear coupling among heart rate variability (HRV), blood pressure variability (BPV), and respiration was quantified by means of two indices according to a multivariate embedding-based approach. Eleven patients developed syncope during the TILT test. We found that during the late TILT phase, the TILT-positive group experienced a significant increase in nonlinear coupling respect to the mid TILT phase (p < 0.01, Wilcoxon nonparametric test for pair data) while the TILT-negative group did not (p < 0.01, Mann-Whitney U-test). If the proposed nonlinear coupling indexes can be considered expression of the coupling mechanisms involved in the vagal regulation of the cardiovascular system, an increase in vagal tone accompanied by a decrease in sympathetic activity seem to occur before a vasovagal event.

Adolescent↗

PubMed2002

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.

Atrial Fibrillation↗

PubMed2002

Coupling patterns between spontaneous rhythms and respiration in cardiovascular variability signals.

We performed a quantitative study of coupling patterns between respiration and spontaneous rhythms of heart rate and blood pressure variability signals by using the Recurrence Quantification Analysis (RQA). We applied RQA to both simulated and experimental data obtained in control breathing at three different frequencies (0.25, 0.20, and 0.13 Hz) from ten normal subjects. RQA succeeded in quantifying different degrees of non-linear coupling associated to several interference patterns. We found higher degrees of non-linear coupling when the respiratory frequency was close to the spontaneous Low Frequency (LF) rhythm (0.13 Hz), or almost twice the LF frequency (0.2 Hz), whereas weaker coupling was observed when the respiratory frequency was 0.25 Hz. Clinical applications of our approach should focus on new experimental protocols, featuring the stimulation of one of the two branches of the autonomic nervous system (ANS) or aimed at the analysis of pathologies linked to the ANS.

Analysis of Variance↗

PubMed2002

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.

Biophysical Phenomena↗

PubMed2001

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.

Aged↗

PubMed2001

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.

Adult↗

PubMed2001

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.

Algorithms↗

PubMed2001

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.

Aged↗

PubMed2001

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.

Arteries↗

PubMed2001

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.

Atrial Fibrillation↗

PubMed2001

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.

Adult↗

PubMed2001

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.

Atrial Fibrillation↗

PubMed2001

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.

Aged↗