1,721,024 research outputs found
I meccanismi elettrofisiologici
No full textLa prima descrizione scientifica di un cuore in fibrillazione è stata data da Harvey agli inizi del seicento. Tuttavia, come per le origini del battito cardiaco normale, i meccanismi di questa aritmia erano a quel tempo " ... as mysterious as the source of the Nile" (vedi Abercromby 1685) e furono necessari più di due secoli prima di dare l’avvio ad una serie di studi sull'origine dei disturbi del ritmo cardiaco. Alla fine del diciannovesimo secolo, numerosi studi sull'attività meccanica cardiaca durante alterazioni del ritmo hanno portato ad una dettagliata descrizione del ritmo e dell'ampiezza della contrazione durante flutter e fibrillazione. Tuttavia solamente con l'introduzione del galvanometro a corda di Einthoven nel 1901 é stato possibile rilevare l'attività elettrica del cuore e quindi studiare la sequenza di attivazione del muscolo cardiaco. Si é dato così l'avvio alla ricerca dei meccanismi elettrofisiologici delle aritmie cardiache. Dagli studi che ne sono seguiti, risulta che é possibile suddividere i meccanismi che stanno alla base delle aritmie atriali in meccanismi focali e attività rientrante. Mentre dati provenienti da modelli sperimentali di flutter e fibrillazione atriale hanno dimostrano come entrambi i meccanismi siano possibili e si manifestino a seconda delle condizioni sperimentali, studi elettrofisiologici condotti in ambito clinico hanno indicato nell’attività elettrica rientrante il meccanismo prevalente alla base del flutter e della fibrillazione atriale nell’uomo. I numerosi studi di mappaggio durante flutter atriale hanno dato indicazioni sulla sede e sulle dimensioni del circuito di rientro. Per quanto riguarda il flutter, la ricerca clinica è oggi indirizzata a definire il ruolo delle strutture anatomiche endocardiche dell’atrio e a caratterizzare il circuito di rientro, indentificando le barriere anatomiche e/o funzionali e le eventuali aree a conduzione critica. Il pattern di attivazione degli atri durante fibrillazione atriale risulta essere invece molto più complesso, essendo costituito dalla propagazione disordinata di fronti d’onda molteplici. Nel caso della fibrillazione sembra oggi tuttavia necessaria una distinzione fra meccanismo di insorgenza e meccanismo di mantenimento. Infatti recentemente un’origine focale del fenomeno è stata indicata da diversi gruppi di ricerca.
L’esatta definizione del meccanismo elettrofisiologico nel paziente, così come l’individuazione del corrispondente parametro vulnerabile, costituisce un elemento fondamentale per una scelta della terapia antiaritmica condotta su basi razional
Spectral Analysis of the Ventricular Repolarisation Duration in 24-hour Holter Monitoring: Technical Requirements and Early Results
No full textThis study examines the feasibility of measuring RT intervals in Holter EGC recordings in order to apply spectral analysis. To obtain a resolution of 1 msec in the RT measurements an oversampling procedure was first introduced and the precision of two algorithms for the detection of the maximum and the end of the T-wave were compared as a function of noise. Following this spectral analysis was applied on RR and RT series measured on five 24-hour Holter ECG tapes. Both RR and RT spectra were characterised by two main bands at low (LF ~ 0.1 Hz) and high (HF ~ 0.25 Hz) frequency. Throughout the 24 hour period RT and RR spectra showed synchronous changing in power spectral distribution but with a different balance between LF and HF band
Mechanoelectric transduction in the isolated cardiac cell: the effects of swelling
No full textCell swelling determines an increase in cell volume and has been shown to induce the activation of stretch activated channels. No direct evidence has been reported concerning the effects of swelling on the action potential of single cardiac myocytes with respect to cell volume changes. Aim of our study was to investigate the effects of cell swelling on action potential shape and duration and on the main ionic currents underlying the action potential of guinea pig ventricular myocytes. Adult guinea pig ventricular myocytes were studied by means of the patch-clamp technique in Whole Cell Configuration (WCR), in current clamp mode and in voltage clamp mode to record membrane potentials and ionic currents respectively. Images of the cells were captured simultaneously with electrical recordings by means of a SIT camera coupled to the microscope to correlate the effects induced by swelling on the electrophysiological parameters with the changes in cell volume. Cell were swolllen by decreasing the ionic strength of the external solution with respect to the intracellular and extracellular control solutions (from 290mOsm/L in control to 172 mOsm/L). The average volume increase during swelling was 45.5±7.2% (n=10, pECl and inward at Vm<ECl observed in our cells, may contribute at positive potentials to AP shortening occurring during the plateau phase and at negative potentials to the depolarization of Vrest. Our data also show that IKl is increased in amplitude by cell swelling and may contribute to the effect observed on Vrest. We conclude that cell swelling, by means of the mechano-electrical feedback, can modify the refractoriness of cardiac tissue (inducing action potential shortening and resting potential depolarization), and may predispose the heart to arrhythmia
A method for quantifying atrial fibrillation organization based on wave-morphology similarity
No full textA 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 (Ï) 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 (Ï = 1) for all atrial flutter episodes and decreased significantly when increasing AF complexity as defined by Wells (type I: Ï = 0.75±0.23; type II: Ï = 0.35±0.11; type III: Ï = 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 Ï 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 Ï, suggesting that our algorithm could improve the understanding of AF mechanisms and become useful for its clinical treatment
Time course of swelling-induced action potential variations and volume in guinea-pig ventricular myocytes
No full textNoninvasive assessment of baroreflex sensitivity in post-MI patients by an open loop model of RR-systolic arterial pressure interactions
No full textNoninvasive evaluation of baroreflex sensitivity is considered an important goal for diagnosis and prognosis in post-MI patients. Methodological approach and physiological measure conditions may be the main causes for the differences found with respect to the standard Phenylephrine test. In this study, three linear parametric models, describing variability and mutual interactions of RR interval and systolic arterial pressure (SAP), were compared in relation to their ability to quantify baroreflex gain, using the Phenylephrine test index (PheBRS) as reference. By monovariate autoregressive (AR) model, bivariate AR model and open loop ARXAR model, specific gain indexes (aAR, a2AR, aARXAR) were calculated. Variance and regression analysis selected aARXAR first in correlation with PheBRS, demonstrating that a better agreement is achieved using the ARXAR model, specifically designed to describe the causal influences of SAP on RR interva
Propagation pattern analysis during atrial fibrillation based on the adaptive group LASSO
No full textThe present study introduces sparse modeling for the estimation of propagation patterns in intracardiac atrial fibrillation (AF) signals. The estimation is based on the partial directed coherence (PDC) function, derived from fitting a multivariate autoregressive model to the observed signals. A sparse optimization method is proposed for estimation of the model parameters, namely, the adaptive group least absolute selection and shrinkage operator (aLASSO). In simulations aLASSO was found superior to the commonly used least-squares (LS) estimation with respect to estimation performance. The normalized error between the true and estimated model parameters dropped from 0.20±0.04 for LS estimation to 0.03±0.01 for aLASSO when the number of available data samples exceeded the number of model parameters by a factor of 5. The error reduction was more pronounced for short data segments. Propagation patterns were also studied on intrac-ardiac AF data, the results showing that the identification of propagation patterns is substantially simplified by the sparsity assumption
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