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R Antolini

Publications and source records attributed to R Antolini.

11 recordsLinked to original sources
PubMed1992

Complex dynamics underlying the human electrocardiogram.

Sequences of different human cardiac rhythms terminating in ventricular fibrillation have been studied, both qualitatively and quantitatively, with methods of nonlinear dynamics. The analysis has been applied to ECG epochs belonging to rhythms of increasing electrocardiographic irregularity: from sinus rhythm to prefibrillatory rhythms and then to ventricular fibrillation. The phase portraits of these rhythms have been reconstructed from the ECG recording with the time-delay technique, and their correlation dimensions have been estimated with the algorithm of Grassberger and Procaccia (1983a, b). Different cardiac rhythms exhibit different correlation dimensions that describe the corresponding degrees of complexity. The correlation dimension increases as one proceeds from sinus rhythm to fully developed ventricular fibrillation via intermediate rhythms. The fully developed ventricular fibrillation shows the highest degree of complexity. The dimensional analysis supports the existence of complex dynamics underlying different cardiac rhythms and reveals an increase in dimensional complexity corresponding to an increase in electrocardiographic irregularity. Our results indicate that nonlinear dynamics may be used to assess various dynamic states of the heart and may offer a non-invasive tool to investigate the complex dynamic phenomena occurring during arrhythmia.

Algorithms↗
PubMed1992

Spontaneous beat-to-beat variability of the ventricular repolarization duration.

The spontaneous beat-to-beat variability of the ventricular repolarization duration was investigated in 21 healthy subjects (age 25-71 years; mean, 40 years) during the basal state in a recumbent position. For each subject, approximately 1,000 consecutive cycles were analyzed with an automated technique. The time series of the RR, QT, and RT intervals generate histograms that approximate normal distributions and have mean standard deviations of 57.0 ms, 5.4 ms, and 4.3 ms, respectively. Spectral analysis was used to detect rhythmical oscillations in these time series. The power spectra densities of both heart rate and ventricular repolarization during show peaks in the same frequency bands: low frequency (0.05-0.12 Hz) and high frequency (0.2-0.4 Hz). The power distribution between these two bands observed in the ventricular repolarization duration spectra was found to be the reverse of that in heart rate spectra (p less than 0.005).

Adult↗
PubMed1991

Activation energy of the cardiac Na+/Ca2+ exchanger in sarcolemmal vesicles and reconstituted proteoliposomes.

Sarcolemmal membrane vesicles isolated from bovine ventricular tissue accumulate Ca2+ through the Na+/Ca2+ exchanger when exposed to an outwardly directed Na+ gradient. This Ca2+ is then released by the same mechanism if the vesicles are transferred to a Ca(2+)-depleted Na+ buffer. Using the Ca+ indicator, arsenazo III, and a stopped-flow spectrophotometer, we can directly follow the kinetics of Ca2+ extrusion. We can thus measure the activity of the Na+/Ca2+ exchanger by the initial rate of Ca2+ release. We found that it depends upon the external Na+ concentration in a cooperative way, with a Hill coefficient of 2. By studying the temperature dependence of Na+/Ca2+ exchange, we found that it can be described by a single activation energy: Ea = 8.3 +/- 0.4 Kcal/mol. When the Na+/Ca2+ exchanger is reconstituted into lipid vesicles of defined composition, we observe a higher activity if cholesterol is among the lipids. The activation energy becomes 6.1 +/- 0.1 Kcal/mol in this system, but the Arrhenius plot shows a decreased slope for temperatures above 33 degrees C.

Animals↗
PubMed1990

Absorption rate density (ARD) computation in microwave hyperthermia by the finite-difference time-domain method.

A mathematical model has been developed, which is able to predict power distributions in biological tissues during microwave hyperthermia delivered by waveguide applicators. The numerical solutions of Maxwell's equations was obtained by the finite-difference time-domain (FDTD) technique. Two improvements with respect to the standard implementation of FDTD were introduced: a separation between the source and load calculations (based on the Schelkunoff equivalence principle) and a simple routine that automatically recognises the steady state. Two commercially available applicators, a dual-ridged and a side-loaded waveguide, were modelled using their theoretical aperture fields. The absorption rate density (ARD) distributions delivered by these applicators were measured through phantom thermal dosimetry and compared with the patterns estimated by the simulation.

Computer Simulation↗
PubMed1990

[Stable ventricular tachycardia in arrhythmogenic dysplasia of the right ventricle in sportsmen].

Right ventricular arrhythmogenic dysplasia (RVAD) is a typical asymptomatic arrhythmogenic cardiopathy in athletes, which is occasionally concurrent with normal ventricular function and life-threatening arrhythmias. A total of 32 athletes (28 males and 4 females, mean age, 23 years, mean follow-up, 6.7 years) were examined for severe cardiac arrhythmias with left bundle branch block. The conclusive diagnosis of RVAD was established from clinical, echocardio-, and angiographic evidence. The protocol of the examination involved Holter monitoring, loading tests, electrophysiological study, two-dimensional echocardiography, cardiac angiography of the right and left ventricles, coronary angiography. The most severe arrhythmias were observed in athletes whose mean age was 23.4 years, 20 patients had sustained ventricular tachycardia (it occurred only in 19 who were indulging in sports), 6 presented with transient ventricular tachycardia, and 1 had ventricular fibrillation. They all had been considered fit for sports. The disease proceeded severely in 16 of 32 athletes (in 13 of 16 while indulging in sports), the conditions close to syncope were seen in 9 patients (8 had sustained ventricular tachycardias and 1 had transient ventricular tachycardias), syncopes were observed in 5 patients (sustained ventricular tachycardias).

Adult↗
PubMed1989

Congenital long QT syndrome inducing 2:1 atrioventricular block: early detection in fetal life.

A case is reported of congenital long QT interval associated with fixed 2:1 atrioventricular block. The bradycardia was detected at 16 weeks of gestational age. The atrioventricular block was due to an extremely delayed ventricular repolarization. Early detection of bradycardia in fetal life and the demonstration of a normal positive correlation between QT duration and ventricular rate suggest that, in this case, the syndrome may be due to an anomaly of the myocardial cells rather than to imbalance of the sympathetic nervous system.

Arrhythmias, Cardiac↗
PubMed1989

Arrhythmia patterns in athletes with arrhythmogenic right ventricular dysplasia.

Arrhythmogenic right ventricular dysplasia (ARVD) is a typical 'silent' arrhythmogenic cardiomyopathy in athletes, with the possibility of normal ventricular performance and life-threatening arrhythmias. We studied 32 athletes (28 M, 4 F), mean age 23 years, follow-up 6.7 years, all previously declared fit for sports activity. They were studied for significant ventricular arrhythmias with LBBB with a final diagnosis of ARVD based on accepted clinical, echocardiographic and angiographic criteria. The study protocol included Holter monitoring (HM), stress test (ST), electrophysiological endocavitary study (EES), 2D echocardiography, RV and LV cardioangiography and coronarography. The most serious arrhythmia appeared at a mean age of 23.4 years, 20 had clinical sustained ventricular tachycardia (VT) (19/20, 95% during sports activity), six non-sustained VT and one ventricular fibrillation (VF). Severe symptoms occurred in 16/32 athletes (50%) during sports activity in 13/16 (81%): presyncope in nine (non-sustained VT in one, sustained VT in eight); syncope in five (sustained VT); aborted sudden death (SD) in one, SD (follow-up) in one. The reproducibility (HM, ST, EES) of clinically severe arrhythmic manifestations which occurred during sports activity was not high. In fact, during sport many factors are at work which may activate several arrhythmogenic mechanisms not easily reproducible in the laboratory. We conclude that a cardioarrhythmological study is mandatory in suspected right ventricular arrhythmias, including morphological study of the RV, to avoid arrhythmic risk during athletic activity.

Adult↗
PubMed1988

On-line interval measurement during invasive cardiac electrophysiologic testing.

A microprocessor-based timer has been developed for routine and research use in cardiac electrophysiologic studies. The cycle length (A-A) and the conduction times through the right atrium (A(HRA)-A(HIS], the AV node (A-H) and the His-Purkinje system (H-V) can be automatically measured beat-to-beat in real-time both during sinus rhythm and during atrial pacing. The design has been refined during three years of use in over 80 clinical studies. A comparison between manual and automatic measurements has been executed for randomly chosen portions of 10 studies. With the manual measurements as reference procedures the sensitivities of the automatic measurements of the A, H and V waves were 0.98, 0.88 and 0.92, respectively, while the specificities were 0.93, 0.92 and 0.93, respectively. For the true positive measurements the correlation coefficients of the intervals were r(A-A) = 0.9998, r(A-H) = 0.987 and r(H-V) = 0.988. The statistical analysis of the differences between manual and automatic readings for the intervals A-A, A-H and H-V yielded mean values of -1 ms, -0.8 ms and 0.6 ms and standard deviations of 3 ms, 4 ms and 4 ms which are smaller than the accuracy of the common manual measurements.

Ajmaline↗