Ultrastructural study of archaeological Vitis vinifera L. seeds using rapid-freeze fixation and substitution.

The ultrastructure of Vitis vinifera seeds from different archaeological sites was studied. Preservation status differed between sites. Preliminary investigations of grape seeds from Poggio Bacherina (Chianciano Terme, Siena) and Miranduolo (Chiusdino, Siena) showed collapsed or charred tegument, making this material suitable for morphometric studies only. Rapid-freeze fixation and substitution of grape seeds from Shahr-I Sokhta in Iran and via De' Castellani in Florence revealed well preserved tegument suitable for chemical and cytochemical analysis. Energy dispersive X-ray microanalysis was used to determine chemical composition. Cytochemical analysis based on fluorescent staining with DAPI suggested the presence of cytoplasm residues.

Noninvasive ECG as a tool for predicting termination of paroxysmal atrial fibrillation.

Atrial fibrillation (AF) is the most common cardiac arrhythmia and entails an increased risk of thromboembolic events. Prediction of the termination of an AF episode, based on noninvasive techniques, can benefit patients, doctors and health systems. The method described in this paper is based on two-lead surface electrocardiograms (ECGs): 1-min ECG recordings of AF episodes including N-type (not terminating within an hour after the end of the record), S-type (terminating 1 min after the end of the record) and T-type (terminating immediately after the end of the record). These records are organised into three learning sets (N, S and T) and two test sets (A and B). Starting from these ECGs, the atrial and ventricular activities were separated using beat classification and class averaged beat subtraction, followed by the evaluation of seven parameters representing atrial or ventricular activity. Stepwise discriminant analysis selected the set including dominant atrial frequency (DAF, index of atrial activity) and average HR (HRmean, index of ventricular activity) as optimal for discrimination between N/T-type episodes. The linear classifier, estimated on the 20 cases of the N and T learning sets, provided a performance of 90% on the 30 cases of a test set for the N/T-type discrimination. The same classifier led to correct classification in 89% of the 46 cases for N/S-type discrimination. The method has shown good results and seems to be suitable for clinical application, although a larger dataset would be very useful for improvement and validation of the algorithms and the development of an earlier predictor of paroxysmal AF spontaneous termination time.

Cardiac resynchronization therapy and phase resetting of the sinoatrial node: a conjecture.

Congestive heart failure is a severe chronic disease often associated with disorders that alter the mechanisms of excitation-contraction coupling that may result in an asynchronous left ventricular motion which may further impair the ability of the failing heart to eject blood. In recent years a therapeutic approach to resynchronize the ventricles (cardiac resynchronization therapy, CRT) has been performed through the use of a pacemaker device able to provide atrial-based biventricular stimulation. Atrial lead senses the spontaneous occurrence of cells depolarization and sends the information to the generator which, in turn, after a settled delay [atrioventricular (AV) delay], sends electrical impulses to both ventricles to stimulate their synchronous contraction. Recent studies performed on heart rate behavior of chronically implanted patients at different epochs after implantation have shown that CRT can lead to sustained overall improvement of heart function with a reduction in morbidity and mortality. At this moment, however, there are no studies about CRT effects on spontaneous heart activity of chronically implanted patients. We performed an experimental study in which the electrocardiographic signal of five subjects under chronic CRT was recorded during the activity of the pacemaker programmed at different AV delays and under spontaneous cardiac activity after pacemaker deactivation. The different behavior of heart rate variability during pacemaker activity and after pacemaker deactivation suggested the hypothesis of a phase resetting mechanism induced by the pacemaker stimulus on the sinoatrial (SA) node, a phenomenon already known in literature for aggregate of cardiac cells, but still unexplored in vivo. The constraints imposed by the nature of our study (in vivo tests) made it impossible to plan an experiment to prove our hypothesis directly. We therefore considered the best attainable result would be to prove the accordance of our data to the conjecture through the use of models and physical considerations. We first used the data of literature on far-field effects of cardiac defibrillators to prove that the pacemaker impulses delivered to the two ventricles were able to induce modifications in membrane voltage at the level of the SA node. To simulate a phase resetting mechanism of the SA node, we used a Van der Pol modified model to allow the possibility of changing the refractory period and the firing frequency of the cells separately. With appropriate parameters of the model we reproduced phase response curves that can account for our experimental data. Furthermore, the simulated curves closely resemble the functional form proposed in literature for perturbed aggregate of cardiac cells. Despite the small sample of subjects investigated and the limited number of ECG recordings at different AV delays, we think we have proved the plausibility of the proposed conjecture.

Revisiting the potential of time-domain indexes in short-term HRV analysis.

In the context of HRV analysis, we evaluated the information content of two measures that can easily be derived from the classical RR time-domain indexes. The two measures are: 1) the ratio sd/rmssd, where sd is the RR standard deviation and rmssd is the root mean square of squared differences of consecutive RR beats; and 2) the ratio sd2/sd1, where sd2 and sd1 are extracted from the Poincaré plot and represent the transversal and longitudinal dispersion of the cloud of points (RR(i),RR(i)(+1)). We compared the performance of the two measures with that of the classical LF/HF ratio in a group of healthy subjects who underwent a 70 degrees upright tilt test. The goodness of the results obtained by the two measures, the simplicity of their calculation and their applicability free from a priori assumptions on the characteristics of the data are proposed to the attention of the community involved in the HRV analysis as a possible alternative to the LF/HF ratio.