Catálogo de publicaciones - libros

Rett syndrome (RS) is a severe neurological disorder, predominant in females, with higher risk of sudden death (SD). So far for risk-assessment, heart rate variability (HRV), QT duration and its dispersion (QTd) were measured with ECG. However SD has occurred in RS also in absence of ECG abnormality. We aimed to evaluate the feasibility of magnetocardiographic (MCG) mapping as an alternative to study ventricular repolarization (VR) alteration in RS patients. 9 female (age: 1-34 years) RS patients were studied with an unshielded 36-channels MCG system. To assess VR, heart rate (HR)-corrected JT, JT, QT, Tintervals and QTd, were measured from both MCG and ECG signals. Moreover the magnetic field (MF) gradient orientation (-angle) during the ST segment and three MF dynamic parameters were automatically evaluated from MCG T-wave. HRV parameters were evaluated from 12-lead Holter ECG. 15 age-matched normal controls (NC) were studied for comparison. HR-corrected JT, JT, QT and T intervals, and QTd were longer in RS than in NC. The differences were more evident with clinical impairment (stage IV). MF gradient orientation and MF dynamic parameters were abnormal in RS patients. As compared to NC, HRV parameters were altered in the time-domain, although still within normal range in the frequency-domain. In RS, ECG recordings are often noisy and BSPM is difficult. On the contrary MCG mapping is easily feasible and discovers VR alteration not evident at the ECG. The diagnostic value of MCG in RS remains to be defined.

Basic electrical properties and electrophysiological mechanisms of cardiac tissue have been frequently researched applying preparations of papillary muscle. Advantages of these preparations are the simplicity to satisfy their metabolic demands and the geometrical elementariness in comparison to wedge and whole heart preparations. In this computational study the spatio-temporal evolution of activation fronts in papillary muscle was reconstructed with a bidomain model of electrical current flow and a realistic electrophysiological model of cardiac myocytes. The effects of two different pacing sites were investigated concerning the distribution of extracellular potentials and transmembrane voltages. Results of simulations showed significant changes of the resulting wave fronts and the related potential distributions inside of the muscle and in the bath for the different pacing sites. Additionally, the results indicated that reliable measurements of activation times can be carried out only in regions adjacent to the wave front. These results can be applied for development of measurement setups and techniques for analysis of experimental studies of papillary muscle.

The stability of induced pacemaker activity in a virtual human ventricular cell is analysed by numerical simulations and continuation algorithms, with the conductance of the time independent inward rectifying potassium current () as the bifurcation parameter. Autorhythmicity is induced within a narrow range of this conductance, where periodic oscillations and bursting behaviour are observed. The frequency of the oscillations approaches zero as the parameter moves towards the bifurcation point, suggesting a homoclinic bifurcation. Intracellular sodium ([Na]) and calcium ([Ca]) concentration dynamics can influence the location of the bifurcation point and the stability of the periodic states. These two concentrations function as slow variables, pushing the fast membrane voltage system into and out of the periodic region, producing bursting behaviour. Moreover, suppressing will prolong action potential duration and may introduce risks of developing stable periodic intermittency and arrhythmia. A genetically engineered pacemaker may appear an attractive idea, but simple analysis suggests inherent problems.

Cardiovascular diseases are a major health concern all over the world and, especially, heart failure has gained more importance in the recent years. Improving diagnosis and therapy is therefore critical and among the several resources at our disposal, implantable devices is expected to have a better rate of success. This paper is focused on two topics: (i) our views of the main challenges to face in order to reach these objectives and (ii) a specific target regarding the pose of leads for multisite pacemakers by means of virtual endoscopy pre-operative planning and path finding throughout the coronary venous tree.

The dangerous cardiac arrhythmias of tachycardia and fibrillation are most often sustained by re-entry. Re-entrant waves rotate around a phase singularity, and the identification and tracking of phase singularities allows the complex activity observed in both experimental and computational models of fibrillation to be quantified. In this paper we present preliminary results that compare two methods for identifying phase singularities in a computational model of fibrillation in 2 spatial dimensions. We find that number of phase singularities detected using each method depends on choosing appropriate parameters for each algorithm, but that if an appropriate choice is made there is little difference between the two methods.

In this article we study the problem of estimating the parameters of a 2-D electrophysiological model of the heart from a set of temporal recordings of extracellular potentials. The chosen model is the reaction-diffusion model on the action potential proposed by Aliev and Panfilov. The strategy consists in building an error criterion based upon a comparison of depolarization times between the model and the measures. This error criterion is minimized in two steps : first a global and then a local adjustment of the model parameters. The feasibility of the approach is demonstrated on real measures on canine hearts, showing also the necessity to introduce anisotropy and probably a third spatial dimension in the model.

Large scale simulations of an anisotropic and heterogeneous cardiac model in three dimensional myocardial blocks are presented. The Monodomain tissue representation used includes orthotropic anisotropy, intramural fiber rotation and homogeneous or heterogeneous intramural Luo-Rudy I membrane ionic models. Simulations of the entire QT interval for epicardial and endocardial pacing show that the effect of intramural heterogeneity on the dispersion of the action potential duration is mostly discernible along the epi- endocardial direction, while in the orthogonal directions the dispersion patterns have the same qualitative features of the homogeneous model.

To investigate the quantitative abnormalities induced by prior myocardial infarction (MI) on the whole electrical cardiac cycle, body surface potential mapping was recorded in 144 patients with prior MI and 75 healthy controls. QRS onset, offset and T-wave end were automatically determined from the averaged signal. Time integrals were calculated for the QRS wave and the STT wave. In MI patient group the average QRS and STT integrals showed strong negative correlation on the body surface ( = – 0.901, < 0.001) in contrast to the positive correlation in the control group ( = 0.285, < 0.001). Sensitivity of an inverted QRS / STT integral relation to detect MI was 79%, as opposed to the sensitivity of the descriptive Minnesota code of 70%. Furthermore the degree of inversion correlated with left ventricular ejection fraction thus relating to the size of MI.

Numerical simulations of re-entrant waves in detailed ionic models reveal a phenomenon that is impossible in traditional simplified mathematical models of FitzHugh-Nagumo type: dissipation of the excitation front (DEF). We have analysed the structure of three selected ionic models, identified the small parameters that appear in non-standard ways, and developed an asymptotic approach based on those. Contrary to a common belief, the fast Na current inactivation gate is not necessarily much slower than the transmembrane voltage during the upstroke of the action potential. Interplay between and is responsible for the DEF. A new simplified model emerges from the asymptotic analysis and considers and as equally fast variables. This model reproduces DEF and admits analytical study. In particular, it yields conditions for the DEF. Predictions of the model agree with the results of direct numerical simulations of spiral wave break-up in a detailed model.

We describe numerical simulations of spiral waves dynamics in the computational model of human atrial tissue with the Courtemanche-Ramirez-Nattel local kinetics. The spiral wave was initiated by cross-field stimulation protocol, with and without preliminary “fatigue” by rapid stimulation of the model tissue for a long time. In all cases the spiral wave has finite lifetime and self-terminates. However the mechanism of self-termination appears to depend on the initiation procedure. Spiral waves in the “fresh” tissue typically terminate after a few rotations via dissipation of the excitation front along the whole of its length. The dynamics of spiral waves in “tired” tissue is characterized by breakups and hypermeander, which also typically leads to self-termination but only after a much longer interval of time. Some features of the observed behaviour can not be explained using existing simplified theories of dynamic instabilities and alternanses.