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Atrial fibrillation (AF) is the most common cardiac arrhythmia and catheter mapping has been proved to be an effective approach for detecting AF drivers to be targeted by ablation. Among drivers, the so-called rotors have gained the most attention: their identification and spatial location could help to understand which patient-specific mechanisms are acting, and thus to guide the ablation execution. Since rotor detection by multi-electrode catheters may be influenced by several structural parameters including inter-electrode spacing, catheter coverage, and endocardium-catheter distance, in this study we proposed a tool for testing the ability of different catheter shapes to detect rotors in different conditions. An approach based on the solution of the monodomain equations coupled with a modified Courtemanche ionic atrial model, that considers an electrical remodeling, was applied to simulate spiral wave dynamics on a 2D model for 7.75 s. The developed framework allowed the acquisition of unipolar signals at 2 KHz. Two high-density multipolar catheters were simulated (Advisor™ HD Grid and PentaRay®) and placed in a 2D region in which the simulated spiral wave persists longer. The configuration of the catheters was then modified by changing the number of electrodes, inter-electrodes distance, position, and atrial-wall distance for assessing how they would affect the rotor detection. In contact with the wall and at 1 mm distance from it, all the configurations detected the rotor correctly, irrespective of geometry, coverage, and inter-electrode distance. In the HDGrid-like geometry, the increase of the inter-electrode distance from 3 to 6 mm caused rotor detection failure at 2 mm distance from the LA wall. In the PentaRay-like configuration, regardless of inter-electrode distance, rotor detection failed at 3 mm endocardium-catheter distance. The asymmetry of this catheter resulted in rotation-dependent rotor detection. To conclude, the computational framework we developed is based on realistic catheter shapes designed with parameter configurations which resemble clinical settings. Results showed it is well suited to investigate how mapping catheter geometry and location affect AF driver detection, therefore it is a reliable tool to design and test new mapping catheters.

Resumen del trabajo presentado a la 20th International Conference on Solid Compounds of Transition Elements, celebrada del 11 al 15 de abril de 2016 en Zaragoza (España)., The magnetocaloric effect of a paramagnetic salt has been used long time ago as the physical mechanism for cooling below 1 K. For weak fields or relatively high temperatures the isothermal entropy change ΔST is proportional to the variation of the squared magnetic field. Therefore, a strong preexisting field increases ΔST for a given external field variation ΔB. In magnetic insulators of rare earth R and transition metal M atoms, the R-R exchange interaction is usually much weaker than the R-M exchange and this one is much weaker than the M-M exchange. At intermediate temperatures between the complete ordering of R\'s and M\'s, the R-M exchange acts as an additional constant external field. The effect was observed time ago in antiferromagnetic perovskites. Now, we study the ferromagnetic case of GdCrO4 zircon polymorph, where an exchange field about 7 T adds on to the external field to produce a large magnetocaloric effect |ΔST| > 20 J/kg·K for an increment ΔB from 0 to 9 T, over a wide temperature range 5 K < T < 35 K, reaching a maximum of 29 J/kg·K at 22 K. These values are very useful regarding to applications for liquefying hydrogen or natural gas as they, at least, double the cooling capacity of the materials (GGG, DGAG, ...) used in recent prototypes of magnetic refrigerators.