Functional mapping to reveal slow conduction and substrate progression in atrial fibrillation

AIMS

The aim of our study was to analyse the response to short-coupled atrial extrastimuli to identify areas of hidden slow conduction (HSC) and their relationship with the atrial fibrillation (AF) phenotype.

METHODS AND RESULTS

Twenty consecutive patients with paroxysmal AF and persistent AF (10:10) underwent the first pulmonary vein isolation procedure. Triple short-coupled extrastimuli were delivered in sinus rhythm (SR), and the evoked response was analysed: sites exhibiting double or highly fragmented electrograms (EGM) were defined as positive for HSC (HSC+). The delta of the duration of the bipolar EGM was analysed, and bipolar EGM duration maps were built. High-density maps were acquired using a multipolar catheter during AF, SR, and paced rhythm. Spatial co-localization of HSC+ and complex fractionated atrial EGMs (CFAE) during AF was evaluated. Persistent AF showed a higher number and percentage of HSC+ than paroxysmal AF (13.9% vs. 3.3%, P < 0.001). The delta of EGM duration was 53 ± 22 ms for HSC+ compared with 13 ± 11 (10) ms in sites with negative HSC (HSC-) (P < 0.001). The number and density of HSC+ were lower than CFAE during AF (19 vs. 56 per map, P < 0.001). The reproducibility and distribution of HSC+ in repeated maps were superior to CFAE (P = 0.19 vs. P < 0.001). Sites with negative and positive responses showed a similar bipolar voltage in the preceding sinus beat (1.65 ± 1.34 and 1.48 ± 1.47 mV, P = 0.12).

CONCLUSION

Functional mapping identifies more discrete and reproducible abnormal substrates than mapping during AF. The HSC+ sites in response to triple extrastimuli are more frequent in persistent AF than in paroxysmal AF.

Dynamics of Pd Subsurface Hydride Formation and Their Impact on the Selectivity Control for Selective Butadiene Hydrogenation Reaction

Structure-sensitive catalyzed reactions can be influenced by a number of parameters. So far, it has been established that the formation of Pd-C species is responsible for the behavior of Pd nanoparticles employed as catalysts in a butadiene partial hydrogenation reaction. In this study, we introduce some experimental evidence indicating that subsurface Pd hydride species are governing the reactivity of this reaction. In particular, we detect that the extent of formation/decomposition of PdHx species is very sensitive to the Pd nanoparticle aggregate dimensions, and this finally controls the selectivity in this process. The main and direct methodology applied to determine this reaction mechanism step is time-resolved high-energy X-ray diffraction (HEXRD).

Interactions in the Thallium(I) Heptanoate and Heptanoic Acid System: Association, Aggregation, and Phase Behavior

The phase, association, and aggregation behavior of the binary system [TlO2C(CH2)5CH3 + HO2C(CH2)5CH3] have been investigated through temperature and enthalpy vs composition diagrams by determination of the thermal behavior of the pure components and 30 mixtures over an interval of nearly 300 K, and by differential scanning calorimetry and polarized microscopy. Total miscibility was observed in liquid and liquid crystalline phases but essentially total immiscibility among crystalline phases. The phase behavior exhibits: (1) Formation of two intermediate compounds which dissociate in the solid state at low temperature; (2) A eutectic reaction at salt molar fraction x = 0.08 about 3 K below the acid melting point; (3) Unimolecular salt:acid association by very strong hydrogen bonding, which undergoes a crystal/crystal transition prior to incongruent melting at 295.5 K, occurring by a highly energetic peritectic reaction in which the compound evolves more than the sum of the total transition enthalpies of both components; (4) Lyotropic mesophase formation at 390.0 K over the x >/= 0.66 composition range by aggregation of a solid and a liquid phase to yield, on heating, a continuous series of liquid crystalline solutions with mixed-lamellar structure and interlamellar spacings around 20 A as determined by powder X-ray diffractometry, their texture being focal conic, consistent with the neat thermotropic mesophase of the pure salt. A tridimensional phase diagram is presented. All these main reactions have been fully characterized by their nature, stoichiometry, and relevant thermodynamic data.