There is evidence that rotors could be drivers that maintain atrial fibrillation. Complex fractionated atrial electrograms have been located in rotor tip areas. However, the concept of electrogram fractionation, defined using time intervals, is still controversial as a tool for locating target sites for ablation. We hypothesize that the fractionation phenomenon is better described using non-linear dynamic measures, such as approximate entropy, and that this tool could be used for locating the rotor tip. The aim of this work has been to determine the relationship between approximate entropy and fractionated electrograms, and to develop a new tool for rotor mapping based on fractionation levels. Two episodes of chronic atrial fibrillation were simulated in a 3D human atrial model, in which rotors were observed. Dynamic approximate entropy maps were calculated using unipolar electrogram signals generated over the whole surface of the 3D atrial model. In addition, we optimized the approximate entropy calculation using two real multi-center databases of fractionated electrogram signals, labeled in 4 levels of fractionation. We found that the values of approximate entropy and the levels of fractionation are positively correlated. This allows the dynamic approximate entropy maps to localize the tips from stable and meandering rotors. Furthermore, we assessed the optimized approximate entropy using bipolar electrograms generated over a vicinity enclosing a rotor, achieving rotor detection. Our results suggest that high approximate entropy values are able to detect a high level of fractionation and to locate rotor tips in simulated atrial fibrillation episodes. We suggest that dynamic approximate entropy maps could become a tool for atrial fibrillation rotor mapping.

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A previous work has shown that DApEn maps successfully detected simulated rotor tips using a high spatial resolution. In this work, it was evinced that DApEn maps could be applied using a spatial resolution similar to that available in commercial catheters, by adding an interpolation stage. This is the first step to translate this tool into medical practice with a view to the detection of ablation targets.

In this work we developed a methodology to manufacture a new type of arterial model that could be used in experimental setting instead of excised arteries while developing new imaging modalities. CT-images of the descending aorta were used to create molds with patient specific morphology. A polyvinyl alcohol (PVA) solution with a reinforcing cotton mesh was used to generate the models. The mesh is circumferentially elastic while non-compliant longitudinally and is responsible for the non-linear anisotropic mechanical behavior of the models. Two models were fabricated following the same manufacturing procedure. Their circumferential and longitudinal mechanical properties were evaluated and compared to those of excised healthy pig aortas via tensile testing. A very good agreement was found for the circumferential direction, while the longitudinal direction showed to have a more marked anisotropic behavior compared to the excise arteries. An increase from 113 kPa at 2.5% strain, to 914 kPa at 40% strain was obtained for the models, while the arteries showed an increase from 172 kPa at 2.5% strain to 922 kPa at 38% strain. Furthermore, by plugging the models into a cardiovascular simulator their mechanical response in a more realistic setting was evaluated under static and dynamic pressure conditions by using shear wave elastography (SWE). Static and dynamic experiments showed an increase in the shear modulus as a function of pressure from 61 kPa to 263 kPa, between 20 mmHg and 150 mmHg for Model 1 (similar values within 10% were obtained for Model 2). These values are in good agreement with those reported in the literature for healthy human arteries. To our knowledge the models presented in this study are the first morphologically realistic phantoms that have demonstrated nonlinear and anisotropic elastic behaviors close to those of healthy arteries.

Complex fractionated atrial electrograms provide an important tool for identifying arrhythmogenic substrates that can be used to guide catheter ablation for atrial fibrillation (AF). However, fractionation is a phenomenon that remains unclear. This paper aims to evaluate the multifractal properties of electrograms in AF in order to propose a method based on multifractal analysis able to discriminate between different levels of fractionation. We introduce a new method, the h-fluctuation index (hFI), where h is the generalised Hurst exponent, to extract information from the shape of the multifractal spectrum. Two multifractal frameworks are evaluated: multifractal detrended fluctuation analysis and wavelet transform modulus maxima. hFI is exemplified through its application in synthetic signals, and it is evaluated in a database of electrograms labeled on the basis of four degrees of fractionation. We compare the performance of hFI with other indexes, and find that hFI outperforms them. The results of the study provide evidence that multifractal analysis is useful for studying fractionation phenomena in AF electrograms, and indicate that hFI can be proposed as a tool for grade fractionation associated with the detection of target sites for ablation in AF.