High-density mapping reveals short-term reversibility of atrial ablation lesions

Cardiac arrhythmias such as atrial fibrillation occur frequently in industrialized countries. Radiofrequency ablation (RFA) is a standard treatment if drug therapy fails. This minimally invasive surgery aims at stabilizing the heart rhythm on a permanent basis. However, the procedure commonly needs to be repeated because of the high recurrence rate of arrhythmias. Non-transmural lesions as well as gaps within linear lesions are among the main problems during the RFA. The assessment of lesion formation is not adequate in state of the art procedures. Therefore, the aim of this study is to investigate the short-term reversibility of lesions using human electrograms recorded by a high-density mapping system during an electrophysiological study (EPS). A predefined measurement protocol was executed during the EPS in order to create three ablation points in the left atrium. Subsequently, after preprocessing the recorded signals, electrogram (EGM) paths were formed along the endocardial surface of the atrium. By analyzing changes of peak to peak amplitudes of unipolar EGMs before and after ablation, it was possible to distinguish lesion area and healthy myocardium. The peak to peak amplitudes of the EGMs decreased by 40-61% after 30 seconds of ablation. Furthermore, we analyzed the morphological changes of EGMs surrounding the lesion. High-density mapping data showed that not only the tissue, which had direct contact with the catheter tip during the RFA, but also the surrounding tissue was affected. This was demonstrated by low peak to peak amplitudes in large areas with a width of 14 mm around the center of the ablation lesion. After right pulmonary vein isolation, high-density mapping was repeated on the previous lesions. The outer region of RFA-treated tissue appears to recover as opposed to the central core of the ablation point. This observation suggests that the meaningfulness of an immediate remap after ablation during an EPS may lead the physician to false conclusions

A computational framework to benchmark basket catheter guided ablation in atrial fibrillation

Catheter ablation is a curative therapeutic approach for atrial fibrillation (AF). Ablation of rotational sources based on basket catheter measurements has been proposed as a promising approach in patients with persistent AF to complement pulmonary vein isolation. However, clinically reported success rates are equivocal calling for a mechanistic investigation under controlled conditions. We present a computational framework to benchmark ablation strategies considering the whole cycle from excitation propagation to electrogram acquisition and processing to virtual therapy. Fibrillation was induced in a patient-specific 3D volumetric model of the left atrium, which was homogeneously remodeled to sustain reentry. The resulting extracellular potential field was sampled using models of grid catheters as well as realistically deformed basket catheters considering the specific atrial anatomy. The virtual electrograms were processed to compute phase singularity density maps to target rotor tips with up to three circular ablations. Stable rotors were successfully induced in different regions of the homogeneously remodeled atrium showing that rotors are not constrained to unique anatomical structures or locations. Density maps of rotor tip trajectories correctly identified and located the rotors (deviation < 10 mm) based on catheter recordings only for sufficient resolution (inter-electrode distance ≤3 mm) and proximity to the wall (≤10 mm). Targeting rotor sites with ablation did not stop reentries in the homogeneously remodeled atria independent from lesion size (1–7 mm radius), from linearly connecting lesions with anatomical obstacles, and from the number of rotors targeted sequentially (≤3). Our results show that phase maps derived from intracardiac electrograms can be a powerful tool to map atrial activation patterns, yet they can also be misleading due to inaccurate localization of the rotor tip depending on electrode resolution and distance to the wall. This should be considered to avoid ablating regions that are in fact free of rotor sources of AF. In our experience, ablation of rotor sites was not successful to stop fibrillation. Our comprehensive simulation framework provides the means to holistically benchmark ablation strategies in silico under consideration of all steps involved in electrogram-based therapy and, in future, could be used to study more heterogeneously remodeled disease states as well

An interactive platform to guide catheter ablation in human persistent atrial fibrillation using dominant frequency, organization and phase mapping

Background and Objective: Optimal targets for persistent atrial fibrillation (persAF) ablation are still debated. Atrial regions hosting high dominant frequency (HDF) are believed to participate in the initiation and maintenance of persAF and hence are potential targets for ablation, while rotor ablation has shown promising initial results. Currently, no commercially available system offers the capability to automatically identify both these phenomena. This paper describes an integrated 3D software platform combining the mapping of both frequency spectrum and phase from atrial electrograms (AEGs) to help guide persAF ablation in clinical cardiac electrophysiological studies. Methods: 30 s of 2048 non-contact AEGs (EnSite Array, St. Jude Medical) were collected and analyzed per patient. After QRST removal, the AEGs were divided into 4 s windows with a 50% overlap. Fast Fourier transform was used for DF identification. HDF areas were identified as the maximum DF to 0.25 Hz below that, and their centers of gravity (CGs) were used to track their spatiotemporal movement. Spectral organization measurements were estimated. Hilbert transform was used to calculate instantaneous phase. Results: The system was successfully used to guide catheter ablation for 10 persAF patients. The mean processing time was 10.4 ± 1.5 min, which is adequate comparing to the normal electrophysiological (EP) procedure time (120∼180 min). Conclusions: A customized software platform capable of measuring different forms of spatiotemporal AEG analysis was implemented and used in clinical environment to guide persAF ablation. The modular nature of the platform will help electrophysiological studies in understanding of the underlying AF mechanisms

Characterization of state and properties of Al-based MMC-components by ultrasonic techniques

In a comprehensive experimental study ultrasonic techniques are optimized and used to characterize the state abd to evaluate the properties of Al-based Al2O3 fiber reinforced MMC-parts. It has been the objective to concentrate on those ultrasonic techniques which can be applied on real parts in order to demnonstrate the ultrasonic potential in a quality assurance concept for MMC-mass products, like automotive pistons and con-rods. It is found that the ultrasonic backscattering to visuakize the distribution of the reinforcing phase in surface layers as well as in bulk of components is very informative although the results are of qualitative nature only. The evaluation of quantitative values of the local concentration on reinforcements as well as the Young's and shear moduli are possible by measuring the ultrasonic velocities or time-of-flight. Information on the elastic anisotropy resp. isotropy is gained from measurements using linear polarized shear waves. The pulse distortion of a l ongitudinal wave is found to be suitable to detect misalignments of continous fibers. Compared with the established techniques to characterize the local distribution of reinforcement, to evaluate elastic constants and to inspect the long fiber alignments, the ultrasonic techniques have the advantage help for the optimization of manufacturing parameters

Experimental Observations of Active Invariance Striations in a Tank Environment

The waveguide invariant in shallow water environments has been widely studied in the context of passive sonar. The invariant provides a relationship between the frequency content of a moving broadband source and the distance to the receiver, and this relationship is not strongly affected by small perturbations in environment parameters such as sound speed or bottom features. Recent experiments in shallow water suggest that a similar range-frequency structure manifested as striations in the spectrogram exists for active sonar, and this property has the potential to enhance the performance of target tracking algorithms. Nevertheless, field experiments with active sonar have not been conclusive on how the invariant is affected by the scattering kernel of the target and the sonar configuration monostatic vs bistatic . The experimental work presented in this paper addresses those issues by showing the active invariance for known scatterers under controlled conditions of bathymetry, sound speed profile and high SNR. Quantification of the results is achieved by introducing an automatic image processing approach inspired on the Hough transform for extraction of the invariant from spectrograms. Normal mode simulations are shown to be in agreement with the experimental results

Ultrasonic characterization of burrs in aluminium pressure castings

There are always burrs in hollow castings. They are caused by the joining of the different streams of molden alloy and they can be areas of poor mechanical properties. Up to now, burrs are checked destructively using samples cut from the head and tail of the pressure casted product. It is found that the ultrasonic backscattering is suitable to visualize the fine grained microstructure of the seam area of the burr and the surrounding coarse grained area with higher content of impurities. The direction dependency of ultrasonic time-of-flight is used to characterize the crystallographic texture in the burr region. The texture is found to be different in the burr and in the adjacent areas and this difference changes along the length of the pressed part. The combination of ultrasonic backscattering and time-of-flight measurements is seen as a very promising nondestructive approach to characterize the burr and to determine the length of the pressure casted product with well developed mechani cal propertie

Ultrasonic characterization of state and properties of Al-based metal matrix composites

In a comprehensive experimental study ultrasonic techniques are optimized and used to characterize the state and to evaluate the properties of Al-based Al2O3 fiber reinforced MMC-parts. It has been the objective to concentrate on those ultrasonic techniques which can be applied on real parts in order to demonstrate the ultrasonic potential in a quality assurance concept for MMC-mass products, like automotive pistons and con-rods. It is found that the ultrasonic backscattering to visualize the distribution of the reinforcing phase in surface layers as well as in the bulk of components is very informative although the results are of qualitative nature only. The evaluation of quantitative values of the local concentration on reinforcements as well as of the Young's and shear moduli are possible by measuring the ultrasonic velocities or time-of-flight. Information on the elastic anisotropy resp. isotropy is gained from measurements using linear polarized shear waves. The pulse distortion o f a longitudinal wave is found to be suitable to detect misalignments of continous fibers

Laser Ultrasonics in Industry

The generation of ultrasound by pulsed lasers and its interferometric detection, shortly called laser ultrasonics, is a well established ndt method in research laboratories. However, until now the transfer into industrial application could be achieved only in a few cases. This paper describes a laser ultrasonic device for in-line wall thickness measurement of hot seamless tubes. It discusses the development work and presents the results during trials in the shop. The general problems related with the industrial application of laser ultrasonics are discussed

High-density Mapping Reveals Short-term Reversibility of Atrial Ablation Lesions

Cardiac arrhythmias such as atrial fibrillation occur frequently in industrialized countries. Radiofrequency ablation (RFA) is a standard treatment if drug therapy fails. This minimally invasive surgery aims at stabilizing the heart rhythm on a permanent basis. However, the procedure commonly needs to be repeated because of the high recurrence rate of arrhythmias. Non-transmural lesions as well as gaps within linear lesions are among the main problems during the RFA. The assessment of lesion formation is not adequate in state of the art procedures. Therefore, the aim of this study is to investigate the short-term reversibility of lesions using human electrograms recorded by a high-density mapping system during an electrophysiological study (EPS). A predefined measurement protocol was executed during the EPS in order to create three ablation points in the left atrium. Subsequently, after preprocessing the recorded signals, electrogram (EGM) paths were formed along the endocardial surface of the atrium. By analyzing changes of peak to peak amplitudes of unipolar EGMs before and after ablation, it was possible to distinguish lesion area and healthy myocardium. The peak to peak amplitudes of the EGMs decreased by 40-61% after 30 seconds of ablation. Furthermore, we analyzed the morphological changes of EGMs surrounding the lesion. High-density mapping data showed that not only the tissue, which had direct contact with the catheter tip during the RFA, but also the surrounding tissue was affected. This was demonstrated by low peak to peak amplitudes in large areas with a width of 14 mm around the center of the ablation lesion. After right pulmonary vein isolation, high-density mapping was repeated on the previous lesions. The outer region of RFA-treated tissue appears to recover as opposed to the central core of the ablation point. This observation suggests that the meaningfulness of an immediate remap after ablation during an EPS may lead the physician to false conclusions