Dynamic behavior of rotors during human persistent atrial fibrillation as observed using non-contact mapping

Rotors have been related to atrial fibrillation (AF) maintenance. We analyzed the behavior of rotors in persistent AF (persAF) utilizing a novel non-contact methodology and compared this to real time dominant frequency (DF) analysis. 2048 noncontact virtual unipolar atrial electrograms (VEGMs) were collected simultaneously (EnSite Array, St. Jude Medical) from 10 persAF patients (duration: 34 ± 25 months) undergoing left atrial (LA) ablation. After QRST-removal, FFT was used to identify the global DF of the LA (range 4-10 Hz; 1 s time-window; 50 % overlap; highest DF (HDF) (DF -0.25 Hz); up to 20 s/patient). The organization index (OI) was measured and phase was found via Hilbert-transform. Phase singularities (PSs) were tracked and were categorized according to their lifespan into short (lifespan 100 ms). A total of 4578 PSs were tracked. 5.05 % (IQR: 2.75 ~ 30.25 %) of the tracked PSs were long-lived and were observed in 11 % (IQR: 2.75 ~ 17.5 %) of the windows. The windows with rotors showed significantly higher HDF (mean ± SD, 8.0 ± 0.43 Hz vs 7.71 ± 0.50 Hz, p<; 0.0001) and lower OI (0.76 ± 0.04 vs 0.79 ± 0.03, p<; 0.0001) when compared with the short-lived PSs windows. During persAF, the LA showed distinct behaviors as characterized by rotors. Often, no rotors were observed during sustained AF and, when present, the rotors continually switched between organized and disorganized behaviors. Long-lived rotors correlated with higher atrial rates. Our results suggest that rotors are not the sole perpetuating mechanism in persAF

Spatiotemporal behaviour of high dominant frequency during persistent atrial fibrillation

Atrial electrograms (EGMs) with high dominant frequency (DF) are believed to represent atrial substrates with periodic activation responsible for the maintenance of persistent atrial fibrillation (persAF). This study aimed to assess the DF spatiotemporal behavior using high density noncontact mapping in persAF. For 8 patients undergoing left atrial (LA) persAF ablation, 2048 noncontact virtual unipolar EGMs were simultaneously collected and after the removal of ventricular far-field activity, Fourier based spectral analysis was used to identify DF on each EGM. Atrial areas with the highest DF (HDF, DF ± 0.25 Hz) were delimited in each frame for all EGMs, creating HDF `clouds'. Cumulative HDF clouds found at each frame were counted in the 3-D LA representation. To further assess the temporal stability of the cloud, the number of EGMs not hosting any HDF was determined for each window over time. The results show the number of occurrences of HDF clouds in the LA. The temporal behavior was analyzed by counting the number of positions on the 3-D representation of the LA not visited by HDF along time. Our results show HDF in persAF is not temporally stable and spatial distribution throughout the atria suggests the existence of driver regions with very rapid and regular activity maintaining AF. Therefore mapping the cumulative HDF might be an interesting strategy for ablation

Systematic differences of non-invasive dominant frequency estimation compared to invasive dominant frequency estimation in atrial fibrillation

Non-invasive analysis of atrial fibrillation (AF) using body surface mapping (BSM) has gained significant interest, with attempts at interpreting atrial spectro-temporal parameters from body surface signals. As these body surface signals could be affected by properties of the torso volume conductor, this interpretation is not always straightforward. This paper highlights the volume conductor effects and influences of the algorithm parameters for identifying the dominant frequency (DF) from cardiac signals collected simultaneously on the torso and atrial surface. Bi-atrial virtual electrograms (VEGMs) and BSMs were recorded simultaneously for 5 minutes from 10 patients undergoing ablation for persistent AF. Frequency analysis was performed on 4 s segments. DF was defined as the frequency with highest power between 4-10 Hz with and without applying organization index (OI) thresholds. The volume conductor effect was assessed by analyzing the highest DF (HDF) difference of each VEGM HDF against its BSM counterpart. Significant differences in HDF values between intra-cardiac and torso signals could be observed, independent of OI threshold. This difference increases with increasing endocardial HDF (BSM-VEGM median difference from -0.13 Hz for VEGM HDF at 6.25±0.25 Hz to -4.24 Hz at 9.75±0.25 Hz), thereby confirming the theory of the volume conductor effect in real-life situations. Applying an OI threshold strongly affected the BSM HDF area size and location and atrial HDF area location. These results suggest that volume conductor and measurement algorithm effects must be considered for appropriate clinical interpretation

Combination of frequency and phase to characterise the spatiotemporal behaviour of cardiac waves during persistent atrial fibrillation in humans

The spatial distribution of atrial dominant frequency (DF), phase and phase singularity points (PSs) may reflect mechanisms driving and maintaining persistent atrial fibrillation (persAF). Here we developed an automatic algorithm that combines the three parameters and depicts the complex spatiotemporal patterns of fibrillation. For 9 patients undergoing left atrial persAF ablation, noncontact virtual unipolar electrograms (VEGMs) were simultaneously collected using a balloon array (Ensite Velocity, St. Jude Medical). After removal of the far field ventricular influence, we used fast Fourier transform and Hilbert transform to detect the DF and phase of each VEGM PSs are detected by finding the curl of the spatial phase gradient. DF along with phase and PSs were plotted for each window and the behaviour of the trajectory of HDF 'clouds' was observed. Our results indicate that spatial and temporal organization correlating HDF and phase exists during persAF. Generating and analysing the maps of HDF and phase may prove helpful in understanding the spatial and temporal activation dynamics during persAF

Investigation on recurrent high dominant frequency spatiotemporal patterns during persistent atrial fibrillation

Atrial regions hosting dominant frequency (DF) may represent potential drivers of persistent atrial fibrillation (persAF). Previous work showed that DF can exhibit cyclic behaviour. This study aims to better understand the spatiotemporal behaviours of persAF over longer time periods. 10 patients undergoing persAF ablation targeted at DF were included. Left atrial (LA) non-contact virtual electrograms (VEGMs, Ensite Array, St Jude Medical) were collected for up to 5 min pre-/post- ablation. DF was identified as the peak from 4-10 Hz, in 4 s windows (50 % overlap). High DF (HDF) map was created and automated pattern recognition algorithm was applied to look for recurring HDF spatial patterns within each patient. Recurring HDF patterns were found in all patients. Patients who changed rhythm to atrial flutter after ablation demonstrated single dominant pattern (DP) among the recorded time period, which might consistent with the higher level of regularity during flutter. Ablation regularized AF as demonstrated by increased DP recurrence after ablation. The time interval (median [IQR]) of DP recurrence for the patients still in atrial fibrillation(AF) after ablation (7 patients) decreased from 21.1 s [11.8~49.7 s] to 15.7s [6.5~18.2 s]. The proposed method quantifies the spatiotemporal regularity of HDF DPs over long time periods and may offer a more comprehensive dynamic overview of persAF behaviour and the impact of ablation

Automatic extraction of recurrent patterns of high dominant frequency mapping during human persistent atrial fibrillation

Purpose: Identifying targets for catheter ablation remains challenging in persistent atrial fibrillation (persAF). The dominant frequency (DF) of atrial electrograms during atrial fibrillation (AF) is believed to primarily reflect local activation. Highest DF (HDF) might be responsible for the initiation and perpetuation of persAF. However, the spatiotemporal behaviour of DF remains not fully understood. Some DFs during persAF were shown to lack spatiotemporal stability, while others exhibit recurrent behaviour. We sought to develop a tool to automatically detect recurrent DF patterns in persAF patients. Methods: Non-contact mapping of the left atrium (LA) was performed in 10 patients undergoing persAF HDF ablation. 2048 virtual electrograms (vEGMs, EnSite Array, Abbott Laboratories, USA) were collected for up to 5 min before and after ablation. Frequency spectrum was estimated using fast Fourier transform and DF was identified as the peak between 4-10 Hz and organization index (OI) was calculated. The HDF maps were identified per 4-second window and an automated pattern recognition algorithm was used to find recurring HDF spatial patterns. Dominant patterns (DPs) were defined as the HDF pattern with the highest recurrence. Results: DPs were found in all patients. Patients in atrial flutter after ablation had a single DP over the recorded time period. The time interval (median [IQR]) of DP recurrence for the patients in AF after ablation (7 patients) decreased from 21.1 s [11.8 49.7s] to 15.7 s [6.5 18.2 s]. The DF inside the DPs presented lower temporal standard deviation (0.18±0.06 Hz vs. 0.29±0.12 Hz, p<0.05) and higher OI (0.35±0.03 vs. 0.31±0.04, p<0.05). The atrial regions with the highest proportion of HDF region were the septum and the left upper pulmonary vein. Conclusion: Multiple recurrent spatiotemporal HDF patterns exist during persAF. The proposed method can identify and quantify the spatiotemporal repetition of the HDFs, where the high recurrences of DP may suggest a more organised rhythm. DPs presented a more consistent DF and higher organisation compared with non-DPs, suggesting that DF with higher OI might be more likely to recur. Recurring patterns offer a more comprehensive dynamic insight of persAF behaviour, and ablation targeting such regions may be beneficial

Carbon Nanotubes in Tissue Engineering

For their peculiar features carbon nanotubes (CNTs) are emerging in many areas of nanotechnology applications. CNT-based technology has been increasingly proposed for biomedical applications, to develop biomolecule nanocarriers, bionanosensors and smart material for tissue engineering purposes. In the following chapter this latter application will be explored, describing why CNTs can be considered an ideal material able to support and boost the growth and the proliferation of many kind of tissues

Fostering coastal resilience to climate change vulnerability in Bangladesh, Brazil, Cameroon and Uruguay: a cross-country comparison

© 2017, Springer Science+Business Media B.V. This paper describes a comparative study of four different cases on vulnerability, hazards and adaptive capacity to climate threats in coastal areas and communities in four developing countries: Bangladesh, Brazil, Cameroon and Uruguay. Coastal areas are vulnerable to sea-level rise (SLR), storm surges and flooding due to their (i) exposure, (ii) concentration of settlements, many of which occupied by less advantaged groups and (iii) the concentration of assets and services seen in these areas. The objective of the paper is twofold: (i) to evaluate current evidence of coastal vulnerability and adaptive capacity and (ii) to compare adaptation strategies being implemented in a sample of developing countries, focusing on successful ones. The followed approach for the case evaluation is based on (i) documenting observed threats and damages, (ii) using indicators of physical and socioeconomic vulnerability and adaptive capacity status and (iii) selecting examples of successful responses. Major conclusions based on cross-case comparison are (a) the studied countries show different vulnerability, adaptive capacity and implementation of responses, (b) innovative community-based (CBA) and ecosystem-based adaptation (EbA) and (c) early warning systems are key approaches and tools to foster climate resilience. A recommendation to foster the resilience of coastal communities and services is that efforts in innovative adaptation strategies to sea-level rise should be intensified and integrated with climate risk management within the national adaption plans (NAPAs) in order to reduce the impacts of hazards