Medical & biological engineering & computing, Jan 3, 2017
The unstable temporal behavior of atrial electrical activity during persistent atrial fibrillatio... more The unstable temporal behavior of atrial electrical activity during persistent atrial fibrillation (persAF) might influence ablation target identification, which could explain the conflicting persAF ablation outcomes in previous studies. We sought to investigate the temporal behavior and consistency of atrial electrogram (AEG) fractionation using different segment lengths. Seven hundred ninety-seven bipolar AEGs were collected with three segment lengths (2.5, 5,and 8 s) from 18 patients undergoing persAF ablation. The AEGs with 8-s duration were divided into three 2.5-s consecutive segments. AEG fractionation classification was applied off-line to all cases following the CARTO criteria; 43% of the AEGs remained fractionated for the three consecutive AEG segments, while nearly 30% were temporally unstable. AEG classification within the consecutive segments had moderate correlation (segment 1 vs 2: Spearman's correlation ρ = 0.74, kappa score κ = 0.62; segment 1 vs 3: ρ = 0.726, κ...
Computer methods and programs in biomedicine, 2017
Optimal targets for persistent atrial fibrillation (persAF) ablation are still debated. Atrial re... more 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. 30s of 2048 non-contact AEGs (EnSite Array, St. Jude Medical) were collected and analyzed per patient. After QRST removal, the AEGs were divided into 4s windows with a 50% overlap. Fast Fourier transform was used for DF identification. HDF areas were identified as the maximum DF to 0.25Hz below that, and their centers of gravity (CGs) we...
Medical & biological engineering & computing, Jan 25, 2016
Ablation of persistent atrial fibrillation (persAF) targeting complex fractionated atrial electro... more Ablation of persistent atrial fibrillation (persAF) targeting complex fractionated atrial electrograms (CFAEs) detected by automated algorithms has produced conflicting outcomes in previous electrophysiological studies. We hypothesize that the differences in these algorithms could lead to discordant CFAE classifications by the available mapping systems, giving rise to potential disparities in CFAE-guided ablation. This study reports the results of a head-to-head comparison of CFAE detection performed by NavX (St. Jude Medical) versus CARTO (Biosense Webster) on the same bipolar electrogram data (797 electrograms) from 18 persAF patients. We propose revised thresholds for both primary and complementary indices to minimize the differences in CFAE classification performed by either system. Using the default thresholds [NavX: CFE-Mean ≤ 120 ms; CARTO: ICL ≥ 7], NavX classified 70 % of the electrograms as CFAEs, while CARTO detected 36 % (Cohen's kappa κ ≈ 0.3, P < 0.0001). Using ...
Background- Phase singularities (PS) and Dominant Frequency (DF) have been proposed to be markers... more Background- Phase singularities (PS) and Dominant Frequency (DF) have been proposed to be markers of abnormal atrial substrate and thereby potential targets for ablation in persistent atrial fibrillation (persAF). This study evaluated the spatiotemporal relationships among the PS and DF regions during persAF in humans. Methods- 9 patients with longstanding persAF (duration: 34 ± 25 months) undergoing left atrial (LA) ablation were recruited. A non contact array catheter (EnSite Array, St. Jude Medical) was used to collect virtual unipolar electrograms (VEGMs) simultaneously from 2048 nodes on the LA. After ventricular far field influence cancellation, high density 3D DF maps were obtained through the fast Fourier transform applied simultaneously to each individual VEGM. DF was defined within the range of 4Hz to 10Hz (4s time-window; 87.5% overlap; up to 30s per patient; total 409 windows). Highest DF (HDF) regions for each individual window were defined as any LA geometry nodes wher...
Atrial Electrograms Complexity as an Objective Measurement of Fractionation during Atrial Fibrill... more Atrial Electrograms Complexity as an Objective Measurement of Fractionation during Atrial Fibrillation TP Almeida, JL Salinet Jr, G Chu, JH Tuan, G André Ng, FS Schlindwein University of Leicester, University of Leicester Hospitals and Leicester NIHR Cardiovascular Biomedical Research Unit Leicester, United Kingdom Introduction: The quantification of CFAEs still relies on subjective methods. In this study we introduce a complexity measurement, NegEntropy (NegEn), as a clinical tool that may provide an objective measurement of fractionation in electrograms (EGMs) during AF. Methods: Five patients with persAF undergoing catheter ablation were enrolled. The ablation strategy was decided by operator preference. In each patient, EGMs were simultaneously recorded over 50s from one of five bipolar contact electrode through a decapolar catheter placed in the coronary sinus (CS 9-10). Signals underwent band-pass filtering (30Hz to 250Hz) and 50Hz notch filter. The analyses were performed for...
Introduction: Preclinical studies suggest that rotors may be responsible for the atrial fibrillat... more Introduction: Preclinical studies suggest that rotors may be responsible for the atrial fibrillation (AF) maintenance but evidence in human is not well defined. This study aims at the spectral property of electrical signals assessing spatio-temporal characteristics of the organization index (OI) of dominant frequency (DF) areas during persistent AF. Methods: Noncontact mapping in the left atrium (Ensite Array, SJM) was performed at baseline for 8 patients undergoing catheter ablation for persAF. DF and OI were tracked from simultaneous unipolar electrograms for 2048 sites over 20 s. DF is defined as the highest frequency peak (4-10 Hz) in 4s windows after QRST subtraction. OI is the ratio of area under the DF and harmonics to the total power spectrum. Sequential 3D DF and OI maps were obtained and ‘clouds’ of the highest DF were identified with its boundary defined as where DF drops 0.25Hz from maximum. Its centre of gravity (CG) was then found. Mean OI at the CG of the highest DF c...
Atrial fibrillation (AF) is the most common heart rhythm disturbance. Once AF is initiated, dynam... more Atrial fibrillation (AF) is the most common heart rhythm disturbance. Once AF is initiated, dynamic alterations of atrial electrophysiological properties occur invoking, in turn, AF inducibility. In patients for whom AF persists for long-term periods (persAF), identification of critical areas for successful ablation remains a challenge. Improving our understanding of the underlying AF behaviour is a key factor to contribute towards improving patient outcome. In this research, spectral analysis of simultaneous high density non-contact unipolar intracardiac atrial electrograms (AEGs) recorded from the left atrium (LA) of persAF patients (AF duration 34±25 months) was applied after a coherent strategy of cancellation of the ventricular influence on the AEGs. Three-dimensional dominant frequency (DF) maps with 2048 measurement points from AEGS were generated over consecutive frames of up to 1 minute (windows of 4s with 50% overlap). The results of this thesis showed a lack of DF spatiot...
The idea of a Web simulator for ultrasound imaging was born in respect to the necessity expressed... more The idea of a Web simulator for ultrasound imaging was born in respect to the necessity expressed by universities for a learning tool easily and freely accessible to all students. Ultrasound simulators do exist but their price range or their applicability often makes them unsuitable. Well known simulators like FIELD II and UltraSim for ultrasound field simulations are used by many researchers and are normally taken as reference because their completeness. Our paper presents a real-time ultrasound acoustical field simulation based on a web environment. The field can be generated by a wide variety of transducer arrays geometries and generic aperture elements and is extremely fast when compared to the existing software, and may be freely accessed by students and senior researchers on the ultrasound research area. Palavras-chave: ultra-som, simulação de campo acústico, transdutores. Introdução
Medical & biological engineering & computing, Jan 3, 2017
The unstable temporal behavior of atrial electrical activity during persistent atrial fibrillatio... more The unstable temporal behavior of atrial electrical activity during persistent atrial fibrillation (persAF) might influence ablation target identification, which could explain the conflicting persAF ablation outcomes in previous studies. We sought to investigate the temporal behavior and consistency of atrial electrogram (AEG) fractionation using different segment lengths. Seven hundred ninety-seven bipolar AEGs were collected with three segment lengths (2.5, 5,and 8 s) from 18 patients undergoing persAF ablation. The AEGs with 8-s duration were divided into three 2.5-s consecutive segments. AEG fractionation classification was applied off-line to all cases following the CARTO criteria; 43% of the AEGs remained fractionated for the three consecutive AEG segments, while nearly 30% were temporally unstable. AEG classification within the consecutive segments had moderate correlation (segment 1 vs 2: Spearman's correlation ρ = 0.74, kappa score κ = 0.62; segment 1 vs 3: ρ = 0.726, κ...
Computer methods and programs in biomedicine, 2017
Optimal targets for persistent atrial fibrillation (persAF) ablation are still debated. Atrial re... more 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. 30s of 2048 non-contact AEGs (EnSite Array, St. Jude Medical) were collected and analyzed per patient. After QRST removal, the AEGs were divided into 4s windows with a 50% overlap. Fast Fourier transform was used for DF identification. HDF areas were identified as the maximum DF to 0.25Hz below that, and their centers of gravity (CGs) we...
Medical & biological engineering & computing, Jan 25, 2016
Ablation of persistent atrial fibrillation (persAF) targeting complex fractionated atrial electro... more Ablation of persistent atrial fibrillation (persAF) targeting complex fractionated atrial electrograms (CFAEs) detected by automated algorithms has produced conflicting outcomes in previous electrophysiological studies. We hypothesize that the differences in these algorithms could lead to discordant CFAE classifications by the available mapping systems, giving rise to potential disparities in CFAE-guided ablation. This study reports the results of a head-to-head comparison of CFAE detection performed by NavX (St. Jude Medical) versus CARTO (Biosense Webster) on the same bipolar electrogram data (797 electrograms) from 18 persAF patients. We propose revised thresholds for both primary and complementary indices to minimize the differences in CFAE classification performed by either system. Using the default thresholds [NavX: CFE-Mean ≤ 120 ms; CARTO: ICL ≥ 7], NavX classified 70 % of the electrograms as CFAEs, while CARTO detected 36 % (Cohen's kappa κ ≈ 0.3, P < 0.0001). Using ...
Background- Phase singularities (PS) and Dominant Frequency (DF) have been proposed to be markers... more Background- Phase singularities (PS) and Dominant Frequency (DF) have been proposed to be markers of abnormal atrial substrate and thereby potential targets for ablation in persistent atrial fibrillation (persAF). This study evaluated the spatiotemporal relationships among the PS and DF regions during persAF in humans. Methods- 9 patients with longstanding persAF (duration: 34 ± 25 months) undergoing left atrial (LA) ablation were recruited. A non contact array catheter (EnSite Array, St. Jude Medical) was used to collect virtual unipolar electrograms (VEGMs) simultaneously from 2048 nodes on the LA. After ventricular far field influence cancellation, high density 3D DF maps were obtained through the fast Fourier transform applied simultaneously to each individual VEGM. DF was defined within the range of 4Hz to 10Hz (4s time-window; 87.5% overlap; up to 30s per patient; total 409 windows). Highest DF (HDF) regions for each individual window were defined as any LA geometry nodes wher...
Atrial Electrograms Complexity as an Objective Measurement of Fractionation during Atrial Fibrill... more Atrial Electrograms Complexity as an Objective Measurement of Fractionation during Atrial Fibrillation TP Almeida, JL Salinet Jr, G Chu, JH Tuan, G André Ng, FS Schlindwein University of Leicester, University of Leicester Hospitals and Leicester NIHR Cardiovascular Biomedical Research Unit Leicester, United Kingdom Introduction: The quantification of CFAEs still relies on subjective methods. In this study we introduce a complexity measurement, NegEntropy (NegEn), as a clinical tool that may provide an objective measurement of fractionation in electrograms (EGMs) during AF. Methods: Five patients with persAF undergoing catheter ablation were enrolled. The ablation strategy was decided by operator preference. In each patient, EGMs were simultaneously recorded over 50s from one of five bipolar contact electrode through a decapolar catheter placed in the coronary sinus (CS 9-10). Signals underwent band-pass filtering (30Hz to 250Hz) and 50Hz notch filter. The analyses were performed for...
Introduction: Preclinical studies suggest that rotors may be responsible for the atrial fibrillat... more Introduction: Preclinical studies suggest that rotors may be responsible for the atrial fibrillation (AF) maintenance but evidence in human is not well defined. This study aims at the spectral property of electrical signals assessing spatio-temporal characteristics of the organization index (OI) of dominant frequency (DF) areas during persistent AF. Methods: Noncontact mapping in the left atrium (Ensite Array, SJM) was performed at baseline for 8 patients undergoing catheter ablation for persAF. DF and OI were tracked from simultaneous unipolar electrograms for 2048 sites over 20 s. DF is defined as the highest frequency peak (4-10 Hz) in 4s windows after QRST subtraction. OI is the ratio of area under the DF and harmonics to the total power spectrum. Sequential 3D DF and OI maps were obtained and ‘clouds’ of the highest DF were identified with its boundary defined as where DF drops 0.25Hz from maximum. Its centre of gravity (CG) was then found. Mean OI at the CG of the highest DF c...
Atrial fibrillation (AF) is the most common heart rhythm disturbance. Once AF is initiated, dynam... more Atrial fibrillation (AF) is the most common heart rhythm disturbance. Once AF is initiated, dynamic alterations of atrial electrophysiological properties occur invoking, in turn, AF inducibility. In patients for whom AF persists for long-term periods (persAF), identification of critical areas for successful ablation remains a challenge. Improving our understanding of the underlying AF behaviour is a key factor to contribute towards improving patient outcome. In this research, spectral analysis of simultaneous high density non-contact unipolar intracardiac atrial electrograms (AEGs) recorded from the left atrium (LA) of persAF patients (AF duration 34±25 months) was applied after a coherent strategy of cancellation of the ventricular influence on the AEGs. Three-dimensional dominant frequency (DF) maps with 2048 measurement points from AEGS were generated over consecutive frames of up to 1 minute (windows of 4s with 50% overlap). The results of this thesis showed a lack of DF spatiot...
The idea of a Web simulator for ultrasound imaging was born in respect to the necessity expressed... more The idea of a Web simulator for ultrasound imaging was born in respect to the necessity expressed by universities for a learning tool easily and freely accessible to all students. Ultrasound simulators do exist but their price range or their applicability often makes them unsuitable. Well known simulators like FIELD II and UltraSim for ultrasound field simulations are used by many researchers and are normally taken as reference because their completeness. Our paper presents a real-time ultrasound acoustical field simulation based on a web environment. The field can be generated by a wide variety of transducer arrays geometries and generic aperture elements and is extremely fast when compared to the existing software, and may be freely accessed by students and senior researchers on the ultrasound research area. Palavras-chave: ultra-som, simulação de campo acústico, transdutores. Introdução
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