| 1. |
- Bachi, Lorenzo, et al.
(författare)
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ECG Modeling for Simulation of Arrhythmias in Time-Varying Conditions
- 2023
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Ingår i: IEEE Transactions on Biomedical Engineering. - 0018-9294. ; 70:12, s. 3449-3460
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Tidskriftsartikel (refereegranskat)abstract
- The present paper proposes an ECG simulator that advances modeling of arrhythmias and noise by introducing time-varying signal characteristics. The simulator is built around a discrete-time Markov chain model for simulating atrial and ventricular arrhythmias of particular relevance when analyzing atrial fibrillation (AF). Each state is associated with statistical information on episode duration and heartbeat characteristics. Statistical, time-varying modeling of muscle noise, motion artifacts, and the influence of respiration is introduced to increase the complexity of simulated ECGs, making the simulator well suited for data augmentation in machine learning. Modeling of how the PQ and QT intervals depend on heart rate is also introduced. The realism of simulated ECGs is assessed by three experienced doctors, showing that simulated ECGs are difficult to distinguish from real ECGs. Simulator usefulness is illustrated in terms of AF detection performance when either simulated or real ECGs are used to train a neural network for signal quality control. The results show that both types of training lead to similar performance.
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| 2. |
- Butkuviene, Monika, et al.
(författare)
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Atrial Fibrillation Episode Patterns and Their Influence on Detection Performance
- 2021
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Ingår i: 2021 Computing in Cardiology, CinC 2021. - 2325-887X .- 2325-8861. - 9781665479165 ; 2021-September
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Konferensbidrag (refereegranskat)abstract
- Existing studies offer little insight on how atrial fibrillation (AF) detection performance is influenced by the properties of AF episode patterns. The aim of this study is to investigate the influence of AF burden and median AF episode length on detection performance. For this purpose, three types of AF detectors, using either information on rhythm, rhythm and morphology, or ECG segments, were investigated on 1-h simulated ECGs. Comparing AF burdens of 20% and 80% for a median episode length of 167 beats, the sensitivity of the rhythm- and morphology-based detector increases only slightly whereas the specificity drops from 99.5% to 93.3%. The corresponding figures of specificity are 99.0% and 90.6% for the rhythm-based detector; 88.1% and 70.7% for the segment-based detector. The influence of AF burden on specificity becomes even more pronounced for AF patterns with brief episodes (median episode length set to 30 beats). Therefore, patterns with briefepisodes and high AF burden imply higher demands on detection performance. Future research should focus on how well episode patterns are captured.
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| 3. |
- Butkuviene, Monika, et al.
(författare)
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Characterization of Atrial Fibrillation Episode Patterns : A Comparative Study
- 2024
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Ingår i: IEEE Transactions on Biomedical Engineering. - 0018-9294. ; 71:1, s. 106-113
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The episode patterns of paroxysmal atrial fibrillation (AF) may carry important information on disease progression and complication risk. However, existing studies offer very little insight into to what extent a quantitative characterization of AF patterns can be trusted given the errors in AF detection and various types of shutdown, i.e., poor signal quality and non-wear. This study explores the performance of AF pattern characterizing parameters in the presence of such errors. Methods: To evaluate the performance of the parameters AF aggregation and AF density, both previously proposed to characterize AF patterns, the two measures mean normalized difference and the intraclass correlation coefficient are used to describe agreement and reliability, respectively. The parameters are studied on two PhysioNet databases with annotated AF episodes, also accounting for shutdowns due to poor signal quality. Results: The agreement is similar for both parameters when computed for detector-based and annotated patterns, which is 0.80 for AF aggregation and 0.85 for AF density. On the other hand, the reliability differs substantially, with 0.96 for AF aggregation but only 0.29 for AF density. This finding suggests that AF aggregation is considerably less sensitive to detection errors. The results from comparing three strategies to handle shutdowns vary considerably, with the strategy that disregards the shutdown from the annotated pattern showing the best agreement and reliability. Conclusions: Due to its better robustness to detection errors, AF aggregation should be preferred. To further improve performance, future research should put more emphasis on AF pattern characterization.
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| 4. |
- Butkuviene, Monika, et al.
(författare)
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Considerations on Performance Evaluation of Atrial Fibrillation Detectors
- 2021
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Ingår i: IEEE Transactions on Biomedical Engineering. - 0018-9294. ; 68:11, s. 3250-3260
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Tidskriftsartikel (refereegranskat)abstract
- Objective: A large number of atrial fibrillation (AF) detectors have been published in recent years, signifying that the comparison of detector performance plays a central role, though not always consistent. The aim of this study is to shed needed light on aspects crucial to the evaluation of detection performance. Methods: Three types of AF detector, using either information on rhythm, rhythm and morphology, or segments of ECG samples, are implemented and studied on both real and simulated ECG signals. The properties of different performance measures are investigated, for example, in relation to dataset imbalance. Results: The results show that performance can differ considerably depending on the way detector output is compared to database annotations, i.e., beat-to-beat, segment-to-segment, or episode-to-episode comparison. Moreover, depending on the type of detector, the results substantiate that physiological and technical factors, e.g., changes in ECG morphology, rate of atrial premature beats, and noise level, can have a considerable influence on performance. Conclusion: The present study demonstrates overall strengths and weaknesses of different types of detector, highlights challenges in AF detection, and proposes five recommendations on how to handle data and characterize performance.
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| 5. |
- Demidova, Marina M, et al.
(författare)
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QRS broadening due to terminal distortion is associated with the size of myocardial injury in experimental myocardial infarction
- 2016
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Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 1532-8430 .- 0022-0736. ; 49:3, s. 300-306
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Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: Not only repolarization, but also depolarization ECG indexes reflect the progression of ischemic injury. The aim was to assess the QRS duration and morphology dynamics during the prolonged coronary occlusion and their association with the myocardial area at risk (MaR) and final infarct size (IS).METHODS: In pigs, myocardial infarction was induced by inflation of an angioplasty balloon in the left descending artery (LAD), and ECG was continuously recorded. QRS duration was calculated on a beat-to-beat basis during the occlusion period. Single photon emission computed tomography (SPECT) was performed for the assessment of MaR, and IS was assessed by magnetic resonance imaging (MRI).RESULTS: All animals developed an anteroseptal infarction with MaR 40±9% and IS 23±7%. Two peaks of QRS widening were found in all animals: the early peak immediately after LAD occlusion and the late one 17.7±4.1min later. No association was found between MaR and IS and either QRS width or the degree of QRS widening at the early peak. QRS duration on the late peak correlated with both MaR (r=0.61; p=0.007) and IS (r=0.55; p=0.018).CONCLUSION: The QRS widening at the late peak, but not at the early peak, is associated with the size of myocardial injury, suggesting different underlying mechanisms.
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| 6. |
- Demidova, Marina, et al.
(författare)
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T wave alternans in experimental myocardial infarction: Time course and predictive value for the assessment of myocardial damage.
- 2013
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Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 1532-8430 .- 0022-0736. ; 46:3, s. 263-269
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: T-wave alternans (TWA) is associated with prognosis after myocardial infarction (MI), however its link to the extent of ischemic injury has not been clarified. We analyzed the course of TWA and its relation to myocardial damage in experimental myocardial infarction. METHODS: In 21 pigs, infarction was induced by 40-minute long balloon inflation in LAD under continuous 12-lead ECG monitoring. TWA was assessed in a 32-beat sliding window, using periodic component analysis and the Laplacian Likelihood Ratio method. Myocardium at risk (MaR) and infarct size (IS) were evaluated by SPECT and magnetic resonance imaging respectively. RESULTS: TWA appeared at 7.2±4.5minutes of occlusion, reached its maximum at 12.7±6.3 and lasted until 26.5±9.2minutes. The maximal level of TWA was associated with both MaR (r=0.499, p=0.035) and IS (r=0.65, p=0.004). CONCLUSION: TWA magnitude is associated with both MaR and IS in experiment, which encourages further studies in clinical settings.
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| 7. |
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| 8. |
- Gomez, Neurys, et al.
(författare)
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Changes in T-Peak-to-T-End Morphology Measured by Time-Warping are Associated with Ischemia-Induced Ventricular Fibrillation in a Porcine Model
- 2023
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Ingår i: Computing in Cardiology, CinC 2023. - 2325-8861 .- 2325-887X. - 9798350382525
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Konferensbidrag (refereegranskat)abstract
- In this work, we use a time-warping-based morphology variation index, d_{w}, computed between the peak and the end of the T-wave, and assess its association with the occurrence of ventricular fibrillation (VF) episodes in ischemic conditions. ECG recordings from 26 pigs under-going a 40-minute coronary occlusion were analyzed. The d_{w} series was obtained by quantifying the morphological differences between the final part of the T wave at different stages of the occlusion and a reference T wave in the control recording. During control recordings, d_{w} remained stationary with a median value along each recording of 1.76 ms, IQR of 1.80, while during artery occlusion followed a well-marked gradual increasing trend as ischemia progressed, with median of 15.47 ms, IQR of 18.53. At the 20-to-25 min period from occlusion onset (and during 5 min prior to VF episode) dw averages in the VF group was significantly higher than in the non-VF group with median values of 40.0 (and 34.4) vs 7.8 (and 7.7) ms, with p-values of 0.002 (and 0.001), respectively. In conclusion, dynamic increases of the d_{w} index during ischaemia progression in pigs are associated with VF occurrence.
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| 9. |
- Gomez, Neurys, et al.
(författare)
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T-wave Peak-to-End Changes Quantified by Time-Warping Predicts Ventricular Fibrillation in a Porcine Myocardial Infarction Model
- 2024
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Ingår i: IEEE Transactions on Biomedical Engineering. - 0018-9294. ; , s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Background: The T-peak-to-T-end ($\mathrm{T}_{pe}$) interval has shown potential in predicting ventricular arrhythmic risk. It is an appealing index to be measured during ischemia since it is less influenced by ST-segment changes than the early part of the T wave. A time-warping-based index, derived from a spatially transformed PCA lead, $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$, quantifying changes in the $\mathrm{T}_{pe}$ morphology, has previously demonstrated utility in tracking repolarization changes induced by a 5-minute ischemia model in humans. The value of $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ as a predictor of ventricular fibrillation (VF) episodes is assessed in a porcine model of myocardial ischemia with ischemia maintained for 40 minutes. Methods: From 32 pigs undergoing a coronary occlusion, pre-occlusion and occlusion ECG recordings from 10 pigs suffering a VF episode after 10 min of occlusion (Delayed VF) and 16 that did not had any episode during the recording were analyzed. The $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ series was measured by comparing $\mathrm{T}_{pe}$ morphologies at different stages of the occlusion relative to the peak-to-end morphology of a baseline T-wave. Results: During baseline, $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ remained stationary with an intra-recording median [IQR] value of 1.60 [1.33] ms. During artery occlusion, $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ followed a well-marked gradual increasing trend as ischemia progressed, reaching a median of 14.58 [17.72] ms. $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ averages were significantly higher (${p< 0.05}$) in the VF group than in the Non-VF group at time intervals 0-5, 5-10, 10-15, 15-20, 20-25 min after occlusion onset and at 10-15, 5-10 and 5-0 minutes prior to VF episode, with median values of 12.5, 18.8, 26.8, 24.0, 31.0, 18.6, 25.0 and 28.8 vs 6.3, 7.6, 8.0, 7.8, 7.8, 8.5, 7.2 and 6.0 ms, respectively. The $\mathrm{T}_{pe}^{\text{PCA}}$ interval was also significantly higher in the VF group at all analyzed time periods, but with a lower significance level. Pigs with maximum $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ $\geq$ 20.0 ms and $\mathrm{T}_{pe}^{\text{PCA}}$ $\geq$ 85.4 ms had significantly higher risk for VF occurring in the early 5-10 minutes interval, with 90.0%/75.0% and 80.0%/69.0% sensitivity/specificity, respectively. Univariate Cox analysis yielded hazard ratios of 12.5 for $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ vs 5.5 for $\mathrm{T}_{pe}^{\text{PCA}}$. Conclusions and Significance: The time-warping-based index, $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$, is a stronger VF predictor than $\mathrm{T}_{pe}^{\text{PCA}}$ during ischemia in a porcine model, advising for further clinical exploration studies in humans.
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| 10. |
- Henriksson, Mikael, et al.
(författare)
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Modeling and Estimation of Temporal Episode Patterns in Paroxysmal Atrial Fibrillation
- 2021
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Ingår i: IEEE Transactions on Biomedical Engineering. - 0018-9294. ; 68:1, s. 319-329
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The present study proposes a model-based, statistical approach to characterizing episode patterns in paroxysmal atrial fibrillation (AF). Thanks to the rapid advancement of noninvasive monitoring technology, the proposed approach should become increasingly relevant in clinical practice. Methods: History-dependent point process modeling is employed to characterize AF episode patterns, using a novel alternating, bivariate Hawkes self-exciting model. In addition, a modified version of a recently proposed statistical model to simulate AF progression throughout a lifetime is considered, involving non-Markovian rhythm switching and survival functions. For each model, the maximum likelihood estimator is derived and used to find the model parameters from observed data. Results: Using three databases with a total of 59 long-term ECG recordings, the goodness-of-fit analysis demonstrates that the proposed alternating, bivariate Hawkes model fits SR-to-AF transitions in 40 recordings and AF-to-SR transitions in 51; the corresponding numbers for the AF model with non-Markovian rhythm switching are 40 and 11, respectively. Moreover, the results indicate that the model parameters related to AF episode clustering, i.e., aggregation of temporal AF episodes, provide information complementary to the well-known clinical parameter AF burden. Conclusion: Point process modeling provides a detailed characterization of the occurrence pattern of AF episodes that may improve the understanding of arrhythmia progression.
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