| 1. |
- Sörnmo, Leif, et al.
(författare)
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Non-invasiv analys av förmaksflimmer
- 2006
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Ingår i: Elektrokardiologi : klinik och teknik. ; , s. 287-309
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Sörnmo, Leif, et al.
(författare)
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Signabehandling av EKG
- 2006
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Ingår i: Elektrokardiologi : klinik och teknik. ; , s. 17-40
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Ahlström, Christer, 1977-
(författare)
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Processing of the Phonocardiographic Signal : methods for the intelligent stethoscope
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phonocardiographic signals contain bioacoustic information reflecting the operation of the heart. Normally there are two heart sounds, and additional sounds indicate disease. If a third heart sound is present it could be a sign of heart failure whereas a murmur indicates defective valves or an orifice in the septal wall. The primary aim of this thesis is to use signal processing tools to improve the diagnostic value of this information. More specifically, three different methods have been developed:• A nonlinear change detection method has been applied to automatically detect heart sounds. The first and the second heart sounds can be found using recurrence times of the first kind while the third heart sound can be found using recurrence times of the second kind. Most third heart sound occurrences were detected (98 %), but the amount of false extra detections was rather high (7 % of the heart cycles).• Heart sounds obscure the interpretation of lung sounds. A new method based on nonlinear prediction has been developed to remove this undesired disturbance. High similarity was obtained when comparing actual lung sounds with lung sounds after removal of heart sounds.• Analysis methods such as Shannon energy, wavelets and recurrence quantification analysis were used to extract information from the phonocardiographic signal. The most prominent features, determined by a feature selection method, were used to create a new feature set for heart murmur classification. The classification result was 86 % when separating patients with aortic stenosis, mitral insufficiency and physiological murmurs.The derived methods give reasonable results, and they all provide a step forward in the quest for an intelligent stethoscope, a universal phonocardiography tool able to enhance auscultation by improving sound quality, emphasizing abnormal events in the heart cycle and distinguishing different heart murmurs.
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| 4. |
- Alcaraz Martinez, Raul, et al.
(författare)
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Application of frequency and sample entropy to discriminate long-term recordings of paroxysmal and persistent atrial fibrillation
- 2010
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Ingår i: Engineering in Medicine and Biology Society (EMBC), 2010 Annual International Conference of the IEEE. - 1557-170X. - 9781424441235 ; , s. 4558-4561
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Konferensbidrag (refereegranskat)abstract
- Atrial fibrillation (AF) is the most common arrhythmia in clinical practice. At an early stage of the disease, AF may terminate spontaneously and is then referred to as paroxysmal AF. On the other hand, when external intervention is required for the arrhythmia to terminate, it is referred to as persistent AF. In this work, a method to discriminate between paroxysmal and persistent AF in the long-term ECGs is presented. The dominant frequency as well as the organization of the atrial activity are employed to characterize AF. The dominant atrial frequency (DAF) is estimated using hidden Markov model based frequency tracking, and organization is estimated by the sample entropy of the main atrial wave (MAW) and the first two harmonics, respectively. Long-term variations in DAF and organization from 50 ECG recordings were evaluated, showing that episodes of paroxysmal AF were consistently associated with lower DAF and organization of the MAW and the harmonics, than was persistent AF. Discrimination of paroxysmal and persistent AF resulted in classification rates of 84.1±26.1%, thus suggesting that it possible to discriminate between paroxysmal and persistent AF in patients without previously known AF history.
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| 5. |
- Alcaraz Martinez, Raul, et al.
(författare)
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Classification of paroxysmal and persistent atrial fibrillation in ambulatory ECG recordings
- 2011
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Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 58, s. 1441-1449
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Tidskriftsartikel (refereegranskat)abstract
- The problem of classifying short atrial fibrillatory segments in ambulatory ECG recordings as being either paroxysmal or persistent is addressed by investigating a robust approach to signal characterization. The method comprises preprocessing, estimation of the dominant atrial frequency for the purpose of controlling the subbands of a filter bank, and computation of the relative subband (harmonics) energy and the subband sample entropy. Using minimum-error-rate classification of different feature vectors, a dataset consisting of 24-h ambulatory recordings from 50 subjects with either paroxysmal (26) or persistent (24) atrial fibrillation (AF) was analyzed on a 10-s segment basis; a total of 212196 segments were classified. The best performance in terms of area under the receiver operating characteristic curve was obtained for a feature vector defined by the subband sample entropy of the dominant atrial frequency and the relative harmonics energy, resulting in a value of 0.923, whereas that of the dominant atrial frequency was equal to 0.826. It is concluded that paroxysmal and persistent AF can be discriminated from short segments with good accuracy at any time of an ambulatory recording.
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| 6. |
- Alcaraz, Raul, et al.
(författare)
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Organization tracking of long-term atrial fibrillation recordings: differences between paroxysmal and persistent episodes
- 2009
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Ingår i: [Host publication title missing]. ; 36, s. 509-512
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Konferensbidrag (refereegranskat)abstract
- In this work, a method for non-invasive assessment of AF organization has been applied to discriminating between paroxysmal and long-term persistent AF episodes. Following extraction of the atrial activity (AA) signal, the dominant atrial frequency (DAF) of the AA was computed based on a hidden Markov model. Finally, the main atrial wave (MAW) was obtained by bandpass filtering centered on the DAF, thus providing a time series suitable for AF organization estimation with sample entropy (SampEn). The performance of the method was evaluated on 24-h Holter recordings with long-term changes in AF organization. The results showed that episodes of paroxysmal AF (0.06930.0147) were consistently associated with lower SampEn than episodes with persistent AF (0.10560.0146). Moreover, 94.2% of 1-min segments with paroxysmal AF and 88.6% of 1-min segments with persistent AF could be correctly classified based on Samp- En information, thus making it possible to classify longterm recordings of patients without AF history.
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| 7. |
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| 8. |
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| 9. |
- Aunes-Jansson, Maria, et al.
(författare)
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Decrease of the atrial fibrillatory rate, increased organization of the atrial rhythm and termination of atrial fibrillation by AZD7009
- 2013
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Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 1532-8430 .- 0022-0736. ; 46:1, s. 29-35
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Tidskriftsartikel (refereegranskat)abstract
- Background: The atrial fibrillatory rate (APR), on AZD7009 as compared to placebo, was investigated as a potential biomarker for electrophysiological effect in early antiarrhythmic drug development. Methods: Patients with permanent AF received infusions of AZD7009 and placebo in an exploratory two-way, single-blind, randomized cross-over study. The ECG was continuously recorded, and following QRST cancellation the APR, its standard deviation (SD), the exponential decay and the atrial electrogram amplitude were determined as 3-min averages. Results: The mean APR rapidly decreased by 43% from baseline (394 +/- 38 to 225 +/- 61 fibrillations/min, p = 0.0003) on AZD7009, but not on placebo. The SD of the AFR and the exponential decay decreased in parallel. In 2 of 8 patients, termination of AF occurred after the APR had decreased by 58% and 53%, respectively. Conclusions: The APR may potentially serve as a biomarker of electrophysiological effects in early evaluation of rhythm control agents. (C) 2013 Elsevier Inc. All rights reserved.
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