| 1. |
- Richter, Ulrike, et al.
(författare)
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Spatial characteristics of atrial fibrillation using the surface ECG
- 2007
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Ingår i: Computers in Cardiology. - 0276-6574. - 9781424425334 ; 34, s. 273-276
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Konferensbidrag (refereegranskat)abstract
- The present study investigates spatial properties of atrial fibrillation (AF) by analyzing VCG loops synthesized from 12-lead ECGs. During intervals with ventricular activity, the atrial signal is extracted using spatiotemporal QRST cancellation, thus making continuous f-wave analysis possible. Spatial properties are characterized through joint analysis of successive fixed-length signal segments, either of 1-s length or related to the typical length of an f-wave. The spatial properties are expressed in terms of loop orientation, i.e., angles of azimuth and elevation, as well as in morphologic terms such as planarity and planar geometry of the loops and related temporal variability. Several parameters have been suggested to characterize the degree of AF organization from electrogram analysis, but only a few parameters for noninvasive, ECG-based characterization of which AF frequency is the most studied. This parameter is related to atrial refractoriness and reflects AF organization. In the present study, the significance of spatial (loop morphology) parameters is studied in relation to AF frequency, hypothesizing that more organized AF, being expressed by a lower frequency, is associated with decreased variability in loop morphology. A total of 26 patients with chronic AF were analyzed with respect to spatial properties, using 60-s ECG recordings. For the database AF frequency ranged from 3.9 to 7.7 Hz, with a mean of 6.4±1.0 Hz (mean±std). The results showed that loop orientation can be determined from global analysis (i.e., the entire 60-s segment was used for determining the two angles) or the mean of segment-based analysis, both types of analysis leading to similar results. The hypothesis that more organized AF is associated with decreased variability in loop morphology was to some extent confirmed for the parameters planarity and planar geometry; for 1-s segments, the correlation to AF frequency was 0.608 (p<0.001) and 0.543 (p<0.005). This finding also applied to segment lengths related to f-wave duration. In conclusion, the simpler analysis based on 1-s segments may be preferred since it does not require f-wave delineation. Global analysis and the mean of segment-based analysis (1-s segments) showed increased planarity and decreased planar geometry for lower AF frequencies, possibly related to higher similarity of successive loops in more organized AF.
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| 2. |
- Richter, Ulrike, et al.
(författare)
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Wavefront detection from intra-atrial recordings
- 2007
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Ingår i: Computers in Cardiology. - 0276-6574. - 9781424425334 ; 34, s. 97-100
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Konferensbidrag (refereegranskat)abstract
- The present study deals with detection of intra-atrial wavefronts from atrial activation times in adjacent bipolar electrograms. A statistic of the delays within each wave-front was calculated and served as a basis for quantifying the wavefront consistency as well as the propagation of the electrical activity along the catheter. The database consisted of 19 patients for which five electrograms were recorded simultaneously during 10 s. The analysis resulted in 38plusmn2 complete wavefronts per patient, i.e., wavefronts consisting of one activation from each recording site. Two parameters were evaluated for quantifying wavefront consistency, which together with the propagation profile well reflect the overall wavefront timing. In most cases, electrical activity was observed first in the high septal right atrium, and then spread along the catheter.
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| 3. |
- Solem, Kristian, et al.
(författare)
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Performance evaluation of heart rate turbulence detection using an extended IPFM model
- 2007
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Ingår i: Computers in Cardiology. - 0276-6574. - 9781424425334 ; 34, s. 821-824
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Konferensbidrag (refereegranskat)abstract
- The well-known integral pulse frequency modulation (IPFM) model is used to generate the occurrence times of normal sinus rhythm. In a previous study, we extended the model to account for ectopic beats and subsequent variation in sinus rhythm that may accompany an ectopic beat; a phenomenon known as heart rate turbulence (HRT). Inspired by the extended model, a new approach to characterize HRT was presented, being based on Karhunen-Loeve basis functions. An HRT detection procedure was developed which involves a test statistic T(x), resulting from the generalized likelihood ratio test of a linear model. In this study, detector performance of T(x) is evaluated on both simulated and ECG data, and compared to the performance of turbulence onset (TO) and turbulence slope (TS). Two types of simulations were performed, both adding simulated heart rate variability and HRT to the input of the extended model. The first simulation evaluated HRT detection performance at different signal-to-noise-ratios (SNRs). The second simulation evaluated the influence of QRS detection inaccuracies on HRT detection. The performance was also studied on ventricular ectopic beats (VEBs) selected from 31 patients with myocardial ischemia. The relation between HRT and the degree of blood pressure reduction induced by a VEB (estimated as proportional to the sum of the coupling interval and the compensatory pause), as well as the relation between HRT and heart rate, were analysed. The simulation results at different SNRs showed that T(x) performs dramatically better than TO and TS. With a 95% sensitivity (Sn), the specificity (Sp) at 5 dB SNR was 94% for T(x), 51% for TO, and 64% for TS. The detection performance of T(x) was equally superior when assuming that QRS jitter was Gaussian with 1 ms std: with Sn=95%, Sp was 99% for T(x), 40% for TO, and 68% for TS. Based on the ECG data, it was found that the degree of blood pressure reduction is essentially proportional to the magnitude of the HRT; this finding was reflected by T(x), TO, as well as TS. Moreover, the three HRT parameters were found to be linearly related to heart rate: low heart rates was associated with large HRT and high heart rates with small HRT. This linear relation is probably due to that a VEB during low heart rates induces a larger blood pressure reduction than during high heart rates.
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| 4. |
- Stridh, Martin, et al.
(författare)
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ECG-based waveform characterization of atrial fibrillation
- 2007
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Ingår i: [Host publication title missing]. - 0276-6574. - 9781424425334 ; 34, s. 269-272
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Konferensbidrag (refereegranskat)abstract
- In atrial fibrillation (AF), the body surface signal pattern varies considerably from one patient to another as well as over time. We have developed a new method for ECG-based characterization of AF which explores the morphology of the f-waves. Following QRST cancellation, the method divides the atrial signal into short blocks and performs a model-based analysis of each block. The blocks are then clustered into different waveform patterns. The method was applied to a database of 36 patients (10-s recordings) with organized AF. The results show that the different waveforms in AF are well represented by the proposed model. Each recording was, in average, represented by 3 clusters of which the main cluster covered 31% of the blocks. In lead V1, the typical phase relationship between the fundamental and first harmonic was -82 degrees, indicating sawtooth-like waves with a steeper downslope than upslope.
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| 5. |
- Bergvall, Erik, et al.
(författare)
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Regularization of phase contrast magnetic resonance images using optical flow and smoothness constraints
- 2005
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Ingår i: Computers in Cardiology. - 0276-6574. ; 32, s. 33-36
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Konferensbidrag (refereegranskat)abstract
- This paper presents a post processing strategy for myocardial velocity fields obtained by phase contrast magnetic resonance imaging. Such data can be used to track cardiac motion and to calculate strain. The method combines data regularization with optical flow estimation to overcome the partial volume effect in the image acquisition. Validation is performed both in vitro and in vivo and it is shown that the method improves the accuracy of cardiac motion tracking.
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| 6. |
- Carlson, Jonas, et al.
(författare)
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Non-invasive assessment of direction of right atrial activation during atrial fibrillation using correlation function analysis.
- 2007
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Ingår i: Computers in Cardiology. - 0276-6574. ; 34, s. 277-280
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Tidskriftsartikel (refereegranskat)abstract
- ECGs were recorded from three electrodes attached at the corners of an equilateral triangle positioned around the location of electrode V1. The atrial signal between QRST complexes was subjected to correlation function analysis to reveal differences in activation times between the electrode sites. The time differences found were used to calculate the direction of activation across the body surface. Twenty-three subjects were studied during sinus rhythm (SR), intraoperatively confirmed typical and reverse typical atrial flutter, or during paroxysmal or permanent atrial fibrillation (AF). Subjects studied during SR and patients with typical atrial flutter exhibited a uniform direction of activation, with the main vector pointing downwards. The propagation of atrial activation during permanent AF did not show a consistent direction, while patients with paroxysmal AF exhibited more uniform activation vectors, corresponding to the direction observed in patients with atrial flutter.
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| 7. |
- Carnicky, J., et al.
(författare)
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Estimation of area at risk in myocardial infarction
- 2007
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Ingår i: Computers in Cardiology 2007, CAR 2007. - 9781424425334 ; 34, s. 169-172
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Konferensbidrag (refereegranskat)abstract
- This study presents a new method for estimation and imaging of the area at risk (AaR) in myocardial infarction (MI). The values of the ST-segment deviations of 12-lead ECG signal were used as input parameters. Based on DECARTO model, the spherical surface was chosen as a reference surface to approximate the ventricular wall. On this surface, the spatial ST vector was projected. The center of AaR was defined as an intersection of the spatial ST vector with spherical surface; the size of the AaR was set to be proportional to the number of electrical leads with ST- segment deviations. The method was tested using data of 10 patients with acute MI. The visual comparison showed good agreement with the AaRECG estimates based originally on the Selvester QRS scoring as well as with a non- electrocardiographic imaging method (SPECT).
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| 8. |
- Corino, Valentina D.A., et al.
(författare)
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A Mathematical Model of The Atrioventricular Node during Atrial Fibrillation
- 2010
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Ingår i: [Host publication title missing]. - 0276-6574. ; 37, s. 117-120
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Konferensbidrag (refereegranskat)abstract
- The atrioventricular (AV) node plays a crucial role during atrial fibrillation (AF). The aim of this study is to present an AV node model which can be fitted to short-term ECG recordings in order to infer certain AV node characteristics. The proposed model is characterized by: i) the arrival rate of atrial impulses; ii) two different refractory periods, corresponding to dual AV nodal paths; iii) the probability of an atrial impulse choosing either of these pathways; iv) a parameter modeling prolongation of the refractory period due to different physiological reasons. The model was tested on atrial fibrillatory ECGs recorded from 33 patients; the average normalized absolute error between the normalized RR histogram and the estimated model probability density function was 0.0023 ± 0.0016, (20-ms bin size, 0–2 s interval). These preliminary results are encouraging as AV nodal properties can be noninvasively assessed by a set of statistical parameters with a simple electrophysiological interpretation.
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| 9. |
- Fors, Carina, et al.
(författare)
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Analysis of breathing-related variations in ECG-triggered laser Doppler perfusion signals measured on the beating heart during surgery
- 2006
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Ingår i: Computers in cardiology. - 0276-6574. ; 33, s. 181-184
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Tidskriftsartikel (refereegranskat)abstract
- Laser Doppler perfusion monitoring (LDPM) is amethod to assess microvascular perfusion. A modified,ECG-triggered LDPM system has been developed tomeasure myocardial perfusion with minimum influencefrom heart motion. With this method, one systolic (PLS)and one diastolic (PLD) perfusion value is obtained.The aim of this study was to analyse breathing-relatedvariations in PLS and PLD measured during open-heartsurgery. The phase delays between PLS, PLD, meanarterial blood pressure (MAP), heart rate and, indirectly,the respiration were determined.MAP tended to be in phase with or precede thevariations in PLD, i.e., PLD was at a maximum at the endof inspiration or at the beginning of expiration. No clearrelation between PLS and any of the other signals couldbe found.
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| 10. |
- Heiberg, Einar, et al.
(författare)
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Automated Calculation of Infarct Transmurality
- 2007
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Ingår i: Computers in Cardiology 2007, vols 1 AND 2. - 0276-6574. ; , s. 165-168
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Konferensbidrag (refereegranskat)abstract
- The aim of this study was to develop all algorithm to automatically calculate infarct transmurality based oil a non dichotomous infarct classification, and to compare with manual delineation. Global transmurality as calculated by the computer algorithm were significantly smaller than the consensus delineation of three observers (p < 0.05). On a regional basis in 6 sectors of each slice the variability of the three observers compared to consensus delineation was 17%, 15%, and 20%. The variability of the automated algorithm was 16%. In conclusion, weighted calculation of transmurality gave smaller global transmurality compared to consensus delineation, but did had the same variability oil a regional basis.
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