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Date 26-29 Sept. 1999

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Displaying Results 1 - 25 of 183
  • Computers in Cardiology 1999. Vol.26 (Cat. No.99CH37004)

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  • Index by author

    Page(s): 715 - 719
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    Freely Available from IEEE
  • Index by title words

    Page(s): 721 - 724
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    Freely Available from IEEE
  • Detection of apneas during 24-Hour ambulatory monitoring of ECG and respiration in chronic heart failure patients with Cheyne-Stokes breathing

    Page(s): 459 - 462
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    Laboratory short-term respiratory monitoring detecting apnea occurrence has a clinical and prognostic role in patients with congestive heart failure. Long-term ambulatory recording of respiration might provide more extensive and specific information about the occurrence of abnormal patterns of breathing. Automatic detection of apneas and periodic breathing should permit an easy interpretation of respiratory signal. Ten patients with congestive heart failure underwent 24-hour recordings of ECG and respiration. The authors then compared 4 different methods for detection of apneas. Results were more satisfying for a technique based on amplitude demodulation, whose application permitted to quantify a high occurrence of abnormal respiratory patterns both at night- and day-time. Quantification of these abnormalities over a circadian period provides new relevant clinical information for diagnostic work-up, therapeutical management and follow-up of patients View full abstract»

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  • Reentry based on the development of early afterdepolarizations in a Purkinje-ventricular muscle ring model

    Page(s): 491 - 494
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    Early afterdepolarizations (EADs) are irregularities that appear in the action potential (AP) of cells before repolarization is complete and that have been implicated in the genesis of certain cardiac arrhythmias, probably in combination with reentry. The purpose of this work was to study the establishment of reentry based on EAD generation and propagation in a ring computer model where Purkinje fibers, under conditions that favor the development of EADs (EAD conditions), connect to ventricular muscle cells, under normal conditions. Our results show that there exist critical EAD conditions under which stimulated APs are followed by two ectopic APs (couplets). This phenomenon is based on the development of triggered activity in Purkinje cells and the subsequent establishment of reentry, and supports the hypothesis suggested by different experimental studies, which propose a similar mechanism to explain the generation of certain cardiac arrhythmias such as torsade de pointes View full abstract»

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  • NEMESIS: a new telemedicine approach to cardiologic software

    Page(s): 37 - 40
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    The present communication describes a telemedicine approach to a computer-aided healthcare system. The application is a comprehensive tool set, structured around a main navigation bar, which leads to every sub-application. Those sub-applications are window based user-friendly tools, comprising specific health tools for physicians, telemedicine/telematics tools and general-purpose tools. The whole application is built in a highly structured and modular way, which allows adding or excluding modules quickly. Portability is guaranteed and achieved by Java programming language, bringing independent platform software. All modules comply with international standards; namely, medical modules comply with European CEN TC 251 approved standards, while telematic modules observe the ITU standards. The present application release offers one specific medical module, videoconference, electronic mail, remote control, electronic healthcare patient record retrieval and knowledge database access View full abstract»

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  • A digital image archive solution for multiple modalities in a cardiological department

    Page(s): 367 - 369
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    The huge amount of data and the different imaging modalities currently in use are the cause, that digital archive systems for images are not very common in cardiology compared with radiology. In many hospitals the digital media, e.g. CD-R, are handled as an 1:1 replacement of the cinefilm: only one record is available, that has to be reviewed on a special viewing systems. A great advantage of digital imaging is the possibility to distribute image data through networks without any loss of quality. Once they are stored on a central server, online access to all examination data of a patient is possible. This contribution describes the conception and practical realisation of a digital image archiving system for a cardiologic department. The archive can handle angiographic and ultrasound image data in different file formats. The design allows an extension to other modalities, and the implementation of hierarchical storage management strategies enables servers with huge data capacity, that can grow with the needs of the department. The application of image compression techniques reduces capacity requirements and network traffic without loss of image quality. The online access of all relevant digital data from all workstations in cardiology as well as in cardiac surgery has enhanced workflow significantly View full abstract»

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  • Autonomic control of the cardiovascular system during acute hypobaric hypoxia, assessed by time-frequency decomposition of the heart rate

    Page(s): 627 - 630
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    The time from onset of severe hypoxia to loss of consciousness (TUC) varies among healthy individuals. We hypothesized that this variance is due to difference in autonomic modulation of the cardiovascular system. ECG and finger oxygen saturation patterns were recorded from twenty-one consenting aircrew members, during controlled altitude chamber training at 25,000 feet. Autonomic activity was assessed by heart rate variability (HRV) using a selective frequency-dependent-window algorithm (SDA) in the LF (0.04-0.15 Hz) and HF (0.15-0.50 Hz) bands. Subjects who displayed the highest HRV integrals during baseline and experimental states, were able to remain conscious longer without supplemental oxygen (mean 364 sec) “at altitude” compared to subjects with low HRV integrals (mean 231 sec). Thus, hypoxia resistance may be related to autonomic activity and its ability to achieve selective blood shunting View full abstract»

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  • Left ventricular shape analysis applied to color kinesis images

    Page(s): 137 - 140
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    Shape changes of cardiac chambers characterize a normal cardiac cycle. The importance of shape analysis is underlined in literature by studies of several forms of cardiac disease, revealing abnormalities in shape deformations. The aim of the paper is to describe an approach to an automated extraction of endocardial contours from a single end-systolic frame obtained by color kinesis technique, applied to 4-chamber apical view echocardiographic images. Then, global and regional indexes are applied to provide a quantification of left ventricular shape both at the beginning and at the end of systolic phase. The results prove that this approach can be useful in the assessment of the cardiac functionality View full abstract»

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  • Computer modeling and experimental validation on effect of bipolar electrode spacing on near field and far field electrogram amplitudes

    Page(s): 201 - 204
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    Far field R wave (FF) oversensing is a common problem associated with dual chamber devices, which may result in delivery of inappropriate therapies. Optimizing bipolar electrode design to increase ratios of near field P wave (NF) to FF and thereby rejecting FF signals is one method of resolving this problem. The goal of this study is to evaluate the effect of bipolar interelectrode spacing (IE) associated with lead orientation in a computer model and to validate the results with a well-controlled study in eight canines. Both model and animal results show that the NF/FF ratios increased with smaller IE. Overall, the amplitude of NF was attenuated with smaller IE. However, the FF amplitude exhibited a larger attenuation resulting in an increased NF/FF View full abstract»

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  • Relative contributions of spontaneous and centrally driven vasomotion in the overestimation of blood pressure variability at the finger

    Page(s): 631 - 634
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    Previous studies showed that nearly 30% of the VLF (0.01-0.04 Hz) power of systolic arterial pressure measured by the Finapres device (F-SAP) is uncorrelated to the brachial intra-arterial signal, this being likely due to the interfering effect of both local and centrally-driven vasomotion of small arteries under the finger cuff upon the measurement process. In this study we estimated the relative weight of these two contributions using a simple linear model of the relationship between intra-arterial and finger signals. We found that VLF fluctuations of F-SAP in contralateral fingers are highly correlated (coherence >0.86, mean±SD: 0.93±0.04) and that the contribution of centrally-driven disturbances to F-SAP was about 6 times that of local disturbances. Spectral indices in the VLF, LF (0.04÷0.15) and HF (0.15÷0.4) bands were very similar in contralateral fingers View full abstract»

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  • Automatic rhythm analysis using SPART method

    Page(s): 515 - 518
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    Accurate identification of ectopic beats is important in frequency HRV analysis. It may be done by classification of QRS planar loop morphology. The objective of this research was to compare results of QRS morphology analysis in different spatial planes: frontal, horizontal, and preferential. The preferential plane of a QRS loop was found with modified SPART method. Fourier descriptors of plane loop were used for classification of QRS loops morphology analysis. The study was performed using ICAR System and Multilead CSE Database. Identification of optimal spatial orientation of QRS loop using SPART method was accurate in all analyzed beats. Statistical indices showed low values for the QRS classification in the frontal plane XY. The results estimated for XZ and UV planes were comparable. Our results confirm usefulness of ICAR System with implemented SPART method for automatic rhythm analysis View full abstract»

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  • Artery skeleton extraction based on consistent curvature labeling

    Page(s): 269 - 272
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    A method for detecting and extracting the skeletons of coronary arteries in coronary angiograms is proposed. The grayscale coronary angiograms are regarded as noisy sampling of the underlying continuous surface. After the application of Gaussian filtering to reduce noise, the topographic features of the smoothed image are detected based on first and second order image derivatives which characterize the local differential image structure. Then, the candidate arteries skeleton areas are detected based on the observation that arteries are smooth elongated objects having approximately a Gaussian smoothed semi-elliptical profile. False skeleton areas are eliminated through connected component analysis and the morphological operation of reconstruction. Experimental results on real digitized coronary angiograms are presented View full abstract»

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  • Multicenter validation study of an easily applicable cybernetic prototype device that assesses electrocardiographic abnormalities

    Page(s): 531 - 533
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    A newly developed digital prototype electrocardiographic device (CardioScanTM) for assessment of electrocardiographic abnormalities was validated in a multicenter study. Recordings from the test device and digital 12 channel electrocardiograms (ECG) were performed at rest for 289 in- and outpatients at three study centers. Sensitivity and specificity of the test device for the correct detection of abnormal ECG were calculated by comparing the results to expert findings from 12 channel ECG. The device correctly assessed 63% of all abnormal ECG with a specificity of 86%. Because of its sufficient sensitivity and its high specificity and its simple and rapid application, this device may be useful for automatic screening tests for electrocardiographic abnormalities, which should be presented to a physician for further evaluation View full abstract»

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  • Wavefront-obstacle interactions: a computational study

    Page(s): 1 - 4
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    In this simulation study, the authors examined the interaction between wavefronts and sharp obstacle corners in cardia tissue. They elicited a single planar wave beneath an obstacle composed of either an insulator, Tyrode's solution, or passive tissue. They examined wavefront detachment from the obstacle for various degrees of excitability. To quantify the authors' observations, they developed a method for calculating safety factors in two dimensions. They found that the ability of the obstacle to act as a source or sink greatly influenced wavefront behavior at the obstacle corner. The high conductivity of the Tyrode's obstacle lead to significant reduction in the safety factor at its corner resulting in wavefront detachment at higher excitabilities than for the other two types of obstacles. The authors' examination of wavefront-obstacle interactions presented here has strong implications for the modeling of various types of myocardial damage as well as for the modeling of natural cardiac obstacles View full abstract»

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  • Remote access to medical records via the Internet: feasibility, security and multilingual considerations

    Page(s): 89 - 92
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    This paper investigates the use of Internet technology to provide secure multilingual access to the medical records of a cardiology clinic. Information extracted from the medical record archive is used to create mini-Webs of interlinked pages that may be viewed using a standard browser. The main features of the reported project are its multilingual nature-of particular significance in Europe, the provision of strict secure measures, and the support of usage profiles. Medical data may be viewed either in Greek-the language in which the data are stored-or in English, through an automated translation process. Security measures are as follows: (1) a password is required for access; (2) all transactions are logged (3) the patient's name and medical data are never transmitted together; (4) mini-Webs are deleted when the transaction is complete, (5) the remote user never has direct access to the central database View full abstract»

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  • Development and clinical evaluation of an online procedure for lesion length measurement in coronary intervention

    Page(s): 375 - 378
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    Presents a procedure for online measurement of a coronary segment length and its clinical evaluation during stent implantation. The procedure calculates the spatial segmental axis from a biplane angiogram and the corresponding projection data. The images and data are captured and combined by an automatic acquisition system. Simple delineation of the proximal and distal segment sites in each image provides the spatial segmental length online. In a clinical evaluation the measured length of 116 stents or carrier balloons was compared with the listed length. The mean ±SD of the time frame, projectional foreshortening and length error were calculated. The device length imaged with a mean projectional foreshortening of 17±17% was measured within 18±4 s. The overall absolute length error was 0.58±0.41 mm. The procedure yields the accurate length of coronary segments within a short computation time taking projectional foreshortening into account. It promises to effectively optimize coronary stent implantation View full abstract»

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  • Computerized ECG diagnosis on a reduced lead set (limb leads)

    Page(s): 687 - 690
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    Increasing interest in home care brings up the question of easy to handle ECG lead sets. Application of electrodes must be simple and not critical regarding electrode placement. For reproducibility requirements limb lead recording is choosen. The objectives of this study were to test the performance of signal processing and to find out the diagnostic power of the reduced lead set ECG for diagnosis. Complex localisation, beat typing and wave recognition are possible within acceptable error tolerances. The standard deviations of QRS-duration and QT-Interval measurement errors obtained with our HES-LIMB algorithm are still smaller than the IEC requirements up to 60 μV added HF noise. Atrial fibrillation or flutter was detected with a sensitivity of 92% and a specificity of 98%. Investigations on diagnostic performance indicate that using Linear Discriminant Analysis for the Normal/Abnormal classification 93% sensitivity and 95% specificity can be achieved. For acute versus non acute ECG's 70% sensitivity and 97% specificity have been obtained View full abstract»

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  • Endocardial border detection in contrast enhanced echocardiographic cineloops using a pulse coupled neural network

    Page(s): 185 - 188
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    Endocardial border detection is a crucial step for the quantitative analysis of overall and regional left ventricular function from echocardiographic images. Echocardiographic contrast agents with transpulmonary passage are being used increasingly in clinical practice for left ventricular cavity opacification. We investigate the feasibility of using pulse coupled neural networks to identify, the left ventricular endocardial border in contrast-enhanced echocardiographic cineloops View full abstract»

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  • ECG feature relevance in a fuzzy arrhythmia classifier

    Page(s): 679 - 682
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    A good fuzzy classifier for a three-class arrhythmia problem is analyzed “a posteriori”, in order to estimate the importance of the ECG features for the final system performance. A set of fuzzy rules is automatically built on forty MIT-BIH database's files, using fourteen ECG measures to characterize each beat. The implemented fuzzy model correctly classifies 92% of normal beats, 80% of PVBs and 56% of SVPBs of the test set. The information contained in the fuzzy model is then quantified and the gain in information, derived from application of the fuzzy rules along a given input dimension, is measured. Only three ECG features (QRS width, PR segment and prematurity degree) seem to carry the main responsibility for the correct classification of the three arrhythmic classes. The uninformative character of ECG measures with lowest information gain is confirmed by the almost unaltered-when not improved-performance of the classifier when these features are removed from the input vector View full abstract»

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  • The use of wavelet packets to improve the detection of cardiac sounds from the fetal phonocardiogram

    Page(s): 463 - 466
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    This work evaluates the influence of preprocessing to defect time references of the first and second cardiac sounds (S1 and S2). Four fetal phonocardiogram (PDGf) signals with different signal to noise ratio (SNR) were simulated (150 cycles, 50-400 Hz) using acquired cardiac sounds. The signals were decomposed by Mutual Wavelet Packets and the best tree was de-noised before the signal reconstruction. The PCGf envelope was obtained by Hilbert Transform (HT), and the starting (S), maximum (M), and ending (E) points were detected for S1 and S2. The results were compared without and with the preprocessing stage, finding that the proposed method improves the SNR and the detection of the heart sounds View full abstract»

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  • Heterogeneity of ventricular repolarisation morphology measured using orthogonal time-scale decomposition of the surface ECG

    Page(s): 61 - 64
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    Recent findings on the contribution of cardiac M-cells in the ventricular repolarization abnormalities generate new interest for analyzing the T-wave morphology. Spatial heterogeneity of the morphology of T-wave may reflect the non-uniform recovery of ventricular excitability contributing to lower threshold for ventricular arrhythmias. The authors investigated a new approach for the analysis of the repolarization based on an orthogonal wavelet transformation of the ventricular repolarization. An index of morphological dissimilarity (IMD) measuring the differences in the distribution of energy in time and frequency domains was used to identify changes in the repolarization process. This method was evaluated under simulated condition and then applied to three populations of healthy subjects, LQTS carriers and non-carriers. The results have shown that IMD parameter is able to quantify morphological changes between leads and have an increase value when T-wave is biphasic, has notches or a U wave. Baseline wandering was not affecting IMD but noise level was increasing IMD values mainly for low-amplitude T-waves. IMD was higher in carrier LQTS patients than in non-carriers (9.5±2.6 mV2 vs. 5.0±3.6 mV2 , p<0.0001) indicating that our method could be a new non-invasive parameter for quantifying abnormalities of the repolarization segment View full abstract»

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  • Semi-automated analysis of color M-mode echocardiographic images for determining transmitral pressure gradients using a simplified Euler equation

    Page(s): 181 - 184
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    We hypothesize that a simplified version of the Euler equation (SEE) utilizing differences in velocity over a distance and time as obtained by color Doppler M-mode (CMM) echocardiography can approximate actual peak transmitral pressure gradients (ΔPTM). In 14 patients undergoing open-heart surgery, ΔPTM was measured under various hemodynamic conditions using 2 high fidelity transducers, 5 cm apart. Transesophageal CMM images were simultaneously acquired and a customized image analysis application was wed to abstract spatiotemporal velocity characteristics. Using both the SEE and a simplified Bernoulli equations, ΔPTM were determined and compared to the actual ΔPTM. While the simplified Bernoulli equation resulted in a poor estimate (y=0.075x+0.71, r=0.45), the ΔPTM obtained using the SEE correlated strongly (y=0.79x+0.48, r=0.91) with the actual measurements. Semi-automated analysis of CMM images using a SEE can accurately estimate actual ΔPTM View full abstract»

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  • Semi-automatic method quantifying T wave loop morphology: relevance for assessment of heterogeneous repolarization

    Page(s): 153 - 156
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    Regional and transmural heterogeneity of repolarization is known to contribute to arrhythmogenic conditions. We aimed to develop quantitative vectocardiographic parameters describing the overall T wave loop shape but more important, measures of subtle changes in the course of T wave loop, possibly reflecting sudden changes in the repolarization wavefront. The spatial vector magnitude, elevation and azimuth angles calculated for each sample of T wave loop were used to develop two tested parameters. The ratio of maximum to mean vector (RMMV) and mean difference of elevation and azimuth (DEA). Both parameters were computed in ECGs of LQTS gene carriers and their non-carrier family members. Increased values of DEA and RMMV found in LQTS carriers may reflect increased complexity (heterogeneity) of repolarization and encourage us to further explore this computerized approach quantifying T wave loop complexity View full abstract»

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