G. Joseph

Compression and encoding of ECG data within the European standard communications protocol

The European Community has launched a project to develop a standard communications protocol for computerized electrocardiography (SCP-ECG). Within this project, compression and encoding of ECG data for transmission and storage has been investigated. A compression scheme with well-specified error limits was developed. Compression ratios for resting ECGs achieved by this method are as high as 20. The reconstruction root mean square (RMS) error can be maintained below 10 mu V. The method provides fully reproducible measurements and allows reliable visual rhythm analysis of the reconstructed ECG. For verification of errors introduced by compression and decomposition a standard test data set from the CSE database has been specified. For digital transmission a general protocol (SCP-Protocol) has been defined which allows communication between ECG carts and hospital information systems.<<ETX>>

A system for comprehensive ECG waveform and trend analysis accompanying polysomnographic sleep apnea detection

Performance of analysis algorithms for sleep apnea detection revealed that results were best when heart rate variability morphologic ECG parameters were also considered. We have therefore set up a system for simultaneous recording of 12 lead ECGs during polysomnographic data acquisition. The PC based system HES LKG has been used and its analysis and data presentation programs have been extended to handle the large data amount of 400-600 MBytes per night recording. The system has been installed at the sleep laboratory of Marburg University. Up to now 50 night recordings from 40 patients have been acquired. The ECG data are processed in 10 s data segments. Raw data and results can be stored in the standard SCP format.

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

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 /spl mu/V 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 ECGs 70% sensitivity and 97% specificity have been obtained.

A system for integrated ECG analysis and cardiac emergency care

During the past decades focus in the development of computerized medical devices was on implementation of device control and analysis programs providing measurements and decision support. Today, the focus has changed to information integration and communication. Continuing miniaturization of electronic equipment and increasing power of portable computers make possible to integrate various types of signal acquisition units (data loggers) and of sophisticated analysis software into notebook type computers. Large storage capacity as well as standardized communication interfaces allow the use of such systems in ambulatory scenarios (emergency care) or monitoring of patients at home. The system described in this paper has been particularly developed for acquisition and processing of various types of electrocardiagrams and includes a module for interactive cardiac risk assessment for decision support whether a patient should be referred to an intensive care unit.

Communication and storage of compressed resting and exercise ECGs using the revised SCP-ECG standard

Exercise ECG (XECG) testing is one of the clinical routine examinations which produces a large amount of data if full-disclosure records aree to be provided. We describe a system for XECG analysis which takes advantage of the data compression procedures and the data format of the SCP-ECG (Standard Communication Protocol for computer-assisted Electrocardiography) protocol. Processing the XECG data in consecutive 10-s data sections resulted in six SCP blocks per minute. Over a test set of 20 XECGs with various test durations, a median compression ratio of 11.1 has been achieved. We have also investigated the influence of noise on the compression ratio. 50 /spl mu/V RMS may reduce the compression ratio from /spl sim/17 to /spl sim/8.

Influence of measurement parameter changes and statistical parameter characteristics on the stability of ECG classification in HES ECG

Increasing needs-and possibilities-for serial comparison of ECG computer analysis results bring up the question of their reproducibility and stability. The authors report here results from systematic measurement manipulation experiments and corresponding changes in diagnostic statements of the HES algorithm. Adding noise or filtering the original data resulted in totally less than 4% changes in any of the diagnostic categories NOR, HYP and INF. Shifting the relevant wave onsets or offsets creates changes in diagnostic statements as well. For classification based on discriminant analysis if is demonstrated in what way classification errors depend on the distributions of discriminant values. A discriminant function becomes as steeper as larger the group mean distances are and as smaller the dispersion of the discriminant values is. Consequently small changes in some measurements will result in large changes of the discriminant value and may cause a reallocation of the case under consideration.