A reference data base for multilead electrocardiographic computer measurement programs.

In an effort to standardize and evaluate the performance of electrocardiographic computer measurement programs, a 15 lead reference library has been developed based on simultaneously recorded standard 12 lead and orthogonal XYZ lead data. A set of 250 electrocardiograms (ECGs) with selected abnormalities was analyzed by a group of five referee cardiologists and 11 different 12 lead and 6 XYZ computer programs. Attention was focused on the exact determination of the onsets and offsets of P, QRS and T waves. The referees performed their task on highly amplified, selected complexes from the library in a two round process. Median results of the referees coincided best with the median derived from all programs. An analysis of stability proved that the combined program median was a robust reference. However, some individual program results were widely divergent. Paired t tests demonstrated earlier onset for P and QRS (p less than 0.001), as well as later offset for P and T waves in the median 12 lead than in the XYZ results. Significant differences also existed among results obtained by programs analyzing all standard ECG leads at one time, the so-called multilead programs, and those obtained by the conventional standard three lead analysis programs. As a consequence, the derived P, PR, QRS and QT interval measurements varied quite widely among the various programs. Significant differences were also observed among measurements of Q, R and S duration. Some programs showed Q waves that were on the average 6 ms (p less than 0.001) longer than those of others. This may significantly influence diagnostic performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of a reference library for multi-lead ECG measurement programs.

The development of a data base is described which can be used as common reference for ECG computer programs analyzing 12 or 15 simultaneously recorded leads. This data base is an extension of the 3-lead CSE reference library, described previously.

Establishment of a reference library for evaluating computer ECG measurement programs.

As a result of an international cooperative project entitled "Common Standards for Quantitative Electrocardiography" (CSE), an ECG reference data base has been established with the aim of standardizing computer-derived ECG measurements. The objective of the project is to reduce the wide variation in wave measurements currently obtained by ECG analysis programs. A library of 250 ECGs with selective ECG abnormalities was established and a comprehensive reviewing scheme was devised for the visual determination of the onsets and offsets of P, QRS, and T. This task was performed by a board of cardiologists on highly amplified, selected complexes from the library. A subset was examined in order to study beat-to-beat and intraobserver variability. By using a modified Delphi approach, individual outlying point estimates were eliminated in four successive rounds. In this way final referee estimates were obtained which proved to be highly reproducible and precise. A reference library has thereby been developed which allows testing of the performance of ECG measurement programs and is a useful instrument in establishing recommendations for more precise measurement rules and definitions.

Assessment of the performance of electrocardiographic computer programs with the use of a reference data base.

To allow an exchange of measurements and criteria between different electrocardiographic (ECG) computer programs, an international cooperative project has been initiated aimed at standardization of computer-derived ECG measurements. To this end an ECG reference library of 250 ECGs with selected abnormalities was established and a comprehensive reviewing scheme was devised for the visual determination of the onsets and offsets of P, QRS, and T waves. This task was performed by a group of cardiologists on highly amplified, selected complexes from the library of ECGs. With use of a modified Delphi approach, individual outlying point estimates were eliminated in four successive rounds. In this way final referee estimates were obtained that proved to be highly reproducible and precise. This reference data base was used to study measurement results obtained with nine vectorcardiographic and 10 standard 12-lead ECG analysis programs. The medians of program determinations of P, QRS, and T wave onsets and offsets were close to the final referee estimates. However, an important variability could be demonstrated between measurements from individual programs and mean differences from the referee estimates amounted to 10 msec for QRS for certain programs. In addition, the variances of all programs with respect to the referee point estimates were variable. Some programs proved to be more accurate and stable when the data from high- vs low-noise recordings were analyzed. Average Q wave durations calculated from ECGs for which programs agreed on the presence of a Q or QS wave differed by more than 8 msec in several program-to-program comparisons. Such differences may have important consequences with respect to diagnostic performance. Various factors that might explain these differences have been determined. The present study demonstrates that to allow an exchange of results and diagnostic criteria between different ECG computer programs, definitions, minimum wave requirements, and measurement procedures urgently need to be standardized.

Oxygen tension measurement using an automatic blood gas analyser.

Two different methods of assessing the reliability of the oxygen electrode of one model of an automatic blood gas analyser (BGA) have been studied. In the first, a single automatic BGA was assessed by using outdated bank blood which was pumped around a small extracorporeal circuit into which known gas mixtures were passed. Oxygen tension was varied between 2 and 16 kPa. In the second, fresh heparinized blood was tonometered with calibrated gases and submitted to the automatic BGA used in the first part of the study and also to three other identical machines. Each of the machines was between 3 and 4 years old.Eighteen different units of blood were used in the first part of the study. The correlation coefficient between the automatic BGA and the Po(2) in the extracorporeal circuit varied between 0.29 and 0.99. 31% of the total of 209 measurements made by the automatic BGA were more than 1.2 kPa from the reference value, 25% of them being between 1.2 and 4.0 kPa from the reference value. In the second part of the study, the correlation coefficient between this automatic BGA and the tonometered blood was 0.96. The correlation coefficients for the 3 other identical BGAs were 0.84, 0.97 and 0.88, indicating that the BGA used in the first part of the study was no worse than any of the others.It is suggested that although clinicians are likely to ignore readings of an automatic BGA that are more than 4.0 kPa from the true value and are likely to repeat the investigation, readings between 1.2 and 4.0 kPa from the true value may adversely affect patient management.

Clinicians, the Mount Sinai program and the Veterans' Administration program evaluated against clinico-pathological data derived independently of the electrocardiogram.

221 electrocardiograms (ECGs) recorded from adult subjects with cardiac symptomatology were interpreted by clinicians and the Mount Sinai (MS) and Veterans' Administration (VA) computer programs. After the clinicians had eliminated their interobserver variability, their interpretations and those of the computer programs were compared with the corresponding clinico-pathological data that had been derived independently of the ECG. A measure of overall diagnostic accuracy was used which showed that the performance of the 2 computer programs was similar and somewhat worse than that of the clinicians. The clinicians and the computer programs were not as good at diagnosing the ECGs of women as at diagnosing those of men. As the VA program's interpretations may be altered by including information about the patient's provisional diagnosis, 6 different sets of these prior probabilities were used to analyse 141 of the original 221 ECGs. Different fixed sets of prior probabilities made only a small difference to overall diagnostic accuracy but a marked difference to the VA program's ability to differentiate Normal from Abnormal. Optimizing the prior probabilities for the individual subjects increased the VA program's overall diagnostic accuracy up to that of the clinicians. Both computer programs correctly diagnosed sinus rhythm as the dominant rhythm in 165 out of 177 subjects. The MS program diagnosed the dominant rhythm as Atrial Fibrillation in 35 out of 41 subjects and the VA program in 27 (X(2) = 3.24; not significant). ECG interpretation; Mount Sinai program; Veterans' Administration program; independent clinico-pathological data; sex differences in the ECG; prior probabilities.

Electrocardiography: right ventricular hypertrophy.

Not only is RVH difficult to diagnose electrocardiographically but it is frequently mimicked by true posterior infarction. The R/S-amplitude ratio in lead V1 and the S wave in lead V5 are the most useful indices of RVH. The ECG in chronic lung disease can be distinguished from that in RVH and is more often confused with that of anterior infarction. The ECG changes found in pulmonary embolism are the same as those found in RVH but they are transient; they are more easily interpreted by means of serial ECGs. In conjunction with clinical data the ECG can be used to predict the severity of pulmonary valve stenosis.