Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
1999-10-20
2001-07-17
Getzow, Scott M. (Department: 3737)
Surgery
Diagnostic testing
Cardiovascular
Reexamination Certificate
active
06263235
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electrocardiogram (ECG) arrangement having m (m≧2) lead channels for locating QRS complexes in an electrocardiogram and having a central logic unit.
As is known, in ECG examinations, it is becoming evermore frequent to use electrocardiogram arrangements having a plurality of lead channels which are usually fitted to the arms and legs (limb lead) and to the chest (chest lead). In the main, electrocardiogram arrangements which have twelve lead channels are available. There are, however, also electrocardiogram arrangements in which more or fewer than twelve lead channels are employed.
By way of example, for measuring heart rate or for analyzing arrhythmia, the redundancy involved with having multiple lead channels provides advantages when this redundancy is used to reduce or eliminate the effect of noise or artifacts in the result obtained using the electrocardiogram arrangement.
Previous electrocardiogram arrangements have exploited the multiple lead-channel redundancy and have collated the individual lead-channel signals by taking their first mathematical derivative. The individual mathematical derivatives are squared and then summed over all the lead channels. The square root of the result obtained in this way is then taken. The signal obtained in this way has the advantage that, compared with the individual original signals, the ratio of the useful signal component to the noise signal component is improved, which in the final analysis means that the QRS complexes can be located better.
Instead of squaring and taking the square root, sometimes only the magnitude of the signals given by the first mathematical derivative is calculated, this being followed by summing the magnitudes obtained for the individual lead channels.
In any event, with both electrocardiogram arrangements, the final result is a one-channel signal which is subjected to evaluation in relation to the QRS complexes.
The conventional electrocardiogram arrangements constructed in this way give reliable results if the level of noise is approximately the same in all the lead channels. However, if some of the lead channels have substantially stronger interference than other lead channels, which is often the case, for example, when recording a stress test electrocardiogram, it is expedient to exclude the signals from the very noisy lead channels from any subsequent processing.
SUMMARY OF THE INVENTION
To that end, there are already electrocardiogram arrangements which, although they are constructed in the manner indicated above, they only use signals from lead channels which are empirically found to have relatively few artifacts and are approximately orthogonal to one another. This is because the orthogonality of the lead-channel signals ensures that the normal QRS complexes or ventricular extrasystoles are well represented in at least one of the signals. The disadvantage with a procedure of this type is, however, that because of the requirement of evaluating mutually orthogonal signals, lead-channel signals which have stronger interference than other signals also have to be used aid, in the final analysis, an electrocardiogram arrangement constructed in this way only gives good results under certain circumstances.
It is known that, in a stress test electrocardiogram, most interference occurs in the heavy load phase. However, the heavy load phase is actually one of the most important phases of a stress test. For example, it is during this phase that the doctor decides, amongst other things, whether or not the examination should be stopped.
In order to decide whether or not the heavy load phase should be stopped, amongst other things the heart rate, the ST segment of the electrocardiogram and arrhythmia results are employed.
It is therefore very important to be able to calculate correctly the data relevant to this decision actually in the heavy load phase, in spite of the greater incidence of interference. One prerequisite for such correct calculation of the data is, however, accurate location of the QRS complexes.
The object of the present invention is therefore to provide an electrocardiogram arrangement which allows accurate location of QRS complexes even during heavy load phases.
This object is achieved according to the invention, with an electrocardiogram arrangement of the type mentioned at the start, in the following way:
n (n≦m) independent evaluation units are provided in the plurality of lead channels, each lead channel being respectively assigned at most one evaluation unit which locates the QRS complexes, classifies the events and assesses the ECG quality,
a comparator, in the central logic unit connected to the individual evaluation units, which compares with one another the ECG qualities obtained by the ECG quality assessments in the individual lead channels and identifies the lead channel obtaining the highest ECG quality as the dominant lead channel, and
a test unit, in the central logic unit, which tests the results of the event classification of the dominant lead channel and, when special events occur in the dominant lead channel, accesses other lead channels in order to correct the results of the QRS complex location and the event classification of the dominant lead channel on that basis.
REFERENCES:
patent: 4987901 (1991-01-01), Kunig
“Arrhythmia Analysis by the Louvain VCG Program,” by Christian R. Brohet, Christiane Derwael-Barchy, Robert Fesler and Lucien A. Brasseur, Computers in Cardiology, 1981, pp. 47-51.
“Multilead ECG Analysis,” by Jan A. Kors, Jan L. Talmon and Jan H. Van Bemmel, Computers and Biobedical Research 19, 1986, pp. 28-46.
Findeis Martin
Kaiser Willi
GE Marquette Hellige GmbH
Getzow Scott M.
Michael & Best & Friedrich LLP
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