Backgrounds, possible views and options in custo diagnostic
Introduction
The ECG provides the experienced user with important information at a glance. The ST segment is an important indicator, as deviations from the isoelectric line, no matter if upward or downward, can give clues as to serious cardiac diseases. It is not always about a myocardial infarction criterion, but anomalies of ST segment deviation must be ascertained in any case. The present custo diagnostic news gives you an overview of the options provided by custo diagnostic.
Background information - What is the ST segment?
Regarding the ST segment it provides significant information for ECG assessment. From an electrophysiologic view, the ST segment represents the phase in which the ventricular contractions are completely terminated, and repolarization begins (see fig. 1).
The ST segment begins with the end of the S wave (deflection) or if this lacks, at the point where the downward branch of the R wave ends (J point). After a more or less short isoelectric interval, the ST segment passes into the T wave. The isoelectric ST segment may also be missing completely, particularly when the QT interval duration is relatively short (e. g. with high heart rates). For measuring the dimension of the ST segment deviation from the isoelectric line (ST segment depression or elevation), the J point is the reference point (see fig. 2). There are no normal values for the duration of the ST segment [5].
Normal ST segments have the following characteristics:
- Progression within a range between -0.05 mV and +0.1 mV in parallel with the isoelectric line,
- right-precordial elevations up to 0.2 to 0.3 mV can be normal, if the T wave is positive [5].
The ST segment shows the phase in which all cells of the ventricle are completely depolarized. Normally no potential can be recorded here, and an isoelectric line is generated in the ECG [3a]. It provides a number of physiological and pathological variants and is influenced by numerous factors.
Figure 1 Segments and intervals in the ECG Figure 2 Excitation lead and ECG curve [1]
Beside the ST segment, T wave changes are important aspects in the ECG as well.
The T wave shows the repolarization of the ventricles. Compared to depolarization, repolarization is subject to a reverse polarity and direction of the excitation flow, and this is why the vector of the T wave is physiologically in concordance with the main vector of the QRS complex [4]. This means: If the QRS complex is positive, the T waves will be positive as well (in I, II, III, aVL, aVF, V2 to V6).
Measurement and change of the ST segment
A normal or physiological ST segment is shown as a straight line in the ECG. In order to determine this line, the J point is defined. The J point is the point in which the QRS complex ends and the ST segment begins. The second measurement point is usually created 60-80 ms later, but it can also be set in dependence of heart rate or be fixed to another value. (see fig. 3).
Figure 3 The J point [3]
ST segments that deviate considerably from the isoelectric line, which means above (ST segment elevation) or below (ST segment depression) and whose progression is ascending or descending, have to be assessed as conspicuous or even pathologic.
Shapes of ST segment depression
If the second measurement point lies closer to the isoelectric line than the first one, the ST segment is ascending. If both measurement points are situated on the same height below the isoelectric line, the ST segment is horizontally depressed. As a third possibility, the second point can be lower than the first measurement point, the ST segment is thus descending. An elevation or depression of the ST segment above or below the level of the isoelectric line is pathologic in most cases. As far as the ST elevation is concerned, a difference is made whether it has its origin in the descending R or the ascending S.
An ST depression is typically observed with myocardial ischemia. However, it may also have a number of other, partly unspecific causes [4].
Figure 4 ST segment depressions [3a]
Shapes of ST segment elevation
Figure 5 ST segment elevation [3b]
Implementation in custo diagnostic – Views and options
During the recording
Select Trend during the current stress ECG:
There, ST can be selected.
View of the ST values of the current situation with changes compared to resting state. The ST segment can be calculated with a fix value depending on HR (e.g. J + 60ms).
Click on ST a second time and the ST changes will be displayed graphically:
The third click on ST shows you the ST segment changes numerically, compared to resting state:
Now click on QRS: ST changes in comparison to resting state are displayed as ECG:
- Click on "Resting": The resting ECG is
- Click on "Zero": The baseline (isoelectric line) is
- With a second click on QRS, a second ECG channel can be used for the ST change
After the recording/ During the evaluation
ST shows the trend of ST changes graphically in mV. Each lead can be easily selected or deselected by clicking:
Click on ST once again and the ST changes are displayed per channel, the third click is to change from the precordial to the limb leads:
With a click on Measurement, the view changes to the summary complexes with information about the changes of ST segments:
For each Load stage a Table of the ST segment can be viewed (click on Measured values):
Stepwise comparison of ST changes (Click on stage comparison from screen Measurement):
With a right mouse click, the Context menu opens
Settings
In menu item Settings for the stress ECG: here you could select if you want to see a fix channel for ST or the channel with the largest deviation.
Do you want to have the ST values displayed in the ECG? If yes, check "ST values" and decide whether you want to have the ST values only, or with J point or with ST elevation.
Conclusion
Changes in the progression of ST segments provide the medical expert with important diagnostic information. In the resting ECG, the ST segment indicates acute or infarction events that occurred long before. In the stress ECG, ST segment changes can be suggestive of ischemia, which means shortages in the supply of the heart. Here we have to consider that a reliable evaluation must be exclusively in the hands of a medical expert, as the J point is situated on the height of the isoelectric line in resting state. With stress however, the J point is lowered physiologically and originating from this point ascending ST segments will develop. A characteristic sign of a clearly stress-dependent ischemia is the ST depression in the left-precordial chest leads. custo diagnostic thus offers multiple option of identifying ST segment deviations and of quantifying their scope. It consequently makes an important contribution to diagnosis and therapy.
Literature
[1] Stimpel, M. (2018). Leben mit Herzerkrankungen. Wenn die Seele mitleidet. Abb. 2.2 S. 12 Deutschland: Springer-Verlag GmbH.
[2] Fikenzer, S. (2009): Physiologische Ursachen für das Verhalten belastungs-spezifischer EKG Charakteristika im Vergleich zu anderen Kenngrößen der Belastung. Dissertation Universität Leipzig. 214 S. https://ul.qucosa.de/api/qucosa%3A10766/attachment/ATT-0/ 22.7.2020.
[3] Kleindienst, R. (o. J.). Veränderung der ST-Strecke 1. http://www.grundkurs-ekg.de/st/st1.htm 27.07.2020
[3a] Kleindienst, R. (o. J.). Veränderung der ST-Strecke 2. http://www.grundkurs-ekg.de/st/st2.htm 20.07.2020.
[3b] Kleindienst, R. (o. J.). Veränderung der ST-Strecke 3. http://www.grundkurs-ekg.de/st/st3.htm 20.07.2020
[4] Steffel, J.; Lüscher, T. F. (2011). Herz-Kreislauf. Heidelgberg: Springer Medizin Verlag.
[5] Rautaharju, P.; Surawicz, B.; Gettes, L. (2009). AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram. https://www.ahajournals.org/doi/full/10.1161/circulationaha.108.191096 21.07.2020.
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