ECGSIM Manual: ECGs

ECGSIM Manual

ECGs

Display properties

The ECGs pane displays ECGs. The Display properties dialog window is activated from the ECGs menu. It allows you to select which ECGs you want to display: the simulated ECGs (i.e. those that result from the transmembrane potentials at the heart as set by the user), the reference (i.e. measured) ECGs, or both. The simulated ECGs are shown in red, the simulated ones in blue. You may also choose which ECGs you want to display by pressing the corresponding tool buttons on the ECGs tool bar.

In the Display properties dialog window you may also choose whether you want to display the standard 12-lead ECG, the ECG at the node selected in the thorax pane, or the vectorcardiogram (VCG) according to the Frank lead system.

Scale

In the scale dialog window, also activated from the ECGs menu, you may set the vertical scale and select the time span you wish to display. You may also activate the scale dialog window by pressing the scale tool button on the ECGs tool bar.

Filtering

In the filtering dialog window, activated from the ECGs menu as well, you may choose the type of temporal filtering applied to the simulated ECGs. This also affects the simulated ECGs in the thorax pane.

If you choose baseline correction (the default value) the potentials at the beginning of the P wave and at the termination of the T wave will have zero potential. This is how idealized ECGs are commonly presented. If you choose AC filtering (the standard type of filtering in ECG recorders) the average of the potential over time will be zero for all leads. If you choose DC filtering the ECGs are in fact unfiltered, i.e. the true potentials are plotted.

At the body surface, no DC recording of the ECG is possible, due to the contact potentials between the skin and the electrodes. These contact potentials slowly vary in time and have magnitudes that are generally much greater than that of the ECG. The AC-coupling that is always involved in ECG recordings effectively reduces the effect of these contact potentials. However, AC-coupling also wipes out any DC component that may be generated by the heart's electric activity. This component can never by recovered. The baseline correction that is commonly involved in the analysis of the ECG tries to overcome this problem, but is only successful if no currents are generated by the heart in the interval between successive beats.

The DC option in ECGSIM allows one to study the effect of the AC and baseline coupling of ECG amplifiers. The DC filtered (unfiltered) ECGs are seen to differ from the baseline corrected ECGs if of regions of reduced action potential amplitude (ischemia) are present. Where in baseline corrected ECGs ischemia leads to ST elevation , the actual (DC) potentials would lead to the depression of the baseline, and vise versa. If the ST segment is much shorter than the TP interval, AC filtering results in a TP interval that is close to zero, and hence ECG recordings may look more like baseline corrected ECGs than do unfiltered ECGs.

Relation with other panes

If surface potentials are displayed in the heart or thorax panes, a vertical yellow line visible in the plots indicates the time instant for which the potentials are displayed. If you click on the left mouse button within the ECGs pane, the potentials for the corresponding time instant are displayed in the thorax pane. You may also press the up and down arrow keys to in- and decrease the time by steps of milliseconds, and the page up and page down keys for in- and decrements with steps of ten milliseconds.

The temporal filtering of the simulated ECGs in the thorax pane and those in the ECGs pane are both controlled by the values set in the filtering option of the ECGs menu.

Copying the content of the ECGs pane

The contents of the ECGs pane may be copied to the clipboard by selecting Copy from the ECGs menu, or by pressing Ctrl-C while the mouse is within the ECGs pane.