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Alternative geometry


You can replace the default (heart and torso) geometry set built into ECGSIM by a set you constructed yourself. You will then also have to supply the corresponding transfer function, the distance matrices used to compute along the heart surface or through the myocardium (see range, and the nodes of the thorax that correspond to the standard ECG leads. You may also supply corresponding reference ECGs, and the nodes at the thorax that correspond to the Frank leads (in order to be able to display VCGs). This section of the manual describes how to incorporate you're alternative geometry data into ECGSIM, and the formats of the files involved. Examples of the files may be downloaded from www.ecgsim.org/downloadalt.html. At the time of writing, you will have to construct these files by yourself, but in the future tools may be available from www.ecgsim.org (e.g. tools to compute the transfer matrix and the distance matrices) .

Loading alternative geometry data into ECGSIM

In order to load the alternative geometry data in ECGSIM, you must specify the file names in the command line by starting ECGSIM in the following way:

ecgsim -alt TransferFile SourceFile heartFile SurfDistFile VolDistFile ThoraxFile StdLeadsFile LungsFile

file format description
TransferFile matrix contains the MCG transfer matrix
SourceFile matrix contains initials source parameters
heartFile geometry contains the triangulated heart
SurfDistFile matrix contains the distance between nodes at the heart measured along the surface of the myocardium
VolDistFile matrix contains the distance between nodes at the heart measured through the myocardium
ThoraxFile geometry contains the triangulated torso
StdLeadsFile see below contains
LungsFile geometry contains the triangulated lungs (may be omitted)

When using the -alt option, you also want to use the -ref option in order to supply an appropriate reference ECG (see below).

Examples of the various files may be downloaded from www.ecgsim.org.

Starting ECGSIM with an alternative reference ECG

In order to start ECGSIM with an alternative reference ECG, you must specify the file name of the reference ecg in the command line in the following way:

ecgsim -ref ReferenceFile

ReferenceFile is the name of the file containing the reference ECG. Its format is the standard matrix format (as used by ECGSIM in saving surface potentials). Each row represents the ECG as a function of time at the corresponding vertex of the thorax. Consequently, the number of rows must match the number of vertices of the thorax.

In the unix version you may just type the command line as described above. In the Windows version you must include the -alt command line option in a short-cut by which ECGSIM is started. For that purpose, right-click on the short-cut, and add the -alt option and its parameters to the command line (after ecgsim.exe). You may want to create a separate short-cut for this purpose. If you don't give the full path of the files, ECGSIM will look for them in the "start in" folder defined in the short-cut.

Format of "Standard Leads" files

A "Standard Leads" file must have the following format:

1 v(1)
2 v(2)
. .
. .
8 v(8)

v(1) to v(6) indicate the index of the vertex at the thorax at which v1 to v6 are located. v(7) indicates the vertex to which VR is assigned, and v(8) the vertex to which VL is assigned (usually the tip op the right and left shoulder respectively).

aVR and aVL are constructed by multiplying the potential at v(7) and v(8) by 1.5. aVF is constructed as follows: aVF=-aVR-aVL (note that this assumes the transfer matrix is referenced to Wilson Central Terminal).

The potential at lead I is constructed by taking the potential at v(8) minus the one at v(7). Leads II and III are constructed in a simular fashion.