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The ECGI Procedure

RT

AT
Electrode
Strips or Vest

Figure 5.1. Block diagram of the Electrocardiographic Imaging (ECGI) procedure. Body surface
potentials are recorded with 250 electrodes. Heart-torso geometry is obtained through a CT or
MRI scan. The ECGI software combines the potentials and geometry to compute epicardial
potentials every millisecond. From these, epicardial electrograms, activation isochrones and
repolarization patterns are obtained. AT: activation time; RT: recovery time; ARI: activation-recovery
interval ARI = RT – AT. Adapted from Ramanathan et. al [278], courtesy of Springer Nature.

5.2 Testing and Validation of ECGI

The accuracy of ECGI depends strongly on the exact methodology used and details of its
execution. Therefore, the results of the many studies summarized below apply to the method and

details of its application in the Rudy lab; they cannot be extrapolated and generalized to other
laboratories. Moreover, even for the same general approach (for example, the Boundary Element
Method with Tikhonov Zero Order regularization), results depend on details such as measurement
noise, signal conditioning (removal of baseline drift; filtering), values of regularization parameter,
accuracy and resolution of segmentation and meshing of the heart and torso surfaces, and more.

Consequently, one can evaluate accuracy of the ECGI procedure within the same lab, but
comparison between labs and generalization of results is limited. This document summarizes
many validation studies of ECGI as implemented and practiced in the Rudy lab over many years.

Validation in Torso-Tank Experiments:

The torso-tank setup consists of an accurate human-shaped torso, with a beating dog heart
placed in the correct anatomical position for human. It allows for precisely controlled experiments.

In these experiments, body surface potentials and epicardial potentials over the entire heart are
recorded simultaneously. The body surface potentials provide the input for the ECGI