Forward problem of electrocardiography based on cardiac source vector orientations

Abstract

To localize the unusual cardiac activities non-invasively, one has to build a prior forward
model that relates the heart, torso, and detectors. This model has to be constructed to
mathematically relate the geometrical and functional activities of the heart. Several methods 
are available to model the prior sources in the forward problem, which results in the lead field 
matrix generation. In the conventional technique, the lead field assumed the fixed prior 
sources, and the source vector orientations were presumed to be parallel to the detector plane 
with the unit strength in all directions. However, the anomalies cannot always be expected to
occur in the same location and orientation, leading to misinterpretation and misdiagnosis. To 
overcome this, the work proposes a new forward model constructed using the VCG signals of 
the same subject. Furthermore, three transformation methods were used to extract VCG in 
constructing the time-varying lead field to steer to the orientation of the source rather than 
just reconstructing its activities in the inverse problem. In addition, the unit VCG loop of the 
acute ischemia patient was extracted to observe the changes compared to the normal subject. 
The abnormality condition was achieved by reducing the depolarization time by 15ms. The 
results involving the unit vectors of VCG demonstrated the anisotropic nature of cardiac 
source orientations, providing information about the heart's electrical activity.