Background. In concurrence of our recent findings of the elevation of QT dispersion (QTd) in the group of pregnant
women, mathematical approaches were developed aimed to give possible geometrical explanation whether the
observed changes result from the rotation or from the changed position of the heart.
Methods and Results. Mathematical model of the cardiac electrical field approximated as a time variable dipole in
a homogenous spatial conductor was developed. From the experimental vectocardiographic records, representing
time course of the cardiac dipole, body surface potential maps were calculated on the basis of the model. To validate
the adequacy of the model, the reconstructed electrocardiograms were compared with the empiric data. To determine
the effects of rotation, original empiric VCG data of the control group were transformed accordingly the hypothetic
pregnancy related changes. Calculated surface electrocardiograms were then compared with empiric cardiograms
of the pregnant women.
Conclusions. Based on the results, several conclusions can be drawn: 1) QT dispersion is associated also with the
geometrical relations between the direction of cardiac vector during the terminal phase of repolarization and the
direction of axes in the given system of leads. The dispersion then has its typical occurrence at the thoracic surface
– minimums of the QT duration are found in the plane perpendicular to the axis of the terminal vector lead. 2) When
the duration of repolarization is estimated from the classic thoracic leads within the phisiological variations of
terminal–depolarization vector orientations, can exist that in some cases the minimum of QT interval is and in others
it is not recorded by the lead system. Value of QT dispersion between these two extremes will be significantly
different. 3) In case of the horizontal declination of the heart, the ECG signal in most of the leads of the body surface
mapping has a higher voltage than in case of vertical declination due to a smaller angle between axes of the terminal
vector and most of the leads. Such factwill contribute tomore accurate reading of the T wave end and to the estimation
of QT interval, usually with smaller value of QTd. 4) The change of the cardiac electrical field corresponding to the
changed position of the heart (rotation) does not result by itself in QTd changes, if it is evaluated from the records
from the whole thorax. Obversely, horizontalization of the heart contributes more to the evaluation of lower QTd
values, as it is given above. 5) More then the result of geometrical changes, QT dispersion found in the group women
in high level of pregnancy is an effect of changes in the T loop morphology, which was observed in this group.
Another possible explanation of the observed dispersion is the non-dipolar character of the electrical field changes
computer models, body surface potential mapping, cardiac electrical field.