Modelling developmental changes of human cardiac electric field in early postnatal period.

In early postnatal life, human cardiac electric field undergoes dramatic changes resulting from the adaptation of the heart to new hemodynamic conditions. For the study of the effect of changes in ventricular geometry as well as in spatial orientation of the heart occurring in this period of life, on the resultant heart vectors, our computer model of propagated activation was used. This model allows to change both mentioned characteristics of ventricles so that they reflect the developmental changes in the human heart. The pattern of activation of the model of newborn heart, characterized by equal thicknesses of the left and right ventricular walls as well as by the planar shape of the septum, showed that the resulting electrical forces were oriented anteriorly, slightly to the right, with clockwise rotation of the cardiac vectorgram in the horizontal plane projection. The gradual increase of the left ventricular wall thickness shifted the cardiac vector loop gradually to the left and anteriorly. When the ratio of the left to right ventricular wall thickness was the same as in adult human heart, the cardiac vector loop was oriented posteriorly, to the left and inferiorly. The left orientation of the initial cardiac vectors, commonly observed in 50% of full-term babies until 24 hrs of life, could be achieved only by the rotation of the heart around its long axis and/or by change of the azimuth of this axis. The simulated cardiac vectorgrams followed the typical early postnatal evolution of the vectorcardiograms of human newborns. (Fig. 4, Ref. 9.)