The spatial vectorcardiogram and mean spatial ventricular gradient in normal pregnant women.

The spatial vectorcardiogram and the spatial ventricular gradient of normal subjects in the last trimester of pregnancy and in some of the same subjects following delivery have been studied. It was found that the vectorcardiograms could be divided into two groups on the basis of the form of the QRS sfi-loops, as has been previously reported for other normal subjects. In some instances records taken after delivery or records taken during pregnancy with the subject in deep inspiration altered both the orientation and the form of the QRS se-loop. Since these alterations were most likely due to changes in position of the heart and extracardiac tissues, it is suggested that these are factors determining the configurations of the two types of normal QRS se-loops. B ECAUSE of the importance of cardiac position in determining the form of the electrocardiogram and the vectorcardi-ogram and because of the difficulty of interpreting the electrocardiogram with a large Q wave in lead III, it was considered worthwhile to investigate the spatial vectorcardiogram and the spatial ventricular gradient in subjects during the eighth and ninth months of pregnancy and following delivery. In a previous study of normal subjects it was found that the spatial vectorcardiogram varied considerably in its spatial orientation and that these variations largely accounted for the marked variations in contour of the plane projections of normal vectorcardiograms.1 In that study it was not possible to evaluate adequately the effect of cardiac position on the orientation or contour of the vectorcardiogram. The present study was undertaken because it was thought that the changes in the vectorcardi-ogram which occurred with changes in cardiac position during pregnancy and following de-381 livery might assist in a better understanding of the relation of cardiac position and the vectorcardiogram. It had been observed in the study of normal subjects that normal vector-cardiograms could be divided into two groups on the basis of the configuration of the QRS sJt-loops.' Since the differences between the two types of QRS st~-loops might be the result of differences in heart position as well as differences in electrical conductivity of the tissues surrounding the heart and differences in the order of depolarization, studies during and after pregnancy might elucidate the role of the first of these three factors in determining the configuration of the spatial vectorcardiogram. METHODS AND MATERIALS Details of the apparatus and methods of recording the spatial vectorcardiogram have been described …