Referential plane of the equivalent dipole of the heart in an orthogonal ECG of healthy adolescents at postural changes.

The authors studied the relation of the position of the equivalent dipole at changes in the position of the examined person to the magnitude of amplitudes of potentials registered from the chest surface at the 4th and 5th intercostal spaces (ICS). The investigated group consisted of 77 healthy boys and male adolescents aged 8.5 to 21.1 years, who were selected on the basis of a special questionnaire. The results showed that the influence of the body position on the location of the electric centre of the heart at ventricular depolarization is insignificant. The amplitudes of the QRST complex in the X and Z leads significantly decreased after the electrodes had been shifted from the plane of the 5th to the 4th ICS, in all postural situations. For clinical practice, it is possible to accept in Frank' lead system the referential plane of the 5th ICS also in recumbent patients. This conclusion applies also to the antiorthostatic position (-45 degrees head down).