Applicability of two different lead systems in studies of the electrical activity of the hearts in newborn guinea pigs.

Recent findings of ours from vectorcardiographic studies with the anatomically orthogonal SVEC II system of Schmitt and Simonson on postnatal guinea pigs did not coincide with earlier VCG findings from preparations of isolated guinea pig hearts beating in a homogenous volume conductor. This suggested that in the guinea pig as in the human a more intricately corrected lead system ought to be used. In order to apply to guinea pigs the electrically corrected lead system proposed by Frank in 1956 for clinical use in human electrocardiography, the underlying biophysical assumptions had to be examined. The electrical center of ventricular depolarisation in the guinea pig heart was determined by measurement of cancellation potentials around the thorax and by geometrical construction of different horizontal loops of the image surface. Cancellation coefficients and ventricular dipole locations of guinea pigs of different ages proved to be in the same range as the corresponding human values. Application of the Frank lead system to guinea pigs two days old and older gave vectorcardiographic parameters which corresponded to those obtained from Langendorff heart preparations.