Longitudinal study of cardiac electrical activity in anesthetized guinea pigs by contactless magnetocardiography.

Guinea pigs (GPs) are used for preclinical evaluation of electrophysiologic effects of new drugs, because their myocytes have human-like action potentials and ventricular repolarization's (VR) ion currents. This study was aimed to assess the reliability of magnetocardiographic (MCG) mapping for longitudinal studies of GP cardiac electrical activity. Eighteen anesthetized GPs were investigated with an unshielded 36-channel MCG instrumentation, at the age of 5 months (268.1 +/- 19 g). Twelve GPs survived and were restudied when 14 months old (595.6 +/- 90.5 g). RR, PR, QRS, QT(peak), QT(end), JT(peak), JT(end) and T(peak-end) intervals were measured from MCG waveforms. Magnetic field (MF) maps, equivalent current dipole (ECD) parameters and current density imaging were also analyzed. A significant prolongation of the PR (p < 0.05) and QRS (p < 0.001) intervals was found at 14 months. Gender-related differences of VR intervals were not significant. P(peak) and QRS(peak) MFs were similar in all animals, while T(peak) MF varied interindividually at 5 months and showed a rotation in some animals, at 14 months. The ECD strengths, measured at the P(peak), QRS(peak) and T(peak) were stronger (p < 0.01) at the age of 14 months than at 5 months. In contrast to findings in Wistar rats, age-related and gender-related differences of MCG VR parameters were not significant in GPs. Further work is necessary to clarify the variability of VR MF observed in healthy GPs.