Magnetocardiographic differences of ventricular repolarization parameters between Wistar rats and guinea pigs

The morphology and range of duration of the action potential (AP) in normal Wistar rat's (WR) myocyte markedly differ from those of guinea pigs (GP), whose plateau (phase 2) duration is longer. Thus a clear-cut T wave can be easy defined in GP but not in WR. The aim of this study was to differentiate magnetocardiographic (MCG) ventricular repolarization (VR) parameters of healthy adult WR and GP. Methods: 10 female animals (5 Guinea pigs and 5 Wistar rats) were studied with a 36-channel MCG system (sensitivity of 20 fT/Hz1/2) and one ECG lead, in an unshielded hospital room. To assess VR, HR-corrected, JTpeak JTend, Tpeak-end and QTend, intervals were measured from both MCG waveforms. Timing was improved by MCG maps analysis. Magnetic field orientation (MFO), its dynamics (MFD) and stability (JTS) during the JT interval, were also automatically computed from MCG maps. Results: All repolarization intervals were significantly shorter in WR than in GP, except the Tpeak-end, which was longer. MFO and MFD also differed. Conclusions: MCG estimate of VR parameters, in adult WR and GP, is precise enough to evidence breed-related differences, consistent with physiological heterogeneity of duration during phases 2 and 3 of the AP, and with an higher degree of transmural dispersion of repolarization in WR.