Contactless magnetocardiographic study of age- and gender-related variability of ventricular repolarization parameters in guinea pigs

Guinea pigs (GPs) are commonly used for preclinical investigation of the ability of new drugs to induce QT alterations and arrhythmias, since their myocytes have an action potential with a well-defined plateau and most of the ion currents present in humans. The aim of this study was to evaluate the accuracy of multi-site magnetocardiography (MCG) for the assessment of age-related variation of ventricular repolarization maps in GPs. Methods: 20 adult GPs (10 males and 10 females) were investigated with the same unshielded 36-channel MCG instrumentation used for clinical recordings, at the age of 5 months [weight: 268.1 ± 19 gr]. Only 12 survived until the age of 14 months [weight: 595.6 ± 90.5 gr] and were restudied. RR, PR, QRS, QTpeak, QT end, JTpeak, JT end and Tpeak-end intervals were measured from MCG waveforms. MCG imaging was automatically obtained as MF maps, and with the Equivalent Current Dipole (ECD) and Effective Magnetic Dipole inverse solutions. Results: In the 12 animals, available for longitudinal MCG evaluation, a statistically significant age-related prolongation of the QRS (p < 0.01) and of the P-R (p < 0.05) intervals was found. On the contrary, neither significant age-related variations of ventricular repolarization (VR) intervals, nor gender-related differences, were found. MF maps calculated at the peaks of the P and R waves were similar in all animals, while the MF pattern at the peak of the T-wave widely varied, at 5 months. At 14 months, the MF distribution at the Tpeak remained unchanged in some animals, but markedly changed in others, with rotation of the dipolar T-wave pattern, in the absence of variations of P and QRS MF. The strength of the ECD, measured at the peak of the P, QRS and T waves, was stronger (p<0.01), at the age of 14 months than at the age of 5 months. Conclusions: MCG is reliable for VR assessment in GP. In contrast from findings in rats, age-related changes and gender-related differences of VR parameters were not statistically significant in GPs. Further works is deserved to understand the physiological meaning of VR MF variability observed in our healthy GPs