Contactless magnetocardiographic study of ventricular repolarization in intact Wistar rats: evidence of gender-related differences.

Introduction: Magnetocardiographic (MCG) mapping is increasingly used for the non-invasive study of coronary artery disease (CAD), cardiomyopathy (CMP) and arrhythmias. MCG study of small animals with ischemia or CMP would provide useful experimental models for the interpretation of abnormal human patterns. The aim of this study was to assess the range of normality of MCG ventricular repolarization parameters, in intact adult rats.

Methods And Results: 10 adult Wistar rats (weight 250 - 350 grams) were investigated with a 36-channel MCG mapping instrumentation (sensitivity is 20 fT/ radical Hz, at 1 Hz), designed for clinical recordings in unshielded hospital laboratories. To assess ventricular repolarization, MCG Q-T(peak), Q-T(end), J-T(peak), J-T(end), T(peak)-T(end) intervals were measured. MCG imaging was obtained by automatic calculation of isofield contour maps, and with inverse source localization based on the Equivalent Current Dipole and Effective Magnetic Dipole models, in a semi-infinite space with homogeneous conductance. Magnetic field (MF) orientation, dynamics and stability during the J-T(end) segment were also calculated. After averaging 300 s of continuous MCG recording, the S/N ratio was good enough for reproducible reconstruction of both atrial and ventricular magnetic maps and for three-dimensional localization of the underlying cardiac generators. Clear gender-related differences in ventricular repolarization duration were found, evidenced by significantly longer Q-T(end), J-T(end) and T(peak)-T(end) intervals in females. The differences in MF orientation, and stability during the J-T(end) segment were not significant. For J-T(peak) MF dynamics, only the ratio between the strengths of the positive and negative poles was significantly lower in the female group ( p < 0.05).

Conclusions: Contactless MCG recording is a novel approach, which simplifies non-invasive mapping in small animals. In normal rats, gender-related differences of ventricular repolarization parameters equivalent to those reported in previous ECG studies were demonstrated.