Magnetocardiographic estimate of cardiac intervals in guinea pigs. Comparison between conscious and anesthetized conditions.

The aim of this study was to assess the feasibility and reliability of Magnetocardiographic mapping (MCG), for the measurement of cardiac intervals and quantitative estimate of other MCG ventricular repolarization (VR) parameters, in unrestrained conscious Guinea pigs (GPs), taking into account possible gender-related differences, and in comparison with MCG of the same animals under anesthesia. 12 adult GPs (6 males and 6 females) were investigated with an unshielded 36-channel MCG system. Two sets of measurements were performed from each animal, at the age of 14 months: 1) awake (prone posture), 2) under anesthesia (supine). RR, PR, QRS, QTpeak, QTend, JTpeak, JTend and Tpeak-end intervals were measured. MCG imaging and quantitative analysis were automatically obtained as magnetic field maps (MFMs) and with the Equivalent Current Dipole (ECD) inverse solutions. As concerns interval durations, measured in the two sessions, a statistically significant difference was found only for the Tpeak-end interval. No gender-related differences of VR intervals were observed. Although MFMs were different as a function of the posture, the ECD localization at the QRSpeak, was properly centered in the heart and coincided within a 3-D uncertainty of less that 10 mm. MCG mapping is reliable for the assessment of cardiac intervals and VR, both in awake and in anaesthetized GPs. In non-aggressive rodents, MCG mapping does not require anesthesia and can be repeated multiple times, for circadian or long-term longitudinal pharmacological studies.