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

Being a contactless method, multi-site magnetocardiographic (MCG) mapping is ideal for non-invasive study of experimental animals electrophysiology. Since Guinea pigs (GPs) are non aggressive, it is possible to study them also in the unrestrained conscious state Our aim was to assess the feasibility and reliability of MCG mapping, for the measurement of cardiac intervals and quantitative estimate of other MCG VR parameters in the awake (Aw) GP, taking into account possible gender-related differences, and in comparison with MCG recordings of the same animals under anesthesia (An). Methods: 12 adult GPs (6 males and 6 females) were investigated with the same unshielded 36-channel MCG instrumentation used for clinical recordings. Two sets of measurements were performed from each animal, at the age of 14 months (weight: 516.8 ± 180 gr): 1) awake, in natural prone posture and 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. Results: The average interval durations, measured in the two sessions, were RR 250± 50 (Aw) 230±50 (An); PR: 60±7 (Aw), 58±6 (An); QRS: 21.2±1.3 (Aw) 223.6±2.4 (An); QTpeak: 239±24(Aw), 235±26 (An); QTend: 270±25 (Aw) 280±21 (An); JTpeak: 195±23 (Aw), 195±36 (An); JTend: 225±23 (Aw), 239±33 (An); Tpeak-end: 30±8(Aw), 44±10 (An). 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. Conclusions: MCG mapping is reliable for the assessment of cardiac intervals and VR, in the awake as in the anaesthetized GPs. No gender-related differences of VR parameters were observed between the two recording settings. In GP MCG mapping doesn’t require anesthesia and can be repeated multiple times, for circadian or long-term longitudinal pharmacological studies