Multichannel Magnetocardiography: a non–invasive tool for acute and longitudinal cardiac electrophysiologic study of experimental animals in anesthetized and awake conditions

Early identification of potential pro-arrhythmic effects of a new drug has become a goal within the drug development process. Several animal models have been used for the early detection of the so-called “Torsadogenic” risk. In order to fill the gap between animal studies in the preclinical phase of new drugs development and clinical assessment of risk indicators, it would be desirable to use the same methods and parameters. 12-lead ECG is the minimum requirement for adequate assessment of the most used risk indexes (i.e. QT/QTc interval prolongation and of its dispersion), although it has been demonstrated that body surface potential mapping (BSPM) is more sensitive than standard ECG for the evaluation of repolarization inhomogeneity. Whilst BSPM is difficult to be performed routinely in small animals, multi-site magnetocardiographic (MCG) recordings can be an alternative to simplify non-invasive cardiac electrophysiologic mapping. Compared to electric recordings, MCG mapping has several advantages: 1) it is contactless, and adequate also for the study of conscious and unrestrained animals without muscle artifacts; 2) the sensors geometry is fixed, which minimize errors in localization of intracardiac sources and of ventricular repolarization (VR) heterogeneities associated with areas of myocardial injury. Thus MCG is ideal for the study of small experimental animals. Mousses, rats and guinea pigs are the most frequently used to evaluate drug effects on VR in normal conditions and to study models of cardiomyopathy. Among them, the guinea pigs, being non aggressive, can be studied also in the unrestrained conscious state. In our laboratory MCG assessment of cardiac intervals and VR magnetic field distribution has been repeated multiple times, for circadian or long-term longitudinal taking into account possible breed- gender- and age-related differences. Finally a percutaneous method for single-catheter recording of multiple monophasic action potentials (Multi-MAP) from the epicardial surface of intact anesthetized spontaneously beathing rodents has been refined, to validate MCG estimate of VR by comparison with Multi-MAP recordings.