High resolution magnetocardiography for the study of dynamic propagation of excitation sites in rat cardiac muscles

The authors have developed a multichannel high-resolution SQUID magnetometer for measuring biomagnetic fields produced by small animals. Using this system, they measured the magnetocardiogram (MCG) of rats. The specifications of the authors´ system were as follows: pickup coils 5 mm in diameter located on a 7.5-mm grid, a 15-mm gradiometer baseline, a one-turn pickup coil with a distance of 5 mm between the pickup coil and the outside surface of the dewar. The field sensitivity was 100-fT/√Hz in the white noise frequency. Five adult rats, ranging in weight from 0.2-0.4 kg were used in the study. Rats were anesthetized intraperitoneally with Nembutal (40 mg/1 kg). Averaging of the magnetocardiogram signals was performed over 2000 cardiac cycles. Existing sites of cardiac muscles were analyzed by minimum norm estimation of MCG. Current sources corresponding to electric activities on the atrium and ventricle of rats were estimated