Multichannel magnetocardiography in unshielded hospital laboratory

Multichannel Magnetocardiography (MMCG), a contactless method for non-invasive imaging of cardiac electrophysiology, was so far possible in shielded rooms only. We tested a novel MMCG system in our unshielded EP cathlab. Method: The 9 channels DC-SQUID MMCG system (CMI, USA) measures cardiac magnetic field (z-component) from a 20 x 20 cm grid. Sensitivity is 20 fT/Hz1/2 at 1 Hz. Signals (BW 0-100 Hz) are digitized (22 bits) at 1 KHz. Postprocessing includes: digital filtering, averaging, isofield mapping, source localization, analysis of HRV, fragmentation and QT dispersion. 100 MCG studies were performed: 20 in a phantom (reproducibility test) and 80 in 67 patients (pts): 15 normals, 10 with CAD, 20 with atrial or ventricular arrhythmias and 22 with WPW syndrome. Results: MMCG sensitivity in the EP cathlab, 20 fT/Hz1/2, provides quasi real time imaging and source localization. Averaging is necessary for atrial studies. The localization reproducibility is within a 3D uncertainty of 0.73 mm. Conclusion: MMCG is reliable, in unshielded EP cathlab, for both fast screening of ambulatory pts and investigation of critical pts. Localization accuracy is good enough for the localization of arrhythmogenic substrates and to guide EP intervention