Non invasive classification and imaging of preexcitation sites by multichannel Magnetocardiography

Multichannel Magnetocardiography (MMCG), is a contactless method which can be used for non invasive localization and imaging of ventricular preexcitation (VPX) sites. Nevertheless so far MMCG studies of VPX patients (pts) had been done in magnetically shielded rooms only, which has limited the acceptance of this new method by clinicians, because of high cost and unfauvorable location of MMCG instrumentation. After positive experience with a single channel MCG mapping system we have fostered the development and recently installed the first instrumentation for MMCG operating in an unshielded hospital environment and evaluated its reliability, with the aim to use this novel method for electroanatomical imaging also in the EP catheterization laboratory. Method: A 9 channels DC-SQUID MMCG system (sensitivity is 20 fT/Hz1/2) (CardioMag Imaging Inc., USA) has been used. Equivalent current dipole (ECD) and magnetic dipole (MD) models in semi-infinite space were used in the inverse calculations and 3D localization of VPX. A distributed currents model (CDI) was also used as alternative imaging procedure. Localization results were also transferred on patients MRI images. 22 WPW pts have been investigated, at least twice , to test for reproducibility, mapping 36 points from the anterior chest wall (measuring grid 20 x 20 cm). In 14 pts the second procedure was carried out on the same day, in 12 MMCG was repeated after approximately 3 months. In 6 pts, MMCG was also repeated during transesophageal atrial pacing-induced maximal VPX and/or AV reentry tachycardia. As this one was designed and ethically approved as a non invasive study only, MMCG localization of VPX was compared with that achiavable with most recent ECG algorithms. Results: MMCG classification of VPX was in agreement with ECG in 18/22 (81.8%). In 4/22 (18%) with conflicting results, MMCG provided a clear-cut localization in all and demonstrated complex activation patters during the delta wave in 3/4. Current density reconstruction and imaging in those cases suggested multiple activation pathways, unpredictable on the basis of ECG, in 1/4. Conclusion: This study demonstrates that MMCG is possible, reproducible and reliable also in our unshielded EP catheterization laboratory. As compared to ECG, MMCG classification of VPX, especially of paraseptal and multiple pathways, is more effective because MMCG provides non invasively quasi real-time 3D electroanatomical integration and imaging of the VPX sites directly on anathomical MRI images or 3D cardiac models