Magnetocardiographic Explanation of Catheter Ablation Failure in Unexpected Complex Ventricular Preexcitation.

Non-invasive classification of ventricular preexcitation (VPX) with ECG algorithms, which reported accuracy ranges between 61 and 92% [1], is considered appropriate to plan ablation approaches. However it is not uncommon that during the EP study unexpected difficulties might arise, due to complex or multiple accessory pathways (APs). Therefore BSPM, Echocardiography and SPECT have been used to minimize the risk of failure, complications and prolonged exposure to radiation. Since 1984, Multichannel magnetocardiographic mapping (MMCG) has been used as an alternative method for non-invasive three-dimensional (3D) localization of arrhythmogenic substrates and of VPX. We recently reported that MCG classification of VPX is more accurate than that obtained with ECG and provides additional information for the localization of septal APs and the identification of multiple APs [2]. In this study we describe two cases of VPX ablation failure, whose classification, based on ECG algorithms only, had provided uncertain or misleading preoperative information. Method: A 36-channels DC SQUID MMCG system (sensitivity is 20 fT/Hz, at 1 Hz) (CMI) was used to record the z component of magnetic cardiac field from a 36-point grid (20 x 20 cm). The total time for cardiac mapping, automatic source localization and 3D imaging was typically 90 seconds. For the solution of the inverse problem and 3D MCG localization of VPX, the Equivalent Current Dipole (ECD), Effective Magnetic Dipole (EMD) and current reconstruction (CR) models were used. Results: Postoperative multimodal MCG imaging (a e b) and data fusion with MRI and 3D model of the patient's heart (c) provided clear-cut demonstration of double septal APs in case 1 (Fig. 1), classified as LPS VPX, both at the ECG and with catheter mapping. In case 2, the ECG criteria suggested a RAS VPX, confirmed by electroanatomical mapping, but masked a RL VPX, evidenced by MCG. Conclusion: The reported cases belongs to that minority of WPW patients, which still have to cope with the frustration of an unsuccessful ablation procedure, and demonstrates that 3D MMCG imaging might be useful to improve preoperative VPX classification and to avoid unsuccessful interventions.