Accessory Pathways Localization with ECG Algorithms under Pacing-Induced Preexcitation versus Multichannel Magnetocardiography at Rest

Since 1984, single or multichannel magnetocardiographic mapping (MMCG) has been used for 3D localization of accessory pathways (APs). We had recently demonstrated that MMCG classification of ventricular preexcitation (VPX) is more accurate that obtained with ECG algorithms [1]. In this study we have compared the localization of VPX, obtained with 12-lead ECG algorithms, applied not only at rest, but also during pacing-induced maximal VPX, with that based on rest MMCG. Method: MMCG was carried out either with a 9-channel system or, more recently with a 36-channel DC-SQUID system. Both systems had the same sensitivity (20 fT/Hz) and recorded the z component of magnetic cardiac field from a 36-point grid (20 x 20 cm). (CardioMag Imaging Inc., USA). The only difference was that the time required to complete mapping was 6 minutes and 90 seconds respectively. 29 patients (pts) with Wolff-Parkinson-White syndrome (WPW) were investigated, at least twice to test for the reproducibility. In 6 pts, the reproducibility was also evaluated with the two MMCG systems. The Equivalent current dipole, Effective Magnetic Dipole and Currents Reconstruction models were used for VPX localization with MMCG. For ECG classification of VPX five most recent algorithms were used [see references in 1]. Results: According to ECG algorithms: a) in basal condition, the localization of the APs was certain in 15/29 (51.7%), uncertain in 10/29 (34.4%) and unreliable in 4/29 (13.7%); b) during pacing, ECG localization was certain in 22/29 (75.8%), uncertain in 3/29 (10.3%) and unreliable in 4/29 (13.7%). MMCG localization of VPX was certain in 26/29 (89.6%) and suggested dual APs in remaining 3/29 with complex patterns. MMCG was in agreement with basal ECG in 20/29 (68.9%), and with paced-ECG in 22/29 pts (75.8%). In the remaining 7/29 pts, with conflicting results between the different ECG algorithms, MMCG provided a clear-cut VPX localization (4/7) (Figure 1), or suggested dual APs, not predictable at the ECG (3/29). Conclusion: This study confirmed that the localization of VPX with ECG algorithms, improves when the procedure is applied on ECG with pacing-induced maximal preexcitation. Moreover it demonstrated that non-invasive classification of VPX obtained with MMCG at rest, is even more accurate. Furthermore MMCG provides additional identification of complex activation patterns during the delta wave, in which a mismatch between basal and pacing-ECG is more likely, and suggested the presence of multiple APs, unpredictable at the ECG.