Clinical application of magnetocardiography.

Magnetocardiography is a noninvasive contactless method to measure the magnetic field generated by the same ionic currents that create the electrocardiogram. The time course of magnetocardiographic and electrocardiographic signals are similar. However, compared with surface potential recordings, multichannel magnetocardiographic mapping (MMCG) is a faster and contactless method for 3D imaging and localization of cardiac electrophysiologic phenomena with higher spatial and temporal resolution. For more than a decade, MMCG has been mostly confined to magnetically shielded rooms and considered to be at most an interesting matter for research activity. Nevertheless, an increasing number of papers have documented that magnetocardiography can also be useful to improve diagnostic accuracy. Most recently, the development of standardized instrumentations for unshielded MMCG, and its ease of use and reliability even in emergency rooms has triggered a new interest from clinicians for magnetocardiography, leading to several new installations of unshielded systems worldwide. In this review, clinical applications of magnetocardiography are summarized, focusing on major milestones, recent results of multicenter clinical trials and indicators of future developments.

Multichannel mapping of fetal magnetocardiogram in an unshielded hospital setting.

OBJECTIVES: To evaluate the feasibility of unshielded in-hospital multichannel mapping of fetal magnetocardiogram (FMCG), with a 36-channel system for standard adult magnetocardiographic (MCG) recordings, and its reliability according to the recommended standards for FMCG. METHODS: FMCG was ambulatory mapped with a 36-channel MCG system, in six normal pregnancies at different gestational ages. MCG analysis included adaptive digital filtering of 50 Hz, signal averaging, reconstruction of magnetic field distribution (MFD) and source localization. Fixed Point Independent Component Analysis algorithm (FastICA) was used to reconstruct the FMCG, separating them from maternal contamination and noise. RESULTS: The quality of FMCG recorded after the 32nd gestational week and reconstructed with FastICA was close to FMCG obtained in shielded rooms, and good enough to measure cardiac intervals and heart rate variability parameters. In two cases, reconstruction of the MFD during the QRS allowed three-dimensional localization of ventricular sources. CONCLUSIONS: A first demonstration has been given that multichannel mapping of FMCG can be performed in unshielded clinical environments, with resolution good enough for contactless assessment of fetal cardiac electrophysiology. FastICA processing on unshielded FMCG, recorded after the 32nd week, provided beat-to-beat analysis and heart rate variability assessment. Further work is needed to improve signal reconstruction in early pregnancy.

Contactless magnetocardiographic study of ventricular repolarization in intact Wistar rats: evidence of gender-related differences.

INTRODUCTION: Magnetocardiographic (MCG) mapping is increasingly used for the non-invasive study of coronary artery disease (CAD), cardiomyopathy (CMP) and arrhythmias. MCG study of small animals with ischemia or CMP would provide useful experimental models for the interpretation of abnormal human patterns. The aim of this study was to assess the range of normality of MCG ventricular repolarization parameters, in intact adult rats. METHODS AND RESULTS: 10 adult Wistar rats (weight 250 - 350 grams) were investigated with a 36-channel MCG mapping instrumentation (sensitivity is 20 fT/ radical Hz, at 1 Hz), designed for clinical recordings in unshielded hospital laboratories. To assess ventricular repolarization, MCG Q-T(peak), Q-T(end), J-T(peak), J-T(end), T(peak)-T(end) intervals were measured. MCG imaging was obtained by automatic calculation of isofield contour maps, and with inverse source localization based on the Equivalent Current Dipole and Effective Magnetic Dipole models, in a semi-infinite space with homogeneous conductance. Magnetic field (MF) orientation, dynamics and stability during the J-T(end) segment were also calculated. After averaging 300 s of continuous MCG recording, the S/N ratio was good enough for reproducible reconstruction of both atrial and ventricular magnetic maps and for three-dimensional localization of the underlying cardiac generators. Clear gender-related differences in ventricular repolarization duration were found, evidenced by significantly longer Q-T(end), J-T(end) and T(peak)-T(end) intervals in females. The differences in MF orientation, and stability during the J-T(end) segment were not significant. For J-T(peak) MF dynamics, only the ratio between the strengths of the positive and negative poles was significantly lower in the female group ( p < 0.05). CONCLUSIONS: Contactless MCG recording is a novel approach, which simplifies non-invasive mapping in small animals. In normal rats, gender-related differences of ventricular repolarization parameters equivalent to those reported in previous ECG studies were demonstrated.