Magnetocardiographic Study of Patients with Coronary Artery Disease in an Unshielded Intensive Care Unit

Multichannel Magnetocardiography (MMCG) is a contactless technique for non-invasive study of ventricular repolarization abnormalities. Previous studies of patients with coronary artery disease (CAD) had been carried out in magnetically shielded rooms only. Aims of this study were to evaluate: 1) the reliability of MMCG in an unshielded intensive care unit and 2) the feasibility of stress-Magnetocardiographic mapping, using a commercial bicycle-ergometer. Method: The MMCG system operating in our unshielded catheterization laboratory measures, with a single data acquisition, the z-component of local magnetic fields at 36 positions from a grid of 20 x 20 cm, with 36 DC-SQUID sensors coupled to second-order axial gradiometers (55/75 mm baselines). The intrinsic sensitivity of the system is 20 fT/Hz1/2 in the frequency range of 1 to 100 Hz. Signals are recorded with a Windows NT-based acquisition system (24 bits A/D conversion, 1-4 kHz sampling frequency and automatic electronic noise rejection). 27 patients with CAD and 33 healthy controls were investigated at rest. MMCG was recorded also after effort in 10 additional subjects. Typical recording time was 90 seconds. All rest studies were repeated at least twice, to test for the reproducibility. Results: Rest magnetic field distribution during the ST interval was abnormal in 97% of CAD patients and in 8% of controls. Quantitative analysis of MCG repolarization parameters, performed according to Hänninen et al. and Park et al, had sensitivity 95.2%, specificity 92.3 %, positive predictive value of 87% and negative predictive value 97%. Good quality stress MMCG was recorded, since first minute after effort, in all subjects. Conclusion: MMCG is feasible in an intensive care room, with quality good enough for non-contact real-time monitoring and imaging of time evolution of ventricular repolarization abnormalities due to myocardial ischemia. Stress-MMCG can be performed, using a commercial bicycle-ergometer and standard protocols. Being a true DC recording, MMCG is an optimal method to localize and study the arrhythmogenic effect of injury currents associated with acute ischemia