Unshielded exercise magnetocardiography. A novel method for quantitative assessment of ischemic heart disease

Magnetocardiography (MCG) is the recording of magnetic field induced by cardiac electric activity. Exercise-induced changes of MCG patterns have been demonstrated in patients (pts) with ischemic artery disease (IHD), investigated in magnetically shielded rooms and MCG has been proposed to image abnormal current flow induced by acute ischemia. We report a method to combine standard exercise-ECG with unshielded multichannel magnetocardiographic mapping in ambulatory patients. Method. 17 IHD pts, 15 with abnormal coronary angiography (stenosis > 70%), 2 with abnormal SPECT, were investigated. 21 healthy controls were also studied. MCG was performed with a DC-SQUID-based mapping system, (sensitivity of 20 fT/√Hz in the frequency range of clinical interest). MCG recordings of 90 seconds were performed before and 1, 3, 5 and 7 minutes after exercise. 12-lead ECG was continuously recorded during exercise and until 10 minutes of recovery. For ventricular repolarization (VR) assessment, the ST Magnetic Field gradient (MFG) orientation, the T-wave MF dynamics, and several quantitative parameters of the effective magnetic dipole (EMD), were automatically calculated. Results. Rest ECG was negative for ischemia in all but one pts, and became positive only in 5/17 pts (sensitivity 29%, predictive accuracy 68%). The diagnostic accuracy of MCG parameters, at rest and after exercise, are summarized in table 1. Exercise-MCG evidenced VR alterations in 11 IHD pts, with aspecific exercise-ECG.Conclusions. Unshielded MCG mapping is feasible in ambulatory pts, simultaneously with ECG, with standard ergometers protocols. As compared with ECG, MCG increases predictive accuracy for IHD, both at rest and after exercise test. Automatic analysis of ST MFG orientation, T-wave dynamics and EMD parameters evidenced VR abnormalities, not apreciable at ECG in some pts.