36-channel magnetocardiographic study of patients with coronary artery disease in an unshielded intensive care unit

Multichannel Magnetocardiography (MMCG) is a contactless technique, which has been proposed for non-invasive study of patients (pts) with exercise-induced myocardial ischemia (Hänninen et al: A.N.E.2000). So far MMCG studies of pts with coronary artery disease (CAD) had been carried out in magnetically shielded rooms only. This has allowed the definition of MCG parameters diagnostic for myocardial ischemia and the development of better imaging procedures, but constrained its clinical use to experimental investigation of a limited number of pts with CAD, because of the high cost and unfavorable location of MMCG instrumentation. We have recently installed the first 36-channel instrumentation for MMCG, reliable in an unshielded hospital unit equipped for intensive care and cardiac catheterization. This pilot study was designed and ethically approved as a non-invasive, no-risk study, aimed to evaluate the predictive value of unshielded rest MMCG for the diagnosis of CAD, under those conditions. Method: A 36-channel DC-SQUID MMCG system (sensitivity is 20 fT/Hz1/2) (CardioMag Imaging Inc., USA) has been used. 19 patients, with CAD documented by abnormal angiography, exercise-ECG or SPECT) were investigated at rest. Magnetic field gradient orientation of the integral of the second quarter of the ST interval from the J-point (STa angle) and that of the T wave apex (Ta angle) were computed according to Hänninen et al, and compared with an automatic ST-T score analysis (ST-ASA) provided by the CMI system software. The same parameters were calculated in 18 age-matched normal subjects. Results: STa angle (180.4 ± 116) was abnormal in 11/19 pts, Ta angle (99.3 ± 109) was normal in all but 2 pts. Control parameters were 59.3 ± 27, 56.7 ± 13.9, respectively, giving a positive predictive value (PPV) of 100%, and negative predictive value (NPV) of 69.2%. ST-ASA was abnormal in 18/19 pts and in 11/18 controls (PPV: 62%, NPV:87.5%). Conclusion: MMCG in our unshielded hospital laboratory has quality good enough to detect ventricular repolarization (VR) abnormalities due chronic myocardial ischemia in CAD pts. The sensitivity and specificity of the two methods used for quantitative analysis of VR was different and affected by proper selection of the baseline. However the integration of the two methods increases both PPV and NPV to 92% and 90% respectively.