Unshielded Stress Multichannel Magnetocardiography of Patients with Coronary Disease and Normal Subjects with standard ergometer. Comparison with ECG.

Multichannel Magnetocardiography (MMCG) has been proposed to detect exercise-induced myocardial ischemia in patients (pts) with coronary artery disease (CAD). Previous studies were carried out in magnetically shielded rooms only, with the patient supine and pedaling a non-magnetic bicycle ergometer. Our study was aimed to test the feasibility of exercise-MMCG carried out, in an unshielded laboratory, with a commercial bicycle ergometer, simultaneously with 12-lead stress ECG. Method: A 36-channel DC-SQUID system (CMI), (sensitivity is 20 fT/Hz), was used to record the cardiac magnetic field component perpendicular to the anterior chest wall (Bz). 6 pts, with CAD, documented by coronary angiography, were investigated. 12-lead ECG was continuously recorded during exercise and until 10 minutes of recovery. MMCG of 90 seconds was performed before and 1, 3, 5, 7 and 9 minutes after exercise. Magnetic field gradient orientation of the integral of the second quarter of the ST interval from the J-point (ST  angle) and that of the T wave apex (T  angle) were computed according to Hänninen et al. (H) [1] and compared with an automatic ST-T score analysis (ST-ASA) provided by our system and used elsewhere for the detection of acute myocardial ischemia [2]. The same parameters were calculated in 7 normal control subjects. Results: At rest, ST  angle was: 121.4° ± 80.6° in pts and 63.8° ± 16.4° in controls (p: n.s.). Within the first 2 minutes after exercise, ST angle was: 189° ± 82.8° in pts and 67.5° ± 13.3° in controls (p: 0.002). T angle was normal in all conditions (p: n.s.). Discussion: Exercise-MMCG is feasible also in an unshielded hospital unit, using a standard ergometer during simultaneous 12-lead ECG recording. MMCG seems to provide high sensitivity to detect ventricular repolarization abnormalities due to exercise-induced ischemia, in pts with CAD.