Age and sex dependent variations in the normal magnetocardiogram compared with changes associated with ischemia

Magnetocardiography is the measurement of the magnetic fields of the heart. Human studies performed in magnetically shielded laboratories have demonstrated that magnetocardiograms (MCGs) can detect ischemia. The aim of this study was to obtain clinically useful MCGs in an unshielded hospital room. Other objectives included understanding the normal variations in MCG during repolarization and determining the MCG parameters that best discriminate patients with ischemia from healthy controls. We measured 51 healthy volunteers of both sexes from 25 to 76 years of age and 11 patients with documented exercise-induced ischemia. Resting and postexercise measurements were taken, and several MCG parameters were defined. For 19 of 29 MCG parameters, there were significant differences between healthy females and males (p < or = 0.05). For nine MCG parameters, there were differences between older and younger healthy subjects (p < 0.01). Therefore the age and sex of a subject should be considered when evaluating the MCG. Thirteen parameters separated the patients from the controls (areas under the receiver operating characteristic curve >80%). The repolarization stabilization interval, a parameter based on the time-evolution of contour maps, performed the best. Magnetocardiography performed in clinical settings is a potential screening tool for ischemia that should be further explored.