A method for detecting myocardial abnormality by using a current-ratio map calculated from an exercise-induced magnetocardiogram

A method for making a current-ratio map to determine the ischaemic area of angina pectoris (AP) patients has been developed. This method uses a current-arrow map calculated using a ORS wave from 64-channel magnetocardiogram (MCG) signals. The current-ratio map can be calculated from the ratio of an exercise-induced current vector to an at-rest current vector. The MCG signals of eight patients with angina pectoris (AP) (six patients with effort AP and two patients with variant AP) and four healthy volunteers were measured before and after a two-step exercise test. The current-ratio maps of the six patients with effort AP showed three distinct patterns: a left-circumflex-artery (LCX) pattern; a right-coronary-artery (RCA) pattern; and a left-anterior-descending (LAD) pattern. The maximum current ratios of these three patterns differed from those of normal patterns. The patterns of two patients with variant AP were similar to normal patterns. Furthermore, a comparison of the current-ratio map before and after percutaneous-transluminal-coronary-angioplasty (PTCA) treatment indicated that the cardiac ischaemia was reduced in all patients. An appropriate criterion to diagnose abnormality in a patient with an ischaemic myocardial area seems to be a maximum current ratio exceeding 0.4 to 0.5. Based on these preliminary results, it is believed that the location of an ischaemic area (the coronary artery part) can be estimated by using the ischaemic current-ratio map pattern.