Magnetic determination of the relationship between the S T segment shift and the injury current produced by coronary artery occlusion

Abstract

Both the S T segment shift and the injury current were measured using the direct current magnetocardiogram (d c MCG) in seven dogs undergoing coronary artery occlusion. The purpose of the measurements was to clarify the origin of the S T shift in acute ischemia and infarction. Previous measurements, consisting of d-c electrograms recorded from the exposed epicardial surface in situ, are partially consistent; also, they are not necessarily representative of the surface electrocardiogram (ECG), which sums broadly over the myocardium. The d c MCG allows steady myocardial currents in the intact torso to be measured externally; because the d c MCG sums broadly over these currents, conclusions drawn from it are applicable to the ECG. Coronary artery occlusion was produced by inflating a tube which, about 1 wk earlier, had been surgically installed around the artery and exteriorized. During occlusions carried out in the MIT magnetically shielded room, a sensitive magnetometer recorded the d c MCG at various locations around the torso. Within 20 sec after occlusion, equal and opposite S T segment and base line (d c) shifts appeared on the d c MCG; these shifts were maintained for at least 15 min, after which they slowly decreased. Therefore during the acute ischemia produced by these occlusions, the S T shift is a secondary result of a primary injury current that is interrupted during the S T interval.