THE STUDY OF STEADY MAGNETIC-FIELDS ASSOCIATED WITH PRIMARY AND SECONDARY ST SHIFT IN ISCHEMIC RABBIT HEARTS

The study of injury potentials associated with DC currents that genera te the primary or secondary ST shifts during cardiac ischaemia is poss ible only through the invasive technique of the DC electrogram. Clinic al surface ECG recordings are AC coupled and cannot be used. This pape r reports the use of non-invasive and unshielded magnetocardiographic measurements to evaluate the DC injury currents associated with ST shi fts during coronary artery occlusions in the isolated rabbit heart. Th e effect on the magnetic ST shift is studied under different ischaemic conditions including regional ischaemia, global ischaemia, global isc haemia following long periods of regional ischaemia, regional ischaemi a after repeated episodes of reversible global ischaemia, and bilatera l regional ischaemia. Recording of DC magnetic fields allows the chara cterization of primary and secondary ST displacement for each induced ischaemic condition. Our measurements show that the ST shift starts ea rlier when inducing ischaemia in hearts previously subjected to ischae mic episodes than in hearts where the ischaemia was produced for the f irst time.