Mechanism of S-T segment alteration during acute myocardial injury.

ELECTEOCARDIOGRAPHIC changes after myocardial injury were first described exactly half a century ago when Eppinger and Rothberger, using an esophageal-rectal lead, noted the "disappearance of the valley between the R and T waves" in dogs which had received injections of 20 per cent silver nitrate solution into the left ventricle. Pardee, in 1920, was the first to note S-T segment changes in a patient with coronary artery disease. The genesis of these electrical changes has since been a subject for disagreement. First, there is controversy regarding the exact nature of the "S-T segment shift." Since the usual electrocardiographic recorders are capacitor-coupled and will compensate for the introduced injury current, differentiation between an apparent S-T shift caused by baseline changes at rest (T-Q segment) and a true S-T deviation from the iso-electric level caused by changes during activity is impossible. True displacement of either the T-Q or the S-T segment cau be observed only when continuous records are taken while the injury is occurring, so that the changes cau be related to the previous iso-electric line. Nahum and associates thought that T-Q displacement was the only significant change with myocardial injury, and Donoso et al. have reaffirmed this belief. Eyster et al., Hellerstein and Katz, and Sodi-Pallares, on the other hand, have observed a combination of T-Q and S-T segment changes. In the present experiments, a