Importance of measurements at or after the J-point for evaluation of ST-segment deviation and resolution during treatment for acute myocardial infarction

BACKGROUND: Determination of ST-segment deviation (STdev) and its resolution (STR) by reperfusion strategies have become important tools in the assessment of patients with acute myocardial infarction (AMI). STdev has been measured at different time-points, i.e. at 20-80 ms after the J-point. There are no data comparing STR at different time-points. METHODS AND RESULTS: STdev was measured using a new computer-assisted workflow. The intraclass correlation coefficients (ICC) for validity and agreement vs. classical manual measurements (n=1020) were both 0.996 (p<0.0001). The reliability indices were 0.991 (95% CI 0.990-0.992) for the manual vs. 0.995 (95% CI 0.995-0.996) for the computer-assisted method, indicating superiority of the latter. 12-lead STdev were determined on ECGs before (baseline) and 180 min after start of thrombolytic therapy, measured both at the J-point (STdev(J)) and 20 ms after the J-point (STdev(J20); n=2400). STdev(J20) was on average 0.01+/-0.03 mV higher than STdev(J) (p<0.0001) with a tendency towards larger differences for higher ST-elevations (p<0.001). Although the average STR calculated from STdev(J20) and STdev(J) was not statistically different in any infarct location group, in 26% of the patients the difference was >10%, and 11% of the patients were classified into another ST-resolution group. Analysing STdev only in the single lead with the highest ST-elevation at baseline (a simplified measurement which may eliminate the confounding effect of ST-depressions) showed an even higher classification discordance (14% of the patients). CONCLUSIONS: The time-point of STdev measurement is an important variable to be accounted for when evaluating ST resolution data. Uncontrolled extrapolation of classification schemes based on STdev(J20) to other time-points cannot be justified.