Defining acute myocardial infarction by ST segment deviation.

those with ST elevation myocardial infarction, whereas ‘primary’ therapy for those with non-ST elevation acute coronary syndromes is antithrombotic therapy (aspirin, heparin or low molecular weight heparin and/or glycoprotein IIb/IIIa inhibitors). Given the importance of ST elevation in discriminating acute myocardial infarction, Menown and colleagues conducted a comprehensive study of the exact sensitivities and specificities of various degrees and definitions of ST elevation and/or ST depression for diagnosis of myocardial infarction. They used univariate and multivariate models to predict development of myocardial infarction. They observed that models with either 1 mm ST elevation or 2 mm in precordial leads V1–V4 had a sensitivity for myocardial infarction of 55·8% and a specificity of 94%. When requiring at least two contiguous leads to demonstrate ST elevation (as used in most clinical trials), specificity for myocardial infarction rose and sensitivity fell slightly. Interestingly, the addition of variables of abnormal QRST features (e.g. T wave inversion) did not improve the model’s performance — indicating the importance of careful examination of the ST segments on the ECG. For patients without ST elevation on the ECG, they observed that the presence of ST depression in 2 leads was very sensitive for the diagnosis of myocardial infarction (80%), but not specific. On the other hand, if 6 leads show ST depression, the specificity for myocardial infarction is 96·5%. There are two other related areas where ST segments are (re)emerging as a clinical tool of great importance. The first is in evaluating the response to thrombolytic therapy (or primary percutaneous coronary intervention). Muller, Maroko and Braunwald identified in 1975 that early resolution of ST segment elevation is a useful means of assessing reperfusion. Schroeder extended these observations using a 12 lead electrocardiogram at baseline and at 3 h post thrombolysis, and found that complete ( 70%) resolution of ST segment elevation from baseline was an excellent marker of a good prognosis. In other recent studies, resolution of ST segment elevation on a 12lead electrocardiogram performed 90 min following thrombolysis has been found to be not only an excellent marker of coronary reperfusion but also of better myocardial tissue perfusion. Most importantly, it was observed in the Thrombolysis in Myocardial See page 275 for the article to which this Editorial refers