Ischemia detection after myocardial infarction: Diagnostic value of exercise-induced QRS duration changes evaluated by a new computerized method

A new computerized optical scanner was used to measure QRS complex duration during exercise stress testing, both pre- and postdischarge, as a means of ischemia detection after acute myocardial infarction. Thallium stress testing was used as a standard of comparison. Each patient underwent predischarge exercise testing (while receiving anti-ischemic drug therapy) and a postdischarge test 1 month later (without anti-ischemic drug therapy), as well as thallium stress testing within 4 months of infarction. In the population of 68 patients, 42 of the predischarge tests and 43 of the postdischarge tests showed an ischemic response of QRS prolongation. When compared with thallium testing for QRS prolongation criteria, the sensitivity was 95% with a specificity of 77% predischarge and 89% with a specificity of 65% postdischarge. According to ST-T criteria, only 12 of 68 patients were positive for ischemia predischarge; this number increased to 29 postdischarge (predischarge sensitivity 24% and specificity 90%, with postdischarge sensitivity 68% and specificity 87%), when compared with thallium testing. Measuring QRS duration during exercise increased the sensitivity of detection of ischemic patients over that of ST-T criteria by 71% predischarge and 21% postdischarge, with a 22-23% loss of specificity, and was apparently not influenced by anti-ischemic drug therapy.