ST-segment level and slope in exercise-induced myocardial ischemia evaluated with body surface potential mapping

Body surface potential mapping (BSPM) is superior to 12-lead electrocardiog raphy for detection of acute and old myocardial infarctions (MIs). We used BSPM to examine electrocardiographic criteria for acute reversible myocardi al ischemia. BSPM with 123 channels was performed in 45 patients with coron ary artery disease (CAD) and 25 healthy controls during supine bicycle exer cise testing. Of the 45 patients, 18 patients had anterior, 14 had posterio r, and 13 had inferior ischemia documented by coronary angiography and thal lium scintigraphy. The ST amplitude was measured 60 ms after the J-point an d the ST slope calculated by fitting a regression line from the J-point to 60 ms after it. The optimal locations for detecting ST depression and ST-sl ope decrease were identified. In the pooled CAD patient group, the optimal location for ST depression was 5 cm below standard lead V-5 (CAD group: -70 +/- 70 muV; controls: 70 +/- 80 muV, p<0.001). Using a cut-off value of -1 0 <mu>V, the ST depression separated the patients with CAD from controls wi th a sensitivity of 84% and a specificity of 96%. The ST slope became more horizontal in the patient group than in the control group. The optimal loca tion for ST-slope decrease was over the left side (CAD group: 20 +/- 20 muV /s; controls: 720 +/- 320 muV/s, p<0.001). Using a cut-off value of 320 <mu >V/s, the ST slope separated patients with CAD from controls with a sensiti vity of 93% at a specificity level of 88%. The area under the receiver oper ating characteristic curve of ST slope tended to be higher than the one of ST depression (970% vs 93%; p=0.097). In conclusion, regions sensitive for ST depression and for ST-slope decrease could be identified in BSPM, despit e variation in the location of ischemia and the presence or absence of a hi story of Mi. ST slope is a sensitive and specific marker of transient myoca rdial ischemia, and might perform even better than ST depression. (C) 2001 by Excerpta Medica, Inc.