EFFECT OF PRECORDIAL ELECTROCARDIOGRAPHIC ELECTRODE PLACEMENT ON ST-SEGMENT MEASUREMENT DURING EXERCISE

Research protocols often utilize serial exercise testing to examine th e efficacy of anti-ischemic therapies. These tests, however, are prone to multiple sources of bias. This investigation sought to determine t he influence of varying precordial electrocardiographic (ECG) electrod e placement on the detection of exercise-induced ST-segment shifts. Fi fteen coronary artery disease patients with abnormal exercise tests we re studied. Based on the previous exercise test, the precordial electr ode position exhibiting the greatest ST-segment shift was selected as the reference electrode, Four additional electrodes were placed around this reference electrode and exercise testing was performed. ECG stri ps were recorded every minute, The time-to-onset and -offset of ischem ic-type ST-segment depression was recorded. ST-segment depression was recorded during exercise front the reference electrode in 12 of 15 pat ients. Ischemic-type ST-depression was also recorded in each of these 12 patients with the surrounding electrodes; however, the time-to-onse t detected by all four surrounding electrodes concurred in only 5 of 1 2 (42%) patients, The time-to-offset of the ST-segment depression conc urred in 9 of 12 (75%) patients. Serial ECGs recorded from similar but not exactly the same precordial ECG electrode position should yield s imilar results for the detection of ischemia, but time-to-onset or -of fset of ischemia may differ by 60 s or more. Small changes in the time -to-onset and -offset of ischemia should not be considered reliable in dicators of anti-ischemia efficacy.