Body surface distributions of repolarization potentials after acute myocardial infarction. II. Relationship between isopotential mapping and ST-segment potential summation methods.

Isopotential body surface distribution derived from 14 subjects with acute anterior and 14 patients with acute inferior myocardial infarction were studied to examine three possible difficulties with ST-segment summation methods as used for evaluation of infarction severity. First, recorded sums of potentials recorded from 150 electrodes placed on anterior and posterior thoracic surfaces and from five subsets of 42 electrodes located only on the left anterior precordium were compared. Lead subsets detected only one-half of total thoracic positivity in acute anterior infarction and the sums of potentials in these sets were significantly altered by small (approximately 1-1.5-inch) deviations in grid location. Second, differing isopotential distributions could yield nearly identical sums of potentials in left precordial electrode grids. Third, the effects of the wide variations in the normal ST-segment isopotential distribution were evaluated by studying 45 normal subjects and application of difference map and departure map and departure map techniques. The results illustrate the significant variation in potentials considered to be generated by the ischemic lesion caused by differences in control patterns. Thus, the recording of potential sums over limited torso areas, the attention to potential magnitudes rather than to distributions and the assumption that the normal ST segment is isoelectric represent significant problems in applying ECG methods to the quantitative evaluation of myocardial infarction.