Body surface low-level potentials during ventricular repolarization with analysis of the ST segment: variability in normal subjects.

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Abstract
Early ventricular repolarization was examined by measuring body surface maps in normal subjects, ages 1-60 yr. Repolarization began with positive potentials. The time of appearance of these potentials from the onset of QRS increased with age. All normal subjects had positive ST segments on the anterior torso. Although the magnitude of the maximal ST-segment voltage varied, maximal ST-segment voltage increased from early childhood into the twenties and thereafter decreased with age. The same age-related trend occurred during other phases of ventricular repolarization, i.e., T wave and U wave. Although ST-segment maxima occurred in a circumscribed area near the heart in all adults, normal ST-segment patterns varied in relation to the vertical distance over which low-level positive potentials extended on the left anterior torso. The ST-segment patterns differed greatly in the low-level potentials in areas distant to the heart. ST-segment patterns indicate that the arrangement of ST-segment current sources is detectably different in normal adults. This variability suggests that evaluation of ventricular ischemia might be enhanced by interpreting a questionably abnormal map (e.g., during exercise) compared with the patient''s own baseline map. Measurement of the total cardiac electrical field on the body surface is important to account for the effects of currents from all areas of the ventricles during the ST segment, rather than emphasizing the proximity effects as is done with precordial maps.