Late potential-like deflections in the ST segment of normal subjects

Irregular high frequency deflections of low amplitude have been found within the ST segment immediately following the QRS complex and in the T wave of high resolution bipolar recordings (lead V4-V7) in single beats as well as in averages of 100 beats. The signals in the T wave, found in six out of 22 normal subjects, coincide with the apex of the T wave in standard lead II. Their amplitude depends on the phase of the respiratory cycle. They were most pronounced during expiration. The occurrence of these signals depends on the position of the electrodes relative to the position of the equivalent current dipole, which is determined from simultaneous magnetocardiographic measurements. When electrode V4 is systematically shifted these signals vanish or increase, respectively become measurable.