There is virtually no information on spontaneous variability of
ECG body surface potential maps (BSPMs) and on dynamics of
their reactive changes in healthy subjects. This study evaluated
quantitatively the depolarization (QRS) and repolarization (QRST)
parameters derived from the respective integral BSPMs,
constructed beat-to-beat, from continual body surface ECG
records in 9 healthy men resting supine, during head-up tilting
and sitting. Spontaneous variability of the BSPMs parameters,
both at rest and during postural reactions, was characterized by
significant respiratory and low frequency oscillations, more
pronounced when related to repolarization. Head-up tilting and
sitting-up evoked significant decrease in the QRST-BSPM
amplitudes, widening of the angle α and reduction of
nondipolarity indexes, compared to the respective supine values.
All these changes were gradual, characterized by transition
phenomena and prolonged after-effects. Tilting back to horizontal
restored the resting supine values. The postural effects on
depolarization were individually more variable and in the average
showed a minimal QRS-BSPM amplitude increase. Beat-to-beat
analysis of a train of ECG BSPMs provided the first evidence of
spontaneous, non-random, respiratory and low frequency
oscillations of the ventricular repolarization pattern, and the first
insight into the dynamics of body posture associated changes in
ventricular recovery.
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