[Changes in electrical systole and heart rate in healthy persons after the exercise test]

Relationships between the electrical systole and the cardiac cycle were evaluated at rest and after exercise in 1083 normal male subjects, aged 18 to 25 years. In a resting condition, most formulas determining proper QT duration were shown to be within the confidence regression limit: QT = 0.138 RR + 0.246 +/- 0.04 s, while the relationship was linear. Rapid heart rate change produced a discrepancy between changes in the duration of electric systole and the changing cardiac cycle, resulting in a continuous variation of the pattern of QT-RR relationship, for which reason its description by the available linear formulas was no longer possible. A systems analysis established major characteristics of the transitional process, such as the maximum readjustment time (18.3 +/- 0.5 s), the stabilization time (67.9 +/- 8.4 s) and the number of readjustments (not more than two).