Effects of aging and beta-adrenergic-blockade on standing-induced QT/QS2 changes

In order to evaluate whether the changes in the electrical systole/electromechanical systole ratio (QT/QS2) may reflect the effects of beta-adrenergic stimulation on the heart, we studied the variations of this ratio induced by active standing. We studied 45 healthy volunteers aged 15 to 82 years, subdivided into three groups; Group 1 (mean age 22 +/- 4 years), Group 2 (mean age 44 +/- 6 years), and Group 3 (mean age 74 +/- 6 years). Fifteen subjects repeated the test after propranolol administration (0.1 mg/kg iv). Resting QT/QS2 ratio increased slightly, but not significantly, with age. Upright position significantly increased QT/QS2 ratio in all groups. Changes in heart rate (r = -.43), electromechanical systole (r = .55) and QT/QS2 were significantly correlated with age. Propranolol prevented the increase in QT/QS2 ratio induced by active standing. Therefore, QT/QS2 changes induced by standing are correlated with age and are inhibited or reduced by beta-blockade. QT/QS2 changes can be used to monitor adrenergic activity, even if their value is limited by the overlapping responses of the individual cases.