Effect of increased adrenergic activity on the relationship between electrical and mechanical systole.

The effect of catecholamines and atrial pacing on the relationship between electrical systole (QT) and mechanical systole (QS2) was studied in 12 normal subjects and in 32 patients. The studied subjects were divided into three groups. Group 1 included 12 normal subjects in whom serial isoproterenol infusions were performed before and after oral propranolol administration, 160 mg daily for 2 days. During the 24-hour control period, the QT was always shorter than the QS2 (from 14 +/- 3 to 19 +/- 4 msec, p less than 0.01), while during isoproterenol infusion the QT was always greater than the QS2 (from 28 +/- 5 to 34 +/- 5 msec, p less than 0.01). Group 2 included 26 patients in whom 24-hour urinary epinephrine (E) and norepinephrine (NE) were measured the same day as systolic time interval measurements. The E + NE was higher in patients in whom the QT was longer than the QS2 compared with patients in whom the QT was the same or shorter than QS2 (107 +/- 9 vs 61 +/- 7 microgram/24 hours, p less than 0.05). Group 3 included six patients in whom the heart rate was increased with atrial pacing, from 80 to 130 beats/min. The QT was always shorter than the QS2 (from 13 +/- 3 to 24 +/- 5 msec, p less than 0.01). Adrenergic stimulation results in a relative prolongation of the QT with the QS2 shortening and the QT remaining unaffected. The QT is normally shorter than the QS2, so the duration of QT should always be considered in relationship to the duration of QS2. Finally, a reversal of the normal QT-Qs2 relationship may provide a simple index of increased adrenergic activity.