Physiologic relation between cardiac cycle and QT duration in healthy volunteers.

To determine the relation between QT duration and RR interval on the electrocardiogram, 2 studies were undertaken in 23 young healthy volunteers (mean age 24 years). In study 1, the electrocardiogram (paper speed at 50 mm/s, 800 measurements/subject) was recorded in 11 subjects (5 men, 6 women) at rest, during dynamic exercise and after rapid intravenous injections of isoproterenol (0.2 to 12.