Normal values for QT intervals in ECG during ramp exercise on bicycle

Summary. The relation between QT interval and heart rate during ramp exercise tests on a bicycle was investigated in 37 healthy individuals (21 women) without regular medication and with a normal thallium-201 exercise scintigram (mean age 52–9 ± 8–3, range 38–68). The test started at 20 W and the load increased by 10 W min^-1. A 12-lead ECG was recorded twice every min and mean complexes (during a 15 s period) were calculated by computer. At rest the QT interval (in s) corrected for heart rate (QT_C) for women and men was 0–408 ± 0–004 and 0–399 ± 0–005, respectively, P > 0–05). During exercise there was no difference in QT interval between women and men or between younger (<50 years) and older (> 50 years) individuals. A straight line was used to describe the relation between QT interval and heart rate (beats min^-1; QT = 0–459–12–3xlO^-4*HR). A 95% prediction interval around the regression line was determined using a non-parametric statistical method. When QT_C was calculated using Bazett's formula with a cut-off value of QT_c= 0–46, 19 individuals (11 women) had a prolonged QT interval during exercise. It is concluded that the relation between QT interval and heart rate can during exercise be described by a straight line for normal individuals. It is not valid to use Bazett's formula for correction of QT intervals during ramp exercise tests.