NORMAL VALUES FOR QT INTERVALS IN ECG DURING RAMP EXERCISE ON BICYCLE

The relation between QT interval and heart rate during ramp exercise t ests on a bicycle was investigated in 37 healthy individuals (21 women ) without regular medication and with a normal thallium-201 exercise s cintigram (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 tw ice every min and mean complexes (during a 15 s period) were calculate d 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, respec tively, P>0.05). During exercise there was no difference in QT interva l 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=0.459-12.3x10(-4 )HR). A 95% prediction interval around the regression line was determ ined using a non-parametric statistical method. When QT(c) was calcula ted using Bazett's formula with a cut-off value of QT(c)=0.46, 19 indi viduals (11 women) had a prolonged QT interval during exercise. It is concluded that the relation between QT interval and heart rate can dur ing exercise be described by a straight line for normal individuals. I t is not valid to use Bazett's formula for correction of QT intervals during ramp exercise tests.