OBJECTIVES The study systematically compared different measures of ST segme
nt depression from the treadmill exercise test.
BACKGROUND The value of the treadmill exercise test for objectively measuri
ng treatment effects is limited by random error in the measurement of ST de
pression and may be biased by regression to the mean or by the decision to
terminate the test.
METHODS Treadmill exercise was performed in 21 subjects with ischemic heart
disease 1 h after isosorbide dinitrate 10 mg or placebo in a double-blind
randomized crossover study. a 12-lead electrocardiogram (ECG) was recorded
every 30 s during and at peak exercise. The relative sample size needed to
detect the nitrate effect was compared for different summary measures of ST
depression.
RESULTS The ST depression measured from a single unmatched lead at longest
equivalent sub-maximal exercise needed the lowest sample size to detect the
nitrate effect in paired comparisons (p = 0.000006). Averaging over multip
le leads or times did not improve detection of the nitrate effect. The rate
of increase in ST depression (in mm/min) calculated by linear regression n
eeded a similar sample size (x1.32, 95% CI 0.62 to 2.58). A larger sample s
ize was needed for ST depression at peak exercise (x2.9, CI 1.3, 11.1) and
exercise duration (x4.5, CI 1.5, 38). Time to 1-mm ST depression was the le
ast efficient measurement (relative sample size x15.5, CI 1.6, >1000). Comp
arison of matched leads resulted in >2-fold differences in estimates of the
nitrate effect because of bias from regression to the mean.
CONCLUSIONS Maximal ST depression at longest equivalent sub-maximal exercis
e and the maximal rate of increase in ST depression had less bias and rando
m variation than did other commonly used measures. The rate of increase in
ST depression is preferred because it call be calculated in either paired o
r unpaired studies. CT Am Coil Cardiol 2000;36:1274-9) (C) 2000 by the Amer
ican College of Cardiology.