Stability of Electrocardiographic Classification Pre- and Postglucose Challenge

Because of validity concerns, electrocardiograms (ECGs) in epidemiologic studies are usually taken in fasting subjects. It would be preferable logistically to record ECGs throughout the day. The authors investigated the stability of ECGs taken while fasting and approximately 1 hour after a 75-g glucose load on the same morning in 89 older men and women who were participants in the Rancho Bernardo (California) Chronic Disease Study between 1984 and 1995. A reader blinded to this comparison classified ECGs using the Minnesota code and Whitehall criteria. Of 75 initially normal tracings, 27% changed to possible ischemia postglucose. Of 12 tracings initially indicating possible ischemia, two reverted to normal (kappa = 0.40, 95% confidence interval: 0.21, 0.59). The two tracings initially scored as probable ischemia remained in that category postglucose. More ECGs worsened than improved, and the variability pre- and postglucose was at least as great as that between clinic visits conducted 8 years apart.