Relationship between fractions of the Q-T interval

¹ The Laboratory of Physiological Hygiene, University of Minnesota, Minneapolis, Minnesota, and The Computation Laboratory, Mathematics Department, New York University, New York City

In 100 healthy men from 40 to 59 years of age, the regressions and correlations between the R-R, Q-T, QRS intervals, S-T segment duration, and T-wave duration were determined by means of computer analysis. The range of heart rate was from 45 to 115 beats/min, with equal distribution of the samples in four ranges of heart rate (45–60, 60–70, 70–80, 80–115). The error of measurement of the S-T duration was determined from independent repeat measurements of one observer and observer variation from measurements of two observers. The regressions of all interval fractions on heart rate are linear. The correlation of the R-R interval and of the Q-T interval with all fractions except the QRS interval is highly significant. The major contributing factor to the slope of the Q-T interval versus heart rate is the duration of the S-T segment. A table with the fiducial normal limits for evaluation of interval changes in individual patients is given.