Abstract

  Background: Analysis of QT duration limited to a single heart rate correction formula might be problematic in cross-sectional studies. The aim of this study was to investigate five frequently used equations with respect to over- and under-correction of QT intervals in a middle-aged population without manifest atherosclerotic disease.
Material and Methods: A total of 1199 individuals (851 males, 348 females, aged 39 to 66 years) of the SAPHIR study (Salzburg Atherosclerosis Prevention Program in Subjects at High Individual Risk) were investigated. Heart rate, RR, and QT intervals were measured automatically from resting ECGs with the 12SL™ ECG Analysis Program (GE Medical Systems). Five methods (Bazett, Fridericia, Framingham, Hodges, and Rautaharju) were used to correct the QT interval for heart rate.
Results: Females had shorter RR intervals than males (963±141 vs. 1022±158 ms, <i>p</i><0.0005), with longer QT (410±28 vs. 404±28 ms, <i>p</i>=0.003) and QTc intervals using all five formulae (<i>p</i><0.0005). No significant differences were observed between the gender groups for the QTc/RR slopes regardless of the formula. The Bazett formula performed the worst and the Fridericia the best in terms of rate adjustment success (slope B=–0.001). The optimal alpha of the best-fit equation (QTc=QT/RR^&#945;) was calculated as 0.326 for males and 0.328 for females.
Conclusions: These results demonstrate that automatic QT measurements can be used reliably in cardiovascular prevention programs, encouraging further investigation of their clinical value in risk stratification. From an epidemiological perspective, however, the selected QT correction formula applied to a specific population has to be evaluated for appropriateness.

Keywords: Austria, Atherosclerosis - prevention & control, Electrocardiography - methods, Heart Rate - physiology, Regression Analysis, Sex Factors