We read with great interest the article by Schillaci et al1 examining the relationship between heart rate–corrected QT (QTc) interval duration and morbidity and mortality in hypertension. This article adds to the numerous articles relating QTc prolongation to increased cardiovascular morbidity and mortality.2
However, the Bazett correction formula, which has been widely used in epidemiological studies, including the study by Schillaci et al,1 is well known to overcorrect QTc interval (ie, to yield falsely prolonged QTc values) when heart rate increases above 60 beats/min.3,4 Schillaci et al found a strong residual direct correlation between QTc and heart rate but apparently did not examine the role of heart rate in predicting the risks they assessed. Surprisingly, they did not include heart rate as a potential confounding covariate for the association between QTc interval prolongation and risks in their multivariate analyses. Since increased heart rate is associated with cardiovascular and noncardiovascular mortality independently from blood pressure,5 as well as with falsely prolonged QTc values when the Bazett formula is used,3,4 we wonder whether Schillaci et al1 would reexamine their data to determine whether heart rate, rather than Bazett-corrected QTc, was associated with cardiovascular morbidity and mortality in their study. In view of the strong, and expected, association they found between Bazett-corrected QTc and heart rate, we believe that alternative (and more appropriate than the Bazett formula) methods of QT corrections should be tested in this data set before QTc can be considered as a useful prognostic factor in hypertension. From a pathophysiological point of view, it is conceivable that both QTc and heart rate may come out as prognostic variables, but both need to be studied and reported in prognostic studies.