Individual patterns of QT/RR relationship.

In clinical practice, an imprecision introduced by ad hoc selected heart rate correction formula of the QT interval is unlikely to lead to erroneous conclusions if all borderline cases are carefully considered. On the contrary, in clinical investigations (e.g., studies of drug effects) the over- or undercorrection of QTc may lead to significant and systematic bias with both false positive and false negative findings. None of the previously published "global" heart rate correction formulae has been universally successful because the QT/RR relationship is different between different subjects and a formula that corrects the QT interval for heart rate acceptably in one individual may be very misleading in another individual. Moreover, it has been recently established that the QT/RR patterns not only exhibit a substantial inter-subject variability but also a high intra-subject stability. Thus, in precise investigations, individual QT/RR relationship should be first established in each subject and subsequently translated into individual heart rate correction formula.