Estimation of the upper limit of the reference value of the QT interval in rest electrocardiograms in healthy young Japanese men using the bootstrap method.

Background: A prolonged QT interval (QT) is associated with cardiac arrhythmia, and methods for identification of QT prolongation are required.

Methods: The relationship between RR and QT was investigated in resting electrocardiograms of 1276 healthy young Japanese men using the bootstrap method.

Results: The upper limit of QT (QT(upper limit)) was approximated well by the exponential equation: QT(upper limit) = 435 x RR(0.3409). We also defined an alternative upper limit of QTc(G upper limit) = 435 milliseconds, where QTc(G) was calculated by dividing QT by RR(0.3409). Thirty-two (2.51%) of the 1276 cases exceeded the criterion and were diagnosed as cases of QT prolongation.

Conclusion: Using this limit, we propose a criterion to discriminate cases with prolonged QT intervals. The accuracy of the estimation of the mean and the upper limit of the reference value of the QT was good within the range of the RR interval from 0.812 to 1.263 s (heart rates from 48 to 74 beats per minute). Our approach for estimation of the exponent of RR differs from the well-known exponential equations proposed by Fridericia, but the exponent of RR in our equation is very close to that of Fridericia.