Prolongation of the QT interval as an indicator of risk of a cardiac event.

The thesis (stated or implied) that acquired QT interval (or QTc) prolongation reflects physiological disturbance similar to those found in the congential syndromes has been assumed to be of central importance in many studies of QT prolongation in the clinical setting. There is no evidence to support this assumption. It is suggested that the use of rate correction of the measured QT interval has obscured our understanding of repolarization abnormalities. Although a QT interval corrected for heart rate may reflect a relationship between the duration of repolarization and heart rate in a single value (e.g. QTc) the corrected value clearly embodies complex influences other than those directly due to rate and for which no 'correction' is, as yet, possible.