To the Editor: In their review of the effects of antipsychotics on the cardiac QTc interval, Alexander H. Glassman, M.D., and J. Thomas Bigger, Jr., M.D. (1), gave a somewhat misleading view. They contended that the QT interval is "modestly associated with torsade de pointes" (p. 1775) and that "the greater the duration, the more likely torsade de pointes becomes" (p. 1776) but cite no references in support of these assertions. An alternative view is that the degree of prolongation of the QT interval is an inadequate and imprecise predictor of the likelihood of arrhythmia. Indeed, this latter view is supportable on theoretical grounds; given the number of processes taking place during the QT interval (depolarization, plateau, repolarization) and the range of ion channels potentially involved (2), it would be remarkable if the extent of lengthening of the QT interval were directly and linearly related to the probability of arrhythmia.