QT Prolongation Following Ectopic Beats: Initial Data Regarding The Upper Limit Of Normal With Possible Implications For Antiarrhythmic Therapy And Concealed (Unexpressed) Long QT.

Background: Ectopic beats are frequently associated with morphologic repolarization alterations of ensuing sinus beats. Less is known about repolarization duration alterations of post-ectopic sinus beats. In one patient who developed long QT and torsades de pointes upon exposure to a class III antiarrhythmic drug, and was later genotyped as being a carrier for long QT syndrome (LQTS) type 1, review of a pre-drug Holter monitor study revealed marked QT prolongation of post-ectopic sinus beats. In wondering whether this might be a common clue to "concealed" unexpressed LQTS, we realized that we must first characterize the range of post-ectopic QT prolongation present in normals. Prolongation beyond the upper limit of this range might then raise suspicion of possible LQTS and alter the antiarrhythmic drug selection process for the suppression of atrial fibrillation or other arrhythmias.
Methods: Accordingly, we assessed the presence/degree of repolarization prolongation following premature ectopic impulses in 166 subjects with normal conduction intervals and normal repolarization on their resting 12-lead ECG, 75 of whom had no known associated cardiovascular disorder of any kind. That is, in our subjects, the maximal prolongation of the QT interval of the sinus beat following isolated ventricular and atrial premature complexes was characterized.
Results: QT prolongation is common in post ectopic sinus beats. However, in our subjects the uncorrected QT interval of post-ectopic sinus beats never exceeded 480 ms in duration [which was much shorter than that seen (510-590 ms) in our gene carrier].
CONCLUSIONS: The QT interval in normal subjects may prolong following premature complexes but not to a value in excess of 480 ms.