Abstract 11400: Treatment With β-blockers Is Associated With Shortening of the Qtc Interval
Introduction Oral beta-adrenergic blockade is the primary treatment for Long QT Syndrome (LQTS). β-blockers have been shown to have several effects on the surface ECG, but it remainsunclear if β-blocker treatment shortens the QTc interval. We hypothesize that β-blocker therapy is associated with a shorter QTc interval on the surface ECG.
Methods This was a retrospective review study, with LQTS subjects and an unmatched control population of patients treated with β-blockers for reasons unrelated to abnormalities of repolarization (Marfan syndrome, hyperthyroidism, SVT, and hemangioma). Inclusion criteria were age 0 days through 18 years with presence of a pre-treatment and post-treatment ECG. A blinded control panel of pediatric electrophysiologists measured QTc intervals. A paired student's t test was used for comparison of QTc intervals in subjects; an unpaired student's t test was used to compare differences across groups. Fisher's exact tests were used for discrete variables. Regression analysis was used for dose-response curves.
Results We included 88 pts with LQTS and 72 control pts. Among those with LQTS, the mean QTc interval decreased by 22 ms after initiation of β-blockers (466 vs. 444 ms; p<0.01). After treatment, LQT1 pts (n=32) demonstrated a significant decrease in the mean QTc interval (480 vs. 455; p<0.01). Those with LQT2 (n=15) and LQT3 (n=2) did not demonstrate a significant decrease. A genetic diagnosis was not available in 39 pts. Among the control pts, mean post β-blocker QTc also decreased (418 vs. 409; p<0.01), however the difference was significantly smaller than in pts with LQTS (p<0.01). There was no association between β-blocker dose and change in QTc interval.
Conclusions Patients with LQTS had a marked decrease in QTc interval after initiation of β-blocker, unrelated to choice of β-blocker, and without a dose-dependent response. Patients without LQTS also demonstrated a decrease in the QTc interval, but to a lesser extent. Interpretation of the surface ECG in patients taking β-blockers must consider the possible effects of β-blockers on the QTc.
- © 2012 by American Heart Association, Inc.