Abstract 2510: Do Beta-Blockers Affect Non-corrected QT Interval in Type 1 Long QT Syndrome?
Background: Beta-blockers are the standard of care for the treatment of long QT syndrome and have been shown to reduce the risk of mortality in patients with LQT1. Beta blockers have been shown to have minimal effect on the resting corrected QT interval. However, the effect of beta-blockers on the dynamic non-corrected QT and peak R to peak T (R-T) intervals has not been assessed.
Objective: To determine the effect of beta-blockers on the QT, QTc and RT intervals during exercise testing at matching heart rates.
Methods: We analyzed the QT, QTc and R-T intervals at identical cycle lengths at 50msec intervals from exercise stress tests before and after starting beta-blockers in patients with genetically proven type 1 Long QT syndrome.
Patients: 20 patients with documented LQT1 mutations performed an incremental bicycle ergometer test before and after beta-blockade. 111 QT, QTc and R-T intervals were measured before starting beta-blockers and compared to those at matched identical cycle lengths following the prescription of beta-blockers. Bisoprolol 5 mg daily was the typical dose of beta-blocker.
Results: Beta blockers demonstrated a differential effect on the QT interval when adjusted for heart rate when analyzing matched sets by heart rate tertile (Figure⇓). In the slowest heart rate (<90 bpm) beta-blockade increased the QT interval (391 vs 398msec; p=0.02). In the fastest heart rate (>105bpm), the use of beta-blocker was associated with a marked reduction in QT interval (349 vs 339 msec; p<0.001).
Conclusions: Beta-blockers increase the QT interval at slower heart rates and decrease the QT interval at faster heart rates. This may explain their protective effect in LQT1.