Abstract 2199: Effects of Beta-Blocker on Dynamic Repolarization Measured by 24-hr Electrocardiography in LQT1 and LQT2 Forms of Congenital Long-QT Syndrome
Backgrounds:Effects of β-blocker on dynamic ventricular repolarization in relation to heart rate (HR) change in patients with genotyped congenital long-QT syndrome (LQTS) are largely unknown.
Methods:The CM5 leads in 24-hr electrocardiographic recordings were reviewed in 23 LQT1 patients (pts) (10 pts with and 13 pts without β-blocker) and 8 LQT2 pts (3 pts with and 5 pts without β-blocker). We measured mean corrected QTend (QTc) and QTpeak-end (TPEc) intervals reflecting transmural dispersion of repolarization, and dispersion of QTc and TPEc, which was the difference between maximal and minimal values, at each low (1000±25ms) and high (700 or 850±25ms) range of sinus HR.
Results:Mean QTc and TPEc were prolonged at high HR in LQT1 pts regardless of β-blocker use, but were not changed in LQT2 pts. At low HR, neither mean nor dispersion of QTc and TPEc were different between β-blocker(+) and β-blocker(−) pts in both LQT1 and LQT2. At high HR in LQT1, the dispersion of QTc and TPEc (QTc-D, TPEc-D) were significantly smaller in β-blocker(+) pts than β-blocker(−) pts (QTc-D: 60±23ms vs. 82±23ms, p=0.029, TPEc-D: 31±14ms vs.51±23ms, p=0.028, respectively), although the mean QTc was longer in β-blocker(+) pts. In contrast, neither mean nor dispersion of QTc and TPEc were different between β-blocker(+) and β-blocker(−) pts at high HR in LQT2.
Conclusions:Increase of HR prolonged the QTc and TPEc, but β-blocker use decreased dispersion of QTc and TPEc in LQT1 pts, contributing specific efficacy of β-blockers in LQT1.