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Effects of Beta-Blocker Therapy on Ventricular Repolarization Documented by 24-h Electrocardiography in Patients With Type 1 Long-QT Syndrome

Matti Viitasalo, MD^_*,_*, Lasse Oikarinen, MD^_*, Heikki Swan, MD^_*, Heikki Väänänen, MSc, Jere Järvenpää, MD^_*, Harri Hietanen, MD^_*, Jouko Karjalainen, MD^_* and Lauri Toivonen, MD, FACC^_*

^_* Department of Cardiology, Helsinki University Central Hospital, Helsinki, Finland
Laboratory of Biomedical Engineering, Helsinki University of Technology, Espoo, Finland

View larger version (70K): [in a new window]   Figure 1 The measurement of QT end and T-wave peak to T-wave end (TPE) intervals as well as the T2/T1-wave amplitude ratio in cases with bifid T waves. Vertical lines show the peak and the end of the T wave; see text for details. In the top panel, with an interpeak difference of 0.08 s, the second peak is a part of the T-wave. In the middle panel, with an interpeak difference of 0.2 s, the second peak is a U wave. In the bottom panel the interpeak difference is 0.18 s, but because the second peak is higher it is interpreted as a T2-wave with a T2/T1-wave amplitude ratio of 3.7.

View larger version (23K): [in a new window]   Figure 2 Maximal QT end intervals (higher two lines) and QT end intervals at stable heart rates (lower two lines) at specified heart rates before the treatment with beta-blockers (broken lines) and during the treatment with beta-blockers (solid lines) in 24 long-QT syndrome type 1 (LQT1) patients. **p < 0.01 before the treatment versus during the treatment with beta-blockers at RR intervals from 600 to 700 ms.

View larger version (20K): [in a new window]   Figure 3 Maximal T-wave peak to T-wave end (TPE) intervals (higher two lines) and median TPE intervals, calculated from all beats (lower two lines), at specified heart rates before the treatment with beta-blockers (broken lines) and during the treatment with beta-blockers (solid lines) in 24 long-QT syndrome type 1 (LQT1) patients. *p < 0.05 before the treatment versus during the treatment with beta-blockers at RR intervals from 600 to 700 ms.

View larger version (22K): [in a new window]   Figure 4 Maximal T2/T1-wave amplitude ratios during 24-h before (pre-BB) and during (post-BB) the treatment with beta-blockers in 24 long-QT syndrome type 1 (LQT1) patients. The broken line shows the average values.