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CLINICAL RESEARCH: HEART RHYTHM DISORDER

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

Manuscript received January 20, 2006; revised manuscript received April 6, 2006, accepted April 23, 2006.

^_* Reprint requests and correspondence: Dr. Matti Viitasalo, Department of Cardiology, University Central Hospital, Haartmaninkatu 4, 00290 Helsinki, Finland. (Email: matti.viitasalo{at}hus.fi).

OBJECTIVES: We tested the hypothesis that in long-QT syndrome (LQT) type 1 (LQT1), beta-blocker therapy may decrease both the diurnal maximal T-wave peak to T-wave end interval (TPE) and the maximal ratio between late and early T-wave peak amplitude (T2/T1 ratio), which are electrocardiographic counterparts of transmural dispersion of repolarization (TDR) and early afterdepolarizations (EA), respectively.

BACKGROUND: Ventricular repolarization duration and increased TDR and EAs are the three electrophysiological components generating the high risk of ventricular arrhythmias and sudden death in the inherited LQT. In the most prevalent LQT1 form of LQT, treatment with beta-blockers reduces serious arrhythmia events dramatically without a known influence on QT interval duration. In experimental LQT1 models, beta-blockers decrease TDR and prevent EAs.

METHODS: We reviewed 24-h electrocardiographic recordings obtained before and during the treatment with beta-blockers from 24 genotyped LQT1 patients to record maximal TPE intervals and T2/T1 ratios as well as maximal and rate-adapted QT intervals using a computer-assisted program.

RESULTS: Treatment with beta-blockers decreased the maximal diurnal T2/T1 amplitude ratio from 3.0 ± 1.0 to 2.2 ± 0.6 (p = 0.002). Beta-blockers also decreased both maximal TPE intervals and abrupt maximal QT intervals at heart rates higher than 85 beats/min, whereas QT intervals measured at steady-state conditions remained unchanged.

CONCLUSIONS: Prevention of abrupt increases of electrocardiographic TDR, EA, and ventricular repolarization duration at elevated heart rates may explain the favorable clinical effects of beta-blockers in LQT1.

Abbreviations and Acronyms   ECG = electrocardiogram/electrocardiographic   LQT1 = long-QT syndrome type 1   LQT2 = long-QT syndrome type 2   TdP = torsades de pointes   TDR = transmural dispersion of repolarization   TPE = T-wave peak to T-wave end interval

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