Effects of β-blockers on ventricular repolarization documented by 24-hour electrocardiography in long QT syndrome type 2

Mikael Koponen; Annukka Marjamaa; Heikki Väänänen; Annukka M Tuiskula; Kimmo Kontula; Heikki Swan; Matti Viitasalo

doi:10.1016/j.hrthm.2022.04.028

Effects of β-blockers on ventricular repolarization documented by 24-hour electrocardiography in long QT syndrome type 2

Heart Rhythm. 2022 Sep;19(9):1491-1498. doi: 10.1016/j.hrthm.2022.04.028. Epub 2022 May 4.

Authors

Mikael Koponen¹, Annukka Marjamaa², Heikki Väänänen³, Annukka M Tuiskula⁴, Kimmo Kontula⁵, Heikki Swan², Matti Viitasalo²

Affiliations

¹ Heart and Lung Center, Helsinki University Hospital, Helsinki, Finland. Electronic address: mikael.koponen@helsinki.fi.
² Heart and Lung Center, Helsinki University Hospital, Helsinki, Finland.
³ Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland.
⁴ Department of Medicine, Helsinki University Hospital and University of Helsinki, Helsinki, Finland; HUS Diagnostic Center, Laboratory of Genetics, Helsinki University Hospital and University of Helsinki, Helsinki, Finland.
⁵ Department of Medicine, Helsinki University Hospital and University of Helsinki, Helsinki, Finland.

PMID: 35525424
DOI: 10.1016/j.hrthm.2022.04.028

Abstract

Background: Long QT syndrome (LQTS) is an inherited arrhythmia disorder characterized by ventricular repolarization abnormalities and a risk of sudden cardiac death. The electrophysiological components generating the high risk of arrhythmias in LQTS are prolonged repolarization, increased dispersion of repolarization, and early afterdepolarizations, which are clinically estimated as QT interval, T-wave peak to T-wave end (TPE) interval, and T2/T1-wave amplitude ratio, respectively. In experimental LQTS type 2 (LQT2) models, β-blockers decrease dispersion of repolarization and prevent early afterdepolarizations. In clinical studies in patients with LQT2 , β-blockers are more effective against exercise-induced than arousal-induced cardiac events.

Objectives: The aim of the study was to investigate the effects of β-blocker therapy on repolarization properties in LQT2.

Methods: QT and TPE intervals and maximal T2/T1-wave amplitude ratios recorded by 24-hour electrocardiograms before and during β-blocker therapy were evaluated in 25 patients with LQT2.

Results: β-Blocker therapy decreased the maximal T2/T1-wave amplitude ratio from 2.9 ± 1.1 to 1.8 ± 0.7 (P < .001), but did not change the pause-induced T2/T1-wave amplitude ratio. Under medication, abrupt maximal TPE intervals were shorter at heart rates of ≥75 beats/min and maximal QT intervals were shorter at a heart rate of 100 beats/min.

Conclusion: β-Blockers stabilize ventricular repolarization in LQT2 by reducing electrocardiographic early afterdepolarizations and by reducing abrupt prolongation of electrocardiographic dispersion of repolarization and ventricular repolarization duration at elevated heart rates. The effect of β-blockers on pause-induced electrocardiographic early afterdepolarizations is weak. The findings provide electrocardiographic explanation for the protective effects of β-blockers against exercise-induced cardiac events in LQT2.

Keywords: 24-Hour electrocardiogram; Dispersion of repolarization; Early afterdepolarization; Long QT syndrome type 2; β-Blocker.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adrenergic beta-Antagonists / pharmacology
Adrenergic beta-Antagonists / therapeutic use
Arrhythmias, Cardiac / drug therapy
Electrocardiography*
Electrocardiography, Ambulatory
Heart Rate
Humans
Long QT Syndrome* / diagnosis
Long QT Syndrome* / drug therapy

Substances

Adrenergic beta-Antagonists