Effect of beta-blockers on QT dynamics in the long QT syndrome: measuring the benefit.
OBJECTIVE
Beta-blockers are the standard of care for the treatment of long QT syndrome (LQTS), and have been shown to reduce recurrent syncope and mortality in patients with type 1 LQTS (LQT1). Although beta-blockers have minimal effect on the resting corrected QT interval, their effect on the dynamics of the non-corrected QT interval is unknown, and may provide insight into their protective effects.


RESULTS
Twenty-three patients from eight families with genetically distinct mutations for LQT1 performed exercise stress testing before and after beta-blockade. One hundred and fifty-two QT, QTc, and Tpeak-Tend intervals were measured before starting beta-blockers and compared with those at matched identical cycle lengths following beta-blockade. Beta-blockers demonstrated heart-rate-dependent effects on the QT and QTc intervals. In the slowest heart rate tertile (<90 b.p.m.), beta-blockade increased the QT and QTc intervals (QT: 405 vs. 409 ms; P = 0.06; QTc: 459 vs. 464 ms; P = 0.06). In the fastest heart rate tertile (>100 b.p.m.), the use of beta-blocker was associated with a reduction in both the QT and QTc intervals (QT: 367 vs. 358 ms; P < 0.0001; QTc: 500 vs. 486 ms; P < 0.0001). The Tpeak-Tend interval showed minimal change at slower heart rates (<90 b.p.m.) (93 vs. 87 ms; P = 0.09) and at faster heart rates (>100 b.p.m.) (87 vs. 84 ms; P = NS) following beta-blockade.


CONCLUSIONS
Beta-blockers have heart-rate-dependent effects on the QT and QTc intervals in LQTS. They appear to increase the QT and QTc intervals at slower heart rates and shorten them at faster heart rates during exercise.
Division of Cardiology, Department of Medicine, University of British Columbia, Arrhythmia Service, 9th Floor, Gordon & Leslie Diamond Health Care Centre, 2775 Laurel Street, Vancouver, BC, Canada V5Z 1M9 matthew.bennett@vch.ca.
Matthew T
MT
Bennett
Division of Cardiology, Department of Medicine, University of Western Ontario, London, ON, Canada N6G 2V4.
Lorne J
LJ
Gula
Division of Cardiology, Department of Medicine, University of Western Ontario, London, ON, Canada N6G 2V4.
George J
GJ
Klein
Division of Cardiology, Department of Medicine, University of Western Ontario, London, ON, Canada N6G 2V4.
Allan C
AC
Skanes
Division of Cardiology, Department of Medicine, University of Western Ontario, London, ON, Canada N6G 2V4.
Raymond
R
Yee
Division of Cardiology, Department of Medicine, University of Western Ontario, London, ON, Canada N6G 2V4.
Peter
P
Leong-Sit
Division of Cardiology, Department of Medicine, University of Western Ontario, London, ON, Canada N6G 2V4.
Ishvinder
I
Chattha
Department of Cardiology, Royal Prince Alfred Hospital, Sydney, NSW 2050, Australia.
Raymond
R
Sy
Division of Cardiology, Department of Medicine, University of Western Ontario, London, ON, Canada N6G 2V4 Department of Physiology and Pharmacology, University of Western Ontario, London, ON, Canada N6G 2V4.
Douglas L
DL
Jones
Division of Cardiology, Department of Medicine, University of British Columbia, Arrhythmia Service, 9th Floor, Gordon & Leslie Diamond Health Care Centre, 2775 Laurel Street, Vancouver, BC, Canada V5Z 1M9.
Andrew D
AD
Krahn
D000319:Adrenergic beta-Antagonists / Q000627:therapeutic use*; D000328:Adult; D004562:Electrocardiography / Q000187:drug effects*; D005080:Exercise Test; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D008297:Male; D029597:Romano-Ward Syndrome / Q000175:diagnosis / Q000188:drug therapy* / Q000503:physiopathology*; D016896:Treatment Outcome
D000319:Adrenergic beta-Antagonists
Beta-blocker; Electrocardiography; Exercise testing; Long QT syndrome; QT interval