• Matthew T Bennett, Lorne J Gula, George J Klein, Allan C Skanes, Raymond Yee, Peter Leong-Sit, Ishvinder Chattha, Raymond Sy, Douglas L Jones, and Andrew D Krahn.
• 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.
• Europace. 2014 Dec 1; 16 (12): 1847-51.

AimsBeta-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.Methods And ResultsTwenty-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.ConclusionBeta-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.Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2014. For permissions please email: journals.permissions@oup.com.

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