Document Detail

Utility of treadmill testing in identification and genotype prediction in long-QT syndrome.
MedLine Citation:
PMID:  20071715     Owner:  NLM     Status:  MEDLINE    
BACKGROUND: The clinical diagnosis of long-QT syndrome (LQTS) remains challenging when ECG abnormalities are borderline or intermittent. Despite issues with access, cost, and heterogeneity of LQTS mutations, genetic testing remains the diagnostic gold standard for diagnosis of LQTS. We sought to develop a provocative testing strategy to unmask the LQTS phenotype and relate this to the results of genetic testing.
METHODS AND RESULTS: From 1995 to 2008, 159 consecutive patients with suspected LQTS underwent provocative testing that consisted of a modified Bruce protocol treadmill exercise test, with ECGs recorded supine at rest, immediately on standing, and at 1-minute intervals during exercise, at peak exercise, and at 1-minute intervals during the recovery phase. Similar testing was carried out on a stationary bike in a gradual and burst exercise fashion. LQTS was confirmed with genotyping in all 95 affected LQTS patients and excluded with negative family screening in 64 control subjects. Patients were studied before and after initiation of beta-blockers. Of 159 patients, 50 had an LQT1 mutation and 45 had an LQT2 mutation. In the LQTS group, 44.3% of patients had a normal-to-borderline resting QTc interval. LQTS patients exhibited a greater prolongation in QTc with postural change than unaffected patients (LQT1: 40 ms [IQR, 42]; LQT2: 35 ms [IQR, 46]; and LQTS-negative: 21 ms [IQR, 37]; P=0.029). During exercise, LQT1 patients had marked QTc prolongation compared with LQT2 and LQTS-negative patients (LQT1: 65 ms [60], LQT2: 3 ms [46], LQTS negative: 5 ms [41]; P<0.0001). QT hysteresis was more pronounced in patients with LQT2 mutations compared with LQT1 and LQT-negative patients (LQT2: 40 ms [10], LQT1: 15 ms [40]; LQTS-negative: 20 ms [20]; P<0.001). beta-Blockade normalized the QTc changes seen with standing and QT hysteresis.
CONCLUSIONS: The presence and genotype of LQTS can be predicted by a combination of postural and exercise changes in the QT/RR relationship. beta-Blockade normalized these changes. Routine exercise testing is useful in predicting and directing genetic testing in LQTS.
Jorge A Wong; Lorne J Gula; George J Klein; Raymond Yee; Allan C Skanes; Andrew D Krahn
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Publication Detail:
Type:  Clinical Trial; Journal Article; Research Support, Non-U.S. Gov't; Validation Studies     Date:  2010-01-09
Journal Detail:
Title:  Circulation. Arrhythmia and electrophysiology     Volume:  3     ISSN:  1941-3084     ISO Abbreviation:  Circ Arrhythm Electrophysiol     Publication Date:  2010 Apr 
Date Detail:
Created Date:  2010-04-21     Completed Date:  2010-05-05     Revised Date:  2012-02-03    
Medline Journal Info:
Nlm Unique ID:  101474365     Medline TA:  Circ Arrhythm Electrophysiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  120-5     Citation Subset:  IM    
Arrhythmia Service, Division of Cardiology, University of Western Ontario, London, Ontario, Canada.
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MeSH Terms
Adrenergic beta-Antagonists / therapeutic use
Atenolol / therapeutic use
Ether-A-Go-Go Potassium Channels / genetics
Exercise Test / standards*
KCNQ1 Potassium Channel / genetics
Long QT Syndrome / diagnosis*,  drug therapy,  genetics*
Middle Aged
Muscle Proteins / genetics
Potassium Channels, Voltage-Gated / genetics
Predictive Value of Tests
Reference Standards
Sodium Channels / genetics
Young Adult
Reg. No./Substance:
0/Adrenergic beta-Antagonists; 0/ERG1 potassium channel; 0/Ether-A-Go-Go Potassium Channels; 0/KCNE1 protein, human; 0/KCNE2 protein, human; 0/KCNQ1 Potassium Channel; 0/KCNQ1 protein, human; 0/Muscle Proteins; 0/Potassium Channels, Voltage-Gated; 0/Sodium Channels; 0/sodium channel protein type 5 subunit alpha; 29122-68-7/Atenolol

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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