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Two automatic QT algorithms compared with manual measurement in identification of long QT syndrome
Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences. Umeå University, Faculty of Medicine, Department of Clinical Sciences, Paediatrics.
Umeå University, Faculty of Medicine, Department of Clinical Sciences, Paediatrics.
Umeå University, Faculty of Medicine, Department of Medical Biosciences, Medical and Clinical Genetics.
Umeå University, Faculty of Medicine, Department of Clinical Sciences, Paediatrics.
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2010 (English)In: Journal of Electrocardiology, ISSN 0022-0736, E-ISSN 1532-8430, Vol. 43, no 1, 25-30 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Long QT syndrome (LQTS) is an inherited disorder that increases the risk of syncope and malignant ventricular arrhythmias, which may result in sudden death.

METHODS: We compared manual measurement by 4 observers (QT(manual)) and 3 computerized measurements for QT interval accuracy in the diagnosis of LQTS: 1. QT measured from the vector magnitude calculated from the 3 averaged orthogonal leads X, Y, and Z (QTVCG) and classified using the same predefined QTc cut-points for classification of QT prolongation as in manual measurements; 2. QT measured by a 12-lead electrocardiogram (ECG) program (QTECG) and subsequently classified using the same cut-points as in (1) above; 3. The same QT value as in (2) above, automatically classified by a 12-lead ECG program with thresholds for QT prolongation adjusted for age and sex (QTinterpret). The population consisted of 94 genetically confirmed carriers of KCNQ1 (LQT1) and KCNH2 (LQT2) mutations and a combined control group of 28 genetically confirmed noncarriers and 66 unrelated healthy volunteers.

RESULTS: QT(VCG) provided the best combination of sensitivity (89%) and specificity (90%) in diagnosing LQTS, with 0.948 as the area under the receiver operating characteristic curve. The evaluation of QT measurement by the 4 observers revealed a high interreader variability, and only 1 of 4 observers showed acceptable level of agreement in LQTS mutation carrier identification (kappa coefficient >0.75).

CONCLUSION: Automatic QT measurement by the Mida1000/CoroNet system (Ortivus AB, Danderyd, Sweden) is an accurate, efficient, and easily applied method for initial screening for LQTS.

Place, publisher, year, edition, pages
2010. Vol. 43, no 1, 25-30 p.
Keyword [en]
Long QT syndrome, QT interval, Automatic measurement, Vectorcardiography, Mutation analysis
National Category
Cardiac and Cardiovascular Systems
Identifiers
URN: urn:nbn:se:umu:diva-32965DOI: 10.1016/j.jelectrocard.2009.09.008PubMedID: 20005993OAI: oai:DiVA.org:umu-32965DiVA: diva2:306858
Available from: 2010-03-31 Created: 2010-03-31 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Long QT syndrome: studies of diagnostic methods
Open this publication in new window or tab >>Long QT syndrome: studies of diagnostic methods
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background: The Long QT Syndrome (LQTS) is a hereditary heart disease with risk of malignant ventricular arrhythmia and sudden cardiac death. Despite our increased knowledge about genotype and phenotype correlation we still rely on the 12-lead ECG for assessment of the QT interval and the T-wave morphology for diagnosis and risk stratification. Intra- and -inter individual variability in manually QT measurement and, e.g., difficulties in defining the end of the T-wave may impair the diagnosis of LQTS. Increased heterogeneity in ventricular repolarization (VR) may be an important factor in the arrhythmogenicity in cases of LQTS. In a LQTS founder population the same mutation is carried by numerous individuals in many families which provide a unique opportunity to study diagnostic methods, risk assessment, VR and the correlation between genotype and phenotype.

Methods: Resting 12-lead ECG and vectorcardiogram (VCG) were recorded in 134 LQTS mutation carriers and 121 healthy controls, to investigate the capability and precision in measuring the QT interval. For assessment of the VR, VCG was compared in individuals with mutations in the KCNQ1 and KCNH2 gene. Genealogical and geographic studies were performed in 37 index cases and their relatives to determine if Swedish carriers of the Y111C mutation in the KCNQ1 gene constitute a founder population. To confirm kinship, haplotype analysis was performed in 26 of the 37 index cases. The age and prevalence of the Y111C mutation were calculated in families sharing a common haplotype.

Results: VCG by automatic measurement of the QT interval provided the best combination of sensitivity (90%) and specificity (89%) in the diagnosis of LQTS. VCG showed no consistent pattern of increased VR heterogeneity among KCNQ1 and KCNH2 mutation carriers. Living carriers of the Y111C mutation shared a common genetic (haplotype), genealogic and geographic origin. The age of the Y111C mutation was approximately 600 years. The prevalence of living carriers of the Y111C mutation in the mid-northern Sweden was estimated to 1:1,500-3,000.

Conclusion: We have shown that VCG provides a valuable contribution to the diagnosis and risk assessment of LQTS in adults and children. No consistent pattern of increased VR heterogeneity was found among the LQTS mutation carriers. The identified Swedish LQTS founder population will be a valuable source to future LQTS research and may contribute to increase our understanding of LQTS and the correlation of phenotype, genotype and modifying factors.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2013. 67 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1583
National Category
Cardiac and Cardiovascular Systems
Research subject
Cardiology
Identifiers
urn:nbn:se:umu:diva-80103 (URN)978-91-7459-693-9 (ISBN)
Public defence
2013-10-04, Hörsal D, Unod T 9, Norrlands Universitetssjukhus, Umeå, 09:00 (Swedish)
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Available from: 2013-09-12 Created: 2013-09-09 Last updated: 2013-09-12Bibliographically approved

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