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Vectorcardiographic recordings of the Q-T interval in a pediatric long Q-T syndrome population
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Cardiology.
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Cardiology.
Umeå University, Faculty of Medicine, Department of Clinical Sciences, Paediatrics.
Umeå University, Faculty of Medicine, Department of Medical Biosciences, Medical and Clinical Genetics.
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2013 (English)In: Pediatric Cardiology, ISSN 0172-0643, E-ISSN 1432-1971, Vol. 34, no 2, 245-249 p.Article in journal (Refereed) Published
Abstract [en]

Measurements of the Q-T interval are less reliable in children than in adults. Identification of superior diagnostic tools is warranted. This study aimed to investigate whether a vectorcardiogram (VCG) recorded from three orthogonal leads (X, Y, Z) according to Frank is superior to a 12-lead electrocardiogram (ECG) in providing a correct long Q-T syndrome (LQTS) diagnosis in children. This LQTS group consisted of 35 genetically confirmed carriers of mutations in the KCNQ1 (n = 29) and KCNH2 (n = 6) genes. The control group consisted of 35 age- and gender-matched healthy children. The mean age was 7 years in the LQTS group and 6.7 years in the control group (range, 0.5-16 years). The corrected Q-T interval (QT(c)) was measured manually (QT(man)) by one author (A.W.). The 12-lead ECG automatic measurements (QT(ECG)) and interpretation (QT(Interpret)) of QT(c) were performed with the Mac5000 (GE Medical System), and the VCG automatic measurements (QT(VCG)) were performed with the Mida1000, CoroNet (Ortivus AB, Sweden). By either method, a QT(c) longer than 440 ms was considered prolonged and indicative of LQTS. Of the 35 children with genetically confirmed LQTS, 30 (86 %) received a correct diagnosis using QT(VCG), 29 (82 %) using QT(man), 24 (69 %) using QT(ECG), and 17 (49 %) using QT(Interpret). Specificity was 0.80 for QT(VCG), 0.83 for QT(man), 0.77 for QT(ECG), and 0.83 for QT(Interpret). The VCG automatic measurement of QT(c) seems to be a better predictor of LQTS than automatic measurement and interpretation of 12-lead ECG.

Place, publisher, year, edition, pages
2013. Vol. 34, no 2, 245-249 p.
Keyword [en]
Children, Electrocardiogram, Long QT syndrome, QT, Vectorcardiogram
National Category
Cardiac and Cardiovascular Systems Pediatrics
URN: urn:nbn:se:umu:diva-67401DOI: 10.1007/s00246-012-0425-2ISI: 000315036500007OAI: diva2:615196
Available from: 2013-04-09 Created: 2013-03-18 Last updated: 2013-09-12Bibliographically 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.
Umeå University medical dissertations, ISSN 0346-6612 ; 1583
National Category
Cardiac and Cardiovascular Systems
Research subject
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)
Available from: 2013-09-12 Created: 2013-09-09 Last updated: 2013-09-12Bibliographically approved

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Diamant, Ulla-BrittJensen, Steen MWinbo, AnnikaStattin, Eva-LenaRydberg, Annika
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