Abstract 13751: Individualized Corrected QT Interval Improves Accuracy to Predict Mutation Carriage in LQTS Families Compared to Bazett’s Formula
Objectives: Diagnosis in familial long QT syndrome (LQTS) remains challenging due to several difficulties in measuring and interpreting QT interval like QT measurement per se, variability over time, QT overlap and last but not least QT correction for heart rate. Therefore we evaluated the hypothesis that an individualized corrected QT interval measured by 24 hour holter recording is more accurate in predicting carriage of a pathogenic LQTS mutation compared to standard QT correction with Bazett’s formula from standard 12 lead ECG.
Methods: We retrospectively analyzed the database of the center of hereditary heart disease at our institiution to find genotype positive LQTS patients and their genotype negative probands who had both ECG and holter available. Automated and manual measurements of QT interval and heart rate with high resolution calipers of signal averaged beats of 10 seconds of ECG in lead V5 were done. An individualized QT correction formula was determined from 24 hour holter data (QTc = α x RR + β).
Results: We included 46 LQTS patients (15 LQT1, 28 LQT2 and 3 LQT3) and 46 controls including 22 genotype negative probands and an additional 24 patients with concealed AVRT after catheter ablation to balance the groups. Demographic characteristics were comparable. Difference in mean QTc between mutation carriers and controls with automated versus manual measurement on ECG versus individually corrected QTc with holter was 50ms, 60ms and 75 ms respectively. Using conventional QTc cut-off criteria (QTc in males >450ms and in females >470ms), a sensitivity of 43%, specificity of 100% and diagnostic accuracy of 72% are achieved with manual measurement on standard 12 lead ECG. Using an individualized correction formula with a cut-off of 445ms (obtained by evaluating a ROC curve of our data), a sensitivity of 87%, specificity of 98% and diagnostic accuracy of 92% are achieved.
Conclusions: We show for the first time that an individualized QTc measurement derived from holter recordings is superior over QTc measured from a standard 12 lead ECG to predict carriage of a LQTS mutation. Therefore this finding provides evidence for the more widespread use of an individualized QTc in the evaluation of a possible LQTS.
Author Disclosures: T. Robyns: None. R. Willems: None. J. Ector: None. H. Heidbuchel: None. S. Janssens: None. D. Nuyens: None.
- © 2014 by American Heart Association, Inc.