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Use of the rate-corrected JT interval for prediction of repolarization abnormalities in children
C I Berul1, T L Sweeten, A M Dubin
1Division of Cardiology, Children's Hospital of Philadelphia, Pennsylvania 19104.
Insights
The rate-corrected JT interval (JTc) is a more sensitive marker for Long QT Syndrome (LQTS) than the rate-corrected QT interval (QTc). JTc accurately measures ventricular repolarization, improving LQTS diagnosis, especially in borderline QTc cases.
Area of Science:
- Cardiology
- Clinical Electrophysiology
- Medical Diagnostics
Background:
- Prolonged rate-corrected QT interval (QTc) is linked to ventricular arrhythmias and sudden death.
- QTc may not be sensitive for Long QT Syndrome (LQTS) repolarization abnormalities, especially with conduction issues.
- The rate-corrected JT interval (JTc) offers a more precise measure of ventricular repolarization.
Purpose of the Study:
- To evaluate the diagnostic sensitivity of the JTc interval compared to the QTc interval in Long QT Syndrome (LQTS).
- To determine if JTc can identify LQTS patients with borderline or normal QTc values.
- To assess the utility of JTc in differentiating repolarization abnormalities.
Main Methods:
- Measured QTc and JTc intervals in 40 LQTS patients, 31 with right bundle branch block (RBBB) post-tetralogy of Fallot repair, and 1,000 controls.
- Compared JTc and QTc measurements between groups.
- Assessed the sensitivity of JTc versus QTc in identifying LQTS patients.
Main Results:
- The RBBB group showed normal JT and JTc, despite prolonged QT/QTc.
- JTc identified 85% of LQTS patients, significantly higher than QTc's 58% sensitivity.
- JTc is a more specific ventricular repolarization measure, excluding QRS duration variability.
Conclusions:
- JTc is a more sensitive predictor of repolarization abnormalities than QTc.
- JTc is valuable for diagnosing LQTS, particularly in patients with borderline or normal QTc.
- JTc enhances the assessment of ventricular repolarization in LQTS.
Abstract:
A prolonged rate-corrected QT interval (QTc) may be associated with an increased risk of developing ventricular arrhythmias and sudden death, particularly in patients with the hereditary long QT syndrome (LQTS), myocardial ischemia, or antiarrhythmic medication toxicity. It is known that there are some patients with LQTS who sometimes have a borderline or normal QTc (< or = 0.45 second). Although the QTc has been the standard measurement of ventricular repolarization, it includes both depolarization and repolarization and may not always be a sensitive indicator of the type of repolarization abnormalities seen in LQTS. Intraventricular conduction abnormalities complicate evaluation of the QTc interval. The rate-corrected JT interval (JTc) is a more accurate measurement of ventricular repolarization, and therefore may be a more sensitive means of assessing abnormalities. The QTc on a resting electrocardiogram was determined in 40 patients with LQTS and in 31 patients with right bundle branch block after tetralogy of Fallot repair. These were compared with 1,000 age-matched control subjects. The right bundle branch block group had normal JT and JTc measurements, despite having prolonged QT and QTc intervals compared with controls. The JTc identified 85% of patients affected with LQTS compared with only 58% identified using only the QTc as a marker for the syndrome. The JTc is a more specific measurement of ventricular repolarization than the QTc by eliminating QRS duration variability. It appears to be a more sensitive predictor of repolarization abnormalities, and may be helpful in identifying patients with LQTS who have borderline or normal QTc measurements on resting electrocardiograms.