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QT Adaptation and Intrinsic QT Variability in Congenital Long QT Syndrome
Srikanth Seethala1, Prabhpreet Singh2, Vladimir Shusterman3
1Scripps Clinic, San Diego, CA (S.S.) University of Tennessee, College of Medicine, Chattanooga, TN.
Journal of the American Heart Association
|December 18, 2015
Summary
Increased QT variability (QTV) in congenital long QT syndrome (LQTS) patients correlates with repolarization delay. This intrinsic QTV, independent of heart rate, may indicate action potential instability in LQTS.
Area of Science:
- Cardiology
- Electrophysiology
- Genetics
Background:
- Increased QT variability (QTV) is linked to arrhythmias.
- Congenital long QT syndrome (LQTS) offers insights into repolarization and QTV.
- LQTS is a pure repolarization disorder.
Purpose of the Study:
- To investigate the relationship between QT interval adaptation to heart rate and intrinsic QTV in LQTS patients.
- To determine if intrinsic QTV correlates with repolarization delay or clinical presentation.
Main Methods:
- Analyzed 24-hour Holter monitor data from 78 genotyped LQTS patients.
- Utilized computer-assisted annotation of RR and QT intervals.
- Modeled the RR-QT relationship to calculate QTc and intrinsic QTV.
Main Results:
- An exponential model with a 60-second time constant best fit the RR-QT relationship.
- Intrinsic QTV was higher in patients with longer QTc and in LQT2 compared to LQT1/5.
- QTc and intrinsic QTV did not differ significantly between symptomatic and asymptomatic patients.
Conclusions:
- QT interval adaptation to heart rate in LQTS occurs with a time constant of approximately 60 seconds.
- Intrinsic QTV correlates with the degree of repolarization delay in LQTS.
- Intrinsic QTV may reflect action potential instability observed in LQTS animal models.
