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Electrophysiologic Substrate in Congenital Long QT Syndrome: Noninvasive Mapping With Electrocardiographic Imaging (ECGI) | Journal Scan
Study Questions:
How does epicardial repolarization and dispersion of repolarization differ between normal patients and patients with long QT syndrome (LQTS) based on electrocardiographic imaging (ECGI)?
Methods:
The investigators performed ECGI on 25 patients with LQTS (9 LQT1, 9 LQT2, 5 LQT3, and 2 LQT5) and 7 normal controls. ECGI is a noninvasive experimental technique using 256 body surface ECGs and cardiac computed tomography images to map and display epicardial surface potentials during the cardiac rhythm. Study measures included activation time (AT), recovery time (RT), activation-recovery interval (ARI), and dispersion of RT (ΔRT) and ARI (ΔARI).
Results:
The phenotypes of included LQTS patients varied from asymptomatic diagnosis by cascade screening to ventricular fibrillation arrest; all had a prolonged baseline QTc. AT was similar in LQTS and controls. LQTS patients had prolonged and heterogeneous RTs and ARIs consistent with delayed repolarization and abnormally long action potential duration. Spatial repolarization gradients (ΔRT/Δdistance or ΔARI/Δdistance) were much steeper in LQTS than in controls, and were additionally steeper in symptomatic LQTS patients compared to asymptomatic LQTS patients. These dispersion measures varied among LQTS types and even families with the same mutation.
Conclusions:
The authors concluded that LQTS patients show significant heterogeneity and steep repolarization dispersion on ECGI compared to normal controls.
Perspective:
This study contributes unique data to the understanding of arrhythmia mechanisms in LQTS. Dispersion of repolarization is a previously hypothesized mechanism of arrhythmia in this disease, and this study using ECGI is supportive. Most interesting is the finding of variable repolarization measures within types and even specific mutations of LQTS, possibly reflecting the role of modifier genes or other individual factors. Since spatial repolarization gradient differences correlated with the severity of the patient’s phenotype, ECGI may be a future test for determination of risk in LQTS.
Keywords: Action Potentials, Arrhythmias, Cardiac, Electrocardiography, Long QT Syndrome, Mutation, Phenotype, Ventricular Fibrillation
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