Interval Representative of Transmural Dispersion of Repolarization in Children and Young Adolescents With Congenital Long QT Syndrome

Abstract

ong QT syndrome (LQTS) is a rare disorder characterized by prolonged ventricular repolarization and a high risk of cardiac events, including sudden cardiac death. 1,2 Among the mutations thus far identified in specific ion channel genes causing LQTS, 3-6 KCNQ1 and KCNH2 have been most commonly identified, and they are known to cause the LQT1 and LQT2 forms, respectively. Recent studies have reported that LQTS-related cardiac events tend to occur under specific circumstances in a genespecific manner. 7 In the LQT1 form, exercise and swimming are the most common triggers, whereas in the LQT2 form they are strong emotions, sleep, and rest. 7 Results of experimental studies suggest that the interval between the peak and the end of the T wave in a transmural electrocardiogram (ECG) reflects the transmural dispersion of repolarization (TDR) when a normal upright T wave is present, and that TDR is linked to the genesis of torsade de pointes. [8][9][10] When complex (inverted, notched or biphasic, and triphasic) T waves are present, the interval from the nadir of the initial negative T wave to the end of the T wave is representative of the TDR. 11 However, the definition of the interval representative of TDR on a clinical surface ECG remains a subject of controversy when the T wave shows a notched or a bifid configuration. [12][13][14][15][16] There has not been a clinical report of the use of the interval from the nadir of the initial negative T wave to the end of the T wave as the definition of the interval representative of TDR when the notched or a bifid T wave is present.A face immersion test was reported to induce an abnormally prolonged QT interval and notched T waves in children and adolescent with LQTS, 17 suggesting that the same test would induce a prolongation of the TDR in these young patients. We used the face immersion test to examine the QT intervals and compare the T wave configuration on ECG before and after treatment with the aim of determining whether the interval representative of TDR based on the experimental study can be adapted for use in the clinical setting, assuming that the decrease in the QTc interval after treatment is associated with a decrease in the TDR. Methods Study PopulationInclusion criteria for the present study were children and adolescents with LQTS who had been treated and undergone a face immersion test before and after treatment. The 3 boys and 2 girls comprised 3 cases of the LQT1 form (KCNQ1 mutation; 2 families) and 2 of the LQT2 form (KCNH2 mutation, 2 families) ( Table 1). ControlsTo determine the normal range of the QT intervals during the face immersion test, 31 control children and adolescents (23 boys, 8 girls; mean age, 12 years; range, 6-17 years) were also examined. Normal ranges were defined as the mean ± 2SD. Background It has been shown experimentally that the interval from the nadir of the initial negative T wave to the end of the T wave is representative of transmural dispersion of repolarization (TDR) when complex T waves are present. In the clinical setting,...

Ventricular Repolarization and Heart Rate Responses During Cardiovascular Autonomic Function Testing in LQT1 Subtype of Long QT Syndrome

“…5 Because of the important role of the autonomic nervous system, both as a modulator of the QT interval, and as a possible trigger of arrhythmia, several studies have assessed the use of different autonomic maneuvers in the diagnosis and management of LQTS. [6][7][8][9][10][11][12] However, genetic heterogeneity of the study populations, as well as methodological difficulties in assessing the complex relationship between rapid changes in HR and the QT interval duration make the interpretation of previous results or practical use of autonomic function tests difficult.…”

Tpeak‐Tend Interval in 12‐Lead Electrocardiogram of Healthy Children and Adolescents Tpeak‐Tend Interval in Childhood

“…Several publications showed that TpTe interval is longer in disorders such as long QT syndrome, polymorphic catecholaminergic ventricular tachycardia and Brugada syndrome. It may be also a predicting factor for elevated risk of sudden cardiac death in patients with heart disorders . It was demonstrated that the ratio of TpTe to QT interval is relatively constant, independent of the heart rate, and it may be a clinically useful marker of ventricular repolarization.…”

Arrhythmogenesis in the Short-QT Syndrome Associated With Combined HERG Channel Gating Defects

“…3 Heterogeneous abbreviation of the action potential duration (APD) in different cell types spanning the ventricular wall seems to create the substrate for the genesis of ventricular arrhythmia in the short-QT syndrome, as is proposed for the long-QT syndrome and Brugada syndrome. [4][5][6][7][8] Brugada et al identified the first mutation associated with the short-QT syndrome. 3 The missense mutation (N588K) involving a substitution of lysine for asparagine in position 588 of KCNH2 was found to cause a remarkable gain of function in the IKr.…”