Abstract
T-wave parameters, especially the Tpeak-Tend interval (TpTe), reflect the total dispersion of repolarization, whose amplification may lead to the development of life-threatening ventricular arrhythmias observed in the long QT syndrome (LQTS). The study attempted to evaluate QT, QTp (Q-Tpeak) and TpTe (Tpeak-Tend) intervals in unaffected and affected blood relatives of children with clinically confirmed LQTS as well as to determine whether the values of these repolarization parameters may be used in clinical practice. The study group included 47 affected blood relatives (27 LQTS1 and 20 LQTS2) and 68 unaffected family members without clinically confirmed LQTS symptoms. The TpTe, QT and QTp intervals were measured manually in the lead V5 of standard ECGs and corrected using Bazett's and Fridericia's formulas. The RR, QT, QTp and TpTe intervals with their corrected values were significantly longer (p < 0.0001) in the affected subjects than in the unaffected subjects and, similarly, in LQTS1 and LQTS2 patients compared with the unaffected family members. The TpTe interval in LQTS2 showed only a tendency to be longer compared to LQTS1, but did not reach statistical significance (p = 0.0933). For affected blood relatives, only the TpTe interval (p < 0.0409) and QT interval, corrected with Bazett's (p < 0.0393) and Fridericia's (p < 0.0495) formulas, enabled differentiation between LQTS1 (mean TpTe = 103 ±15) and LQTS2 women (mean TpTe = 106 ±17). Moreover, there were statistically significant differences (p < 0.05) in the TpTe interval between the 6 sex subgroups: unaffected women and men as well as women and men with LQTS1 and LQTS2. The electrocardiographic Tpeak-Tend parameter, in addition to the QT interval, is helpful in identifying affected blood relatives of children with LQTS, particularly for the group of LQTS1 and LQTS2 women. Further studies are required to assess the clinical importance of the TpTe interval in families with long QT syndrome.
Highlights
The RR, QT, QTp and Tpeak-Tend interval (TpTe) intervals with their corrected values were significantly longer (p < 0.0001) in the affected subjects than in the unaffected subjects and, in LQTS1 and LQTS2 patients compared with the unaffected family members
Further studies are required to assess the clinical importance of the TpTe interval in families with long QT syndrome
The criteria for long QT syndrome (LQTS) diagnosis, valid since 1993 and comprising a point scale, based on clinical presentation, family history and the electrocardiographic analysis of the QT interval, do not include the classification of the most common types of LQTS: LQTS1 and LQTS2.1,6 the criteria do not consider the diagnostic importance of the QTp (Q-Tpeak) and TpTe (Tpeak-Tend) intervals in the resting and exercise ECG that help differentiate between LQTS1 and LQTS2 and assess the risk of malignant ventricular arrhythmias.[7,8,9,10,11,12]
Summary
Congenital long QT syndrome (LQTS) is a disease manifested by electrocardiographic repolarization abnormalities with the QT interval prolongation and predisposition for malignant ventricular tachyarrhythmias (torsade de pointes), potentially leading to recurrent syncope and sudden cardiac death (SCD).[1]Among 15 types of LQTS mutations far identified, the most common LQTS1 (KCNQ1) and LQTS2 (KCNH2) genotypes differ in the clinical course, symptom-related triggers, duration and morphology of the repolarization wave in the ECG, determined by various action potential durations in cardiac myocytes, dependent on malfunctioning ion channels: slowly repolarizing cardiac potassium current IKs in LQTS1 and rapidly repolarizing cardiac potassium current IKr in LQTS2.2–5The criteria for LQTS diagnosis, valid since 1993 (improved in 2012) and comprising a point scale (the Schwartz score ≥4), based on clinical presentation, family history and the electrocardiographic analysis of the QT interval, do not include the classification of the most common types of LQTS: LQTS1 and LQTS2.1,6 the criteria do not consider the diagnostic importance of the QTp (Q-Tpeak) and TpTe (Tpeak-Tend) intervals in the resting and exercise ECG that help differentiate between LQTS1 and LQTS2 and assess the risk of malignant ventricular arrhythmias.[7,8,9,10,11,12]T-wave parameters, especially the Tpeak-Tend (TpTe) interval, may provide a more accurate electrophysiological marker of ventricular arrhythmia risk than the QT interval.[12,13] The question of whether TpTe reflects transmural repolarization heterogeneity or total dispersion of repolarization is still a matter of debate.[5,14,15,16]The study attempted to evaluate the QT, QTp and TpTe intervals in unaffected and affected blood relatives of children with long QT syndrome as well as to determine whether the values of these repolarization parameters may be used in clinical practice as a possible method of identifying affected and unaffected subjects, and whether they may help differentiate between LQTS1 and LQTS2 types. The criteria for LQTS diagnosis, valid since 1993 (improved in 2012) and comprising a point scale (the Schwartz score ≥4), based on clinical presentation, family history and the electrocardiographic analysis of the QT interval, do not include the classification of the most common types of LQTS: LQTS1 and LQTS2.1,6 the criteria do not consider the diagnostic importance of the QTp (Q-Tpeak) and TpTe (Tpeak-Tend) intervals in the resting and exercise ECG that help differentiate between LQTS1 and LQTS2 and assess the risk of malignant ventricular arrhythmias.[7,8,9,10,11,12]. T-wave parameters, especially the Tpeak-Tend interval (TpTe), reflect the total dispersion of repolarization, whose amplification may lead to the development of life-threatening ventricular arrhythmias observed in the long QT syndrome (LQTS)
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