Stramba-Badiale M, Locati E H, Martinelli A, Courville J, Schwartz P J
Centro di Fisiologia Clinica e Ipertensione, University of Milan, Italy.
Eur Heart J. 1997 Jun;18(6):1000-6. doi: 10.1093/oxfordjournals.eurheartj.a015357.
There are gender-related differences in the QT interval measured from standard ECG tracings. However, these observations are based on a limited number of beats recorded in resting conditions. Computerized Holter techniques enable ventricular repolarization and its relationship with cardiac cycle length to be analysed long term. Previous studies used only the initial portion of the QT interval to the T wave apex (QTa) to measure ventricular repolarization; however, QTa may underestimate the total QT duration (QTe). The aims of this study were to verify whether QTa and QTe had similar rate-dependence in normal subjects and whether gender-related QTe differences observed in the resting ECG were also present in the long-term QT intervalcycle length relationship.
Twenty-four hour Holter recordings were obtained in 40 healthy young subjects. 20 females and 20 males (mean age 28 +/- 9 and 26 +/- 5 years, respectively ns). Two-channel ECG digitized signals were processed using new automatic QT analysis software (Ela Medical), which converted the 24-h recordings into 2880 30-s templates. It also measured the QT apex (QTa) QT end (QTe) and the RR interval (ms) of each template, and computed the slopes of the linear regressions of QTe and QTa values plotted against the corresponding RR interval (QTe/RR and QTa/RR). Females had a shorter RR interval than males (803 +/- 129 vs 877 +/- 86 ms. P = 0.037), with longer mean QTc (420 +/- 17 vs 400 +/- 200 ms. P = 0.0005). In both genders. QTa/RR slopes were steeper than QTe/RR slopes (P = 0.0001). Both QTa/RR and QTe/RR slopes were steeper in females than in males (QTa/RR 0.20 +/- 0.04 vs 0.16 +/- 0.03, P = 0.001; QTe/RR 0.16 +/- 0.04 vs 0.13 +/- 0.03, P = 0.027). Of note, QTa and QTe at fixed long cycle lengths (1000 ms) were longer in women than in men (QTa1000 330 +/- 20 vs 309 +/- 18 ms: P = 0.002; QTe1000 410 +/- 17 vs 389 +/- 19 ms: P = 0.002), while they did not differ at fixed short cycle lengths (600 ms).
This study demonstrates that both the initial portion of the QT interval (QTa) and the entire QT interval (QTe) are useful since QTa is more prolonged than QTe at increasing cycle lengths, and thus includes most of the heart rate dependency of ventricular repolarization. In normal subjects, both the QTc and the long-term relationship between ventricular repolarization and heart rate are affected by gender. The differences in QTa and QTe duration between males and females are more marked at long cycle lengths and disappear at short cycle lengths. Finally, this study also proves the clinical feasibility of assessing the long-term relationship between ventricular repolarization and heart rate by utilizing the automatic measurement of the QT interval from 24-h Holter recordings.
从标准心电图记录测量的QT间期存在性别相关差异。然而，这些观察结果基于静息状态下记录的有限心跳数。计算机化动态心电图技术能够长期分析心室复极化及其与心动周期长度的关系。以往研究仅使用QT间期至T波顶点的初始部分（QTa）来测量心室复极化；然而，QTa可能低估总QT持续时间（QTe）。本研究的目的是验证正常受试者中QTa和QTe是否具有相似的心率依赖性，以及静息心电图中观察到的性别相关QTe差异在长期QT间期-心动周期长度关系中是否也存在。
对40名健康年轻受试者进行24小时动态心电图记录。20名女性和20名男性（平均年龄分别为28±9岁和26±5岁，无显著差异）。使用新的自动QT分析软件（Ela Medical）处理两通道心电图数字化信号，该软件将24小时记录转换为2880个30秒模板。它还测量每个模板的QT顶点（QTa）、QT终点（QTe）和RR间期（毫秒），并计算QTe和QTa值相对于相应RR间期绘制的线性回归斜率（QTe/RR和QTa/RR）。女性的RR间期比男性短（803±129 vs 877±86毫秒，P = 0.037），平均QTc较长（420±17 vs 400±200毫秒，P = 0.0005）。在两性中，QTa/RR斜率比QTe/RR斜率更陡（P = 0.0001）。女性的QTa/RR和QTe/RR斜率均比男性更陡（QTa/RR 0.20±0.04 vs 0.16±0.03，P = 0.001；QTe/RR 0.16±0.04 vs 0.13±0.03，P = 0.027）。值得注意的是，在固定的长心动周期长度（1000毫秒）时，女性的QTa和QTe比男性长（QTa1000 330±20 vs 309±18毫秒：P = 0.002；QTe1000 410±17 vs 389±19毫秒：P = 0.002），而在固定的短心动周期长度（600毫秒）时它们没有差异。
本研究表明，QT间期的初始部分（QTa）和整个QT间期（QTe）都是有用的，因为在心动周期长度增加时QTa比QTe延长得更多，因此包含了心室复极化的大部分心率依赖性。在正常受试者中，QTc以及心室复极化与心率的长期关系均受性别影响。男性和女性之间QTa和QTe持续时间的差异在长心动周期长度时更明显，在短心动周期长度时消失。最后，本研究还证明了通过利用24小时动态心电图记录自动测量QT间期来评估心室复极化与心率长期关系的临床可行性。
