Molnar J, Zhang F, Weiss J, Ehlert F A, Rosenthal J E
Reingold ECG Center, Department of Medicine, Northwestern University Medical School, Chicago, Illinois 60611-3008, USA.
J Am Coll Cardiol. 1996 Jan;27(1):76-83. doi: 10.1016/0735-1097(95)00426-2.
This study sought to evaluate the range and variability of the QT and corrected QT (QTc) intervals over 24 h and to assess their pattern and relation to heart rate variability.
Recent Holter monitoring data have revealed a high degree of daily variability in the QTc interval. The pattern of this variability and its relation to heart rate variability remain poorly characterized.
We developed and validated a new method for continuous measurement of QT intervals from three-channel, 24-h Holter recordings. Average RR, QT, QTc and heart rate variability were measured from 5-min segments of data from 21 healthy subjects.
Measurement of 6,048 segments showed mean (+/- SD) RR, QT and QTc intervals of 830 +/- 100, 407 +/- 23 and 445 +/- 16 ms, respectively (mean QTc interval for men 434 +/- 12 ms, 457 +/- 10 ms for women, p < 0.0001). The average maximal QTc interval was 495 +/- 21 ms and the average QTc range 95 +/- 20 ms. The maximal QTc interval was > or = 500 ms in 6 subjects and > or = 490 ms in 13. The 95% upper confidence limit for the mean 24-h QTc interval was 452 ms (men 439 ms, women 461 ms). The RR, QT and QTc intervals and the high frequency component of heart rate variability were greater during sleep. Both the QTc interval and the variability between hourly minimal and maximal QTc intervals reached their circadian peak shortly after awakening, before declining to daytime levels.
The maximal QTc interval over 24 h in normal subjects is longer than heretofore thought. Both QT and QTc intervals are longer during sleep. The QTc interval and QTc variability reach a peak shortly after awakening, which may reflect increased autonomic instability during early waking hours, and the time of the peak value corresponds in time to the period of reported increased vulnerability to ventricular tachycardia and sudden cardiac death. These findings have implications regarding the definition of QT prolongation and its use in predicting arrhythmias and sudden death.
本研究旨在评估24小时内QT间期和校正QT间期（QTc）的范围及变异性，并评估其模式以及与心率变异性的关系。
近期动态心电图监测数据显示QTc间期存在高度的每日变异性。这种变异性的模式及其与心率变异性的关系仍未得到充分描述。
我们开发并验证了一种从三通道24小时动态心电图记录中连续测量QT间期的新方法。从21名健康受试者的数据5分钟片段中测量平均RR、QT、QTc和心率变异性。
对6048个片段的测量显示，平均（±标准差）RR、QT和QTc间期分别为830±100、407±23和445±16毫秒（男性平均QTc间期为434±12毫秒，女性为457±10毫秒，p<0.0001）。平均最大QTc间期为495±21毫秒，平均QTc范围为95±20毫秒。6名受试者的最大QTc间期≥500毫秒，13名受试者≥490毫秒。24小时平均QTc间期的95%置信上限为452毫秒（男性为439毫秒，女性为461毫秒）。睡眠期间RR、QT和QTc间期以及心率变异性的高频成分更大。QTc间期以及每小时最小和最大QTc间期之间的变异性在醒来后不久达到昼夜峰值，然后下降到白天水平。
正常受试者24小时内的最大QTc间期比以往认为的更长。睡眠期间QT和QTc间期都更长。QTc间期和QTc变异性在醒来后不久达到峰值，这可能反映了清晨自主神经不稳定性增加，且峰值时间与报告的室性心动过速和心源性猝死易感性增加的时期在时间上相对应。这些发现对QT延长的定义及其在预测心律失常和猝死中的应用具有启示意义。
