PDF(Pubmed)
Abstract：
Increases in beat-to-beat variability of electrocardiographic QT interval duration have repeatedly been associated with increased risk of cardiovascular events and complications. The measurements of QT variability are frequently normalized for the underlying RR interval variability. Such normalization supports the concept of the so-called immediate RR effect which relates each QT interval to the preceding RR interval. The validity of this concept was investigated in the present study together with the analysis of the influence of electrocardiographic morphological stability on QT variability measurements. The analyses involved QT and RR measurements in 6,114,562 individual beats of 642,708 separate 10-s ECG samples recorded in 523 healthy volunteers (259 females). Only beats with high morphology correlation (r > 0.99) with representative waveforms of the 10-s ECG samples were analyzed, assuring that only good quality recordings were included. In addition to these high correlations, SDs of the ECG signal difference between representative waveforms and individual beats expressed morphological instability and ECG noise. In the intra-subject analyses of both individual beats and of 10-s averages, QT interval variability was substantially more strongly related to the ECG noise than to the underlying RR variability. In approximately one-third of the analyzed ECG beats, the prolongation or shortening of the preceding RR interval was followed by the opposite change of the QT interval. In linear regression analyses, underlying RR variability within each 10-s ECG sample explained only 5.7 and 11.1% of QT interval variability in females and males, respectively. On the contrary, the underlying ECG noise contents of the 10-s samples explained 56.5 and 60.1% of the QT interval variability in females and males, respectively. The study concludes that the concept of stable and uniform immediate RR interval effect on the duration of subsequent QT interval duration is highly questionable. Even if only stable beat-to-beat measurements of QT interval are used, the QT interval variability is still substantially influenced by morphological variability and noise pollution of the source ECG recordings. Even when good quality recordings are used, noise contents of the electrocardiograms should be objectively examined in future studies of QT interval variability.
摘要：
心电图QT间期的逐搏变异性的增加与心血管事件和并发症的风险增加反复相关。QT变异性的测量经常针对潜在的RR间隔变异性进行归一化。这种归一化支持所谓的即时RR效应的概念,其将每个QT间隔与先前的RR间隔相关联。在本研究中，研究了该概念的有效性，并分析了心电图形态学稳定性对QT变异性测量的影响。分析涉及523名健康志愿者（259名女性）记录的642708个10sECG样本的6,114,562个个体搏动的QT和RR测量。仅分析了具有高形态相关性（r>0.99）的搏动与10-sECG样本的代表性波形，确保只包括高质量的录音。除了这些高相关性之外，代表波形和个体搏动之间的ECG信号差异的SD表示形态不稳定性和ECG噪声。在个体搏动和10秒平均值的受试者内分析中，QT间期变异性与ECG噪声的相关性明显高于与基础RR变异性的相关性。在大约三分之一的分析心电图搏动中，先前RR间期的延长或缩短后,QT间期发生相反的变化.在线性回归分析中，每个10秒ECG样本中潜在的RR变异性仅解释了女性和男性的5.7％和11.1％的QT间期变异性，分别。相反,10-s样本的潜在ECG噪声含量解释了女性和男性的QT间期变异性的56.5％和60.1％，分别。研究得出的结论是，稳定和均匀的即时RR间期对随后的QT间期持续时间的影响的概念是非常可疑的。即使仅使用QT间期的稳定的逐次搏动测量，QT间期变异性仍然受到源ECG记录的形态变异性和噪声污染的影响。即使使用了高质量的录音，在未来的QT间期变异性研究中，应客观地检查心电图的噪声含量。
