Lombardi F, Sandrone G, Porta A, Torzillo D, Terranova G, Baselli G, Cerutti S, Malliani A
Centro Ricerche Cardiovascolari, CNR, Milano, Italy.
Eur Heart J. 1996 May;17(5):769-78. doi: 10.1093/oxfordjournals.eurheartj.a014945.
Analysis of heart rate variability has been proven useful in stratifying post myocardial patients at risk and in evaluating autonomic dysfunction. Recently augmented inter-lead variability of the QT interval has been associated with increased mortality as a result of arrhythmia and proposed as a marker of dispersion of ventricular repolarization. As the duration of the QT interval is largely dependent upon the length of the preceding cardiac cycle it is tempting to analyse whether neural mechanisms might also directly exert additional modulation. Using autoregressive algorithms we therefore analysed RR and R-Tapex interval variabilities in 15 normal subjects during sinus rhythm and in six patients with a fixed atrial rate. In controls mean R-Tapex interval and variance measured on the vector magnitude were, respectively, 245 +/- 6 ms and 5.1 +/- 0.7 ms2. Spectral analysis of R-Tapex indicated the presence of two spectral components which corresponded to the low and high frequency components of heart rate variability. In R-Tapex variability, high frequency (44 +/- 4 nu) was predominant over low frequency (29 +/- 4 nu). During controlled respiration, a manoeuvre associated with enhanced vagal modulation of sinus node, there was a further increase in high frequency (58 +/- 4 nu) whereas during tilt the low frequency component of R-Tapex variability became predominant (57 +/- 6 nu). In patients with a fixed atrial rate, variance was extremely low (3 +/- 0.9 ms2) and only a respiration-related high frequency component was recognizable in spectral analysis of RR and R-Tapex variabilities. This component was likely to depend upon mechanically induced changes in cardiac vector orientation. These data indicate that during sinus rhythm short-term R-Tapex interval variability is characterized by the same rhythmical components present in RR variability. However, the presence of a very low variance and of only a high frequency component in patients in whom the physiological variability of sinus node is abolished by atrial pacing. suggests that neural modulatory mechanisms do not exert a direct effect on the length of the R-Tapex interval.
心率变异性分析已被证明在对心肌梗死后有风险的患者进行分层以及评估自主神经功能障碍方面是有用的。最近，QT间期导联间变异性增加与心律失常导致的死亡率增加有关，并被提议作为心室复极离散度的标志物。由于QT间期的持续时间在很大程度上取决于前一心搏周期的长度，因此很想分析神经机制是否也可能直接施加额外的调节作用。因此，我们使用自回归算法分析了15名正常受试者在窦性心律期间以及6名心房率固定的患者的RR和R-Tapex间期变异性。在对照组中，在向量幅度上测量的平均R-Tapex间期和方差分别为245±6毫秒和5.1±0.7毫秒²。R-Tapex的频谱分析表明存在两个频谱成分，它们分别对应于心率变异性的低频和高频成分。在R-Tapex变异性中，高频（44±4 nu）比低频（29±4 nu）占优势。在控制性呼吸期间，这是一种与迷走神经对窦房结的调节增强相关的操作，高频进一步增加（58±4 nu），而在倾斜期间，R-Tapex变异性的低频成分占优势（57±6 nu）。在心房率固定的患者中，方差极低（3±0.9毫秒²），并且在RR和R-Tapex变异性的频谱分析中仅可识别出与呼吸相关的高频成分。该成分可能取决于心脏向量方向的机械性诱导变化。这些数据表明，在窦性心律期间，短期R-Tapex间期变异性的特征是RR变异性中存在的相同节律成分。然而，在通过心房起搏消除窦房结生理变异性的患者中，存在非常低的方差且仅存在高频成分，这表明神经调节机制不会对R-Tapex间期的长度产生直接影响。
