Raghunandan D S, Desai Nagaraj, Mallavarapu Mallika, Berger Ronald D, Yeragani Vikram K
Department of Cardiology, MS Ramaiah Medical College Hospital and Banlgalore University, Banlgalore.
Indian Heart J. 2005 Mar-Apr;57(2):138-42.
QT interval on the surface electrocardiogram reflects the time for repolarization of myocardium. Prolongation of rate-corrected QT interval, QTc is strongly associated with sudden cardiac death. Recent studies using novel techniques on beat-to-beat QT interval variability have shown that an increase in QT interval variability is associated with increased sympathetic activity and is a predictor of sudden cardiac death. We studied QT variability in patients with congestive cardiac failure, as it is associated with an increase in cardiac sympathetic activity and also sudden death.
We compared beat-to-beat heart rate and QT interval data in 2 3 patients with congestive cardiac failure and 19 age-matched normal controls. The electrocardiographic data were acquired in lead II configuration at a sampling rate of 1000 Hz. Heart rate variability was found to be significantly lower while QT variability measures were significantly higher in patients compared to controls. QTvi (a common log ratio of QT variability normalized for mean QT interval squared divided by heart rate variability normalized for mean heart rate squared) was also significantly higher in patients compared to controls. Clinical improvement in some of these patients is associated with a decrease in QTvi, due mainly to an increase in cardiac vagal function.
Our results suggest a decrease in cardiac vagal and an increase in cardiac sympathetic functions in patients with congestive cardiac failure. QTvi may prove to be a useful surrogate end point to evaluate treatment effect in these patients.
体表心电图上的QT间期反映心肌复极时间。校正心率后的QT间期（QTc）延长与心源性猝死密切相关。近期利用逐搏QT间期变异性新技术进行的研究表明，QT间期变异性增加与交感神经活动增强有关，是心源性猝死的一个预测指标。我们研究了充血性心力衰竭患者的QT变异性，因为它与心脏交感神经活动增加以及猝死有关。
我们比较了23例充血性心力衰竭患者和19例年龄匹配的正常对照者的逐搏心率和QT间期数据。以1000Hz的采样率在II导联配置下采集心电图数据。与对照组相比，患者的心率变异性显著降低，而QT变异性测量值显著升高。与对照组相比，患者的QTvi（QT变异性的常用对数比，通过平均QT间期平方归一化后除以平均心率平方归一化后的心率变异性）也显著升高。这些患者中的一些人的临床改善与QTvi降低有关，主要是由于心脏迷走神经功能增强。
我们的结果提示充血性心力衰竭患者心脏迷走神经功能降低，心脏交感神经功能增强。QTvi可能被证明是评估这些患者治疗效果的一个有用的替代终点。
