Lee K W, Kligfield P, Dower G E, Okin P M
Department of Medicine, New York-Weill-Cornell Center of New York-Presbyterian Hospital, New York 10021, USA.
Am J Cardiol. 2001 Jan 15;87(2):148-51. doi: 10.1016/s0002-9149(00)01306-0.
The clinically useful prognostic value of precordial QT dispersion in patients with heart disease is generally attributed to its measurement of regional heterogeneity of ventricular repolarization. However, when repolarization is abnormal, differences in measured QT intervals might result simply from variation in projection of the T-wave loop. To provide insight into the mechanism of QT dispersion, we used an analog device to transform conventional 12-lead electrocardiograms (ECGs) of 78 patients to derived 12-lead ECGs based on the heart vector. Because the electrical activity of the heart is represented by a single dipole, all QT dispersion in the transformed ECGs results from variation in projection of the T-wave loop and cannot be due to local heterogeneity of repolarization. Measured as the difference between the longest and shortest precordial QT intervals, QT dispersion in the derived ECGs, with no local heterogeneity of repolarization, was 53 +/- 49 ms (mean +/- SD). QT dispersion in these derived ECGs was similar in magnitude to that measured from the original standard 12-lead ECGs in these patients (49 +/- 23 ms, p = NS). Therefore, the precordial QT dispersion measured from standard ECGs of patients with coronary artery disease can be explained by interlead variation in precordial projection of the T-wave loop. Although regional heterogeneity might still contribute to precordial repolarization findings and to prognosis, this is not required to explain the QT dispersion observed in patients with coronary artery disease. Therefore, QT interval dispersion is not equivalent to heterogeneity of repolarization.
心前区QT离散度在心脏病患者中具有临床实用的预后价值，这通常归因于其对心室复极区域异质性的测量。然而，当复极异常时，测得的QT间期差异可能仅仅是由于T波环投影的变化所致。为了深入了解QT离散度的机制，我们使用一种模拟装置将78例患者的常规12导联心电图（ECG）转换为基于心脏向量的衍生12导联ECG。由于心脏的电活动由单个偶极表示，转换后的ECG中所有的QT离散度均源于T波环投影的变化，而非复极的局部异质性。以心前区最长和最短QT间期之差来衡量，在不存在复极局部异质性的衍生ECG中，QT离散度为53±49毫秒（平均值±标准差）。这些衍生ECG中的QT离散度在幅度上与这些患者原始标准12导联ECG测得的QT离散度相似（49±23毫秒，p=无显著性差异）。因此，从冠心病患者标准ECG测得的心前区QT离散度可由T波环心前区投影的导联间差异来解释。尽管区域异质性可能仍对心前区复极表现及预后有影响，但这并非解释冠心病患者中观察到的QT离散度所必需的。因此，QT间期离散度并不等同于复极异质性。
