Sylvén J C, Horacek B M, Spencer C A, Klassen G A, Montague T J
J Electrocardiol. 1984 Apr;17(2):179-88. doi: 10.1016/s0022-0736(84)81093-6.
To assess the effects of measurement methodology on QT determinations and to define the spectrum of QT values, including interlead variability, on the body surface, we measured QT in each of 120 simultaneously-recorded, signal-averaged ECG leads in 10 normal subjects and 14 patients with QT prolongation (lead II QTc greater than 440). Two separate, but related, methods of QT measurement were utilized. Method A was a relatively conventional technique in which ST-T offset was defined as the time instant of return of the T wave to a P-P baseline, or as the point of U-on-T intersection. Method B was a more rigorous method, which defined ST-T offset in a similar manner, and in addition discarded from analysis all QT values from leads with monophasic ST-T waveform in which the QT values were greater than the longest QT from leads with definite U waves. Method B was utilized to minimize factitious prolongation of QT by inapparent U-on-T. By both methods the mean body surface QTc values were significantly greater (p less than 0.001) in the patient group (482 +/- 65 [S.D.] msec, method A; 447 +/- 43 msec, method B), than in the normal subject group (399 +/- 14 msec, method A; 396 +/- 12, method B). Interlead QTc variability (difference between the longest and shortest QT) was considerable with both methods and in both study groups. Expressed as percent of average body surface values, the mean interlead QTc variability in normal subjects averaged 22 percent with method A and 19 percent with method B; in the patient group, however, it averaged 32 percent with method A and only 18 percent with method B. In absolute terms, the mean variability in the patient group with method A (155 +/- 62 msec) was significantly greater (p less than 0.001) than that of the normal group (89 +/- 33 msec); with method B, interlead variability was the same (p = NS) in the normal (76 +/0 27 msec) and patient groups (80 +/- 44 msec). This latter finding suggests the possibility that the repolarization abnormality in patients with QT prolongation may occur relatively uniformly throughout the ventricular myocardium. Thus, measurement techniques are important in multiple-lead QT determinations. Although reduced by techniques designed to minimize factitious QT prolongation, interlead QT variation is considerable over the torso surface, in both normal subjects and patients with repolarization abnormalities.(ABSTRACT TRUNCATED AT 400 WORDS)
为评估测量方法对QT间期测定的影响，并确定体表QT值的范围，包括导联间变异性，我们对10名正常受试者和14名QT间期延长患者（II导联QTc大于440）的120个同步记录的信号平均心电图导联分别进行了QT间期测量。采用了两种独立但相关的QT测量方法。方法A是一种相对传统的技术，其中ST-T偏移定义为T波回到P-P基线的时刻，或U波与T波交点。方法B是一种更严格的方法，它以类似的方式定义ST-T偏移，此外，对于ST-T波形为单相且QT值大于有明确U波导联的最长QT值的导联，其所有QT值均从分析中剔除。采用方法B是为了尽量减少因不明显的U波与T波重叠导致的QT间期假性延长。两种方法测得的患者组平均体表QTc值（方法A为482±65[S.D.]毫秒；方法B为447±43毫秒）均显著高于正常受试者组（方法A为399±14毫秒；方法B为396±12毫秒）（p<0.001）。两种方法在两个研究组中，导联间QTc变异性（最长与最短QT间期之差）都相当大。以平均体表值的百分比表示，正常受试者中，方法A导联间QTc变异性平均为22%，方法B为19%；然而，在患者组中，方法A平均为32%，方法B仅为18%。从绝对值来看，患者组采用方法A时的平均变异性（155±62毫秒）显著高于正常组（89±33毫秒）（p<0.001）；采用方法B时，正常组（76±27毫秒）和患者组（80±44毫秒）的导联间变异性相同（p=无显著性差异）。后一发现提示QT间期延长患者的复极异常可能在整个心室心肌中相对均匀地发生。因此，测量技术在多导联QT间期测定中很重要。尽管旨在尽量减少假性QT间期延长的技术降低了变异性，但在正常受试者和有复极异常的患者中，躯干表面导联间QT间期变化仍相当大。（摘要截短至400字）
