Sun Z H, Swan H, Viitasalo M, Toivonen L
Helsinki University Central Hospital, Finland.
J Am Coll Cardiol. 1998 May;31(6):1400-5. doi: 10.1016/s0735-1097(98)00104-1.
Measurement of QT interval dispersion during pharmacologic adrenergic stimulation was used to assess the effect of alpha- and beta-adrenergic stimulation on arrhythmic vulnerability in familial long QT syndrome (LQTS).
Nonhomogeneity in the ventricular action potential duration causes electrical instability leading to life-threatening ventricular arrhythmias and is markedly increased in LQTS. QT interval dispersion measured from the electrocardiogram (ECG) can be used as an index of nonhomogeneous ventricular repolarization.
Sixteen symptomatic patients with LQTS and nine healthy control subjects were examined at baseline and during epinephrine (mainly beta-adrenergic agonist, 0.05 microg/kg body weight per min) and phenylephrine infusions (alpha-adrenergic agonist, mean 1.4 microg/kg per min). QT interval dispersion was determined from a 12-lead ECG as interlead range and coefficient of variation measured to the end (QTend) and apex (QTapex) of the T wave.
At baseline QTend dispersion was greater in patients with LQTS compared with control subjects (mean [+/-SD] 68+/-34 vs. 36+/-7 ms, p=0.001). QTend dispersion was markedly increased in patients with LQTS by use of epinephrine (from 68+/-34 to 90+/-36 ms, p=0.002), but remained unchanged in control subjects. Phenylephrine did not affect QT dispersion in either group (all p=NS). Atrial pacing to achieve comparable heart rates during baseline and epinephrine and phenylephrine infusions did not influence the magnitude of QT dispersion in either group. QTapex dispersion analysis gave congruent results.
Epinephrine but not phenylephrine increased QT dispersion, suggesting that beta-adrenergic stimulation provokes arrhythmias in patients with LQTS by aggravating nonhomogeneity of ventricular repolarization, whereas alpha-adrenergic stimulation is less important for arrhythmic vulnerability. The results also suggest that rapid pacing may not reduce vulnerability to arrhythmias in congenital LQTS.
通过测量药物性肾上腺素能刺激期间的QT间期离散度，评估α和β肾上腺素能刺激对家族性长QT综合征（LQTS）心律失常易感性的影响。
心室动作电位持续时间的不均一性会导致电不稳定，进而引发危及生命的室性心律失常，且在LQTS中显著增加。从心电图（ECG）测得的QT间期离散度可作为心室复极不均一性的指标。
对16例有症状的LQTS患者和9名健康对照者在基线时以及静脉输注肾上腺素（主要为β肾上腺素能激动剂，0.05微克/千克体重每分钟）和去氧肾上腺素期间进行检查。QT间期离散度通过12导联心电图测定，以导联间范围以及测量至T波终点（QTend）和顶点（QTapex）的变异系数来表示。
在基线时，LQTS患者的QTend离散度高于对照者（均值[±标准差]68±34 vs. 36±7毫秒，p = 0.001）。使用肾上腺素后，LQTS患者的QTend离散度显著增加（从68±34增加至90±36毫秒，p = 0.002），而对照者则保持不变。去氧肾上腺素对两组的QT离散度均无影响（所有p值均无统计学意义）。在基线以及输注肾上腺素和去氧肾上腺素期间进行心房起搏以达到可比心率，对两组的QT离散度大小均无影响。QTapex离散度分析得出了一致的结果。
肾上腺素而非去氧肾上腺素增加了QT离散度，提示β肾上腺素能刺激通过加重心室复极的不均一性诱发LQTS患者心律失常，而α肾上腺素能刺激对心律失常易感性的影响较小。结果还提示，快速起搏可能无法降低先天性LQTS患者的心律失常易感性。
