左束支传导阻滞患者实际QT间期的计算公式
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A New Formula for Estimating the True QT Interval in Left Bundle Branch Block
背景与目的
QT间期延长是心源性死亡的独立危险因素。随着患者的年龄增加，左束支传导阻滞（LBBB）越来越常见。QRS波的增宽导致假性QT间期延长，使得如何评估实际QT间期变得困难。本研究旨在开发一个简单的公式用于计算左束支传导阻滞患者实际QT间期。
方 法
为了确定QRS波宽度对QT间期的影响，对行电生理检查的62例患者，平均年龄55+-11岁，其中60%为男性患者，分别测量窦性心律和右心室心尖部起搏时QRS波宽和QT间期。根据右心室心尖部起搏时模拟LBBB所致QRS波增宽对QT间期影响推导出实际QT间期的计算公式。随后，纳入22例间断LBBB的患者（平均年龄66+-13岁，其中64%为男性），根据公式计算实际的QT间期，并与之前的QT计算公式和JT指数做对比，以验证新公式的准确性。
结 果
LBBB患者所致QRS波净增宽值平均占QT间期的净延长值的92%。新的计算公式QT-LBBB=QTLBBB-(0.86*QRSLBBB-71)，将LBBB时QRS增宽的因素考虑在内，与基础值和之前的公式相比，能更好地根据LBBB心电图预测与心率相关的QT间期。
结 论
本研究开发的QT-LBBB公式能够很好地估算LBBB时QT间期。该公式用于临床工作简单易行.JT指数：JTI=JT(HR+100)/518
原始文献摘要
BINHAO WANG, M.D.,LI ZHANG, M.D., PEIXIN CONG, M.D.,HUIMIN CHU, M.D.,YING LIU, M.D., JINQIU LIU, M.D., WILLIAM SURKIS, M.D.,and YUNLONG XIA, M.D.,Ph.D.A New Formula for Estimating the True QT Interval in Left Bundle Branch Block.
J Cardiovasc Electrophysiol, Vol. pp. 1-6
A New QT Formula for LBBB. Introduction: QT prolongation is an independent risk factor for cardiac mortality. Left bundle branch block (LBBB) is more common in patients as they age. Widening of the QRS in LBBB causes false QT prolongation and thus makes true QT assessment difficult. We aimed to develop a simple formula to achieve a good estimate of the QT interval in the presence of LBBB. Methods and Results: To determine the effect of QRS duration on the QT interval, QRS and QT were measured in sinus rhythm and during right ventricular apical pacing in 62 patients (age 55 ± 11 years, 60% male) undergoing electrophysiology studies. A QT formula for LBBB (QT-LBBB) was derived based on the effect of increased QRSLBBB on QTLBBB. The predictive accuracy of the QT-LBBB formula was then tested in 22 patients (age 66 ± 13 years, 64% male) with intermittent LBBB with comparisons to prior QT formulae and JT index. On average, the net increase in QRSLBBB constituted 92% of the net increase in QTLBBB. A new formula, QT-LBBB = QTLBBB – (0.86 * QRSLBBB – 71), which takes the net increase in QRSLBBB into account, best predicted the QT interval with heart rate corrected QTc in the test set of LBBB ECGs when compared to the baseline value and prior formulae. Conclusion: The QT-LBBB formula developed in this study best estimates the true QT interval in the presence of LBBB. It is simple and therefore can be easily utilized in clinical practice.
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