交感神经张力对犬QT滞后现象的影响

Effects of sympathetic activation on QT hysteresis

目的 探讨交感神经张力改变对犬QT滞后现象的影响.方法 用右心房（RA）起搏为基本方法造成犬心率的动态变化,静脉注射异丙基肾上腺素（ISO）或普萘洛尔干预交感神经张力,设计5套实验方案：A：RA增减频起搏;B：静脉注射ISO;C：普萘洛尔＋RA增减频起搏;D：普萘洛尔＋静脉注射ISO;E：毁损窦房结＋小剂量ISO持续静脉注射＋RA增减频起搏.同时记录犬的体表心电图,测量RR间期和QT间期,绘制QT-RR曲线,并计算QT滞后指数.比较不同实验方案的QT滞后指数,观察交感神经张力改变对QT滞后现象的影响.结果 方案A的QTe滞后指数和QTp滞后指数显著低于方案B[QTe：（0.56±4.56） ms对（17.96±8.22） ms,P＜0.05; QTp：（0.50±3.14） ms对（11.33±13.47） ms,P＜0.05].方案A的QTe滞后指数和方案C相比差异无统计学意义[（0.56±4.56）ms对（2.34±2.84）ms,P＞0.05],但QTp滞后指数高于方案C[（0.50±3.14）ms对（-5.45±2.13）ms,P＜0.05].方案B和方案D相比,QTe滞后指数和QTp滞后指数均差异无统计学意义.方案C的QTe滞后指数和QTp滞后指数均显著低于方案D[QTe：（2.34±2.84） ms对（15.77±14.89） ms,P＜0.05;QTp：（-5.45±2.13）ms对（17.12±10.47）ms,P＜0.05].方案A的QTe滞后指数明显低于方案E[（0.56±4.56） ms对（8.42±7.86） ms,P＜0.05],QTp滞后指数差异无统计学意义.方案B的QTe滞后指数和QTp滞后指数显著高于方案E[QTe：（17.96±8.22）ms对（8.42±7.86） ms,P＜0.05; QTp：（11.33±13.47） ms对（0.62±7.46）ms,P＜0.05].结论 交感神经过度兴奋是引起QT滞后现象的重要原因,交感神经对QT滞后的影响并不依赖于心率的动态改变.QT滞后的程度与交感神经兴奋程度相关,轻度的交感神经兴奋主要影响T波终末部.

Objective To investigate the role of sympathetic activation in the mechanism of QT hysteresis.Methods Dynamic heart rate fluctuation was produced by right atrium（RA）pacing,and sympathetic activity was regulated by isopropylarterenol（ISO） or propranolol intravenous injection.Five protocols were used for investigating the effects of sympathetic activity on QT interval hysteresis,including A：right atrium increase-decrease frequency pacing,B：ISO intravenous injection,C：propranolol intravenous injection ＋ protocol A,D：propranolol intravenous injection ＋ protocol B,E：destroy sinoatrial node ＋ low dose ISO intravenous injection ＋ protocol A.The surface electrocardiogram was recorded,RR and QT interval were determined.Plotted the QTRR and calculated the QT hysteresis index.The QT hysteresis index was compared among different protocols,and the effects of autonomic nerve on QT hysteresis index were evaluated.Results The QTe and QTp hysteresis index in protocol A were significantly lower than that in protocol B [QTe：（0.56±4.56） ms vs.（17.96± 8.22） ms,P＜ 0.05 ; QTp：（0.50 ± 3.14） ms vs.（11.33 ± 13.47） ms,P＜ 0.05].There was no significant difference in QTe hysteresis index between protocol A and C [（0.56±4.56）ms vs.（2.34±2.84）ms,P＞0.05],but the QTp hysteresis index in protocol A was significantly higher than that in protocol C [QTp：（0.50± 3.14）.ms vs.（-5.45±2.13）ms,P＜0.05].There was no significant difference between protocol B and C [QTe：（17.12± 10.47） ms vs.（15.77± 14.89） ms,P＞0.05 ; QTp：（11.33 ± 13.47） ms vs.（17.12± 10.47） ms,P＞0.05].The QTe and QTp hysteresis indexes in protocol C were significantly lower than that in protocol D [QTe：（2.34± 2.84）ms vs.（15.77±14.89） ms,P＜0.05 ;QTp：（-5.45±2.13）ms vs.（17.12±10.47） ms,P＜0.05].The QTe hysteresis index in protocol A was significantly lower than that in protocol E [QTe：（0.56±4.56） ms vs.（8.42± 7.86） ms,P＜0.05],but not QTp [（0.50±3.14）ms vs.（0.62±7.46）ms,P＞0.05].The QTe and QTp hysteresis indexes in protocol B were significantly higher than that in protocol E [QTe：（17.96±8.22） ms vs.（8.42± 7.86） ms,P＜ 0.05 ; QTp：（11.33± 13.47） ms vs.（0.62± 7.46） ms,P＜ 0.05].Conclusion Sympathetic activation plays a key role in QT hysteresis,and this effect is independent from the dynamic fluctuation of heart rate.The degree of QT hysteresis associated with the degree of sympathetic activation.Moderate increase in sympathetic activation affects the end part of T wave mainly.