不同部位起搏对正常犬楔形心肌块跨室壁复极离散的影响及其机制研究

摘要

Objective To investigate the effects of different pacing sites on the transmural dispersion of myocardial repolarization time in a left ventricular wedge preparation model of normal canine. Methods According to the protocols of our lab and those reported in previous publications, after the heart was excised from an anesthetized and anticoagulated dog, transmural wedges with dimensions of( 2. 0 - 4. 0) cm( 1. 0 - 2. 0) cm( 1. 0 - 1. 5 ) cm were dissected from the free wall of the left ventricle. The tissue was cannulated via a native branch of left descending coronary artery and perfused with Tyrode ' s solution. Transmembrane action potentials from sub-epicardial , mid-myocardial , and sub-endocardial sites were simultaneously recorded by using floating glass mtcroelectrodes. A transmural ECG calculated by subtracting the transmural activities from sub-epicardium through the sub-endocardium was recorded concurrently. Stimulations were delivered from single or dual sites of endocardium( Endo)or epicardium ( Epi) , and simultaneously from both endocardium and epicardium( Bi). Parameters representing myocardial repolarization time and its transmural dispersion , such as QT interval , T wave peak-to-end interval( Tp-Te) , and TpTe/QT, were measured and compared between different pacing strategies. Arrhythmias induced during the stimulation were also recorded. Results The Tp-Te interval was (83. 63+19. 30) ms( Epi) , (75. 63+ 16. 47) ms ( 13i) , and ( 54. 75+ 13. 18) ms( Endo) respectively( all P<0. 01) , and Tp-Te/QT was 0. 28+0. 05 ( Epi) , 0. 27+0. 04 ( Endo) , and 0. 20+0. 04 ( Bi) respectively( all P<0. 01) ,indicating that simultaneous pacing from Endo and Epi increased the transmural dispersion of myocardial repolarization and could induce arrhythmias more significantly(75% for Epi,60% for Bi vs 13% for Endo.P = 0. 03). However,if the stimulations were delivered from dual sites of ipsilateral endocardium or epicardium, both Tp-Te and TpTe/QT were decreased as compared with those of single site pacing(P<0. 01). Conclusion Simultaneous pacing from Endo and Epi increased the transmural dispersion of repolarization and the risk of developing ventricular arrhythmias, which might be avoided by multiple sites pacing from ipsilateral endocardium or epicardium. These findings call for further studies on improving the pacing system and its implant techniques utilized in the heart failure patients.%目的 以正常犬左心室楔形心肌块为模型,观察不同部位起搏对3层心肌跨室壁复极离散的影响并探讨其可能的机制.方法 按文献方法制备带冠状动脉分支的犬左心室楔形心肌块模型,将3根玻璃微电极插入心肌块的不同位置记录心内膜下心肌、中层心肌和心外膜下心肌的跨膜动作电位;同时记录心肌块的整体电活动(容积心电图).从心肌块的心外膜面、心内膜面分别、同时或多部位发放刺激,记录并分析不同部位起搏时的QRS时限、QT间期、Tp-Te间期及心律失常的诱发率.结果 反映心肌跨室壁复极离散的心电图指标如Tp-Te间期在心外膜刺激(Epi)时最大:(83.63±19.30)ms,其次为内外膜同时刺激(Bi):(75.63±16.47)ms,最小为心内膜刺激(Endo):(54.75±13.18)ms(两两比较,均P＜0.01);Tp-Te指数(Tp-Te/QT)也有相似变化,上述部位刺激时分别为(0.28±0.05),(0.27±0.04)和(0.20± 0.04)(两两比较,均P＜0.01).但是当从心内膜面或者心外膜面双部位发放刺激时,Tp-Te间期或Tp-Te /QT较单部位刺激时均明显缩短或减小(P＜0.01).此外,心外膜刺激、内外膜同时刺激及心内膜刺激时分别有6例(75%)、5例(60%)和1例(13%)诱发了室性心律失常(χ2=7.0,P=0.03).结论 心内、外膜面同时刺激使心室肌跨室壁复极离散度增大,发生恶性心律失常的危险性增加;而从心内膜面或者外膜面同一面双部位发放刺激并不延长心肌复极时间,与单部位刺激相比跨室壁复极离散度反而减小.这一发现或许能为改进心力衰竭时心脏再同步治疗的起搏方式提供借鉴.