长QT综合征T波电交替及其致尖端扭转性室速的电生理学基础

T wave alternans (TWA), a beat-to-beat alternation in the morphology, amplitude and/or polarity of the ECG T wave, is often associated with ischemic and hypertrophic heart diseases as well as acquired or congenital long QT syndrome. It has long been recognized as an important prognostic indicator of life-threatening ventricular arrhythmias and sudden cardiac death. However, the precise cellular and ionic mechanisms of TWA are not fully understood. We have recently established a unique arterially perfused rabbit left ventricular wedge preparation recording system, in which a pseudo-ECG, endocardial and epicardial action potentials (AP) and contraction force will be simultaneously recorded. Our most recently results have shown that a sea anemone toxin (ATX-II, a late sodium current enhancer) caused a significant QT prolongation as well as an increased of transmural dispersion of repolarization (TDR). TWA could also be recorded at slow pacing rates (0.5 Hz or 0.2 Hz), mimicking the clinical TWA observed in patients with congenital LQT3 syndrome. TWA in LQT3 condition is associated with a beat-to-beat change in endocardial APD. Phase-2 early afterdepolarization (EAD) could be recorded in endocardium that had a longer APD. TWA could frequently precede episodes of Torsade de Pointes (TdP). Moreover,late Na+ currents play an important role in thi process. In this proposal, we will elucidate the mechanism of TWA under long QT conditions (congenital LQT3 and LQT8) using slow rhythm-dependent rabbit model and patch-clamp, Ca2+ spark scanning techniques, which focus on late sodium currents and intracellular Ca2+ sparks. The data obtained from ionic, molecular, cellular and tissue levels will greatly expand our knowledge regarding the mechanism of TWA and initiation and maintenance of TdP under long QT conditions.

T波电交替（TWA）是一种严重的体表心电图异常现象,表现为体表心电图同一导联T波在形态、振幅和/或极性呈随搏交替变化。TWA见于多种心脏疾病，特别是遗传性长QT综合征，常并发尖端扭转型室速（TdP）及心脏瘁死，已成临床识别恶性心律失常及心脏瘁死的重要指征。然而，其发生的细胞和离子机制及其诱发TdP的电生理学基础仍不清楚。申请人已建立wedge系统(同时记录心电图，内、外膜动作电位和心肌收缩力四个参数)，并发现：ATX-II毒素诱发的长QT综合征(LQT3)常伴有增大的跨膜复极离散度(TDR)和TWA，并可发展为TdP。且晚Na+电流在此过程发挥重要作用。本课题将以慢心律依赖性TWA兔为模型，以膜片钳和钙火花测定等技术为手段，以晚钠电流和胞内钙火花为突破口，从离子、细胞、组织、器官等多个水平入手，揭示长QT综合征(获得性LQT3和LQT8)TWA发生的分子机制及其诱发TdP的电生理基础。

申请人前期已建立wedge系统（同时记录心电图，内、外膜动作电位和心肌收缩力四个参数）。并发现ATX-II 毒素诱发的长QT综合征（LQT3）常伴有增大的跨膜复极离散度(TDR)，并可发展为TdP。且晚钠电流在此过程发挥重要作用。本课题旨在以慢性心律依赖性TWA兔子为模型，以膜片钳和钙火花测定等技术为手段，以晚钠电流和胞内钙火花为突破口，从离子、细胞、组织和器官等多个水平入手，来揭示长QT综合征（获得性LQT3和LQT8）TWA发生的分子机制及其诱发TdP的电生理基础。我们成功的搭建起了wedge系统，并记录到了心电图、肌张力等技术指标。同时，我们也成功的分离到了兔子心肌单细胞。并成功地将钠离子通道基因导入到293细胞中获得了稳定表达细胞系。我们的研究结果发现：仅在慢频率刺激下，ATX-II可诱发TWA,但是在快频率刺激下，无法使用ATX-II刺激来诱发TWA。在慢心率依赖性TWA中，心内膜APD呈现长短交替。且长APD极不稳定，并诱发出EAD。随后APD和TDR将进一步延长，从而形成R-on-T现象；并且，我们的研究显示APD延长剂(E-4031)对TWA对EAD、TdP的产生无显著的诱发作用。同时，发现钠离子在TWA形成过程中发挥重要作用。这一发现将为LQT3和LQT8的治疗和预防提供新的思路和选择。

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