Tse Hung-Fat, Xue Tian, Lau Chu-Pak, Siu Chung-Wah, Wang Kai, Zhang Qing-Yong, Tomaselli Gordon F, Akar Fadi G, Li Ronald A
Department of Medicine, Queen Mary Hospital, University of Hong Kong, Hong Kong.
Circulation. 2006 Sep 5;114(10):1000-11. doi: 10.1161/CIRCULATIONAHA.106.615385. Epub 2006 Aug 21.
The normal cardiac rhythm originates in the sinoatrial (SA) node that anatomically resides in the right atrium. Malfunction of the SA node leads to various forms of arrhythmias that necessitate the implantation of electronic pacemakers. We hypothesized that overexpression of an engineered HCN construct via somatic gene transfer offers a flexible approach for fine-tuning cardiac pacing in vivo.
Using various electrophysiological and mapping techniques, we examined the effects of in situ focal expression of HCN1-DeltaDeltaDelta, the S3-S4 linker of which has been shortened to favor channel opening, on impulse generation and conduction. Single left ventricular cardiomyocytes isolated from guinea pig hearts preinjected with the recombinant adenovirus Ad-CMV-GFP-IRES-HCN1-DeltaDeltaDelta in vivo uniquely exhibited automaticity with a normal firing rate (237+/-12 bpm). High-resolution ex vivo optical mapping of Ad-CGI-HCN1-DeltaDeltaDelta-injected Langendorff-perfused hearts revealed the generation of spontaneous action potentials from the transduced region in the left ventricle. To evaluate the efficacy of our approach for reliable atrial pacing, we generated a porcine model of sick-sinus syndrome by guided radiofrequency ablation of the native SA node, followed by implantation of a dual-chamber electronic pacemaker to prevent bradycardia-induced hemodynamic collapse. Interestingly, focal transduction of Ad-CGI-HCN1-DeltaDeltaDelta in the left atrium of animals with sick-sinus syndrome reproducibly induced a stable, catecholamine-responsive in vivo "bioartificial node" that exhibited a physiological heart rate and was capable of reliably pacing the myocardium, substantially reducing electronic pacing.
The results of the present study provide important functional and mechanistic insights into cardiac automaticity and have further refined an HCN gene-based therapy for correcting defects in cardiac impulse generation.
正常心脏节律起源于解剖学位置位于右心房的窦房结（SA）。窦房结功能异常会导致各种形式的心律失常，需要植入电子起搏器。我们假设通过体细胞基因转移过表达一种工程化的HCN构建体为体内微调心脏起搏提供了一种灵活的方法。
我们使用各种电生理和标测技术，研究了HCN1-ΔΔΔ原位局灶性表达对冲动产生和传导的影响，其S3-S4连接子已被缩短以利于通道开放。从体内预先注射重组腺病毒Ad-CMV-GFP-IRES-HCN1-ΔΔΔ的豚鼠心脏中分离出的单个左心室心肌细胞独特地表现出自动节律性，且发放频率正常（237±12次/分钟）。对注射Ad-CGI-HCN1-ΔΔΔ的Langendorff灌注心脏进行高分辨率离体光学标测，揭示了左心室转导区域产生自发动作电位。为了评估我们的方法用于可靠心房起搏的疗效，我们通过引导射频消融天然窦房结建立了病态窦房结综合征的猪模型，随后植入双腔电子起搏器以防止心动过缓引起的血流动力学崩溃。有趣的是，在患有病态窦房结综合征的动物的左心房中局灶性转导Ad-CGI-HCN1-ΔΔΔ可重复性地诱导出一个稳定的、对儿茶酚胺有反应的体内“生物人工节点”，其表现出生理心率，并且能够可靠地起搏心肌，显著减少电子起搏。
本研究结果为心脏自动节律性提供了重要的功能和机制见解，并进一步完善了基于HCN基因的治疗方法以纠正心脏冲动产生缺陷。
