ANIMAL MODEL OF HEART FAILURE, ACQUIRED LONG QT AND SUDDEN DEATH

充血性心力衰竭是一种常见的疾病，每年 死亡率为20-45%。近一半的死亡是突然发生的，其中许多人 可能是室性快速性心律失常的结果。最大的努力是 确定猝死风险最高的患者并进行干预 降低这一风险并不成功，这在很大程度上是因为 对心律失常的潜在机制缺乏了解。 对这些机制的研究最理想的是在受控的 提供整个器官、细胞和分子分析的模型 水平，这最大限度地减少了不同的病因和治疗 通常会使人类研究复杂化的历史。狗走来走去- 心动过速衰竭模型似乎非常适合于这一目的，因为它 显示恶性室性心律失常的高发生率，并有 许多机械、生化和分子变化类似于 人类的心力衰竭。这一提议检验了以下假设：1) 这种动物模型确实为研究提供了相关的底物 心力衰竭的心律失常，2)这些心律失常相关 随着时间的延长和空间/时间离散的增加 复极(Q-T间期、动作电位时程)，并降低 触发心律失常的阈值，3)两个复极化钾 电流--内向整流器和外向瞬变电流-- 在这个模型中，随着心力衰竭的发展而显著减少， 造成复极延迟和心律失常，以及4)这些 与变化平行的是相应基因表达的减少 可通过心内膜心肌信使核糖核酸分析测定的通道蛋白 活组织检查。成年的混血狗长期被用来治疗 舱内压力的测定--清醒状态下的尺寸力学 州政府。犬的心脏起搏速度为240分钟-1，持续2-3周， 210min-1直到出现心力衰竭。Holter监护仪是 在每周24小时的起搏间歇期获得，以研究心律失常 频率、Q-T间期延长和变异性。在基线、1周和 心力衰竭时间点，狗服用镇静剂，心内膜心肌活检 在无菌技术下获得的。活检是通过定量的方式进行的 聚合酶链式反应检测上述两种基因的mRNA水平 提到的K+通道，以及其他心力衰竭的“标记”基因，如 作为SR-Ca~(2+)-ATPase和磷蛋白。单相动作电位和 在同一时间进行的氯化铯挑衅研究将 测量复极异常并测试假设 底物失效与长Q-T综合征有力学上的相似之处。 最后，在三个时间点的每个时间点，动物的子集将被 处死，分离心肌细胞，用于膜片钳和单个... 再极化K+电流的通道记录。这些研究的目的是 统一最近的数据表明改变的一个重要作用 复极化，特别是减少外向K+电流 充血性心力衰竭的致心律失常。基因表达减少 这些通道蛋白可能被证明是一种有价值的标记 增加猝死风险，并提出未来更好的途径 有针对性的治疗。

Congestive heart failure is a common disorder with a high annual mortality rate of 20-45%. Nearly half these deaths are sudden, and many are likely the result of ventricular tachyarrhythmias. Most efforts to identify patients at highest risk for sudden death and to intervene to lower this risk have been remarkable unsuccessful, in large part due to a lack of understanding of the underlying mechanisms of arrhythmia. Investigation of these mechanisms is ideally conducted in a controlled model that affords analysis at whole organ, cellular, and molecular levels, and that minimizes the variable etiologies and therapeutic histories that typically complicate human studies. The canine pacing- tachycardia failure model appears highly suitable for this purpose as it displays a high incidence of malignant ventricular arrhythmias, and has many mechanical, biochemical, and molecular changes similar to those of human heart failure. This proposal tests the following hypothesis: 1) that this animal model indeed provides a relevant substrate to study arrhythmias of heart failure, 2) that these arrhythmias are associated with prolonged and increased spatial/temporal dispersion of repolarization (Q-T interval, action potential duration), and reduced threshold to triggered arrhythmias, 3) that two repolarizing potassium currents - the inward rectifier and outward transient current - are markedly reduced with development of heart failure in this model, contributing to repolarization delay and arrhythmia, and 4) that these changes are paralleled by reduced gene expression of the corresponding channel proteins, measureable by mRNA analysis of endomyocardial biopsies. Adult mongrel dogs are chronically instrumented for determination of chamber pressure-dimension mechanics in the conscious state. Dogs are ventricularly paced at 240 min-1 for 2-3 weeks, followed by 210 min-1 until development of heart failure. Holter monitors are obtained during weekly 24 hour pacing-off periods to study arrhythmia frequency, Q-T prolongation and variability. At baseline, 1-week, and heart failure time points, dogs are sedated, and endomyocardial biopsies obtained under sterile technique. Biopsies are processed by quantitative polymerase chain reaction to measure mRNA levels for the two above mentioned K+ channels, and for other 'marker' genes of heart failure such as SR-Ca2+-ATPase and phospholamban. Monophasic action potentials and cesium chloride provocation studies performed at these same times will measure repolarization abnormalities and test the hypothesis that the failure substrate bears mechanical similarities to long Q-T syndromes. Finally, at each of the three time points, a subset of animals will be sacrificed, and myocardial cells isolated for patch-clamp and single- channel recordings of repolarizing K+ currents. These studies aim at unifying recent data suggesting an important role of altered repolarization and in particular reduced outward K+ currents in arrhythmogenicity in congestive heart failure. Reduced gene expression of these channel proteins could prove to be a valuable marker for enhanced sudden death risk, as well as suggest future avenues for better targeted therapies.