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， 死亡率为20- 45%。 近一半的死亡是突然的，许多人 很可能是室性心律失常造成的 大多数努力， 识别猝死风险最高的患者，并进行干预， 降低这种风险已经显着不成功，在很大程度上是由于 对心律失常的潜在机制缺乏了解。 这些机制的研究理想地在受控的环境中进行。 提供整个器官、细胞和分子分析的模型 水平，并最大限度地减少可变病因和治疗 通常会使人类研究复杂化的历史。 犬类起搏- 心动过速失败模型似乎非常适合于此目的，因为它 恶性室性心律失常的发病率很高， 许多机械，生物化学和分子变化类似于 人类心脏衰竭 本提案检验了以下假设：1） 这个动物模型确实提供了一个相关的研究基质 心力衰竭的心律失常，2）这些心律失常与 随着空间/时间分散的延长和增加， 复极（Q-T间期，动作电位时程），并减少 触发心律失常的阈值，3）两个复极钾 电流-内向整流器和外向瞬态电流-是 在该模型中随着心力衰竭的发展而显著降低， 导致复极延迟和心律失常，以及4）这些 这些变化被相应基因表达的减少所掩盖， 通道蛋白，可通过心内膜心肌mRNA分析测量 活组织检查 成年杂种狗长期被用于 有意识的腔室压力-尺寸力学的测定 状态 将狗以240 min-1心室起搏2-3周，随后 210 min-1，直至发生心力衰竭。 霍尔特监测仪 在每周24小时起搏期内获得，以研究心律失常 频率、Q-T延长和变异性。基线、1周和 在心力衰竭时间点，使狗镇静，并进行肌内膜活检， 在无菌技术下获得。 活组织检查通过定量 聚合酶链反应来测量上述两种基因的mRNA水平 提到的K+通道，以及其他心力衰竭的“标记”基因， SR-Ca ~（2+）-ATPase和受磷蛋白。 单相动作电位和 同时进行的氯化铯激发研究将 测量复极异常，并测试假设， 衰竭基底与长Q-T综合征具有机械相似性。 最后，在三个时间点中的每一个时间点， 处死，并分离心肌细胞用于膜片钳和单- 通道记录复极化K+电流。 这些研究旨在 统一最近的数据表明， 复极化，特别是减少外向K+电流， 充血性心力衰竭的促血管生成作用。 基因表达降低 这些通道蛋白可以被证明是一个有价值的标记， 增加猝死风险，并建议未来更好的途径 靶向治疗。

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.