Detection of Salvageable Myocardium by Contrast MRI

临床心脏病学中最重要的问题之一是检测受损但可挽救的心肌。对比剂MRI在检测可挽救心肌中的潜在作用尚不完全清楚，可能是由于心肌损伤和愈合的复杂性以及MRI技术的进步。我们认识到三个关键问题的解决将为未来的研究提供重要的指导：1)遭受严重但可逆的缺血损伤的区域是否过度强化？2)过度强化的空间范围是否高估了急性坏死的程度？3)慢性脑梗塞(胶原瘢痕)是否过度强化？在过去的一年里，我们在长期使用器械的狗身上研究了这些问题(附录1)。我们发现，尽管存在持续性的室壁运动异常，但严重但可逆的缺血损伤后不会出现延迟高增强(Gd-DTPA后5分钟获得的图像)(初步研究的第一部分)。我们发现，在0.5x0.5x0.5 mm的空间分辨率下，MRI高强化区域的大小和形状与梗塞后2小时(有再灌注)、1天(无再灌注)和3天(初步研究第二部分)的急性心肌细胞坏死的大小和形状相同。我们还发现，胶原性瘢痕高度强化，疤痕大小与高度强化的大小相匹配(初步研究第三部分)。在迄今研究的病理生理学中，这些数据提出了一个潜在的重要假设：在造影剂MRI空间分辨率的限制下，无论收缩功能和梗死年龄如何，没有过度增强的心肌是可行的。为了进一步研究这一点，我们建议确定MRI高强化的空间范围与损伤和愈合过程中心肌细胞坏死和瘢痕的空间范围之间的关系(目标1)，确定支持对比增强的机制(目标2)，并了解个体内部对比增强模式的纵向变化如何与损伤的演变相关(目标3)。我们建议的五年计划将使我们能够建立MRI对比增强模式与存活心肌的存在和范围的关系。

One of the most important issues in clinical cardiology is the detection of injured but salvageable myocardium. The potential role of contrast MRI in detecting salvageable myocardium is not fully understood perhaps secondary to the complexity of myocardial injury and healing and advances in MRI technology. We recognized that resolution of three key issues would provide important guidance for future investigations: 1) Do regions subjected to severe but reversible ischemic injury hyperenhance? 2) Does the spatial extent of hyperenhancement overestimate that of acute necrosis? 3) Do chronic infarcts (collagenous scar) hyperenhance? Over the past year we have studied these issues in chronically instrumented dogs (Appendix 1). We found that delayed hyperenhancement (images acquired >5 min after Gd-DTPA) does not occur following severe but reversible ischemic injury despite a persistent wall motion abnormality (Part 1 of Preliminary Studies). We found that at a spatial resolution of 0.5x0.5x0.5 mm the size and shape of MRI hyperenhanced regions appear to be identical to those of acute myocyte necrosis at 2 hours (with reperfusion), 1 day (without reperfusion), and 3 days post-infarct (Part 2 of Preliminary Studies). We also found that collagenous scars hyperenhance and that scar size matches the size of hyperenhancement (Part 3 of Preliminary Studies). In the pathophysiologies investigated to date, the data suggest a potentially important hypothesis: to the limit of the spatial resolution of contrast MRI, myocardium that does not hyperenhance is viable irrespective of contractile function and infarct age. To investigate this further, we propose to determine the relation between the spatial extent of MRI hyperenhancement to that of myocyte necrosis and scar throughout the processes of injury and healing (Aim 1), to determine the mechanisms which underlie contrast enhancement (Aim 2), and to understand how longitudinal changes in contrast enhancement patterns within individuals relate to the evolution of injury (Aim 3). Our proposed five-year plan will allow us to establish the relationship of MRI contrast enhancement patterns to the presence and extent of viable myocardium.