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MRI在检测可挽救心肌中的潜在作用尚未完全了解，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性损伤的区域是否过度增强？2)超增强的空间范围是否高估了急性坏死的空间范围？3)慢性梗塞（胶原性瘢痕）是否增高？在过去的一年里，我们研究了这些问题在长期仪器狗（附录1）。我们发现，尽管室壁运动持续异常，但在严重但可逆的缺血性损伤后不会发生延迟性高增强（Gd-DTPA后>5分钟获得的图像）（初步研究第1部分）。我们发现，在0.5x0.5x0.5 mm的空间分辨率下，MRI超增强区域的大小和形状似乎与梗死后2小时（有再灌注）、1天（无再灌注）和3天的急性肌细胞坏死的大小和形状相同（初步研究的第2部分）。我们还发现胶原性瘢痕高度增强，并且瘢痕大小与高度增强的大小相匹配（初步研究的第3部分）。在迄今为止研究的病理生理学中，数据表明了一个潜在的重要假设：在对比MRI的空间分辨率的限制下，无论收缩功能和梗死年龄如何，不hyperenhance的心肌都是可行的。为了进一步研究这一点，我们建议确定整个损伤和愈合过程中MRI超增强的空间范围与肌细胞坏死和疤痕的空间范围之间的关系（目标1），以确定对比度增强的机制（目标2），并了解个体内对比度增强模式的纵向变化如何与损伤的演变相关（目标3）。我们提出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程度的关系。

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.