VENTRICULAR FUNCTION FOLLOWING MYOCARDIAL INFARCTION

急性心肌梗死（MI）后的重构是改变左心室（LV）腔几何形状的适应性机制。 本研究旨在确定这一过程如何影响左室大小和功能及其对血流动力学变化的反应。 在23只成年绵羊中，通过结扎冠状动脉前循环或后循环的动脉来制造MI。 24小时（组I; n=10）或6个月（组II; n=13）后对动物进行研究。 在两组中遵循相似的冠状动脉闭塞手术，以实现相同大小的MI。 在每项研究中，在开胸麻醉动物的基线、血管紧张素II和硝普钠（SNP）输注期间以及下腔静脉部分结扎期间获得实时三维超声心动图（RT 3D回波）图像。 使用基于Silicon Graphics工作站的交互式追踪技术，从RT 3D回波图像离线测量LV体积。第I组与第II组的基线LV舒张末期（EDV）、收缩末期（ESV）和每搏（SV）容积以及射血分数（EF）分别如下：EDV（ml）44.4+/-6.9 vs 64.7+/-6.6（p<0.0001）; ESV（ml）15.6+/-3.3 vs 35.0+/-4.9（p<0.0001）; SV（ml）28.8+/-4.9 vs 29.7+/-4.3（p=0.67）; EF（%）65+/-5 vs 46+/-5（p<0.0001）。 两组对血管紧张素II给药或下腔静脉结扎的反应无差异。 然而，SNP仅在组I中诱导SV增加（P=0.005）;因此，与组II动物相比，组I中在SNP输注期间测量的SV显著更大（33.2+/-2.1 vs. 27.6+/-2.6 ml; P=0.01）。 因此，MI后的重构导致LV扩张和整体功能降低，而不改变SV。 后负荷减少仅在MI的早期阶段对LV功能产生积极影响，因此在此阶段比重塑过程完成后更可能有益。

Remodeling following acute myocardial infarction (MI) is an adaptive mechanism that changes the geometry of the left ventricular (LV) chamber. The present study was designed to determine how this process affects LV size and function and their response to hemodynamic changes. MI was created in 23 adult sheep by arterial ligation on the anterior or posterior coronary circulation. Animals were studied either 24 hours (group I; n=10) or 6 months (group II; n=13) later. Similar coronary occlusion procedures were followed in both groups to achieve equivalent size of MI. In each study, real-time 3-dimensional echocardiographic (RT3D echo) images were obtained in the open-chest anesthetized animals at baseline, during angiotensin II and sodium nitroprusside (SNP) infusion, and during partial ligation of the inferior vena cava. LV volumes were measured off-line from RT3D echo images using an interactive tracing technique based on a Silicon Graphics workstation. Baseline LV end-diastolic (EDV), end-systolic (ESV) and stroke (SV) volumes, and ejection fraction (EF) in Group I vs Group II, respectively were as follows: EDV (ml) 44.4+/-6.9 vs 64.7+/-6.6 (p<0.0001); ESV (ml) 15.6+/-3.3 vs 35.0+/-4.9 (p<0.0001); SV (ml) 28.8+/-4.9 vs 29.7+/-4.3 (p=0.67); EF (%) 65+/-5 vs 46+/-5 (p<0.0001). There was no difference between the two groups in the response to angiotensin II administration or inferior vena cava ligation. However, SNP induced an increase in SV only in group I (P=0.005); consequently, SV measured during SNP infusion was significantly greater in group I compared to group II animals (33.2+/-2.1 vs. 27.6+/-2.6 ml; P=0.01). Thus, remodeling following MI leads to LV dilation and reduced global function without changing SV. Afterload reduction positively affects LV function only during the early phases of MI and therefore is more likely to be beneficial at this stage than after the remodeling process has been completed.