CONTRACTILE STATE OF MYOCARDIUM IN MYOCARDIAL INFARCTION

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Spontaneous improvement in left ventricular function may occur after myocardial infarction (MI) due to recovery of stunned myocardium. However, whether changes in the contractile state of neighboring myocardial regions may contribute to this process is unknown. Therefore, the present study was designed to investigate changes in the relation between the extent of myocardial injury and wall motion abnormalities in the early phase of MI. MI was created in 21 adult sheep by permanently ligating arterial branches on the anterior or posterior coronary circulation. Real-time 3-dimensional echocardiographic (RT3D echo) images were obtained either immediately (group I; n=10) or 24 hours (group II; n=11) after coronary occlusion. In group I animals, Evans blue dye was injected into the occluded coronary artery after image acquisition for subsequent anatomic identification and planimetry of abnormally perfused myocardium. In group II animals, direct planimetry measurements of the anatomic infarct were obtained from the pathologic specimens. Extent of wall motion abnormalities was measured off-line from RT3D echo images using an interactive tracing technique based on a Silicon Graphics workstation and expressed as endocardial surface with abnormal wall motion. The difference between endocardial surface with wall motion abnormalities and the anatomic extent of perfusion deficit (group I) or myocardial necrosis (group II) was considered neighboring myocardium. Results: The anatomic extent of myocardial necrosis at 24 hours (group II) was significantly greater than the anatomic extent of perfusion deficit (group I) (15.8+/-2.8 vs.11.6+/-2.7 cm2; P=0.002). In contrast, there was a trend toward decreased extent of wall motion abnormality at 24 hours compared to immediately following ligation (21.9+/-4.4 vs. 25.9+/-5.9 cm2; P=0.09). Of note, the extent of neighboring myocardium with wall motion abnormalities was significantly reduced at 24 hours compared to immediately after coronary occlusion (6.1+/-2.1 vs. 14.2+/-2.7 cm2; P<0.0001). Conclusion: In an animal model of permanent coronary occlusion, there is an early reduction in the extent of dysfunctional myocardium surrounding the infarcted area. This phenomenon may partly explain the spontaneous recovery in left ventricular function which may be observed following an acute MI.