| Background and ObjectAcute myocardial infarction (AMI) is a cardiovascular disease which has seriously impacted human survival and quality of lives. After acute coronary circulation failure happened, understanding of regional myocardial systolic function, microcirculation perfusion status and viability is very important to guide the selection of treatment and the prediction of prognosis.Myocardial contrast echocardiography (MCE)-the imaging of a contrast agent within the myocardial capillary vascular bed-offers the potential of real time, noninvasive assessment of myocardial perfusion. The contrast agent formed a great many micro-babbles with diameter of 2-5μm, smaller than red blood cells, which can be freely through the microcirculation. By combined second harmonic imaging and intermittent triggered imaging technology, MCE can quantitatively evaluate regional myocardial perfusion. At present, a number of studies have shown that qualitative and quantitative assessment of myocardial perfusion can be achieved by observation of the intensity and distribution of myocardial contrast agent. Assessment of myocardial viability can be achieved furtherly. However, the security of the application MCE in AMI patients has not been identified.Microcirculatory perfusion disorders accompany with abnormal regional myocardial systolic function. At present, the study of the relationship between myocardial systolic function and microcirculation perfusion are still less. The studies on to the relationship and the exploring which speculate the regional myocardial microcirculation perfusion and viability by systolic function can provide a more convenient and safety measures for clinic. Speckle tracking imaging (STI) is a new technique which uses standard B-mode images for speckle tracking analysis, in which the speckled pattern is followed frame by frame.The displacement of this speckled pattern is considered to follow myocardial movement and a change between speckles represents myocardial deformation. A software algorithm follows the change in geometric position of this region, frame by frame, and extracts the displacement, velocity, strain and strain rate of a defined myocardial segment. In contrast to TDI (Tissue Doppler imaging) derived parameters, STI is an angle independent technique as the movement of speckles can be followed in any direction. STI was more reliable and comprehensive than SRI (strain rate imaging).In the present study, the left anterior descending coronary arteries (LAD) of adult dogs were occluded. STI and RT-MCE were combined to study the changes of myocardial systolic function and microcirculation perfusion status, as well as the relationship between them, after acute coronary occlusion. A new method to evaluate the myocardial viability was discussed furtherly.MethodsFifteen adult healthy open chest dogs, weighing 12-15kg were used for the study. All animals were subjected to left anterior descending coronary artery occlusion for at lest 3 hours. Images including two-dimensional images and myocardial contrast images were performed respectively in 15 minutes before occlusion,15 minutes,1 hour,2 hours, and 3 hours after occlusion. Two-dimensional images of at least three consecutive cardiac cycles were recorded from the short-axis views at the levels of mitral annulus, papillary muscle and apex of the LV respectively. Contrast agent SonoVue was continuously infused through femoral vein, and we use the intermittent trigger imaging, Space is set to trigger cardiac 1-20 cycle. Imaging was performed consistently with the 2D images. At the end of the experiences, animals were killed with hearts took out, Evans blue and TTC staining were used to identify t the infracted segments, ischemic segments and normal segments. Images were transfer to Echo PAC workstation for off-line analysis. The software algorithm segmented the LV short-axis into 18 equidistant segments respectively (anteroseptal, anterior, lateral, posterior, inferior and interventricular). The curves of radial strain(SR) and circumferential strain(SC) and the values of Peak systolic radial strain (SRpeak) and peak circumferential strain (SCpeak) were acquired. MCE analysis acquired indexes including the video intensity (A), micro-bubble replenishment velocity (β) and myocardial blood flow (A×β). SPSS 13.0 were used to analysis the changes including STI parameters and the RT-MCE parameters of infarcted segments, ischemic segments and normal segments, before and after occlusion,as well as in different time intervals after occlusion. The correlation between segmental systolic function and microcirculation perfusion was discussed too.Results1.After coronary occlusion, the SRpeak was reduced than before in all segments, which more significantly in infarcted segments and ischemic segments (P<0.01).The SRpeak increased with time in ischemic myocardium (P<0.01), while continued to decline in infarcted segments (P<0.01). The SCpeak reduced in infarcted and ischemic segments whereas increased in normal segments (P<0.01), and the change over time has no statistical significance.2.After coronary occlusion, significant contrast agent perfusion defection appeared in LAD feeding area, A and A×βvalue is reduced significantly(P<0.01). Contrast agent delayed filling over time in ischemic area, meanwhile A and A×βvalues increased(P<0.01). Contrast agent continued filling defect in infarcted area, A and×βvalues remain low level as well.3.In the ischemic area, SRpeak was positive correlative with A and A×βvalue (R1=0.59, P<0.01; R2=0.63, P<0.01).4.Diagnostic value analysis:3 hours after occluded, the area under the ROC curve of SRpeak, A and A×βwhich represent the value of distinguish viable myocardium SRpeak in area was 0.875,0.932, and 0.839 respectively.Conclusion1.Myocardial microcirculation perfusion is positive correlative with peak systolic radial strain in ischemic myocardium.2.Severity of myocardial ischemia can be speculated by SRpeak. SRpeak is of certain diagnostic value to identify viable myocardium.
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