Experimental Study Of E-Speed Electron Beam Computed Tomography Myocardial Perfusion And Heart Function In Dogs Acute Myocardial Infarction Models

ObjectiveTo study the electron beam computed tomography (EBCT) myocardial perfusion appearance of acute myocardial infarction, and preliminary explore the changes of cardiac function in acute myocardial infarction models of dogs. Integrated the changes of myocardial perfusion and cardiac function between normal myocardium and acute infarction myocardium to test the sensibility of EBCT in diagnosis of acute myocardial infarction and provide the experimental basis for EBCT using in coronary heart disease clinically.Methods1. Thirty healthy mongrel dogs were anesthetized through croup muscle after fasted 8 h. Lidocaine was injected through saphenous vein during 10 min. After exposured and segregated the right carotid artery, punctured it and Inserted the 4F or 5F Cobra catheter to the main left coronary and carried out the coronary arteriongraphy under the fluoroscopic monitoring, then inserted the microatublar in the direction of micro-guidwire to the middle–distal segment of left anterior descending branch. Two pieces of 0.5 cm length stitches or granulo-gelatin sponge particles were injected to embolism the coronary artery. When coronary artery angiography displayed blood flow discontinuance and then put out the opacification tublar.2. Six healthy dogs were Randomly selected to build the control group and twenty-four dogs were selected to build the acute myocardial infarction group (12 dogs after AMI 2 h and 12 dogs after AMI 4 h ). The dogs were placed in EBCT examining unit with right arm recumbent to guarantee the scanning with brachyaxis heart as far as possible. After scount scanning, the myocardial perfusion scan was carried out using multiple target perfusion scanning procedure. Cardiac Perfusion software were used to analyze the perfusion imagings in the region of interesting of the left ventricle,interventricular septum,anterior wall of left ventricular,posterior wall of left ventricular,lateral wall of left ventricular and abnormal perfusion area, and TDC,perfusion parameters and artificial colored images were also mapped . Myocardial infarction scope was drawn by hand and infarciton volume was calculated using Simpson formula.3. Step volume scan was carried out to analyze the cardiac function after EBCT myocardial perfusion scanning.Determined circulation time and definited the delayed time in order to guarantee the highest density when scan started. Transferred the images to AW 4.2 workstation, Split the four-cavous heart to brachyaxis which was perpendicular to left ventricle long axial.Measured the left ventricle end diastole volume and left ventricle end systole volume and caculated the stroke volume and ejection fraction.Chosen the brachyaxis imags of end diastole and end systole to measure the wall thickness of left ventricle anterior segment,left ventricle posterior segment,left ventricle lateral segment and interventricular septum, and then caculated the thickening rate .4. The dogs were killed by large dose narcotic after exam was completed. Heart was taken out and splited followed brachyaxis. Firstly, macroscopic observed the color and infarction scope of the pathological changes. Secondly , Cutting the heart to intersect tissue mass and put the tissue mass into 1% triphenyl tetrazoliumchloride solution to balneum tepidum for 30 min in the 37℃balneum tepidum box. Thirdly, took the tissue mass to exam the infarction scope and draw the materials from the normal and infarctione myocardium separately. The mass was put in the 10% formalin to fix for 48 h and was done the conventional hematoxylin- eosin staining.Result1. Twenty-four dogs were successfully embolised the left anterior descending branch . One dog were dead of overdose of anesthesia before the operation; one dog was embolised the diagonal branch by mistake; one dog was embolised the right coronary arteary by mistake; three dogs were embolised the left main coronary arteary and dead of ventricular fibrillation. Coronary angiography indicates that 22 dogs were predominated by left circumflex .Left anterior descending branch has finer and fewer branches compared with the circumflex .Left anterior descending branch and left circumflex were distributed equally in two dogs. The successful rate using coronary cannula technology to establish the dog acute myocardial infarction models was 80%. 2. The left ventricular wall were enhanced uniformly and TDC appeared as a quickly ascended and slowly descendedγ-curve sequentially. The artificial colored images of EBCT myocardial perfusion after embolism 2 h displayed the hypoperfusion area in the lef ventricle anterior wall,the lateral wall and interventricular septum. TDC appeared as a slowly ascended and descendedγ-curve, MTT was prolonged and RS,BV and PV was smaller than the normal dogs'. The artificial colored images of EBCT myocardial perfusion after embolism 2 h displayed thetransmural hypoperfusion area. TDC obviously appears slow and flat and peak value was delayed, and evenly similar to a piece of horizontal line. Compared with the TDC of embolism 2 h , RS was highly significantly different (P<0.01), RS was significantly different(P<0.05),MTT was not significantly different(P>0.05).Compared with the control group ,the perfusion parameters of AMI 4 h had significantly or highly significantly differences.3. The motional function of heart decreased gradually after acute myocardial infarction. Along with accrescence of embolism time, left ventricle end systole volume increased gradually, stroke volume and ejection fraction decreased. Local left ventricle wall thickness thinningzed , especially the anterior wall and interventricular septum. The changes of posterior wall thickness was most insignificant. The thickening rate of left ventricular wall had the same changes with left ventricle wall thickness accordingly.4. TTC staining and conventional HE staining indicated that myocardial infarction area mainly located in the left ventricle anterior wall,the anterior part of interventricular septum and apex of heart in accordance with the distribution of left anterior descending branch which was equal to the discovery of EBCT myocardial perfusion and EBCT heart function analysis.ConclusionDog acute myocardial infarction model through closed-chest coronary cannula technology was less traumatic and has less influence on the physiological functions. The study has approved the feasibility of this method to build AMI animal model. Using e-Speed EBCT multiple targets perfusion procedure can quantitatively measure the scope of acute myocardium ischemia and infarction. The ability of finding abnormal myocardial ischemia :TDC > myocardial perfusion artificial colored images >original images. PV and BV exhibited the obvious differences and MTT and RS were also useful in the diagnosis of myocardial infarction. Heart motion function can be evulated by EBCT. Left ventricle stroke volume,ejection fraction and end systole volume decreased when acute myocardial infarction happened. The dysfunction of local ventricle motion manifested that left anterior descending branch suppied wall thinningzed and ventricular wall thickening rate decreased. The combination of the EBCT myocardial perfusion and heart functional analysis can discover the myocardium ischemic diseases much precisely.