The Establishment Of Animal Model Of Acute Ischemic Mitral Regurgitation In Goats And Early Reperfusion Therapy

Objectives: Ischemic mitral regurgitation (IMR) is a common complication of acute myocardial infarction (AMI), which is recognized as functional regurgitation. Acute IMR is present in 17% to 55% of patients with AMI, and chronic IMR will occurs in approximately 15% of patients without acute IMR several months later. Even the presence of mild MR is a powerful independent predictor of reduced survival after AMI.The pathophysiology of IMR is complex, and its mechanism is various in different location of infarction. In this study, we explored a approach of inferior myocardial infarction model in goat, by learning about the coronary artery and left ventricular cavity casting. Infarct-related artery was reperfused after the animal models established, and therapeutic effect of reperfusion therapy was observed.Methods: 1 The study of arterial supply of posterior papillary muscle and adjacent ventricular wall in goat heartSelecting 20 goat hearts, blood clot in coronary artery and left ventricular cavity were rinsed with heparin solution. Perfusate was made with ABS resin and Acetone at the proportion of 1:20, which was injected into the coronary arteries and left ventricular cavity. And then put the goat heart into the 37% hydrochloric acid solution. 48 hours later, the residual myocardium was removed with running water, and researching the castings.2 The establishment of acute IMR model in goat and reperfusion therapyEleven local goats between 15 and 20kg were randomly divided into control group (n=3) and experimental group (n=8). All goats were detected by Doppler Echocardiography before operation. Mitral regurgitation, left ventricular cavity size, left ventricular function and other data were measured. Total goats were anesthetized with sodium pentobarbital (30mg/kg IV), intubated and ventilated. A surface ECG was monitored and a sterile left thoracotomy performed. Heparin sodium were injected with dose of 1mg/kg after thoracotomy in order to prevent thrombosis after blocking coronary artery. In experimental group, the second or third obtuse marginal branches of the left circumflex coronary artery(2cm below the atrioventricular groove) was ligated. In control group, the suture was put in the same position but wasn't ligated. The electrocardiogram of control group had no change. The S-T segment of II, III, AVF lead rose in experimental group. The incision was closed, and echo images were repeated after 6 hours, scanning methods were the same as preoperation.A second thoracotomy was performed after Echocardiography. The ligature was cut and the infarct-related artery reflowed. Echocardiographic data were collected again after 72 hours. Taking 2ml venous blood before operation, 6h, 12h, 24h and 72h after operation in every goats. And centrifuged them by 1000 roll/minute for 10 minutes, extracting the supernatant stored in -80℃refrigerator. ELISA was used to measure content of CK-MB in blood serum. Tissues were taked in infarct zone and papillary muscles after goats were sacrificed. These tissues were placed in 5% formalin solution for making pathological sectionResults: 1 By studying the coronary-ventricular castings, we found that the artery supply to posterior papillary muscle and adjacent ventricular wall comes from the second or third obtuse marginal branches of the left circumflex coronary artery.These branches locate approximately at the same position before them entering the myocardium: inferior-lateral wall and 2cm below the atrioventricular groove. (Fig.1)2 There was no death in two groups. The incidence of ischemic mitral regurgitation was 100% in experimental group. The control group had no regurgitation occurred. In experimental group, the echocardiographic data of 6h after operation shows EDD, EF, Left ventricular sphericity and Mitral Annular diameter did not change significantly compared with those preoperative(p>0.05). ESD, APM-PPM, PPM-AMA were obviously higher than those preoperative, there was statistical significance (p<0.05).PPM contracted values and WMI were decreased significantly in data of 6h after operation (p<0.05).The differences of echocardiographic data before and after operation in control group were not significant (p>0.05).MR was obviously reduced after reperfusion in experimental group. The differences were statistical significance (p<0.05). ESD, APM-PPM, PPM-AMA were obviously lower than those in 6h after infarction (p<0.05). PPM contracted values increased,there were statistical significance (p<0.05). Mitral regurgitation were still exists compared with preoperation, there were statistical significance (p<0.05). APM-PPM, PPM-AMA were still larger than preoperation, there were statistical significance (p<0.05).The PPM Contracted values significantly decreased compared with preoperation(p<0.05).Conclusions: 1 The left circumflex of goat coronary artery is bulky and superficial. The branches supply to posterior papillary muscles is relatively fixed under epicardium, and easily to be located.2 The incidence of IMR is higher in inferior myocardial infarction. Infarction involving the posterior papillary muscle and adjacent left ventricular wall result in displacement of papillary muscles and segmental post-wall movement disorders and left ventricular dilatation at the End of systole, which are the major determinants of IMR .3 IMR decreased after reperfusion, indicating that early coronary revascularization has a therapeutic effect for ischemic mitral regurgitation. That is because of the improvement of regional wall motion function and mitigation of the displacement of papillary muscles.4 Part of posterior papillary muscle and adjacent left ventricular wall were necrosis after the coronary artery obstruction, so coronary artery revascularization could not reverse infarct lesions and could not cure IMR.