| Objective: Coronary heart disease has become the major killer of world's human health currently. With the development of medical science, the awareness, prevention and treatment are becoming mature. However, ischemic mitral regurgitation has not caused widespread awareness and attention. Ischemic mitral regurgitation is not only endangering the health of patients with coronary heart disease, but also a major cause of death of patients with coronary heart disease. The mechanism of ischemic mitral regurgitation is complex and there is no clear conclusion so far. Currently most scholars believe that cardiac function and structure will appear a series of changes which relate to the occurrence of ischemic mitral regurgitation after myocardial infarction. For example, papillary muscle dysfunction or even rupture, infarcted wall movement disorders, regional wall bulging, left ventricular cavity expansion, mitral ring expansion and so on. In this study, goats'left ventricular branches are ligated which causes small size myocardial infarction in posterior papillary muscle and its adjacent wall and then leads to mitral regurgitation. This method can keeps the myocardial infarction confined to the posterior papillary muscle and its adjacent wall, to reduce the complex changes in heart structure because of the large area myocardial infarction, in order to further explore the mechanism of ischemic mitral regurgitation and provide experimental evidence for clinical prevention and treatment of ischemic mitral regurgitation.Methods: 11 healthy Dairy Goats (without mitral regurgitation, male and female informal)15-20Kg, supplied by the Experimental Animal Center of Bethuen International Peace Hospital. 11 goats are divided into two groups:Random-Blank Group-3 goats; Experimental Group-8 goats. To be sure these goats have no mitral regurgitation by Cardiac color Doppler ultrasound, measure the systolic and diastolic left ventricular diameter, EF value(Left ventricular ejection fraction), left ventricular sphericity(The ratio of left ventricular short axis and long axis), spacing between anterior and posterior papillary muscle, mitral annulus diameter, spacing between anterior papillary muscle and mitral annulus(from the anterior papillary muscle root to the anterior leaflet root of mitral valve), spacing between posterior papillary muscle and mitral annulus(from the posterior papillary muscle root to the anterior leaflet root of mitral valve), anterior papillary muscle contractile function[(systolic anterior papillary muscle thickness-diastolic anterior papillary muscle thickness)/systolic anterior papillary muscle thickness], posterior papillary muscle contractile function[(systolic posterior papillary muscle thickness-diastolic posterior papillary muscle thickness)/systolic posterior papillary muscle thickness]. Random-Blank Group: Left thoracotomy between the third and forth ribs and embedding under the left ventricular branch(the second branch of Circumflex) are performed without ligation, and then close the chest, record the ECG changes before and after the surgery, exam the incidence of mitral regurgitation by Cardiac color Doppler ultrasound again after 24 hours, measure the area of mitral regurgitation and left atrium and indicators above; Experimental Group: Left thoracotomy between the third and forth ribs and ligation of the left ventricular branch with 5-0 Polypropylene Line are performed, Record the ECG changes before and after the surgery, the ST-segment inⅡlead elevates, model-making is successful, close the chest. Exam the incidence of mitral regurgitation by Cardiac color Doppler ultrasound again after 24 hours, measure the area of mitral regurgitation and left atrium and indicators above. Draw and analyze the geometry changes of anterior and posterior papillary muscle and mitral annulus. After the second Cardiac color Doppler ultrasound kill the goats with 10%KCl injection, remove the hearts quickly, and place the hearts in formalin solution immediately. Fish out the hearts after 12 hours, calculate the infarct size. Cut the anterior and posterior papillary muscle tissues and observe them through the HE staining by electron microscopy, and then capture the images. All data are recorded as x±s, and analyzed by SPSS13.0. Analyze these data before and after the surgery by t test, analyze the relationship of infarction size, spacing between anterior and posterior papillary muscle, spacing between posterior papillary muscle and mitral annulus, posterior papillary muscle contractile function and angle between two lines(one from the anterior papillary muscle root to the anterior leaflet root of mitral valve, another from the posterior papillary muscle root to the anterior leaflet root of mitral valve) to the mitral regurgitation by Linear correlation.Results: The 3 goats of blank group all did not have myocardial infarction, mitral regurgitation and significant changes in left ventricular structure after operation. All 8 goats of experimental group had small size acute myocardial infarction in posterior papillary muscle and its adjacent wall, the infarction size was 4.69±0.83cm2; and all 8 goats had mitral regurgitation, the ratio of mitral regurgitation size and left atrium size was 0.29±0.15; left ventricular end systolic and end diastolic diameter, left ventricular ejection fraction, left ventricular sphericity, mitral annular diameter, spacing from the anterior papillary muscle to the mitral annulus and the anterior papillary muscle contractile function had no significant changes(p>0.1), spacing between anterior and posterior papillary muscle and between the posterior papillary muscle and the mitral annulus enlarged significantly(p<0.001), posterior papillary muscle contractile function decreased significantly(p<0.001), the degree of the angle enlarged significantly; posterior papillary muscle was far away from the anterior papillary muscle and mitral annulus, the relationship of geometry position between posterior papillary muscle, anterior papillary muscle and mitral annulus changed significantly. Mitral regurgitation had linear correlation with the infarction size(r=0.942)spacing between the anterior and posterior papillary muscle(r=0.865)and between the posterior papillary muscle and mitral annulus(r=0.742), posterior papillary muscle contractile function(r=0.942), degree of angle(r=0.739). The mitral regurgitation enlarging is directly proportional to the enlarging of infarction size, spacing between anterior and posterior papillary muscle, spacing between posterior papillary muscle and mitral annulus and degree of the angle, and is inversely proportional to posterior papillary muscle contractile function.Conclusions: 1.The posterior papillary muscles and its adjacent ventricular wall infarction can lead to acute ischemic mitral regurgitation: Ligation goat's second small branch of LCX - branch of left ventricular can lead to small area of acute myocardial infarction in posterior papillary muscle and its adjacent wall. Then the region of left ventricular heart wall does not shrink or even move reversely, the posterior papillary muscles is displaced, posterior papillary muscle contractile function is weakened, spacing between anterior and posterior papillary muscle and between posterior papillary muscle and mitral annulus is increased, degree of the angle is increased, which are followed by mitral regurgitation.2. Changes of left ventricular cavity size, left ventricular sphericity, EF value (Left ventricular ejection fraction) and the mitral annular size are not necessary factors for the occurrence of acute ischemic mitral regurgitation.3. The increase of infarct size of posterior papillary muscle and its adjacent wall, spacing between posterior papillary muscle and mitral annulus, decreasing of posterior papillary muscle contractile function, and changes of the relationship between anterior, posterior papillary muscle and mitral annulus are the important factors of the occurrence of acute ischemic mitral regurgitation, but they also have linear relationship.
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