The influencing factors for establishing a model of acute myocardial infarction in rats

Objective: To study the effects of weight and anteroposterior diameter-to-transverse diameter ratio on establishing a model of acute myocardial infarction (AMI) in rats without artificial ventilation and changes in left ventricular function after infarction. Methods: Healthy SD rats were randomly divided into group A (200-250 g), group B (250-300 g), group C (>300 g), and group D (control group). The left anterior descending (LAD) coronary artery was ligated to establish a model of myocardial infarction under spontaneous breathing condition immediately after thoracic lines were measured. And changes of electrocardiography were recorded after model establishment. At 2 and 4 weeks after AMI, we observed ventricular wall thickness and ventricular wall motion and measured the changes of cardiac function. Histomorphological changes and myocardial ultrastructure of the heart were observed under thoracotomy 2 weeks after operation. The above data were analyzed by SPSS13.0 statistics software. Results: (1) The first AMI rat model was established successfully after 30 times of experiments, and after 100 times the model's success rate gradually stabilized at about 83%. (2) Group B and group C had a higher model success rate than group A (P<0.05), but group B and group C did not differ in modeling success rate (P>0.05). (3) There was no association between the rate of rat thoracic line and modeling success rate (P>0.05). (4) Two weeks after thoracotomy, ischemic myocardial color was white, and ventricular wall motion decreased. HE staining revealed that cardiomyocytes disappeared and were replaced by fibrous tissues and collagen. Remnant cardiomyocytes were arranged disorderly and myofibers were fractured, with interstitial damage and hyperplasia of fibrous tissue. Visible muscle cells were sparse and dissolved, the mitochondria had darker staining, blurred cristae, and edema under electron microscopy. (5) Compared with group D, 2 weeks and 4 weeks after myocardial infarction, left ventricular end-diastolic diameter (LVEDD) and left ventricular end systolic diameter (LVEDs) increased (P<0.05), but EF values and heart rate dropped (P<0.05). Conclusion: By this method, a model of AMI in rats can be established successfully and the heart function is changed. Under the condition of non-artificial ventilation, the weight of rats is an important factor for establishing AMI model. However, we have not confirmed the effect of thoracic lines on establishing AMI model yet.