Modeling Principle

The Pig Myocardial Infarction Model is a SCI gold-standard large-animal pathological model of acute myocardial infarction established by thoracotomy and ligation of fixed segments of left anterior descending coronary artery (LAD). It accurately recapitulates the complete cascaded pathological process induced by clinical coronary occlusion, including local myocardial ischemic necrosis, apoptosis and disintegration of cardiomyocytes in infarcted area, inflammatory cell infiltration around infarct zone, abnormal collagen deposition, thinning and bulging of ventricular wall, pathological left ventricular remodeling, progressive deterioration of cardiac function, and long-term progression to ischemic heart failure. It remedies the experimental limitations of rodents, which have prominent differences from human ischemic cardiomyopathy in coronary anatomical course, myocardial thickness, ventricular mechanical characteristics, evolution law of infarct size and remodeling cycle of myocardial repair.

The coronary anatomical distribution, cardiomyocyte arrangement, ventricular wall thickness, coronary microcirculation perfusion pattern, post-ischemia inflammatory response, TGF-β1/Smad fibrotic pathway and neurohumoral compensatory activation pattern of Bama minipigs are highly homologous to the human heart. The heart is exposed via left intercostal thoracotomy, the pericardium is bluntly dissected for cardiac suspension, and the middle-distal segment of left anterior descending artery is ligated under direct vision to cause complete ischemia and hypoxia of myocardium in the coronary perfusion area. Immediate blood flow block after ligation leads to disorder of myocardial energy metabolism and coagulative necrosis of cardiomyocytes within a short period. A large number of neutrophils and macrophages are recruited around the infarct lesion to initiate acute inflammatory response. In the late stage of infarction, necrotic myocardium is gradually absorbed by the body, fibroblasts proliferate massively and secrete collagen fibers to form dense scar tissue in the infarcted area. The mechanical strength of ventricular wall decreases, accompanied by ventricular dilatation, abnormal wall motion and reduction of left ventricular ejection fraction. Under long-term infarct load, viable normal myocardium presents compensatory hypertrophy, and the overall systolic and diastolic function of the heart is impaired, stably forming a complete pathological phenotype of acute myocardial infarction → myocardial fibrosis → ventricular remodeling → chronic heart failure. This model fully recapitulates the classic pathogenic cascade of human myocardial infarction caused by coronary occlusion: coronary blood flow blockage – acute myocardial necrosis – local inflammatory response – scar tissue repair – ventricular geometric remodeling – ischemic heart failure.

Minipigs have large cardiac volume and coronary artery diameter similar to humans, the ligation site can be precisely controlled to standardize infarct size, the progression of myocardial infarction is mild with low individual data dispersion, and there is no spontaneous cardiomyopathy. Three pathological stages can be clearly distinguished: acute myocardial infarction necrosis stage, infarct inflammatory absorption stage, and terminal scar formation & ventricular remodeling stage. It serves as a standardized large-animal gold-standard model for translational researches on first-aid drugs for myocardial infarction, myocardial protective preparations, stem cell transplantation, cardiac stents & occlusive devices, and intervention strategies for ventricular remodeling.

Modeling Success Criteria

In-vivo Cardiac Function, ECG and General Cardiac Phenotype

No pathological ST-segment elevation was observed on electrocardiogram of animals in the sham control group, echocardiographic LVEF was maintained within normal range, the general heart was ruddy with uniform ventricular wall thickness and no scar lesions. At Week 8 terminal point, old myocardial infarction waveforms could be seen on electrocardiogram of the model group, echocardiographic LVEF decreased significantly by more than 20% compared with the sham group, and the wall motion in infarcted area was weakened or paradoxical. Gross cardiac dissection revealed gray-white dense scar tissue on the anterior wall of left ventricle accompanied by ventricular cavity dilatation and ventricular wall thinning. The macroscopic phenotype of ventricular remodeling after myocardial infarction was typical with extremely significant statistical difference between groups, which could preliminarily confirm the successful construction of coronary ligation myocardial infarction model.

Quantitative Biochemical Gold-Standard Serum Indexes

The serum levels of cTnI and CK-MB in the acute phase of the model group were extremely significantly higher than those in the sham group; serum TNF-α, IL-1β and IL-6 were persistently highly expressed in the long term; the contents of TGF-β1 and type Ⅰ/Ⅲ collagen in myocardial tissues increased greatly, and Ang Ⅱ and ALD of RAAS system elevated compensatorily, which fully matches the biochemical diagnostic characteristics of clinical acute myocardial infarction: release of injury markers due to cardiomyocyte necrosis, persistent existence of local chronic inflammation, excessive deposition of myocardial collagen leading to fibrosis, and compensatory activation of neurohumoral system.

Myocardial Histopathological Characteristics

Sequential pathological injury changes after myocardial infarction can be observed via combined multiple staining of myocardial tissues with TTC, HE, Masson, TUNEL and WGA:

1. Acute stage at Week 2 after modeling: massive coagulative necrosis of myocardium in ligation perfusion area, massive inflammatory cell infiltration, significantly increased number of TUNEL-positive apoptotic cells and minimal collagen deposition shown by Masson staining;
2. Middle repair stage at Week 5 after modeling: necrotic myocardial tissues were gradually dissolved and absorbed, interstitial fibroblasts proliferated massively in infarcted area, blue-stained collagen fibers increased gradually, and compensatory hypertrophy occurred in cardiomyocytes around the infarct;
3. Terminal remodeling stage at Week 8 after modeling: the infarcted area was completely replaced by dense and thick collagen scars with thinned ventricular wall, accompanied by cardiomyocyte hypertrophy and extensive interstitial fibrosis around the infarct, which perfectly recapitulates the progressive pathological evolution law from necrosis and inflammation to scar fibrosis and ventricular remodeling after acute myocardial infarction in human beings.

Gold-Standard Indexes for Fibrosis, Inflammation and RAAS Pathways

The NF-κB inflammatory pathway in the myocardial infarcted area of the model group was activated for a long time to continuously recruit inflammatory cells and aggravate myocardial damage. The TGF-β1/Smad fibrotic pathway in myocardium around the infarct was overactivated to induce fibroblasts to synthesize and secrete a large amount of collagen. Compensatory activation of RAAS system further aggravated vasoconstriction and myocardial interstitial fibrosis, and compensatory hypertrophic changes appeared in viable myocardium. It accurately conforms to the complete pathological mechanism of coronary ligation-induced myocardial infarction: blood flow interruption – myocardial necrosis and apoptosis – inflammatory storm – fibrotic scar formation – pathological ventricular remodeling – cardiac function decline, serving as the core academic basis for verifying effective model formation.

Model Advantages

This model is a well-recognized large-animal gold-standard model for acute myocardial infarction constructed by surgical LAD ligation in cardiovascular SCI field. The 8-week standardized surgical modeling can stably reproduce the complete pathological phenotype of ischemic heart disease highly consistent with humans, including acute myocardial necrosis, inflammatory response, scar fibrosis, left ventricular remodeling and decreased cardiac function. The coronary anatomy, myocardial structure, cardiac hemodynamics and post-infarction repair sequence of minipigs are highly matched with human beings, the infarct size is controllable with mild disease progression and low intra-group individual differences, and the experimental repeatability is far superior to small experimental animals such as mice, rats and rabbits. The modeling method adopts physical coronary occlusion, which conforms to the pathological essence of clinical acute thrombotic coronary occlusion without non-specific systemic toxic damage caused by chemical induction. Non-invasive echocardiographic follow-up and venous blood sampling can be carried out for many times with abundant myocardial tissue samples, which is suitable for preclinical pharmacodynamic and safety evaluation of anti-myocardial infarction drugs, myocardial protective agents, anti-ventricular fibrotic preparations, cardiac interventional consumables and cell therapy systems. Data obtained from this model are widely recognized by high-impact SCI journals of cardiovascular medicine, pharmacology and interventional medicine, which is applicable for National Natural Science Foundation projects, master & doctoral proposal writing, cardiovascular graduation theses and translational medical researches on myocardial infarction repair and heart failure intervention.

Research Applications

The Pig Myocardial Infarction Model is mainly used to analyze basic pathological mechanisms including blood flow blockage by mechanical coronary ligation, acute myocardial ischemic necrosis, recruitment of inflammatory cells and release of inflammatory mediators, cardiomyocyte apoptosis, fibroblast activation & collagen deposition, scar tissue formation inducing pathological left ventricular remodeling and decreased cardiac function. It is specially adopted to screen and verify small-molecule first-aid drugs, active extracts of traditional Chinese medicine, myocardial protective biomaterials, stem cell repair preparations and coronary interventional supporting treatment schemes with effects of reducing the degree of myocardial necrosis, inhibiting inflammatory storm, alleviating cardiomyocyte apoptosis, blocking fibroblast activation and collagen secretion, restraining excessive scar formation, reversing adverse ventricular remodeling and improving cardiac systolic & diastolic function. It is widely used for excavation of repair targets for myocardial infarction injury, elucidation of regulatory network among inflammation, apoptosis and fibrosis, as well as preclinical in-vivo efficacy verification of various anti-myocardial infarction drugs and medical interventional materials in large animals. It is an indispensable essential standardized large-animal gold-standard model in the fields of cardiovascular pharmacology, interventional cardiology and myocardial injury repair.

pig myocardial infarction model, coronary artery ligation, acute myocardial infarction, ventricular remodeling, heart failure, cardioprotective drugs & myocardial repair biomaterials preclinical evaluation